Carburetor Magic
 

Hey, you guys that remember me extolling the virtues of the Mikuni VM26 with a starting circuit instead of a butterfly choke, but tripped over your chain-drive-wallet, here's a real deal, as long as they last. https://www. amazon.com/dp/BOOBXLOQSM Such a deal.

new parts!
 

hi everyone! Just wanted to say that everyone on here is full of great knowledge and thank you for sharing all of it. I ordered sprockets and chains, carbs, a rear shock, and a feeler gage for the hawks I bought for the wife and myself based on what Iv read on the different forums on this page. Parts are supposed to be arriving as early as Tuesday! Ill be putting them on as I get them and ill finally get to adjust the valves. I have almost 1000 miles on my bike and my wife has 300 on hers. I have watched the Motocheese videos on YouTube and can't wait to get hands on with the Hawks. I'm sure ill have questions that have probably been asked and answered on here several times so please be patient with me haha... Again thanks to all of you for your infinite wisdom! :D

Just ordered 1 of the 4 left.

Top end horsepower
 

One of the chief advantages of the engine used in the Hawk (and others) is the absolutely rigid and stiff crankcases. You would be amazed how much engine horspower is eaten up by panting engine cases. This is one of the many things that let engines get horsepower to the ground. Non-rigid crankcases absorb horsepower by getting slightly out of true, and then putting loads on the main bearings that they were never designed to deal with. When the main bearings do not run absolutely true to the crankshaft, two primary things happen. 1) Overloading one end or the other of the main bearings, especially roller bearings. This leads to short bearing life, and, by running out of true, increased friction. 2) And very serious, putting bending loads on the crankshaft. And worse yet "panting" means not a steady off center load, but repeating the whole bending process every other revolution, during the power stroke, and then whipping back to where it was designed to be for the next two strokes. Now crankshafts are made of very high tensile steel, and then hardend where the bearings run. The rod bearing, and the two or three main bearings. High tensile steel, hardened, is pretty well bullet proof as long as the crank cases are rigid. But put bending loads on them and crank failure is inevitable.

And some more of the story
 

It took about 25 years before it perculated through the engineering world how important rigid crankcases were. I would not be at all surprised to learn that this knowledge came with the introduction of the dynomometer metheod of taking torque readings. The Prony Brake metheod led to flash readings because you couldn't cool them effectively. But a dynomometer can be cooled, and so allowed long dyno runs. When an engine is pulled down after a long dyno run, one can measure where wear is occuring in the engine. I would bet that the bearing wear after 100 hours at 85% of full power came as a real wake-up call to those engineers. There was no excuse for the accelerated bearing wear. They used to just shrug it off as dirty oil, or too much spark advance, or whatever. But no way to shrug off engine wear on a dynomometer in a lab with controlled conditions.

High compression
 

Although I started this about high-end horsepower, upping the compression ratio adds power all the way up the scale. There is more than one way to up compression ratios, two rather obvious ways, and one not so obvious. The most obvious way might be to lower the head as compared to the piston at TDC. Either by milling the head or by turning a few thousandths off of the bottom of the cylinder. I would do the latter, because 1] No chance of weakening the head/cylinder joint, 2] Easy to adjust compression ratios by various shims between the bottom of the barrel and the engine cases. Then the not-so-obvious way mentioned above, which is for you that have TIG welders lurking in the garage, which is to add metal inside the combustion chamber to reduce the cc's of the combustion chamber, as compared to the swept volume of the piston. Even better when adding metal, is to add squish bands to the equation. Squish bands cause more turbulance in the mixture. This causes the mixture to burn faster, leaving more time for the expansion of the gases of combustion, and thus add more pressure on the piston. I don't know whether the younger set can think in steam engine terms, like some people of my age can, But if you can, it really simplifies the grasping of the concept. Imagine a steam locomotive of the turn of the last century, running about 250 lbs of steam pressure, and a temperature of 275 degrees f. Now look at the 1950's engine, running steam at 600 degrees, and 300 lbs pressure. The 600 degree steam is what is causing the great increase in power over the engine of 50 years earlier. Because 600 degree steam expands much more than 275 degree steam. So, too the air in the cylinder expands more than an engine of lower compression. And because of the added turbulance, all of the fuel is consumed earlier, leaving more time for expansion of the exhaust gases. So it is really quite similar to a steam engine, in that the goal is to get as much push out of these expanding gases as is possible. One engine is classed as internal combustion, and the other is external combustion, but expanding hot gases do the work in both cases.

ARH I enjoy reading all of your posts, you have such an amazing amount of information and I have the utmost respect for you. Can you give us a rundown of your career so we can better understand how you came to be so knowledgeable about motorcycles and engines?

I happened to be a young man in southern California when the British bike boom occured. Not yet old enough for a drivers licence. So the first wave of British bikes had come, and gone, leaving masses of bikes that were not the latest and newest languishing all over Southern Calif. for short money. I was working for ridiculesly low wages in a SoCal bike shop, when a 1949 Ariel Red Hunter 350 was traded in on a new A.J.S. 350. That '49 Ariel had my name on it, if I could lie, cheat, or steal my way into it's saddle. The owner of the shop sold it to me for $200.00, on the famous "Dollar a week, and the chase is on" finance plan. Except I really did paid for it. Actually at $5.00 a week. I bought the book "Speed, and how to Obtain it" from which I learned a lot of things to do to that lovely Ariel to make it give of its best. I eventually rode it in SoCal's version of TT races, some desert races, and a trial or two. I learned a lot, working at the bike shop, especially just before closing, when the racers and their wrenches came to the shop to shoot the bull. By this time I was starting to get a rep as a carb tuner, so people came to me about carburetor problems. I found that most people had not read "Speed and how to obtain it". They bought it, but didn't study up on it, if you know what I mean. Later, I got a copy of "Tuning For Speed" which was even better. You would be surprised how many people could read these books, and not get much out of them. I know it surprised me. Well, that's enough for today - - ARH

"Well that's enough for today"
Please continue soon... we're all ears ready to hear more

Really? I don't really like tooting my own horn. Can't imagine why any one would be interested in this stuff......ARH

ARH you're not tooting your own horn at all. It's very interesting, to me at least and I would imagine several others.

Great story ARH. :clap: We are lucky to have someone here like you with your knowledge.

He he he, and cheap price of admission. :lol:

And some more of the story
 

By now it's time to do my duty for God and Country, so I enlisted in the Navy. 2 years active-4 years in the reserves. When I got home, the Ariel Red Hunter had "dis-appeared". But now we had a new bike shop in Woodland Hills. Kolbe-Ekins BSA & Honda. So, naturally, I hung around that shop. Originally, Dave Ekins did the wrench work, and Andy Kolbe got the business going, doing up all the paperwork, making sure warranty claims were handled the way they should be, and all of that stuff. Kolbe was carrying the shop out of his wages at Rocketdyne, until it started breaking even, and then started making money. It is a sad fact that if you make no money, you will fail at business. And then you won't have a local Motorcycle Shop. At the time, they weren't selling very many BSA's, as people wanted those step-through Honda Fifties. But, as time went on, and Honda offered the 250 and 305 Sports models they started getting customers in interested in go-fast machinery. In addition to the step-thru customers. Unlike most bike shops, Andy kept everybody happy. Then I got a week-end job at Alan Fortney's Honda of Santa Monica. They were happy with me because they had a lot of older bikes they had taken in on trade, and I sold pretty near all of them in a couple of months. I kinda had my own clientele after I had been there a month or so. People wanting something cheap to run for going to work. There was a 250cc Pannanonia 2-strocker there that was in like new shape that they had traded for 8 months earlier, and the new sales manager told me they were going to have to junk it because no one wanted it. Really, I said, how deep are you in it? Don't worry about that, he said anything over scrap metal money will be considered manna from heaven. Wouldn't you know it but here comes a guy the very next Sunday looking for something to ride to work. I had been riding the Pannanonia around for a few days to limber it up, and make sure there was nothing wrong with it, then a good wash and wax and parked it right in front of the door, kinda' like bait. This guy shows up with his wife and 3-4 kids, and says he's looking for something to ride to work so his wife can have the car for emergencies and stuff. Anyway, he bought that cherry Pannanonia for $250.00 plus registration and title. Did I just turn him loose? No I made sure he knew how much oil to add to the gas, where to check for loose nuts, all that kinda stuff. Basically I sold most of their trade ins that way. Next installment- Gold Stars, and flat tracking.

What were some of the nasty things said about those Japanese motorcycles in those early honda days?

The same things, virtually word for word as is said now about China Bikes.....ARH

And the story goes on. And on.
 

About this time, Dave Ekins (Bud Ekins younger brother) decided that working for himself was not making him happy. He preferred working for someone else. Nothing wrong with that. So he sold out his share to Andy Kolbe (Exactly how I don't know, besides it wasn't any of my business) and Andy built a new shop a few blocks away on Ventura Blvd in Woodland Hills. Much nicer than the old shop he had rented. Not overdone, just.....nice. It drew in more customers. Sold loads of those Super Hawks. BSA's started selling better as well. And then Andy hit on that famous idea that has worked a thousand times. Race on Sunday, Sell on Monday. So he bought from someone else a "Bent-frame BSA" with an engine, trans, and wheels. All the successful BSA flat trackers had "bent" frames. They were bent a little bit to reduce the head angle, and trail. Quickened up the steering. This wasn't done on Triumphs and Harleys, because they would break loose too quick coming out of the turns. Remember, a twin fires once per revolution of the engine, and a single fires once every other revolution. So a single had a better chance to catch full traction coming out of the corners then twins had. If you have ridden your Hawk much off road, you might have noticed this. This was on half-mile tracks. On the mile tracks, basically you could not make up in the corners what you lost to the K-Model Harleys on the straights. That was the theory, but reality is something else. BSA's won plenty of mile races. Why? Very simple. A single is easier to tune to get maximum horse power than is a twin, and, generally is more reliable. I heard one Harley rider telling his mechanic "Yeah it's really pulling good on one cylinder, but the other one is just going along for the ride". The hardest engine to tune, in those days was a Harley. 45 cubic inch flathead. 750cc to those of you who are confused as to which country you live in. It took a real artist at the flow bench to get that thing to not only breathe, but breathe the same on both cylinders. Overhead valve production engines ran 30.50 cubic inches, or 500cc. That was the "Class C Rule" in effect at the time. Until later......ARH

Class C rules
 

Class C rules meant that you had to run the manufacturers product all the way. If you ran a BSA, you had to use a BSA frame, and forks and, on road racers, brakes out of the catalog of readily available BSA parts. Like wise for Triumph, Norton, and Harley-Davidson and Indian. Yes, there were a few 45 inch Indians running at that time. Norton could run the single overhead cam "International" but not the double overhead cam "Manx". This was because the International was a series produced motorcycle, that anyone could buy, and the "Manx" was not series produced for the road, and not anyone could buy one. So, what was the best single cylinder bike available, that fit class C rules, at that time? The BSA Goldstar! The Goldstar had the benefit of developement by two near geniuses. The man who initially designed it, Val Page. He also had designed the Ariel Red Hunters, another superb single. The second breath of fresh air for the Goldstar was the result of the work of Roland Pike, the famous tuner-rider of Rudge-Whitworth 250's well into the fifties, running a team of Pike-Rudge's until BSA hired him to work his magic on the Goldstar. Remember, the last Rudge was made before September, 1939, so it was quite an achievement to still be competitive 14 years after production ceased. That was Roland Pike. I posted a link to a youtube video of a historic race in England of a Rudge laying an ass whipping on a whole field of bikes as late as 2005. And that one was not even a Pike-Rudge. One of the Rudge's victoms was a 1960 something 250 Ducati, over head cam, telescopic forks and swing arm suspension at the rear and all. The Rudge had a rigid (Hardtail) frame, and girder front forks. You'll know a Pike-Rudge when you see one. It has girder front forks, and long travel shocks on the swing arm.

Would that also be Kolbe Can Am from back in the day ?

That was after I left the motorcycle racing scene the first time. Andy's rider on his Gold Star was Preston Petty.

I put a Preston Petty black fender on the front of my 1974 Yamaha GT80. I think I ordered it from JC Whitney, but I still couldn't keep up with the Honda XR75's.

Yeah, but in your mind it turned that GT80 into a rocket ship.

The nitty-gritti
 

At that time, I had somehow gotten the possesion of a 350 AJS, popularly known as an "Ajay". I ran that bike on SoCals idea of TT races. A dirt road track with a jump. Right and left turns. A miniature road racing track on dirt, in other words. The engine was not as free revving or as powerful as the Ariel, but the suspension was much better. I finally got around to going to Cooper Motors, the west coast importer of AMC motor cycles (James, Francis-Barnett, AJS, Matchless, and Norton), in and out a few times, buying stuff like oil filters (a felt cartridge that fit in the oil tank on the return side) , carburetor jets, and so on, getting acquainted with the guys that worked there. You guys surely know that technique. Pretty soon I got to go back in the shop, and exchange a few words with one of the mechanics. See, you had to know your way through the parts list to find the real goodies. And then would be revealed the greatest secret of all - - - there was ANOTHER parts list with all the factory racing goodies on it. Top secret shit! My tongue was hanging out! I noticed a special scrambles head for AJS/Matchless scramblers. Expensive. I asked about getting one. Oh no, can't be done. For factory supported racers only. Luckily, I had the short stroke engine. Mechanic suggested that I take my head to Jerry Branch, who had a flow bench, and would get out of that head every thing possible. I waited a couple of weeks (next paycheck) to take the head to Jerry. I'd been by his shop to enquire about this, and he said sure, bring it by. So I did, and picked it up a week later. He said you should be happier now, this head was really constipated on the exhaust side. Learn something new every day, right? Put the new head on, and engine came to life. Over the next winter, bought scrambles cams, and a little better top end. I was doing pretty well until one of the other guys bought a Gold Star 350. Partly he was a better rider than I was, and partly that Gold Star was a better engine. See a trend here? About this time, Andy Kolbe was working at night in the shop (He had a lathe, milling machine and a scraper back there, in addition to what every one else had.) putting that BSA together. Any part he couldn't buy, he made in that shop. Jerry Branch worked his magic on that head. Several trips to Los Angeles to C.R. Axtell's dyno. He bored out the 38mm Amal Grand Prix carburetor to 1 9/16ths choke (Or venturi) We tried aluminum intake valves. An intake valve to seat technique, that I was forced to agree to never divulge, not even after death! Now a lot of guys own lathes and can make stuff on it. But Andy was an artist in metal on that lathe and milling machine. About this time, a tall gawky teenager started hanging around the shop. He was looking over that Beezer like it could give milk. He was just 18. The youngest you could get a profesional licsence was 18, in the AMA. Typical goofy teen-ager. I thought. Until I saw him ride. A natural, really the only one I had ever seen. His name was Preston Petty. We started going to Ascot Track in Gardena when the season started. He wasn't just faster than the other Amateur racers, he was a lot faster. Well, my typing fingers are getting tired - so 'til later ---Sincerely, ARH

Arh... is this that track?
Pictured is preston
http://www.motorcyclemuseum.org/hall...ttyhonda_s.jpg

Preston is apparently in hard times...there is/was a go fund me for him.
https://www.gofundme.com/jvu3uaw4

Yeah, I just visited that site. Sad. He came from a very well to do family. And the girl he married was from a wealthier family. But I don't think her name was Mary. She must be wife number 2. Or 3. Or who knows. You can see from this picture how confident he was as a rider. He approached that jump perfectly in order to be that perfectly set up for his landing. No, that's not Ascot. That's one of the TT Scrambles tracks. My favorite was Prado Park, very smooth, and the surface held up really well, which was good for me, as I used the front brake a lot. Most, if not all dirt racers of those days did not ever touch the front brake. I used to go fartur into the corner doing that. If I won, guys would come up and tell me that I had some engine in order to win like that. Hah!......ARH

So amazing you guys rode those "tanks" as hard as you did. Without the modern suspension, and nimble light weight bikes of today. Answer, like doing without air conditioning , didn't know any different and pushed the tcecnoligy it to the limit , naturally :clap:



As culcune would say in his reporter like style, member 2lz reports that divorce is not good for the finances :wtf:

Tanks? These bikes were 100 to 200 lbs lighter then what people were riding in the forties. They were light-weights! I remember a quote from a Swedish moto-crosser who wanted to try a Harley 74 off road. He ran it over some jumps on a TT track, and said "Yah, goes gutt, but yumping Yesus, it sure hurts ven it come down". My Ajay weighed 370 lbs. Less when stripped for racing. A Harley Sportster weighed around 500 lbs, maybe 480 stripped for racing. I eventually ended up on a Triumph 500cc Tiger Twin. About 320 lbs. I was 6' 1", and weighed 217. I found that Triumph the easiest handling bike I ever rode. You rode it sitting down, except when going over jumps. It felt light to me. It had enough suspension travel for the way we rode in those days. And the way I still do. I don't like mucho suspension travel. Four inches at the back is plenty. More than that upsets the rake and trail too much for me.

My comparison was between the "tanks" of the 50's racers vs the "nimble light weight bikes of today. "

And yet more stuff no one wants to know!
 

By the way, when you took your scoot down to C.R. Axtell's, you were there, of course for the dyno run. You had to write the numbers down, because there were no print-outs in those (to you guys) pre-historic times. We ran the bikes with full gear (air cleaners, megaphones, etc. on the bike). After the tests were over, over a tall cool one, C. R. would never tell you what someone elses bike pulled on the dyno. If you wanted to know how your bike stacked up against the others, all he would say was "You still got work to do", which meant (or at least this is my understanding) You don't know what you are doing. "You're in the ballpark" meant middle of the pack. "Top shelf" meant you were ready to go head to head with the big boys. Amongst the Beezers of course. And since the Beezers pretty well owned that track, it also meant you were shitting in tall cotton. That also meant when they hung that bag of green lettuce at the finish line, you were in a good position to grab it. That also meant that whatever you had, had to be reliable enough to make it to the finish line under it's own power. One reason the BSA's were so fast on that track was because it had a seperate transmission, so you could change primary drive ratios as well as final drive ratios. The Harleys, Indians and Triumphs all had unit construction, so you could only change the final drive ratios. I carried a notebook with me, as well as an instrument that measured relative humidity, and temperature. I wrote all of that stuff down for every race meet, and cross referenced it to jetting and drive ratios. For each heat race, the semi, and the final (The money) event. And which rear tire for each of the races. Because the races were at night. And the temperature went down, and the humidity went up every hour past sundown. So you changed main jets, gearing, and rear tires for every race, as the night went on. Well, boys, chew this one over for a while....ARH

So why do I belabor you guys with all these factoids?
 

All of the things we did on Gold Stars can be done on our little Hawk engines. I go into this in considerable detail because the engine used in the Hawk has a truly rigid bottom end and crank cases. You must have these for a foundation to build your engine on. Otherwise horsepower and reliability will be used up in over coming crank flexing, caused by crank case "panting." Because of the rigid foundation of this engine used in the Hawk (and others), it is possible to build this engine as far as your pocket-book will allow. Or common sense tells you when to stop. You can not take power out-put to the maximum possible, because this engine does not have enough cooling fins to sustain such a power loading. But that is not true of an engine used in a dual sport or a dirt bike, because maximum power is used only for a few seconds at a time. If you build the engine to the max, take it easy on the highway. Long stretches at high power out put, pulling a tall gear, is where you will find the Achilles heel of this engine.

Carburetors.
 

It seems that after a period of time, a bunch of new people show up on this forum with carb problems. Perhaps you will forgive me when I think to my self, "Jeez, I've talked myself hoarse on tuning carburetors. Why do they keep asking the same questions!" Of course I'm from a previous generation (or 2!), where, you write something down, and remember where to find the info from then on until Brunhilde rides to your side and carries you to Valhalla. To the music of "The Ride of the Valkeries". Whether you are ready to go, or not. So, once again, here goes. Although I prefer Mikuni carburetors because they are easier to tune, even that thingy that comes hung on a Hawk does basically the same things. But, as you may have heard before, the devil is in the details. There are a few things that you should know before even looking at this carburetor. It is not a "pumper" carb. It does not have a "Power Jet". It is relatively simple to set up correctly. But it is also easy to set it up so far out of whack, it will drive you crazy. This is a variable venturi carburetor. The richness of the fuel mixture up to about halfway to 1/4 throttle is controlled by three things. The pilot jet, the cut-away on the lower front lip of the slide, and the idle mixture screw. The mid-range is controlled by the needle, and above 3/4 throttle the main jet controls virtually all of the fuel flow above 3/4 throttle. There is an easy way to set up these carbs, and there is the hard way, where you run from one adjustment to another trying to get good results, usually to no avail. Naturally, I'm going to tell you the easy way. Because I've always been described as lazy. Lazy people always look for the easy way to do things. People who always do things the hard way hate us, because after they have spent hours fouling something up, guys like me come along and fix the problem in a surprisingly short time. So here's the lazy man's way to do this. You start by putting the needle clip in the center notch. Then you set the idle mixture screw out 1 1/2 turns. Yes, I know it doesn't run right. Yet. Next, run it around town for twenty minutes, or so, to get the engine to operating temperature. Then run it wide open for a half mile or more and do a plug chop. A plug chop means you whip out the clutch, and kill the spark at the same instant, keeping the throttle wide open while letting the bike come to a stop, and never allowing the engine to turn even one extra revolution as the engine slows down to a stop. If the plugs firing parts are white to cream color, main jet is too lean. If the firing parts of the plug look sooty or black, main jet too rich. Now you should have a smooth power flow from just above 1/4 throttle all the way up to top speed. Now from idle to 1/4 throttle is pretty well controlled by the pilot jet. Usually, the throttle cut-away from the factory is spot on from idle on up. I like to set an engine like this to idle at 1350-1400 rpm. And then I play with the throttle cut-away to get a hearty "Thump" at the first little twist of the wrist. With the clutch hooked up.

Even though you consider it almost common knowledge ARH, just keep repeating yourself because some of us knew it and forgot it, some of us didn't know it, but ALL of us learn so much from you. Thanks

plug chop.... voodooo. :) If I can find the sensor that goes with this It will be on my hawk. still researching.

where should the sensor be mounted? before cat or after?

https://www.aliexpress.com/item/Air-...0-bfeda64d9636

Doing a plug chop is voodoo? It may be Mojo, but it ain't voodoo. It has worked for over 100 years, so it can't be all bad.

what I mean by Voodoo is that I have trouble walking a chewing gum. I worked at a gas station in the 80's,like a real gas station that fixed cars and Ed the owner, awesome mechanic too had this chart on the wall with like 16 images of plugs to read them. Except for the extremes, they all looked the same to me. But 14.7 on a digital gauge, even I can read that. :)

Gold Star's - - Again?
 

I wrote an article yesterday about tuning the Mikuni carb on a Hawk. Did I learn that on a Mikuni? No. I learned it on an Amal GP 1 1/2 inch (38mm) carburetor. Mounted on a bent-frame BSA Gold Star flat tracker. We proved to our satisfaction that the Gold Star put out more horse power with that carb than any other on the dyno. But was it fussy? Oh my, yes. It was fussy because it was a remote needle carburetor. Huh? The needle was off set in a little compartment all its own, next to the slide. This was worth about 2 hp on a 500cc engine. The extra power came from the reduction in turbulance from the air-stream going around the needle in the standard Amal Monoblock, or TT9 carburetor. Now do you guys believe me maybe a little about turbulance caused by the butter fly choke on the standard Hawk carb, and the $30.00 Mikuni? H-m-m? Tuners hated those GP carbs with their remote needles because they were so hard to get right. They had to be spot on or you were out of the money. This is why we all carried a little notebook where were noted the temperature for every hour from 6:30 pm to eleven pm, and the relative humidity as well. And the jets that worked the best at those temps and humidity points. Even then you could be a little off. The trick was to be right more often than your competitors were. I carried about 20 main jets, 5 pilot jets, and 5 throttle slides in a case down to the track on race night. But, by consulting the notebook, I could get pretty close before the end of practice. By the way, another guy was shaving the tires, because dirt tracks changed traction constantly.

Will I fit comfortably in a hawk 250
 

I'm 5'9 and weigh about 170lbs I wear a 36/32 size jeans and I was wondering if I could fit on a hawk 250 all the videos I've seen was with people over 6'

Just get one landed in your driveway. Worry about the details later. Go try on a honda in the showroom to compare. You will figure it out....minus the 5 thousand dollar price tag, you'll be convinced quickly.

I'm 5'7 and 165 lbs and I was able to plant one of my feet down by sliding slightly on the seat. until I replaced the seat the one that csc is selling,so I can plant both feet down.The seat height did not effect my riding,I just did'nt want people to see me tip toeing.

I'm 5-10 and wear 32-32's and I fit fine. I touch flat footed with a little lean to one side or slightly tip-toed and both feet touch.

I agree with what BlackBike said, go to a Honda dealer and sit on a CRF250L. The seat height is almost identical, but the Hawk's suspension is a little softer.