Project: Hawk Stage II - Head Work and Nibbi

[Megadan]

A dyno would be the best way by far, but for many the access to one is either limited, or otherwise impossible. Only one in my city, and you have to book it 8-10 weeks in advance, and even then there is no guarantee of getting the day you scheduled because they don't run the dyno if the temps go above 90F outside, or below 50F.

What is kind of funny is the influx of bigger carb installs and ported heads as of late. My first year or so on this forum, the biggest and baddest mods people ever talked about was exhausts or decats, VM26 car clones, airbox mods or pod filters.

Then one day I post a thread about head porting after buying a head, then a couple other guys, ie Jerry, Silva, and at least one other I can't remember all decided it was a good idea too, and thus in a short span all of us had ported heads. Not one dyno.
No quantified results with a dyno or otherwise, just people taking our word for it, and the proof was in the pudding.

Then for a while, nobody else really dove in right away. Not sure if they were too afraid or what, but it stayed pretty mute.

Then Jerry installed his PWK carb, and not long after I installed me PE30. I made a couple of videos and posts here exclaiming "Holy Moly!" at the increase in power and torque across the entire rpm range. Up to that point I was running the PZ30B, and with the ported head it felt decently stronger than before, but the result felt about the same as installing the exhaust on the bike. A good increase, but nothing too outrageous on its own. Once I gave the head the air to actually breathe, it was a completely different story. Jerry posting similar results with his PWK carb.

Within a few months of us posting our results, a few more popped up here and there and they back up our own words, and thus a chain reaction. Now it almost seems like everybody with a chinabike and a youtube account has to follow suit or be left in the dust. Especially after Redbeard's Garage posted his video of the ported head install on the Motomax, although he is still running a weaksauce carb.

Would I like to know what I got for all of my time and money? Sure, I guess, but to tell the truth I don't really need it. I know how the bike felt with every change, and I know that compared to my last Hawk, the current one is much more powerful. Top speed is a little better, maybe 5mph faster more consistently with the same gearing. The real difference is the acceleration and tractor factor pulling up hills. Something I got to witness first hand with a stock TT250 slowing down up a fairly steep hill that I had to let off just so I wouldn't hit the guy because I was still pulling, with basically 5 less teeth out back than him, a heavier chain, and about 80lbs more weight.

If anything I often have to temper peoples enthusiasm with the gains in question and the idea that they formed in their head of what it is like vs. reality. Especially with the younger guys. They seem to think big carb and head porting will turn an anemic air cooled 229cc OHV engine into a 90mph capable dual sport. We all know that isn't the case, which is why I tend to underplay it a bit, and try to shift the focus away from top speed and more toward pulling power. Going faster than 70 on one of these bikes isn't for the faint of heart, which is why I have mine geared the way I do.

[Baskt_Case]

Well said Dan, keeping traffic off my tail in hilly 55 zones is one of my top goals here.

[Megadan]

Originally Posted by Baskt_Case

Well said Dan, keeping traffic off my tail in hilly 55 zones is one of my top goals here.

I can pull most hills in 5th at 55mph until we start talking steeper grades like 6%+, or one heck of a head wind on a milder grade. Even then I can usually still hold 55, although I might be pretty pegged lol. Again, gearing plays a factor, and never forget that I am a big heavy guy, so smaller people may struggle less on inclines. I am literally the worst person to put on one of these bikes for a top speed or hill test

[China Rider 27]

I have only been around here for a little over a year and I can see, you and Jerry, Silva, and others have been the innovators on the head porting and other performance improvements. I mean we all copy and follow you guys! Imitation is the best form of flattery! We do all admire your work and appreciate your knowledge, suggestions, and assistance.

Head porting is going to be a big thing in the future and the PE30 carb arrangements too. That is due to you and Jerry Hawk some others. Good job!

I agree about top speed, it does not really mean much and depends on so many variables. People will always be interested in top speed at the expense of other considerations. Speed is thrilling. It is something people just got to know. On my HAWK it is sketchy at WOT and I agree frankly without some good suspension modifications not somewhere I want to spend a lot of time, nor do I recommend other do either. My real interest is as a measure of performance. "Experience" is just as valuable and real as a number and maybe at the heart of satisfaction. If it feels like it is going fast and your satisfied, do you really need anything else.

One day I will be in the Head porting club!

[Megadan]

Originally Posted by China Rider 27

I have only been around here for a little over a year and I can see, you and Jerry, Silva, and others have been the innovators on the head porting and other performance improvements. I mean we all copy and follow you guys! Imitation is the best form of flattery! We do all admire your work and appreciate your knowledge, suggestions, and assistance.

Head porting is going to be a big thing in the future and the PE30 carb arrangements too. That is due to you and Jerry Hawk some others. Good job!

I agree about top speed, it does not really mean much and depends on so many variables. People will always be interested in top speed at the expense of other considerations. Speed is thrilling. It is something people just got to know. On my HAWK it is sketchy at WOT and I agree frankly without some good suspension modifications not somewhere I want to spend a lot of time, nor do I recommend other do either. My real interest is as a measure of performance. "Experience" is just as valuable and real as a number and maybe at the heart of satisfaction. If it feels like it is going fast and your satisfied, do you really need anything else.

One day I will be in the Head porting club!

Just like when I arrived here and borrowed ideas and upgrades from those before me. It's the evolution and progress at work lol. A vast majority of my Resource guide is information passed on from other guys that I just collected.

I look forward to your thread on it. Just as I can't wait to see the results from this one. This is the first bike where somebody decided they were going to go all out. Most of us just took the cheap bastards route and made the most of what was already there.

[China Rider 27]

There is nothing wrong with the cheap route, that is why we are all here. Thinking about this testing issue some, and I have to say, High speed testing is to dangerous. Especially with these head ported, compression stoked, engines. Baskt case I suggest what you should do is set some assessments based upon speed going up hills and just control for everything but throttle application. Similar to a Dyno, you could apply all out throttle in each case. That way it would be at a slower speed overall speed depending on the hill but give a good comparison.

[TheChairman]

Just want to say that this thread here is one of the reasons I bought this bike. These super simple engines are always good candidates for building on because it doesn't take a small nestegg, a ton of experience, or specialized tools to get inside there. If you ruin a part, the replacement is cheap and easy to install. 1 or 2HP gains can feel huge.

You mention a cam. Is there a cam available, or is this something that will need to be custom ground? So far the only off the shelf aftermarket performance I've come across is exhaust, intake, and ignition modifications.

[Megadan]

Originally Posted by TheChairman

You mention a cam. Is there a cam available, or is this something that will need to be custom ground? So far the only off the shelf aftermarket performance I've come across is exhaust, intake, and ignition modifications.

It's buried back on page 15 of my "New Hawk, New Adventures" thread where I go over the cam I have, how I ordered it, how others can order it, and other related information.

http://chinariders.net/showpost.php?...&postcount=221

[Baskt_Case]

Originally Posted by Megadan

This is the first bike where somebody decided they were going to go all out.

Well, this project sure didn't start out that way, but things kinda got outta hand and now I'm just goin with it!

If the weather cooperates, today is Nibbi day.

OneLeggedRider gave me the fantastic idea to check port volume on the Brozz head before I ship it off. Has anyone checked port volume on a stock Hawk head, or can they? I'm gonna grab a big syringe and some ATF this morning.

And I just found these incredibly helpful calculators this morning. Calculate HP from E/T, Speed, and Weight. Need to find a good app that logs speed vs. time better. My current app only has 1.0 second resolution.

http://www.wallaceracing.com/Calculators.htm

[OneLeggedRider]

Glad I could be of assistance Basket_case. It's actually pretty common to check head and port volume with a graduated buret and ATF in high performance cylinder head work, especially on multi cylinder engines, besides Flo-bench testing.

Do you need dyno testing to tell if you're making more power? No. But it's the only accurate way to measure gains. When I lived in Florida I had regular access to one thanks to becoming very good friends with Don, my former high performance instructor who had worked for some of the biggest name drag racers. That taught me you can't always go by "feel", which is often inaccurate.

And you gave me an idea on weighing the rotating mass before and after on the trike project. And it got me to thinking about selling the 200X rear end and buying something newer that came with 12" rims because of parts availability and the ability to buy much larger aftermarket rims that I can mount DOT approved tires on.

I haven't been posting much because of being sick for 3 weeks and working on my cabin. And also I'm a little aggravated with this site and uploading pics. Even on poor service days I can upload multiple pics to FB in less than a minute, but on here one pic might take a half hour or not at all, which seems screwy to me.

[JerryHawk250]

Originally Posted by OneLeggedRider

I haven't been posting much because of being sick for 3 weeks and working on my cabin. And also I'm a little aggravated with this site and uploading pics. Even on poor service days I can upload multiple pics to FB in less than a minute, but on here one pic might take a half hour or not at all, which seems screwy to me.

I was just about to text you to see how you wee doing. Hoping you're doing better.
Yeah, uploading pictures to this site takes longer because it resizes the picture. Even on high speed internet it takes time to process it.

[Baskt_Case]

Was finally able to at least get the Nibbi mounted and briefly run the motor before I ran out of daylight. Lots of loose ends to tie up tomorrow. Throttle cable was too short, carb touches frame, barely got air filter on it. I sent the Nibbi intake to the builder so I'm using the shorter generic rubber Amazon one. At least the rubber filter adapter is now cushioning the carb against the frame. Longer Nibbi intake will put the bowl on the frame. Not sure what I will ultimately do. Also need to stretch out the spring on the idle knob, or add a star washer. The knob vibrates a ¼-turn either way.

Initial jetting is 40 slow, 115 main, clip in middle, 1½ turns out, 700 feet elevation. Have not been on the road yet. Snap throttle off idle has a tendency to kill it. It'll pop occasionally on come down. Plan to install 45 and 120 and methodically work each. I had not started the bike in a week. Pulled plunger, hit starter, instantaneous light-off. She runs. Would probably get to town in an emergency. I'm tickled for the moment.

Head is on its way to California. Now I wait. Dont ask how long, were just not gonna talk about that right now. However, I did get a chance to measure port volume before I packed it up...

Intake = 51 cc
Exhaust = 24 cc

[Megadan]

I found a 40 pilot to be way too big and I am at 1100ft. I was running a 35 for a while but it proved to be a hair lean at part throttle in these cooler temps and just recently upped to a 38 at 2 turns out on the air screw. Admittedly, my intake is longer than the one you are using and that may affect jetting slightly.

The frame issues you are having are the same ones I was having. That is the reason I ended up running the rubber CQR 250 intake. Unlike the Nibbi one, it doesn't put the carb into the frame. All of the shorter angled intakes I tried were even worse.

[Baskt_Case]

Originally Posted by Megadan

...just recently upped to a 38 at 2 turns out on the air screw.

Would you kindly expound on the logic here? This is the first carb I have ever tuned in my life. So now I am applying the sum of six months of learned theory. I'm assuming the 38 was then a hair too rich for your liking so you used the air screw to effectively split the difference between 35 and 38?

[Megadan]

Originally Posted by Baskt_Case

Would you kindly expound on the logic here? This is the first carb I have ever tuned in my life. So now I am applying the sum of six months of learned theory. I'm assuming the 38 was then a hair too rich for your liking so you used the air screw to effectively split the difference between 35 and 38?

Ok, so the slow jet, aka pilot jet, is primarily responsible for the majority of fueling from just barely off idle to about 1/8 throttle, and about half of the fueling from 1/8 to 1/4 and then it tapers off to a minimal amount after that.

The air screw for the idle mixture only affects the idle circuit, with the throttle closed. The pilot jet does affect how much fuel can flow through the idle circuit, so with the two different sizes, a different setting is required, but that's about where it stops. With the 35 I needed around 1 1/2 turns out while the 38 required about 2 turns out. The more turns out on the air screw, the more air is allowed into the idle circuit, which leans the mixture.

The reason I switched to the 38 had nothing to do with the idle mixture itself. Either jet had a setting that allowed for a proper idle mixture. The reason I swapped up to a 38 had to do with light throttle going lean.

When a pilot jet is a little lean, what you will run into when either maintaining a low speed in a higher gear, or just slightly applying throttle on a down hill, usually about 1/8th throttle or less, you will get some bucking, hesitation, and even afterfire from the exhaust as the mixture goes lean. I was getting those symptoms with the 35, so I went up a size. Now they are gone. I ran into the same issue with the VM26 Mikuni after installing the exhaust and a 25 pilot jet. I had to up to a 27.5. Idle was fine, but light throttle was lean.

The main thing to remember about these types of slide valve carbs is that the main and pilot jets have their own main purpose, but also affect another circuit or jet. The main jet is primarily there for fueling from beyond 3/4 throttle to full throttle, but the main jet size can also affect the amount of fuel that flows through the needle jet, and thus alter either the needle setting itself, or possibly even requiring a different needle jet in some circumstances. You most likely wont ever run into that here, but if you really delve into hardcore carb tuning, it all plays a role. Even the angle of the cutaway on the throttle slide affects the jetting in a certain portion of the throttle sweep, causing a weaker or stronger pull on the jets.