Less than $28 for carb + jet kit

[Megadan]

The injection pump is there to eliminate on-throttle lean conditions common on standard carburetors. It's hard to explain to people that have never experienced the two types side by side, but on the standard carb, when you crank open the throttle there is a delay there between opening and acceleration. With the pumper carbs the throttle response is much more immediate, which some people often describe as a "light switch" on and off feeling.

While on a standard bike just used for riding around town, tuned a bit safe, it's not really necessary. I personally prefer them, especially if you are trying to tune the engine for optimal performance. The inverse of that is you will often see a small drop in fuel economy, but that only comes into play during acceleration. During constant throttle and cruising it will be the same as always.

[Ariel Red Hunter]

Originally Posted by Megadan

The injection pump is there to eliminate on-throttle lean conditions common on standard carburetors. It's hard to explain to people that have never experienced the two types side by side, but on the standard carb, when you crank open the throttle there is a delay there between opening and acceleration. With the pumper carbs the throttle response is much more immediate, which some people often describe as a "light switch" on and off feeling.

While on a standard bike just used for riding around town, tuned a bit safe, it's not really necessary. I personally prefer them, especially if you are trying to tune the engine for optimal performance. The inverse of that is you will often see a small drop in fuel economy, but that only comes into play during acceleration. During constant throttle and cruising it will be the same as always.

On a round slide Mikuni, changing the throttle slide to a smaller one also improves throttle response. By smaller I mean one with less cut-away...ARH

[pcspecialist]

I may replace the 42 with a 40 slow, after a long ride I had to turn the idle mixture screw in 1/2 turn so it is now only 1/2 turn out.

[BigWeld]

Originally Posted by Megadan

I forgot to mention something else I wanted to point out. Many people that re-jet the stock PZ30 clones often run a Mikuni 110 main jet. If you use actual Keihin jets in a PZ30, the jet sizes you see are going to actually be different.

The orifice size equates to a different jet number between the two.

I.E. A 110 Mikuni main jet uses a #56 drill bit size. The equivalent Keihin jet size that uses the same 56 drill bit is a 125. A 105 Mikuni is equivalent to a 118 Keihin.

Megadan, is there a chart somewhere with these jet sizes in comparison? Since before I bought my Bashan, I've been mentally keeping track of elelvations in comparison to jet sizes, and what would work for me and how I wanted to build my bike. Now that it's almost done, I realized that the jetting that works best for my Keihin is way higher than those typically used in a Hawk or

What I experienced is exactly how you described, and I think that if there's a comparison chart for Mikuni/Keihin jet sizes available, it would help alleviate a lot of confusion for the newer guys buying Bashans that come stock with the Keihins........just my 2 cents.

[emptypockets]

Ok, I ordered one of these carbs and jet kits. What should I try first for mostly trail riding, stock exhaust, between 4,000 and 9,000 feet? I assume too rich is better than too lean. With the stock carb, the hawk seems to be running a little hotter than I would like.

[Megadan]

Originally Posted by BigWeld

Megadan, is there a chart somewhere with these jet sizes in comparison? Since before I bought my Bashan, I've been mentally keeping track of elelvations in comparison to jet sizes, and what would work for me and how I wanted to build my bike. Now that it's almost done, I realized that the jetting that works best for my Keihin is way higher than those typically used in a Hawk or

What I experienced is exactly how you described, and I think that if there's a comparison chart for Mikuni/Keihin jet sizes available, it would help alleviate a lot of confusion for the newer guys buying Bashans that come stock with the Keihins........just my 2 cents.

http://www.jetsrus.com/FAQs/FAQ_miku...ihin_sizes.htm

[emptypockets]

I've tried 120/42, 110/40 and 105/38. It stumbles, runs like crap, and dies. Doesn't seem to matter where I have the idle adjustment screw. Not sure what else to do but put the stock carb back on.

[pistolclass]

I took the easy way out. I got a mikuni VM26 and a 110 main. I have the stock pilot but I make up for it with the needle thingy being on the fattest setting and the screw being out 2 turns. I know I should change my pilot, heck I even have some pilots, but the bike runs great right now so why mess with it. For me I think the Mikuni is just easier to set up. IMHO.

[Megadan]

Originally Posted by emptypockets

I've tried 120/42, 110/40 and 105/38. It stumbles, runs like crap, and dies. Doesn't seem to matter where I have the idle adjustment screw. Not sure what else to do but put the stock carb back on.

I am assuming you have the Keihin clone mentioned in this thread. \ Which idle screw are you adjusting, idle speed or idle mixture?

First thing I would recommend doing is cleaning the heck out of that carburetor. Blast compressed air through all of the passages in the carburetor, and if you have small brushes, or wires, try to pass them through to clear any potential blockages.

Second, check the float height. If the float height is too high or too low it will affect the mixture. IE. If the float height is too high, too much fuel in the bowl will actually cause it to be richer on the same sized jet. With the carb turned upside down the floats should sit level with the bottom flange the bowl seals against.

Third. Once those two things are done, start with known variables and use genuine jets if at all possible. If your bike is completely stock, then a 40 pilot and a 118 or 120 main jet would be the rough equivalent to a Mikuni on a 25 pilot and a 105 or 107.5 main jet. Set the needle jet in the center or 1 notch down from center. If you have mods done to the bike, ie - intake and exhaust then start with a 130 main and leave the pilot as a 40 for now.

Originally Posted by pistolclass

I took the easy way out. I got a mikuni VM26 and a 110 main. I have the stock pilot but I make up for it with the needle thingy being on the fattest setting and the screw being out 2 turns. I know I should change my pilot, heck I even have some pilots, but the bike runs great right now so why mess with it. For me I think the Mikuni is just easier to set up. IMHO.

I agree, which is why so many of us went that direction. More success stories and more jetting info readily available.

[emptypockets]

Thanks for the replies. I threw in the towel and went back to stock. I don't know what's wrong with the new carb, and after 5 hours of fiddling, I don't think it's ever going to work. Guess I'll try a mikuni next.

[HILL]

Originally Posted by emptypockets

Thanks for the replies. I threw in the towel and went back to stock. I don't know what's wrong with the new carb, and after 5 hours of fiddling, I don't think it's ever going to work. Guess I'll try a mikuni next.

Sucks to have to give up on the Keihin. There've been quite a few people who found that a thorough cleaning of a carb, even though it's brand new, can get that bit of whatever out of a passage and have a running engine.

It's really pretty amazing how small a piece can disrupt flow in a carb - little bitty shavings or whatever that need a magnifying glass to see once out and on a clean white paper towel.

Sometimes that little chunk can reside at the end of a passage that joins another passage in a "T". It can stay there through the most energetic cleaning, compressed air blowing, or whatever else might be tried.But it may come out enough in a low fuel flow to play all hell with carburation. Something like that makes a mystery carb that probably will never work right.

Lucky for us though, these Keihins are cheap.

[pete]

a little trick to help clean a carb if compressed air dosn't work..
fill the air line/hose from the compresser with water... high pressure
water can move things air won't...


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