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Help me with Carb tuning!!!

  • Thread starter Thread starter akreider
  • Start date Start date
A

akreider

Guest
Setup -

Mukuni BS34SS carburators with K&N pods, Dynojet stage 3 jet kit, replaced fuel air mixture screws, aftermarket performance header (not sure what it is previous owner put it on), and Yoshimura R3 race pipe.


What I did -

When I installed the jets I screwed them all in until they were snug not torqued in hard. Used a digital caliper to set the floats at the proper height of 24.6 I think (I set it according to the suzuki shop manual). Checked for vaccum leaks by misting starter fluid around the boots to see if idle increased and I found none. Set the air screws by screwing them in till they were snug marked their position then set them at 2.5 turns (1 turn = screw turning 360°). Petcock was checked and everything was fine.

Problem -

From what I understand for the suzuki manual is that the air screw is used only for the slow system (with throttle closed or engine at idle).
The bike will start up only with the choke on and after it is running I can push in the choke only partially and still keep the engine running. And when I twist the throttle when the bike is idling with the choke on it will bog down and die if I keep the throttle open. But if I keep twisting the throttle and let off the rpms will increase then once the engine's rpms are over 6000 the engine responds right away to throttle without any hesitation. I assume that this is because at that point the engine is not using the "slow system" therefore not using the air screw.

Question -

How can I solve this problem? Did I properly install all the jets by just setting them snug? Also when I read the settings for the carbs, it said 1.2 for the air jet, does the mean the size or how many turns I should set it at? And finally what is the bypass and pilot outlet and what do their settings of 0.8 and 0.9 respectively mean?

Thanks for all your help
 
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On mine with a very similar setup went up to 47.5 pilot jets and 170 pilot air jets. Screw the jets until snug.
 
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If you set the floats at 24.6 you are most likely starving the carbs. Most models call for the floats to be set at 22.4.
 
Thats what I set them at I just couldnt remember the number when I was posting this thread.

Why did you change your jets? To correct what problem?
 
I went up on the pilot jet because I couldn't get a good idle to 1/4 throttle. It didn't matter how I adjusted the idle adjustment screws. I went up to 170 air jet because of the jump in the main jet size. If you're messing with a Dynojet try setting the needle on the second notch up or the fifth down. Dynojets setting suggestions are usually lean. I'm also using the 132 dynojet main. My bike runs absolutely kick &ss with this set up. Did you have your cams degreed in?
 
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You need adjustable cam sprockets and a buddy who knows what he's doing.
 
Air Screws

Air Screws

If I'm not mistaken, you may have tweaked your air screws/jets. They are not supposed to be snugged when adjusting, as this can damage the jets. They should be threaded in until just making contact, then set at proper number of turns. If I'm wrong, somebody please correct me.
 
That is one thing I made sure not to do is to tighten them in, I only set them right when they touched.

Ok I have to admit my major lapse in thought while installing the jet kit, I didnt read the fine print that says to only change the air screws if it is running to rich. So I reinstalled the stock one earlier today and that solved the problem of the engine dying when twisting the throttle. The bike was just getting to much air. But I still have the problem of having to use the choke to keep the engine running. It will only run around 2000 rpm, I cannot back the choke off enough to get it to normal idle speed. I currently have the e-clips in the 2nd groove up or 5th from the top on the needle. I also have the 138 main jet installed.
 
You are adding fuel with the choke on during the pilot circuit. Try going up to the 47.5 pilot jets like I suggested earlier. If your running strong and not rich on your main leave it alone. Your idle adjustment screws should be 1.5 to 2.0 turns out. When I was referring to snug it was with the jets not the screws. My setup on an 80 1100. Dynojet stage 3. 132 main jet. 47.5 pilot jet. 170 pilot air jet. Needle two notches up or 5 down. Idle adjustment set to highest rpm method. Mercury stick synchronized. Took me alot of trial and error to get this right.
 
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Time to get back to work on the bike... just got back from vacation.

When the mixture screw is turned in or (tighter) does that lean the mixture out for the idle circuit? Or is it just the opposite?
 
I must have shut my brain entirely off, even with every one telling me to change the pilot jet. I never thought to do it. I must of been thinking that the stock jets would be good enough for some crazy reason.

I figured I would just swap in the kit and fuel mixture screws and I would go. (KN really should put pilot jets into their kits) Then it hit me like a ton of bricks (reason to change it) with the kn pods 4into1 header and yoshi can my bike is running crazy lean at idle with the stock pilot jets and no matter how many times I turn the mixture screw it would never deliver enough fuel to the engine.

I feel like the biggest moron for total neglecting the pilot jets and assuming the stock ones would suffice.

Now when I bump up the pilot jets to 47.5s will the 160 pilot air jets from dynojet work?

Adam
 
I use Mikuni 170 pilot air jets. I don't know the difference between the mikuni and dynojet pilot air jets. I assume it's bigger since your stock jet is mikuni 160.
 
You are still starving your carbs somehow. You probably have a vacuum operated petcock, have you checked that you are getting vacuum on the line from the carbs to the petcock?

I am assuming that you did set the floats correctly, that was covered in earlier responses.

Try setting up an alternate gasoline supply - a suspended funnel or water bottle (make sure it doesn't dissolve with gas in it), and some spare gas line straight to the input on the carbs. If it runs OK, you have a petcock/vacuum/boot leak issue.

Or you could just disconnect the petcock vacuum line from the carb it's connected to, plug the carb connector & suck on the vacuum line. You should not end up with a mouthful of gas - if you do, you definitely have petcock issues.

Just for funzies, release the gas cap before you start it - if the tank cooled off overnight and your gas cap bleeder is clogged, you might have a vacuum in the tank.

These are just some possibilities, I guarantee nothing, but I hope this helps eliminate a few items.
 
I have already eliminated the petcock as a problem, tested the vaccum by sucking on the vaccum line. I also have made sure that there are no leaks around the intake boots, which would lean the mixture. And the gas cap is works good, the carbs get the right amount of gas. The only thing left is the pilot jet because the bike runs great once I get it out of the lower rpm range that is controled by the idle circuit of the carbs.

adam
 
O.K., so it's not the petcock. Still doesn't make sense that it would be your pilot size. I mean, the size may actually be wrong, but your theory that the high RPM's are getting you into the needle/main jet range doesn't make 100% sense - that is not controlled by RPM's but by throttle opening/slide position. Admittedly, the higher RPM's you have at a given throttle opening, the higher the slide is going to be, but with no load, 6000 is not probably more than 1/4 throttle.

And unless the pilot size is wayyy the hell off, (like 250 pilots in a 750) it should make it lean, but not so much that it won't run at all without the choke.

I don't have much more to suggest except to look for obstructions in the pilot circuit, diaphragm leaks, or your float level being way off.

I am sure that other (better than me, which is not hard) expertise here will put you on to something, though.

Good luck.
 
Still trying, just got the pilot fuel jets in and have to try them out. I'll let you know how it goes.

Adam
 
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