Custom Fighters - Custom Streetfighter Motorcycle Forum banner
1 - 20 of 24 Posts

·
Registered
Joined
·
705 Posts
Discussion Starter · #1 ·
I have a 600 gsxr 1992, runs lean at WOT (cuts out) but rich everywhere else. The carbs say 18E0. I have 105 for main jet, 5FZ91 for needle (just one circlip position), and 32.5 for what I guess is pilot jet. I also have a spare set of carbs that came with the bike. The main jet is 115, needles are the same but the pilot jet is messed up and I don't think I'll be able to remove it.

Any thoughts on new jet sizes? It has the original airbox, just a screen filter, and full headers 4-2-1 with a LeoVince muffler no dB killer. I live at around 6000 feet. Thanks!
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #2 ·
Okay, I'm not sure that was correct. Looking back at my videos, the a/f ratio is always lean.

I did some searching and it looks like the carb is right for the engine.
I looked up dynojet's kit for the carb: http://www.dynojet.com/pdf/3140.pdf
but the document says to use a DJ112 main jet with headers, exhaust and filter (stage 1). I looked up this conversion: http://www.jetsrus.com/FAQs/FAQ_mikuni_vs_dynojet_vs_keihin_sizes.htm
and the DJ112 is equivalent to the mikuni 105 I have right now. Dynojet only lists stage 1 as an option, no stage 2 or 3.
I also can't find anything about the needles, and I don't have the ones with multiple grooves so you can move the circlip.

Oh and the spare carb has 105s, the one I pulled off had a 110. I got the pilot jets out and they are the same, 32.5.
 

·
Remi's Dad
Joined
·
17,593 Posts
you can't move the clip but you can put a shim under the needle. Are the floats adjustable?

I'm not convinced about the needle position/taper being an issue, especially for a near stock bike
my first thoughts are float levels (probably not adjustable.) maybe toying with opening the air screws a hair, and upping the main jet one step


this might help your quest as, i don't have the carb/bike in front of me. Good luck!
 

·
Remi's Dad
Joined
·
17,593 Posts
I cant help much at that effect other than to say. Give the bike what its asking for with your a/f gauge and plugs chops. Carbs are dumb you have to tell them what to do.

Also no 2 bikes share the same tuning. The basics are a starting point.
 

·
Remi's Dad
Joined
·
17,593 Posts
try keeping the pilot stock to start out. A stock "slow jet" doesn't necessarily need changed unless you have open carbs and open header. It really doesn't get used past 1/3 throttle.

If it is still lean off idle to 1/3 swap them out
 

·
Registered
Joined
·
463 Posts
Let's back up a couple steps here:

Why do you think it's cutting out at WOT over lack of fuel? There's a different things that can cause you to cut out at WOT that aren't fuel related. A 115 should be plenty for 6k.
 

·
Registered
Joined
·
463 Posts
I watch my a/f gauge
Answers that...

Okay...what else is done? Factory header or a full setup? filter?

How long does it take to lean out? Is it an instant thing or does it take a second or two? Instantly lean means you're not flowing enough fuel (dirty jet/too small jet), petering out means you don't have enough supply (float level/filter/fuel line size).

You might also have a vacuum leak allowing more air in and until high speeds you're pilot is able to compensate...but I don't think that's likely.

Have you tried throwing the choke on at WOT to see if it evens out?
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #11 ·
Like I said in my first post: It has the original airbox, just a screen filter, and full headers 4-2-1 with a LeoVince muffler no dB killer.

I checked for vacuum leaks quite a while ago. I set the float level to the spec. Doesn't setting float level change the a/f ratio for a couple circuits? I haven't tried adding the choke. Honestly I haven't been able to ride it much to troubleshoot because I need to get the tires replaced. They are totally shot, last time I rode it I dumped it so I'm not taking it out again until I can get the tires done.

Based on this: https://www.jetsrus.com/FAQs/FAQ_rejetting_101_how_to_rejet.htm
I've decided to just move up one pilot jet size first since I have about 2.5 turns out on the mixture screws to get a decent idle.

I remember why I thought it was rich originally, the pipe tip is black and when you slow to a stop you can smell fuel/exhaust.

Right now I can only start it with starting fluid and the choke as far on as it will go. Takes forever to warm up and not have an off-idle stumble. fucking carburetors.
 

·
Registered
Joined
·
463 Posts
Right now I can only start it with starting fluid and the choke as far on as it will go. Takes forever to warm up and not have an off-idle stumble.
Sorry I'm mobile and it's hard to flip back to old posts...I'll dive into this a bit more later but this line right here throws up red flags. Have you checked compression? Do you know when the valves were checked last?
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #13 ·
Ditch the mobile page, it's more trouble than its worth.
Take a look at the first few posts on the bike in my sig. I replaced the piston rings and shimmed the valves about a year ago, ran great and I rode it for about six months before tearing into it again. It runs the same as it used to (except for the cut out at wot) once it's warmed up but it's hard to start now. It's also cold right now so it may still start okay when it warms up outside.
 

·
Hack in a barn
Joined
·
4,409 Posts
Just a suggestion but having a couple of air filter options can come in real handy with the carb tuning. My R6 started with a K&N, and after messing with main jetting and needle shims I switched back to a stock filter. The stocker gave me good results with the fatter mixture from less air flow. Then I switched out the pilot jets, shim the needles again and adjusted the float all fatter and was able to run the K&N.

Long story short, if you have a couple of filters, one stock (less air) and one aftermarket (more air). It is easier to change the filter to affect the jetting than it is to remove the carbs to change jetting.

Oh and M2.5 washers are usually the perfect needle shims. Dremel the hole open a hair to fit the needle through. 2 washers = 1mm of height, which is usually one clip position.
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #16 ·
Ok, keeping this thread updated in case someone else has this problem.

Moved up one pilot jet size. Rechecked float height, making sure not to depress the spring in the float needle. Found out that the one float bowl that I pulled to check main jet size was a 105, the rest were 115s. :nuts: Since I had 115 main jets in the spare carb I switched out the 105 so they are all 115 now.

I set the mixture screws to 1.5 turns out, still wouldn't start without help. Once I got it running and warmed up I was showing lean so turned the mixture screws back out to 2.5 to get a steady 14.5 a/f ratio. So apparently I need one size bigger pilot jet. Hopefully it will start on it's own next time.

Can't test ride it since there is still sand everywhere and piles of snow making the street wet.

Oh and thanks to makenzie for suggesting fuel flow. I found one of the gas lines from the tank had a bit of a weak spot that kinked with the tank all the way down (it's hard to see in there). I cut it off and checked it, so hopefully that's why it was cutting out.

Adjusting those mixture screws without burning your hands is a total PITA.
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #17 ·
Ok, new info: I've ridden the bike a couple times, it does start on it's own but needs a lot of choke so probably still needs a bigger pilot jet.

What I have figured out is that it's not actually running lean at mid / full throttle it's rich. It's hard to watch the numbers real close when you're on the throttle but what I've found is that it goes rich from 14ish down to about 10 before it bucks. So apparently that's my problem. I don't know why it never did this before, I didn't really change anything with the engine when I had it torn down. I did install the db killer because the exhaust was just really annoying. It didn't change anything.

So from what I gather this is probably needle / needle jets. Isn't the needle jet pressed in and you change the needles?
 

·
Registered
Joined
·
388 Posts
Nevermind. I rode it last night and second gear went out. RIP poor gsxr you had it rough.
Sorry to hear that guy.

Might not matter to you now but when I had my FZR600 I messed around with Dynojet jets and eventually went back to mikuni jets. Because they measure them differently you are in the dark as soon as you start using the dynoshits!

Here at 2500 ft I ended up with 112.5 mains (up from 107.5) with a full exhaust and K&N.
Pulled real hard up to the limiter. I didn't have an AF gauge so it was all butt dyno, Probably had those carbs off 25 times before I was satisfied. I got to where I could change jets or needle position in about 30 minutes.

One of these days I will get a fuel injected bike!

Have a good one, Jon.
 

·
Hack in a barn
Joined
·
4,409 Posts
1 - 20 of 24 Posts
Top