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Discussion Starter · #1 ·
Hello

I've just finished rebuilding my 1109cc Gixxer with wiseco pistons, k&n single pod filters and such but now my carbs are runnin real lean. :nono

The had orginal Mikuni 130 Main jets wich i switched out for Dynajet 136 Mains and also lowered the float height to 10,6mm (14,6 original)

Strangely it seems to be running even worse with the 136 Dynajets :confused
I tried adjusting the float height back but it didn't help.

I can only start it with the choke fully out and then it runs a lean 18:1 AFR (i'm going for 12,5:1 AFR)


What would you guys suggest? :) Sounds like I need bigger Mains no?
 

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Discussion Starter · #2 ·
Hmm talked to a mechanic who knows somewhat about these bikes and he informed me that the Main jets don't supply any fuel at idle.

Think the mixture screws will do the trick or where should I look?
 

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OskarV said:
Hmm talked to a mechanic who knows somewhat about these bikes and he informed me that the Main jets don't supply any fuel at idle.

Think the mixture screws will do the trick or where should I look?
Pilot jet/mix screw/ float height are your idle to 4kish circuit

What was it....if you go more then 2.5-3 turns out you need to change the pilot jet
 

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Discussion Starter · #4 ·
kan3 said:
Pilot jet/mix screw/ float height are your idle to 4kish circuit

What was it....if you go more then 2.5-3 turns out you need to change the pilot jet
Ok excellent :) Will try that tomorrow... finally my bike is getting ready :) Just in time for winter :rolleyes
 

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idiot
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u can't use mikuni mains and dynajet mains unless u change emulsion tubes - different threads as I understand????

It's also usless comparing 130 mikunis to 136 dynajets as they are numbered using different systems - i.e a 130 mikuni isn't the same as a 130 dynajet.

Kan3 is right. Mains are responsible for top end full throttle AND IN THEORY IT IS MAINS U SHOULD BE SORTING FIRST ELSE U'LL HAVE TO DO IT ALL AGAIN LATER.
 

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mark_E said:
u can't use mikuni mains and dynajet mains unless u change emulsion tubes - different threads as I understand????

It's also usless comparing 130 mikunis to 136 dynajets as they are numbered using different systems - i.e a 130 mikuni isn't the same as a 130 dynajet.

Kan3 is right. Mains are responsible for top end full throttle AND IN THEORY IT IS MAINS U SHOULD BE SORTING FIRST ELSE U'LL HAVE TO DO IT ALL AGAIN LATER.
Problem is, it was mentioned above that the bike won't even run without full choke. You'll have to at least get it to run with no choke or you're not going to be able to do much for testing on the street
 

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I know some of this stuff seems obvious but sometimes the best of us forget the simple stuff.

Double check all of your clamps between carbs and engine & pods, check tubes for kinks and make sure the fuel system has been primed(theres fuel in the bowls)

Check and clean your spark plugs to make sure they're not fouled (from running to rich/lean on the previous run).

You don't want to change the idle mix, it's factory preset on the 36mm mikunis and shouldn't need to be changed. There will be another problem.

And yes, the AMAL (hex) mains will not fit the mikuni main jet thread properly, the mikuni uses a Reverse (slot) mains jet. an AMAL 136 is equivalent to a Reverse 105~107.
 

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I have an Amal monoblock on my Triumph
 

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Discussion Starter · #10 ·
Well I put the 130 mikunis back in and screwed the mixture screws almost fully out. Got it to run without choke at about 3500RPM but it is still too lean.

Do the main jets supply any fuel at idle?

Should I get bigger pilot jets then? The stock ones are 32,5, what size should I get?
 

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If you have to go more than 3.5 turns out you need to go up to the next pilot jet which is a 35. The dynojet 136 mains are smaller than a mikuni 130. You need 135 or 137.5 mikuni main jet or possibly bigger. Definitly put your float height back to 14.7 mm. Make sure you sync the carbs when you get it close.
 

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Discussion Starter · #12 ·
I put the float height up to 13,7mm ... better richer then leaner as of now.
Also damaged one of my diapraghms when I was cleaning them thouroghly so now it leaks a bit, is that a big problem? Could be hard to find a new one around here.

I saw in the Haynes manual that stock UK 1052 bikes with BST34SS carbs run 42 pilot jets. Thinkin of getting three sets og pilot jets since they take about 3 weeks to get here. Think I might need bigger then 42?

Thx for the great advice by the way guys :D
 

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Diaphragms should shrink back down. With patience you can get them back in even if they're swollen. If your o-rings got swollen the float housing ones may now be damaged and causing you issues with fuel leaking into the float chamber - bear this in mind if your bike exhibits signs of running really rich (as mine did :))
 

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Discussion Starter · #16 · (Edited)
Yes the diaphragm was fine after the night. So I could close it up. Does it matter if the seal between the diaphragm inside the carb isn't airtight?

I tested the carbs by filling them up with fuel so I could see if any of the O-rings leaked. They are all good.

But it ran just as lean after I cleaned them so that wasn't the problem. Gotta get me some bigger jets
 

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OskarV said:
Does it matter if the seal between the diaphragm inside the carb isn't airtight?
Yes - I imagine this would have a pretty big effect on performance but I'm not entirely sure I know what you mean. If they r seated correctly they must seal. What makes u think they r not?
 

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Discussion Starter · #18 ·
mark_E said:
Yes - I imagine this would have a pretty big effect on performance but I'm not entirely sure I know what you mean. If they r seated correctly they must seal. What makes u think they r not?
Hehe I knew this would get confusing .. hard to explain

As the rubber expanded on the diaphragm the base (where the diaphragm connects to the metal slider wich houses the needle) got damaged and now it isn't airtight. I'm not talking about the seal between the inside of the carb to the outside, that's all good. But mearly the seal between the top chamber (inside the black top cover) and the middle of the carb.

Just wondering if it has to be airtight? would guess thats the purpose of the diaphragm.
 

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Yeah, it will have to be airtight but it shouldn't effect your idle or starting.
Unless, the hose that connects to the top of one of the carbs and goes to the petcock is not getting enough vacuum to suck the diaphragm in the petcock open to let the fuel out.

edit: you could put the petcock to PRI then the petcock is open regardless of engine vacuum
 

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Discussion Starter · #20 ·
turbo.gsxr said:
Yeah, it will have to be airtight but it shouldn't effect your idle or starting.
Unless, the hose that connects to the top of one of the carbs and goes to the petcock is not getting enough vacuum to suck the diaphragm in the petcock open to let the fuel out.

edit: you could put the petcock to PRI then the petcock is open regardless of engine vacuum
Oki thanks.

I don't use the petcock. Just a fuel line and a big syringe filled with fuel so I don't have to worry about the petcock working.
 
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