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Discussion Starter #1
I've been having an erratic running problem and feel that it is in the carbs after messing with the ignition and getting no improvement. So I pulled off the stock air box and ran the engine to see the carbs in action. I noticed that there are two small ports at the bottom of the entry of each carb. One of the ports on carb #4 has been closed with rtv. If I cover the ports on carbs 3 or 4, the engine losses rpms. There is no change when I cover the ports on carbs 1 or 2. What are those ports for?

Engine always starts and runs normally when cold, after a few sessions on the track or when the engine gets hot the bike starts to run poorly.
 

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That definitely doesn't sound right. If Mikuni put those jets there, then you can bet they are there for a purpose..!!

Is the RTV a definite addition, or maybe just a loose peice that got stuck in there..??

I know one of the jets is for slow running, and the other for when the bike is on the go and more fuel / air flow is required. Try pulling it out and trying the bike on the road.

Dave....
 

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Discussion Starter #3
The rtv is fit very nicely to plug the hole so I would guess that a previous owner did it on purpose.

So if two of the carbs don't react to me covering the hole at idle then they must be plugged. I'll also try reving it up and covering them.

Thanks
 

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Sounds like the previous owner was a poor backyard mechanic.

I'd pull the carbs. Do a complete tear down and clean them out thoroughly making sure everything looks good and proper.

You may want to post here what needles and jet numbers are in your carb before reassemblly to make sure they're in the ball park for decent running.
 

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Those are the main air jet and pilot air jet openings.

I've seen some DynoJet kits which tell you to close off the main air jet with a supplied plug but can't imagine why someone would only do that to one of the carbs (unless it was just a Band-Aid for a problem elsewhere in the carburetor)... probably best to get them up onto the bench and find out "why".

Running good when cold, then progressively worse as the engine gets hot is typically a symptom of being too rich.

Ed

.
 

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Discussion Starter #6
Originally posted by gsxr1198:

Running good when cold, then progressively worse as the engine gets hot is typically a symptom of being too rich.
<font size="2" face="Verdana, Arial">Thanks for the info...I did first try leaning out the main one jet size but I didn't notice any difference. It doesn't act like a jet size problem. The engine can run fine while hot, then it will suddenly not be able to pick up the rpm's. This will sometimes clear up and then run fine again. That's why I pulled the air box, I want to be able to look down the throat of the carbs when the engine is acting up. Hopefully I will be able to see one or more flooding.
 

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Cool... just remember to put on some eye protection if you have your face directly in front of a carb throat while the engine is running
 

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Discussion Starter #9
Originally posted by jeff:
it could be an ignition problem, i've experienced that before....
<font size="2" face="Verdana, Arial">I've been messing with the ignition for about a month now with no improvement. I've replaced the coils/wires and module with used parts...but it still acts the same. Using my Sheffield TA100 (indicates peak KV)I can always find some coil output showing 0 KV...yet if I remove the wires and use spark testers, all of the coils are firing. Since I can visually see a strong spark, I've decided that the TA100 just doesn't work well with wasted spark systems.

gsxr1198...glad to see that I'm not the only safety minded person around. I've seen enough flames comming out of carbs to wear eye protection, but thanks anyway.
 

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Rbike,

A couple of months ago a guy had a post on here about engine stutter or rpm loss and his solution if I can recall had to do with synching the carbs and replacing the Jet emulsion tubes, because when they begin to wear they will change your air/fuel ratio and cause you some problems.

I hope this may help, the guy was from Sudi Arabia I believe and he had pics and everything of the wear on the slides and the slide hosuing within the CV carbs and this may be what is causing your problem....

I have a few sets of 38 mm CV's and I am actually using a set on my 88 750 while the 91 1127/1216cc is being rebuilt and prepped to be sprayed, and they seem to be working better than the 36 Cv's that came with the 88 750 originally.

My 36's did that same thing to me that you are experiencing, until I had them professionally rebuilt, then dyno'ed...

Good Luck. Hope this Helped.

JDB1371
 
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