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low rpm cruise breakup

  • Thread starter Thread starter gsx1100
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gsx1100

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I got an 83 gs 1100 that i just rejetted with a dyno jet kit for my vance and hines pipe. Bike starts , idles and runs smooth under full throttle, but when cruising at like 4 to 5k it breaks up and surges. Upon research correct me if im wrong adjusting the mixture screws will help this. There at 2.5 turns out now should i bring them in or out.
 
what if i have adjustable needles can i just richen it like that or is shimming like a half step up
 
Hi,

Believe me, I'm no carb expert. This adjustment is known to help in the mid-range, which is where you seem to be stumbling. If you have adjustable slots for your needle clips then it couldn't hurt to experiment a bit. Use some extra, thinner washers to make adjustments between the slots.


Thank you for your indulgence,

BassCliff
 
gsx1100 said:
what if i have adjustable needles can i just richen it like that or is shimming like a half step up
Click to expand...

Yes, and Yes..

Sounds like the mid range circut is running lean. But,

Cruise and RPM measures can mean a few things as to which fuel circut is the problem child. It would be easier to go by throttle position. To do this is easy, just make a scale. ;)

Take a piece of masking tape and place it on your right control/kill/starter switch next to the grip. A stick pin can be pushed into the grip as an indicator, good placement would be close to the top on the grip next to the tape.

Then make a mark on the tape with a pen at idle and full throttle positions. Then 1/2, 1/4 and 3/4 positions.

The air screw will control most of the Idle up to the pilot jet both tend to blend into mid range, which is affected primarily by the slide needle/needle jet. A similar transition happens with the slide needle/needle jet and main jet.

With the stock air box there should not be much to adjust.

Then not to forget the pre-requsites here, boots/o-rings if equiped, sealed air box, and at least bench synchronized carburetors.
 
DO STEP #1 FIRST
DO STEP #1 FIRST
MAINS MUST BE RIGHT SO THAT YOU CAN PULL HARD TO REDLINE THEn PROCEED TO NEXT STEP
DO STEP #1 FIRST
DO STEP #1 FIRST
http://www.factorypro.com/tech/carbtun.html

To properly tune, you MUST:
1. Have selected the BEST main jet for full throttle power (not just a "good" main jet - we mean "the BEST main jet" for power at high rpm).
That eliminates the common severe tweaking of the midrange and lower tuning ranges to compensate for a "wrong" main jet.
Click to expand...
On yea I forgot

DO STEP #1 FIRST
 
LOL... :lol:

Yes, Factory Pro has priceless information on their site. There are some other very good reads as well. Take time to browse the site.

But, still Step #1 still requires that the pre-reqs are in check. Oh, and also including confidence in petcock operation, which is one of the pre-reqs I forgot to list.

A main jet can be dialed in for the best power with an air leak.
 
The bike pulls real strong from a wide open throttle pass, with a bit of backfiring when deaccelerating. I just synched the carbs and it didn't help much. The only real problem is when taking off slowly from idle it breaks up around 3 to 4 k rpm. Im gonna try richening the needle and see if it helps.
 
did all the steps for a stage 1 which would be 114 mains, stock pilots, lift hole drilled. needle on notch 3. Just changed the needle height to notch 4 runs 100% better so that was the problem.
 
Get a set of 117.5 Mikuni main jets and put the needle back where it was.
I bet your plugs are white as snow with a wot throttle chop.
 
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