weird surge and pulling on throttle grip @idle

hi folks ~

bike won't start or run right after i've rebuilt the motor and trans from the bearings up. i also did the carburator. well not really though i did clean the thing and put new jets to fatten up the mixture for the supertrap i bolted to it. it's a 1988, and runs tits mid to high range but as soon as i let off the throttle or even think about letting off the throttle it is all snappy and powers down like a vacuum cleaner. i can get the rpm back up and it sounds nice except for a little stuttering but i attribute that to minor jetting or needle adjustment.

the problem i'm having is damn strange. i pull into the driveway after bumpstarting it down the street and hold the throttle while adjusting the idle screw and i can screw the knob all the way in sometimes with nothing happening. the right grip pulls and yanks like someone else is controlling the throttle and after a few seconds it'll surge waaay up in idle like it shoulda done. i adjust it down and it idles fine until i look at it funny. then it dies.

i've done this a number of times. i'm thinking the spring isn't wrapped tight enough for the throttle cable attachment? something loose? how many moving parts in this simple carb would cause a random occurance like this?

rock on. scale a rock with internal combustion


What bike are you talking about the R or the L model???

Check your pilot screw. It may be too worn if you're having problems with the idle.

If your bike is an L with the CV then you might want to check the diaphram. If the diaphram has the tiniest hole or leak in it, that would cause some problems.

You came to the right place for help with your bike.

I recently uncorked my 600R and had all kinds of grief with proper jetting and starting procedures. Thanks to the input from several people here, I finally managed to get everything figured out and I couldn't be happier with how my bike performs.

I'm not familiar with the '88 model, but I'm guessing you're talking about the 600R.

What's your jetting right now, what's the position of your fuel screw, and did you change the air box configuration also (uncork) or just add the Supertrap?

You say it runs great mid to top end, so the needle and main sounds good. Did you change the pilot jet also, or just the main jet?

If you're having a hard time starting, you may need to go from your 60 pilot (?) to maybe a 65. Keep track of your fuel screw settings and how the bike reacts to them.

If you opened up the air box to let it breathe better, your mixture will be too lean on start up.

I'm sure someone else will come along with more info, good luck :smirk:

yes whoops well i believed that they only made R's during 1988. isn't the L a relatively new thing? mine is an R

i haven't uncorked this bike but believe it was done prior to me owning it. the airbox is open on the top and bigger jets than stock were found in the carb.

speaking of jets, the sizes installed on my pig are as follows:


slow jet-62 or 63

fuel screw-3 turns out

exhaust baffles-7

i'm going to pull the carb this weekend to verify these numbers. would it be a jetting or mixture problem? i prob have that too because it doesn't exactly start with a kick but i feel like the surge is a separate thing.

dldav-s_66, what do you mean by "worn" pilot screw? would that little needle thing wear out and cause symptoms like this?

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