I pulled the brass plug out of the carb. No problem. Turned the mix screw in 1/2 turn it stopped. Turned it out just over 1&1/2 turns, not quit 2 and it stops. Not forcing anything. This just doesn't seem right to me. Turned out all the way it doesn't seem to make any difference. Still surges slightly at part throttle steady, say 35 in third, and still has the little pop when I shut it down. Everything else is bone stock 1988. Right about 600 feet here.

You could try 35 mph in 2nd (you could be "dogging "the motor).  Surging in mid range may require the spacer mod be done or adjusted.

That brass plug has a tiny hole in it.....and it allows moisture to get to the threads for the mixture screw.  The aluminum threads corrode, and when you try to back the brass screw out it stops when it hits the corroded threads.

Trying to muscle the brass screw past the corroded threads often results in stripping that small fragile slot in the head of the mixture screw.  Then the only way to get it out is to drill and use and easy out (or the torx bit method suggested in another thread).

If you do get the screw out.....it is suggested you take a tap and clean up the threads in the carb body.

GOF wrote on 08/29/18 at 04:33:39:



It is: M6x0.5.

Using E10 seems to make everything worse in this bike. Many stations now sell non-ethanol premium now, so try to find that. I went to using STA-BIL all the time, and that helps considerably.

I worked on a members carb this weekend....bone stock and never been fussed with by anyone.  There was some corrosion on the outside of the carb body - but not an excessive amount and the steel parts are not rusty.

When I pulled the plug, I was surprised that the screw only turned in 1/4 turn until it seated.....that doesn't match the stock setting of 3 turns that is published as the "pre-set".

I added some penetrating oil and started to back the screw out and it turned easily.....at about 5 turns is got stiff.  I turned it back in and worked it back and forth - then I began to try and force it past the corroded threads.  I noticed that when I turned it back in - the screw was now stiff everywhere.....I believe the corroded aluminum had started to distort the threads on the soft brass screw.  I had a screwdriver that fit the slot very well - however ultimately the screw got stuck on the way out and the soft brass screwdriver slot stripped.  I was able to get the screw out using a 5/64" drill and the #8 Torx bit.

If you can get the fuel mixture screw out using the a screwdriver - consider yourself fortunate.......but don't be surprised if the soft brass screw doesn't come out and you have to revert to drilling to get it out!  Once it is out you must retap the hole to clean up the corrosion on the threads......the new screw will not go past the corroded threads and the soft brass threads will be distorted by the harder aluminum, and you are likely to strip the screwdriver slot on the new screw when you are installing it (been there....almost did that).

For those of you contemplating pulling that brass plug... try my way

https://youtu.be/PXbVyH-XbMk

At this point I am planning to wait until I start the over winter work and pull the carb to work on it. It almost looks like when they pressed the plug in it pushed up a ridge in the bore.