I got a screw or two loose

[DGXSER]

More like lost.....Mixture screws that is. While at XSEast, it appears I lost the mixture screw out of no 1 carb. After months of playing with this thing I finally got it running decent. Couple days later, it is running like crap....again. Now I figure out no 3 header is cold as ice after idling. Go to adjust the mixture and.....no screw!!!

Any one ever had this happen to them? The threads are not stripped, the screws are out proabbly 5-8 turns from seated (more than typical) but my exhaust is pretty open and no crossover. Anyway, been considering putting thread lock on them, or at least installing those silly little factory covers.

[XS1100 Newbie]

Are you hung over? You lost the mixture screw out of number 1, but you are trying to adjust number 3 without a screw. LOL

[TomB]

The little spring is there to stop the screw turning when riding, buuuuut 5 to 8 turns out!!!!!

I think 5 turns out is where the screw lifts all pressure off the spring, its not compressed any more, so it can't stop the screw unscrewing out with vibration.

I think 8 turns out would be pretty much threads not actually engaged so the screws were just sat in the holes waiting for you to go over a bump to bounce them out.

[natemoen]

I agree with tom! That is too far out on those screws. Might need to go up one step on the jets.

[motoman]

Likely missing the tiny washer and o-ring too...............and once replaced, CORRECTLY re-sync, re-set idle mix(highest in. vacuum on each), re-sync. If idle mix screws are still out more than 3.5-4 turns, then you have a PILOT jet or pilot circuit issue goin on.

[DGXSER]

Ok, I had replaced the no mix screw some time ago, the bike was runnign decent, had not tuned it in yet. Started missing bad low end under power, that is when I tried to tune no 3 and found it was then missing the screw. Two separate occasions of missing screws.

I have found that it takes abotu 12 turns out to completely unthread the mix screws (yep, counted more than once as I thought I was way to far out.). But I agree 8 is alot of turns out, but any less and the cylinders will not fire at idle.

All have the tiny o-ring and washer. I had to make the washers for the two I replaced, I had spare screws and springs, but had to make the washers and use o-rings from my HF kit. I rebuilt the carbs a few years back so I know the washers and o-rings are in the other two.

With stock airbox and a 4-2 exhaust I would not think I would need to rejet, but it is starting to look more likely.

[TomB]

I have found that it takes abotu 12 turns out to completely unthread the mix screws (yep, counted more than once as I thought I was way to far out.).

Sorry, the last time I did mine it was on my MKIII BS34's on my Euro Sport (5K7) they may be different to MKII carbs. Maybe






.

[bikerphil]

Don, you could try stretching the spring some, that might make it fit a bit tighter. maybe put one of those larher vacuum caps over the tower so at least it won't get lost again. JAT

[WMarshy]

If you are 8 turns out then its time to change pilot jets until you get back into the 1-4 turns out area...

[DGXSER]

Well, althoguh I made the cardinal sin of changing two things at once, I am happy to say I feel I have engine humming nicely now.

I noticed when I put the new mix screw in the three carb it tuned in at 4-5 turns. So I decided to pull all the mix screws and check them out. What I noticed was that the new mixture screws came with a much shorter spring than the stock ones. This seems to play he!! with the mixture. So, I stretched the springs out to the correct length.

At teh same time I decided to go ahead and put the 120 mains in I had laying around. Well, I am here to tell you, that bike is a handful now!!! I thought I had experienced the madness of this things torque and pull, but putting those 120 jets in, with this exhaust anyway, has turned this thing into a BEAST!!

Thanks for the suggestions and help!! I am officially not going to throw it over a cliff anymore!!!

[DGXSER]

Just to close this out properly, I got the bike out for about 100 miles today. Not one bit of problems. Not 100% smooth idle, but pretty dang close. Need to read some plugs to adjust the mixture a little I am sure.

Anyway.....here is the cliff I was considering....ok, not really, but a cool view on the ride today.

[jwhughes3]

. Anyway, been considering putting thread lock on them, or at least installing those silly little factory covers.

I would skip the threadlock. Too much chance it will get buggered up or be hard to adjust. Try a small piece of vacuum hose stuffed into the "pipe" or something.

John

[kevxs]

i'm no expert by any means but wouldn't raising the floats a little make it so you wouldn't need to have your screws out so far? you could richen your mix a bit with the floats instead of doing it all with the screw

[TomB]

i'm no expert by any means but wouldn't raising the floats a little make it so you wouldn't need to have your screws out so far? you could richen your mix a bit with the floats instead of doing it all with the screw

Your mixture screws are to adjust the mixture at idle/tickover fueling circuit, of course that will affect the whole throttle opening mixture to some extent but mainly the tickover. Raising the level in the float bowl will do the same thing but over the whole throttle range, meaning you'll have to set up the rest of the carb again. Much better to change the mixture jets to the next size up.

Unless the rest of the throttle positions are giving weak plug chops, then float height would definitely be a consideration

[DGXSER]

Float height does effect the full throttle range. You do want to set the main jet first for max power. I always went wiht factory jetting becuase it worked well for me, but this bike has an aftermarket exhaust that is more free flowing (less baffling, and louder). So it seems it likes more fuel.

Next you would adjust the needle jet height fofr mid range, but the 81 carbs do not have adjustable needles.

Now set the float height for best low end in the 2-3k rpm range. I have always found that factory float height works best for me. YMMV as they say.

Then adjust the mix screws for best idle. As i said, I believe the issue I was having was with the spring not being long enough to really get the o-ring to seal properly and I was getting air leaking past. Once I lengthened out the springs, and upped the mains, it tuned in the right range.