Carb balancing...

[Cammo]

Everything that you've mentioned points towards the throttle butterflies not being synced correctly in my opinion.

The bike is struggling to idle at the proper revs because all 4 throttle butterflies are not open far enough - when the last butterfly/s open enough for the bike to hold idle, the others are further open hence the high idle.

This does happen, always causes lots of head scratching on the forum!

Forget vacuum balancing for now - take the carbs off, drain the petrol and sync the butterflies by eye (carefully lining all 4 up at the same point, use the 2 holes in the venturi as a positioning guide). Adjust them each to the same position following the balancing order in the haynes manual. While you have the carbs off adjust the pilot screws to 2 (stock) or 2.25 (exhaust mods) turns out. When the carbs are back on remember that it will take some time for them to fill with fuel when you go to start the bike (I usually put a couple of syringes full of petrol down the carb fuel pipe which gets around this).

Regarding the air leak on cyl 4, the gt85 might just be drawn into the airbox intake. Anyway, try above before worrying about any leak.

[bikemonkey]

Right so I balanced the carbs using the drill bit method, which didn't work so well as there is quite a bit of play in the linkage between the front and rear carbs, so I finished it off by eye.

I then adjusted the mixture screws to 2 turns out.

Stuck it all back together and the idle is much less erratic, but it's back to doing the little rev then dead thing. And it slowly dies after adjusting the idle from 2.5k down to under 1.5k and I have to up the idle again to get it started again.

I have 2 videos which I shall upload in a bit.

Just to add, my choke mechanism is a bit dodgy, the arm is pulled back by an extra spring zip-tied to it and the throttle cable, it pulls it back most of the way but the last mm or so it doesn't, although that mm or so doesn't seem to do much anyway (it's quite loose, like taking up slack).

[bikemonkey]

Right first video is me adjusting the idle to where it should be, then the bike dying slowly. The idle rose at first on it's own, no idea why, but when adjusting the idle I only have to slightly turn the adjuster (about half a turn) and the revs change from about 1.3k to 2.5k. It's hard to describe.

http://s1126.beta.photobucket.com/user/ ... 1.mp4.html

This video is the bike warm and a little rev with the idle set to about 1.6-1.7k, still doesn't like idling lower to be honest. As you can see the bike dies after the rev slowly, I have no idea why.

http://s1126.beta.photobucket.com/user/ ... 2.mp4.html

EDIT: Actually I do have an idea why, it's the mixture screws too rich I think, like last time. But technically speaking I shouldn't have them screwed in that far for it to be right. Can't be arsed to go try it now, and I've got work in a bit and all day tomorrow, so it'll be Monday for more changes now.

[Neosophist]

Right first video is me adjusting the idle to where it should be, then the bike dying slowly. The idle rose at first on it's own, no idea why, but when adjusting the idle I only have to slightly turn the adjuster (about half a turn) and the revs change from about 1.3k to 2.5k. It's hard to describe.

http://s1126.beta.photobucket.com/user/ ... 1.mp4.html

This video is the bike warm and a little rev with the idle set to about 1.6-1.7k, still doesn't like idling lower to be honest. As you can see the bike dies after the rev slowly, I have no idea why.

http://s1126.beta.photobucket.com/user/ ... 2.mp4.html

EDIT: Actually I do have an idea why, it's the mixture screws too rich I think, like last time. But technically speaking I shouldn't have them screwed in that far for it to be right. Can't be arsed to go try it now, and I've got work in a bit and all day tomorrow, so it'll be Monday for more changes now.

Wow that sounds rough!

Firstly, Is it firing on all 4? (have you cheked all 4 header are hot? spray a spray bottle of water on them and youll soon find a cold one.

If it is firing on all 4 then I concur with cammo in that your carbs are really really really REALLY out of balance.

Usually it will just cause a lumpy idle so as cammo said it can be overlooked.

I would check its firing and then re-do the drill bit method but not by eye with an actualy drill bit, do you know how to do it properly?

[bikemonkey]

I have balanced them, those videos you quoted on were the best ones I thought for it being balanced.

I used the drill bit at first but it didn't look right by eye, so I did them by eye.

It's popping a little at the exhaust but I haven't tested the headers yet.

[bikemonkey]

Got bored after work so I decided I'd have another fiddle.

This is 1.75 turns out on the mixture screws and I didn't touch the butterflies/balance at all, they are still the same as in the last video I linked to. Start from cold, full choke no throttle, a little adjustment of the idle down to where it should be, then the odd rise for a good few seconds or so and back down, then slow return to idle after each rev. But it doesn't die. Exhaust still seems to be popping a little though, but each header was hot, could be a slight mis-fire?

http://s1126.beta.photobucket.com/user/ ... 3.mp4.html

I'm stuck where to go with this now, it's working for now so when I can get a period of time where I can do without the bike I'll send the carbs off to be ultrasonically cleaned, then replace all the seals and send them to anyone willing to balance them for me. It seems carbs have me stumped.

[Cammo]

Anyway when I took the carbs off I noticed a small amount of petrol sitting in the rim of each carb rubber. The bike hadn't been turned off long though.

This is usually caused by a leaking float valve.

This, combined with slop in the balancing linkages and dodgy choke mechanism means the carbs are really stuffed and it's quite likely that the bike will never run how it should.

I'd be getting hold of another set of carbs, sounds like the current set is plagued with problems. And that's only the problems that we know about...

[Neosophist]

Anyway when I took the carbs off I noticed a small amount of petrol sitting in the rim of each carb rubber. The bike hadn't been turned off long though.

This is usually caused by a leaking float valve.

This, combined with slop in the balancing linkages and dodgy choke mechanism means the carbs are really stuffed and it's quite likely that the bike will never run how it should.

I'd be getting hold of another set of carbs, sounds like the current set is plagued with problems. And that's only the problems that we know about...

That could be the case that they are just knckered.

I think firstly unscrew all the balance screws and then tighten them all up until they first contact the area and do the drill bit method again but USE the drill, don't do it by eye.

You seem to be doing a bit of a xilvia with the mixture screw. 1.75 isnt right for stock carbs. If you have to put it there to get any kind of run then something isnt right.

Leave it at 2.0 and focus on getting it running there.

There shouldnt be much diference anyway between the two, just slightly lean which could explain your hunting.

You could check them for leaking floats / sticking floats when you have the carbs off again to re-do the balance.

[bikemonkey]

I know the carbs aren't fantastic by a long shot, they have quite a history of people fucking about with them.

I found 38 pilots in them with 124 mains, 2 washers under each needle, float bowl seals looked like they had never been replaced just gunked, slides crudely widened dodgy choke mechanism, and this was all on a bike that's intake and exhaust was standard when I got it!

I think I may have to agree with cammo here, it's probably going to be easier to get another set known to be working than do I don't know how many trial and error fiddles/changes to these. It's payday soon so hopefully someone on here will have a good set to save me paying over the odds and chancing my arm on eBay.

[Cammo]

Sounds like they have had a hard life!

it's probably going to be easier to get another set known to be working than do I don't know how many trial and error fiddles/changes to these. It's payday soon so hopefully someone on here will have a good set to save me paying over the odds and chancing my arm on eBay.

If the funds allow try and get hold of a set of rvf carbs. Being newer and an updated design there's a better chance of them having no wear issues. All you need to fit them is an rvf throttle pull cable (and push cable if you must use one ).