Carburation Questions!

[RPM - Robert]

Rolf, that is incorrect.

3 Is the throttle cable carb. Also, it is possible to have the adjustment so far off on 1/2 & 4 that you can not adjust 3 closed or open in some case. Then the bike will either be idling too high or way too low to get it to run. You can take the idle adjustment screw completely out and the 3 carb will be hung open.

It really doesn't matter which side you start on. If I am doing a valve adjustment I sync them 1/2 then 3/4 & then 2/3. Simply because I am usually standing on the left side of the bike with the Aux. fuel tank.

When I tear the carbs down and break them into individual bodies, the carbs can be wildly off after reinstalling the springs. In this case I actually start on number 3 as I am shooting for a certain number with the vacuum of the bench sync, to let the bike idle. If I can't get it close, I know one of the other 3 carb bodies, or a combination of them, is holding the 3 carb either open or closed.

So long story short. It 100%, does not matter if you start left or right. You are adjusting 1 to 2 and 3 to 4 and then you finish by adjusting the left 1/2 combo to the 3/4 combo or vice versa

[Old Rider]

Rolf, that is incorrect.

3 Is the throttle cable carb. Also, it is possible to have the adjustment so far off on 1/2 & 4 that you can not adjust 3 closed or open in some case. Then the bike will either be idling too high or way too low to get it to run. You can take the idle adjustment screw completely out and the 3 carb will be hung open.

It really doesn't matter which side you start on. If I am doing a valve adjustment I sync them 1/2 then 3/4 & then 2/3. Simply because I am usually standing on the left side of the bike with the Aux. fuel tank.

When I tear the carbs down and break them into individual bodies, the carbs can be wildly off after reinstalling the springs. In this case I actually start on number 3 as I am shooting for a certain number with the vacuum of the bench sync, to let the bike idle. If I can't get it close, I know one of the other 3 carb bodies, or a combination of them, is holding the 3 carb either open or closed.

So long story short. It 100%, does not matter if you start left or right. You are adjusting 1 to 2 and 3 to 4 and then you finish by adjusting the left 1/2 combo to the 3/4 combo or vice versa

Ok that's strange i always thought that the bracket that the idle adjustment screw pushes on and throttle cables are connected to sits on carb 2
and only moves the nr 2 carb butterfly. But seems I'm wrong and don't want too argue with professionals.

[RPM - Robert]

It is, on the number 2 carb, if you are counting cylinders from right to left.  

Regardless. It doesn't matter on these carbs, which side you start to adjust on.  

[pict]

OK making progress. Coil mod done. Carbs cleaned and set up with 42.5 pilots, 112.5 mains with needle in middle of 5 notches. Mixture screw out 2.5 turns on all carbs. Rigged up auxiliary tank, blanked the no.1 manifold port normally connected to the petcock and pushed start. Fired up pretty quick with a touch of choke. Idle seems pretty good and even, so presuming balance is decent, but plan to put the carbs on a manometer tomorrow. It revs freely with a slow roll on of the throttle, but if I blip it open quick it threatens to die. Am I correct in thinking that I am probably too lean on the idle mixture screws? Wondering do I try and fix this first and then balance or is it just an iterative process and could go ahead and set balance first and then visit the mixture screws - then back to check balance?

[Pat Conlon]

Get the balance done first....then fine tune your idle mixture.

You want your air flow even across the board before final tuning.

[pict]

Warmed it up, and put it on my DIY manometer and balanced as best I could. The small divisions are 0.02 psi and the large ones are 0.1 psi. The balance drifts around a little but generally stays within 0.15 psi max difference between the highest and lowest cylinders. My Haynes manual states the max difference should be 0.19 psi so I assume I am good. Once balanced, there was no hesitancy in the throttle response so I didn't adjust the idle mixture from 2.5 turns out on all carbs. Thanks for all the input everyone.

[Pat Conlon]

Yes, it's amazing how carb balancing cures different symptoms.

I expect you will also notice a smoother running engine.

[pict]

I'm very pleased. Responds much better than before and sounds happier.

[Dads_FJ]

Too late for this thread, but when syncing carbs don't forget to turn your front wheel so you don't cook the fender and be sure to use a big ol' fan to move some air through the engine.   The fan should be obvious but you never know...