After Carb Cleaning Question

[mavpsa]

Hi,

Cleaned the carbs on a '77 GS550. Put everything back together according to the specs outlined in this forum. Followed the PDF supplied in the 'garage section' for VM carbs.

Question is: on the air screw, the specs indicate two turns out from gently seated. On the write-up, prior to syncing the carbs, it states to warm up and let idle at about 1100RRP, then turn the air screw left or right until the speed tops out. Continue to do this on each carb.

Well, i did that and nothing happened. is that because they were already set at oem specs and that's what the procedure in the PDF is trying to accomplish? or, am i doing something wrong?

thanks in advance.

[Nessism]

Many people experience the same thing as you; the idle speed doesn’t change a whole lot when tweaking the screws. I wouldn’t worry about it.

My VM carb 550 ran best with the fuel screw at 7/8 – 1 turn out, and the air screws at 1.5 – 1.75 turn out. And don’t forget to vacuum sync the carbs once you get the bike together – this step is manditory.

Good luck.

[trippivot]

it is called a lean idle drop procedure

you first need new or freshly cleaned spark plugs. and contact breaker points in fresh condition.

what the goal is is to get each cylinder to respond to the idle screw adjustment.

go outward (leaner) in 0.5 turn increments and wait a second or 4 until the engine speed begins to fall off or run worse than before the adjustment. when you find where it begins runs worse, go back inward until the same thing happens. you with me here?? find the middle point of those two positions and "BINGO"!! that is it!! you will hear the engine pick up when it is right in the middle of too lean and too rich. simple but re do all 4 cylinders one at a time. you may need to just find a happy medium with rev up and fall to idle time. also if the bike needs more air or more gas than the adjuster allows a pilot jet change may be necessary

and as it runs better and better per cylinder lower the idle speed screw back to a good idle speed you prefer 1100 rpm or wherever you like it.

[mavpsa]

Great, thanks for the advice. I think i understand. hope nothing else needs to be replaced. I want this bike running already. So far, i have rebuilt the forks, front caliper, replaced the brake shoes and cleaned the carbs. All w/the help from you guys. I truly appreciate it all!!!

Last question. On the idle knob, it says to screw it in until it reaches the pulley, then add another two turns. Well, once it makes contact w/the pulley, it's a real PIA to continue turning. the resistence felt is strong. Once it's set against the pulley, it appears as though there is much screw left to turn (i could be wrong--it was really late when i finished last night) Is that normal also? I can't see the logic behind that, figuring it's a turn knob. does it need some extra lube?

Again, is something wrong here?

[Nessism]

Sounds like something is wrong. The idle stop screw should be easy to turn, but not so easy that the screw moves by itself due to vibration. The two turn business is just to get you in the ballpark of where the idle should be; adjust the knob with the engine running and warm until the proper idle speed is achieved.

And just want to reiterate the need to vacuum sync the carbs. Many people skip this step because they don’t have the tool – just as they skip valve adjustment.

[trippivot]

on a set of mechanical carbs you can adjust the slides off of or out of the adjuster screw range. just make sure it touches the center moving part and goes in and out to adjust the idle up high and down low just be sure the screw controls the positive stop for accurate idle control high idle all the way to stall.

it will be stiff but not frozen it is a finger knob after all

just know you are doing a real technical job here 8 out of 10 scale for difficulty .

[trippivot]

Vacuum sync is just a super fine tunning for idle smoothness and harmonics. you can look at the light size under the slides with the carbs off of the bike ( bench sync) if the idle is nice enough for you and it is a confident running machine don't worry yourself sick.

but it is a nice touch when they are in tune perfectly I will admit.

after they are set they won't come out of tune unless a tinkering fool messes them up.

[mavpsa]

Nessim: i have a home made contraption for the vacuum sync. basically, 4 bottles half filled with water. 4 hoses leading into each bottle from one another, into the water. then four hoses that would attach to the carbs (these stay suspended in the bottle, away from the water). idea is, keep the water level in all four bottles. cost nothing to make.

valve adjustment---wish i had the funds. unfortunatley, i ran out of money. probably should've waited, but i was eager to get the bike running. but, i plan on doing this over the winter.

trippivot--i think i can do it. I just may need it explained a little better (if you have the time. I know you are probably working (i am) so i understand if you can't. the knob is hard to turn--really. i though i almost busted my thumb at one point.