can't get over 2000 RPM

[sissonk]

I have a 81 GS850 with CV carbs. I have completely rebuilt this bike 2 yrs ago and it has ran perfectly until about two months ago. It had been unused for about 4 months when I went to ride it , it would rev over 2000 Rpm only after much difficulty and once to 3000 it was off. But if reved at stand still it just will not rev over 2k. It gags and gasps and farts at 2k , but will recover and idle very well. I have just finished lapping the valves as compression was very low but ok now. I have checked the Carbs at least twice and can't find the problem.
Anyone got any ideas ?????

[DimitriT]

It sounds like you have a carb issue or intake leak issue. I'm guessing clogged idle circuit but you should check for intake leaks too. When was the last time you've cleaned the carbs? Synced the carbs?

The reason it can run into the higher RPMs while moving is because you are able to get the slides to lift as you open the throttle and that allows fuel to flow up via the main jets. But so long as you are running just on the idle circuit (while the bike is stationary) the mxiture leans out and the motor stalls.

Check the headers for temperature. Are they all heating up evenly? That may help isolate it to a single carb.

[49er]

You said that you have just lapped the valves. Did you do the lap job since the bikes 4 month layoff? Did you dis-assemble the carbs from the mounting plate assembly? If so, you may have lost sychronisation of the carbs. You said that you have checked the carbs at least twice. Your symptoms are classic fuel leanness. Either your pilot jets are partially blocked, or the fuel/air screws are incorrectly adjusted, or your carb sync is way out, or you have bad air leaks on your intake system. Do you have the airfilters attached to the carbs?
Do as Dimetri has suggested and check the temperature of your header pipes.

[sissonk]

can't get over 2000 RPM

Thanks for your advice . last week I put the head back together with lapped valves and checked compression - all is ok. The exhaust headers all get very hot equally. Before I took the head off I did all the carb. checks you memtioned as I thought it was a classic lean problem which I am still sure it is as the color tune plug shows. I will put the vac gauges on and check the sync and look for air leaks. As even if 2 carbs worked properly I would think it would go over the 2k . Interestingly before I did the valves no. 3 cylinder I could never get to burn properly at ideal the exhaust header stayed cold for ages but not now , it heats the same as the others.
I will do some more testing and get back , thanks

[chef1366]

Sounds like stuck slides or bad diaphragms to me.

[Dink]

Just behind the throttle butterfly are some small holes in the side of the venturi, these are the "idle progression holes" ( they enrichen the mixture to cover coming off idle speed before the needle starts to kick in)it sounds as if these are clogged, use a bristle out of a "brass wire brush" to clean these out.

Dink

[argonsagas]

I would follow Dink's idea, but add this to it:


Use a carb cleaner or air spray with a long nozzle to place against the carb body and blow any debris back and out.

My experience has been that the tiny bit you dislodge may not have enough weight to simply fall out, and so it can come back into place as soon as the fuel flow is restored.

The carb spray nozzle is very effective.

[sissonk]

finally got the head job completed and fired it up , it ran better but still is hard to get to 3k rpm . So I took the carbs off to check out the idle circuits and these tiny holes . didn't find anything plugged . I checked them by spraying some foam carb cleaner on the holes then blowing compresser air thro the idle air inlet and thro the idle needle . on these BS32ss carbs there are 3 tiny holes do they all get fed thro the idle circuit ?
well I will run it tomorrow and see how it goes .
thanks again for your help.
PS does anyone know what the final year of production was for the GS1000 ?

[Steve]

Quick question here...do you have an air filter installed? Whether you use a stock airbox and filter or individual pods does not really matter. If you do not have ANYTHING on the intake side of the carbs, THEY WILL NOT WORK.

If you need to do a test ride and don't want to take the time or effort to install whatever you are using, fold a shop rag in half, hang it over the intakes, zip-tie the rag to the throats of #1 and #4 to hold it in place. It provides just enough restriction to let the carbs work.

I don't think it would be good enough if you were trying to jet the carbs, as the restriction (and airflow) would not be the same as your filter(s), but for a quick ride, it works GREAT. \\/


.

[sissonk]

Thanks everyone for your help, got it going and everything runs pretty well .

[49er]

Great. What was the cause of your problem?