GS850- no vacuum at idle

[Poot]

Hi all,

I've got a '80 GS850, and the problem is that the bike wont idle properly, and when I give it all right off the bat, it bogs.

I have replaced the manifold boots + orings, and have cleaned the carbs completely (new orings, etc.), and again cleaned the jets after I had some top end problems. solved those. (i had my tank painted, and i think there was some ****e that got into the fuel).


I have checked for intake leaks, by lacing all areas (boots, carbs, airbox) with quickstart, but with no affect. The bike is currently running lean.

When I was at my mechanics, for a carbsync, the bike was running without any vacuum at idle , but fine in other ranges.


Since i just took out and cleaned the jets, its still there. the only thing is, that i didn't remove the air jet, and the air-screw (forgot the air jet).

could this be it? The float levels should be fine, seeing as the bike worked great before i took apart the engine block.



POOT

[Poot]

sweet..didn't realise i passed 1000 posts!


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[chiphead]

"the bike was running without any vacuum at idle , but fine in other ranges"
Do you mean that at idle and vacuum gauges hooked up, there is absolutely no draw or needle movement on the gauges?

"seeing as the bike worked great before i took apart the engine block"
I think being a tooth off on the valve timing may cause similar symptoms to what you're experiencing. Why did you take the motor apart and how far apart did you go?
Just an idea.

[flyingace]

If the bike runs well at any RPM but idle/off-idle (if that's what you're saying), I'm not sure the problem is a vacuum leak. Seems this would show at all RPMs. Something must be wrong with the carb idle circuits. Was the mechanic able to synch the carbs?

[nabrams]

My CB750 ran great at everywhere but idle (it was very choppy and would stall out ocassionally) and was hard to start. I messed with carbs for ages to no avail. Then I did a compression check and found that my compression was really low for #1. There was zero valve clearance for that cylinder. After getting valve clearances into spec, the bike idles and starts well. I could have saved myself MANY hours of aggravation if I'd just done a compression check.

[Poot]

thanks for the tips guys.


The vacuum was tested with the mercury-levels at the mechanics (while i was watching). The carbs were, and are in perfect sync.


I do know that the 1 in/ex valves are too loose, b/c when i did the clearance i didnt have the right shim, so i couldnt improve it as much as it should have been.


I will check the compression, and i guess this will tell me if the clearance is the problem.



POOT

[flyingace]

The first post you say the carbs had no vacuum at idle. Then you say the carbs were in perfect sync. These items are not compatible - if there is no vacuum at idle, the carbs can't be in perfect synch.

Which is it?

[Poot]

the carbs were /are in synce at all ranges above idle.

for some reason, there is no vacuum at idle, and the mercury readings are extremely low, but uniform. also uniform at all ranges of RPM's.


BtW , i changed the head and basegasket.

POOT

[Poot]

The Cam timing was off 1 on both intake and exhaust.


My compression went from 100- per cylinder to 145 to cylinder.

[nabrams]

Happens to the best of us. The worst is when I don't learn from my mistakes and fail to verify the basics (spark, compression, etc.) the next time I have a problem.

[Poot]

ditto for me too.



POOT

[BigDaddyKool]

guess what

hello, I also have a gs850 and feel like an idiot for what I did. I painted my tank, etc, put it back together, would not idle and would die exactly like yours did,I wracked my brain about carbs, intake leaks, etc, touch the exhaust pipes quick you will know which ones are working or not. lucky for me I had a parts bike with a set of ngk B8es plaugs sitting there, so I said lets swap em. VOILA now a perfect running bike just like I had before I painted it, strange as it may sound, new plugs did the trick.