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#4 Cylinder Colder

  • Thread starter Thread starter relcock
  • Start date Start date
R

relcock

Guest
I have been doing a lot of reading on these forums to get help with fixing my bike. Thanks a lot for everyones suggestions.
Anyway I think I have narrowed down the problem with my bike but I want to make sure.

I have a 1981 GS850G with approximately 31,000 miles on it. I noticed recently (although I can't say that it hasn't been like this all along) that the #4 cylinder doesn't warm up as fast as the the other 3. I mean after 5 minutes you can still grab the #4 exhaust pipe and can hardly put your hand anywhere near the other 3. Hoping that it was just the plugs or wires, I switched the 1 and 4 wires and started the bike up. Same problem. Then I switched the 1 and 4 plugs and put the 1 and 4 wires back in their original spots. Same problem. So I am pretty sure that it is not the plugs and wires or anything electrical. I decided to do a compression test. I took off all the wires and plugs, disconnected the coils, held the throttle open (w/ the throttle lock) and tested each cylinder by cranking the engine for exactly 7 secs each. In order 1-4: 130, 120, 105, 120. I know that 105 is a little low (never mind that it isnt even the problem cylinder) it probably just needs a valve adjustment or something. Anyway, obviously 120 psi is good. So, does that eliminate everything but the carbs? Any suggestions would be helpful. Thanks a lot!

By the way, I have never worked on carbs and know very little about them. Please keep that in mind when suggesting what could be wrong with them.

Ryan
 
It could also be a vacuum leak from the carb boot for that cylinder. I had this problem on my 85 700E when I had taken the gas tank off and forgotten to put the vacuum line for the petcock back onto the fitting. I was sucking air into the number 3 cylinder and it was not firing. I felt something was wrong but couldn't figure it out. I had to take the tank off for something else and that was when I noticed it and when I put it back on the cylinder started up right away and the bike ran like a scalded dog. If you spray some carb cleaner around the boot on the number 4 cylinder you might hear the engine start running a little better to indicate whether the boot is at fault.
 
Yes, it's probably a fuel delivery problem. You say after 5 minutes it's still cold - but is that all at idle? Perhaps #4's throttle is out of ajustment and it's not open at idle. Have you had the carbs sync'd? If you open up the throttle will it get hotter?

What's the history on the bike? Do you know if the carbs have ever been rebuilt? When was the last valve adjust?

When you did the compression test, was the engine cold or hot? It should be hot. You can try doing the compression test "wet" also. First get the dry numbers, then add about 1/2 teaspoon of oil down the spark plug hole for each cylinder, crank a couple of times, put your compression tester back on and re-run. If a cylinder jumps up a lot, you may have bad rings or cylinder damage on that cylinder. You really shouldn't trust a compression test though until you've gotten the valves into adjustment.

Search the forums for "mega-welcome", or look through almost any thread in the GS Owners forum and you'll find BassCliff's mega-welcome with the top 10 issues. Unfortunately he recently took a spill and I'm not sure when he'll be up to give it to you personally. Lots of really, really good info on his site. Full picture guides for valve adjust included (hint, hint).
 
Pull the plug on the #4 hole and if it's wet, it most likely is a spark problem. If dry and white in color, it's time to do the carbs correctly. There are links to the carb clean series here on the fourm, that will make the process fun and easy.

Welcome to the fourm. THE BEST SOURCE for GS info ANYWHERE on the web! ;)

YO Basscliff, where be thou? :p
 
First of all,
welcome1.gif




Also, just to make sure we're all on the same page, which one are you calling #4? :-k

The cylinders are numbered from left to right as you are sitting on the bike.

This means that #1 is under your clutch hand, #4 is under your throttle hand.

Other than that, all the above advice is good. Let us know what you find.


One other suggestion, ... where are you? Add that little tidbit to your profile, please.
There's a pretty good chance that one of us lives close enough to stop by and help you. :eek: :D

.
 
jmanz6 -
Vacuum line is attached to petcock.
If you spray some carb cleaner around the boot on the number 4 cylinder you might hear the engine start running a little better to indicate whether the boot is at fault.
Click to expand...
See that is the funny thing. The bike runs fine. After i choke it and warm it up it will idle around 1000 rpm. After it is warmed up I can rev it really high and it wont backfire (the right pipe will back fire when revved cold) it just falls back down to idle when i let go. I just think that if I was able to fix the problem then i might see a lot more performance out of it.

mike_of_bbg -
Its not cold. Its just not hot like the others. When I start the bike I pull the choke and normally have to keep it idled up till the bike warms just a bit. After a few minutes the choke will rev it up to 3000 rpm by itself so I let it warm there for awhile then push the choke back in and it drops to 1000 and idles.
History of bike (as best as I can remember):

Friend purchased bike from his brother years ago

Bought from friend late summer of 2008

Bike had been sitting in barn for a couple of years with fresh gas and stabil added once or twice a year.

Took bike to guy in nearby town that works on bikes

Carbs rebuilt and synced (he said he had a hell of a time with them - dont know any details..something about syncing)

Plugs replaced

New clutch

New air filter (K&N)

New seals (head gasket, boot, etc I believe it was some $100 dollar seal kit)

New oil and filter

Overall check and tuneup

---

Mostly I have done cosmetic work with a little tinkering here and there. I probably will be doing most of the mechanic work from now on though.

I did the compression test hot. Did not do a wet compression test. Wouldnt the fact that it was at 120 psi eliminate the cylinder from the list of possible problems even without a valve adjustment (I plan on doing one this winter anyway)

Dave8338 -

Carbs are slightly darkish in color but are dry. Thanks for the welcome

Steve -

I am calling #4 the far right cylinder if you are sitting on the bike as you are. :) I live in La Crosse, IN.
 
Hmmmm...

Methinks if he had a time with the sync he probably didn't get it right, and you probably have a vacuum leak. Yes, these bikes can seem to run pretty well on only 3 cylinders :lol: Jmanz6 probably hit the nail right on the head. Spray carb cleaner or starting fluid (be careful - don't start a fire!) around the intake boots next to the head while the bike is running. If there is ANY perceptible difference in the way it runs, you have a vacuum leak. The most common causes are failed o-rings at the head or cracked boots. See this page:

http://www.cycleorings.com/intake.html

If you have a vacuum leak, you're going to have a hell of a time vacuum syncing the carbs.

Good luck, and please keep us posted.
 
Ok, sounds good. Ill give it a shot. May even go ahead and replace the o-rings just to be sure. I think the boots are alright but Ill make sure while I have them apart. Will let you all know! :)
 
If their is no indication that the intakes have been removed ? (check the screws) Just Replace the O rings, look over the Boots carefully Then Clean the carbs Short cuts usually just make more work..
 
UPDATE:

Sprayed carb cleaner all around the boots and nothing. RPMs didnt change, no sound difference. Pretty sure boots and o-rings were changed (at least o-rings) because there are bolts instead of screws holding the boots on.

Went up to fire training yesterday. One of our firefighters is a mechanic. He happened to be there at training (havent seen him in a couple of months) he looked it over with me.
mike_of_bbg - Yes, it's probably a fuel delivery problem. You say after 5 minutes it's still cold - but is that all at idle? Perhaps #4's throttle is out of ajustment and it's not open at idle. Have you had the carbs sync'd? If you open up the throttle will it get hotter?
Click to expand...
It got very hot after we throttled it up. He thinks that I need to sync the carbs. Does anyone know if my carbs are the CV or BS carbs? (81 gs850g)
 
The BS series of carbs that are on Suzukis starting in 1980 are a CV-type carb, so the answer to your question would be, "Yes, they are". :D

The other carbs you are thinking of are the VM series.

Where are you located? Maybe one of us is within striking distance and can help you with a carb sync.

.
 
relcock said:
It got very hot after we throttled it up. He thinks that I need to sync the carbs.
Click to expand...

Sounds pretty likely that #4 is all the way closed at idle and yes, you need to sync. The little heat you feel is from the tiny bit it can breathe through the air jet. Off idle that 2 degrees or so that #4 is off will make less difference. Make sure your idle speed adjustment is effective; you should be at 1750 RPM or so for a sync IIRC. If #4 is all the way closed that may be limiting your idle speed too :-k BTW, on your bike cylinders #1 and #4 should be pulling a bit more vacuum than 2&3.

Lots of GSers in IN IIRC, though I guess it's a pretty big state. You know, you can add that info to your profile so it shows up on every post. And put your bike year/model in your sig, too - hint, hint.
 
Thanks for the tips.
Hows that for my signature? Hopefully will be able to get a better picture up soon.
 
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