Wacky idle...bad head gasket?

[VP1]

Hi all,
I'm new to motorcycles after just selling my last vintage scooter.
I just bought an '82 GS850G with 16,000 miles. The PO said it'd been sitting for a year. I cleaned the carbs, replaced the spark plugs, and replaced the battery.

There is a problem with the idle unfortunately. When I rev it up sometimes it'll return to idle and sometimes it'll hesitate at the high RPM before settling back down. Sounds like it's too lean or has an air leak right?

Needles are 3.5 turns out (started at 2) and all of the boots look ok, and have been tested by spraying carb cleaner on them while idiling. No change in RPMs.

I checked my compression today and cylinder #3 only read 55 lbs. It was hard to get the compression guage fitting to sit tightly in the plug hole due to how recessed it is but using the same method resulted in reading of around 130 lbs for the other 3 cylinders. I need to find a way to tighten it in there better but it definitely seems suspect.

I admit that when I cleaned the carbs I did not replace any o-rings but upon inspection they all appeared ok. the fact that the compression is low in that cylinder makes me think I have bigger problems than o-rings.

Would bad rings or a leaky head gasket produce the symptoms I'm having? Anyway to double check my findings with the compression guage?

Any advice, or tips would be greatly appreciated!
thanks, Todd

[BassCliff]

Greetings and Salutations!

Hi Mr. VP1,

The old "spray around the intake boots" trick is not a reliable test for air leaks. Chances are good that new intake boots and o-rings will save you a lot of headaches. Also make sure your airbox is properly sealed. Now for the reason I came...

Please click here for your mega-welcome, chock full of suggestions and links to vendors and other information. Then feel free to visit my little BikeCliff website for lots of GS lovin' and to peruse the wisdom I've been collecting from this generous community. Thanks for joining us. Keep us informed. And we like pictures. Not you, your bike!


Thank you for your indulgence,

BassCliff

[GSJim69]

Have you checked the gas tank for rust. I had some similar symptoms caused by rust from the gas tank.

[Nessism]

Sounds like an intake airleak. Cycleorings.com has what you need.

[VP1]

Basscliff! Oh how I have enjoyed reading your site for the past week while waiting for my forum registration to go through.

From reading your site I have learned that the boots and o-rings in the intake system are very important. I can't argure with that. But, seeing as how I have low compression (yet to be verified) in cylinder #3 makes me wonder if that problem needs to be fixed first. I had planned on replacing the boots and o-rings even though they visually checked out ok if nothing else seemed to be wrong...that was until today when I found the low compression.

Please don't think I'm ignoring your advice. I just have to wonder if the low compression is the problem..
Thanks, Todd

[cbxchris]

If you have no air leaks its a classic example of your carbs out of sync. You will need a set of gauges or mercury sticks to see what's happening.

Other problems in no particular order are sticking intake valve(bent?...leak down test can confirm that. Tight intake valve needing adjustment. Low compression. Twisted crank. Blown crank case seal somewhere. Blown head gasket.

On that low cylinder it will be easy to find out what is the issue. Put a leak down tester on it and just listen. You will either have air going in to the crank case,carbs or pipes. That means piston issues,intake or exhaust valve problems. Check for tight valves first. I have seen bikes that are left to sit bend a exhaust valve on start up. The valve stem gets rusty and dosen't go all the way back in then hits the piston bending it.

[feelergaugephil]

sounds like an intake airleak. Cycleorings.com has what you need.

+1.............................................

[Nessism]

I doubt the cylinder would fire if the compression was actually 55 psi. Best to check it again. And remember to check with the engine hot and holding the throttle wide open.

[Suzuki mad]

So what was the question.......

Hi all,
I'm new to motorcycles after just selling my last vintage scooter.
I just bought an '82 GS850G with 16,000 miles. The PO said it'd been sitting for a year. I cleaned the carbs, replaced the spark plugs, and replaced the battery.

There is a problem with the idle unfortunately. When I rev it up sometimes it'll return to idle and sometimes it'll hesitate at the high RPM before settling back down. Sounds like it's too lean or has an air leak right?

Needles are 3.5 turns out (started at 2) and all of the boots look ok, and have been tested by spraying carb cleaner on them while idiling. No change in RPMs.

I checked my compression today and cylinder #3 only read 55 lbs. It was hard to get the compression guage fitting to sit tightly in the plug hole due to how recessed it is but using the same method resulted in reading of around 130 lbs for the other 3 cylinders. I need to find a way to tighten it in there better but it definitely seems suspect.

I admit that when I cleaned the carbs I did not replace any o-rings but upon inspection they all appeared ok. the fact that the compression is low in that cylinder makes me think I have bigger problems than o-rings.

Would bad rings or a leaky head gasket produce the symptoms I'm having? Anyway to double check my findings with the compression guage?

Any advice, or tips would be greatly appreciated!
thanks, Todd

Firstly Hi to the GS resources. I see basscliff got to you already.....

You should have over 100lbs in each of the cylinder on a compression test. I am guessing that you know how to do a compression test so we'll skip most of that part. (Throttle full open hopefull!) Did you put a small amount of oil down the bores for a second test?

As for a compression test kit you can get the adapters that screw into the spark plug hole or the push fit versions for bikes (can cost a bit so try and borrow one from a local dealer if poss.)

The next step is to check the valve clearances so pull the rocker box lid off and see. Make sure that the buckets move properly and that all seems fine for clearances even spinning the motor over on the 19mm socket to check.

If all seems OK I would suspect that the motor has a problem with either the valve, valve seat or a worn bore. It could be a head gasket gone but that would show oil coming out from that area which you haven't mentioned unless its gone towards the cam chain tunnel.

Run the bike and squirt some water at the exhausts and see if No3 is getting hot. I would suspect that it isn't.

Once you have comfirmed that No3 is that low then only sensible step that you have is pulling the head, barrels, homing the bore's, new rings, base gasket plus O rings, sorting the cylinder head out (new valve in No 3 [exhaust] as a guess), lapping or reseating the valves, new intake rubbers and seals (the philips screws may not come out so its easier to work on off the bike), new cylinder head gasket, re-shim the engine (do it on the bench before refitting for ease) new rocker gasket and rocker box back on.

After that its a re-synic the carbs and she should be good to go for a few more years yet.

Suzuki mad.

[trippivot]

I doubt the cylinder would fire if the compression was actually 55 psi. Best to check it again. And remember to check with the engine hot and holding the throttle wide open.

I've seen these bikes run on 60 psi on all 4 cylinders.


the hang up can be a combination of multiple factors.

information is way too vague for an exact diagnosis

I say start at the obvious and the cheapest then work towards the expensive

[BassCliff]

Hello again Mr. VP1,

I'm glad you've found my site somewhat useful. All of the PDF files can be downloaded for your convenience. For GS resurrection basics, I think Mr. bwringer said it best:

Every GS850 [and most other models] has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.

Keep us informed.

Thank you for your indulgence,

BassCliff

[VP1]

Thanks again to everyone. I really really appreciate it.

Last night I ordered the carb o-ring kit and intake o-ring kit from Cycle O-Rings. I really wish I knew this was the problem but the kit is cheap enough to buy and rule that problem out.

I have been working my way through the Top 10 to fix, I have a few more things to do on that list before I'm done. Mainly I need to do the valves and install new intake o-rings.
I disassembled the airbox and everything looked ok. Nothing obviously wrong with it and all of the seals looked ok to me..

One thing I'm a little unsure about though is synching the carbs. I've read the tutorial and did the paperclip in the throat trick...I guess I just don't know how accurate I can get it without any of the proper guages etc.

Well anyways, I'm going to check the valves and replace some o-rings and I'll report back.

Cheers, Todd

[VP1]

I wanted to answer a few other questions that were posed so I make sure I'm putting out all the info I have.

I cleaned and flushed the gas tank and rebuilt the fuel tap. I also ordered a new tap even though the old one seems to be working fine and will install that before I proceed any farther.

I did pull off the intake boots and check the o-rings. No cracks... They were a little flattened but I think there was enough protuding to form a seal. New ones have been ordered and will be installed before proceeding.

I did check compression with a warm engine and throttle wide open. I don't feel I was able to adequetly screw the fitting into the spark plug hole so that may be the reason for low compression. I can confirm that cylinder 3 is firing via the lick the fingers and touch the headers method. HOT!

I have not checked valve clearance. I will do that before proceeding also.

I've taken it for a few spins around the block and it sure does pull well, just won't idle happily.

[VP1]

Oh and I meant to ask about the jet needle. On 2 of the slides the needle was nice and rather firmly set in place, that is, still movable yet obviously not loose and flopping around. One can hold the needle and pull it down about 1/4" and then a spring returns it back up.

The other 2 needles were obviously not being held the same and were rather loose for lack of better terms. I could also pull them and they would return back to position via the spring but the movement was not smooth or very repeatable. so I pulled out the circlip and reassembled the component. With the circlip in place, I put the spring on the needle from the base so the circlip is above the spring and then put the little, approx 1/8" thick plastic washer above the circlip on the end of the needle shaft. Needle movement is now smooth like the others.

Did I get the reassembly correct?

[VP1]

Wanted to show you all what I hope to be riding soon. Paint isn't as nice as it looks in the pics

-Todd