#3 cylinder running hot - too lean?

[stupiferodious]

Got a '80 GS850G given to me as a resurrection project...after 9 months of project work, it's *just about* ready. However, it shakes under load (idles and revs smoothly in neutral). I put an infrared thermometer on the exhaust pipes at idle and I'm getting 130 F on cylinders 1 and 2, 100 F on cylinder 4, and 390 F on cylinder 3. Not good. All carbs have been re-jetted for pod air filters and vacuum-sync'd. Valves have been re-shimmed, compression readings 135-140 PSI in all cylinders. I now have a 132.5 main jet in the #3 carb, float level is good, slide is set full rich, pilot screw out 4.5 turns. All intake boots and o-rings are new, I tried swapping boots 3 and 4, no help. Matter o'fact, this hot cylinder 3 condition has persisted through 2 sets of carbs (boogered up the first set thru overzealous drilling of pilot screws ). About the only thing left I can think of is a crack in the cylinder head between intake boot and intake valve. Is there anything I'm overlooking? Let me know. Thanks!

 

[Steve]

A couple of thoughts come to mind that did not seem to be addressed in your narrative. :-k

1. Are you sure you are numbering the cylinders correctly? #1 is under your clutch hand, #4 is under your throttle hand. I ask that because, if you number them the other way, #3 would be the one with the vacuum fitting to the petcock. If that is left open, it will be a very lean mixture (which will run hot) and will also cause rough running.

2. You say that you re-jetted the carbs for pods and pipes (the 132.5 seems a bit large, but might be close). One thing I did not see mentioned is whether the carbs have been CLEANED. By "cleaned", I mean a full "strip and dip" cleaning and putting them back together with new o-rings from cycleorings.com.

3. Are you sure that you have all the spark plug wires on the correct plugs? If plug wires are crossed, you will obviously have rough running, and it's possible that one cylinder will be firing such that the temperature goes considerably higher.

.

 

[Badooka]

Absolutely on what Steve just said, if all of that is good to go- check your valves- you might have and exhaust valve hanging up. Possibly a bad spring or adjustment.

 

[stupiferodious]

Thanks for the quick response. Yep, #1 is clutch #4 is throttle, numbered left-to-right as you're sitting on the bike. And the carbs were stripped-and-dipped using a new tub of carb cleaner and new o-rings. All passages were flushed with spray carb cleaner. The re-jet kit said to use 127.5 main jets on 1 and 4, 130.0 main jets on 2 and 3. The kit also included a 132.5, which I put at #3 as (hoped for) correction for the hot cylinder. As far as the valves, initially found #2 and #3 intake and all 4 exhaust valves at zero clearance. Replaced the 270.0's in those positions with 260.0's, now get about .003" clearance - a bit loose but should be OK. This also corrected varying compression readings (60 - 120 PSI initially). Could a hanging exhaust valve be picked up with a compression check? When I was checking and re-shimming them all tappets were well-oiled and moving with the cam (admittedly as fast as the 19mm wrench could turn).

 

[barnbiketom]

I think that you have one cylinder running ok (390 degrees)
and 3 are not running correctly.

100 or even 130 degrees is not even hot. thats what your hot water tank puts out at home.

the exhaust pipes should be MUCH HOTTER

someone will correct me if i am wrong, but I suspect your carbs are plugged internally, or "jetted" too rich, or your valves are dirty/too tight/floats all wrong etc....

 

[Steve]

Thanks for the quick response.

Quick?? That was almost an hour.

Yep, #1 is clutch #4 is throttle, numbered left-to-right as you're sitting on the bike. And the carbs were stripped-and-dipped using a new tub of carb cleaner and new o-rings. All passages were flushed with spray carb cleaner.

Thanks for adding that, it's just that you did not mention it the first time around, and it's a point that is often overlooked.

The re-jet kit said to use 127.5 main jets on 1 and 4, 130.0 main jets on 2 and 3.

I am not going to say it's wrong, but the only bike for which I have seen different jets recommended is the 1150. I am not sure that the 850 needs them. Personally, for your setup, I think that 127.5 might be correct, but you won't know until you get it on the road and do plug chops.

The kit also included a 132.5, which I put at #3 as (hoped for) correction for the hot cylinder.

If you have not gotten the engine above idle speed, it really won't matter whether if the main jet is plugged almost solid or even missing, so a larger main is not going to cool the engine down unless you are running well over half-throttle.

As far as the valves, initially found #2 and #3 intake and all 4 exhaust valves at zero clearance. Replaced the 270.0's in those positions with 260.0's, now get about .003" clearance - a bit loose but should be OK.

That sounds good, so far. Have you by chance gone back to verify that the clearance is still good? I ask that because when the valves have "zero" clearance, there might have been some deposits around the seats. Now that the valves have been opened and closed a few hundred times, those deposits might have been removed, reducing clearances. It would make sense (to me) to go back and verify your clearances.
This is also the perfect time to take advantage of the invite in my signature.

Could a hanging exhaust valve be picked up with a compression check?

That depends on how/why it was "hanging". If there were deposits, as I just mentioned, yes, the valve could be held open enough to allow enough leakage to affect your compression numbers. Yet another reason to go back and verify your clearances.

.

 

[stupiferodious]

Ok, I'll re-check the valve clearances...small grouse on that, the reason the bike was parked was it was originally wrecked in front, some nice person replaced the steering head and forks and made a game try at straightening the frame but it's still bent some in the front (horn area)...gotta pull the exhaust pipes, remove front mounts, loosen rear mounts and jack up the front of the engine to take off the cam cover. Maybe while I'm "at it" I'll also get a cylinder head gasket and pull off the cylinder head, get a GOOD look at what's up....the cam chain sorta scares me tho.

Also, will fully verify the plug wires are right, trace em from the coils down, won't assume the number label is correct.

Can I get a consensus on what temp the exhaust should be?

 

[Guest]

Exhaust temp will depend upon how long the bike has been running. But if you fire a bike up and let it run 3-4 minutes I would gues pipe temp would get up to 250-300 degrees pretty easily .

 

[Guest]

It sounds like # 3 is the only cylinder acting normally. I'm running 132.5's (Dynojet 142 jets) on my stage 3 jet kit, but my carbs are VM's. I have no idea how that would compare to your CV carbs. Reading the pipe temps, at the middle of the first bend after idling for a while, 360 to 400 degrees is about normal, but not a very accurate test. What you are looking for is to have all the pipes close to the same temp. By the way I'm running slightly fat, not lean at all. If you are using larger jets for # 2 & 3, keep the jets the same size, same for 1 & 4. My Dynojet kit came with DJ 138's and 142's but made no mention of using different jets on different cylinders. The second set was was for more choices for dialing the carbs in.

 

[Steve]

.., some nice person replaced the steering head and forks and made a game try at straightening the frame but it's still bent some in the front (horn area)...gotta pull the exhaust pipes, remove front mounts, loosen rear mounts and jack up the front of the engine to take off the cam cover.

Are you sure you want to even ride this bike?

Maybe while I'm "at it" I'll also get a cylinder head gasket and pull off the cylinder head, get a GOOD look at what's up....the cam chain sorta scares me tho.

The cam chain is the EASIEST part of that process.

If you do choose to go that route, you should also get a base gasket, because it will be compromised when you release the pressure on it when you remove the head. Also, the process of removing the head will physically move the cylinders, which will further disturb the integrity of the base gasket.

Also, it is HIGHLY recommended that you get OEM head and base gaskets. Note that the OEM head gasket alone will cost about as much as a full aftermarket gasket kit.

Also, will fully verify the plug wires are right, trace em from the coils down, won't assume the number label is correct.

Unless somebody has done some creative re-wiring (and, with that front-end smash-up, it's possible), the wires from the left coil should go to cylinders 1&4, the wires from the right coil will go to 2&3. Except for the fact that one wire on each coil might be a bit longer than the other, making it easier to reach to the other side of the frame, it does not matter which wire goes on which plug.

Can I get a consensus on what temp the exhaust should be?

That will depend on what pipes you have, how long the bike has been running and your pilot mixtures.

Stock pipes are double-walled, so if you fire it up from cold, the outer pipe will take a while to reach operating temperature, although all four should be rather close at all times. Aftermarket headers are usually single-walled, so temp rise will be quicker, but should still be even.

You may think that your mixtures are the same because you have the screws set to the same number of turns out, but if there is something blocking the passages inside the carbs, it won't necessarily be correct. On my son's 650, I have found that one carb needs to have the mixture screw out one full turn more than the others. Only by adjusting each screw and observing the changes in the engine will you know that that setting is correct for that carburetor. We can only suggest what have been typical settings for most of us, your bike can/will be different.

.

 

[stupiferodious]

The frame bending is actually pretty subtle....maybe I'll send a pic later. The bike maneuvers and tracks ok best I can tell, and all the frame welds have held up. The steering head's a bit more vertical, meaning I have to keep the forks aired up to about 20 PSI to keep the front fender away from the exhaust pipes. Progressive springs are bought and on their way...

The cam cover is a trick to get off anyway.

By the base gasket I presume you mean between the cylinder head and crankcase.

Thanks for info on plugs, I knew it was a dual-coil wasted-spark design, first year for electronic ignition.

 

[Steve]

By the base gasket I presume you mean between the cylinder head and crankcase.

Actually, between the cylinders and the crankcase.

The "cylinder head" is the part on top of the cylinders that holds the cams and valves.

.

 

[Guest]

My exhaust temps on my GS1100E runs in about the 200 degree range when the bike is fairly hot. I have one cylinder that runs hotter than the rest, number 3, which runs about 30 degrees hotter. The pipe for this cylinder has a tendancy to want to blue on me.
It used to run alot hotter, but the number 3 cylinder always ran hotter than the others, even after I put a different set of rebuilt carbs on it and adjusted the valves.

 

[stupiferodious]

A little bit of follow-up

A little bit of follow-up

Put in some drydock time on the bike as inspired by your replies, found that one of the bolts holding the #3 intake boot was stripped. M6-1.0 Helicoils were too short, so put in a longer bolt that grabbed the remaining threads. Haven't had a chance to measure the temps since, but seems better using the hand-as-close-as-possible check.

Also found that the #1 pilot screw had fallen out along with its friends the spring, washer and o-ring. Re-installed these from the old set of carbs. This explains how I lost idle all of a sudden, or it may just be God punishing me for driving the GS to a Harley dealer to look for a scooter for the wife. At least I made the sales guy look at the GS .

Currently dealing with trying to get the old tach drive gear out, mounting the speedo/tach wrong caused the external part to snap off flush with the head when the forks were turned hard left. Also got progressive fork springs/oil seals and a full set of steel braided brake lines to install, but all that doesn't belong in this section so I'll just say ta-ta for now.