1982 Suzuki GS1100E #4 cylinder reads 100 F while #1,2 and 3 read 300 F

[Daimler]

Hi, I am working on a GS1100E (1982). The bike belonged to a buddy and was parked for like 25 years. 48,000 kilometers. I decided to get it running better but no matter what I do, # 4 cylinder runs way cooler than the other three. I have gone through the carbs for the third time. I have a manometer to sync the carbs with and did so. First the idle mixture screws were set to 3 1/2 turns out and the highest idle was achieved. Then the sync was done. The valves were set to .004. The compression test is #1 -105, #2 - 103, #3 - 102, #4 - 114.
The ohm check for the coils checked out OK both the primary ( 200 scale = 4.3 ohms on both coils) and secondary ( 200 K scale = 22.1 and 20...with the new NGK spark plug boots in place.) The STD passed too.
New NGK spark plug boots and spark plugs were installed. The coils were reversed and #4 stays cooler. Number 4 plug is just slightly damper than the other three spark plugs - (which are all the perfect colour.) When #1/3 coil was accidentally left disconnected - the bike started and ran fine on just #1 and 4 until #4 spark plug wire was removed and the engine stumbled down and ran on just #1 and recovered when #4 was reattached. So if it's working why is the #4 exhaust header showing 100 degrees F when the other three are showing 300 degrees F ? That is my question. The bike runs out quite nicely on the highway and pulls strong. I am thinking I might try the GM V-6 coil installation, increase the gap and see if that sorts it out, but I am not entirely optimistic it will.

 

[Nessism]

Stash the temp gauge and ride.

 

[Daimler]

Same thing my buddy in Kelowna said. Which I will be doing. But I would like to know the cause. Today I was setting the carbs and sync and found that when I removed the vacuum lead to the manometer from any of the first three cylinders the motor stumbles and recovers when reattached. Number four cylinder however shows no noticeable change in RPM when the vacuum line is removed. It has been suggested to me that the cams are prone to excessive wear? Maybe The intake cam lobes are worn too much on that cylinder? I should have checked the cam lift on that cylinder when I was setting the clearances but I did not know that story then. I will ride the bike for a while and see if it smartens up with a little use.

 

[bonanzadave]

Try running it with the petcock set to PRI

 

[Daimler]

Thanks for the reply's, I did rebuild the petcock and sending unit and they work fine. I finally just set the carbs at three and one half turns out ( where it idled best) and synced at about 1100 RPM's. Took it for a ride and it came back into the shop with the number 4 pipe up to temp. I will just be happy with that. Like Ness said - just ride it. I do not have time to sort this out with the low compression, ghost vacuum, etc. Seems good enough to just ride the bike. Thanks again.