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1981 GS1100 Exhaust temps- Problem?

  • Thread starter Thread starter solo 2
  • Start date Start date
S

solo 2

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So I'm putting my 1100 back together after 10 years of sitting around (heated garage) and took some exhaust temp readings at the start of the curve on the header. Going across 1-4, 350F-600F-600F-275F. The 2-3 seems hot even being in the center, idles nicely. I just cleaned the jets and sonic cleaned the bodies. The valves were adjusted when it was put away. If this is a problem, where should I be looking.

Stock 1100 16V motor
Supertrapp header
Mikuni RS36 carbs, factory settings
K&N filters
Dyna 3ohm coils
 
Most likely? I appreciate the answer but it would be good to know for sure. Like I said it seems a little warm even for 2-3, I'd hate to cook the valves or motor. I thought someone on here said 350F across the board but that seems a little too even. Anyone taken temp readings on the header pipes before, I'd think someone must have.
 
Okay, just noticed you have aftermarket carbs. Do they have provision to be vacuum synced, or is it mechanical sync only? If so, have you done a mechanical sync?

How does the bike run? With aftermarket carbs you may have some lean mixture issues until the carbs are properly jetted. Have you done some plug chops to verify mixture? I'd be concern with running too lean unless you have verified they are jetted correctly.

Checking the temperature of the exhaust pipes isn't overly useful. The inner cylinders are always going to run hotter, particularly when the bike is just sitting in the garage.
 
I might try syncing the carbs tomorrow, they're bench synced about perfect right now. I was under the impression that vacuum syncing didn't work all that well on flat slide carbs due to the engine pulses moving the slides. Bike isn't on the road yet so plug chop is out and I'd prefer to know if these temps are OK before taking it out for a real blast. I put the carbs to the mikuni factory settings before iinstall.
 
Sorry if this sounds a tad cynical but the introduction of these types of tests often leads to far greater confusion and anguish than it does to proper scientific analysis.

The same goes for compression testing and oil pressures. How many threads do we now have with guys getting upset about their compression readings and oil pressures?

The thing is these instruments were originally used by workshops that were dealing with 100s of cars and bikes every week. The technicians had years of experience analysing the results and comparing them with others. What we do is to think one set of readings give us the insight to make a judgement about our beloved bike. The opposite is true. We just get upset.

Most of us don't have the training or experience to use these instruments correctly. How do we know it is not tester error, that the manufacturing tolerances of the header pipes don't lead to weird reading or that the instrument is not faulty?

Most of us here can set up a four cylinder bike to run perfectly well simply by listening to it. I don't know what the exhaust temps are on my bikes or the compression or oil pressure. I just don't need any more spurious worries to detract from my enjoyable riding. It's bad enough worrying about the shims flying out of the buckets at 7K rpm.

What's wrong with looking at the plugs? Tells you all you need to know. These bikes are 30 years old and not built to the same tolerances as the sophisticated engines of today. Lets not blight them with modern day technical analysis that makes us all lose sleep at night.

Greetings

P.S. Sorry this sounds like a bit of a rant - I do apologise - but I'm sure your bike will give you hours of fun with worrying about exhaust temps. I know "to measure is to know" but sometimes it doesn't help.
 
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I use a infraRed across the pipes now and then.
I use it for help in diagnosis of problems.
It helps to know which cylinders and are affected.
I do not look for high or low temps but at the ones most off from the rest.

Incoming PM
 
londonboards said:
Sorry if this sounds a tad cynical but the introduction of these types of tests often leads to far greater confusion and anguish than it does to proper scientific analysis.

The same goes for compression testing and oil pressures. How many threads do we now have with guys getting upset about their compression readings and oil pressures?

The thing is these instruments were originally used by workshops that were dealing with 100s of cars and bikes every week. The technicians had years of experience analysing the results and comparing them with others. What we do is to think one set of readings give us the insight to make a judgement about our beloved bike. The opposite is true. We just get upset.

Most of us don't have the training or experience to use these instruments correctly. How do we know it is not tester error, that the manufacturing tolerances of the header pipes don't lead to weird reading or that the instrument is not faulty?

Most of us here can set up a four cylinder bike to run perfectly well simply by listening to it. I don't know what the exhaust temps are on my bikes or the compression or oil pressure. I just don't need any more spurious worries to detract from my enjoyable riding. It's bad enough worrying about the shims flying out of the buckets at 7K rpm.

What's wrong with looking at the plugs? Tells you all you need to know. These bikes are 30 years old and not built to the same tolerances as the sophisticated engines of today. Lets not blight them with modern day technical analysis that makes us all lose sleep at night.

Greetings

P.S. Sorry this sounds like a bit of a rant - I do apologise - but I'm sure your bike will give you hours of fun with worrying about exhaust temps. I know "to measure is to know" but sometimes it doesn't help.
Click to expand...

Not sure it's really rocket science to read a compression gauge. It's a very useful diagnostic tool as is a leak down tester. I surely wouldn't discourage anyone from using them. Can they be used incorrectly?... Sure. But it doesn't take years to learn how to use one correctly either. In reality it's harder to read plugs correctly then a compression gauge.
 
I want to sincerely thank everyone who has replied so far but what I really would like is someone to measure the exhaust temps on a know good runner or get info from someone who has. I'm not a noob at this and have all the fancy tools, the only reason I even checked was because the paint was smoking on the 2/3 and not on the 1/4. I've been playing with 2 strokes for about the last 6 years so temps and jetting are very important, maybe I'm being paranoid. I wouldn't be concerned if the center temps were 100F different but 300F seems excessive. I'm going to do a few more tests today, maybe even check the valve clearances again.

Please feel free to keep chiming in. Thanks
 
Comparing temps from another person's bike may not be relevant. Depends on too many factors. If you have the stock exhaust on it then it's a double tube arrangement with an air gap between them and that will effect the temps read. They will be lower then expected. Suzuki used the double tube design in order to keep the pipes from bluing. Made the exhaust very heavy as well.
 
JTGS850GL said:
Comparing temps from another person's bike may not be relevant. Depends on too many factors. If you have the stock exhaust on it then it's a double tube arrangement with an air gap between them and that will effect the temps read. They will be lower then expected. Suzuki used the double tube design in order to keep the pipes from bluing. Made the exhaust very heavy as well.
Click to expand...

It's a Supertrapp 4-1 header and I'm looking more for the difference than the outright temps for comparison purposes.
 
Look all you want, but I think you may still be chasing your tail on this. As Londonboards did state, reading the plugs will tell you much more. Pull the 1 and 2 plugs and compare. Do some plug chops if you're concerned.
 
richen up #2 and #3 mixture screws, the 600 range is too high. -assuming you have sync set - and clean plugs and a distinct lean idle drop on every cylinder ..

get a fan on the cylinders and don't over do it on one try , 20 minutes is enough time to start over cool down and re-test until you begin to get similar readings time after time. you'll get to know the strong cylinder and the lazy one by the temps and cold start up personality your bike has.

since you are choosing such a precise way to tell how your bike is running don't be alarmed how far off you tune settings can be and still have a decent running bike. 200 to 600 is WAAYY off but idles fine - not surprised at all. .

I try to get them balanced within 50 degrees -1000/1100 rpm idle temps can vary from the 300 range or mid 400 range experiment to give you the best transition to your needle. and don't be surprised if you have to adjust the needle since you are going from a semi-accurate to exact-precise tune.

who would spend that much time on their idle? yeah - me.

do not drive yourself crazy trying to achieve perfection . It is a very durable four stroke and there is a lot more room for error compared to a air cooled piston port 2 cycle.
 
Well after much reading I finally just went ahead and threw the Morgan Carbstix on the bike and low and behold even with a pretty perfect bench sync 1/4 were way out. The amount of movement needed to correct this was very small and the results were incredible. She now idles nice and smooth, and responds almost instantly to throttle blips. Still a bit of a bog but nothing a little jetting won't cure, pipe temps are in the 600F area across the board but that's in the garage idling for a while. Quite surprised at the difference this made across a range of problems. Thanks for all the input and don't let anyone tell you a bench sync is close enough, while most of my experience is with 2 strokes (which I've always vacuum synced) you get the same results.
 
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