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RSRBOB, Technician
Category: Motorcycle
Satisfied Customers: 1078
Experience:  Former Factory Service Rep, Dlr Line Tech, Service Manager, General Manager, Store Owner
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I got a 82 GS1100GL about a month ago and It was falling

Customer Question

I got a 82 GS1100GL about a month ago and It was falling flat after about 3500rpm and also I noticed #1 cylinder was back firing a little on start up (cold) and occatioanly whale riding but the cylinder seemed to be working OK it had good torque as it should up to 3500rpm. I blew the carbs out with carb cleaner and a air hose I put a rebuild kit in all carbs last week and also went from 116 main jets to 120 and one size bigger on smaller jet, air I think. I dident check float level when I put them back together. Got them back on and #one cylinder is not running. Its really got me puzzled. I have checked compression and its got 160 and its got lots of gas on the plug when I take it out almost seems like to much gas not 100% tho. the other cylinders are working great #2,3,4 I also swamped the plug cap and plug with #4 and still the same #1 not working #4 runs great. and The spark looks to be the same on #1 as #4 also when running the spark look very bright on #1 and when I take it for a ride I can hear and feel #1 wanting to work cuts in and out very weekly not strong at all very subtle. and #1 will pop/backfire just a little every so often not much but it does do it. The bike has two coils and the coil running #1 and #2 are the same coil I believe. so was kinda thinking maby the coil is bad? or the valves are out a little because of the back fire but is has really good compression so that dosent seem to likely? or I was thinking if the float is set wrong it may be flooding the plug not yo run. But any way before I do anything just need some advice on witch way to go valves, carbs ECT. Also after I got the carbs back on after working on them and running the bike I noticed a bunch of very black oil/crap coming out of the muffler and pooling on the garage floor I though I may have a head gasket or valve seat problem but the more I ran it. It slowed down to pretty much a stop now I am thinking this was caused by unburned gas cleaning the crap out of the pipe. The bike came from San Deago and has 5,900 miles on it. Please only expert mechanics that are well versed in older jap bikes thanks.
Submitted: 1 year ago.
Category: Motorcycle
Expert:  RSRBOB replied 1 year ago.

Hi and thank you for your question.

In reading what you have done so far, the one thing I do not see is that you synchronized the carburetors. Even if the carbs were spotlessly clean, if they are out of sync, the bike will never run correctly. Since you swapped the plug caps and spark plugs from 1 to 4 and 4 to 1 and it didn't help, it definitely sounds like a fuel problem.

For the record, cyls 1 and 4 are on the same coil, and 2 and 3 are on the other. If you don't have your spark plug leads connected in that order, it is not going to run correctly.

Back to the original statement of the bike not wanting to rev above 3500 RPMS. I have 2 questions, what are you running for an air filter and do you have all of the hoses for vent lines connected to the carbs and are they routed correctly (towards the back of the bike).

Let me know about those things, sync the carbs and we can go from there if we need to.



Customer: replied 1 year ago.
Ya after cleaning the carbs and new kits it revs up to high rpm no problem but just on three cylinders. To sync the carbs I'll have to find a shop that can do that. What is your bike experence expertise did you go to school for bike mechanic or other
Customer: replied 1 year ago.
I got it figured out. I have to pull the head and replace old leaky valve seals. Getting a bit to much oil in #1 but thank anyway.
Customer: replied 1 year ago.
Question closed.
Expert:  RSRBOB replied 1 year ago.

You may be on to something with a spark plug that is oil fouled. I would be guarded about putting too much stock in it being a valve guide seal however. Typically, when valve guide seals start giving problems, you see it on more, if not all, cylinders. Typically they fail from age, and equally typically, they are the same age. Also, based on that, valve guide wear could be contributing as well, but again, most likely indicated on more than just one cylinder.

You did mention compression on a cylinder of 160, but you didn't clarify if that was all 4 cylinders. If only one spark plug is coming out oily black, it would be more common to be related to a ring or cylinder wall problem. Since you have to remove the head to check the valve guides and seals anyhow, I would suggest removing the cylinders to inspect the affected piston, rings and cylinder while you have the head off. If nothing is wrong, the only additional part you are risking is a base gasket, which is relatively inexpensive. If the bike is high mileage, at the very least you could replace the rings and help the overall performance of the bike.

Bear in mind that you really need to get the carbs synced to ensure the bike is running properly. Any motorcycle shop should be able to sync them for you, and most shops charge about 1 hour labor for that job.

You have thrown out a lot of variables here so it is difficult to give you specific advise. it is confusing that in your original post you said it has good power/torque up to 3500 RPMs, then in your last post it revs higher but only on 3 cylinders.

Before you take it apart, if it truly is a problem of the spark plug oil fouling, which is what it is called for what you described, replacing the affected spark plug will allow the bike to run correctly for a short time until the oil fouls the new plug. One spark plug should cost you less than $5 and it is the cheapest easy diagnostic tool at your disposal now. If I were in your shoes, I would definitely replace the spark plug and see if it runs normally on all 4 cylinders. If it doesn't, there is still something else wrong with the bike. To reiterate, replacing the one apparent bad spark plug with a new plug is for the purposes of testing and eliminating variables. It is not intended to be a fix for the symptoms, we are just trying to affect the symptoms.

Depending on how severe the problem is about oil getting to the spark plug, the new plug could last a short time or quite awhile. The important point is, it should last long enough to verify that was the real problem or not.

If you have any more questions, feel free to ask.



PS, as far as my experience, I went to the American Motorcycle Institute and became a certified motorcycle technician in 1976, and since then have worked in motorcycle dealers continuously since 1984 as everything from a line technician, service manager, general manager of a franchised dealer, a factory service road rep for Yamaha Motor Corp and owned my own motorcycle repair shop/retail store. I have worked in dealers and have factory training in Suzuki, Yamaha, BMW, Kawasaki,Honda, KTM, Polaris and Eton. In addition to that, during my time with Yamaha, I was signing the certificates for Yamaha dealer technicians verifying they had successfully completed Yamaha technical training. With Yamaha, I as personally certified in and trained techs on the service and repair of Motorcycles, ATV's, Side by sides, Scooters, Outdoor Power Equipment, Personal Water Craft and Jet Boats.