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Been a while since I worked on my bike (81 GS850GL). Early on I rebuilt the carbs, cleaned the tank, rebuilt the petcock and rebuilt the brakes. All well and good AND I got er' running! Problem was, for a long time, there was barely enough power to pull out from a stop.
So - I figured with a power loss this big it's gotta be plugs, cylinder rings, or maybe valve lift/stuck valve? Anyhoo one easy test was to pour some marvel mystery oil into the spark plug holes (just a bit) to see if I could free a stuck ring. Well I did just that, and after ~ a week I took her out to see what happened. Rode for ~ 10 mins with no improvement, when all of a sudden I could barely hang on to the bike!
About two seconds later this power faded back to the old performance, and then all of a sudden, bang - tons of power. Well this happened maybe 2x more, and then she was runnin great for quite a while. Pot the bike away, and basically did the exact same thing again yesterday. So: my initial suspicion is one of two things: either I have a sticky valve or a barely working valve, that is simply not working when the bike is cool, but once the engine warms up the valve loostens up a bit and starts working. I can't see how clearances would be the problem, but I'm going to check them this weekend. The other possibility might be bad rings, but I've performed an FAA spec leakdown test and they hold real well (like 78psi held when 80psi is applied, which is really good at least compared to aircraft engines).
One more thing - my # 3 carb is leaking fuel into the air box, which is the side of the engine where the power problem is occuring (I confirmed this just by placing my hand over each exhause pipe, left side is strong, right side weak - once the bike warms up, exchaust power feels equal). So I'm thinking the intake valve is stuck / no depressed, causing the carb to flood (or rather no fuel to be sucked out).
Does this seem reasonable, and does anyone have advice for a remedy beyond just clearances? I mean what is step 2 if I check the clearances and they are good? Should I drop the valve into the cyl and perform the old mechanic rope trick?
Any advice is appreciated!
BTW this forum has made this bike restoration possible, you guys have really helped so much in your advice and direction, when I though I'd never get it done. Looking at getting it registered and all this spring, what a journey! (9 months of various tinkering and work).
Here's a pic.
So - I figured with a power loss this big it's gotta be plugs, cylinder rings, or maybe valve lift/stuck valve? Anyhoo one easy test was to pour some marvel mystery oil into the spark plug holes (just a bit) to see if I could free a stuck ring. Well I did just that, and after ~ a week I took her out to see what happened. Rode for ~ 10 mins with no improvement, when all of a sudden I could barely hang on to the bike!
About two seconds later this power faded back to the old performance, and then all of a sudden, bang - tons of power. Well this happened maybe 2x more, and then she was runnin great for quite a while. Pot the bike away, and basically did the exact same thing again yesterday. So: my initial suspicion is one of two things: either I have a sticky valve or a barely working valve, that is simply not working when the bike is cool, but once the engine warms up the valve loostens up a bit and starts working. I can't see how clearances would be the problem, but I'm going to check them this weekend. The other possibility might be bad rings, but I've performed an FAA spec leakdown test and they hold real well (like 78psi held when 80psi is applied, which is really good at least compared to aircraft engines).
One more thing - my # 3 carb is leaking fuel into the air box, which is the side of the engine where the power problem is occuring (I confirmed this just by placing my hand over each exhause pipe, left side is strong, right side weak - once the bike warms up, exchaust power feels equal). So I'm thinking the intake valve is stuck / no depressed, causing the carb to flood (or rather no fuel to be sucked out).
Does this seem reasonable, and does anyone have advice for a remedy beyond just clearances? I mean what is step 2 if I check the clearances and they are good? Should I drop the valve into the cyl and perform the old mechanic rope trick?
Any advice is appreciated!
BTW this forum has made this bike restoration possible, you guys have really helped so much in your advice and direction, when I though I'd never get it done. Looking at getting it registered and all this spring, what a journey! (9 months of various tinkering and work).
Here's a pic.
Bob
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