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Runs great! after warming up?

  • Thread starter Thread starter a_man0311
  • Start date Start date
A

a_man0311

Guest
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.
mGUQlHQyplUjW_JtOe_kmKPRvikXFhuz3lTT2cvIPNg
 
Sounds like one of the cylinders is misfiring. When you cleaned the carbs did you follow the GSR rebuild tutorial and replace all the O-rings? Did you spray carb cleaner though all the various carb passages (including the choke pick up tube) to make sure they were open? Did you replace the intake pipe O-rings? If #3 is overflowing then the float needle is not sealing as it should which is bad. If there is rust inside the gas tank some may have come loose and is now blocking #3 from sealing. Any which way you need to figure why the carb is overflowing before going any further.

Needless to say the engine valves should be checked/verified, as well as the condition of the spark plugs. It also wouldn't hurt to refresh the attachment of the spark plug caps to the high tension wires (snip off about 1/4" of wire and screw the caps back on).

All basic stuff that should be done or at least verified as correct.

Good luck and hope this helps.
 
Hi,

I agree with Mr. Nessism. Go over all the basics. Are you getting good, consistent spark on all four cylinders? Click the link below to go to my website then visit the READ ME page. There you will find the "Top 10 Common Issues" and the "Top 15 Tips To GS Happiness". Do it right and take no shortcuts. Get that stuff squared away and you should be good to go. :)


Thank you for your indulgence,

BassCliff
 
Just to be sure- when you say #3 carb, you mean the one that's third from the left as you sit on bike?
 
Ok....

Ok....

So yes the carb I'm describing is the third from the left side as you sit on the bike.

Re the rebuilt carbs. Took 6 weeks and dipped each for 8 days. Fully cleaned and checked per gsr method. I'm thinking maybe I broke something on # 3 during rebuild?

Anyways I'll do the lifters, but why would warming up change the symptoms (I.e. Bike runs good after a while) if this were a carb problem? More curious than anything at this point...sounds like I have a lifter AND a carb problem!
 
power surge

power surge

I would have to agree with a plug wire or the spark plug boot itself. Had a problem on my 450, two cylinder's were easy to confirm. Replaced with new boot and ran great. Just curious, are you getting a backfire or a popping through the exhaust and or is that exhaust header cooler than the others? Careful upon INSPECTING though.:eek: Bob
 
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