sudden, dramatic lack of power in '80 GS550E

[Anonymous]

first post and it's a doozy....

last friday i bought a 1980 GS550E with 22500 miles for $750. the guy i bought it from had had it for a year and hadn't ridden it much. i don't think he had changed the oil either (the oil indicator showed a good level tho). i checked the compression in the two outermost cylinders on both sides and they were both around 110psi. the bike started quick and idled well, but maybe not as smoothly as it could. when i test rode it it was very quick and had lots of power tho.

i went away for the weekend and after coming home sunday i took it for a ride sunday evening (i know i should have changed the oil first). it was very quick and powerful and i rode it for probably 20 minutes around town and on th freeway. after about 35 minutes of good, quick riding the bike died on me at a stoplight. i pushed over to the side of the road and got it going again, but when i tried gunning the throttle the bike would die. if i twisted the throttle a bit slower it would hesitate then give gas, but not nearly to the extent as before. now the bike is rather sluggish, lacking power and there is a slight delay between twisting the throttle and acceleration.

i've since changed the oil, lubed and cleaned the chain and put new plugs in but it's still sluggish. the wheels rotate as smoothly as before the loss of power so it's not anything binding the wheels.

any suggestions? my next step is to check the fuel system starting at the petcock and working through the carbs. i admit i'm a bit intimidated by having 4 carbs. my last bike was a single 500cc with one carb and i felt quite comfortable completely overhauling that.

thanks in advance

[Anonymous]

First thing I would do is check the compression on the inboard cylinders, then sync the carbs. My 750E did exactly the same thing until I adjusted the valves and synced the carbs. Runs like a top now.

[Anonymous]

You might think about checking the cam timing. With the lack of riding for the last year the automatic timing chain adjuster may be frozen and let it jump time. I had an intake cam out of time by one tooth and it made it very sluggish.

[AOD]

i think the carbs might have sucked in some dirt or rust since it sat a while. you can try a little carb cleaner (little please) or take off the carbs and clean them out a bit. probably a good idea since it sat for a while.

also check the petcock filter, as it might have clogged up a bit too.

~Adam

[Don Lobacz]

The suddeness of the problem would make me think that you dropped one or more cylinders. Check the exhaust temps of all the pipes by running the bike for a few hundred feet, stopping the motor, wetting your fingers and quickly tapping the exhaust pipes (hot pipes will be very hot! be careful!). If 1&4 or 2&3 are cool as a pair then a coil is not working: could be a bad coil, bad pickup, bad module or just a wiring problem (I once had a wire come loose). Anything else would most likely be carb-related: a plugged main jet, water in the gas, a leaking diaphram, torn carb boots, etc... Let us know which pipes are cooler.

[Anonymous]

compression in all four is 110, 115, 120 and 110. all four are hot so they all seem to be firing.


i changed the oil, replaced the plugs and cleaned the air filter. cleaning the air filter feels like it helped a little, but it's still lacking pickup. i've let the bike sit for nearly a day and i think i'm going to tackle the valves this afternoon and hopefully the carbs as well if i have time. i drained the bowls of all four yesterday and they all had clean, fresh gas come out.

how would i check the cam timing? i have the clymer manual, where would that info be found?

is it ok to put an additive in the gas that's supposed to clean out the cylinders? i've heard mixed info on this.

thanks.

[AOD]

i'm guessing you're carbs are gummed up...so just draining the bowls isn't going to fix that. if you're getting spark at each cylinder, then its a carb problem.

~Adam

[Anonymous]

i took off and cleaned up the carbs this afternoon. i gotta say they were in very good shape inside and i don't think i really needed to take them apart. they were spotless inside and it looked as tho they had been rebuilt relatively recently as the gaskets looked pretty new.

they were, however, way out of sync. i got them pretty well synced and BOOM!, power came back. that must have been it.

thanks for all the suggestions. cleaning the air filter and re-syncing the carbs seems to have done it.

-john

[AOD]

glad to hear. 8)