Stumped - maybe...

[Anonymous]

1981 550T
18k on the clock
completely stock

Recently purchased and changed oil, plugs, replaced r/r and all connections to said r/r, added ground to battery -
checked with stator papers, and charging fine.

Here's the issue.

1 thru 3 gears pull fine, 4, 5, and 6 top out. The bike will pull in those gears, but seems to max out around 7.5krpms in 4th, 7k rpms in 5th and 6 to 6.5k rpms in 6th. Bike will max around 65-70mph in 6th due to no pull from motor..will pull higher in lower gears. Notice some hesitation in upper (over 7k rpms) Rpms in lower gears. Bike pulls ok up to that 6.5k rpm line in 6th gear.

Had this problems, so changed the r/r and checked. Synched the carbs, new boots recently installed from carbs to heads, replaced air filter.

Here is what I think could be the problems. What I want to know is if I am missing anything that could also cause said symptoms, and what order to look at them.

1. charging system - fixed. Still need to clean connections, as there is an RPM drop when headlights are turned on. So a draw/resistance on the circut somewhere. (Bad ground?) Lights on or off has no effect on maxed out RPM problem.
2. Bad fuel petcock, causing fuel starvation (line is not kinked) - kit on order - no inline-fuel filter. Tank shows no rust, did remove and clean screen that is in tank.
3. Carbs dirty with partial clogging- will be cleaning, resynching this weekend.
4. Air leak in intake manifolds. Will remove, check o-rings to head when carbs are removed. All boots are new.
5. Air filter is clean, replaced, and sealing well, as far as I can tell.
6. Bad coils? Will run test on them this weekend as well. I have replacements.
7. Timing? Stock ign. is electronic on these bikes, no adjustment.

Thanks all...I can ride this now, but want to finish the repair before I store it for the winter.

[Anonymous]

no speed

One test is to take it up in the high gears, and when it max's out slowly back off the throttle and see if it wants to pick up speed or revs as you very slowly roll back the gas, if so then you are to lean in the upper throttle settings, what do your plugs look like?? and if you got crap in the carbs then sync-ing and every thing else you did is a waste of time, start with the basic stuff, carbs will very rarely clean them selves out by running them

[Anonymous]

Yes - I agree about the carbs. The new petcock and sundry other things (hoses, gaskets, fuel and vacum line, some wiring for the battery connections) arrrived today, so I will be doing a swap out tonight. I am also going to be swapping in another set of carbs ( cleaned by myself) that I have. I will also check the manifold O rings and the connections on the boots for any air leaks. Then synch and test ride.

I will update after I am done this....keeping my fingers crossed.

Rob

[Anonymous]

So after a 7 hours repair job - tinkering, always tinkering - I replaced the carbs with a back up set, replaced the boots from air box to carbs (old ones had no metal rings in them, and bad seals., replaced the air box (not the filter box) replaced the air filter, replaced the old petcock, fuel and vacum lines, replaced the postive cable from the battery, replaced the R/R, added extra ground wire, changed fuse box and starter solenoid and main fuse box, new battery, and then about 2 hours to synch...and presto - idles like a champ, no drop when the headlights come on, and only minimal choke to keep it a 2Krpms to warm up. Idles at 1k rpm when warm, no choke. Still need to tinker, as there is a slight hesitation when opening throttle, but my prior problems seem to have gone...

Seems like the original #3carb has a broken diaphram or one that isn't seated right. Pushing up on the slide, the sound it makes is not right, and the return is not crisp.

So - Thank you all! Now it's painting, polish and cleaning time....


Rob