550 running poorly

[Guest]

Hi all, I just posted as a new member with a 1981 550T and I could use some help.
OK, bike was running pretty well after carb rebuild. Valves were in speck, though on the tight side. have new OEM air filter, good plugs, changed wires on one coil (what a pain!). Spark seems OK. So here is the problem: eight or so miles into my maiden voyage it started to sputter and lose power. I limped it home and it has run poorly ever since. It starts fine cold with choke, and idles pretty well when warm, no choke. As soon as I pull the throttle a little under load it bogs down and sputters and will barley go 40mph. The mixture screws are out about 11/2 turns. Playing with them does not seem to enhance performance. Bike seems to run rich. I tried running it without the air filter and that actually seemed to help a bit. Incidentally (or not?!) the tachometer stopped working around the same time that the engine started to run bad. I will check compression this weekend. Any ideas much appreciated.

[slayer61]

I'm gonna go out on a limb and guess you somehow managed to loosen a connection on your ignition coil, if the bike's suddenly running poorly AND the tach doesn't work... this is of course purely speculation. Hell, for all I know, you have a mechanical tach driven off the exhaust cam and there's something else awry. Good luck in your adventure! Paul

[tom203]

Since you've been lurking since March, I'm sure you followed the proper carb cleaning method, right???? Did you check main jet sizes in case a PO got ambitious? Set float levels correct? And you are sure both coils are firing right- nice bright spark at plugs?
1 and half turns out on mixture screw is pretty meager-yet more doesn't seem to do anything? Did you do a bench sync after reassmbling carb rack?

[Davey550]

#2 plug

Hi, thanks for the reply
Checked compression and it is good. Spark looks good on both coils. 3 Plugs now show signs of running lean (not surprising at 1 1/2 turns). #2 plug is carbon fouled. from researching on the site it seems the petcock may be the problem here?

-carbs were cleaned and dipped, new o-rings, float level carefully checked. think I got it right though this was my first time doing a full carb service.

[Davey550]

Update: 550T now running well

Just an update: I got her running pretty nice now by adjusting the carbs correctly. Mixture is at about 4 turns out now (factory is 3 1/2, I originally thought it was 2 1/2- rookie mistake). problem with #2 plug fouling turned out to be a bad plug (actually two, the bad one and the used one I tried to replace it with!). So, remember to check the obvious stuff first. cheers