Stumped

[Guest]

As the title says. Like my signature states, I also own an 80 Interstate I bought last May. I went through alot to get it to finally run properly with the issue being a plugged low speed circuit. After much work I got it sorted out. Now I bought an 86 Aspencade that has an issue, although different, I believe it is carburetion related.
The bike idles perfectly, exibits perfect throttle response, and pulls strong from closed throttle to half. Typically, if I'm cruising in 4th gear at 30 mph and whack the throttle open , it will pull good until around 4000 rpm at which point it begins to run rough and not pull as hard any more. I just got the bike so I haven't taken the carbs off yet to inspect them. The guy I bought it from stored it for 2 years with fuel in it and the petcock on also. I was suprised at how easily it started up after we replaced the battery. I can't see it being the slide diaphrams as it has such excellent throttle response. I also cant see it being the needle jet or main, although it is in that range of throttle position. I ran 2 tanks of gas through it with tons of Sea Foam in it with no results. I replaced the plugs, fuel filter by the way. I suspect it's running rich in that area for some reason. The fuel economy isn't as good as my 1100 Wing either.

[SIR tricky]

Have you sync'd the carbs yet?

I would do that prior to any pulling apart.

[Guest]

Are you sure the problem isn't the charging system? When the battery is at miminal voltage the bike will run rough before eventually stalling out completely. At this minimal voltage level before the bike stalls out completely the problem will seem like a fuel or carburetor problem, but it isn't.

[Guest]

Have you sync'd the carbs yet?

I would do that prior to any pulling apart.

I could be wrong and often am but wouldn't out of sync carbs affect low end performance not top end?

I would suspect the diaphragms and it's not hard to check the back two.
Also it has been mentioned here that after market chrome diaphragm covers can be a problem.

Ken

[Guest]

Hello and welcome!
Before you start tearing things apart, make sure that's a fuel related problem. If you can't verify it's carburetion, eliminate spark and mechanical.
An inductive timing light should tell you if you have spark going away. If it does, it should help you identify which cylinder(s) is causing it.
Coils can do the same thing, if the can't saturate fast enough. Ever put a 4cyl coil on an eight cylinder? Don't go racing.

Ken....yes and no......

[Guest]

Thanks for all the suggestions. While out today in cool weather with only one bar showing on the temp guage i noticed the problem is much less pronounced. It still occured but at a much higher rpm.

[edbikerii]

Like Ken said, some aftermarket chrome carb tops (diaphragm covers) are crap. I had very similar symptoms to yours, until I got stock carb tops. Do you have chrome or aluminum carb tops?

Thanks for all the suggestions. While out today in cool weather with only one bar showing on the temp guage i noticed the problem is much less pronounced. It still occured but at a much higher rpm.

[Guest]

Ken....yes and no......

Thanks Mike.
That answer was as clear as mud and I'm no wiser. :oops:

Ken

[Guest]

Go here Ken. Take someone with you. :lol:
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[Guest]

Well I finally got around to pulling the carbs off my 86 and wouldn't you know I found a main jet had unscrewed completely out and was laying in the bottom of the bowl.

[AzWing]

Surprised it ran at all.

[Guest]

Actually, it ran near perfect except when you called the main jet circuit into play. It also explains why it smoked as much as it did on start up, no matter if I just shut it down and restarted it. It now doesn't smoke anymore.