Throttle power dies after 5min of riding each morning

Every morning my '82 Seca 650 starts relatively well. I get about 5min (1/2mile) down the road and my throttle power instantaneously drops. The bike idles normally, but giving the bike throttle produces a puttering with no power added. I turn off the bike for 10 minutes at usually it starts and runs fine the rest of the day. The problem occurs in the mornings (which are are typically dewy and humid in Alabama) or after a rain, so I think there is definitely a moisture element to it. When the problem is taking place, using started fluid in the intake while throttling does nothing. I also looked at the spark plug which appears fine when idling, but when throttling the spark rate appears to slow down, not speed up. The plugs are fine/new, the air filter is new, the fuel is flowing from the tank fine. The guy a bought it from said he cleaned the carbs right before selling 6 months ago (no reason for him lie about that now). It has run fine for 4 months before this started and since then it has been getting slowly worse. Cannot figure this one out?

 

First I would test the coils.

 

Check FUEL Level.
Check Vacuum Hose.
Check Petcock Function.

Also, ... You may be "Living off the Top of the Battery"

Have Charged Battery Load Tested.
Measure Charging Current at Battery Terminals
(+14.2 ~ 14.5V @ 2000 rpm's)

Inspect Alternator Brushes.
Very easily done.
Remove the 3 Bolts on Alternator Cover.
Pull-off Cover.
L@@K --- Inside the Cover for Brush Platform
Measure Brushes:
(10mm -or- less = Replace Brushes))

 

He said he has good flow from the tank.

 

Next time it happens, try opening the fuel tank cap. There is a vent in the cap that can get pluged. If the engine runs better after you open the cap, then a cap re-build will be needed. Len has the parts!

Kenneth

 

I second the make sure you aren't living off the top of the battery comment. This phenomenon produces some very strange and seemingly inconsistent effects. Basically, if you do a lot of slow riding when you first get on the bike, it could be that the battery has so little charge that the bike cuts out. If you let the battery rest it will often start back up. So check it!

 

I will do this, but what exactly is the story behind calling it "Living off the Top of the Battery."

Thanks for all the advice everyone. I plan going through all these checks after work.

 

It means you're taking more out of the battery than the generator is putting back in.

 

Easy enough to test, since your bike is dying pretty quickly:

Measure the battery voltage, then start the bike. Measure the battery voltage again. Let it idle a few minutes and measure it again. Let it idle a few more minutes, and hopefully it dies... measure it again.

If you see the battery voltage dropping at each measurement, and, especially, getting pretty low (like <= 10V) around where it dies, then you've got a battery or charging problem.

You mentioned, though, that it restarts OK after 10 minutes or so. Does it crank slowly when you restart it, or pretty fast... basically, does it seem like the battery is weak at that point? If the battery doesn't seem weak at the restart, I think it's unlikely that this is the root of the problem. If moisture really is a contributor, then the problem may be hairline cracks in the ignition coils.