Idle problem, 4000Rpm!

Hi everyone,

Just bought myself a 82 650 Seca. The bike has not been used in a year or two.
I have a problem with the idle, it starts up just fine. And after having the Choke on for 2-3 minutes. It idles fine around 1000Rpm, but when it gets hotter. After 10-15minutes the idle goes up to around 3-4000!

I have opened the carbs, spraying the jets with carb cleaner, checked the diaphragm, everything seems to be OK. But i have not dismantled the carbs completely. (i'm afraid to break something)

If i stop the bike when it idles at 3-4000, and wait a few minutes. It starts up fine, and idles around 1000, before i shots up to 3-4000 after a minute or so.

Doesn't seem to be any leeks, sprayed a lot of carb cleaner around the carbs when it's running, the idle stays approximately the same.

Does anybody have any clue what might be the problem?

The owner said it worked just fine when he used the bike last time.

I'll be very grateful for any help

 

That's what EVERY PO says.... Never trust what the PO says

What have you done to the bike since you got it? Just fiddled with the carbs a bit?

Start at the beginning... do your valve shims and a complete carb clean. bench sync then running sync

 

That's pretty much the answer. Anything less won't get it right.

 

Remember you can only set the idle properly, when fully warmed up.

 

Thanks for replying

I was hoping there would be an easier fix, but guess i just have to begin from scratch and do the carbs properly.

And check the valve clearance.

I've adjusted the idle screw after it's been running for 3-4 minutes. Idles fine around 1000, but then suddenly after 5 more minutes it goes up to around 3-4000.

Should i adjust the idle after its been running for 10 minutes, or 5?

 

How about 20. FULLY warm.

 

4,000 rpm's is NOT Idle.
Above 15-Hundred revs the Plant requires more Fuel than can be supplied by the Pilot Fuel Jets.
4-Thousand revs generally indicates that the Throttles are open.

Inspect the Throttle Cable.
Seat the Throttle Cable Sheath Ferrule firmly in the receiving bracket.
ANCHOR the Sheath too the Frame with Duct Tape.

Test the Linkage.
Undo the Cable from the Linkage. If the rpm's are still elevated; manipulate the Linkage ... by hand ... and see if the Linkage is binding.

Assure that the Carbs are fully seated in the Manifolds.
Make sure the Manifold Clamps are Stock, ... NOT automotive Hose Clamps.
Look to see that the Clamps are not fouling the Linkage keeping Throttles open.

 

One other thing. When fully warm, and you try to adjust the idle down, if you back the idle screw off and t doesn't come down, obviously there are still issues. I piddled with mine attacking various possibilities, stuck throttle, bad cable, dirty carbs, etc. What my issue was with that same high idle range was cracks in the carb manifolds that didn't seem to go all the way through, but yet when the bike warmed up, it would leak vacuum there horribly. Replaced the boots, and that solved my idle issues.

 

One more thing i noticed when opening the carbs.

The springs for the diaphragm were not identical.

Two of them were longer than the rest.
Aren't they supposed to be the same length?

And the butterfly valves were slightly opened, 1-2 mm opening.

When idling normally, are the supposed to be completely shut?

 

You can Tune the Plant to IDLE with the Throttles Closed using the "ColorTune Plug".

Setting the Mixture is done visually.

The Inventor should have got a medal!

 

Check the valve clearances then then clean the carbs till they are absolutely clean!! Then bench sync and then sync on the bike. You have DIRTY GUMED up carbs. The bike has sat for 1 to 2 years, they are varnished up inside!

 

Yes, those springs are all supposed to be the same length. The length (and hence spring force) will affect mixture ratio. Longer springs will result in a richer mixture.

As for the butterfly openings at idle... I can't attest that all the carbs are the same, but my butterflies are virtually closed at idle. Haven't measured it, but probably less than 1mm.

 

Thanks for the help everyone


To do list:

-Check vavle clearance
-Clean carbs / replace diaphragm springs
-bench synch
-running synch