640 wont stay running

Jtex · Apr 29, 2019

My 640 will start and idle for a couple of minute
Then sputter and die, I have rebuilt carb,
New plugs and wires, new cap and coil.
I have great fuel flow, thought maybe was a venting
Issue on the cap but that wasnt the case, any
ideas???

Sean in PA · Apr 30, 2019

Will it start up again tight away or do you have to wait before it will start again? If you have to wait, then how long before it will start again?

Have you tested for a good spark when it dies? Have you checked to see if the wire from the coil to the points might be intermittently shorting to ground where it passes through the distributor body?

Ultradog MN · Apr 30, 2019

Back in the mid 70s I had a VW camper van.
It died on me on the highway so I had a friend tow me home.
After I had rebuilt the engine and was putting the the final touches on the engine I noticed the hot wire had broken off the coil and that was likely the original problem.
That was the last time I just started throwing new parts at a machine without doing some checking First.
When the engine dies, immediately check your spark. It requires NO tools to pull a plug wire, hold it against the engine and look for a bright bluish-white spark that will jump at least 3/8". Short or yellowish spark will NOT do.
Get a VOM - a $15 analogue job from Home Depot is fine and do some checking. Check for continuity across the key switch. Check for voltage at the coil. Check both sides of the ballast resister.
Others here will give you more things to check.

640 wont stay running

Jtex

New User

Sean in PA

Well-known Member

Ultradog MN

Well-known Member

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