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Q & A: Run-on, Hard Start

77 MGB, Z/S carb, full emission equipment

Electronic Ignition Allison - been using it for the past 10 years (56,000 miles)

Recently had the engine rebuilt. I had not been using the vaccum advance since it was not connect when I purchased the car over ten years ago. The rebuilder reconnected the vaccum advance via a tee in the run-on control pipe and the manifold said it work correctly and I should use it. Engine does not ping under any driving conditions.

Engine now has about 1200 miles on the rebuild and runs great. EXCEPT when I want to shut it down or start it up when it is hot.

Likes to run on when I shut it down. Oil pressure switch, Ignition switch and run-on valve all work correctly , verified pressure switch ground, verified ignition (off) switching voltage, verified run on value switching (it clicks when I shut down and the oil pressure drops back to 0), cleaned connections.

When I start the engine hot it is very hard to start, starts ok if cold or cooled down for half hour or more.

Neither of these conditions is 100%, sometimes it shuts down quickly and sometimes it starts OK. I have renewed the carbon in the canistor. All hose connections are tight. I had the carb check by a local rebuilder who is experienced on Z/S he gave it a OK and I replaced the fuel line filter, has new plugs, new plug wiring, new distributor cap. A lot (most) of the tubing is also new. Once started purrs..... Just does not want to stop running and I am afraid I am going to pull in someplace for a coke or gas and not be able to restart it.

I have ran out of things to check. Any suggestions ? Thanks, Stan

STAN!

Your problems of run-on and hard start may be related. Look at the anti run-on system first.

When you place your finger over the end of the anti run-on valve inlet tube (located to the right of the radi... read more