Stuck intake valve?

[WhitePony]

Hi all,

Well I think the vert has caught wind that I'm going to be swaping the engine soon, cause now she won't start. When I try to start it it almost seems like it has a backfire, except that it's not really backfiring, just squirting a puff of fuel out the top of the carb about once every full cycle of the engine. I thought at first that maybe the timing had slipped, but have adjusted it through the range without effect. Every now and then I can get it to fire up for a couple of seconds, but then it bogs and dies. No backfires, but the fuel is being ejected WITH FORCE from the top of the carb.

I haven't pulled the valve cover to look at the top end yet, but can't figure out what it could be other than an intake valve not closing. This is not something that came on slowly. It started all at once a few days ago when I backed the car out of the garage to replace those pesky plastic rollers on the window regulators.

Any ideas?

Kris

 

[mustang6]

Timing chain has jumped a tooth or two? Possible in a high mile engine, when it does happen it usually happens when an engine is shut down, and you can never get it to run right again without replacing the chain.

 

[WhitePony]

Ack! That's not the answer I wanted to hear! In the last 3 weeks the car hasn't even been driven, just started and run in the garage with no load. It sounds strange that a chain would be loose enough to jump gears just coming off idle.

Kris

 

[mustang6]

Well you can check your intake valve theory easy enough, just pull the valve cover and look for a valve that should be closed but isn't. I'm not 100% sure on the chain, but it would fit the description I believe.

 

[Lazy JW]

I would definitely check the cam timing before wasting any more time trying to start it. If the timing chain has jumped, you don't have an engine to drive until it is fixed.
Joe

 

[Anonymous]

As Joe mentioned, check the valves position relative to TDC. Pull the valve cover and the #1 plug. Verify that it is at TDC. Also verify that the timing mark on the balancer has not slipped and the engine is at TDC when the balancer indicateds it is.

You might also consider swapping the condensor on the distributor if you have a points type ignition. Those dang things have given me problems trouble shooting. Somethimes they can be bad right out of the box.
Doug

 

[80broncoman]

you might see if ALL the exh vales are opening. If one won't open for what ever reason next time the intake valve open here it all comes back at you out the carb.
Jim

 

[MustangSix]

a quick compression check would tell you if a valve were stuck open. A stuck intake would allow fuel and air to be sucked in and when the cylinder fired, it might do so with a blowback thru the carb.

 

[Greg]

I had very similar symptoms when I upgraded my ignition system. I wasn't getting power to the control module so I got a spark when I first started to crank the engine and a spark when I stopped cranking the engine. No sparks in between. It sent puffs of smoke from the carb.

Just something to try.

Greg

 

[mikeyo]

Hi all,
Just wanted to add, another indication of a stuck intake valve would be to pull the coil wire and ground it to prevent spark to the plugs, then have someone crank the engine while you listen at the top of the carb. A stuck open intake valve would result in air "puffing" back through the carbuerator as the engine is cranked.
Hate to say it, but had a similiar problem on an old chevy motor, found all the rocker arms cycling as they should, gave up and pulled the head. The entire face was missing from the intake valve!, only a stem going up and down. What was really suprising, and this was a little 4cyl. chevette motor, is that the dang thing would actually still start and run a bit! Wouldn't have believed that if I hadn't seen it.

 

[WhitePony]

mikeyo, that's exactly the problem that I have. I't actually puffing fuel out of the carb.