choke heat tube, hissing and hard start

[jbutler67]

1988 OMC 5.0
502APRGDP
2 bbl Rochester carb - heat choke
Intake Manifold - GM 14096284

Would a leak from where choke heat tune comes out of intake manifold cause hard starting or enging not turning over? (see picture)

I replaced the choke heat tube that sits inside the intake manifold. Started engine up on muffs to test her out. Ran fine. Day later, started engine again to adjust the carb air/fuel mixture. Engine started fine and got up to operating temperature. Shut engine down to adjust something. When I did, could hear a loud hissing coming from the lower right corner of the plate that secures the choke heat tube to the manifold (see picture). Hissing eventually died out. Tried to restart engine again but would not turn over.

Two mistakes I made. I did not put a gasket under it. I did not tighten it down. (Hand threaded it and forgot to go back and tighten it down.)

I am waiting for the gasket to arrive in mail. Have not tightened down and tried starting again. But, got me wondering if a leak from where choke heat tune comes out of intake manifold cause hard starting or enging that won't turn over.

 

[jbutler67]

Hiss came from lower right corner of plate -- where choke heat tune comes out of intake manifold.

 

[Maclin]

Nope. Not related.

Could be electrical connections, or could be a hydrolock.

If you think it may be Hydrolocked you need to pull the spark plugs and see if anything comes out. If water comes out, then try a short cranking to see if that was it.

If suspect of electrical connections, scrub all connections on all touch points back to shiny, positive and negative, at battery and starter and any "big" grounds. Be sure battery is charged.

 

[jbutler67]

Pulled plugs. No water. Scrubbed battery cable connections to shiny on both ends; at battery and at ground on block for black cable, at starter for red cable.

Just before I shut engine off, i was adjusting the idle speed screw... backing it out so it just touched the idle cam. As RPMs dropped, engine was getting close to stalling so I shut it off before screwing the idle speed screw back in. Adjusted screw back in two turns and tried to start it up again. It wouldn't fire up.

Mixture screws on carb are 2.5 turns out from seated.

Starter turns the engine over but it won't fire up. I thought maybe the hissing was air getting sucked into manifold making mixture too lean. Guess I was wrong.

 

[jbutler67]

I haven't checked the battery yet. Possible it has just enough charge to turn over starter but not fire up? Or the fact that it turns starter (and rotates engine - I can see pulleys and belts turning) mean that battery should have enough juice for spark plugs.

 

[jbutler67]

Battery checked out fine. I turn the key just one quick turn to hear the starter. It not only turned over the starter, but the engine fired right up. I wasn't expecting that. I shut it down immediately.

Not sure what I did that day and why it wouldn't fire up. Maybe I flooded it? Hiss might have been hot air escaping.

Bottom line - I learned that a leak at choke heat tube plate on manifold is NOT related to engine not firing up.

Thanks for your response Maclin.

 

[Maclin]

You bet.

The hissing could have been some compressed air escaping just as an exhaust valve started to open if the engine turned even just a fraction.

 

[Maclin]

Meant to add that the choke stove sits in a well that is totally open to the exhaust passage, to pick up heat.