351 W won't run up after restart

Well, here is good news. Removed carb and the riser under carb. Gasket between riser and manifold was broken and apparently leaking .Replaced both gaskets and all runs well. Still doesn't make complete sense to me but I like the end result. I would like to thank everyone who helped along the way to a solution... 

When you swapped the carb , did you verify that the carb linkage is the same and provides the same throw as the old carb? What I'm getting at is do the butterfles go to wide open with the throttle is wide open.

Yes we replaced it with a new Pertronix ignition and epoxy coil. thanks 

Seems like the key piece here is that it runs fine when cold, but not once it’s warm. When we first got our boat it would run fine cold and then wouldn’t idle when warm. It turned out to be a vacuum leak at the carb spacer once it heated up. When things get hot they can warp differently, and I think that’s what was happening at the spacer: everything sealed up fine when cold but then once it warmed up and warped enough it wouldn’t run worth a darn. Fixed with a new spacer and the thick gaskets from skidim. Maybe not the same issue you’re having since I’d think a vacuum leak would present in a horrible idle rather than a top end restriction, but maybe you’re looking at something similar.

KENO,

First sentence:  yes all correct

Second: 

Yes idles smoothly, accelerates smoothly up to 32 and then won’t go any faster. Beyond 32, throttle does nothing 

Third: Yes after swim starts fine and idles as normal 

Carb swap:

No it did not do this before the swaps…. just was hard starting and rough idle and occasionally backfiring

Lastly 

Runs smooth at 32 until 

Also prior to last voyage, installed new springs in distributor. Also checked gas cap for vacuum noise, same engine performance. Note when we removed the tank we also replaced the vent line.

Ordered vacuum and fuel pressure test kits, arrival early next week.  Suppose we remove the carb and riser and seal the gaskets with permatex. One more thing checked off the list?

Ps: no stereo in boat

Find it parts is cutting edge as far as marketing.  They pay google a large amount of money every month to make sure they pop up at the top of the list when you search.   I had no idea this was possible before I worked with this account.   If you pay google they will move you to the top of searches.  Kind of defeats the neutral search option.  You get to see what they choose to show you in the order they choose to show you.

and checking...One doesn't have the key on for a stereo during that time, yes?

FYI:  Find it Parts used to be a customer of mine.  The owner was probably a genius, built a few companies before starting this one.  They owned a heavy duty truck warehouse and brake lining company.  He used all his contacts from that business to start find it parts.   They hold no inventory at all.  He is just a go between, his expertise is his computer system.   Someone asks for a part and his guys do the legwork to find it and supply it.  His vendors take the order and ship it.   They do have one of the best computer systems out there doing this work but they offer little information or details about the parts for you.   Nothing like an old time parts store where they helped solve your problems.   I usually look for suppliers that actually stock the part and offer some information about the part if needed.

Rich 28 wrote: The link is above from GottaSki. Will test fuel pressure but don't know where we would connect the vacuum Gauge... TY

If you drive the boat with no issues for more than an hour , shut it off and the issue comes up right after you start it, I don't think the issue is that you're suddenly sucking a vacuum in the tank. It would have happened sometime during that hour or so and not right after startup..

Gas tanks have a vent and usually an anti siphon valve at the tank.   It sounds like you are not venting and the tank is creating a vacuum that stops your gas flow.   Next time it bogs down on you go back to the gas filler cap and loosen it.  If you feel vacuum as you loosen the gas cap you found the issue.   Just one more thing to rule out.

Received and installed the new springs yesterday, thank you for the link.  Drove to the lake and water tested. Boat ran fine for 1.5 hrs.... great out of the water, right up to max throttle engine temp 170 +/-. Sopped to swim maybe 10-15 minutes. Starts right up, gets right out of the water and runs fine until  1/2 to 3/4 throttle. When throttled beyond that point engine looses steam as if it is not getting any more fuel. When throttle pulled back runs fine (at 1/2 -3/4 ) but will not go beyond 32-35 mph. Thinking that vapor lock may be an issue or maybe fuel pressure? Wondering if should put a pressure gauge inline and check results.  

Thanks for any thoughts…. 

Ps: Yes PCM with Prestolite clip down, its a 85 MC but thinking maybe we should 

sell it and buy a correct craft lol

after some thought experiment, old stretched out small spring can limit the available max advance,  if its sloppy and using up too much of the span at idle, leaving less available as revs increase

The heavy spring is supposed to be a little slack. the light spring is typically first to fail.