Carburator Enigma

[skipperdave28]

Mt friend's newer model Atomic 4 who I have been helping him with has the following problem. It will only start with choke all the way out (air intake throat closed). Okay normal enough.... but it will stall out once the engine heats up as soon as the choke is pushed in, even very gradually. So no choke- no running engine. Also as we advance throttle for higher RPMS it also stalls out with with choke in or out. Per Ken at Moyer's sugestion I did open the main passage plug and back flushed fuel. I did set the idle adjustment screw one revolution from its seat. Has brand new spank plugs, coil, condenser, fuel filter and distributor cap. Fuel tank was flushed and getting good clean gas from line into carb. My friend, the owner (who sometimes hears things not there, says he has occaissionally head vacuum, hissing noise when choke is closed and engine running which, I suppose could suggest gap at gasket between upper and lower body of carb?
Any hints, suggestions, theories would be greatly appreciated!! By the way my own boat, an Ericson 35, also has an Atomic 4 so I am no stranger to these enginesbut sure am puzzled by this problem. Thanks in advance for any input.

[ndutton]

Your friend's hearing indicates exactly what I was thinking as I read the symptoms. It sounds like (heh-heh, sounds like - get it?) he has a massive vacuum leak and the choke is compensating for it.

Welcome to the party.

[romantic comedy]

I am hearing that vacuum leak too.

[Jim Booth]

I tested vacuum leak theory on mine by spraying starter fluid around the gasket area while it was running. No change in how it ran, so I moved on to other things.

[Marian Claire]

Another welcome. When was the carb last rebuilt/cleaned. This part "Also as we advance throttle for higher RPMS it also stalls out with with choke in or out." Has me wondering about lack of fuel reaching the venturi.
"I suppose could suggest gap at gasket between upper and lower body of carb?" or carb to manifold connection or throttle shaft seal.
O yea is a PCV installed?
Dan S/V Marian Claire

[romantic comedy]

air leaks can happen in a few different places.

carb halfs
carb to manifold
manifold to block
manifold itself
fittings in the manifold
internal carb leak

[tenders]

I agree, this sounds like a vacuum leak, but my engine makes a wheezing sound and it's just the normal vacuum of the engine around the carb breather element.

If you're hitting a dead end on the vacuum leak, could the centrifugal advance weights be stuck, or perhaps the timing is a bit out of whack?

[skipperdave28]

Further Resonse to Suggestions

The vacuum leak in carb certainly sounds like the most logical explanation. A few further questions: The previous owner did run engine with some pretty bad gas ( water diluted, full of particulate matter, etc.) As per previous explanation this should be all flushed out by now but could have earlier clogged main "rich/lean" needle valve which on this model carb as I understand is internally fixed and can be removed on adjusted externally--- only the idle valve with screw on top of carb at an angle?? I have not really messed much with timing because it seems to run steady at low RPMs. Would it make sense to just try to remove tip half of carb, check and get new gasket? Or, to take whole carb off and begin tedious rebuild and cleaning job? Thanks so much for your help I have always found this site extremely helpful ---Skipperdave28

[Dave Neptune]

Leaks?

skipperdave, it does indeed point to the carb or an air leak. If the carb is not metering enough fuel to run it will have a hissing sound as the engines draws what it can. You can find the leak by spraying a bit of "motor crack" at various connections and see if the engine revs up some from it. Just a tiny spritz pointed to these areas and you'll hear the engine rev! Do check to be sure the scavange tube is not leaking and functioning. It could be the carb is just plugged up inside. It does not matter how much you flushed and cleaned unless you have a good filtration system in front of the carb. There is no internal "jet" adjustment, it is a fixed jet! If you have the adjustable jet it is mounted at the bottom of the bowl. If you don't see it it is a fixed jet and the carb will need to be done. Be sure and have at least a new polishing filter in the feed line at the carb!!
I too have the E35-MKII, an early 1970 boat!

Dave Neptune

[romantic comedy]

Whenever there is any problem like this, I always take the carb apart and investigate. Just a good cleaning and new gaskets often solve these type of problems.

Using ether to find an air leak may be hard to do. If you spray is near the air intake, some will find its way in, and cause a change in running. Be aware of that. Something with a straw to be able to surgically direct the spray would help also. I have used all sorts of fluids, including water.

[hanleyclifford]

Although you did remove the main jet plug and backflush, unless you clean out the bowl the crud can come right back into the jet.