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Hard Starting When Warm

troym

troym

Advanced Contributor
"5.7L Merc. Alpha 1 Gen II, 2b

"5.7L Merc. Alpha 1 Gen II, 2bbl mercarb, Thunderbolt IV ignition.
Starts great when cold. Runs fine once it's started. If I shut the engine off and drift a while, when I go back to start it, it's a real bear.
I've had the most success by pumping the throttle a few times, putting it at full open, and then start cranking... and cranking... and cranking... finally it starts.
Any ideas?
Plugs, wires, cap and rotor are all new. Carb disassembled and cleaned about 6 months ago, maybe 10 hours of run-time since. Fuel is fresh, with stabilizer. Fuel filter / seperator is new."
 
Check the automatic choke. If

Check the automatic choke. If it senses that the engine is still warm it might not be choking enough. A weak coil can also act like that. Weak coils tend to get worse after they have been warmed up. Coils are rarely a problem and they usually last many years but if it is 5 or more years old and given the symtoms you describe you might consider changing it out
 
"Thanks Eddie. The coil is abo

"Thanks Eddie. The coil is about the only thing besides the distributor itself in the ignition system I haven't changed and I've been thinking about it. It's definately more than 5 years old and the problem has been nagging long enough, so it's worth a shot. And hearing it from another perspective is reassuring.
I haven't completely eliminated the choke, but since I have to open the throttle almost all the way to get it to fire, if anything, wouldn't that indicate the choke's not open enough?"
 
"Yep, that's what I was th

"Yep, that's what I was thinking about the choke. The only other thing is what I said about the coil. The coil could be the problem or a contributing factor. Being that the coil is a possibility and it is far from new I'd change it out myself, figuring that that'll take care of the coil situation anyway for the next ten years. or so."
 
"Eddies suggestion about the c

"Eddies suggestion about the coil sounds good. If that's not it, the usual causes for hard starting when hot is either vapor lock, or flooding. If raw gas leaks into the intake manifold from leaky carb channel plugs, this will make it hard to start, requiring open throttle so as to get more air into it. I am not sure if this is typical with the 2 bbl Mercarb, but it sure is common for the Quadrajet and Webber carbs after they get a few years old.
I don't think the choke has anything to do with it when she is warmed up; it should stay wide open. Even if she has sat for an hour, you should not need any choke at all.
Rod"
 
"Troy; another thought. When s

"Troy; another thought. When she finally starts, is there a bunch of smoke for the first few seconds? This would be a strong clue supporting the flooding theory.
Rod"
 
"I haven't noticed any smo

"I haven't noticed any smoke, certainly no big huge billowing clouds. But, most of the instances of having this problem, I was dirfting (fishing) and starting to get too close to something, so I was a little more focused on collision avoidance.
I picked up a new coil and will put it in tonight. Fishing tomorrow, so if the problem persists, I can have someone else watch for smoke."
 
"1. Check to see if the choke

"1. Check to see if the choke hasn't closed on you.

2. When it does this, STOP and have someone check for spark. That will eliminate or show whether it's the problem.

3. Try the Fastjeff carb flooding test: While fully warmed up, turn each idle mixture screw all the way in. Did the motor speed up or stall (it should only slow down)? If it did, you've got the dreaded Rotten-Chester slow flooding problem.

Jeff

PS: My money's on a slow flooding situation."
 
"Replaced the coil... now I ha

"Replaced the coil... now I have two perfectecly functioning coils. One looks better than the other, but apparently nothing wrong with either. I like spare parts anyway.

The problem however, persists. While playing with the idle mixture, I can't tell if any adjustment makes any difference at all. It idles like crap regardless, full open to full shut and everything in between.
The choke is not an issue. It's not hard starting with the engine cold, even with the choke fully open. The choke is adjusted far enough over, it's not going to shut.
I'm not afraid to throw another carb kit at it, but I need some advice on what I'm looking for.
Last time I had it apart, the problem was pretty obvious... a hunk of goo glogging the low speed jet. Now, it sounds like the opposite: too much fuel at idle may be the issue.
Thanks for the continued support."
 
"Troy; it sounds like you have

"Troy; it sounds like you have a leaking seal plug allowing fuel to leak from a lower fuel passage directly into the venturi in the baseplate area, as Jeff said above. Older Quadrajet carbs are notorious for this, and just doing a regular carb kit won't usually fix it because you do not remove them. There is a kit avialable at places like AutoZone to fix this problem, but you may be better off to get a rebuilt carb, where they would have dissassembled it completely and replaced all passage plugs.
Just my opinion.
Rod"
 
Is this seal plug something th

Is this seal plug something that is pressed in? or threaded? Does it appear on the typical exploded veiw parts diagram?
Does it have a part number?
Could it be the gasket leaking on either or both the low speed (main) or high sped (power) jets? Or the gasket beneath the venturi?
 
"These are usually a pressed i

"These are usually a pressed in plug used to block off the end of a drilled passage the intersects another. Typical for the feed to the accelerator pump, and low speed jet circuits for instance. I know the Q'jet for instance has several of these, and they are prone to leaks after a few years. They may be on a blowup, not sure. The low speed jet circuit is the most likely culprit. If you check with your local auto parts store there is an epoxy compound that can be used to seal them; can't remember the name just now, but it has been around for years.
Rod"
 
"Thanks for the gouge Rod. I&#

"Thanks for the gouge Rod. I'll yank it out this weekend and very carefully disect it. Maybe I can find the smoking gun. If that doesn't get it, I guess the next step is a new or rebuilt carb... maybe I'll make the jump to a 4bbl."
 
"Troy;
A 4 bbl Q'jet &#40

"Troy;
A 4 bbl Q'jet (love em/hate em) will give you a nice bump in hp, and there should be plenty around. Not a big dollar upgrade. Any marine bone yard should have a 5.7 around with everything you need on it waiting to be unbolted.
Rod"
 
Troy:

Rod has a great upg

Troy:

Rod has a great upgrade suggestion. You'll also need a throttle cable bracket and manifold for the 4 BBL. Going this way will improve your low speed fuel economy since that is apparently how you use your boat for the most part. Guy
 
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