bwiencek

Got a question for all you experts out there... I've been fighting this problem ever since I built a 355 for my boat.... When stopping for a few minutes (1-30min) then trying to start the engine back up the engine takes quite a long time to fire - 30 to 45 seconds AT LEAST. At that point it may stumble to life and then smooth out.

Here's the specifics:
'96 5.7 bored .030, Forged flat-top pistons, freshened Vortec heads w/stainless valves. Cam/lifter/spring kit is a Comp Xtreme marine XM262H 262/268 (218/[email protected]) .462/.477 lift 112 LC. Intake is a Holley Street Dominator dual plane mid-rise (like performer RPM), ignition is stock Thunderbolt IV, Carb is an edelbrock 750 marine unit. The engine runs strong, idles smooth, and has no stumbling or bucking when taking off WOT

Here's what I've tried so far with almos NO change!
1) checked all ignition components, vacuum leaks, checked vacuum with gauge, verified choke fully open, verified fuel not dripping down carb throat after shutdown, ran with engine cover off, carb is COOL to the touch (not enough to percolate fuel?), new fuel filter/water separator
2) adjust carb - checked float level, lowered float level .1", adjusted idle mixture as per edelbrock then another time for max vacuum. Checked plugs, changed jetting 2 steps leaner on primaries (went back to stock) (float bowl clean - no garbage in it)
3) checked ignition timing, tried bumping +-2 degrees then +- 4 deg.
4) ran with flame arrestor on, ran with flame arrestor off, ran with engine cover off (eliminated heat concerns?)
5) tried new ignition wires, new coil, cap & rotor.
6) Ran compression & leakdown tests (all good)
7) Tried 89 octane gas (usually run 92).
8) tried warmer thermostat (160* Vs stock 145*), went back to 145*.
9) tried hotter ignition coil (Accell Super Stock) & Accell 'performance' wires
10) checked spark strength during cranking, checked coil voltage during cranking and battery voltage during cranking (Battery is new this year)

WHEW - That's about it, probably some more in there but can't remember everything. Each change was made one at a time and some were repeated just to make sure. Outside temps have ranged from a brisk 65-68* (last fall) to low 90's (recently)

Any input is GREATLY appreciated! Even if it's a "That's common edelbrock carb problems - you're going to have to live with it or get a holley"

- Brian

P.S. a friend with a 4.3l and a 650 edelbrock carb is having the same problems and he's taken it to "professional" mechanics only to have them say they don't know... Hence I suspect the carb.

mopower

I would suspect the carb too. You said it would "stumble" to life? Kinda like it was flooded? Sound as if the carb is leaking interally after you shut it off. After 30 minutes it's ok and if you shut it off and restart immediately it's ok. Any black smoke when it starts? Try cranking it (without touching the throttle) after maybe 10-15 minutes. See if the plugs are wet. If so , pressure between pump and carb could be bleeding off and flooding it.

bwiencek

That's what it seems like to me. - Forgot to mention have tried an adjustable fuel pressure regulator and gauge setup - tried running down to 1 PSI and up to 5 PSI with no change. The edelbrock tech's last suggestion was fuel percolation and lowering the float level should eliminate that (didn't make a difference). Fuel pressure after shutdown doesn't drop indicating that the fuel pump isn't leaking back down (bad valve) or the carb isn't sticking it's float open causing flooding....

There is no fuel dripping from the carb when it's shut off - haven't tried immediately turning around and cranking as a test but I recall it starts fairly quickly (have to make a test of that one) It stumbles like it's flooded but I haven't noticed black smoke - of course exhaust is going thru prop at the time.. (waiting on getting some tips installed). Pulling the plugs after the engine cools a bit (hey it's hot down there!) and they all look fine, nice whiteish-tan and not wet.

I'm about at a loss - the darn thing runs so good otherwise - sitting idling for long periods and it doesn't load up on fuel so that's leading me to believe idle mixture is OK.

Turbojack

Carb is the problem. I am at a lost as to how you can fix it. Looks like you did everything I would have tried. I had a holley carb that had same problem. I rebuilt the carb about 3 times trying to get it to work correctly. I finally gave up & put another carb on. After that, motor started perfect first time, every time.

mopower

My idea of shutting it off and waiting 10-15 minutes( without touching the throttle) is to see if the plugs are wet then. If the carb is leaking internally , you will have raw gas in the intake and any cylinders with open intake valves. By cranking it (only 2 or 3 rotations) will be enough to deposit the gas on the plugs. Because , up to this point it's either laying above the intake valve or down on the piston. And you don't want to hit he throttle because the acellerator will only and more gas. If the plugs are wet , dry them , reinstall ,and try to start again.
Also , when it doesn't start , have you tried opening the throttle all the way? This will help to empty fuel from the engine since at cranking speed you have low vacuum and with the carb wide open you have virtually none there to draw gas from the jets.
Hope this has helped since it seem like you've tried everything else.
P.S. I have had cars do the exact same thing. Good Luck

Vinny P

Since you stated that the plugs are not wet after you pulled them, I wouldn't think that it is a carb leakdown problem. Maybe you should experiment with different starting techniques. Such as varying the amount of pumps you give the throttle before you hit the start key. Also, try to vary where you leave the throttle while cranking. Maybe you have just not found where this combination likes to be at.

Waterfoul

I had a motor that did this several years ago. Had a Holley 650 on it. Tried rebuild. Nothing. Did a lot of other "things" with no good results. New carb (same CFM Holley) and the problem went away. Magic?? Demons in the carb?? No idea. Mechanic told me that sometimes you just "get a bad carb out of the box." Had this same issue with a Holley fuel pump. First one leaked. Second one leaded worse. Third one worked fine until this season when it blew the upper seal and let oil in.

Mike

bwiencek

Well, glad to hear that others have had the problems too and my thinking that it was the carb is right on.

mopower - I'll try pulling the plugs after 2 rotations soon and let you know what I find - that's a good ideal that it's sitting puddling in the intake and when cranking it floods the cylinders with fuel. Along those lines of thinking I'll probably run it up a few RPM's and then shut it off and go WOT and let the fuel evaporate then close the throttle and crank and see what happens

checkmate454mag - 1 or 2 pumps when COLD and it fires right up. When it's warm I don't touch the throttle at all and it takes a while. I'll try and pump the throttle once and crank it up and see what happens also try giving maybe 1/6-1/4 throttle and cranking to see if it's any better at all.

Tinkerer

After the boat sits for 30 minutes remove the flame arrestor and have someone look down the barrels of the carb with the choke held open. and pump the throttle a few times. Do you get a spray of fuel out of the squirters each time you pump the throttle ( it should be a steady stream - not a spray of fuel and air ) If you don't than the problem the problem is that the carb is siphoning back into the tank and leaving the carb dry of fuel. You have to crank and crank to refill the carb. When you are cranking the engine do you pump the throttle untill it fires? If you do than this is more than likely your problem.

Turbojack

Tinkerboater just brought up a point I was not thinking about. Does your carb have a choke on it? Could it be closing when engine is warm & thus causing engine to be over rich. The carb I had did not have a choke so I know that was not my problem.