Warm Start issues... HELP!!!

[AlpineGuy]

I have a 1998 Cobalt 206 with a MerCruiser 5.7 carbureted I/O. It's a great boat but a few years ago it started to develop some issues cold starting (needed a lot of gas and took for ever) and occasional sputtering. My marine mechanic recommended replacing the ignition coil, which did seem to solve the sputter but it still had issues with cold starting and seemed to flood after shutting the motor off for a few minutes. Last year he recommended rebuilding the Carb, specifically replacing the "Well Plugs". I pulled the carb (Q-Jet) at the end of the season and sent it to a Q-Jet "expert" who rebuilt it. That solved the cold start and flooding issues but now there is still a problem with warm starting. The motor runs great but as soon as I stop, shut off the motor (to swim or change skiers) for literally more than 2-3 mins, I have to crank it over for like 20 sec for it to start. It's not flooded (there is no smell of gas like before and I don't have to WOT to get it to start)... it's almost like there is no gas in the line and the full pump needs to crank over to get gas up to the carb. My mechanic said it was vapor locking so we re-routed and insulated the fuel line but that seemed to change nothing. Now he's recommending replacing the fuel pump. I've already spent a fair bit of time and money on this issue so before I splash down for a new fuel pump I thought I'd see if anyone on this forum has any other recommendations/suggestions?

 

[Scott Danforth]

check your anti-siphon valve.

 

[alldodge]

Howdy
First you don't have a marine mechanic, you have a marine parts changer

What is your engine serial number?

 

[Rick Stephens]

I had the same kind of issue. Adding a one way check valve between fuel separator and fuel pump resolved what I figured was fuel draining back to the tank. As per Scott's answer in post #2, the anti-syphon valve is supposed to do that - I should have probably just replaced that instead.

 

[alldodge]

literally more than 2-3 mins, [

Note

 

[tpenfield]

+1 for the anti-siphon valve (fuel fitting at the tank) . . . maybe the fuel pump as well. But check the valve first.

 

[Scott Danforth]

the 2-3 minutes means that the carb may be dribbling fuel or the choke is not set properly.

 

[Rick Stephens]

Can't disagree with AD, tpenfield and Scott. 2-3 minutes is a fraction of the time my drain back issue took to appear. half hour, or a couple days, yeah. I'd have to go with something happening directly to the fuel in the carburetor to cause this. The MOST often needing to be redone procedure on any engine is a carb rebuild. So easy to miss something. May even be something worn out, like butterfly shaft holes, or a check valve seat that has a ding in it. Damn hard to see in a rebuild yet screws you over every time. You might even end up replacing the carburetor, which is a whole nuther set of issues since you ain't gonna get a new Roc.

 

[AlpineGuy]

Thanks for all the input guys! I checked the anti-siphon valve... or at lease I can see it has one. Hard to check but I guess I could try replacing it. It really does happen within a few minutes. If I shut the motor off and immediately restart it... no problem. I never really used a stop watch but the time it takes a skier to climb back in the boat... certainly 5 mins max... and it takes 10-20 sec to restart.

I checked the choke and it looks fine. I had the wife shut the motor off so I could look directly in the carb as it was shut off and I couldn't see any fuel being dumped in there after shut off.

Definitely a bummer if it's the carb. All the posts I've read about put a new carb/non-ROC on that motor don't sound like fun.

Oh, the serial number for my motor is 0D843555.

 

[Rick Stephens]

I swapped out a Roc for an Edelbrock 1409. Not as bad a deal as it may sound, although you do end up having to recalibrate the new carburetor.

 

[alldodge]

It really does happen within a few minutes. If I shut the motor off and immediately restart it... no problem. I never really used a stop watch but the time it takes a skier to climb back in the boat... certainly 5 mins max... and it takes 10-20 sec to restart.

I think your flooding, and if so the carb would be the issue

Look at the carb throat when running

 

[Lou C]

Hmmm a Quadrajet on a 1998 boat? Sure about that? Because Quadrajet production stopped about 1989 or so and after that OMC & Volvo changed to Holley and Merc changed to the Weber (Edelbrock). If there is really a Quadrajet on a 98 engine which should be a Vortec I’d like to see how the choke is set up. Normally the Qjet marine units used a manifold heated choke spring to open it heated by the exhaust crossover in the intake; which the Vortec engines do not have! They can only use electric chokes.

 

[Lou C]

Post up a pic of what you have; pix of the intake & carb & choke set up.
8 bolt or 12 bolt intake?
Was the engine replaced with an older pre Vortec engine?