First ride after top end and manifolds. Won't idle

[cliffblue]

2001 4.3 OM060235 Mercarb.
After reassembly of heads, intake and new 2 piece exhaust manifolds, there was 1-2 hours of idling while I checked and adjusted timing, idle, mixture etc over 3-4 different days. I went through this carb a year ago, so I just removed it and scraped the gasket off of it and reinstalled it. Started perfect at the launch and proceeded down a no wake channel for 10 min at 1000 or so rpm. Brought it up to 3000 all the way to the other end of the lake. Probably 20-30 minutes. Backed off to stop and it died. It would start and die right away unless I worked the throttle or kept it over 2000. No amount of mixture adjusting or a turn or two on the idle screw would help. Started up and got it in gear as fast as possible and headed back. Spent a couple of minutes at WOT to verify my tach against the digital timing light then back to 3000. Slowed a couple of times to check it and when it dropped below 1800 she faltered and died. Thankful no one saw me in the channel, big wake! I'm thinking obstruction in the idle circuit. Opinions? PS, the mixture screw is pretty floppy almost till it bottoms out. It has a cone head with a small slot for the screwdriver. Might need to replace it? Thanks, Cliff

 

[dubs283]

Re: First ride after top end and manifolds. Won't idle

sounds like its dumping fuel, running way rich - carb inspection, cleaning, rebuild...

 

[Bondo]

Re: First ride after top end and manifolds. Won't idle

sounds like its dumping fuel, running way rich - carb inspection, cleaning, rebuild...

Ayuh,.... Agreed,....

 

[NHGuy]

Re: First ride after top end and manifolds. Won't idle

If the mix screw is floppy that's no good...unless it's snug where adjusted. So recheck the idle adjustment before removing it for repair. And it would be smart to check the idle mix adjuster with a shot of carb cleaner to see if it's leaking. If it's leaking the carb stuff will affect idle. Then you'd need to repair or replace that part.
You're going to open it. I'd get a carb kit and a new mix adjuster screw to start with.
The way it was running indicates the problem is in the low speed and idle section. As said, could be that idle circuit being too rich.
If it turns out that the casting is bad that would be the stinker.

But if you're lucky maybe there's a piece of junk in the low speed section.

 

[cliffblue]

Re: First ride after top end and manifolds. Won't idle

I didn't consider too much gas. Gaskets, screw, spring, check ball and accelerator pump ordered. Agreed on casting bad sucking. I checked the screen in the carb upon reassembly and it was clean. Admit I haven't changed fuel filter yet. Keeps slipping my mind. It's on the shelf. Will do Saturday. Any suggestions on cleaning besides spray carb cleaner and an air hose? Thanks, Cliff

 

[NHGuy]

Re: First ride after top end and manifolds. Won't idle

to clean it all the way you dissassemble it,remove any rubber, plastic, phrenolic parts. and dip it in carb cleaner. Then brush off any stuck stuff. Pass a thin strand of copper wire through any gooped up orifices, being careful not to change their size. Rinse & dry it out. Put it back together.

 

[cliffblue]

Re: First ride after top end and manifolds. Won't idle

Have I read that the Mercarb was based on a Rochester design? I can't believe how expensive the accelerator pump for the Mercarb is. Would one for a non marine Rochester be the same piece for less moola?

 

[Walt T]

Re: First ride after top end and manifolds. Won't idle

Idle circuit plugged which was your initial guess. Check choke flap first though, free and easy. Already ordered the stuff so you'll have it available if you go through it anyway.

 

[cliffblue]

Re: First ride after top end and manifolds. Won't idle

Thanks Walt, first thing I checked

 

[Silverton34c]

Re: First ride after top end and manifolds. Won't idle

with the motor reving, put your hand over the top of the throat of the carb until it almost stalls several times. you may have water in your carb bowl...this process will suck all the crap out of the bowl and run it thru the combustion chamber

 

[cliffblue]

Re: First ride after top end and manifolds. Won't idle

Two questions. Would closing the choke do the same thing? Aren't the main jets in the bottom of the bowl?

 

[cliffblue]

Re: First ride after top end and manifolds. Won't idle

Ok, as I expected, completely disassembled the carb, probed every passage, did not find anything except a small patch of corrosion in the bottom of the bowl. I believe this spot is from the previous time I went through it. Looks like if you don't clean any corrosion completely down to bare metal, it must fester back up. I tried rubbing with soctchbrite but can't completely get it. I wonder if naval jelly would get it? Also, are there no opinions on an alternate accelerator pump?

 

[Maclin]

Re: First ride after top end and manifolds. Won't idle

I believe there is a welch plug, maybe 2, in the bottom of the fuel bowl on those, and those can corrode and begin to leak fuel from the bowl directly into the intake manifold. If it has those and they leak it is pretty easy to remove and clean it all up and epoxy back in.