Logo
FULL SITE MENU

4.3 loses power under load

J

James Marcellus

New member
I have a 2007 Tahoe 196 Q4 with a 4.3 2bbl and Alpha I that I've had for 3 years. The engine has always been a little cold natured (prev owner said same), let it warm up for 4-5 minutes and it has been running great. After sitting for 4 months this winter with a full tank, we took it out in late April with no problems. On Memorial Day weekend, it started fine but when we would take off it would run up to 2300 rpm, start to bog and drop back to 1800. It didn't matter whether I throttled up slowly or quickly. In neutral the engine revs up normally, on the lift with the prop engaged and about 2-3" deep in the water, it revs up just fine. I removed the fuel filter, dumped out the contents, refilled it with new gas, remounted it with the same results. The dumped gas had a couple of drops of water in it and a few tiny black particles. I've purchased a new filter and plugs that I'll install this weekend. Any suggestions?
 
On the lift there is no load on the engine so it doesnt mean much. Would check general condition of ignition cap and rotor, if you have a timing light check that your getting ignition advance. The fact that there was some water in filter is likely the culprit, can try running of a separate tank but most likely looking at a carb rebuild and inspection of rest of fuel system. If you have water in the tank you'll need to clean it as well.
 
I'll bet the fuel strainer in the cab is plugged up with crud. Remove the line to the carb and unscrew the big nut. The strainer is inside it.

Had that problem a LOT when I first started running mine. Not sure where the crud came from, but after cleaning the entire system out it has not (yet!) returned.

Jeff
 
James Marcellus said:
I have a 2007 Tahoe 196 Q4 with a 4.3 2bbl and Alpha I that I've had for 3 years. The engine has always been a little cold natured (prev owner said same), let it warm up for 4-5 minutes and it has been running great. After sitting for 4 months this winter with a full tank, we took it out in late April with no problems. On Memorial Day weekend, it started fine but when we would take off it would run up to 2300 rpm, start to bog and drop back to 1800. It didn't matter whether I throttled up slowly or quickly. In neutral the engine revs up normally, on the lift with the prop engaged and about 2-3" deep in the water, it revs up just fine. I removed the fuel filter, dumped out the contents, refilled it with new gas, remounted it with the same results. The dumped gas had a couple of drops of water in it and a few tiny black particles. I've purchased a new filter and plugs that I'll install this weekend. Any suggestions?
Click to expand...
I have a 1990 4.3 2 bbl merc with alpha outdrive and am having same problems as James Marcellus. I have changed all filters including strainer at carb. I have checked cap and rotor and no moisture or corrosion. have also ran more seafoam through tank. Gas is new from marina. Boat had power when first took out but would stutter every so often while under load. Thought it was fuel issue which is why changed all filters. since doing that boat will run at low idle when moving but as soon as put throttle down it's completely gutless. Cant get over 5 mph or on plane. any suggestions?
 
One of the issues I have found with carbs is if you suck any gunk in there at all you really have to remove and clean out your jets and passages. Seafoam is great stuff but it has been known to loosen crud up and clog new filters….especially if you have a dirty fuel tank. It can also loosen up stuff downstream of the filter. (They need to invent a way to run Seafoam backwards through the fuel system in my opinion.) Those jets are so small that even a little dirt will plug them up.

All that being said, it might be a spark issue…
 
braol911 said:
One of the issues I have found with carbs is if you suck any gunk in there at all you really have to remove and clean out your jets and passages. Seafoam is great stuff but it has been known to loosen crud up and clog new filters….especially if you have a dirty fuel tank. It can also loosen up stuff downstream of the filter. (They need to invent a way to run Seafoam backwards through the fuel system in my opinion.) Those jets are so small that even a little dirt will plug them up.

All that being said, it might be a spark issue…
Click to expand...

Thanks very much. Removing carb for good cleaning seems to be next step. Have mechanic coming by to go out to see what he thinks it could be as only does it under load but most things I've heard and read point to clogged jets.
 
Back
Top