5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in gear

For the first time in nine months, I operated the boat towing a tube up to 3000 rpm for about 2.0 hours. It worked great with smooth acceleration and operation. Prior to this event, I had sprayed the carb linkage, choke pivots, and the carb throat with Carb Cleaner while the engine was at idle.

Then two days later I replaced the fuel filter, checked the spark plugs (great condition with unblemished insolators), checked the secondary fuel screen and siphoned most of the year old fuel into autos.

Added about 10 gallons of fuel for a short test run.

The accelerator worked fine at idle but not in gear.

The tach would register about 1500 rpm and sometimes struggle to 2000 rpm with the throttle in a stationary position.

The engine sound like normal then stumbled and rumbled with no smooth operation to above 1500 rpm.

When returned to idle, it would slowly die.

I pulled two spark plugs. They were now very black, no burn build up, just black all over the isolator and threads.

So, what is the likely culprit from my maintenance steps that caused the change in operation?

I appreciate any help that can be offered.

Dean
2000 Maxum 2100SR

Re: 5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in

be sure the choke is opening and not stuck closed.

Re: 5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in

Jopes, thank you for the quick reply.

The choke is open.

Re: 5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in

deandec said:

Jopes, thank you for the quick reply.

The choke is open.

Click to expand...

Ayuh,... The plugs are Black, it's Over-fueling...

Re: 5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in

Sounds like you may have gotten water with that last 10 gallons of gas. Pull the fuel filter element and empty it into a clear container and see if it has a lot of water in it. Do not reuse the filter either way, put a new one on.
If the filter is clean, hook up a remote tank to the fuel filter and run on it and see if it runs better.

Re: 5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in

as the throat of the carb was sprayed with cleaner, it's possible you sprayed some gunk into the air bleeds or the float is stuck down or something like that. black plugs = running way rich. too much fuel is getting in somewhere.

Re: 5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in

Ok, possible gunk stuck in the carb. Spray some more carb cleaner.

Water in new gas. Will change fuel filter/water separator filter and check for water. (wish they had mounted it in a more accessible location!)

Thanks to all. Will report back in a couple of days.

Re: 5.7L Thunderbolt Ignition Alpha One Gen II will not accelerate above 1500 rpm in

Well more carburetor spray, and changed fuel/water separator filter, but no joy.....

Two things:

We will likely have to have the carb rebuilt as that seems to be the culprit.

The points were installed by a shop about 85 operating hours ago. Is there any chance their operation would cause the symptoms of inability to accelerate above 1500 rpm along with over fueling and blackened spark plugs?

Thanks for any insights

Dean
5.7L Mercruiser 2000