Engine begins to die if I push throttle forward slowly

[omgitzdave]

I have a 1988 Thundercraft Regency (Alpha One B869837 - MCM 2.5 Litre), and I am having an issue when I push the throttle forward slowly to accelerate. When the throttle is 10% forward, the boat runs good. When I slowly push the throttle 20 - 30% forward, the boat begins to die and eventually will unless I quickly push the throttle to the 60 - 70% range. If I go ahead and push the throttle forward quickly after idle, the boat will pick up and plane as it should.

Any ideas why this is happening? I recently cleaned the fuel/water separator, changed the carb fuel filter, and cleaned the flame arrestor. Finally I sprayed some carb cleaner into the carb after I opened it while it wasn't running.

The boat will also begin to hesitate randomly while running if I allow it to run poorly at the 20-30% throttle range.

 

[Rob454]

Re: Engine begins to die if I push throttle forward slowly

Check to see if the interrupt switch is engaging at the wrong time. There shoudl be a ignition interrupt module ( not sure what the actual name is) its possibly misadjusted so the interrupt switch comes on when youre already past the point where it actually needs to be

 

[Reel Poor]

Re: Engine begins to die if I push throttle forward slowly

What your describing sounds like a lean fuel condition. May be time for a carb overhaul.

 

[Boatist]

Re: Engine begins to die if I push throttle forward slowly

My guess would be an accelerator pump in the Carburetor. At low RPMs when you start to open the throttle the butterflys open in the carb letting more air in, at the same time the accelerator should squirt in some fuel to get a proper air fuel mixture but when carb been dry for a long time the accelerator pumps drys out and does not work very well. It can get better with time or have to be replaced.

Also could be have the carburetor set a little lean or and fuel jet part way plugged up.

After the engine been running turn it off and pull the flame arester. With a flash light look into the carburetor make sure the choke butterfly is open so you can see all the way to the throttle plate. Then while your watching with the engine off have someone else advance the throttle a couple of times.
As you see the throttle plate open you should also see the accelerator pump squirt in some fuel. This will work only until the carburetor bowl if full. Then you would need to restart the engine for the fuel pump to refill the carburetor bowl.

 

[omgitzdave]

Re: Engine begins to die if I push throttle forward slowly

Thanks for all the suggestions. I am going to take the boat out again this weekend to see if I can make any more observations. I actually planned to have the carb rebuilt, so that will definitely be done. Also, I will ask about the accelerator pump.

Where exactly is the interupt switch located? I will also check that.

Thanks again, you are all very helpfull.

 

[Haut Medoc]

Re: Engine begins to die if I push throttle forward slowly

The shift interrupt switch is located on the shift plate where the cables meet....
I doubt that is your problem, very much so......
But it would not hurt for you to know what it looks like.....​

 

[paulrfrancisco]

Re: Engine begins to die if I push throttle forward slowly

I'm with Reel poor, lean fuel condition... When you quickly move the throttle and it dies, is the classic bad Accelerator pump problem.. but it works fine when you do this... Slowly throttleing up has little need for the acelerator pump...

 

[omgitzdave]

Re: Engine begins to die if I push throttle forward slowly

How much does an accelerator pump cost? Are there any stores online that sell them?

Also, how difficult is it to replace?

 

[Coors]

Re: Engine begins to die if I push throttle forward slowly

It comes with the carb rebuild kit.

 

[omgitzdave]

Re: Engine begins to die if I push throttle forward slowly

So I took it to a local marine mechanic and at first he said he wanted to rebuild the carb and replace all fuel filters. After he started the boat up he noticed that it ran smooth, so he told me there was no need to rebuild the carb and it sounded good. He also said the accelerator pump was operating as normal.

He did the following:

1.) Adjusted the timing by 4 degrees. He's assuming this should fix my hesistation problem. Is 4 degrees a large number when it comes to timing?

2.) Adjusted my shift cable. No more grinding and engages quickly.

3.) Replaced main alternator belt. No more squeeling.

4.) Adjusted engine idle speed. Idle was too high.

5.) Replaced carb fuel filter, and ceramic fuel pump filter.

He tested my boat in a small pond while it was on my trailer and he said it ran better than most of the boats at his place. He did not test my boat off the trailer.

So I'm going to pick up the boat today and hopefully take it out on the water this weekend. I will keep you all updated.

 

[Haut Medoc]

Re: Engine begins to die if I push throttle forward slowly

So I took it to a local marine mechanic and at first he said he wanted to rebuild the carb and replace all fuel filters. After he started the boat up he noticed that it ran smooth, so he told me there was no need to rebuild the carb and it sounded good. He also said the accelerator pump was operating as normal.

He did the following:

1.) Adjusted the timing by 4 degrees. He's assuming this should fix my hesistation problem. Is 4 degrees a large number when it comes to timing?
4* is significant.......
2.) Adjusted my shift cable. No more grinding and engages quickly.
Hmmmmm......OK.....

3.) Replaced main alternator belt. No more squeeling.
Good.....
4.) Adjusted engine idle speed. Idle was too high.
Good.....
5.) Replaced carb fuel filter, and ceramic fuel pump filter.
Good.......
He tested my boat in a small pond while it was on my trailer and he said it ran better than most of the boats at his place. He did not test my boat off the trailer.

So I'm going to pick up the boat today and hopefully take it out on the water this weekend. I will keep you all updated.

Sounds like you had multiple issues.........
It has to be an improvement......

 

[omgitzdave]

Re: Engine begins to die if I push throttle forward slowly

Well, I took the boat out on the water 2 days in a row and all my issues have been fixed!