Hesitation when giving 'er the throttle

[mr.box]

I recently purchased a 1985 Chris Craft Scorpion Limited and very pleased with this purchase, but would like to get the engine running in tip-top shape

She has a 1985 Mercruiser I/O 5.7L 260hp (350 Chevy) and runs great as long as I gradually increase speed. If I go from a stand still or a low speed and give her the full throttle there is a slight hesitation and then she kicks in. While this currently isn't an issue since we aren't using the boat for water sports, we would still like to get her working right.

Here is what I do know: I took a look at the engine with my father-in-law and discovered when I press down the accelerator pump, the engine hesitates as it does when giving her the full throttle. So this would lead me to believe I have found the issue, but due to my lack of knowledge I am not sure how to proceed.

Do I need to install a new accelerator pump? A new carb? Run some Seafoam? Fill 'er up with Premium fuel? Your knowledge and assistance is greatly appreciated.

Thanks!

 

[Don S]

Re: Hesitation when giving 'er the throttle

Do I need to install a new accelerator pump? A new carb? Run some Seafoam?

Carb may need a rebuild, it is over 25 years old. Have you checked the fuel filter for water, and change it yearly? Tuneup?? Timing, compression check etc?

 

[mr.box]

Re: Hesitation when giving 'er the throttle

Thanks for the reply Don. The boat was just tuned-up, etc., so everything should be in order and the previous owner was the service manager at the marine shop and I have all the receipts showing me the boat was well maintained.

She runs great except when I go to give her the full throttle and there is a hesitation before kicking in. I could mimic this same event by pressing the accelerator pump down. What I don't know is can the accelerator pump be serviced separately or is it part of the carburetor and that needs to be replaced/rebuilt.

 

[searay3]

Re: Hesitation when giving 'er the throttle

What carb are you working with?

 

[Limited-Time]

Re: Hesitation when giving 'er the throttle

Thanks for the reply Don................................................................................................................What I don't know is can the accelerator pump be serviced separately or is it part of the carburetor and that needs to be replaced/rebuilt.

You'll find the accelerator pump is included in the card rebuild kit and not available separately. You may as well replace all the gaskets and seals while servicing the accelerator pump.

 

[tfret]

Re: Hesitation when giving 'er the throttle

I have the same engine, 1984 model, with the same issue. I put a new carb on, new plugs, new wires, checked and double check timing, and still have the same problem. A vacuum gauge attached to the intake manifold reads around 7 at idle when it should be around 15. I've leak checked with every method I can find and can't find any leaks. I slalom ski so it's a bit annoying on the hole shot, but I've just learned to live with it.

 

[Bondo]

Re: Hesitation when giving 'er the throttle

The boat was just tuned-up, etc., so everything should be in order and the previous owner was the service manager at the marine shop and I have all the receipts showing me the boat was well maintained.

Ayuh,.... Sounds like he missed the Carb....

 

[nikogto]

Re: Hesitation when giving 'er the throttle

Just go to NAPA or Advance and give them the carb number, it will be on the rear body of the carb. Just overhauled mine and the kit was less than $25, gonna put it back on in the next couple days. Mine did'nt look bad for being 22 years old.

 

[nikogto]

Re: Hesitation when giving 'er the throttle

You're going to get some hesitation since it is carburated, they are not as snappy as fuel injection, especially if it's a 4v carb. The 2v carbs were a little better response wise.

 

[Don S]

Re: Hesitation when giving 'er the throttle

You're going to get some hesitation since it is carburated, they are not as snappy as fuel injection, especially if it's a 4v carb. The 2v carbs were a little better response wise.

Where did you come up with that tidbit? Carbs work without hesitation all the time when setup properly.

 

[egldvrbags]

Re: Hesitation when giving 'er the throttle

I recently purchased a 1985 Chris Craft Scorpion Limited and very pleased with this purchase, but would like to get the engine running in tip-top shape

She has a 1985 Mercruiser I/O 5.7L 260hp (350 Chevy) and runs great as long as I gradually increase speed. If I go from a stand still or a low speed and give her the full throttle there is a slight hesitation and then she kicks in. While this currently isn't an issue since we aren't using the boat for water sports, we would still like to get her working right.

Here is what I do know: I took a look at the engine with my father-in-law and discovered when I press down the accelerator pump, the engine hesitates as it does when giving her the full throttle. So this would lead me to believe I have found the issue, but due to my lack of knowledge I am not sure how to proceed.

Do I need to install a new accelerator pump? A new carb? Run some Seafoam? Fill 'er up with Premium fuel? Your knowledge and assistance is greatly appreciated.

Thanks!

Had the exact same problem before. Mine was the accelerator pump in the carb.

Bags

 

[mpdive]

Re: Hesitation when giving 'er the throttle

Accelerator Pump. A small rubber diaphram in the carb that suppies an additional amount of fuel on quick acceleration due to the momentary lean condition caused by opening the throttle quickly. More than likely that is your problem.

 

[nikogto]

Re: Hesitation when giving 'er the throttle

Where did you come up with that tidbit? Carbs work without hesitation all the time when setup properly.

Over 33 years working on these carbs and many others, I guess what I meant to say was that you will have better throttle response out of a fuel injected set-up than a carb, that's a no brainer. Overhaul it and it should take care of the problem to some extent, to rule out the accelerator pump, just remove the flame arrestor and with the motor off, open up the choke and look down into the carb while slowly moving the throttle, you should see a steady stream of fuel in both primary (front) ports until the throttle is fully opened up, it the pump is bad it will spray, stop, spray, or all together not spray at all or stop right away.

 

[nikogto]

Re: Hesitation when giving 'er the throttle

Here is what I do know: I took a look at the engine with my father-in-law and discovered when I press down the accelerator pump, the engine hesitates as it does when giving her the full throttle. So this would lead me to believe I have found the issue, but due to my lack of knowledge I am not sure how to proceed.

I should have read the post a little better, looks like that's what's going on, bad pump.

 

[mr.box]

Re: Hesitation when giving 'er the throttle

Thanks for all the information. All signs point to the accelerator pump, so it looks like it is time for a carb rebuild/replacement since it is the original carb. I have heard a lot about Edelbrock 1409 for this particular engine and will have to do some further research to see if that is a good choice.

 

[Glastron175]

Re: Hesitation when giving 'er the throttle

I am having the same problem with my Volvo Penta 3.0L. I had rebuilt the carb with a Sierra kit and it still has this problem, but solved an idle problem that I had. I believe it was the power valve was bad. However, it runs great now until I punch it, then it always hesitates or even dies. If I double punch it (with the throttle) it goes ahead and accelerates. So I still suspected the accelerator pump. So I put in another kit, this time from Holley since somewhere I read that the other kits did not always work out. I still have the problem. I am now wondering if the power valve needs to be a different one. It has a 3.5, but my vacuum is about 15" at idle, and the Holley manual says to use a power valve of 1/2 the vacuum reading. Maybe mine is not opening quick enough to get the boost I need on acceleration?? Any comments on this?