Chrysler 120 HP Shuddering Under Load

[Ghatz]

Hi.
Hoping someone can assist with where to start looking for a problem my 120 HP 1975 Chrysler engine has.
The engine starts first time every time and runs well in neutral.
Once the boat is on the water and I try to get the boat on the plane, the engine shudders. If I continue to accelerate through the shudder, the engine will then overcome the shuddering and run cleanly at higher revs once the boat is on the plane. This occurs whether I accerate slowly or apply the throttle quickly.
I'm not sure whether it's a fuel or ignition problem.
The engine is a dual carb version. It runs a Magnapower Ignition box with a points distributor.
If anyone has any idea where to start looking, I would really appreciate it.
Thank you.

 

[Justinde]

Re: Chrysler 120 HP Shuddering Under Load

If it was me, I'd check the compression anyways. Always a good place to start. If compression is good, I would then do a link & sync ( sticky thread or Clymers), and timing. I don't mean to state the obvious, but engines need compression, spark and fuel. Take any of that away, and it won run. Add any of it the wrong way, and the engine will run bad. IMHO it sounds like a fuel problem. Check the fuel supply ( fuel pump), carb mixtures and adjust. I would think that an ignition problem would not be intermittant, and compression would also be consistant. POints to fuel for mine.

 

[Frank Acampora]

Re: Chrysler 120 HP Shuddering Under Load

You can clean the carbs, reset them, and check the fuel supply. You can also change the plugs and re-synchronize the carbs and timing. However, a lot of Chrysler engines run rough in the 1500-2500 RPM range. Push through it and they run like gems again. It's just the nature of the beast.

 

[Ghatz]

Re: Chrysler 120 HP Shuddering Under Load

Thanks guys.

I'll have a go at cleaning and resetting the carbs and see how we go.

 

[foodfisher]

Re: Chrysler 120 HP Shuddering Under Load

'86 force 125 hp. That's the nature of my beast also.

 

[woody66912]

Re: Chrysler 120 HP Shuddering Under Load

Hey guys quite some time ago I ran into this. What I found was that the trim tab/ exhaust snout had fallen off. the anti-ventilation plate. The best I could figure is that while getting on plane water would be forced back up the exhaust tuner. And the engine could not breath. Installed a new snout and that fixed it. Not saying that is what's wrong but just a though.