A challenge to the experts/Acceleration Issue

[Michael Cain]

Boat- 96 Speedster with twin 717s. One grey motor, looks newer, and one white motor- the one with issues

I have an acceleration problem- The white motor is slow to accelerate. It accelerates fine up to about 2000 rpms and then really hesitates from there. Seems like a fuel delivery issue but I cannot pinpoint it. Here's what i've done;

- Does not have the grey fuel lines. I've removed both fuel selectors to make sure there is not blockage. Blew through all of the lines as well. No issues here.
- Swapped the carbs from 1 engine to the other. Same motor same issue. Not the carbs(((
- Ran compression check. 135 +/-10 on all 4 cylinders.
- Purchased degree wheel and verified that the rotary valve was on the correct tube.
- Oil pump lever is lined up with the notch on the block.
-Sparkplugs are not fowling.
-Motor that is having issues feels like it has about 20% less power than the other one.

Question 1-
Does my engine have some sort of water pressure regulator? I saw someone mention it on a 787, I believe.

Questin 2-
If I had a air leak in the crank case, would it cause this issue? (I hope this is not it...)

I want to thank you all for answering my other post! Let me know what you think about my issues
:willy_nilly:

 

[LouDoo]

Well your compression is getting low, should be in the 140 to 150 range, 135 - 10% is too low, get some more accurate readings. At 122psi you're ready for a top end rebuild.

An air leak will cause a lean condition and the motor will over rev. No your boat does not have a water regulator.

The gray motor, if it's silver is a SBT rebuild. The white motor is most likely original.

Lou

 

[Dr Honda]

Yep... what lou said.

135 +-10 isn't good. at 125 psi, it's going to be weak.

I know you said you checked the timing of the valve... but did you check the clearance?

 

[Michael Cain]

I did not check the clearances. Would I use plastigauge to measure the squish gap?

 

[Michael Cain]

I've also reringed the motor that has issues. The cylinders still had visible honing marks all the way around the cylinder. I went ahead and re-honed it and replaced the rings. I do not recall what the ring gap was, but it was well within spec. Piston to cylinder clearance was well within spec as well.

 

[Dr Honda]

I did not check the clearances. Would I use plastigauge to measure the squish gap?

You can... but you can just slip a feeler gauge into the intake runner.

I've also reringed the motor that has issues. The cylinders still had visible honing marks all the way around the cylinder. I went ahead and re-honed it and replaced the rings. I do not recall what the ring gap was, but it was well within spec. Piston to cylinder clearance was well within spec as well.

Well... if the Cyl wasn't out of taper... and you honed/ringed the engine... it should be showing good compression. (around 150 psi) Did you properly set the squash gap? If it's on the big side... the compression will be low.