Chrysler 75 horsepower seems to lack a lot of power at wot

[1978Galaxie]

At wot the boat seems to lack power and it also seems to ping a little bit too. I just rebuilt the carburetors this spring. It seems when setting the idle, even with the idle speed screw on the timing tower not touching the block, and pushing it in, the side of the rod hits the block, it still seems to idle high. I pressure tested the crank case for leaks, and I’m hearing air hissing out of that opening in the lower unit. Is there some kind of vent that’s supposed to be there? Or is that where my crankcase leak is at? The timing was at 39 degrees btdc at wot, and I’ve adjusted it to 32. This boat is a 1978 Galaxie with a 757h8c motor I believe.

 

[stresspoint]

been a long time since i touched a Chrysler , so a guess here would be to check the points , probably replace if available?.

i do remember the distributor adjustment and dwell had to be spot on to run correctly.

 

[racerone]

How did you pressure test the 3 crankcases ???

 

[jerryjerry05]

Compression and spark tests???
Tachometer? Yes: what rpm's at wot? No: get something to measure the rpm's.
What prop are you using? Pitch?

 

[Scott Danforth]

pinging could be running lean. could be timing

either way, its the motor eating the pistons

what are the compression numbers?

 

[1978Galaxie]

So the compression is 135 psi on Cylinder 1 and 130 psi on cylinders 2 and 3. This was just the engine cranking over, not running. It’s a 1978 so it has the magnapower electronic ignition. I hooked up that hose that runs from the intake where the reed plates bolt up to, to the air horn, and I blocked off all three carbs using cork gasket material on a metal plate, and oddly enough nothing came out of the exhaust. Sounds like all the air was escaping from the bottom and coming out of that big hole behind the propeller. I don’t know if this is a proper way to pressure test these engines.

 

[racerone]

There are 3 separate crankcases.-----If a piston is at the bottom of the stroke the intake ports and exhaust ports would be open.----And air would simply go out the exhaust at the prop

 

[1978Galaxie]

There are 3 separate crankcases.-----If a piston is at the bottom of the stroke the intake ports and exhaust ports would be open.----And air would simply go out the exhaust at the prop

Okay, so there’s 2 places the exhaust would exit? Because there’s the exhaust holes that come out the back of the whole outboard assembly just below the power head. But they also have exhaust go through the bottom right by the prop as well?

 

[Nordin]

Never heard about pressure test the crank case.
Most important things for these two stroker are compression and maybe a leak down test of the crank case.
Compression 120 PSI or more and quit equal for the cylinders, no more then +- 10-15%.
The leak down test show how well the crank seals, reed valves and the piston rings seal for over pressure when the pistons moves down.

 

[The Force power]

Okay, so there’s 2 places the exhaust would exit? Because there’s the exhaust holes that come out the back of the whole outboard assembly just below the power head.

These two holes are your pressure release ports; exhaust fumes & water will come out of there while the engine is running in neutral / in water.(not on hose)
This is to relief the back pressure that the water is causing, the minute the engine is in forward gear and the lower-unit is going forward the drag through the water causes a vacuum and the exhaust fumes/cooling water will start flowing through the snout (at this point very little/or none will come out of the pressure relief ports.
We usually don't see this as at this point we're going forward & can't be looking at the back of the motor

 

[racerone]

What are the cylinder compression values ?----And do you have spark on 3 leads that jumps a gap of 3/8" or more?-----Flywheel key checked ?

 

[1978Galaxie]

Okay, so I did a leak down test on it, and when I put cylinder 1 at bottom dead center, and I can hear air coming out of all 3 carburetors. I pulled one of the reed valves out, and I tried flipping the plates around on the body of the valve, and it made the gaps bigger. What should I do about getting new reed valves?

 

[racerone]

???----Learning more about how a 2 stroke engine works will also help you.----Sorry to be blunt here.-----It is normal for reeds to be open a bit.-----Note , the reed valves have nothing to do with compression in the cylinders !!

 

[racerone]

Looks like 2 reed assemblies are available on another site at $48 each.

 

[racerone]

What trouble shooting has been done?----How did the motor run last season ?----What condition is the boat in ?

 

[1978Galaxie]

???----Learning more about how a 2 stroke engine works will also help you.----Sorry to be blunt here.-----It is normal for reeds to be open a bit.-----Note , the reed valves have nothing to do with compression in the cylinders !!

I did do a compression test on it, and I am registering 135 psi on cylinder 1, and 130 psi on cylinders 2 and 3.

 

[1978Galaxie]

What trouble shooting has been done?----How did the motor run last season ?----What condition is the boat in ?

The motor ran great last season, and the beginning of this season. I noticed every once in a while when I hit the throttle, it would seem to cut out, and not want to go occasionally like halfway through the season. The loss of power though was very sudden. Like literally the last time I brought it out, it would set you back in your seat when you open the throttle. And now, it very sluggishly revs up, and then the boat slowly lifts up out of the water. And it doesn’t even seem like it goes as fast at top speed. I do hear it pinging a small amount as I open the throttle, and that’s a new symptom as well.

I did a leak down test to confirm if the crankcase had any air leaks causing a lean condition, and found air coming out of the reed valves through the carburetors.

The boat is excellent condition for it’s age. It’s been kept inside pretty much it’s whole life. But due to moving circumstances, it was kept under a tarp last winter.

 

[racerone]

Run with a timing light 1 cylinder at a time observe spark behaviour.----Sounds like there may be ignition issues.