50 hp high speed misfire

[kalebsheridan]

No I haven't. What would that do?

 

[The Force power]

No I haven't. What would that do?

A faulty rectifier can cause the ignition-system to misfire at high-speed
Are you using the correct spark-plug that this engine is prescribed?
Are you running this on muffs or in a test tank in gear?
Ideally it would be best to run it on water full tilt for a bit to clear/clean the whole system

 

[kalebsheridan]

A faulty rectifier can cause the ignition-system to misfire at high-speed
Are you using the correct spark-plug that this engine is prescribed?
Are you running this on muffs or in a test tank in gear?
Ideally it would be best to run it on water full tilt for a bit to clear/clean the whole system

Oh okay cool. Didn't know what rectifiers do. I will try disconnecting it and see what happens. Now it only misses while revving down. Revving up it's super smooth. I was running in a test tank without the prop. I know it's best to use a test wheel but I don't have one. I'll have to get it out on the water and do a test run for sure. I think it needs to be run pretty good for sure. Lots of blue smoke, and when I had the PH off there was so much sludge in the exhaust system. Do fuel pump diaphragms get worn out? Or just tear and then need replacement?

 

[The Force power]

Now it only misses while revving down. Revving up it's super smooth. I was running in a test tank without the prop. I know it's best to use a test wheel but I don't have one

There's your answer! running it without a prop will make it sound like a misfire! put a prop on and it will not sound like it.

Do fuel pump diaphragms get worn out? Or just tear and then need replacement?

They can tear that's an easy check (although I'm not familiar with your engine)

 

[Nordin]

Yes as The Force power says when throttling down when running in a tank and without a prop some two strokers can behave like it is misfire.
I think it depends on if it is a cross flow engine or a loop charger.
From my experience it will arise more at 2 cylinders then 3 or 4 cylinders.
Maybe some other can chime in at explain more why it happens.
Check the fuel pump diaphragm and change it if it is stiff.
The 50Hp use the same diaphragm as the larger 3 and 4 cylinder engines.
Actually it has the same fuel pump as the 3 and 4 cylinders.
The 140 and 150Hp Chryslers had two fuel pumps.
The diaphragm is cheap and you can buy a kit with the gaskets included.

 

[The Force power]

From my experience it will arise more at 2 cylinders then 3 or 4 cylinders.
Maybe some other can chime in at explain more why it happens.

I think........it is because there's no resistance/load whatsoever on the motor

 

[kalebsheridan]

There's your answer! running it without a prop will make it sound like a misfire! put a prop on and it will not sound like it.

They can tear that's an easy check (although I'm not familiar with your engine)

Oh okay awesome! So my engine must be good to go then that's been my only problem up to this point. How did my idle sound in that video? Because Ive never owned a properly running force, I don't know how it's supposed to sound. Oh okay I gotcha. I checked my diaphragm and it looked stretched out. The new ones look perfectly flat.

 

[kalebsheridan]

Yes as The Force power says when throttling down when running in a tank and without a prop some two strokers can behave like it is misfire.
I think it depends on if it is a cross flow engine or a loop charger.
From my experience it will arise more at 2 cylinders then 3 or 4 cylinders.
Maybe some other can chime in at explain more why it happens.
Check the fuel pump diaphragm and change it if it is stiff.
The 50Hp use the same diaphragm as the larger 3 and 4 cylinder engines.
Actually it has the same fuel pump as the 3 and 4 cylinders.
The 140 and 150Hp Chryslers had two fuel pumps.
The diaphragm is cheap and you can buy a kit with the gaskets included.

I think mine is a cross flow? Not sure I'll double check. Okay sweet yeah that makes so much sense. I'll get it out on the water in a few weeks and see how it does. I tried not to run it too much without the prop too, I can't imagine that's good for the motor. Yup my diaphragm was still and stuck in a dish shape. I will order a new one. Sometimes the motor sounds like its getting pauses in fuel delivery.

 

[The Force power]

Also, I did check the recirc. Had some junk in it but symptoms appear to be the same

Did you check the passage behind the screens? verify if there not plugged

 

[kalebsheridan]

Did you check the passage behind the screens? verify if there not plugged

Behind the diaphragms?

 

[Nordin]

The Force power, yes of course the no load situation with no prop will cause the stumbling acting, you are right.
My experience is that the cross flow engines like Chrysler/Force are more sensitive to it then OMCs and Mercs that are loop charged and direct charged.
2 cylinders are more sensitive than 3 or 4 cylinders
But it is my felling and experience, no scientifically conclusion behind it.

 

[jerryjerry05]

ANYTIME!!! you have a miss you should do the starting fluid test.
Start the motor, spray starting fluid around the intake side .
This includes under the coil/pack bracket the carb bases and around the port covers.
If the spray makes any difference?? then it's got a bad gasket and sucking air.

 

[The Force power]

Behind the diaphragms?

No, behind the screens from the recirculating.
Carefully remove the screens and you'll see a tiny hole, poke with stiff wire through or blow compressed air through

 

[The Force power]

But it is my felling and experience, no scientifically conclusion behind it.

yeah, I discovered this by running a late '70's Merc. with no LU and it did the exact same thing.
and for cooling.......I had shoved a garden-hose onto the copper water-tube.
Man, it was loud!!!! without having water as a sound damper. lol

 

[kalebsheridan]

ANYTIME!!! you have a miss you should do the starting fluid test.
Start the motor, spray starting fluid around the intake side .
This includes under the coil/pack bracket the carb bases and around the port covers.
If the spray makes any difference?? then it's got a bad gasket and sucking air

Sorry Jerry, yeah I sprayed it down with starter fluid earlier on, found a leak behind the carb but the problem persisted. I believe my problem was when I was trying to tune my motor, I was using a cheap induction tach. Worked pretty well, and according to instructions I was to set my tach to 2 pulse per revolution. Since then, I learning on another thread that my motor likely uses 4 pulse per revolution. So in my attempt to adjust the idle as per the manual, I tried adjusting the idle screw from 1600 rpm (actually 800) down to 800 rpm (actually 400). The motor ran terrible, hence me starting this thread. Big facepalm. So putting that out there. I since set it back to what I believe is the right idle rpm and the motor seems to run well. You could balance a glass on wine on the cowl while I rev it! Almost at least haha. My only remaining issue was the bucking while revving down, which as we have established is likely a result of running in a tank with no prop.

 

[kalebsheridan]

No, behind the screens from the recirculating.
Carefully remove the screens and you'll see a tiny hole, poke with stiff wire through or blow compressed air through

Oh okay I see. Yup I cleaned the recirc plate thoroughly. I had to take the PH off last week to replace the exhaust gasket so I did it then. Lots of junk in my recirc, especially in the screens. Are there any check valves beyond the reeds that I should be concerned with? I tried blowing and sucking air through the tubes after the recirc plate and I could just about get air both ways.

 

[racerone]

Set idle RPM with boat in the lake.----Warmed up and in gear.---Testing in a bucket with no prop is a waste of time.

 

[kalebsheridan]

Okay cool I'll try that once I get the boat out.

 

[kalebsheridan]

Also, how should the timing marks on my motor look with a timing light, at cranking speed and WOT? It's a prestolite system.

 

[racerone]

The timing on these motors rarely goes out of adjustment.---Well a sheared flywheel key throws timing out.----And no you can not find a sheared key condition with a timing light.---Well , at least not on most motors.