1968 Starcraft

[Dan1982]

Good Afternoon,

I have a 68 Starcraft with the original 40HP Johnson electrimatic and I'm having a little trouble someone might be able to help me with.

The motor fires right up but will die if I leave it at idle more than 20-30 seconds, it hasn't been a real issue since it starts right back up but now it's not accelerating more than 5-10 miles per hour and after a few minutes of run time the idle seems to peak and valley. It's done this the last 2 times out.

My first thought is replacing the spark plugs and wires and that's the plan this weekend but could it also be a bad fuel pump? I had the original rebuilt last summer? What about an external fuel pump?

Thanks!

 

[jbcurt00]

Moved to the Johnson motor forum

 

[F_R]

5-10 MPH tells me it is running on one cylinder. Time to remove the flywheel and check the ignition.

 

[Dan1982]

That was my first thought too, especially with the rpm issue but wasn't sure about the fuel pump. Would a low volume external fuel pump work? I see a few on Amazon with 5-7 PSI pretty cheap.

 

[racerone]

Those pumps from the factory are nearly bullet proof.----Will work even if hit by a small atomic bomb.-----Concentrate on finding the real issue with the motor.----Post compression numbers.----And does spark jump a gap of 5/16" on a test device, yes or no ?

 

[Watermann]

Before spending start testing. Compression check first if good numbers move on. Spark test. Check wiring for bad wires and connections.

Fuel related repairs and things to check over, filters, tank vent, pump rebuild, fuel line/primer bulb and carb cleaning.

 

[Dan1982]

I'm going to run some test this weekend, I'll post what I find. Thanks for all the advise!

 

[Dan1982]

Checked compression and it's at 90 PSI on each, good spark too. I did change the plugs just to be safe since they were so cheap.

I haven't had a chance to get it on the water and put any kind of load on it yet, hopefully the wind will die down this weekend long enough to get a good test run in. Thanks again for all the advise!

 

[Watermann]

90 PSI is low, indicating a rebuild is in the near future if true and there should be some difference between each cylinder with a high and low within 10% of each other. Pull all the spark plugs and open throttle wide open. Shoot some fogging oil in the cylinders through the plug holes and turn motor over to lubricate cylinders. Run compression test again. If numbers are all the same again, try using a different compression tester.

 

[racerone]

The term ----" good spark " ---means nothing to me.----Does spark jump a gap of 5/16" on both leads on a test device ( not sparkplug ) on this motor , yes or no ?

 

[racerone]

The term ----" good spark " ---means nothing to me.----Does spark jump a gap of 5/16" on both leads on a test device ( not sparkplug ) on this motor , yes or no ?----Compression is way low too.----Perhaps test with another gauge.

 

[RaisedByWolves]

90 PSI is low, indicating a rebuild is in the near future if true and there should be some difference between each cylinder with a high and low within 10% of each other. Pull all the spark plugs and open throttle wide open. Shoot some fogging oil in the cylinders through the plug holes and turn motor over to lubricate cylinders. Run compression test again. If numbers are all the same again, try using a different compression tester.

90psi may be low.

Or it may be the tester.

Or OPs testing method.

Or the motor may be a model with lower compression as they had for different years.

Or any combination of the above.

90/90 to me is a viable motor as long as it starts and idles well.

I would guess ignition or carb issues.

 

[Dan1982]

racerone - Yes, spark jumped 5/16.

I bought a new compression gauge for this test and both checked out at 90 - 92 PSI on each. I would think one would be lower than the other if something was wrong, right?

The motor is a 40hp 1968 Johnson Electramatic.

Motor starts fine, I just have to leave the warm up bar on for a while.

I took it out last weekend but the throttle wouldn't respond using the forward controls so I bought a new cable. I assume it's stretched out since it's the original cable.

Other than the throttle response the motor idles fine now. I couldn't put a load on it due to the throttle cable not working.

I did have the motor rebuilt/gone through last year and was told it was in good shape for being 50 years old.

 

[racerone]

?----Is the thermostat installed and working properly.-----They usually warm up fairly quickly.----Like less than a minute.----Is the " hot air choke " working properly ??