1978 Johnson 35HP suddenly starts hard

[TerryMSU]

Hi:

I have a Johnson 35HP that suddenly starts hard. When I first bought the motor, it would not run on both cylinders until it warmed up, but once it warmed up it ran like mad. To get it to warm up I ran it at the maximum (as set by the stops) throttle in nuetral. Yesterday evening, it would crank like crazy, but not fire. Eeventually, it suddenly started and then ran (and re-started) just fine. Today, it would not start, but eventually, it did start, just would not run well. As soon as I put it in gear, it would stall. Again, after I let it warm up, it would eventually run OK. It just took longer.

Two possible issues...
1. Yesterday was the last of an old tank of gas. Today was new gas.
2. Yesterday and today, we had rain. boat is stored on trailer out-doors. (We have had rain before with no issues.

The motor is new to me, but the coils look fairly new, with no indication of ageing or damage.

I am skeptical of fouled plugs. When I bought the motor, I cleaned the plugs (with a shot of ether as a solvent... no I did not use the ether to prime the motor, just to clean the plugs) and it did improve the motor running. This was probably 30 to 50 hours of running time on the motor ago.

Terry

 

[tashasdaddy]

Re: 1978 Johnson 35HP suddenly starts hard

start with the basics, check your compression, spark,spark should jump atleast 1/2 inch. if your compression is close or above 100 psi, and with in 10 % of each other, and your spark will pump 1/2 inch, suspect carbs, and fuel delivery. when were the carbs, last cleaned and rebuilt?

 

[TerryMSU]

Re: 1978 Johnson 35HP suddenly starts hard

Checked the spark strength. It jumps at least 3/8" so plenty strong. Replaced plugs. I had to pump it up twice. The first time it did not start, but after the second prime cycle it started OK and I did not have to warm it up to get it to run right. I could hear the gas squirting with both prime cycles. By prime cycle, I mean pumping it up till it gets hard to pump.

Terry

 

[tashasdaddy]

Re: 1978 Johnson 35HP suddenly starts hard

what is your starting procedure, step by step?

 

[TerryMSU]

Re: 1978 Johnson 35HP suddenly starts hard

1. Pump bulb until firm (cannot get it truly hard. Could it be the check valve in the bulb?)
2. Make sure in nuetral
3. Slide throttle to fastest nuetral (at stop)
4. Push key in (to activate choke. Choke solenoid does activate.)
5. Turn Key to start.

When it does not start, I repump if soft and try again.

Terry

 

[BoatBuoy]

Re: 1978 Johnson 35HP suddenly starts hard

Two or three things come to mind. First, make sure you're using Champion QL77JC4 plugs gapped at .030.

Next, since you mentioned the gas as suspect, you probably need to remove,dis-assemble, soak, and re-assemble the carb using a carb kit. It's really simple, but removing everything to get to it is aggravating.

Finally, your power pack could be weak even though you throw a 3/8's inch spark. Put some kind of spark plug checker on it and see if it will throw 7/16" blue spark with a snap.