Motor tune up

[coyote101]

70hp johnson has been running rough. i bought some crc engine tune up spray. when i spray it in the bottom two carbs, the motor idles slightly higher and exhaust turns white. when i spray in the top carb it instantly kills the motor. what is she trying to tell me?

 

[F_R]

It tells me that a can of magic potion is not going to fix it. Now do some trouble shooting, beginning with a compression test.

 

[coyote101]

top cylinder reads about 123, middle 130, bottom 135. i noticed a lot of fuel blowing out of the cylinders when i was doing the compression test which makes me believe it is not burning the fuel properly. maybe insufficient spark? plugs are gapped to .4

 

[boobie]

Got a model # ??

 

[coyote101]

70el79r

 

[coyote101]

im fairly new to these old motors and just boating in general. Are these old motors like car engines in that its a good idea to replace the spark plug coils, they look like they have never been replaced? At this point i know my compression is good, ive taken the carbs off and cleaned them really well, ive replaced the entire fuel system(tank, all lines, pump), replaced spark plugs. thanks for your responses guys

 

[jakedaawg]

Your compression is not good. I would pop the head off and have a look see. You are barely within acceptable spec. I would guess you will find some scoring o. The top hole.

 

[coyote101]

My compression is not perfect. but i thought that since they were within 10% of one another it was good enough to run the engine better than it is running currently(it barely stays running). I will take the head off and see if that what it comes down to but i thought i would eliminate some easier things first. If there is some scoring on the top hole there is basically nothing i can do correct? Also, i bought an open air spark tester. It will jump a 7/16 gap. however, it is not super bright, you have to be close to see it. I guess im not sure how bright it needs to be.

 

[coyote101]

Update. put on the new head gasket and my compression has evened out quite a bit. top cyl now reads 120. middle 121 and bottom 123. And some advice for other newbies. Make sure and clean your head bolts up really well and the bolt hole threads with a non abrasive brush and oil them up. I snapped a bolt while torquing down to spec.

 

[racerone]

Was it fuel or water blowing out the sparkplug holes !-----These motors are notorious for leaks on the gaskets of the exhaust manifold.

 

[oldboat1]

Gap the plugs to .030.