compression question

[Dawgs]

1990 johnson 150....the motor is not on the boat...i tested the compression on all cylinders...they were all around 70...seems low to me...i removed ALL the plugs when i did the test but i didnt seem to get a really strong crank with the battery i was using......then i did the test with 5 plugs in and the tester on the other cylinder and couldnt get a strong crank at all....any input?

 

[ondarvr]

Re: compression question

Sounds like a dead battery to me. Unless you can get it to spin at a good clip the test will be meaningless.

 

[Dawgs]

Re: compression question

the battery i used to jump the starter was actually in a jeep and it was running...just didnt seem to crank real hard

 

[countvlad]

Re: compression question

the battery i used to jump the starter was actually in a jeep and it was running...just didnt seem to crank real hard

i dont think it works very well that way.. i would disconnect the battery from the jeep and then try... and you should be able to spin the motor.... and yeah 70 sounds low...

 

[Bifflefan]

Re: compression question

get a better set of jumper cables.

 

[countvlad]

Re: compression question

1990 johnson 150....the motor is not on the boat...i tested the compression on all cylinders...they were all around 70...seems low to me...i removed ALL the plugs when i did the test but i didnt seem to get a really strong crank with the battery i was using......then i did the test with 5 plugs in and the tester on the other cylinder and couldnt get a strong crank at all....any input?

when you have the plugs you are compressing the fuel/air or air... so by removing the plugs there's no compression, easier on the starter.. ive checked the compression both ways and the numbers were the same....

but in your case get a good battery then try.. come back with the numbers

 

[captgm]

Re: compression question

You need a good HOT battery
Leave the plugs in, except for the one your testing
make sure your gauge is accurate
if your not pleased with the results. Try a De Carb on the motor with sea foam, then re check compression again
If you want to know the true life of the motor do a leak down test. if its just a pleasure/fishing motor tune it up and hit the water.

 

[Dawgs]

Re: compression question

ok i just took my buddies battery out of his dodge pick up....tried again...60 psi ...so im thinking the cylinders are good just not getting an accurate reading...the cables arent the best...does the quality of cables make a BIG difference?

 

[countvlad]

Re: compression question

ok i just took my buddies battery out of his dodge pick up....tried again...60 psi ...so im thinking the cylinders are good just not getting an accurate reading...the cables arent the best...does the quality of cables make a BIG difference?

depends on how bad of a shape they are, sure it does... you wouldnt run ****ty wires i your house to run electricity would you???

does it seem like it struggles or turns pretty good? and btw 60 its pretty low.. 60 on all of em????

 

[Dawgs]

Re: compression question

i didnt try all of them...originally i got 70 across the board....now it seems like its struggling to crank strong......seems like the battery is dieing but its right from the truck

 

[countvlad]

Re: compression question

i didnt try all of them...originally i got 70 across the board....now it seems like its struggling to crank strong......seems like the battery is dieing but its right from the truck

if you claim that the battery its good, its very possible your stater might be shot.... are you going through the solenoid or bypassing the starting solenoid?

 

[Dawgs]

Re: compression question

i was by passing the solenoid..........i used jumper cables from the battery ....+ to the positive on the + on the starter itself...and neg from the batt to a mounting bolt on the starter

 

[countvlad]

Re: compression question

i was by passing the solenoid..........i used jumper cables from the battery ....+ to the positive on the + on the starter itself...and neg from the batt to a mounting bolt on the starter

ok... if the battery is good then you might need a new starter...

 

[Benny1963]

Re: compression question

clean and check fittings also put amprobe on starter your starter may be bad you need 300 rpm or better to get a good reading 70s are very low for that motor is a crossflow or looper, pull all the plugs it doesnt change reading much and it easier to turn over ,most of the time its cables or grounds
if ya went strait to the starter with a cable then ya might have a bad starter

 

[Dawgs]

Re: compression question

what fittings are you talking about?

 

[countvlad]

Re: compression question

what fittings are you talking about?

i think he meant wire connectors... change the starter