air, fuel, compression, spark, now what?

[N Wolf]

I found out why my 74' 135 rude wont spin a 19p prop. I have 125lbs of compression on all four cylinders. With a spark gap tester on all four plugs, it runs and jumps spark on all four. After running, all plugs have a little bit of fuel on them. The fun part is that when its running on the muffs and you ground the plug leads one at a time, it makes almost no noticeable difference on any cylinder except #3. On that one the engine dies. Infact, pulling any two plug leads allows the engine to keep running so long as #3 isnt one of them. What could possibly cause this?
I used my timing light to make sure the carbs were all spraying fuel, they are.

 

[kenmyfam]

Re: air, fuel, compression, spark, now what?

What are you trying to push with the 19" pitch prop ???
When was the last time the carb's were re-built ??
How is the timing ??

 

[N Wolf]

Re: air, fuel, compression, spark, now what?

1) 17' bass boat
2) two weeks ago
3) 18 degrees static

 

[kenworth747]

Re: air, fuel, compression, spark, now what?

I found out why my 74' 135 rude wont spin a 19p prop. I have 125lbs of compression on all four cylinders. With a spark gap tester on all four plugs, it runs and jumps spark on all four. After running, all plugs have a little bit of fuel on them. The fun part is that when its running on the muffs and you ground the plug leads one at a time, it makes almost no noticeable difference on any cylinder except #3. On that one the engine dies. Infact, pulling any two plug leads allows the engine to keep running so long as #3 isnt one of them. What could possibly cause this?
I used my timing light to make sure the carbs were all spraying fuel, they are.

did you try swapping #3 plug with one of the others to see if the plug is good, maybe its that simple the plug could just be bad
Steve

 

[kenworth747]

Re: air, fuel, compression, spark, now what?

Oh yea make sure to check plug wire check known good one for #3 im not sure what ohm rateting there suppost to have but its another op
Steve

 

[N Wolf]

Re: air, fuel, compression, spark, now what?

I have already done all of that. No matter what I swap the #3 is allways the good one. I think I found the answer to my own question but Im not sure where to go from here. One thing we all forget about two strokes is that they have two compressions, cylinder, witch we all check, and case presure, witch you cant. If this was a one cylinder it would have to be the reeds. But its a four so I dont know what else is in there that afects the crank case seal. There are little square covers on the outside of each cylinder. Do those give me access to anything? I noticed that the one on #3 has blue rtv on it and the rest just have black gaskets.