Dead cylinder after carb cleaning on 55EL78S

[BigLantastic]

Picked up an old 55EL78S. It would start an run for about 5 seconds. Then die. So I took off the carbs, cleaned them and put them back on. Then it started and ran rough, and poured gas out of the bottom carb. I decided the float was hung up and that was probably flooding out the bottom cylinder....well...I freed up the float and the fuel stopped spilling out. I fired it up and it would still only run on the top cylinder. Cleaned the spark plugs and checked the spark with a spark tester. They are both sparking while it's running. But I can take the bottom wire off while it's running and nothing changes. It was running on both before, but only for a few seconds. Now it keeps running, but only on one cylinder. What did I do wrong?

 

[racerone]

Does spark jump a gap of at least 3/8" on a test device ?------Is the high speed jet in the very bottom of the float bowl clean ?

 

[Faztbullet]

Checked compression as motor had hi ring pistons?

 

[BigLantastic]

Does spark jump a gap of at least 3/8" on a test device ?------Is the high speed jet in the very bottom of the float bowl clean ?

I have an enclosed spark tester,.but it appears to have a decent spark. When I rev it way up, it seems to pick up fuel in the bottom carb. It runs without dying on one cylinder, just not clear down to idle. And if I squirt gas in the bottom carb, it takes off and runs smooth.

 

[BigLantastic]

Checked compression as motor had hi ring pistons?

No, I haven't checked compression. Now that I think about it, that could be the issue. It fires on both when I rev it high, but at lower idle, it doesn't draw enough air to pull fuel. Is that how low compression would effect idle?

 

[BigLantastic]

I have an enclosed spark tester,.but it appears to have a decent spark. When I rev it way up, it seems to pick up fuel in the bottom carb. It runs without dying on one cylinder, just not clear down to idle. And if I squirt gas in the bottom carb, it takes off and runs smooth.

Yes, Ive run more than a can of carb cleaner thru every port I could find. Including the bottom one, although I didn't know that was the high end jet. Plus blasted it with shop air.

 

[BigLantastic]

Yes, Ive run more than a can of carb cleaner thru every port I could find. Including the bottom one, although I didn't know that was the high end jet. Plus blasted it with shop air.

Checked compression as motor had hi ring pistons?

What does his ring pistons mean?

 

[BigLantastic]

Yes, Ive run more than a can of carb cleaner thru every port I could find. Including the bottom one, although I didn't know that was the high end jet. Plus blasted it with shop air.

Checked compression as motor had hi ring pistons?

And...thanks so much for your insights. Im sure I'm close to getting it

 

[Faztbullet]

The piston had the first ring 1/8 inch from top of piston and used compression to keep it seal against cylinder. These failed due to carbon build up and rolling ring and damaging cylinder. I rebuilt over 2 dozen 55hp for high ring damages as factory would foot the bill in 1978-79

 

[racerone]

Does spark jump a gap of 3/8" or more on both leads , yes or no.-----Those inline test lights can mislead you.---You should see 140+ PSI on a good motor.

 

[BigLantastic]

The piston had the first ring 1/8 inch from top of piston and used compression to keep it seal against cylinder. These failed due to carbon build up and rolling ring and damaging cylinder. I rebuilt over 2 dozen 55hp for high ring damages as factory would foot the bill in 1978-79

Wow, that's good info. I mean...really bad info,.but good to know

 

[BigLantastic]

Does spark jump a gap of 3/8" or more on both leads , yes or no.-----Those inline test lights can mislead you.---You should see 140+ PSI on a good motor.

Ok thanks, I'll go check the compression and the spark gap.

 

[BigLantastic]

Wow, that's good info. I mean...really bad info,.but good to know

Hey fast bullet, you sounded like the voice of experience, so I borrowed my millwright buddy's digital compression tester (quickly while he is still at work) .
If I got 154 psi on the top cyl.
&
I got 31 psi on the bottom cyl.
Would that mean you nailed it from 100s or 1,000s miles away?

 

[BigLantastic]

Wow, that's good info. I mean...really bad info,.but good to know

 

[racerone]

Blown head gasket or rebuild time.----Simple as that.

 

[BigLantastic]

The piston had the first ring 1/8 inch from top of piston and used compression to keep it seal against cylinder. These failed due to carbon build up and rolling ring and damaging cylinder. I rebuilt over 2 dozen 55hp for high ring damages as factory would foot the bill in 1978-79

What does rebuilding high ring damage entail?

 

[racerone]

Take motor apart.----Inspect all parts.----Bore engine and fit O/S pistons at $100 each.