Dead cylander: spark,compression;reed ok: NO GAS

[adamj]

Evinrude 51 fleetwin 3 hp.
I have a bottom cylander dead. The spark is there, the compression is ok, the reed switch seems clean and working. The only thing I can figure, is the crankshaft seal, but there is compression. There is NO GAS coming into the cylander.
Advice?

thanks,

Adam

 

[BaitThrower]

Re: Dead cylander: spark,compression;reed ok: NO GAS

fuel blockage to third cylinder?

 

[F_R]

Re: Dead cylander: spark,compression;reed ok: NO GAS

Evinrude 51 fleetwin 3 hp.
I have a bottom cylander dead. The spark is there, the compression is ok, the reed switch seems clean and working. The only thing I can figure, is the crankshaft seal, but there is compression. There is NO GAS coming into the cylander.
Advice?

thanks,

Adam

As long as the reeds are OK, and you say they are, and as long as there is no big hole in the crankcase, and the piston skirts are not trashed, and the main bearings are not totally worn out, that is impossible.

There are no crankshaft seals on that motor, so it isn't that either.

Are you SURE it has good spark? How did you check it? Laying the plugs up against the head is not a spark test. It needs to be able to jump a 1/4" gap in open air. I have to assume you tried new plugs, right?

 

[JB]

Re: Dead cylander: spark,compression;reed ok: NO GAS

Sure sounds like loss of scavenging if you really do have a good spark. That would be a gasket or reeds, and you say the reeds are okay.

BTW, please give us a model number. I thought Fleetwins were 7.5HP and Lightwins were 3HP .

Given the engines age the first suspect should be a bad coil, which might fire the plug weakly at very low speed and not at all at higher speeds.

 

[adamj]

Re: Dead cylander: spark,compression;reed ok: NO GAS

As long as the reeds are OK, and you say they are, and as long as there is no big hole in the crankcase, and the piston skirts are not trashed, and the main bearings are not totally worn out, that is impossible.

There are no crankshaft seals on that motor, so it isn't that either.

Are you SURE it has good spark? How did you check it? Laying the plugs up against the head is not a spark test. It needs to be able to jump a 1/4" gap in open air. I have to assume you tried new plugs, right?

I switched with the good cylander spark plug. No difference. I did what you said, oaying it against the head and looking for a spark. I think the issue however is gas, as there is no gas on the plug, and no ignition in the cylander.
How can I check the reeds? they seem clean, flat and seated.
I do have one cylander working.

 

[tx1961whaler]

Re: Dead cylander: spark,compression;reed ok: NO GAS

What I would do is switch the coils, and see if the problem follows. If you have good compression on both cylinders, and it runs on one, then it's normally an ignition problem. Normally the problem is with the coils on these old ones, unless you are sure they have been changed in the last 10 years. Your may be 50 years old! I have a 6 hp that is not running even though it sparks OK on one real plug, but the spark will not jump a 1/4" gap on a tester so it won't work in the cylinder while under normal compression.

 

[F_R]

Re: Dead cylander: spark,compression;reed ok: NO GAS

First, let's clear up the question of what you are working on. A Fleetwin is 7.5hp, a 3hp is a Lightwin.

Second. like I told you, it is not a gas problem. The same carburetor feeds both cylinders. So how can it only feed one and not the other?

That statement does not include the possibility that there may not be other powerhead problems such as trashed pistons. The reeds are flat and laying against the plate, that is all they have to do.

The plugs are not supposed to be wet. If they were, it would indicate too much gas (flooded).

Quit fooling yourself, do a proper spark test. That is almost certain to be where the trouble is.

 

[adamj]

Re: Dead cylinder: spark,compression;reed ok: NO GAS

Re: Dead cylinder: spark,compression;reed ok: NO GAS

Sorry all, I just got back from a week camping on a lake. Thanks for the good replies!!

Yes it's a lightwin, 3 hp, serial # 3012-25817. my mistake, just saw other posts of fleetwins and got mixed up. I think it's 1951, my dad said that, but I'm not positive. I know there's a way to tell with the serial number somehow.

Certainly the carburetor feeds both and is working.

Your explanation of the spark makes sense to me. I'll test for a 1/4" gap spark, which like I said, I didn't do before. I never knew that the spark could be supressed under pressure, as implied in the post by tx1961whaler, (thanks!!!). Switching coils is a good idea albeit a bit time consuming. However, it's definitely a good troubleshooting thought.

Do I need to purchase a spark tester or is there some other way to do it? 1/4" bent out spark plug?

Compression meaures good in both cylinders, so I don't think it's a trashed cylinder.

Sounds like you don't think I'd see gas on the plugs if there was no ignition. I thought the gas would be sucked in from the piston moving, but perhaps it needs ignition to generate enough vacuum. This makes sense the more I think about it. Yes?

thanks again, good thoughts all around!

yours
Adam

 

[adamj]

Re: Dead cylander: spark,compression;reed ok: NO GAS

Make that a 1954.... Listed 52-54 with a good sized serial number ? sounds like 54 ish.