60' Lark 40hp stumbling at WOT

[surlyjoe]

the motor was running great since a full rebuild last winter, then last week I had to change the filter bowl gasket on the water because the methanol in our gas out here ate it. Then I did the de-carb over the weekend. Now it will only make 4000rpm at WOT and starts stumbling when the cruise throttle kicks in. seems to run fine other than at WOT, fuel bowl is full, and pumping the bulb doesn't help.

Any ideas of what may be going on? any other rubber parts the alcohol eats up that I need to keep an eye on?

I backed the high speed needle all the way out to try and clearany gunk out, but I will pull it this morning along with the flywheel and have a look, but I'm not really sure what I'm looking for.


TIA!! Joe

 

[steelespike]

Re: 60' Lark 40hp stumbling at WOT

Have you checked the plugs? Decarb will tend to foul plugs sometimes.You may want to check the plug wires for wear.Where they may rub as the throttle is moved.
Sometimes methanol will clean the system but unfortunately the loosened dirt can cause problems.
Try to carefully adjust the high speed to the best performance and leave it just slightly toward rich.

 

[tashasdaddy]

Re: 60' Lark 40hp stumbling at WOT

just in case you missed it.
http://www.iboats.com/bbboard/bbBoard.cgi?a=viewthread;fid=28;gtid=818798;gpid=818802

 

[surlyjoe]

Re: 60' Lark 40hp stumbling at WOT

DOH! I forgot to do the plugs after I did the de-carb this time, so maybe thats it. All the new hose is 1534 or whatever the new stuff is, so it should be OK, I am just afraid that gas is eating something else I am forgetting about...:/

 

[R.Johnson]

Re: 60' Lark 40hp stumbling at WOT

How long has it been since the ignition has been looked at on this 1960 engine?

 

[Paul Moir]

Re: 60' Lark 40hp stumbling at WOT

A previous post mentions he replaced the ignition last fall. How about the carb? Still running a cork float? Fuel pump diaphragm and carb bowl would be the last two things, though they usually don't cause much trouble.

 

[Chinewalker]

Re: 60' Lark 40hp stumbling at WOT

Also, check the point gap. If you didn't oil the cam wick it is possible that the points are closing up as the cam rider wears down. Usually manifests itself as a skip at some RPMs and gets progressively worse...
- Scott

 

[surlyjoe]

Re: 60' Lark 40hp stumbling at WOT

ya, cork float, but OEM new when carb was rebuilt last fall, will the meth eat the cork as well? is there a metal/bakelite one available for it?

I put a new felt on the cam as well. but haven't pulled the flywheel since march, I'll be getting the puller out now...

the fuel pump diaphragm was new as well, but I suspect that it will get eaten more rapidly as well, but I am without a spare at the moment.
although squeezing the primer bulb didn't help, at least its a backup for a failed pump.

I am just getting home so I am gonna attack it, I'll keep ya posted.. d

 

[surlyjoe]

Re: 60' Lark 40hp stumbling at WOT

one of the coils I replaced is spitting out pieces, I would assume thats it.. I'm off to the yard for a new coil!!

 

[Paul Moir]

Re: 60' Lark 40hp stumbling at WOT

Man, new ones shouldn't be doing that. You sure 12v isn't finding it's way into the ignition?

About the cork float, that's a bit of a problem. Old stock that they shouldn't sell. The new carb kits have a plastic float and have for many years. If you get a cork float, you should refuse it.

 

[surlyjoe]

Re: 60' Lark 40hp stumbling at WOT

well, i guess i'll try and get a plastic float, dont suppose they sell just that tho... any places you might recommend?



the new coil is in and seems ok, but I won't know till tomorrow at 5am when we hit the water 8)

thanks for all the help!!

 

[surlyjoe]

Re: 60' Lark 40hp stumbling at WOT

welll, that was the problem, she runs like a dream again! d

 

[Texasmark]

Re: 60' Lark 40hp stumbling at WOT

Well what was the problem/what fixed the problem....for historical purposes? The float or the coil?

Mark