1965 Evinrude Ducktwin

[mark38090]

I have a 1965 Ducktwin 3hp, I rebuilt the carb, new plugs, new headgasket and new impellor. It starts first or second pull everytime but when its running it has a light surge. It acts like it starts losing power but then picks back up. I have gone thru carb several times and finally took it to someone else to give it a try but it still does it. Mine doesn't have the high speed needle, it has the on adjustable jet in the bowl. My question, the high speed jet will not come out of the carb, the ears(?) are broken off so that a screw driver will not turn it. Could that effect the way it runs? Also, what kind of plugs do you recommend? I know it calls for champions
j6c but nobody carries those around here so I bought the equivalent. Could that be the issue? Thanks.

 

[oldcatamount]

Re: 1965 Evinrude Ducktwin

I have a similar situation with my '69 4hp Johnson. Come to find out, it was the water intake port/screen was plugged with fine debris and causing an overheat that would slow the motor and then it would speed up again. Luckily, there was no damage (that I can tell).

 

[Shakedownscott]

Re: 1965 Evinrude Ducktwin

Have you looked at the fuel pump? The engine might be starving for fuel at high RPM's. If that is Ok, the air/fuel mixture is probably off. I am not familiar with the type of carb you are describing or how to adjust it. The plugs should not cause this.

 

[Daviet]

Re: 1965 Evinrude Ducktwin

You should have a screen on the fuel valve in the fuel tank, is it plugged or restricted? Is the high speed orifice and the high speed nozzle really clean in the carb? You can clean the high speed orifice without takeing it out, but you will have to remove the float bowl to do it, and yes it can cause your problem.
Are you sure it's a fuel problem and not dropping a cylinder?

 

[Daviet]

Re: 1965 Evinrude Ducktwin

Oh I forgot, make sure the tank vent is not restricted.

 

[mark38090]

Re: 1965 Evinrude Ducktwin

Daviet,
what would cause it to drop a cylinder? I have replaced both coils, points and condensors, plugs and even plug wires. I removed the screen in the tank and went with an inline filter. It definitely seems like a fule/carb issue but then again, I am by no means an expert. Thanks for the help.

 

[Daviet]

Re: 1965 Evinrude Ducktwin

Point gap correct, .020. Coil spacing from flywheel, should be even with mounting bosses. Defective or corroded internal plug wire, did you trim 1/4" off off the end of the plug wire that went into the coil when you replaced the coil?
You can use an inductive timing light to check spark when it is acting up, will tell you if you have a spark problem and which cylinder is missfiring. Will elimate or confirm the ign system.

 

[nwcove]

Re: 1965 Evinrude Ducktwin

my 62 lightwin was doing the exact same thing, it was the filter in the tank. i cleaned it with brake cleaner, blew it out with air, then no more surging. (maybe your inline filter is to restrictive for gravity feed? just a thought)

 

[lindy46]

Re: 1965 Evinrude Ducktwin

Did you rebuild the carb with a new gasket on the high speed nozzle?

 

[1946Zephyr]

Re: 1965 Evinrude Ducktwin

That surging sounds to me like a coil droppin in and out. Make sure the coils aren't cracked. If they are, then they need replacing. I would replace the leads ate the same time too.

 

[mark38090]

Re: 1965 Evinrude Ducktwin

I replaced the entire ignition system, points and condensors, coils, plug wires, plugs all new. Rebuilt carb with new complete kit. Removed welsh plug in carb and cleaned those passages. Got new high speed jet today gonna install tommorrow and then try it again. Not sure on the gap for points so I'll check that again too.