1971 Evin 4HP runs better with cover off

[Dude]

What causes my motor to run better with the cover off? I put the cover on and attempted to get a smooth running motor but I didn't have any luck. I
adjusted the top mixture screw and there was some difference but not as good as when the cover was off. Thanks

 

[DJ]

Re: 1971 Evin 4HP runs better with cover off

You have exhaust leaking under the hood.

The two most like culprits are the exhaust plate on the side of the cylinder block or the powerhead to midsection gasket. Both are easy fixes.

 

[freddyray21]

Re: 1971 Evin 4HP runs better with cover off

ditto

 

[Dude]

Re: 1971 Evin 4HP runs better with cover off

From what you told me the exhaust gases affect the motor's operation. Is that correct?

 

[freddyray21]

Re: 1971 Evin 4HP runs better with cover off

exhaust gases have less O 2 in them more CO 2. It changes the mixture to the carb as the carb is sucking in it's own exhaust. Enough exhaust gas and they won't even run. I have to run a fan on mine when I am running them in a barrell or it will affect them with the cover off.

 

[Dude]

Re: 1971 Evin 4HP runs better with cover off

Hi DJ, Freddy, You indicated that it was a quick repair to solve my exhaust escape problem. I don't think I have a problem with the side cover to do the necessary repair, but I'm not sure about the bottom of the motor for a repair. Should I remove the lower unit first before unbolting the powerhead from the mid-section?

 

[DJ]

Re: 1971 Evin 4HP runs better with cover off

Hi DJ, Freddy, You indicated that it was a quick repair to solve my exhaust escape problem. I don't think I have a problem with the side cover to do the necessary repair, but I'm not sure about the bottom of the motor for a repair. Should I remove the lower unit first before unbolting the the motor from the drive shaft housing?

I would, it's a good time to service the water pump too, unless it's fresh.

It's also easier to "stab" the driveshaft re-installing the lower unit than it is to line it up with the powerhead.

Pay special attention to the exhaust and water ports. I just did this to my 4 HP a year ago. The ports were nearly clogged. That probably had something to do with the gasket failing.

 

[freddyray21]

Re: 1971 Evin 4HP runs better with cover off

getting the lower out of the way is how I would do it and like DJ says replace the water pump while you are there.