1941 Champion does backfire

[Dennisanoka]

I had mentioned how well this runs but one thing it does do is backfire but ONLY when starting it. I have tried different throttle level positions but so far it seems to do it regardless of where I set it. It has new plug, cleaned points, new gas. Once it starts up it runs smooth. I suspect timing but that's what the throttle lever does. The label is gone for where the exact start position is but I know it must be on the lower end.

Any other ideas?

 

[Lodgepole]

Re: 1941 Champion does backfire

Start on the 3 champions I have used has always been a little advanced past mid throttle position. My 16.5 has lots of compression and is sort of high strung and will kick back at me sometimes. Yours sounds like timing so might check linkage to see if all is working right and try decarbing it. If it runs great, run it.

 

[Dennisanoka]

Re: 1941 Champion does backfire

Thank you for your input. So far I think just past half on the throttle control is about where this one likes to start the best too. I did run a strong dose of Seafoam thru it, letting it soak in between but based on the appearance of the water in the tank it may need it some more. Regarding timing it doesn't look like there's much to do other than keep the points clean. Now I must admit I did not check and re-gap them when I had the flywheel off. Any input on the gap would be nice.

Thanks

 

[F_R]

Re: 1941 Champion does backfire

If it is a Bendix Scintilla mag (round rotating magnet in the center) it is .018". The other kind with magnets in the flywheel is .020" There is no other timing adjustments. Does it backfire through the carburetor or through the underwater exhaust? Do you happen to know if that motor has a rotary valve? They can give off a pretty good backfire through the carb. It's been a long time since I've looked at one.

 

[steelespike]

Re: 1941 Champion does backfire

If your motor is a 41 then it was an early motor built by Scott Atwater.
Point gap on most Champions is .018.If set at .020 it would be a smidge advanced.If worn down it could be late.Plug gap is .025 or .030.

 

[tmcalavy]

Re: 1941 Champion does backfire

Steele is correct...the point gap is .018. Make sure you set the gap against the eccentric/cam when the points are supposed to be wide open...sometimes there is a little arrow stamped on the cam/eccentric to guide you. When you look down on the flywheel, imagine it is a clock face...starting position is usually at 5 or 5:30...with full range of advance lever being from 3 to 9 or vice-versa.

 

[Dennisanoka]

Re: 1941 Champion does backfire

The backfire is thru the carb. I will re-gap the points to .18 and the plug to .25-.30 I have it at .35.

One more question please. The exhaust has 3 little holes a 1/3 of the way down the exhaust tube are they supposed to be under water too? I am beginning to think so based on how loud it is.

 

[Dennisanoka]

Re: 1941 Champion does backfire

I am embrassed to say that my 18 yr. old son just told me that he had the instruction book for this motor. Didn't know he had gotton that too. I thought he just had some piece of advertising for it. Points are to be .015 and the plug at .027.

It doesn't say what the water line is though, if those 3 exhaust ports in the exhaust tube are to be below water. Please help if you know.

Thank you,

 

[tmcalavy]

Re: 1941 Champion does backfire

My guess is they're an exhaust relief of some sort, for gas or unburned fuel, IF they are one third down from the power head. Your exhaust exits under water at the open end of the exhaust tube. Don't know if those holes are stock...maybe a former owner drilled the tube...you know, like the young guys who put trash-can size tips on their dual exhaust?

 

[F_R]

Re: 1941 Champion does backfire

Most all outboards have exhaust relief holes above the water line. Even modern ones. They are there to relieve the exhaust back pressure to help starting and idle. Modern motors use methods to silence them. Old motors just let 'er blast.

 

[Dennisanoka]

Re: 1941 Champion does backfire

I believe you are exactly correct that they are stock and are meant to be above the water line.

Thank you for your replies.

 

[Lodgepole]

Re: 1941 Champion does backfire

My dad had an early 40's Champ 4.2. As I remember, it had holes in exhaust above water line.