1964 28 hp backfires

[monriverguy]

Thanks in advance to all who reply to this as i have a few questions. I just got this motor Model # 28402 it is a 1964 evinrude 28 hp, The motor starts easy and idles good but every now and then it sounds almost like a back fire coming out of the exhaust. The motor will rev up good but still will miss /cough now and then.

So question 1 how do i do a compression test on this motor it is a pull start only.

question 2 What should the reading be ?

question 3 Do i have to ground out the spark plug wire when i do this?

question 4 how many times do i pull on the rope for a good reading ? Just once ?

question 5 what all should i look for to find the cause of the backfire ?

Thanks again to all........................

 

[F_R]

#1 Same as any other two-stroke outboard. Remove plugs and ground the wires. Install a compression gauge in one plug hole and crank it till highest reading is obtained. Repeat with other hole. It will start an argument, but it is not necessary to have the throttle wide open on a two-stroke. And do not add oil to the cylinders--that is cheating.

#2 I dunno, probably around 100? Should be within 10% of ech other

#3 and 4 See #1​


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[F_R]

#5 Are you sure it is a backfire? At what speed is it happening?

 

[monriverguy]

It happens at low and high rpms i have only ran it in a barrel so far

 

[F_R]

Oh well, get it on a boat on the lake and adjusted out properly before fixing something that may not need fixing. Check back if you still have trouble. Your symptoms and description are classic for a worn out clutch dog. But make sure before tearing into it.

 

[monriverguy]

clutch dog worn out ? it happens even in neutral is that still the clutch dog ?

thanks for all your help

 

[F_R]

No, it's not the clutch dog if it does it in neutral. Running too lean will cause a "lean sneeze" or cough at idle speeds. I don't know what's going on at higher speeds. Besides, how big is this barrel you are running it in? It would have to be a mighty big one to run a 28hp at high speeds. Even then you would need a test prop. As I said, get it on a boat where it was designed to run.