1985 evinrude 25 popping/surging

[joseph1980]

I just got this motor a week or so ago. I was unsure of its history so I rebuilt the carb, new plugs and did a decarb treatment. It does this weird popping/surging like the video shows. Any ideas what it could be? I know the video may not show it but it kinda backfires through the carb when it happens. It seems to be intermittent it may stop doing it for a few minutes then it will start up again. I've tried adjusting the low speed carb needle from 1/2 turn out to 6 turns out and this made no difference in the popping. Did the the decarb with seafoam cause this? Is this a fuel pump issue?
the changes in the rpm at about the 40 second mark was me idling it down. sorry for the video quality....

http://www.youtube.com/watch?v=61PXF1a3R8k

[Cofe]

I had this same problem with a 1990. Found the water cooled exhaust plates were warped, and the gaskets were bad. This let cooling water into the cylinders and made it backfire once in awhile.

[joseph1980]

thanks for the reply cofe, you always seems to have an answer. I was reading through my manual and it said a broken reed valve may cause this type of popping. what are your thoughts on that possibility? I just cant understand why it would be intermittent though, to me if one was broken it would be an all the time problem. I just put it in the tank and ran it for probably 30 minutes without a hiccup. This is really bizarre!

[Cofe]

If it just ran fine for 30 minutes, there may have been something in the carb idle circuit. A reed valve has similar symptoms, but would be very constant. Sounds like you may have got the cobs out. Time to fish?

[78 mckee]

If you turned the low speed needle 6 turns out and it didn't stall, you have a problem with the carb and it should be disassembled and cleaned. The popping is often caused by too lean a mixture at low speed. Disassemble and clean all passages in the carb with carb cleaner before moving on to more complicated fixes.

[joseph1980]

it seems to not do it in the water, only on the muffs...guess it needs the backpressure?

[78 mckee]

I love happy endings...