25hp Evinrude. Finally running good an then. Missing?

[camarokidz28]

1979 Evinrude 25905R 25hp

I had some troubles getting it running. Put a new power pack on and that fixed that problem. Then couldn't get it to idle. So I pulled the carb and cleaned it out. Finally had it running great for about 3 miles.
Was cruising 20mph with about 600lbs in a 16ft Lowe V when it slowly began to miss. First I thought I was crazy and then it got worse and worse and worse. By the time I admitted defeat it was running at full throttle at a pop pop pop - vroooooooooooom- pop pop pop - vroooooooooom. This would happen with no change in throttle it would go from full power to sputter back to full power.
I'm not really sure where to go from here.

Could be fuel? Bad power pack?

any ideas? this boat is driving me up a wall

 

[interalian]

Sounds like fuel pump. Try pumping the primer ball when it's falling on its face and see if you can keep it going.

 

[AlTn]

if pumping the primer ball doesn't correct the problem...take an ignition timing light along with you and clamp to each spark plug lead in turn... A.does one lead show a consistent flash and the other doesn't?... B.are the flashes inconsistent < random > on both leads?....C. are the flashes consistent on both leads, but the engine is still going from full throttle to sputter?...test and post back results

 

[gm280]

Yea sure sounds like a fuel delivery issue to me also. JMHO

 

[camarokidz28]

Sounds like fuel pump. Try pumping the primer ball when it's falling on its face and see if you can keep it going.

​I tried pumping the fuel bulb. I also inspected all fuel hoses and replaced the primer bulb. I installed an in-line filter and checked the pump screen. I jar tested the fuel for water and found none. Nothing made a difference. I pulled the plugs which were covered in thick tar like oil. Which indicates to me that it's getting fuel. I replaced the plugs with brand new plugs and I have the same result. Intermittent power. Seems like at first the boat wants to run but a minute or 2 in it just starts doing this and there is nothing I can find to correct it. I did not bring a timing light with to the river. The launch I use is about 40 minutes away so it's no easy task to go there.

I have read that people were getting bad powerpacks out of the box. The brand I got I believe is Airtex? I should have returned it right away because it doesn't even physically fit on the bolt holes. But it made the boat start and run like a champ so I left it with only 1 bolt. I contacted the distributor I purchased from and they do not take returns on electronics.

 

[oldboat1]

Fuel mix would be 50:1 (a little less than 3oz oil for every gallon of gas). Too much oil can foul plugs. Fresh plugs are good, but doesn't tell you about spark -- need to check that with a separate spark tester that you can buy at auto stores. Quality of the spark tells you how well your ignition system is doing (Get an adjustable open air tester and look for a sharp 1/2 inch spark when you crank it with the plugs out.)

Your carb has an adjustable idle mix needle (air/fuel), and a fixed high speed jet. It sounds like you have problems at higher rpms, but probably wouldn't hurt to set the low speed needle again (1 1/2 turns out from seated, then look for the leanest setting from there (clockwise) -- motor has to run smoothly at idle with no popping/lean sneezing, and throttle up smoothly. It may be that your choke plate is not fully opening, giving you rich running and fouling plugs.

 

[boobie]

Do a cylinder drop test on it. That may tell you something.

 

[camarokidz28]

Fuel mix would be 50:1 (a little less than 3oz oil for every gallon of gas). Too much oil can foul plugs. Fresh plugs are good, but doesn't tell you about spark -- need to check that with a separate spark tester that you can buy at auto stores. Quality of the spark tells you how well your ignition system is doing (Get an adjustable open air tester and look for a sharp 1/2 inch spark when you crank it with the plugs out.)

Your carb has an adjustable idle mix needle (air/fuel), and a fixed high speed jet. It sounds like you have problems at higher rpms, but probably wouldn't hurt to set the low speed needle again (1 1/2 turns out from seated, then look for the leanest setting from there (clockwise) -- motor has to run smoothly at idle with no popping/lean sneezing, and throttle up smoothly. It may be that your choke plate is not fully opening, giving you rich running and fouling plugs.

​Fuel was mixed 50:1 and I have not tried a spark tester. I will have to pick one up and check spark. The low speed needle was adjusted.

​By cylinder drop test is that a leakdown test?

 

[oldboat1]

By a drop test, Boobie means checking to see if one plug is not firing (cylinder "dropping out") when you are having problems. There are a few ways of doing that -- can use a timing light clamped to individual plug wires (just look for flashes. No flashing means no firing), or pull individual boots and see if operation changes (look for stalls or stumbles. If no change, the cylinder tested is dropping out.) Or, can check plugs. Clean them first or use new ones, then check after running. If one isn't firing, it will remain essentially as clean as when it went in (wet if fuel is entering the cylinder).

Do the spark test first at idle, using a tester. You may find the problem doing that.