1973 Evinrude Ignition problem

DarleneD

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Got this 1973 Evinrude model 25302A outboard and I was told that it runs poorly at idle and it seams to be running on one cylinder. The motor is currently running on one (bottom) cylinder. I changed the spark plugs and made no difference. When I take out the top plug, it is fuel wet and the bottom one is dry. I did an ignition test and got very good spark. The compression is 110 pounds. I tested all the ignition parts, coils, charge coil, etc. All is good according to the manual. I even replaced the CD unit, thinking it was the problem, but as usual, it made no difference

One thing the motor does, while it is running, every so often it will fire on the top cylinder and get a nice large puff of smoke. I even took off the carburetor, cleaned it out, but it did not make a difference also. While the carburetor was off, I did my best to look at the reeds and they too looked good. Has anyone got any suggestions?
 

F_R

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Got this 1973 Evinrude model 25302A outboard and I was told that it runs poorly at idle and it seams to be running on one cylinder. The motor is currently running on one (bottom) cylinder. I changed the spark plugs and made no difference. When I take out the top plug, it is fuel wet and the bottom one is dry. I did an ignition test and got very good spark. The compression is 110 pounds. I tested all the ignition parts, coils, charge coil, etc. All is good according to the manual. I even replaced the CD unit, thinking it was the problem, but as usual, it made no difference

One thing the motor does, while it is running, every so often it will fire on the top cylinder and get a nice large puff of smoke. I even took off the carburetor, cleaned it out, but it did not make a difference also. While the carburetor was off, I did my best to look at the reeds and they too looked good. Has anyone got any suggestions?

Changed the CD unit??? On a 1973??? They didn't have a CD unit.

The fuel pump is mounted on the bottom cylinder (or at least it is supposed to be). So a leaking diaphragm would make the lower cylinder run rich.

Having said all that, those motors had the crankcase drain discharged into the upper cylinder, so there was a problem with the upper running rich at idle, even when new. If you suspect that is the problem, pull the drain hose off and see if it runs any better. I know of a way to improve the idle, but won't say because it might be illegal.
 

DarleneD

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(Changed the CD unit??? On a 1973??? They didn't have a CD unit)

I stand corrected. Got it mixed up with my friends motor. The one I am trying to fix is a 1995 Johnson, model J25REOR.
Noting the mention of the fuel pump, it is mounted at the top cylinder and I will look at it tomorrow. Sorry for the wrong info
folks.
 

DarleneD

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UPDATE.... I dis-mounted the fuel pump (plugged the port) but, I left it still connected in the system. Hooked up a fuel line and water. Got the motor started and it still has the misfire, but sort of like every few cycles of rpm's (not as much smoke this time) Note: the fuel pump did not leak any fuel while running. It did this even when I removed the fuel line and ran the motor till it ran out of fuel. I took out he spark plugs and the top plug had a charcoal powerish tip and slightly wet on the outer ring/edge of the plug. The bottom plug was the same as the top, but the outer edge/ring of the plug was the same as the tip. I put in new spark plugs and it did the same thing again.
 

oldboat1

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The carburetor should have a needle valve on top, toward the rear (air mix). Adjust it slight counter clockwise and see if operation improves.

The oem fuel pump gets its pulse from the hole in the powerhead, and mounts flush -- didn't follow your description. The pump has a thin rubber diaphragm on the inside, and the diaphragm may have a hole in it -- may need replacement.
 

DarleneD

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In response to what has been suggested, I just completed the spark gap test and "yes" it has a very strong spark for the 7/16 gap. After that I put the plugs back in and got the motor started and adjusted the little screw (mixture screw) at the top of the carb. I tried adjusting it out and in about 1 to 1 1/2 turns and the motor still does the misfiring. It does this at all rpm's, but not as bad at the higher rpm's though.
 

racerone

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Run with a timing light hooked up.----Observe the flashing light.----Test both cylinders.----Might help to determine the problem.
 

DarleneD

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Run with a timing light hooked up.----Observe the flashing light.----Test both cylinders.----Might help to determine the problem.

The timing light is a good idea. I hooked up the timing light and ran the motor observing the light and did this for both cylinders. When the motor did the misfire, the timing light made/showed no difference ignition wise at idle or high rpm's, The cylinders are both getting good spark. Hopefully someone can come up with another suggestion. Thanks
 

oldboat1

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Sometimes carb cleaning takes a couple of tries. The idle circuit in yours may be partially blocked, for example. I soak the tops and bottoms (metal parts) in lacquer thinner after opening up the domed core plug on top (replacement plug is in the carb kit). After soaking, run soft wire in every opening, and finish with carb cleaner spray using the plastic nozzle.

There is a nozzle gasket in your carb assembly, and that needs to be in place when the carb top is reconnected to the bowl. Perhaps that was overlooked in reassembly.

It is difficult to tell offhand if the condition you describe is ignition or carb related (or perhaps an air leak somewhere). You seem to rule out ignition problems, based on your description.
 

DarleneD

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Sometimes carb cleaning takes a couple of tries. The idle circuit in yours may be partially blocked, for example. I soak the tops and bottoms (metal parts) in lacquer thinner after opening up the domed core plug on top (replacement plug is in the carb kit). After soaking, run soft wire in every opening, and finish with carb cleaner spray using the plastic nozzle.

There is a nozzle gasket in your carb assembly, and that needs to be in place when the carb top is reconnected to the bowl. Perhaps that was overlooked in reassembly.

It is difficult to tell offhand if the condition you describe is ignition or carb related (or perhaps an air leak somewhere). You seem to rule out ignition problems, based on your description.

Since I got the suggestion it could be the carb, I took it apart and put in B-12 cleaner. This is not the same as the small B-12 spray can.See photo. Had it in the solution for 5 days and put in a fresh oem carb service kit. I even took off the intake to make a better examination of the reeds. They were good. Got the carb back on and got the engine started and it still does the same thing, even when I did the idle mix screw, no change.

This has me baffled. Based on the book I have (its an oem shop manual) all the electronics are in specs, although I did in the beginning, put in a new charge coil and made no difference, even tried a new CD unit and no change. Again has anyone got any suggestions. thanks in advance for the help so far.
 

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oldboat1

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https://www.iboats.com/shop/engine-p...tor-Parts.html

Not much to add, except your reference to the idle screw. If there is no effect on engine operation when the needle is adjusted, something is wrong. Missing or backfiring aside, adjusting the idle speed screw one way or the other should produce a change in idle rpm, likely stalling if either too rich or too lean. It's possible there is a broken point of an adjustment screw jammed in the orifice -- might be able to see that with the plug (#5) removed. It's a good idea to direct carb spray through the opening from the front so you can see the orifice is clear.
 

juno pierrat

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he made a correction awhile back
" I stand corrected. Got it mixed up with my friends motor. The one I am trying to fix is a 1995 Johnson, model J25REOR.
Noting the mention of the fuel pump, it is mounted at the top cylinder and I will look at it tomorrow. Sorry for the wrong info
folks "
 

juno pierrat

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so one carb for two cylinders, both must be getting fuel, i'd think its an electrical thing
 

racerone

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Is throttle plate opening too early ?-----Do you know how to adjust check for that?
 

DarleneD

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I would like to define what I said in my last post. When I was running the motor and did the carb idle mixture screw adjustment, when it was turned in, the motor would want to die/stall and when I would turn the screw out the motor ran rough. During this run the motor still has the erratic misfire. Also After putting the carb into the B-12 chemtool solution, I rinsed out the carb using hot water and then blew out all passages and then followed that with using the B-12 (small pressurized can) to further flush out all the passages, and again blew out the passages. I did remove the two plugs when this was done.

I think I will re-test the parts that are under the flywheel. Who knows, I may have missed something. In the meantime, I am open to any suggestions. I really want to get this motor to run correctly.
 

DarleneD

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Is throttle plate opening too early ?-----Do you know how to adjust check for that?

When I first started working on this motor, In the process I did check to see if the carb and timing adjustment was ok and according to the book it is correct, so I ruled that out and that is when I thought the carb was bad and when it was first taken off, and apart it was very clean inside of it, but I did a quickie clean out (used B-12 spray can) at that time and installed only a needle and seat.
 
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