Help 1981 Johnson 25 surging

[LAYCO]

Hello all and thank you in advance.
Just returned from overseas (military). Had my ‘81 Johnson 25 Model J25RCIM in storage, winterized. Cranked first pull.
PROBLEM: fuel lines were dry rotted and leaking
REPAIR: changed fuel lines
Ran great for a few trips. Then,
PROBLEM: severe surging at WOT. Stalled a few times. Then couldn’t go WOT without dying. Idles great.
REPAIR: new fuel pump. Carb rebuild, no shellac, did have black stuff in bottom of bowl. Figured it was from the bad fuel lines. Very clean otherwise. Checked reeds. New spark plugs .30 gap per everything I could find online. Old plugs were worn bad but perfect color. Added fuel filter from tank and after fuel pump. Re-adjusted idle mix.
RESULT: still idles perfect. Still surging at WOT. No stalling now. Ran this way for a few tanks of gas. Still surging though.
REPAIR: fuel flow out of tank hose fuel filter good. Removed filter between pump and carb (figured two maybe too many). Took apart pump (it seemed poor quality, made in China, not Johnson, but it seemed fine visually). Took carb apart to check for contaminants and plugged main jet. Carb was perfectly clean. I noticed the needle was sticking slightly. Valve seat seemed to have burs where the needle tip seats. Polished with q-tips and jewelers rouge. Perfect seal now, no sticking. Re-adjusted float, everything seems perfect. Not flooding engine.

PROBLEM: Ran it again. Still surging . Perfect idle. Pumping bulb while WOT…no change. Pulling choke knob a very small amount while WOT…runs great, no surging. Push choke back in, then would stall out and die if opening throttle more than idle.

Pulling choke a small amount while at WOT does not affect throttle linkage. It only closes the choke butterfly ever so slightly. (I thought maybe the linkage was out of adjustment and choke opened it to WOT, but no)

The fuel pump is still suspect to me. But no change when pumping the bulb. So that dosent make any sense to me.

I don’t know what else to check or what could be causing the surging and/or stalling.

Sorry for the lengthy read. I wanted to post all relevant info.
Please help. Again thank you.

 

[racerone]

Test run with another tank and hose.-----Make sure high speed jet in bottom of float bowl is clean.

 

[LAYCO]

Thank you for the reply.

The hose and filter in image are new. I separated the hose, after the filter, and squeezed the bulb. Seemed like a lot of fuel flow without restriction. The motor surges when tank is full or almost empty, and when the tank is hot from sun and pressurized, when first started and when ran for a while. Is there something I could look for/inspect on the tank? I would have to buy another tank to do that test run.

 

[LAYCO]

Photos for reference.

 

[LAYCO]

Oh. I also checked inside the breather box. It is clean, no fuel splatter.

 

[LAYCO]

Test run with another tank and hose.-----Make sure high speed jet in bottom of float bowl is clean.

Yes high speed jet in bottom is clean and clear.

 

[LAYCO]

Here are the plugs after running for a bit as described above.

 

[LAYCO]

Compression is 120 top cylinder and 125 bottom cylinder, wet.

 

[racerone]

That is one of the good metal tanks, I like them.-----Have you replace the 3 o-rings on the outlet fitting on the tank , yes , no or no idea ?----Water pump serviced ?-----I think there is more junk in carburetor.---No need to remove the carburetor.-------Remove bowl drain plug.-----Remove the high speed jet found way inside.----Clean it and test run.

 

[LAYCO]

That is one of the good metal tanks, I like them.-----Have you replace the 3 o-rings on the outlet fitting on the tank , yes , no or no idea ?----Water pump serviced ?

Nope. I didn’t know there were o-rings in there.

It was leaking from under the outlet block(?) where there is an obvious cork gasket. I tightened the 4 screws and leak stopped.

I wanted to take the block off but was worried that it’s nuts and bolts not screws. Wasent sure how I was going to get the nuts back on from inside of the tank. Lol

 

[racerone]

Just screws.-----See those 2 little pins on there ?----They are valves.-----When connecter is put on one valve opens to vent the tank.----Other one lets fuel out.-----Do both pins stick out the same amount ?

 

[LAYCO]

That is one of the good metal tanks, I like them.-----Have you replace the 3 o-rings on the outlet fitting on the tank , yes , no or no idea ?----Water pump serviced ?-----I think there is more junk in carburetor.---No need to remove the carburetor.-------Remove bowl drain plug.-----Remove the high speed jet found way inside.----Clean it and test run.

I’m confused. I took the outlet assembly off. I don’t see any o-rings.

 

[LAYCO]

Just screws.-----See those 2 little pins on there ?----They are valves.-----When connecter is put on one valve opens to vent the tank.----Other one lets fuel out.-----Do both pins stick out the same amount ?

Yes. Both stick out same amount.

 

[LAYCO]

Not sure if it matters. When the new fuel hose is connected there is about 1/16 gap between the hose connector and the fuel tank/engine.

 

[racerone]

Confused ?----See the 2 wee core plugs.----They come out.----for service of this fine , fine tank.----See the parts book to clear up the confusion.

 

[LAYCO]

Confused ?----See the 2 wee core plugs.----They come out.----for service of this fine , fine tank.----See the parts book to clear up the confusion.

No longer confused. I did look at parts blowup. Parts ordered. Wish they had a complete rebuild kit vs individual parts.

Please correct me if wrong.

If the vent side o-ring was bad wouldn’t the tank not pressurize when hot? It does, so does that indicate that the vent o-ring is good?

The fuel valve o-ring. Fuel does not leak anywhere.

I’m still going to replace them. I’m sure they are original ’80. But I don’t have the knowledge to understand how that could cause my surging issues.

Please educate

 

[racerone]

I can not see , hear or feel your motor.-----You say there is something wrong with your motor.----Myself I test everything on a motor , hose and tank instead of throwing expensive parts at a motor.----Everybody uses a different approach.----Good luck in finding the issue with it.----Should not be hard to find what is wrong.-----I was given a 79 model motor like yours.----I think I should concentrate on it first.

 

[LAYCO]

I can not see , hear or feel your motor.-----You say there is something wrong with your motor.----Myself I test everything on a motor , hose and tank instead of throwing expensive parts at a motor.----Everybody uses a different approach.----Good luck in finding the issue with it.----Should not be hard to find what is wrong.-----I was given a 79 model motor like yours.----I think I should concentrate on it first.

I apologize for any disrespect. I thought my post was as humble as possible. I simply want to learn from more experienced mechanics and to understand how functions of different parts could cause my issues.

I greatly appreciate your time and help.

I too do not like throwing new expensive parts at an issue. The tank for example: I do not have another nor access to another. So to test the engine with another tank would cost me about $200 for a new tank, hose, and fittings. Plus I love that old metal tank and despise anything made cheaply.

Thank you again for your time and help.

 

[racerone]

Smooth surging is usually a leak in fuel lines.-----fuel pump pulling air instead of fuel------Use a 1 gallon paint can or similar with the hose stuck in for test running.