1969 evinrude 25hp requires choke at WOT

[Sascwatch]

Been toying with this motor and I cannot figure out why I have to use the choke at WOT, motor starts up fine and idles all day.

I've done quite a bit of work to it and can't figure this problem out. So far I've cleaned the carb twice, first time I didn't remove the lead plugs, second time I did. I noticed the new needle and seat were smaller in the rebuild kit so I put the old ones back in with no change.

all ignition components are new and I've checked that both plugs are firing, don't have a spark tester but I think the spark is good. Can pull each plug wire and it'll run on one cylinder.

Fuel pump has been rebuilt, new gas lines, tank and bulb. Bulb stays hard even at wot with the choke pulled.

new upper crankshaft seal, old one was leaking.

Carb and timing are linked and synced, carb is wide open when the timing is fully advanced, and lined up in the 2 notches at idle. Starts in 2 pulls no problem.

I cleaned the carb once more today removing all lead plugs and jets, sprayed out all orifices with carb cleaner and compressed air. Float is set correctly (level with rim of bowl when upside down) bulb gets hard and stays hard. I think the high speed jet said 72 on it.

Im thinking the fuel pump wasn't rebuilt correctly, but it seems fine. Compression is good aswell, I want to say it was over 100lbs on both cylinders.

Any suggestions? Thanks.

 

[lindy46]

I assume you're testing it on the boat and on the water? So what does it do at WOT without choke? If you need to choke it to achieve full rpm's/speed, that sounds like it's running too lean. Open the high speed needle to richen it up and see what happens. The high speed needle needs to be adjusted on the water at full throttle for maximum RPM's.

 

[racerone]

I do not believe there is a high speed needle on this motor !!----There is a fixed high speed jet screwed horizontally into the carburetor bowl.----Was it removed for cleaning ?

 

[Sascwatch]

Yes, it only has a low speed adjustment. In gear I can gun it and it'll surge onto plane then nearly die out, if I continue to hold it at WOT the motor will just run slow and have no power, pull the choke and it revs back up and zooms along without problems.

If if I leave the choke on and return to slower speed the engine will flood and die.

 

[racerone]

??---So was the high speed jet removed for inspection ?-----Is the vent for the carburetor bowl plugged ?----Have you done a compression test ?

 

[Sascwatch]

The orifice plug was pulled and cleaned, carb cleaner sprayed through it and the high speed passage along with compressed air.

Not sure what the bowl vent is, but any and all passages have been blown out and look clean with light clearly shining through them.

i did a compression test last fall, and I recall both cylinders being over 100lbs after a couple pulls. I will get a tester again and see what it's got.

I think I will pull the carb, take it apart minus the lead plugs which I just replaced and soak it for a day or 2 in carb cleaner. Will also pick up a new orifice plug if the local dealer has one.

 

[Crosbyman]

bad hose, fuel pick up in the tank clogged ? tried a new hose and tank ??
vent working on the tank ??? twist open the cap while running wot

does it run ok if you prime the bulb at wot if yes ...work towards the fuel pump as suspect if carb is clean

run some monofilament in all orifices of the carb..resoak and air blow dry

 

[jimmbo]

Is the gasket between the carb and Manifold in good shape and the carb tight? A very low fuel level or gummed up main circuit in the carb can cause a lean condition, but you said you blew it out.

the lead plugs you replaced, were any of them involved with the main fuel circuit? If so maybe they need to be tapped down wee bit harder

I doubt you need a new jet orifice

 

[kbait]

When you have the carb off next time, shine a light in the intake and make sure all the reeds are seated. Don't think that possible problem matches your symptoms, but it won't hurt to look..

 

[Sascwatch]

Tank, hose, bulb and fittings are all brand new. I've got another tank I can try but not a bulb. Vent is open and allows airflow in and out of the tank.

Bulb pumps up and stays hard even at wot, I tried pumping it today and it didn't make a difference.

i rebuilt the fuel pump, but I'm not sure if it is all put together correct, I think since the bowl is staying full it's not a pump issue.

There were 3 lead plugs I removed, I believe the one inside the carb was for the high speed circuit. All looked well and carb cleaner closed through with ease.

Carb gasket is new and carb is tightened down good.

I did not look at the butterflies but I will pull the carb, soak it and reclean everything. Will also test with a different tank.

I will probably order a new fuel pump and high speed jet either way so I have spares.

Thanks for for all the help.

 

[jimmbo]

After you use the choke the engine revs up, you open the choke and the engine continues to run at high speed?

 

[Sascwatch]

No, it slows right down again if it's left at wot and the choke is opened.

 

[racerone]

Is the float bowl venting ?

 

[Sascwatch]

Not sure what you mean by venting. There's no fuel leaking from anywhere and the bowl is staying full.

Im fairly new to carbs, so all the info is appreciated.

 

[Sascwatch]

One thing I just noticed is that the new bowl gasket I got does no have material around the center tube in the bowl, would this cause this problem?

Hmm, looking at part 0384409 it's got a second smaller gasket which I think I have in my kit, it looks like it goes around the center fuel pickup tube?

 

[jimmbo]

The new gasket is different from the old one?

 

[racerone]

The fuel in the bowl must have atmospheric pressure on it.----------The venturi is at a lower pressure than the fuel and the nozzlle to it ( lower pressure ) must dip into the fuel.

 

[Sascwatch]

The old gasket I believe was original and was one piece, the new one has an outer and inner gasket, looks like the smaller one goes onto the Venturi tube, sealing it to the bowl.

So if I understand correctly, the difference in air pressure is used to push fuel up the Venturi tube which varies depending on the difference in pressure, the amount of fuel that can be passed through is limited by the orifice plug in the bowl.

I'm going to take the carb off on my next day off and inspect it really well, from what I've seen the vent is usually near the air intake. Will soak it for a day or 2 in carb cleaner and put it back together, this time with the second smaller gasket on the Venturi tube.

Will update after test drive.

 

[jimmbo]

There is a pressure drop in the carb venture. The higher atmospheric pressure in the fuel bowl pushes the fuel up the tube into the lower pressure venture.

I don't think you need to resoak the carb, just put it back together with the extra gasket and see how it runs. make sure to set the float correctly

 

[AlTn]

+1 with jimmbo...just install that "boss" gasket and see what you have