25 HP Johnson Carb

[Frank Acampora]

My friend has a tiller model, pull start, short shaft, thru-hub exhaust Johnson, model J25( )CUR. ( ) is a missing letter.

When running this engine, It will start very quickly and idle well, but as soon as it is given throttle it will sag and stall. It does not get fuel from the high speed dip tube.

Carb is rebuilt, all passages are clean and open, high speed jet is clear.
Fuel pump is delivering plenty of fuel
Float level is correct
Low speed needle is set to 1 1/2 turns out as manual directs.
Clean tank and no restrictions in the fuel line.
Pumping the primer bulb does not help--There is plenty of fuel to the carb.

If I hold two fingers over the carb intake, blanking off about 1/2 of it, The engine screams--runs like a champ and will do so all day. Remove my fingers and it will sag and stall for lack of fuel--looking in the throat, I can see that under any conditions past fast idle, the high speed dip tube is not delivering fuel without some restriction over the carb intake

I have no history on this engine but was wondering: Is there supposed to be a blanking plate or restictive screen bolted to the front of the carb?

Thanks.

 

[Cofe]

Re: 25 HP Johnson Carb

There is air in leakage somewhere. Make sure it has a gasket from the carb to intake.
Another thing to look at is the o-rings in fuel line connections. I once had these same symptoms and found a slightly nicked o-ring that let air in.

If this is a older motor, I would suspect the crank seals are letting air get by them.

 

[kevlad]

Re: 25 HP Johnson Carb

I agree,I had the same problem and it was a blown gasket

 

[tx1961whaler]

Re: 25 HP Johnson Carb

It has a silencer cover and may not run correctly without the cover and plates.