Fuel pump pressure

[scatgo]

Any one know what the fuel pump pressure should be for a 1980 Johnson two cycle should be? And what about shut off pressure? My guess is when the float valve closes the pump should stop pumping. How about the pulse pressure and or vacuum?

 

[racerone]

You are looking at about 3 or 4 psi pressure.-----What motor ?---What pump ?-----Why the question ?-----Most pumps operate on a POSITIVE pressure pulse from the crankcase.----And not so much on vacuum as is commonly believed !

 

[rothfm]

Ah, the pump never "shuts off"...always pumping from Crank like Racer said. The needle valve simpily closes blocking flow.

 

[scatgo]

1980 35HP two cyclinder Johnson. When I get on it from a stand still it pulls hard. But not for long. The power falls flat after that. The RPM seem to build up but after the kick off the line MPH dont seem to pick up at all.

 

[racerone]

Likely it is running on just 1 cylinder.-----Some testing needs to be done.

 

[oldboat1]

What testing have you done? Compression and spark testing would be standard procedure.

Because the problem is at speed, use a timing gun on each plug wire (may need a helper). No flash, no spark.

 

[scatgo]

Did That. Spark is good. Havent got to the compression test yet. Do you think low compression would also cause low fule pump pressure?

 

[F_R]

Did That. Spark is good. Havent got to the compression test yet. Do you think low compression would also cause low fule pump pressure?

In theory, it would if the piston was totally shot. But it would stop running on that cylinder long before the fuel pump would stop working.

 

[racerone]

It only takes a few minutes in trouble shooting to see what is wrong !-----Does motor keep running when you operate the manual fuel pump ??

 

[scatgo]

Easy brother. Time ,money and the weather dictate. My brother and I got this boat two months ago and only had one chance to take it out for a test ride. Your suggestion about the use of the manual pump is great info. Obviously need to know this for the next time the time money and weather let us get to it. Hoping for this weekend. This is why I am picking peoples brain now.

Peace

 

[Tim Frank]

????
The tests racer is suggesting take minutes and cost 0.

From the limited description, it sounds like the HS jet may be partially obstructed. Easy to pop out and clean.
But first do the three tests that have been suggested. Compression, spark test with an adjustable air-gap tester ( Oldboat will hopefully post the pic he has on "speed dial; ) , and cylinder drop test.

That will give you a baseline for your motor.

 

[oldboat1]

So you need some advice on a 35 Johnson, and I need some advice on adjusting secondaries on a Rochester quadrajet (1980 305 MIE 228). Maybe if we're all still around later this Spring, we can share tips.

(Buy an open air adjustable spark tester at an auto parts store [$10 or so] -- not the inline type. And see if they will loan out a compression tester.)

Peace and brotherhood and keep a safe distance .

[ed, courtesy of speed dial ]

 

[scatgo]

Tested the ignition system and things look great. Previous owner said he replaced the module and coils and they look new and the spark was jumping a big gap on the spark tester I have. Got a nice fuel pressure tester that reads in half psi increments and the fuel pressure was at 3 at idle and never went below 2 at full wide open in neutral. FYI The way this engine is set up wide open throttle in neutral will be about 1/8 throttle. There are two mechanical stops that limit throttle in N and R . Compression test was a bust. My old gauge read 100 on one cylinder and 105 on the other. New gauge read 80 on one cylinder and 85 on the other. Now the interesting part. Full throttle in N for about a minute things seem ok but then the RPMs rise all by them self and it will run a bit rough. Did this test a few times and same thing after a minute RPMs rise to the same point and it will run rough. I heard what may be a engine knock when the RPMs whet up. And a very obvious knock. I did try to spray some WD 40 on the carb to manifold gasket thinking might be a air leak but no change.

 

[oldboat1]

Does sound like it might be leaning out at high idle, so might be on track looking for a leak. Try spraying the base of the engine, blocking the carb with a piece of cardboard or similar. Could be the lower shaft seal. The float valve might be an issue if the needle isn't opening. If the motor runs out of fuel, it will rev like you describe. Might let it run at idle for 10 or 15 minutes and see you get similar results -- rpm may increase, then the motor may stall for lack of fuel.

 

[F_R]

You wrote:

Full throttle in N for about a minute things seem ok but then the RPMs rise all by them self and it will run a bit rough. Did this test a few times and same thing after a minute RPMs rise to the same point and it will run rough. I heard what may be a engine knock when the RPMs whet up. And a very obvious knock. I did try to spray some WD 40 on the carb to manifold gasket thinking might be a air leak but no change. ​

It obviously is beginning to do what we call runaway. It might go crazy and do just that---run faster and faster--wild runaway. out if control. The knock you are hearing is fuel exploding in the crankcase. Sneezing, if you will.

Why do you feel the need to run it for a minute up against the neutral stop anyway?? Don't do that. That is just begging for runaway.

 

[oldboat1]

^^Agree. Good advice given.

I was suggesting running at low/normal idle and see if it runs out of fuel (lean running, increase in rpm, sneezing, finally stalling). This is a procedure many outboarders use regularly -- runs the carb out of fuel (some suggest draining the bowls is better -- no particular preference here, although my habit is to run them out after docking). But the idle is maybe 600 rpm or so, maybe higher depending on engine tuning. And the fuel line is disconnected. If you have a carb issue or air leak somewhere, the motor may shut down earlier than the normal 3 to 5 minutes (my experience), and may do so with the fuel line connected.

 

[scatgo]

What would be the cause of a runaway?

 

[hardwater fisherman]

What would be the cause of a runaway?

Running at high rpms without any load.

 

[scatgo]

Delet

 

[oldboat1]

Running on muffs (no load) contributes, or running in a barrel and blowing out the water, exposing prop.