FUEL PUMP OUTPUT - just need to verify this with the experts

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

Thats compression sounds approx even so seems ok since you mention you couldnt seal it properly.
Yes run a decarb through it ,but it doesnt seem to be running right when you say its at full bore.
It doesnt seem to rev up much with fuel tank above the engine so it should be running properly now.
Have you checked spark on both cylinders?

 

[Seahorse16]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

I haven't check for spark yet, but I will try that next.

 

[F_R]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

If the darn thing runs when you manually pump gas to the carburetor, you already know there is nothing wrong with the motor, and it has to be the pump or tank/hose. It simply cannot run on both cylinders if the crankcase pressure is too low to operate the fuel pump. Or any of that other stuff that was suggested.

You do know that fuel pumps can be tested, right? All you need is a pressure gage, usually combined with a vacuum gage for cars. They don't cost much. Pressure should be somewhere around 2-4 psi, depending on RPM, and tank height relative to motor height.

Or, bite the bullet and buy a fuel pump......after borrowing and trying another tank and hose.

 

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

It simply cannot run on both cylinders if the crankcase pressure is too low to operate the fuel pump. Or any of that other stuff that was suggested.

.

Yeah but he doesnt know its running on both cylinders, if you watch the video it doesnt seem to get any acceleration that id expect if it was running on two cylinders.
I think its his fuel pump and another problem causing it to run bad, maybe spark or maybe timing.
We will see

 

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

It actually looks really bad at full bore, its spluttering and not revving up

 

[F_R]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

OK, so I went back and watched the video. I don't think it is running on both cylinders. That is another problem that needs to be addressed. However, I still maintain that it should still have enough crankcase compression to operate the fuel pump, unless something is drastically wrong, like a tossed rod or blown piston or busted reed. Oh, and he isn't running it at full bore, he is running it at the neutral limiting position. Troubleshooting required.

BTW, fuel pump can still be tested.

EDIT: I just watched the video again. Do I hear a hissing sound, like a hole in the crankcase? Maybe it DOESN'T have crankcase pressure after all???

 

[Seahorse16]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

Still haven't testing for spark yet, but I have searched everywhere online for a fuel pump kit and nobody sells the diaphragm for this. I can only find a new fuel pump. I will go that route if necessary. 1976 15hp Johnson. Not even eBay!

 

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

Still haven't testing for spark yet, but I have searched everywhere online for a fuel pump kit and nobody sells the diaphragm for this. I can only find a new fuel pump. I will go that route if necessary. 1976 15hp Johnson. Not even eBay!

Hook up a reliable fuel tank to gravity feed the carb.
You need to troubleshoot why its running bad before you spend $65 on a fuel pump.
Start with sparkplugs, Check they look even and look inside the cylinders, see if any cylinders are scratched up bad. Then check for sparks.
Its not running the way it should be with that gravity fuel feed.
If you have time pull the prop off and post a video of it reving with more throttle than at neutral limited

 

[F_R]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

You probably have already heard this, but those motors were absolutely notorious for fouling spark plugs. That could be the only thing making it run badly.

 

[Seahorse16]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

I did replace the sparkplugs first thing. The plugs that were in there were fouled.

Good catch on the one cylinder firing thing! So I pulled both plugs out and pulled the starter. Sure enough, only the bottom cylinder is firing!!! If i pull the prop and rev it with no prop, will that not damage things since there is no resistence?
What's my next step now? I do have a multimeter tester.

 

[racerone]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

Pull flywheel and clean set the points.

 

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

I did replace the sparkplugs first thing. The plugs that were in there were fouled.

Good catch on the one cylinder firing thing! So I pulled both plugs out and pulled the starter. Sure enough, only the bottom cylinder is firing!!! If i pull the prop and rev it with no prop, will that not damage things since there is no resistence?
What's my next step now? I do have a multimeter tester.

Thats good progress. No need to bother pulling the prop now that you know one cylinder is the cause of it running like that. Since its running on just the bottom cylinder then it sounds like its the fuel pump that needs replacing and getting that spark sorted.
You could swap the coils over to see if the one not sparking has failed. Check all the wiring is all tight and all grounds are cleaned.
If that doesnt sort it then you will need to pull the flywheel.
You will need a special puller for that. They arent expensive, $15 or so and are quite handy to have.

 

[Seahorse16]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

So is my fuel pump running off the bottom (working) cylinder? Is that why you say the fuel pump needs replacing?

When you say swap the coils, bascially I disconnect the wires from the functional coil/wires and attach the wires from the non-function one? If I do this and I get a spark that would mean a bad coil but that my wires are ok, correct? Just making sure I understand correctly (after checking wiring carefully).

Thanks for hanging with me on this. I really appreciate it.

 

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

So is my fuel pump running off the bottom (working) cylinder? Is that why you say the fuel pump needs replacing?

When you say swap the coils, bascially I disconnect the wires from the functional coil/wires and attach the wires from the non-function one? If I do this and I get a spark that would mean a bad coil but that my wires are ok, correct? Just making sure I understand correctly (after checking wiring carefully).

Thanks for hanging with me on this. I really appreciate it.

Im quite sure that its the bottom cylinder where the fuel pump pulse hole comes out of, i only say that as ive never seen one attached to the top cylinder. Post a photo of where the fuel pump sits if you arent sure, but someone will probably say if its not on bottom cylinder. If its running just on the bottom cylinder then that bottom crankcase definitely has enough pressure to work the pump, so seems the pump is at fault.

Yes thats exactly right about swapping the coils.

 

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

Clean the bolts that the coils use for grounds too. Sometimes they get rusty and the connection goes, normally killing the coil eventually too

 

[Seahorse16]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts


Here is a picture of the fuel pump in relation to the cylinders. Hard to tell, looks like in between?

According to the shop manual that covers multiple years, doesn't it look like it uses both cylinders?

 

[racerone]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

These fuel pumps must be assembled and oriented the correct way.---The factory repair kit has full instructions on that.

 

[Seahorse16]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

However I just noticed on the bottom of my crankcase there is a wire that is attached to a bottom bolt and then not grounded or attached to anything else. Can't even see where it could go!

 

[Seahorse16]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

Yeah I have now verified on several sites includin my manual that there are no parts for this fuel pump. You must buy the entire pump to replace

 

[Bosunsmate]

Re: FUEL PUMP OUTPUT - just need to verify this with the experts

Id almost say it looks like its on the top cylinder.
That bottom wire may be a ground strap from the leg to the engine. If it is it wouldnt be the cause of spark on only one cylinder.
Did you manage to swap over the coils?