Fuel pump, primer and compression issues 98 115 Johnson crossflow

[GatorMike]

I have been struggling with 2 problems that I have pretty much figured out.

1. Cold starts--- I believe I have found the problem here, I had been thinking the primer was OK because when the engine was running and I pushed in the key it would kill the motor. However I reciently discovered if I used a spray bottle to put a shot of fuel in the carbs before starting my cold start problems went away. So at this point I did a little experimenting. I unplugged the primer hoses and cranked the motor with the key pushed in. I got no fuel from the primer at cranking speeds. I rebuilt the fuel pump with and got the same results. I think I have determined there is not enough compression in the crankcase to run the fuel pump.

2. A lack of power with the throttle down. I think although it is getting fuel at running speeds I suspect the fuel flow is weak due to the fuel pump problems.

So I started checking out where my problems might stem from and I discovered the lower left cyl has just 60 psi compression. I decided to tear it down and rebuild it. I just started and the first thing I did was remove the heads to look at the cyls. The lower left has some scoreing so I proceeded to start removing the various parts so I can pull the powerhead. When I removed the fuel pump I got an idea I put a straw into the hole where the fuel pump gets its compression and blew cigarette smoke through the straw. The smoke comes out along the left side of the lower left piston not at the bottom where the scoreing is. Would this point to a broken ring?

Another question, does crankcase compression from the lower left cylendar drive the fuel pump or is it crankcase pressure from all cyls that drive the fuel pump? And does it sound like I am on the right track?

 

[Solittle]

Re: Fuel pump, primer and compression issues 98 115 Johnson crossflow

I'm gonna shoot in the dark - -

Re #1. I suspect that part of the issue here is with the primer & not necessarily with the fuel pump.

Re #2+ With a 60 psi compression you have to tear it down and while you are at it replace the fuel pump & primer.

 

[daselbee]

Re: Fuel pump, primer and compression issues 98 115 Johnson crossflow

Hey GatorMike...where you been?

Ok to your questions...

Only one cylinder's crankcase pressure drives the fuel pump. On a V6 looper it is #6. Not sure which one on your 115, but probably #4.

You should have a fitting that the fuel pump pulse line attaches to at the block. That is the pulse limiter. It is a fancy check valve that blows thru both ways, UNTIL an extra strong pulse hits it, like a crankcase backfire, and then it kicks in and limits damage to the fuel pump from the backfire. It would be normal for smoke to pass thru and into #4 crankcase area if you blew it into that fitting.

Are you saying that the scoring and cylinder marking is lined up with the pulse fitting on #4? If you have 60 psi on #4, the cyl compression is probably blowing by the scoring and the rings. It follows that if it can blow by one direction, it should also leak in the other direction...when the piston is going down in the cyl, and not allow enough crankcase pressure/pulses to build up to run the fuel pump.

I know for a fact that if you blow out the cyl that drives the fuel pump, i.e. zero compression, the engine will not run because the fuel pump is inoperative.

 

[GatorMike]

Re: Fuel pump, primer and compression issues 98 115 Johnson crossflow

Been doing good daselbee how have you been?

Yeah I'm pretty confident that is the problem, it apeared to me the #4 cylendar was the one driving the fuel pump because the hole the pump bolts to is on the lower left side. I just was not sure if the pump was driven by just one cyl or all 4. The fact that smoke blown into that hole comes out the #4 cyl and not the others kind of backs that up.

I have the power head ready to come off now and reguardless it needs rebuilding with the low compression. This is the same motor I rebuilt a couple of years ago. I knew I screwed up back then when I didn't rebore #4. #1 & 4 were the two that had got salt water in them and rusted up on me before. The machine shop rebored #1 and we discussed # 4 but they didn't think it was necessary. After the rebuild #4 was 10 to 15 lbs lower than the other 3 and I knew eventualy I would probably have problems with it. Lesson learned.

Anyway I know the primer works when the motor is running but does not work when cranking the motor. I am fairly sure she just does not build up enough compression in that cylendar to operate the fuel pump at cranking speed. A shot of gas in the carbs with a spray bottle and she fires right up, with the motor running there is enough compression to run the pump. I'll know for sure when I get the motor rebuilt but I am about 99% sure this is the case.

 

[daselbee]

Re: Fuel pump, primer and compression issues 98 115 Johnson crossflow

Mike..instead of taking a bottle of spray gas with you, just turn the red lever to manual, and pump the primer bulb two more times. This will enrichen the mix for starting just like the spray bottle, you don't have to carry one with you, and you were taking the hood off anyway...
A bit simpler.