what are we missing, 1995 48 spl Johnson?

[tashasdaddy]

1995 48 spl Johnson, starts easily compression well in range, spark as should be, been thru carbs twice. it will run fine for 8 minutes, then bog out, and only idle. we have taken compression, and spark with spark tester, and with induction timing light, results all normal. it is getting fuel, as we disconnected the fuel line, and removed the drain plugs on the carbs.

it will start to surge, then bog out and quit, unless you bring it back to idle.

 

[mikesea]

Re: what are we missing, 1995 48 spl Johnson?

Is the 8 min.only at idle? My thought is,a fuel restriction somewhere under the cowling,your carbs fill,then for some reason ,once emptied ,fill slowly only allowing an idle.Your fuel lines may have internal problems,I had one where it was like a blocked artery ,the inner hose delaminated from the outer jacket ,only found it after I cut the hose open,took a long time to figure out

 

[F_R]

Re: what are we missing, 1995 48 spl Johnson?

If it were me, as a troubleshooting test, I would tee a fuel pressure test gauge into the line between the fuel pump and carbs to monitor the fuel pressure as it runs.

 

[tashasdaddy]

Re: what are we missing, 1995 48 spl Johnson?

will try pressure guage tomorrow.

 

[jimdd810]

Re: what are we missing, 1995 48 spl Johnson?

Tashasdaddy, Please dont take this wrong but is your vent cap on your tank open and clean? I have had many a vent caps cause this problem. Also make sure your fuel lines are not colapsing from weakness any where. Good luck

 

[tashasdaddy]

Re: what are we missing, 1995 48 spl Johnson?

jimdd810, first thing we checked. pumping bulb does not help either.

 

[kenmyfam]

Re: what are we missing, 1995 48 spl Johnson?

Have you tried it with an alternate pump just to test ???

 

[tashasdaddy]

Re: what are we missing, 1995 48 spl Johnson?

rebuilt existing pump. new gasket to block.

 

[kenmyfam]

Re: what are we missing, 1995 48 spl Johnson?

Is it pulsing O.K. ???

 

[Faztbullet]

Re: what are we missing, 1995 48 spl Johnson?

Hey TD, does it act like it "jumped time" when this happens and is it sudden or comes on slowly? Does engine have to cool to get it to run correctly or have to set a coulpe of hours?

 

[Haffiman]

Re: what are we missing, 1995 48 spl Johnson?

A lot of 'loose' advice, but not much system in the fault searching.
Being a 48 it should have the 'old' small fuel pump and no VRO.
Start with the basic test, fuel supply.
Disconnect the pump from the carb, remove the quick connector from the tank fuel hose and hook it directly on the plastic fitting that goes to the carbs.
Start and run and use the primerbulb as pump.
If engine runs OK, then start fault searching the fuel system.
If engine still has the problems, tripple check the carbs and hoses from pump to carb.
Install a clear plastic hose, make it a loop, between pump and carbs.
Is any air building up on top of the loop?
If yes, move the loop to suction side and re-test.
If still air, hook the fuel line directly onto the pump (by-pass quick connectors), re-test.
Keep on, step by step.
Be systematic.

 

[tashasdaddy]

Re: what are we missing, 1995 48 spl Johnson?

Faztbullet , yes when cool runs great. but used infrared gun, and motor is not running hot. 140* as should be. have checked timing by Joe Reeves system, hot and cold. as should be.

 

[bktheking]

Re: what are we missing, 1995 48 spl Johnson?

Powerpack has SLOW function on that motor, retest with the sensor disconnected.

 

[tashasdaddy]

Re: what are we missing, 1995 48 spl Johnson?

no oil alarm 48 spl is a premix motor from factory.

what we found today, is that, on the botttom carb, if you block 3/4 of the carb barrel, with you hand it will run fine. i am thinking reeds. fuel pressure test was fine. temp sender disconnected made no difference.

 

[Faztbullet]

Re: what are we missing, 1995 48 spl Johnson?

Could be a bad carb casting and at temp its porosity opens up creating a lean condition. I had a lil Honda ouboard that drove several shops and me crazy with bogging problems. Changed carb with a known running motor and shazam!!! fixed it!!! Ordered a carb and sent it on its way. Pm me the carb number and will look to see if I got one and if so will ship it to ya...

 

[Haffiman]

Re: what are we missing, 1995 48 spl Johnson?

no oil alarm 48 spl is a premix motor from factory.

what we found today, is that, on the botttom carb, if you block 3/4 of the carb barrel, with you hand it will run fine. i am thinking reeds. fuel pressure test was fine. temp sender disconnected made no difference.

It might even be a leaking lower crankshaft seal.

 

[boobie]

Re: what are we missing, 1995 48 spl Johnson?

If at all possible swap the carbs between cyls and see where the problem goes.This may tell you if you have a carb prob or p/h prob.

 

[tashasdaddy]

Re: what are we missing, 1995 48 spl Johnson?

will try the swap.

 

[tashasdaddy]

Re: what are we missing, 1995 48 spl Johnson?

swapped carbs. problem followed carb.

 

[boobie]

Re: what are we missing, 1995 48 spl Johnson?

Now you know you have a carb prob and nothing in the p/h. Take the carb apart, take your time and look at everything real closely. I'm sure you know how the fuel circuits work in the carb so check them out. It could also be a porrus carb. It could also be something really stupid. Been there and done that. Remember, "It's always the little things that get you". One dumb question, is nozzle gasket 338881 in place?