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Author Topic:   Sudden Power Loss
minimontauk posted 10-14-2003 05:31 PM ET (US)   Profile for minimontauk   Send Email to minimontauk  
I tried this post before, didn't get too many bites:
My 96 Johnson 48SPL idles crappy, run good at mid throttle, great at WOT, for about one minute. Then it suddenly conks out. Sounds exactly like it's running out of gas. Pump up the bulb, restart, and away you go, till the next time you try to go fast. The plugs have a shiny black baked on glaze on the tips. I thought I had an air leak in the hose or tank, but I tried switching these to no effect. The fuel pump screen is clean. My current theory is a bad fuel pump. Sound reasonable? I don't know how to check it, as they are non-repairable. I'd hate to drop $75 only to find out it's some stupid adjustment problem.
JBCornwell posted 10-14-2003 07:32 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Ahoy, Minimontauk.

Did you try pumping the primer when the engine tries to die? That would verify your suspicion that it is a fuel supply problem.

Fuel supply problem could be restriction in the pickup or fuel line, air leak or failing pump.

Don't spring for a new pump until you have eliminated other possible causes.

Red sky at night. . .

ShrimpBurrito posted 10-16-2003 02:53 PM ET (US)     Profile for ShrimpBurrito  Send Email to ShrimpBurrito     
According to my OMC manual, "acceptable fuel" is gas with an octane rating of at least 87 and NO MORE than 10% ethanol or 5% methanol. However, it continues with a warning, stating "alcohol extended fuels may result in engine running quality problems, vapor lock or fuel starvation problems, or moisture absorption (phase separation) problems."

I believe the alcohol content in consumer gasoline increases in the winter. If this just started happening, it might be worth addressing.

Sal DiMercurio posted 10-16-2003 04:09 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Does the ball go flat , then go back to normal after the engine stops ?
If so you have crud in your tank & it's clogging the inlet where your fuel pickup is.
One way to check to see if your fuel pump is bad is to, remove the black fuel line "AFTER" the fuel pump & replace it with a clear line & have someone watch it as you go from idle to wot, if the pump is bad or sucking air, you will see bubbles in the line & if theres no fuel going through the line at wot, you know it's the pump.
You have to remove the clear fuel line after the test because it's not fuel line & will eventually leak.
Tom2697 posted 10-16-2003 04:15 PM ET (US)     Profile for Tom2697  Send Email to Tom2697     
Definitely try JB's advice on pumping the primer. If the engine performance improves, hook up a fuel pressure gauge (most auto parts stores will lend one to you with a credit card) to your fuel line. Follow the instructions with the gauge and it will help you pinpoint the source (bad pump or blockage).
brisboats posted 10-16-2003 09:31 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Try a new set of plugs too. Hook up an auxilary fuel tank and if you can observe and then pump the primer bulb while she falls off all the better. Sal is right the bulb will flatten or at least start to suck in as the motor runs lean. Idles crappy and the black glaze on the plugs sound like fuel mixture/ quality to me. Good luck.


brisboats posted 10-16-2003 09:41 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Just had another thought, that motor has the clear fuel filter bowl. Another thing to try is next time it quits at WOT take a quick look at the bowl. Is it running dry there?. If so the problem is either a partially clogged fuel line or pickup, and /or the fuel pump itself.

Try the auxilary tank (with fresh gas and a different fuel line) to rule out the clogged line/pickup . If that doesn't work try the primer bulb pump as she runs at wot to rule out the fuel pump. Hope this helps.


Tom2697 posted 10-17-2003 03:30 PM ET (US)     Profile for Tom2697  Send Email to Tom2697     
One last thing...check to make certain your tank vent line is not blocked. Open the fill cover immediately after the engine stalls...If you hear a vacuum noise, you found your problem.

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