Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

[Skippy the skipper]

Hi, I have a 1985 140HP Johnson that will die after throttle is cut from running at WOT. It doesn't matter if I lower the throttle slow or quick, it will still die after I slow down just a little, not at wide open. I can run for as long as I give her full throttle, pull back on the gas and instatly stops running. Throttling up seems ok but the boat doesn't seem to perform all that well either, slow to get on plane. I have rebuilt the carbs( were dirty), tested the VRO fuel pump (13PSI at WOT), fuel bulb is good after a run, checked the spark and done a link and sync. After a run I have pulled the spark plugs out and they show no signs of water (but have fuel on them) and my compression is around 120 more or less on all cyl. BTW I put a pump in the lower unit and changed the T-stats before I ran this as it had been sitting up for a year +, temperature looks good with my handy temp gun. I am normally a pretty good mechanical kinda guy but this is driving me CRAZY! HELPPPPP!

P.S. once she dies I have to choke hard to start her, will not just fire up!

 

[HighTrim]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

When you cleaned the carbs did you pay attention to the intermediate or low speed / idle jet? Was it removed and thoroughally cleaned? You will need a specially made tool for this.

May also want to look for any air leaks into the fuel system(Condition of fuel line and clamps, etc....) although Im leaning towards the jet being not sufficiently clean.

 

[tashasdaddy]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

agree^^^ it has 3 jets, high speed, intermediate, and low speed. did you remove and clean all of them???

 

[Skippy the skipper]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

Yes if you are talking about the two brass orifices on the upper left of the carb removed(with modified screwdriver) and cleaned them in good carb cleaner, very clean and shiny. High speed at bottom of the bowl was cleaned as well. I will check them tomorrow though in case I missed one or it has new crud. Now that I think about it are the idle and intermediate jets different sizes, could I have possibly installed them in the wrong position?

 

[Faztbullet]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

Yep...

 

[Skippy the skipper]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

Checked the jet placement this morning and they are in the right spots 40 in upper and 14 in lower (went to BRP site to confirm). Any other ideas guys?

 

[CharlieB]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

Spark test

If the kill wire within the console has chaffed through and grounding as the throttle is pulled back, killing the engine, then un-grounds as the throttle is moved forward.

Test the spark, see if it fails when the throttle is pulled back from WOT. This can be done with the engine NOT running, plugs out and wires connected to a spark tester and a remote starter switch.

 

[Skippy the skipper]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

Great thought but no dice. Hooked up a sparkie and gave her a try but nothing. Arggg!

 

[HighTrim]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

Have you checked to see if the vent on the fuel tank is free of debris? Ensure that the anti syphon valve is not stuck in a semi closed position? They are notorious for that.

Other than that I would get a vaccuum gauge and hook it inline on the fuel hose before the engine, along with a clear section of hose. Take it for a spin, noting the readings and monitor the fuel flow through the clear hose.

Findings:

-Vacuum of less than 2 inches and air bubbles in the clear hose indicates an air leak into the fuel system
-No air bubbles and less than 2 inches indicates a bad fuel pump
-Vacuum over 4 inches indicates a restriction.

Sample gauge

"http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&sspagename=STRK%3AMEBTOX%3AIT&viewitem=&item=4610113711&_trksid=p3984.cTODAY.m238.lVI"

 

[marinegrh]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

just a thought but what do your reeds look like, Is this a loss of fuel stoping the engine where the engine dies down or a complete shut down like you pulled the kill kord. Sounds like may be a harness issue, or sounds like fuel. Do you have access to a test harness to eliminate the boat from the engine. Key switch elimination/harness is a really good test in situations like these. Also a vac test on the fuel side to see if you sucking air

Fairwinds

 

[Skippy the skipper]

Re: Help!!! OMC Pros!! 85 140HP dies when throttle is cut from WOT

Have not tried a vacuum guage yet, will tomorrow. I have the motor hooked to a remote tank. Is there an anti syphon on the motor? I have also looked at the reeds when the carbs were off (as well as you can, look ok). When the engine dies, the bowls still have fuel in them and the sparkplugs are still wet when pulled (I was checking for water). When it dies its in an instant, just like a kill switch or the key was shut off. I think that is why the sparkplugs still have fuel on them when pulled. Motor still turning as it stops keeps sucking fuel flooding the engine making it hard to start. Does this sound possible. Could a bad powerpack do something this odd? Before I get off this for the night, thanks in advance from everyone for the great ideas and advice. Skippy