88 OMC 5.0 Back firing through carb.

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jarrod1995

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Oct 13, 2011
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Hello
I have a 88 Bayliner Trophy 2159/60 with a OMC 5.0l and Cobra Outdrive. I have changed Fuel filters, Water Sep, Plug Wires, Rotor, Distributor Cap, Carb is rebuilt from company out of Jax, Fl. Timing is on and has been moded to Electronic Ing. It will start and run on the ears just back fires through the carb if you give it the gas to fast. Do it slow and it will run all the way up to 4500 RPM?s no problems, put it in the water and it?s very hard to start let alone keep running. Tank is clean fresh gas treated with Sea Foam and Ethanol fuel treatment. It has roughly 150 hrs on the engine according to the meter. Just don?t know what else to do, Thanks Jarrod.

P.S. I just read the Fuel check in adults only, The clear hose that comes up from the Fuel pump to the carb, should there be fuel flowing through that. Mine is bone dry no way to check for bubbles. I guess this might be my next route after everything else.
 
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john4040

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Aug 21, 2011
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Re: 88 OMC 5.0 Back firing through carb.

check the anti syphon valve on the fuet tank and check fuel pressure and volume sounds like it is lean
 
J

jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

I have taken the valve out, ball isn't stuck and moves freely. At this point I can't check the pressure, but would like to know if I am supposed to see fuel in the clear line. Thanks Jarrod.
 
I

indybleck

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Sep 29, 2011
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Re: 88 OMC 5.0 Back firing through carb.

No you should not see fuel in the clear tube. Make sure that your vent tube for the tank doesn't have any obstructions or sags in it.
 
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jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

Thank you i will check it when I get home, I know fuel came out when I was filling the gas tank, but ill take it out and check it.
 
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indybleck

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Re: 88 OMC 5.0 Back firing through carb.

One way to see if it makes a difference is run with the fill cap loose or open.
 
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jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

Well i took the fuel pump out do to not being able to test it, by the way the vent flows fine. I took the hose off at the tank and blew through it and was able to suck some stinky air in so I guess the vent is fine.

Back to the fuel pump, the fitting where you would slide the clear hose over was completely clogged up. If you accuated the pump it wasn't making any noise, cleaned it out the best I could with some carb spray and pipe cleaners and its making a sucking blowing noise I guess you could describe it now. I assume that was bad or now its toast. Thanks for the comments so far.
 

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J

jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

Well she now has new plugs and Fuel pump also, the people who I bought the carb through say only two and a half turns for the mixture screws. Just wondering idf this might be the backfiring through the carb. Manual also says .035 for the plugs but mechanic says .045 due to being a better plug. Still doesn't run perfect, if you move the throttle slow it will go all the way. Hit it fast and the back firing and cutting out comes back, thanks for ideas, Jarrod.
 
A

a70eliminator

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3,694
Re: 88 OMC 5.0 Back firing through carb.

Double check the firing order, it's easy to mix up 7-8 wire, it will run just like you described, been there...
 
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jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

Its funny you mention that, I pulled the plugs after running it, and going through the RPM ranges. Both back plugs are black, ill check this tomorrow, I have duty today and will let you know how that turns out.
 
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jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

Well I checked the wires, all in the right spot. I did put octane booster in the tank, and shot the engine down with a water displacer. In the yard now it runs and idles like nothing before. Will go through all RPM ranges, to fast now caught me off gaurd. I will be putting it in the water hopefully tomorrow to check it in the water. Who knows.
 
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jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

Well took her out today and it ran like a champ, right up to the point the rubber bulb on the bottom of the exhaust manifold let loose. Limped it home and now to replace those. Thanks for the ideas and suggestions. I still have no idea if it didn't like the 87 octane or it was shooting it down with water displacement compound. Either ways she will get up on plane. Only goes about 35 but thats to be expected with a 305. :)
 
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jarrod1995

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Re: 88 OMC 5.0 Back firing through carb.

One quick question, does anyone know the name of those rubber bulbs on the bottom of the exhaust manifolds are called.
 
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