OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

joshuas33

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Sep 27, 2012
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My boat will no start. If I pour a little bit of gas into the carb it starts for a second and then turns off. The fuel pump is brand new and pumping fuel to the carb. (I removed the inlet side to verify fuel is arriving to the carb) The carburetor has been rebuilt and I think that was rebuilt correctly but I still cannot get it to fire. The boat cranks and cranks but will not fire the engine. Any thoughts? The spark plugs, rotor, distributor cap, plugs are all brand new. Everything on the starter side appears to be good but I cannot get it to start.
 

Artwerke

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May 22, 2013
Messages
33
Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

Crank the engine, shut off ignition.Look down the carb throat while opening the throttle fully, if you do not see a spray of fuel in the barrels, the carb most likely was not rebuilt correctly. Either the Float/needle valve is not operating correctly, or the accelerator pump is not working correctly.
 

joshuas33

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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

When I crank the engine and shut off the ignition the carb throat is dry but as soon as I open the throttle fully it sprays two streams of fuel into the throat. Is it supposed to be wet if the throttle is in neutral?
 

joshuas33

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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

When I crank the engine and shut off the ignition the carb throat is dry but as soon as I open the throttle fully it sprays two streams of fuel into the throat. Is it supposed to be wet if the throttle is in neutral? WHen it idles, where does the fuel come from to keep it started?
 

Renken1

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Aug 14, 2013
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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

The fuel comes from the center of the boosters ( the round piece that hangs in the center of the barrel ). Engine vaccum pulls the fuel out.

Is your choke blade closed before you crank it? Are your idle mixture screws out about 2 turns each? If not, adjust choke til its about 1/2 closed to begin with ( final adjustment will come later ). Disconnect the throttle linkage so you can work it by hand. Pump it twice, then have someone to spin the starter. Once the engine fires, work the throttle just enough to keep it running and adjust the idle speed screw in until it keeps it running. Once it gets a little heat in it, back the idle screw down til it almost quits, then slowly turn one of the idle mixture screws in and listen if it helps or hurts idle. Once the sweet spot is found with that screw, move to the other one and repeat. After that the engine should be idling faster, so back the rpm back down and go over the mixture screws again. If done right, by the end of the 3rd set of adjustments your idle mixture should be good. Now turn the idle speed screw in until the engine is at about 700rpm or so. Now shut it off and it should refire fine ( choke blade should be open fully now due to warm engine )
 

joshuas33

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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

I will run through all of those things that you suggested. You mention the idle mixture screws and I know where those 2 are but then you also reference the idle speed screw. Are these the same screws or is the idle speed screw a completely different screw? I am not sure what you are referring to. Thanks for the info.
 

fincastle

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Jul 6, 2012
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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

Idle speed screw is a single screw at the end of the shaft where the cable attaches to the linkage. Turn it in to increase rpm, out to decrease.
 

joshuas33

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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

Thank you for the info. I will try all of the above suggestions.
 

joshuas33

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Sep 27, 2012
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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

Now I have something odd happening. I tried everything that you suggested and the boat started finally and with the tweaking it seemed to work great. I had muffs attached and water running through and everything was working great. I was able to adjust everything and it was running great and then the odd thing happened. The engine started to die so I backed off the accelerator and put it back into neutral and that satisfied it for a few extra seconds and then it shut off. I tried to start it again but it just turned and turned but would not fire. I decided to push the fuel rod and make it spray a few times but I noticed that it was not spraying like it used to be so I figured that it had to be low on fuel. Easy fix, just add gas. I added more fuel and tried to start it up and still nothing. I pulled the inlet side of the fuel pump off and tried to start it and no fuel is pumping to the carburetor. There is fuel in the gas tank because I just added a gallon more. Is it possible that as the engine gets hot the rods that push down on the mechanical fuel pump becomes misaligned and do not cause it to pump fuel from the gas tank to the carb? Any thoughts? Any idea what could be happening? Thank you.
 

Silvertip

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Joined
Sep 22, 2003
Messages
28,758
Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

No! IT cannot get misaligned. You have a fuel pump problem or a fuel restriction problem between the pump and the bottom of the pickup in the fuel tank. An air leak in the fuel line is also a possibility.
 

joshuas33

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Joined
Sep 27, 2012
Messages
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Re: OMC 2.5l 4cylinder Rochester 2G Carburetor Issues

Ok. The fuel pump is two days old so I doubt that is the problem although stranger things have happened. I also recently replaced the fuel line so that should not be a problem either. Perhaps there is an issue with the pickup in the fuel tank. I will try and discover the problem. Thank you.
 
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