Engine questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ryhan87 · 12-05-2009, 06:52 PM

My 72 Gmc has a 250 inline six in it with a single barrel rochester carb. And i have been having problems with it. It starts fine with the choke when the engine is cold. But after running for a bit and warming up if you shut it off and leave it for like 10 min or so when you go to start it, its really hard to start. It will turn over but wont fire unless you give it full throttle. Any suggestions?

cdowns · 12-05-2009, 08:05 PM

have you done any maintenance to it like ccleaning changing gapping plugs or points air and fuel filter change set check timing etc??also called a tuneup

Wrenchbender Ret · 12-06-2009, 11:40 AM

Your carb is flooding. After you shut it down, look down the throat of the carb & see if any gas is running in. If so you need to put a kit in the carb.

ryhan87 · 12-06-2009, 01:03 PM

Ya i've done a bit of work too it. Pulled the head off and put in new seats and reground all the valves. New head gasket when i put it back together. Put in new spark plugs, checked the timing. I also put a rebuild kit in the carb. I also removed the in carb fuel filter and put in a inline filter in its place. If im leaking fuel after shutdown I would just need to adjust the arm that holds the needle in its seat to a little less height? The thing with that is though wouldnt i still have a problem starting when its cold? Because all of the fuel would have drained out of the bowl? I have no trouble starting it when its cold.

68gmsee · 12-06-2009, 02:24 PM

Good info in above posts.

fyi: it takes just a few seconds to pump enough gas to start the engine when you choked and pumping the gas pedal -even if it was empty. You're basically sucking gas out of the carb with the choke closed.

To check it take the breather off. Run it. Shut it. Look in throat to see if gas is dripping or if there's a heavy smell of gasoline fumes.

Another test. After you stop, step on the pedal all the way and leave it there without pumping it. Do not choke it and do not pump the pedal. Crank it and see if it starts quicker that way. Also, have someone look at the exhaust to see if there's black smoke coming out when it starts.

If all of that checks out and still fails to start. You may have ignition problems, vacuuum leak or vapor lock.

12-05-2009, 06:52 PM	#1
ryhan87 Registered User Join Date: Sep 2009 Location: Lloydminster Alberta Posts: 32	Engine questions My 72 Gmc has a 250 inline six in it with a single barrel rochester carb. And i have been having problems with it. It starts fine with the choke when the engine is cold. But after running for a bit and warming up if you shut it off and leave it for like 10 min or so when you go to start it, its really hard to start. It will turn over but wont fire unless you give it full throttle. Any suggestions?

12-05-2009, 08:05 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Engine questions have you done any maintenance to it like ccleaning changing gapping plugs or points air and fuel filter change set check timing etc??also called a tuneup __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

12-06-2009, 11:40 AM	#3
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: Engine questions Your carb is flooding. After you shut it down, look down the throat of the carb & see if any gas is running in. If so you need to put a kit in the carb.

12-06-2009, 01:03 PM	#4
ryhan87 Registered User Join Date: Sep 2009 Location: Lloydminster Alberta Posts: 32	Re: Engine questions Ya i've done a bit of work too it. Pulled the head off and put in new seats and reground all the valves. New head gasket when i put it back together. Put in new spark plugs, checked the timing. I also put a rebuild kit in the carb. I also removed the in carb fuel filter and put in a inline filter in its place. If im leaking fuel after shutdown I would just need to adjust the arm that holds the needle in its seat to a little less height? The thing with that is though wouldnt i still have a problem starting when its cold? Because all of the fuel would have drained out of the bowl? I have no trouble starting it when its cold.

12-06-2009, 02:24 PM	#5
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Engine questions Good info in above posts. fyi: it takes just a few seconds to pump enough gas to start the engine when you choked and pumping the gas pedal -even if it was empty. You're basically sucking gas out of the carb with the choke closed. To check it take the breather off. Run it. Shut it. Look in throat to see if gas is dripping or if there's a heavy smell of gasoline fumes. Another test. After you stop, step on the pedal all the way and leave it there without pumping it. Do not choke it and do not pump the pedal. Crank it and see if it starts quicker that way. Also, have someone look at the exhaust to see if there's black smoke coming out when it starts. If all of that checks out and still fails to start. You may have ignition problems, vacuuum leak or vapor lock.

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