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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 81K10 on June 27, 2010, 11:22:55 pm
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Hi all, I'll try to explain the best I can...freshly rebuilt 350, performer intake, Rochester 4 brl carb.
Seems to idle smoothly but pretty rich, and while driving the engine often cuts out and then after a second or two with my foot off of the throttle the engine will cut back in. This will happen repeatedly once it starts, uphill or flat, and regardless of fuel level in the tank.
New plugs, wires, mechanical fuel pump, fuel filter, air cleaner.
Is this a carb problem or what do I need to look at?
Thanks in advance for you time.
Tony
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Is your carb rebuilt?
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check for vacuum leaks.
check for back pressure (ie: clogged catalytic converter)
could also be accelerator pump on carb
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the carb has not been rebuilt while I've had it (6 months) but ran well when first installed, Exhaust is brand new dual 2.5" manifold back through flowmaster 40's, no cats. Accelerator pump squirts fuel with the engine off.
where and whats the best way to check for vacuum leak?
thanks.
Tony
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idle your engine. Spray WD-40 all around vacuum lines, carb gasket, intake gasket, etc... If rpm's go up, you found a vacuum leak.
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thanks. I'll try that and post what happens.
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Sounds like lack of fuel when you get on it.
Rebuilt motor, carb tuned for the pre-rebuilt motor-
Cutting out when getting under load...... leads me to believe you need to fatten the secondaries, and check the accelerator pump.
Prolly need more fuel than you did prior to the rebuild
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a blown accelerator pump would cause that. have you had any backfires out the carb lately they will usually blow it depends on the type of carb and all
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Sounds like the problem I had. After a lot of time and parts. I fixed it by changing the fuel strainer sock in on the fuel sending unit.
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Finally had time to work on this...Sprayed wd-40 all over while idling and it had no effect on the idle, no backfires through the carb that I know of, Vaccuum lines are in good shape...Perhaps I should just buy a new carb since everything else on the engine is new. Might just bolt on a known running carb and see if that eliminates the carb itself as the problem.
I'll check the sock on the sending unit if the borrowed carb does the same thing.
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Is it cutting at when you are going a constant speed? Or does it cut out when you mash on the gas peddle harder?
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fuel pump?
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But he's got a new mechanical fuel pump. Those "usually" don't fail outta the box.
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had this problem on the 84's q-jet it was the carb starving the motor of fuel and only did it under load.
I'd try another carb or check the filter/strainer in the inlet of the carb, we did that and changed the pump, put in an in line filter and blew air back thru to clean the fuel strainer in the tank and still got nothing, no vac. leaks, complete tune up and all, ended up putting on an edelbrock carb I rebuilt and solved it for good.
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i heard that a double pumper will solve the problem of when you mash the gas the fuel will be pushed to the rear of the bowl causing it to starve the motor for a sec
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I have the same problem but my carb needs to be rebuilt.
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If it's cutting out when he mashes the gas it may just be that the air flaps on the secondaries are opening too fast. That's a simple fix that cost zero dollars.
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I haven't really been mashing on the pedal, still just trying to get it running right after the engine swap. But it happens while accelerating from say 50km/h(30mph) to 80-100km/h (50-60mph) while getting on the highway as opposed to accelerating off the line.
If it's cutting out when he mashes the gas it may just be that the air flaps on the secondaries are opening too fast. That's a simple fix that cost zero dollars.
What do I have to look at to determine if this is the problem? I like the price!
thanks
Tony.
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I determined my problem: a spark plug boot that melted on my #5 cylinder header and was grounding out! I could see the spark when I turned the lights out in the garage. I waited a couple of minutes and then could see it. I could see it when I turned the lights on too after I knew where to look. I had to put a shorty spark plug in and changed the wire and problem gone!! It also helped that I changed the accelerator pump nozzle head, since once side was plugged up. I think I had that problem for quite a while. Now when I punch the gas from an idle it will actually light the tires up instead of bogging down!
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Amazing how things work out, especially looking at a different area. Glad you got it fixed!
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I haven't really been mashing on the pedal, still just trying to get it running right after the engine swap. But it happens while accelerating from say 50km/h(30mph) to 80-100km/h (50-60mph) while getting on the highway as opposed to accelerating off the line.
If it's cutting out when he mashes the gas it may just be that the air flaps on the secondaries are opening too fast. That's a simple fix that cost zero dollars.
What do I have to look at to determine if this is the problem? I like the price!
thanks
Tony.
Usually they bog down when you romp on it like when you are going to pass someone and you floor it. It'll cut out, then you have to let off some for the engine to catch back up. If it's cutting out just cruising at a steady speed it's probably not that.