stumbles up hills

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Jan 17, 2005 | 09:41 PM

74hiboy

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stumbles up hills

I have a 74 F250 w/ a 390 and a Holley carb. Two weeks ago I did a tune up which included replacing the inline fuel filter. The truck has always run well with no problems. Today under acceleration up a hill the truck stumbled and chugged, it felt like it was running out of gas so I immediateley got off the throttle and was able to baby it up the hill. I was at about 1/8 of a tank of gas and thought maybe low fuel/sloshing around in the tank so I filled it and and the same thing happened again. It seems to run fine under hard acceleration on flat roads.

Where do I start?

Thanks

Last edited by 74hiboy; Jan 17, 2005 at 10:20 PM.

Jan 17, 2005 | 11:03 PM

olfordsnstone

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From: Other side of the sunrise

Change the fuel fulter again to see if you picked up some crud from the low tank. If that dont do it, check the fuel pump pressure.
Does it smell like gas in the engine compartment. If so, look at the fuel pump to see if it is leaking gas.
Check to see if the gas hose is old and cracked. Especially between the tank and fuel pump. Air might be getting sucked in.
When's the last time you gave her a tune up?
That should keep ya busy for a while. I'll check back here tomorrow.
Good Luck

Jan 17, 2005 | 11:07 PM

olfordsnstone

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From: Other side of the sunrise

OOps, I just read your post again stating that you did a tune up. Maybe check your work. We're all human and mistakes can be made. Wires snapped in tight? Points set and snug?

Jan 19, 2005 | 03:35 PM

Matt99362

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Check the floats in the carb. You may be running out of gas as far as the carb is concerned.

Jan 19, 2005 | 03:44 PM

SwOkcOffRoader

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From: okc

check the accelerator pump under the front bowl of the carb, is there any moisture or does it look like gas may be leaking, turn the throttle by hand and see if any gas comes out the bottom of the pump, those go out occasionaly and arent hard to fix at all......a bad pump gasket will make your engine "stumble" like that......

Jan 19, 2005 | 05:37 PM

74hiboy

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I will check the lines, new fuel filter and fuel pump this week.

Is it possible that the problem could be in the carb, maybe a float problem since it only happens when going up a hill will accelerating and does not happen at any other time?

Thanks for the info.

Jan 19, 2005 | 07:14 PM

willow_tree

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From: springstead

im thinking its in the carb. im also thinking it is the accelerator pump. my 79 had a similar problem. could be the filter?

Jan 20, 2005 | 07:21 PM

willow_tree

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From: springstead

how would the accelertor pump have nothing to do with it. if you need throttle the accelerator pump provides a boost of gas to get you there. if its stumbling, then it could be it, but it doesnt help that i dont know how long the stumble is.

Jan 20, 2005 | 07:41 PM

#10

jfinlen

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I'm having a similar problem. I have no power above 3K rpm. It falls on it's face. So far I have 6 psi fuel pressure when it happens so fuel isn't the problem. I cleaned the carb out and couldn't find anything wrong. I put on a new coil, rotor, ignition box ( duraspark), timed it etc. I'm stumped right now. I'm going to try a different carb and see where that takes me. Right now I have no clue what's going on with this thing.

Anybody else have any ideas. Do you know how to test the pickup in the distributor? I have new vacuum advance and everything works just fine. It will hit 5K no problem without a load, but as soon as you load it up it falls flat. If I back out of the throttle it will even out, but it won't rev any higher. If it had points, I'd say they were dead or the condenser was bad, but I've never had this problem with a duraspark before.

Thanks.

Jan 20, 2005 | 07:43 PM

#11

willow_tree

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From: springstead

did you change the fuel filter?

Jan 20, 2005 | 07:43 PM

#12

SwOkcOffRoader

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From: okc

Quote:

Originally Posted by willow_tree

exactly, when an accelerator pump goes, it will cause the engine to miss and hesitate and stumble, ive seen them so bad that the engine wouldnt even run anymore, if the pump has a tear in it, it allows air to suck into it and make it run poorly........ive changed more of these things than i can count,it might not be the problem in this case, but its definitly a possibility....if it only happens while going up hill, its very possible that the float is set too high and only overflowing on an incline, i would definitly say the problem lies in the carb...........

Jan 23, 2005 | 09:55 AM

#13

74hiboy

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Sorry It took me so long to reply but I havent been able to work on the truck until today. I took your advise and installed a new fuel pump. I also checked all of the fuel lines, they were all in good shape, the majority of the line is steel. While checking the lines I found another metal fuel filter which is located between the tank and the fuel pump. I replaced it with a see through filter. The metal filter that I replaced was in bad shape, it took a lot of effort to blow through. The fuel pump was also bad. I took the truck for a test drive accelerating hard up hills and it drove great, no stumbling.

Thanks for all of the information everyone responded with.