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#1 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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AAAHHHHHH!!!! Fuel problems
Truck seems to be starving for gas. Started a couple weeks ago. When I get into the peddle to pass or get up to speed it will start stubbling and I have to let off to let it recover. It was happening only when the secondaries kick in, but now it will do it with moderate sustained throttle. I thought it might be something in the carb so I took it apart today and all was well. I changed the neddle and seat just for grins and checked the float level, still no help. I changed the fuel pump still no help. I had changed the fuel filters about 3K miles ago and they all look good. I'm running external filters for the dual tanks and all the fuel hoses have been changed. No filter in the carb. It does the same thing with either tank.
This is on a stock 350 with a Q-Jet.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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#2 |
Moderator
![]() Join Date: May 2007
Location: Southern Cal
Posts: 20,006
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Re: AAAHHHHHH!!!! Fuel problems
Did you check your ignition system? Seems as though you have everything covered concerning fuel delivery.
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#3 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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Re: AAAHHHHHH!!!! Fuel problems
I haven't check the ignition. Doesn't feel like an ignition problem the way it surges when it starts stubling. I updated to an HEI system about 5K miles ago. I try a new module just in case.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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#4 |
Old Shovel Rider
Join Date: Oct 2007
Location: Rain City, WA.
Posts: 117
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Re: AAAHHHHHH!!!! Fuel problems
Could be spark advance. Do you have a vacuum advance hose from the distributor to the carb?
Last edited by DB Smith; 11-02-2008 at 08:40 PM. |
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#5 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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Re: AAAHHHHHH!!!! Fuel problems
Yes I am running vacuum advance. It will rev all day while parked and not do this.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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#6 |
Moderator
![]() Join Date: May 2007
Location: Southern Cal
Posts: 20,006
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Re: AAAHHHHHH!!!! Fuel problems
If you are only having problems as you increase RPM's and not at an idle, I would say you have an ignition problem. If it "surges" I would also suspect an ignition problem. Just my opinion
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#7 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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Re: AAAHHHHHH!!!! Fuel problems
It will rev fine in park with no problems. It revs fine under load, but then falls off like it is starving. I'll check out the ignition system and advance just in case.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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#8 |
Old Shovel Rider
Join Date: Oct 2007
Location: Rain City, WA.
Posts: 117
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Re: AAAHHHHHH!!!! Fuel problems
So, it's idling and revving normally with no load, right?
It sounds like it's doing it under load only...like hills, sudden acceleration, and passing? A little less advance on the timing might help performance under a load. How many degrees BTDC are you running? |
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#9 |
Son of a gun
Join Date: Jan 2007
Location: Hot Springs, Arkansas
Posts: 1,636
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Re: AAAHHHHHH!!!! Fuel problems
changing the needle and seat won't help the secondaries, is it a quardrajet? If so, sent the wind-up spring tension. The secondary flapper is probably opening up too early.
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Bill BEATERS ARE NEATER |
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#10 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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Re: AAAHHHHHH!!!! Fuel problems
The carb is responding right. The secondaries open up fine and stay open until it starts to stubble, then they shut down. I can make this happen without opening up the secondaries, and it had been running great. When it started doing this it was only doing it after holding the secondaries open for quite a while, then it started getting worse over a couple weeks. Now it will do it with moderate throttle, no secondaries. At highway speeds if I try to speed up just a little(60 to 70) it will start stubbling and surging like it is running out of gas. I can back off and cruise and then slowly build speed.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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#11 |
Hollister Road Co.
Join Date: Apr 2005
Location: Houston
Posts: 6,134
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Re: AAAHHHHHH!!!! Fuel problems
whats your fuel pressure. Sounds like it running out of gas.
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#12 |
Senior Member
![]() Join Date: Dec 2006
Location: Studio City, Calif.
Posts: 2,873
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Re: AAAHHHHHH!!!! Fuel problems
When I run into a problem like this that totally baffles me I've learned to not take ANYTHING for granted. If it was me I'd disconnect the fuel line at the carb and watch/measure the flow and also check the pressure. Check the accel.pump action while manually opening the throttle linkage and make sure it sprays.
Then I'd check the spark. Pull a plug and watch the quality of the spark. Then put a timing light on it and watch the advance.
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'69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme. |
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#13 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,275
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Re: AAAHHHHHH!!!! Fuel problems
I think it'd be a good idea to get the fuel pressure checked first.
And even though your fuel filters look good it is possible the pickup screens in the tanks are clogging up thereby restricting the fuel supply upon acceleration with a load on it.
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Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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#14 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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Re: AAAHHHHHH!!!! Fuel problems
I put a fuel pressue guage on it. I've done this before and it always bothers me, since the guage will drop down to almost no pressure. This is right at the carb and after the fuel filter. I'm not sure if the pump is suppose to read full pressure even at idle when it doesn't need the pressure. Either that or the guage is bad. The low pressure is one reason I replaced the fuel pump, but I had checked this in the past and it has always been this way. I get some wide spreads in pressure. If you rev it it really doesn't do much. The pump is pumping, since you can see it at the filter(clear plastic type).
I will pull the fuel line off and check flow rate. I was also thanking about pulling the fuel line off at the pump and blowing the lines out back to the tank.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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#15 |
Registered User
Join Date: Oct 2006
Location: Rock Hill, SC
Posts: 421
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Re: AAAHHHHHH!!!! Fuel problems
I had the same problem, it was the fuel pump, so I changed it and still had the same problem. After a lot of whining I replaced "THE NEW" pump with another and problem fixed. Bad pump. Good luck...
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1968 chevy shortbed, Dark Shadow Gray 4 bolt 383 Stroker,Weiand Super Charger, disc brakes, 9 inch, 391 gear, 20" Eagle wheels, muncie 4 speed/ Hurst shifter, 4/7 drop, Hedman midlengths, 3 inch exhaust w/ 2 chamber flows. 1966 Mustang with 306 roller, c-4, 9 inch Detroit locker rear. 1965 Fastback Mustang w/347 stroker, top loader 4spd, 9 inch detroit locker. 1966 Mustang coup, 306 roller, c4, 9 inch. 65 Cobra, 427, T6oo, 9inch, of course. First gen Hayabusa, airbox mod and running 2 exhaust cams.. Zoom Zoom Zoom |
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#16 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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Re: AAAHHHHHH!!!! Fuel problems
I hate to hear that. That pump is a pain to get off. If anybody needs to change the pump remember to use the trick of putting in a longer bolt in the bolt hole that lines up with the pump rod. It holds the pump rod in place so you don't have to mess with it.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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#17 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,275
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Re: AAAHHHHHH!!!! Fuel problems
Go with an AC pump and you may not have to do this again. I've never had any complaints with them.
__________________
Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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#18 |
Hollister Road Co.
Join Date: Apr 2005
Location: Houston
Posts: 6,134
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Re: AAAHHHHHH!!!! Fuel problems
If you have a 3 line pump plug the small return. It cleared up my problems.
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#19 |
Registered User
Join Date: Apr 2006
Location: Spring, Texas
Posts: 167
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Re: AAAHHHHHH!!!! Fuel problems
Fixed it. I had one fuel hose from the tank switch to the hard line that I did not replace when I was putting on new lines. It looked good at the time and still looks good, but the inside is goo. This new gas is eating rubber lines fast. I'm going to replumb all my lines after seeing this.
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'72 3/4 Cheyenne Super 402/TH400 Gear Vendors '72 3/4 Cheyenne Super 350/200R4 '50 1/2 Chevy 3 Window |
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