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1985 chevy PU wont run after warmup
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rkptrobert
New User
Aug 25, 2012, 10:15 AM
Post #1 of 11
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1985 chevy PU wont run after warmup
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Hello, I have a 1985 chevy PU with a rebuilt 350 engine ( probable not original and most done by a home mechanic in OK. ) The carb is just a basic 4 barrel with most vacuume lines plugged and kinda rigged up, but ran great for the first 4 months I got it down here to south texas. I drove it down from OK at highway speed and up to 85mpg and it even got 16 mpg. It then began acting like it was running out of fuel when you pushed down too hard on the pedal. as long as you eased into it I could get it up to 60mph and cruise fine, just could not open it up or it fell on its face. I noticed it was much worse towing my boat, now it has gotten worse, It runs ok when you first start it, you can wing it on up and it sounds great, but as soon as it warms up a little (or I assume the electric choke goes off) it will only idle, as soon as you try to rev it up it sputters and dies. I have changed the fuel filter and checked the fuel pump (which is mechanical) and seemed to pump great. When you wing it and it dies it wont start again until you pour fuel down the carb but the filter is still full right up to the carb. I have new plugs, cap and rotor but cannot see them causing this type of problem, got them just for preventive maintenance before all this started and have not put them on yet. Any ideas what I should try next. I need the truck to haul trash into town ect.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 25, 2012, 1:07 PM
Post #2 of 11
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Re: 1985 chevy PU wont run after warmup
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This will be wide open to possible problems but sounds like lack of proper fuel delivery. It's a bit tricky but you can get an in-line fitting for the 5/8th flare nut at the fuel filter or at the pump to see actual fuel pressure live while running.
Probably won't find that gizmo so just get a plain fuel tolerant gauge and see pressure from removed line at carb with a fuel tolerant hose to a real low pressure fuel gauge. DUH - watch out for raw fuel spilled!
If pressure is probably 4 to 6 psi that's good but guessing at that spec for now.
Then it should with longer rubber hose be able to pour out volume. This is shade-tree but a glass jar and see how fast it can fill it. It should put out a pint or so in just 'say' 15 seconds +/-.
If this carb is from a much older 350 with no electronics except a choke heater wire say so and I should be able to describe other reasons it could starve for more fuel,
T
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rkptrobert
New User
Aug 26, 2012, 3:42 AM
Post #3 of 11
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Re: 1985 chevy PU wont run after warmup
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Started it last night and drove it around the property to move it out of the way of our other cars. Cold it reved up and sounded good. as soon as it ran for about 3 minutes or so and I tried to rev it up and it started to go up on rpms and then just died. I tried to start and nothing, I opened the hood and the clear inline fuel filter right by the carb was completely full of fuel. I pulled the top off the air cleaner, poured a little gas down the carb and it started and ran untill it ran out of that fuel. I am beginning to think I have trash in the carb and when the choke is on it pulls more fuel. As long as I dont try to rev it up it will idle ok even warmed up, but I will try the fuel pressure first before tearing into the carb. Thanks for the advice.
Robert
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rkptrobert
New User
Aug 26, 2012, 3:45 AM
Post #4 of 11
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Re: 1985 chevy PU wont run after warmup
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Forgot to say I did the jar thing first and it filled it up pretty fast and when I put my thumb over the line it forced it out with what I thought was plenty of pressure, but will still try the presure guage if I can gather one up.
Thanks again
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rkptrobert
New User
Aug 26, 2012, 3:54 AM
Post #5 of 11
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Re: 1985 chevy PU wont run after warmup
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I have one more queston, if it turns out to be a carb overhaul, the kit and cost to rebuild is pretty high now a days and I have not done one in almost 20 years. Not sure if it is like riding a bike and would all come back to me. I have been rebuilding outboard and small engine carbs up to last year, but nothing lile the old quadrajunk. lol. Found a used one online for $45.00, would anyone take the chance on the used one sitting on a shelf for who knows how long or just suck it up and try to rebuild mine. Cant afford to pay someone, but I could do the swap out for sure. It is just an old fishing truck and does not have anything connected to it except one vaccuume line, and the elec choke. All the rest have been plugged off and all the rest of the lines come off a fitting on the intake manifold. Kinda been rigged when the rebuilt the motor, but used to run great.
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Tom Greenleaf
Ultimate Carjunky
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Aug 26, 2012, 4:36 AM
Post #6 of 11
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Re: 1985 chevy PU wont run after warmup
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Actually "Quadrajets" are very high ends carbs when all is exactly right and that's the issue. They are intolerant of being messed with and one adjustment wrong causes others to be wrong. They made many brand new all wrong! Owned several brand new on new Chev 350s to boot.
Check choke pull off. Front one is most important. Note that rear will not open until choke on front two smaller barrels is wide open via rods that some are bent to adjust or screw adjustment.
It like cold apparently so choke as a circuit is operational and since it reacts to priming up when acting up the fuel isn't getting thru presumably inside with clogged something.
If you've done these before you know to watch your step but can take just the top off with it in place. It may have a muddy bottom in float bowl or who knows but probably need to look.
New, all fuel filters were right on the carb not a clear something in line but still a good idea now as the smaller filter couldn't hold much dirt. The use of alcohols in fuel now is creating problems with intolerant materials in fuel systems plus it suspends junk in the gas rather than just let heavier junk fall to bottom of tanks - mostly the source where the fuel comes from where you buy it more than the vehicles. Not blaming anyone but now the filtering of the vehicle is primary.
I'll probably fail to find a nice diagram and spec for adjustments but you should know the carb # embossed on driver's side towards rear on middle of the housing. Look for something like 17051234 -- all #s for just an example. I might actually still have specs for it on paper.
Just for my info can you see the two idle mixture adjustment screws or are there metal plugs still over them? Those plugs were so you couldn't play with the idle mixture and can be removed with the carb off vehicle and I'll wait on how to if you need to go there as with plugs on you can't clean out those ports with those needle valves covered up which are in there.
Not here constantly but a lot. Can work with this carb hopefully as it behaved before so something was right. A used one is a total unknown so let that wait a bit,
T
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Hammer Time
Ultimate Carjunky
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Aug 26, 2012, 5:33 AM
Post #7 of 11
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Re: 1985 chevy PU wont run after warmup
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Has anyone verified that there is sufficient fuel supply coming into this carb?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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Aug 26, 2012, 7:43 AM
Post #8 of 11
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Re: 1985 chevy PU wont run after warmup
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HT - Seems to be at carb but uncertain how much gets in so far. Now I wonder about some silly things like the aftermarket filter installed backwards or absence of the OE one now after that or if missing if that plays into this. Some had check valve some didn't and some real old ones were brass packed pellets that people would just light on fire to burn off dirt (not dependable way) to clear those up. There may be a problem right there. Can't know without some investigating.
Other + Warning: OP (original poster) don't use Teflon tape on any of those threads for fuel filter. Lost several hours cleaning that shredded stuff out of jets and no solvent known to me will dissolve it!
T
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Hammer Time
Ultimate Carjunky
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Aug 26, 2012, 8:07 AM
Post #9 of 11
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Re: 1985 chevy PU wont run after warmup
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I think it's totally premature to be talking about carbs until someone has done pressure and volume testing on the fuel supply coming into the carb.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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Aug 26, 2012, 8:35 AM
Post #10 of 11
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Re: 1985 chevy PU wont run after warmup
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Some gets in if it starts cold and that's where it ends - reason unknown so far. IDK - I'd have a good look inside OE filter, pressure and flow known then have the top off for a look??
T
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nickwarner
Veteran
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Aug 26, 2012, 6:13 PM
Post #11 of 11
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Re: 1985 chevy PU wont run after warmup
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I would agree that you need to verify proper fuel supply first before condemning the carb. But a q-jet isn't the worst thing to work with, just have to do it by the book. Tom was right about them not being a bad carb, although by design not much good for anything other than a stock vehicle as vacuum controlled throughout.
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