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Old 02-03-2019, 03:14 PM   #1
smoking59
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Truck will not start

My 59 355 4bl was running fine then it just died. Put gas in the carb start then dies. Have 5lbs. of fuel pressure at the gauge . Carb was still in warranty so sent back. New Demon 625 doing the same thing? Took fuel lines off fuel runs out. Seeing how it runs when I put fuel in the carb wouldn't that eliminate an electrical problem ? So what am I missing? Got to figure it out before super bowl starts LOL????
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Old 02-03-2019, 05:19 PM   #2
Rickysnickers
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Re: Truck will not start

What kind of ignition system are you running? Is there an external fuel filter? If so, how long has it been since it was changed?
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Old 02-03-2019, 05:34 PM   #3
smoking59
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Re: Truck will not start

stock ignition, fuel filter only 3 months old with only a few hundred miles on it, but I was going to check it any way cause I am scratching my head here??
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Old 02-03-2019, 10:57 PM   #4
dsraven
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Re: Truck will not start

do a fuel flow test when cranking to see what the output is. run the line that supplies the carb into a jug so you can see what the flow is like when somebody cranks the engine over, mechanical pump. if electric pump turn on the ign and see what the flow is like. remember there is the electrical hazard and you have raw fuel so have a fire extinguisher handy and be careful. no smoking etc (yep, laugh, but it happens). when you hit the gas pedal a few times, engine off, do the accel pump nozzles squirt fuel? no squirt probably means no fuel in the carb.
if it starts with fuel dumped down the carb throat then it is likely not ign based but still could be. some systems have a start circuit and a turn circuit so if it starts then dies as soon as the starter is let go you could check for spark as well, but gotta do that after the starter is let go but before the rotation of the engine stops.
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Old 02-03-2019, 11:28 PM   #5
smoking59
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Re: Truck will not start

Thanks for the reply, that is the one test I have not tried, but wouldn't the fuel pressure be a lot lower if there is not good flow? Also I do not see any squirter gas. This is a demon carb.
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Old 02-04-2019, 01:02 AM   #6
dsraven
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Re: Truck will not start

if it is a carb it will have an accelerator pump. if not mistaken here, the 625 has the accel pump linkage right off the front corner of the carb where the main linkage to the pedal connects. the linkage will go to a lever at the top of the carb and that is the accel pump plunger below that. ensure the linkage is connected and the pump is operational when the linkage is moved with the accel pedal. if nothing comes out of the accel pump squirter when you pump the gas pedal then there is insufficient fuel in the carb, the squirter is plugged or the accel pump is bad. since it is a new carb I would have to say it is usually not the carb, especially when you had the same issue with the previous carb. if it is a used carb, and it ran well before, and not that long ago so the gaskets and rubber parts should still be in workable condition, and it wasn't tipped upside down so any old sediment sitting in the bottom of the fuel bowl got into the jets and orifices, then it should still be serviceable.

see page 11 of this demon carb manual for accel pump linkage adjustment and squirter nozzle identification location.

https://static.speedwaymotors.com/pd...structions.pdf

you can have pressure with little flow. it is the flow that will fill the carb when needed. pressure is a result of flow against a closed system, like when the float inlet needle shuts the inlet off. if you have a restriction somewhere you will get pressure even if the pump has a less than adequate flow. a small flow in a closed circuit will cause pressure. like putting your thumb over the end of a garden hose that is hardly flowing. sooner or later it will pressure up but as soon as you release your thumb there is a quick burst of residual built up fluid that will flow then it tapers off as soon as that is released.

first, check the fuel that comes out of the tank to ensure it is nice and clean and has a good flow. check the fuel lines all the way from the tank to the carb. look for suspect rubber lines, kinks or tight bends etc. if there is an inline fuel filter take it off and quickly drain the contents into a clean white container, like a yogurt container or the like. look for anything that isn't nice clean fuel. rusty stuff, water bubbles, etc. drain a bit from BOTH ends of the filter, not just the outlet. the outlet really should have nice clean fuel because it has been filtered. it is more the inlet side that will show you what the filter is dealing with as far as crud coming from the tank. also ensure the filter is installed the right way around for flow direction.

check the fuel cap to ensure it is vented properly. it is tough to get fuel out of a closed tank with no vent.

disable the ignition system so no spark can happen later while cranking the engine. remove the fuel line at the carb and attach a length of appropriate hose to reach a jug on the floor. I say "on the floor" because I have seen this system of testing go bad when the jug is accidentally dropped or the testing person didn't account for the fan turning and yanking the hose out of the jug. anyway, you get my drift. be careful, it's fuel around electrical stuff. have a buddy crank the engine over for about 30 seconds to do a flow test into the jug to see what the flow is actually like. you should get nice full bursts of fuel. a small flow may indicate a poor fuel pump. don't do a whole lot of cranking at one time or the starter can be damaged. 60 second bursts would be a lot at one time then the starter should be left alone to cool off.

if the pump passes the flow test, and since the fuel line is off anyway, now would be a great time to do a fuel pressure test. use a known "good" gauge and tight fittings for an accurate reading.

since the fuel line is off, and assuming there is little or no fuel coming from the accel pump squirters, it could be assumed that the carb is low on fuel so the inlet needle valve should be open. you could slip a clean length of hose onto the inlet of the carb and simply blow into the tube. if you come up against a dead head for pressure that would indicate the inlet needle is closed and there is an internal problem in the carb. if you blow into the tube and it seems to go somewhere and not build pressure then that would indicate the inlet needle is actually open and the carb is looking to be filled up. this scenario would indicate there is not fuel getting to the carb. fix that issue and you will likely have a running engine again. next would be to start tuning the new demon carb. the above link has a few suggestions for that if you read through it.

if you have gotten this far then you will likely already have your issue solved. hopefully it was the easy way out.
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Old 02-04-2019, 05:51 AM   #7
mr48chev
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Re: Truck will not start

Did you make any changes before or even during the last time you had it out? Or since the last time it ran right?

That can be anything.

New gas cap

Worked on unrelated wiring under the dash

Then how many miles have you put on the truck lately before this issue?

If the truck sat in the garage for over five or six months while you were working on it with gas in the tank it could be bad gas gumming things up.
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Old 02-04-2019, 10:34 AM   #8
smoking59
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Re: Truck will not start

Dsraven and Mr48chevy thans for the input some really great trouble shooting techniques that I was not thinking of, be tomm 5th before I can get back at it.
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Old 02-04-2019, 12:32 PM   #9
dsraven
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Re: Truck will not start

yep, bad gas can really mess with you. my mower won't even run right on last seasons gas. dump it while you are checking whats in your fuel filter, the line is gonna be off anyway. filters are cheap so stick a new filter on while you're there. you could siphon the tank down to near empty but that usually means a bad taste in your mouth, haha. hope you don't smoke after.......
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Old 02-04-2019, 03:03 PM   #10
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Re: Truck will not start

I am not sure if a fuel pressure gauge is even close to accurate if the engine isn't actually running.

As DSRaven said, change the fuel filter just as insurance. We don't know the build that well but if it has the original tank and the tank wasn't thoroughly cleaned while you were working on the truck you may have dirt, crud or trash in the tank. I pulled the tank off my 51 Merc after I got it back together because it was plugging fuel filters and among other things found the neck of a broken ketchup bottle in it. I've found shop rags, sheets of paper and a lot of other stuff that didn't belong there in tanks I have pulled off vehicles that came in with fuel feed problems.

That same Mercury would quit about 3 miles from the house acting like it ran out of gas because the "vented" gas cap I had installed (new cap) wasn't venting. The pump created a vacuum in the tank when it drew fuel out until the vacuum overcame the suction of the pump. 3 caps later I finally got one that worked.

The biggest problem we run into when troubleshooting is ASSUMING we assume that the problem is a certain thing and can't seem to get past that. Quite often our level of experience has nothing to do with getting past that point.

Troubleshooting has to be a somewhat orderly process of elimination.

You have to eliminate things from the list one at a time and go from there.
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Old 02-05-2019, 09:19 PM   #11
smoking59
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Re: Truck will not start

Well after taking my fuel line off at the carb, and having someone crank on it, I had really good stream of fuel. Hooked it back up and finally saw fuel coming out of the squirters. STill did not start. Took a spark plug loose to check and did not have any spark? So now lets have some tips on what/how I should check on my electrical system?I have a spare dist. that was working when changed out.
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Old 02-05-2019, 09:51 PM   #12
Rickysnickers
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Re: Truck will not start

What kind of distributor/ignition do you have? If it's an HEI, I've read that the ignition modules can fail. Here's link to Hemmings that describes ways of testing your HEI ignition.

https://www.hemmings.com/magazine/mu...I/1719426.html
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Old 02-05-2019, 11:45 PM   #13
dsraven
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Re: Truck will not start

if it is HEI,
-check for power at the plug on the distributor,key on.
-pull the coil cover off and check to ensure there is a ground strap in there from the coil steel body part over the plug in from the truck harness
-since the coil cover is off, check the ignition coil for heat discoloration marks
-pull the distributor cap off and check the underside to ensure there is a carbon conductor coming through the cap to contact the rotor
-check the rotor to ensure it is still all intact
-flip the cap over and check the electrodes for the spark plug terminals for corrosion pitting and general wear
-since the cap is off tun the engine by hand to ensure the distributor shaft is also turning when the engine turns
-with the cap off, check the wires that come from the pick up coil, that's the donut shaped thing in the bottom of the distributor. just give them a little tug, they shouldn't get longer. if they do the wire inside the insulation is broken.
-check the centrifugal advance while youre there to ensure it isn't siezed up or worn out
-next you will need to remove the ignition module from under the rotor area and either test it or replace it. there is some gel temp conductor that needs to go under the new one, like thick vaseline

so, distributor shaft turns when the engine turns and it has a star attached to it so the star also turns. the star turning inside the donut induces a pulse voltage in the donut and since the donut is wired to the ignition module it turns the module on and off, the module is the thing that replaces the points from the old style ignition so it makes the ignition coil power up and power off.doing this to an ignition coil induces a voltage in the secondary windings of the coil, which is basically a step up transformer, so there is enough voltage induced to fire a spark plug. this voltage is directed down though the center of the distributor cap through that carbon conductor mentioned earlier. the conductor contacts the rotor center electrode and is directed to a contact terminal on the outside ring of the cap, which coincides with a spark plug wire. BOOM. the plug fires.
ok, thats pretty basic, but if any of these things isn't right then you will get little or no spark. check the complete system
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Old 02-06-2019, 12:10 AM   #14
smoking59
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Re: Truck will not start

Thanks good article
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Old 02-06-2019, 12:49 AM   #15
smoking59
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Re: Truck will not start

Thanks, love the details, oh and I want to thank you also for the safety concerns on my fuel issues. The search continues...
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