Weak fuel pump?

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Dusterdude72

Dusterdude72

IN MOPAR MUSCLE MAGAZINE
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Ok guys.....I am going to try to give you all a run down on things and see what you think.

I am thinking weak fuel pump or maybe some a little blockage in the fuel line PRE fuel pump.

72 duster.....I built the 67 318 for it...all new for the most part....its punched .030 over making it a 323,heads have been milled and block has been decked (not sure how much ...it was done by previous owner). it has dished poly styled pistons in it. mild cam,eddy performer series dual plane intake,eddy 1406 electric choke carb,long tube headers,2.5" dual exhaust all the way back,904 trans with 2500 tci stall converter,b&m pro ratchet shifter,4.56 gears out back in the 489 center sure grip 8 3/4,with 28" tall tires out back and some other odds and ends.

The engine only has about 6 or 7 hours of run time on it since I built it last year,everything is still new,I have set the timing,new points and condenser,points set,new plugs,wires,cap,rotor,new accel coil and so on and so forth....I know the ignition is up to par.

I have the carb tuned in and it works fine aswell.

it has a new mechanical fuel pump on it that came with the engine when I bought it .

now here is the deal.....

if I let the car sit for a week or two....sometimes it has a chance to lose fuel prime and it will not prime back up from cranking the engine over....IK have to dribble gas down the carb and THEN crank it....once it fires and spins over fast enough then the pump will prime the fuel system.

here is another problem ......when sitting at an idle I can look under the hood ( I am using a see through fuel filter right now so I can diagnose things easier) and the fuel filter bowl will be full with fuel...... however when I rev the engine....right around 4,000 rpm I can feel/hear a little hiccup/bogg in the engine (at this point in time you can look at the fuel filter and there is barely any fuel in the bowl of the filter and looks like its having trouble keeping up). ALSO when I put it in gear and break torque the car or even try doing a burnout from a stop.....for a second the engine will come on strong and then almost flatline at around 3,000 rpm and does not want to gain any R's....just sounds like it boggs down.

also if in gear and I tap the gas it will raise RPM's and then when I let of the gas the engine stalls.....almost like when I tap the gas it empties the fuel in the filter and when it comes down from its rev there is no fuel left for it to idle on.

it will do the same thing if I try to do a burn out and smash the gas and let off......stalls out.

and it normally takes a couple of cranks to fire it back up after it stalls (like it has to send fuel back up to the carb before it fires).

sorry for the big long explanation here guys and I hope you were able to follow along with what I am saying here.

it runs great it seems except under the conditions I mentioned above......which makes me think I either have a weak fuel pump and its not sending enough fuel to keep up with the engines demand OR maybe some scale from the tank made its way down the line and is sitting infront of the inlet on the fuel pump and restricting fuel flow.

what do you guys think?
 
I dont think the pump is the problem. Have you checked the sock inside the tank or the small hose at the sender ?
Easy way to test it... bungie cord a gas can to the open hood hinge, drop a length of hose from there to the fuel pump. If it works right from there , delivery from the tank is the problem.
 
RedFish said:
I dont think the pump is the problem. Have you checked the sock inside the tank or the small hose at the sender ?
Easy way to test it... bungie cord a gas can to the open hood hinge, drop a length of hose from there to the fuel pump. If it works right from there , delivery from the tank is the problem.
Click to expand...


It use to run fine....it just started acting like this not long ago and progressively got worse to the point it is now.

yeah I know the ole gas can trick....just wanted to get some opinions on it first before I go out and take it apart and get splashed with fuel lol.

but thanks for the input!

I also thought about disconnecting the feed line to the pump and capping off my vent line and try blowing air down the filler neck to build pressure and send the fuel down the line in the bucket to see if any gunk came out.

someone put a new tank and filler neck in the car at one point.

the car sat for a good 2 years....when I first put gas in it I seen some rust particles in my fuel filter but cleared up not long after.

Ill go through trial and error and save dropping the tank as a last resort if I have to.
 
Not relative to the current problem but I have to ask,
Why in the world are you still running a point ignition system ?
 
RedFish said:
Not relative to the current problem but I have to ask,
Why in the world are you still running a point ignition system ?
Click to expand...

Thats what came with the engine I bought and what my car was already set up for.

I plan on upgrading eventually......But I need to finish body work first.

Ill start driving it next spring most likely at which point Ill upgrade.
 
You could test your pump by running the gas line up front into an empty 2 gallon gas can, it should darn near fill it in a minute. I believe that pump you're running free flows at 125 GPH. If it does then the pump is probably OK.

Keep in mind if that tank is dirty, you're filter is only going to keep out so much. I just went through all of this in the spring. I dropped my tank, cleaned it well and blew the line. Even though I had changed the filter 3 times last summer with minimal driving, like 200 miles at the most, my rebuilt carb was full of junk in the bowls and throughout. I tore it down after cleaning the tank only to find a mess, so I had to clean it again and put it back on, now all is good.

One other thing you say you're level drops in the filter, is your tank vented? Have you tried running it with the gas cap off to see if it acts differently?
 
I still dont have a definite answer.
I have a see through plastic fuel installed and positioned higher than the inlet on the carb. At idle the filter will run nearly dry
( or should I say filled with air? ) Then the fuel pump begins to spit,spit, spit, until the filter is a little over half full. This cycle repeats again and again.
I'm not sure if the float level in the bowl is an issue or just the positioning of the filter.
I'll get back out there when the sun goes down.
 
OK, While screwing around with the height of the filter ( bending the metal lines ) of course the inlet fitting on the front of the 2 brl. broke loose. So grabbed another line wrench and snugged it up again.
When i started the engine the fuel filter filled to just over half way. So far so good until the engine loaded up and choked down. Now I have a fuel fog coming up out of the air horn. Bowl is running over. Turned the ignition off, smoked a cig' then took the fuel line and fitting almost all the way out of the carb. This back washed the needle and seat while dumping fuel on the intake.
Put it back together again and tad-ah, Its cured.
Fuel level in the filter doesn't change. Engine idles smother too.
All I need to do now is install a brand new filter.
 
RedFish said:
I still dont have a definite answer.
I have a see through plastic fuel installed and positioned higher than the inlet on the carb. At idle the filter will run nearly dry
( or should I say filled with air? ) Then the fuel pump begins to spit,spit, spit, until the filter is a little over half full. This cycle repeats again and again.
I'm not sure if the float level in the bowl is an issue or just the positioning of the filter.
I'll get back out there when the sun goes down.
Click to expand...

RedFish said:
OK, While screwing around with the height of the filter ( bending the metal lines ) of course the inlet fitting on the front of the 2 brl. broke loose. So grabbed another line wrench and snugged it up again.
When i started the engine the fuel filter filled to just over half way. So far so good until the engine loaded up and choked down. Now I have a fuel fog coming up out of the air horn. Bowl is running over. Turned the ignition off, smoked a cig' then took the fuel line and fitting almost all the way out of the carb. This back washed the needle and seat while dumping fuel on the intake.
Put it back together again and tad-ah, Its cured.
Fuel level in the filter doesn't change. Engine idles smother too.
All I need to do now is install a brand new filter.
Click to expand...

yours ran correctly though right? what you are saying you managed to fix was an air bubble trapped in the fuel filter....by cracking open the fuel line and reinstalling?.

carb is brand new and I have had 4 other carbs on it that were also new (1 was an eddy 600 I built then sold,then I had 2 summit racing carbs in a row that were defective....one was leaking fuel from the body and the other the electric choke did not work on,then I bought a new eddy 600 but the passenger side adjustment screw did not work so I sent it back and got this new eddy 600 that has worked great....I was getting tired of getting junk carbs there for awhile LOL).

I have my fuel filter sitting in the same place I have had them on any other vehicle in the passed and never had a problem.....sits just below level with the fuel inlet on the carb.

mine does like you are talking and "spit spit spits" inside the fuel filter when its trying to send out fuel.....but my filter bowl doesnt really ever fill back up unless I let it idle for a few minutes......when I rev it I can watch it run "dry".

I do not get the fuel vapor coming out of the carb like you mentioned.....I have NOT tried running it and letting things warm up and then shut it down and try cracking the fuel line open to "back wash" .....but I can give it a try and see what it does.

I havent had much time to mess around with it and do any trial and error work but I appreciate your help and throwing ideas out there for me to try!
 
In the end I was wrong. After all the sweating I had cured nothing. At start up the fuel filter will stay full for a while , just long enough to make a fool of me.
When the filter emptied again I noticed a faint knocking sound. A I thought it was coming from the front main bearing area. It is the fuel pump. Listening through a trans funnel confirmed it.
New Carter fuel pump already ordered at RockAuto.com. My total cost was 33.03
Happy moparing
 
RedFish said:
In the end I was wrong. After all the sweating I had cured nothing. At start up the fuel filter will stay full for a while , just long enough to make a fool of me.
When the filter emptied again I noticed a faint knocking sound. A I thought it was coming from the front main bearing area. It is the fuel pump. Listening through a trans funnel confirmed it.
New Carter fuel pump already ordered at RockAuto.com. My total cost was 33.03
Happy moparing
Click to expand...

AHA......well that makes me feel a little better about my first assumption of it being a weak fuel pump.

I however do not have the knocking sound coming from my pump that you mentioned you found on yours.

did your car run fine? any bogging or anything? or did you just have the knocking sound coming from the pump and seen it was not keeping your fuel filter full of fuel and decided it was time for a new pump based off those 2 things?.

On any other carbed car I have owned I can remember the fuel filter staying full......and I can visibly see the lack of fuel in my system.

so it either has got to be a fuel pump problem OR some sort of debris on the sock or restricting the flow at the pumps inlet.

ill mess with it sometime and find out for sure.
 
Just went through that. Got filter level, squirt etc. Tightened every clamp again; full filter.
 
green1 said:
Just went through that. Got filter level, squirt etc. Tightened every clamp again; full filter.
Click to expand...

Dont take anything for granted. It sure fooled me by working properly for a short while.
 
New fuel pump installed yesterday. No change. Took all of 15 minutes to snatch the top off the carb, pull float, needle seat, drian and clean bottom of bowl. No fault found.
I've just about decided to install a new filter that I can't see through.
My carpenters level doesn't give me trouble since I filled those little viles the rest of the way up . ROFL
Seriously though... I dont know where the air is coming from or how it draws nearly every drop of fuel out of that filter when the line is routed through its center.
 
How about temporarily adding another clear filter on the other side of the pump? That should show weather its a flow problem from the tank/sock/lines or a pump problem.
 
I called up an old friend last night to pick his brain. First he stated the factory used crimped band clamps on the rubber hoses then asked me if I see any of those clamps. "Yep at the frame rail where the steel line changes to rubber.
He proceeded to tell me a "Once upon a time, many years ago" story about a U-Haul Rental truck that kept failing with the renters.The guys in Texas had tried a lot of different things to fix it. Long story short, That hose was deteriorated.. It is pushed about a inch and a half over the metal line and the clamp sits back there near its end.
There wasn't any pressure so it wouldn't leak fuel at the overlap but..
With a little warmth and engine movement the fuel pump could suck air through it.
I know what I'll be doing later today . Fingers crossed. :)
 
This is more common than you think. My 440+6 did the same thing, the rubber fuel line from the tank had a crack on top that I couldn't see. The car would run once you got it started but would not draw fuel up to the carbs when it was cranking. Replaced the hose and it was instantly fixed.

Rod
 
I didn't mean to hijack this thread.
I still haven't found the fix. I might be closing in on it.
I finally crawled under the car and removed the fuel sender that was installed about 5 years ago. The sock is missing from the end of the tube. I wont know if that is/was the root of the problem until I reinstall with a new sock and the seal for sender to tank.
 
Where to get both strainer and seal, or at minumum a new seal ?
Link, part numbers, anything will help
 
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