More fuel related issues, now the pump!

[747mopar]

Well fellas I feel like I've finally zeroed in on my setup to where everything is in harmony or at least until this issue popped up.
I just wanted to pick your brain on fuel delivery mostly the pump. I have an issue, I'm running out of fuel during full throttle runs where I'm hammering down for long durations. Yesterday I put a fuel pressure gauge in the window in hopes of getting it to repeat but no luck but during a long full throttle pull I did get the fuel pressure to drop from 5.5 to under 2 so even though I didn't get it to repeat the issue I feel there's definitely an issue with pressure. I'm running a QF 750 so it shouldn't require a ton of fuel and am running a 3/8" sending unit, line and a Holley mech fuel pump. I don't want an electronic pump so are thete any other good options that have threaded ports and not just barbs? I'll be checking fuel lines and hoses before I purchase a new pump.

 

[kjalltrac]

Have you checked the float and fuel level in the carb?

 

[dla4567]

I run a carter M6903, high volume/ low pressure. Has threaded ports. It might be worth looking into.

 

[4spEd]

I have the same fuel setup on my 440, I ran in to similar problem, I changed pickup to 3/8, changed pump, the item that finally solved it was hose from pickup to hard line, it was of smaller dimension, and it had a sharp bend as well.

 

[747mopar]

Well fellas I feel like I've finally zeroed in on my setup to where everything is in harmony or at least until this issue popped up.
I just wanted to pick your brain on fuel delivery mostly the pump. I have an issue, I'm running out of fuel during full throttle runs where I'm hammering down for long durations. Yesterday I put a fuel pressure gauge in the wi dow

Have you checked the float and fuel level in the carb?

Yeap, floats are good.

 

[747mopar]

I run a carter M6903, high volume/ low pressure. Has threaded ports. It might be worth looking into.

I'll look at that one, I was very disappointed when the Holley pump showed up in a Made in China box.... or maybe it was Taiwan??

 

[747mopar]

I have the same fuel setup on my 440, I ran in to similar problem, I changed pickup to 3/8, changed pump, the item that finally solved it was hose from pickup to hard line, it was of smaller dimension, and it had a sharp bend as well.

That's one of the area's I want to look at before I buy a pump, that hose could be soft or pinched? Also gonna make sure something didn't smash the hardline. My system consist of a hose connecting the sender to hardline then a compression fitting adapting the hardline to AN fitting with everything else being AN all the way to the carb with braided hoses. Also already changed the fuel filter which was fine.

 

[kjalltrac]

Once me and my brother had a similar problem with our barracuda 69,
Finally we put some air pressure in the fuel line and sprayed soapy water on the entire fuel line under the car, and sure enough there where tiny bubbles coming from one location on the fuel line.
The pump sucked some air from that tiny crack. changed the fuel line and all went good.

 

[747mopar]

I'll be looking for leaks but it has a new aluminum fuel line..... wonder how that ethanol reacts with the aluminum?

 

[747mopar]

I run a carter M6903, high volume/ low pressure. Has threaded ports. It might be worth looking into.

I see they're made in the USA, might go with the CRT-M4862 if that is indeed the cause of the problem. Thanks

 

[747mopar]

Another question if I go to a high psi pump I'll need a regulator, running a return fuel line to the tank helps keep the fuel cooler as well correct?

 

[Cranky]

I'll be looking for leaks but it has a new aluminum fuel line..... wonder how that ethanol reacts with the aluminum?

It's corrosive....even the 10% crap goes bad a good deal quicker than 100% gas but it shouldn't be acting up with a new line at least not yet. What's the rpm when you it acts up? Where is your fuel gauge connected and do you run a regulator? Also, does your fuel line run close to the exhaust anywhere?

 

[lewtot184]

the only mech pump i've ever had issue with was a holley. i'm a die-hard for the carters, but sometimes they have issues too. i do take the 6903's apart and mess with them. i have a carter 4862 that i've bench tested and it's a real gusher; a gallon in 30 seconds. the 4862 will need a regulator that will work with a pulse pump. i don't know your power level but almost always needle and seat size is over looked. most people think bigger is better but i have my doubts. sometimes the floats can't control the bigger sizes, and that can lead to flat spots and low pressure.

 

[747mopar]

It's corrosive....even the 10% crap goes bad a good deal quicker than 100% gas but it shouldn't be acting up with a new line at least not yet. What's the rpm when you it acts up? Where is your fuel gauge connected and do you run a regulator? Also, does your fuel line run close to the exhaust anywhere?

It acts up right around my shift point (6,000), when it does you can feel the motor falling off like it's running out of gas.... take your foot off and wait a couple seconds and it's normal again. I had vapor lock issues before but it didn't matter the rpm whereas this only happens at long full throttle pulls. I've insulated all the plumbing near the headers (mounted to the frame rail about 2" from header) and it fixed the previous issue, fuel pressure is being read from the T in the carb plumbing and I'm not running a regulator (this fuel pump is designed to not require one and runs 5.5-6 psi).

 

[747mopar]

the only mech pump i've ever had issue with was a holley. i'm a die-hard for the carters, but sometimes they have issues too. i do take the 6903's apart and mess with them. i have a carter 4862 that i've bench tested and it's a real gusher; a gallon in 30 seconds. the 4862 will need a regulator that will work with a pulse pump. i don't know your power level but almost always needle and seat size is over looked. most people think bigger is better but i have my doubts. sometimes the floats can't control the bigger sizes, and that can lead to flat spots and low pressure.

HP is only a guess, I studied several dyno tested builds and would guess I'm in the 500 hp range. I wouldn't think the needle and seat would be an issue with a Q series QF, it's a choke delete race carb? Even if it isn't the pump I'll be buying Carters now, not at all happy with Holley's import status.

 

[Gpuller]

I run the M6903 too, to problems. 1/4npt female ports.
Have you checked the pump push rod length?
The 10% ethanol hasn't hurt your aluminum line.

 

[69 GTX]

I agree with G puller

 

[747mopar]

Had an interesting talk with someone who's been at it a long rime and has a bit of inside info. According to him the pumps used to use a 3/8" NPT but because customers kept over tightening the fitting they were breaking the casting so instead if making a beafier casting they all started making the threads 1/4" restricting the flow. Because the pump now is restricted it causes the diaphragm to work harder and not last as long? His suggestion is to buy a Carter, disassemble it and drill and tap it to a 3/8" NPT.

 

[69 GTX]

That's why I bought the Carter, 3/8 NPT.

 

[747mopar]

That's why I bought the Carter, 3/8 NPT.

So you can buy the 3/8"? I'll have to do some looking.