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Fuel Starvation

Posted By: GTXKen

Fuel Starvation - 06/10/09 02:01 PM

I rarely post in the race forum but I think this the best place for this one...

I think I have a fuel starvation issue. I am running a carter M6903 with 3/8 fuel line through a 40 micron Russell in line filter from on my 500 inch stroker motor. Stock style fuel tank and pickup. Carb is a Quickfuel 830. It pulls fine up until about 4000 RPM and then it falls flat and bogs down completely until I let off the throttle.
Like I said I think it’s a fuel issue but maybe I’m wrong. If it is a fuel issue where do I start troubleshooting? How do I check a mechanical pump? I don’t have a fuel pressure gauge in the car, just one on the carb.

Thanks
Ken
Posted By: Challenger 1

Re: Fuel Starvation - 06/10/09 02:04 PM

Maybe hookup a temp fuel pressure line at the carb and put the gauge temp somewhere where you can see it when the car falls off?
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 02:09 PM

I think a gauge is in order. If pressure falls off at 4k that dosen't mean its the fuel pump though right, just that its a fuel issue for sure?
Posted By: MR_P_BODY

Re: Fuel Starvation - 06/10/09 02:09 PM

Quote:

Maybe hookup a temp fuel pressure line at the carb and put the gauge temp somewhere where you can see it when the car falls off?



or if you have jets you can jet it up 2 or
3 jet sizes... if it does the same thing its more than
likely a supply issue
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 02:12 PM

Quote:

Quote:

Maybe hookup a temp fuel pressure line at the carb and put the gauge temp somewhere where you can see it when the car falls off?



or if you have jets you can jet it up 2 or
3 jet sizes... if it does the same thing its more than
likely a supply issue




I have jets, I'm running 80s and 88s now and have a very minor bog at 1200 RPM. Are you saying jetting could be the issue?
Posted By: MR_P_BODY

Re: Fuel Starvation - 06/10/09 02:17 PM

I have jets, I'm running 80s and 88s now and have a very minor bog at 1200 RPM. Are you saying jetting could be the issue?



If its super lean it can be... if you can jet up and
not have it slow down its a supply thing(keep jetting up)
but at those jet sizes I dont think its the problem
Posted By: emarine01

Re: Fuel Starvation - 06/10/09 02:17 PM

Nappa sell flex gauge extentions, if you can find a spot to run the gauge where you can see it you can troubleshoot
Posted By: savoyracer

Re: Fuel Starvation - 06/10/09 02:25 PM

Quote:

I rarely post in the race forum but I think this the best place for this one...

I think I have a fuel starvation issue. I am running a carter M6903 with 3/8 fuel line through a 40 micron Russell in line filter from on my 500 inch stroker motor. Stock style fuel tank and pickup. Carb is a Quickfuel 830. It pulls fine up until about 4000 RPM and then it falls flat and bogs down completely until I let off the throttle.
Like I said I think it’s a fuel issue but maybe I’m wrong. If it is a fuel issue where do I start troubleshooting? How do I check a mechanical pump? I don’t have a fuel pressure gauge in the car, just one on the carb.

Thanks
Ken

Sure sounds like a fuel delivery problem. in my humble opinion everything you have is way to small for a 500 inch motor. you also might have another self-inflicted problem. If I were you, I would cut open my oil filter, and get a magnifying glass, and look in the pleats for brass. If it is there, time to put new bearings in it. Inadequate fuel delivery will cause a lean condition, which can take out bearings. not saying that it has happened yet, just saying you should look at it.
Posted By: Anonymous

Re: Fuel Starvation - 06/10/09 02:27 PM

I would think that the pump/line setup is your issue...A stock tank pickup with a 3/8" line and a mech pump pulling for fuel is asking alot to supply a 500cu.in. motor with a big carb. I would suggest a small electric pump (Like a Holley Blue) to push the fuel up to the mech pump. Install a regulator between the pumps to limit pressure to 6.5-7.0 lbs. This will insure constent fuel supply to the mech. pump..It is better to push the fuel rather than pull it...This will correct you problem and wiring the pump t the ignition will make it as stock as possible. (No switches to remember to turn on).I have seen this problem several times on street/strip cars...poppaj

Attached picture 5283703-04-108.JPG
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 02:40 PM

A fuel pressure gauge is certainly in order. I'll stop by napa but I doubt mine will have what I need. The engine hasn't spent much time near 4000 so I don't expect I've done any harm.

The pump was suspect to me, any way to check a mechanical fuel pump or is it all or nothing?

I'll look into adding an electric pump at the tank. I heard the Holly blue was really loud, not that my exhaust won't be louder, any other good pumps?
Posted By: hemi-itis

Re: Fuel Starvation - 06/10/09 03:06 PM

A stock pump will not feed the hungry animal You can start by checking volume and pressure.But imho a fuel system upgrade is in order.
Posted By: emarine01

Re: Fuel Starvation - 06/10/09 03:16 PM

Just a thought, you may want to run it till the bog and shut down and pull the plugs, no money spent just a little time & go from there
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 03:17 PM

Quote:

I would think that the pump/line setup is your issue...A stock tank pickup with a 3/8" line and a mech pump pulling for fuel is asking alot to supply a 500cu.in. motor with a big carb. I would suggest a small electric pump (Like a Holley Blue) to push the fuel up to the mech pump. Install a regulator between the pumps to limit pressure to 6.5-7.0 lbs. This will insure constent fuel supply to the mech. pump..It is better to push the fuel rather than pull it...This will correct you problem and wiring the pump t the ignition will make it as stock as possible. (No switches to remember to turn on).I have seen this problem several times on street/strip cars...poppaj



Sounds like this is where I will be headed, is my (all new) 3/8 line big enough? Holly wants the regulator by the carb. I assume that you suggest putting it between the pumps because my mechanical dosen't require a regulator and we don't want the electic fuel pump over powering the mechanical pump?
Posted By: BobR

Re: Fuel Starvation - 06/10/09 04:45 PM

Quote:

Quote:

I would think that the pump/line setup is your issue...A stock tank pickup with a 3/8" line and a mech pump pulling for fuel is asking alot to supply a 500cu.in. motor with a big carb. I would suggest a small electric pump (Like a Holley Blue) to push the fuel up to the mech pump. Install a regulator between the pumps to limit pressure to 6.5-7.0 lbs. This will insure constent fuel supply to the mech. pump..It is better to push the fuel rather than pull it...This will correct you problem and wiring the pump t the ignition will make it as stock as possible. (No switches to remember to turn on).I have seen this problem several times on street/strip cars...poppaj



Sounds like this is where I will be headed, is my (all new) 3/8 line big enough? Holly wants the regulator by the carb. I assume that you suggest putting it between the pumps because my mechanical dosen't require a regulator and we don't want the electic fuel pump over powering the mechanical pump?



I would advise you to throw the mechanical pump in the trash and replace it with a BG HR220 electric pump. This pump has a return style regulator which is needed for street driving. Using an electric to feed a mechanical is not a good idea. If the diaphram in the mechanical fails you could get fuel pumped directly into your motor. I don't use cam driven mechanical pumps for anything.
Posted By: mikemotorhead

Re: Fuel Starvation - 06/10/09 05:03 PM

"you also might have another self-inflicted problem. If I were you, I would cut open my oil filter, and get a magnifying glass, and look in the pleats for brass. If it is there, time to put new bearings in it. Inadequate fuel delivery will cause a lean condition, which can take out bearings. not saying that it has happened yet, just saying you should look at it"

I assume you mean from missfires pounding the bearings??? If so I think it would take a lot of this to cause bearing failure!
Mike
Posted By: B3422W5

Re: Fuel Starvation - 06/10/09 05:07 PM

My guess is that its a pickup issue in the tank..


Few years back i was running low 11's with stock tank, mech pump and a 3/8 pickup..

I always left the tank full...one time i raced the car with 1/2 tank of gas in it and ran into same symptoms you are dealing with.(fuel sloshing around uncovered the pickup)

As others have stated, a cell and electric pump would solve your problems, but putting one of those sump/pickups in the bottom of your stock tank might well solve it as well....
Posted By: sixpackgut

Re: Fuel Starvation - 06/10/09 05:14 PM

i have a 1/2" pickup in stock tank with a mallory 140 pump and return style regulator. works great

-8an lines for both supply and return
Posted By: Anonymous

Re: Fuel Starvation - 06/10/09 05:41 PM

Quote:

Quote:

I would think that the pump/line setup is your issue...A stock tank pickup with a 3/8" line and a mech pump pulling for fuel is asking alot to supply a 500cu.in. motor with a big carb. I would suggest a small electric pump (Like a Holley Blue) to push the fuel up to the mech pump. Install a regulator between the pumps to limit pressure to 6.5-7.0 lbs. This will insure constent fuel supply to the mech. pump..It is better to push the fuel rather than pull it...This will correct you problem and wiring the pump t the ignition will make it as stock as possible. (No switches to remember to turn on).I have seen this problem several times on street/strip cars...poppaj



Sounds like this is where I will be headed, is my (all new) 3/8 line big enough? Holly wants the regulator by the carb. I assume that you suggest putting it between the pumps because my mechanical dosen't require a regulator and we don't want the electic fuel pump over powering the mechanical pump?



Exactly Ken, it will supply the mech pump with fuel without over running it. MSD makes a nice quiet inline pump that would be perfect for your car, and it is only $100. poppaj
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 05:45 PM

Quote:

Quote:

Quote:

I would think that the pump/line setup is your issue...A stock tank pickup with a 3/8" line and a mech pump pulling for fuel is asking alot to supply a 500cu.in. motor with a big carb. I would suggest a small electric pump (Like a Holley Blue) to push the fuel up to the mech pump. Install a regulator between the pumps to limit pressure to 6.5-7.0 lbs. This will insure constent fuel supply to the mech. pump..It is better to push the fuel rather than pull it...This will correct you problem and wiring the pump t the ignition will make it as stock as possible. (No switches to remember to turn on).I have seen this problem several times on street/strip cars...poppaj



Sounds like this is where I will be headed, is my (all new) 3/8 line big enough? Holly wants the regulator by the carb. I assume that you suggest putting it between the pumps because my mechanical dosen't require a regulator and we don't want the electic fuel pump over powering the mechanical pump?



I would advise you to throw the mechanical pump in the trash and replace it with a BG HR220 electric pump. This pump has a return style regulator which is needed for street driving. Using an electric to feed a mechanical is not a good idea. If the diaphram in the mechanical fails you could get fuel pumped directly into your motor. I don't use cam driven mechanical pumps for anything.



I can see where using both an electric and mechanical pump cpould be a problem. Before I jump to an electric fuel pump I need to remove any other issues there may be.
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 05:57 PM

Well, thanks for the replys

I really need to do some troubleshooting here before I throw money at more parts.

I have a checklist...

Pull the outlet side of the pump hose off and use the started to see if its putting out the fuel it should.

Pull the fuel pickup in the tank and see if there is anything clogging it or if its possible it could colapse.

Check the lines and connections for any obstructions or leaks.

Check the tank vent.

Check the stator to rotor clearence to see if its a spark issue at speed.

Check the powervalve size.

Make a run without an air cleaner (new)

Finally, get a fuel pressue gauge. This will take the better part of an evening, if anyone has any other ideas let me know.

Thanks again
Posted By: dOOc

Re: Fuel Starvation - 06/10/09 06:04 PM

What type of AIR FILTER are you trying to run through ? ... if any.
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 06:07 PM

Quote:

What type of AIR FILTER are you trying to run through ? ... if any.



K&N 14x3, I could do a run up to 4000 without one to eliminate that as a variable.
Posted By: hemi-itis

Re: Fuel Starvation - 06/10/09 06:23 PM

Quote:

Well, thanks for the replys

I really need to do some troubleshooting here before I throw money at more parts.

I have a checklist...

Pull the outlet side of the pump hose off and use the started to see if its putting out the fuel it should.<<<<<<<>>>>>>>>

Volume check off starter only is not enough,the car should run for 20 seconds on what is in the fuel bowls.Check with car running
Posted By: dOOc

Re: Fuel Starvation - 06/10/09 06:29 PM

Quote:

Quote:

What type of AIR FILTER are you trying to run through ? ... if any.



K&N 14x3, I could do a run up to 4000 without one to eliminate that as a variable.



A 14x3 on a 500 inch motor ? ....

Yes .. try a shot WITHOUT an filter. Or at least double-stack them.
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 06:36 PM

Quote:

Quote:

Well, thanks for the replys

I really need to do some troubleshooting here before I throw money at more parts.

I have a checklist...

Pull the outlet side of the pump hose off and use the started to see if its putting out the fuel it should.<<<<<<<>>>>>>>>

Volume check off starter only is not enough,the car should run for 20 seconds on what is in the fuel bowls.Check with car running



Better idea, I can do that
Posted By: GTXKen

Re: Fuel Starvation - 06/10/09 06:39 PM

Quote:

Quote:

Quote:

What type of AIR FILTER are you trying to run through ? ... if any.



K&N 14x3, I could do a run up to 4000 without one to eliminate that as a variable.



A 14x3 on a 500 inch motor ? ....

Yes .. try a shot WITHOUT an filter. Or at least double-stack them.



If I double stack them I will have to pull off the hood, as it is I have maybe 1/4" clearence between the lid and the hood. I'll do a run without but if thats the issue I don't know how to get more air filter under there.
Posted By: challenger70

Re: Fuel Starvation - 06/11/09 04:20 AM

Quote:

Quote:

Quote:

Quote:

What type of AIR FILTER are you trying to run through ? ... if any.



K&N 14x3, I could do a run up to 4000 without one to eliminate that as a variable.



A 14x3 on a 500 inch motor ? ....

Yes .. try a shot WITHOUT an filter. Or at least double-stack them.



If I double stack them I will have to pull off the hood, as it is I have maybe 1/4" clearence between the lid and the hood. I'll do a run without but if thats the issue I don't know how to get more air filter under there.



K&N makes a filter lid http://www.knfilters.com/universal/X-stream.htm I have a spare HR 220 what fuel doesn't leak out might help your possible fuel starvation issue
Posted By: GTXKen

Re: Fuel Starvation - 06/11/09 02:55 PM

I did a couple of the easy items last night...

Pulling the air filter had no impact whatsoever

The fuel pump is pumping within spec

The tank vent is clear
Posted By: dOOc

Re: Fuel Starvation - 06/11/09 03:03 PM

Fuel pressure ?
Posted By: emarine01

Re: Fuel Starvation - 06/11/09 03:04 PM

You can try pulling the linkage off the back side if the carb and run on the front 2 bbl , may help you with fuel volume or squirter problems
Posted By: GTXKen

Re: Fuel Starvation - 06/12/09 03:35 PM

Quote:

Fuel pressure ?



Fuel pressure at idle and under no load is fine, it stays steady as I open the trottle as well but this is under no load, the only fuel pressure gauge on the car is under the hood.
Posted By: moper

Re: Fuel Starvation - 06/12/09 04:18 PM

Rig up something so you can see a gage while you drive it. I rigged a simple mechanical gage up into my car for this before. It's fine for a testing prurpose, but take it out if you do any real driving. It sounds to me like it might be something else, but do those tests first and see what results. You should be moving enough fuel for what you have.
Posted By: GTXKen

Re: Fuel Starvation - 06/12/09 04:27 PM

Quote:

Rig up something so you can see a gage while you drive it. I rigged a simple mechanical gage up into my car for this before. It's fine for a testing prurpose, but take it out if you do any real driving. It sounds to me like it might be something else, but do those tests first and see what results. You should be moving enough fuel for what you have.



I need to figure out how to do that. I was hoping to rig it outside the car but its not going to happen, maybe a temporay fuel pressure rig inside would be a good idea, maybe vac too?
Posted By: JimG

Re: Fuel Starvation - 06/12/09 04:29 PM

Another easy test:

Make sure the float level is correct, find a stretch of deserted road, hold it wide open until it falls on it's face then turn the ignition off immediately, without letting up on the throttle. Coast to a stop and check the float level again. If the bowls are dry, you just eliminated a bunch of stuff on your checklist.

Jim
Posted By: GTXKen

Re: Fuel Starvation - 06/12/09 05:18 PM

Quote:

Another easy test:

Make sure the float level is correct, find a stretch of deserted road, hold it wide open until it falls on it's face then turn the ignition off immediately, without letting up on the throttle. Coast to a stop and check the float level again. If the bowls are dry, you just eliminated a bunch of stuff on your checklist.

Jim



I can try that tomorrow, I will be on some back country roads. If the bowls are empthy after this test I just prove there is a fuel problem but it doesn't help me identify where the problem is right.
Posted By: GTXKen

Re: Fuel Starvation - 06/12/09 05:22 PM

Quote:

Quote:

Rig up something so you can see a gage while you drive it. I rigged a simple mechanical gage up into my car for this before. It's fine for a testing prurpose, but take it out if you do any real driving. It sounds to me like it might be something else, but do those tests first and see what results. You should be moving enough fuel for what you have.



I need to figure out how to do that. I was hoping to rig it outside the car but its not going to happen, maybe a temporay fuel pressure rig inside would be a good idea, maybe vac too?



Moper, I'm thinking a couple 1/8 npt fittings and a length of hose and I can move the gauge from under the hood to under the dash. You said you think it may be something else, care to take a stab?
Posted By: JimG

Re: Fuel Starvation - 06/12/09 06:47 PM

Quote:



I can try that tomorrow, I will be on some back country roads. If the bowls are empthy after this test I just prove there is a fuel problem but it doesn't help me identify where the problem is right.



Right, it simply tells you that you're running out of fuel, but tells you nothing else.

It will, however, eliminate things that have been discussed such as improper jeting, air filter, wrong power valve, etc.

Jim
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