Engine Starves for Fuel When I Hit Second Gear

[Old Yeller 1970]

After a forever restoration/rebuild project I'm finally getting Old Yeller out of the garage and back on the asphalt. No surprise I still have some bugs to work out and this one has puzzled me for a while. I'm running the engine described in the signature. The truck comes out of the hole hard but when I shift to second you can tell it isn't getting all the fuel it wants. It really falls flat and you can tell it's starving for gas

I have the fuel bowls set a little low right now and I'll raise them tomorrow but it was doing this when they were high. I have a Holley mechanical fuel pump that is rated for the HP of my engine combo. However, Barry Grant says a 625 Road Demon should have at least 6-7 1/2 PSI of pressure on it. Today I noticed (at idle) it was sitting around 2 1/2 - 3 PSI. This is the second Holley fuel pump I've had on the engine and I hate to toss out another one if that's not the problem. I wondered if the stock fuel lines could be at fault? Could they be restricting the flow? It seems like that wouldn't keep the fuel pump from delivering enough pressure at idle. I could also have an issue with the pump rod not actuating the pump correctly I suppose? Maybe I should ditch it and put on an electric fuel pump?

Two other items of note, the fuel tank is a new Blazer tank and new sending unit mounted under the bed. And BG says that with my cam I should be running a 650 Mechanical Secondary Speed Demon. If money were no object I'd buy one and bolt it on. But money is an object and I have to make do with what I have.

Here's a photo of the finished product.

[Marv D]

I surely wouldn't second guess an expert, but do a search about the BG carbs just about anywhere,, then tear it apart and see if it isn't full of macnining debris. The vacuum secondary is prefered on ANYTHING on the street by most everybody. I wouldn't go to a mechanical secondary till you had more proof you really needed one.
Might go over to nastyz28.com and search down BGtech and send him a PM. He is good people and will give you the straight skinny.

[383Ram]

I agree about the carb teardown. I would not trust anything about/from/advice from BG anyhow, but thats just me. If you find no debris in the carb, then i say start chking fuel lines if possible. Are they old and original? what size are they? You need a minumum of 5/16" lines, in my opinion, you cant go wrong with 3/8". How about the filter too? Thats a simple check and change also. Pull the pump and check the ends of the pushrod. If you can get a light in to see, see how the lobe on the cam looks. If all of this turns out to be good, i would do the following. Go get a generic stock pump and put it on---see if the pressure comes up at all. It is not going to be enough to power through all the gears, but you need 6.5-7 psi just to start with idleing before you can get down through the gears. 2-3 psi is not going to cut it at all.

If all else fails or you decide you just want to switch to an electric, that can be done also. I am one of those guys that doesn't mind the buzzing of a Holley blue pump,, some cant stand the noise. Areomotive makes a nice entry pump too, i personally don't like the Mallory stuff, but again, thats just me.

[cableguy0]

3/8's line is needed. the 350 came factory with 3/8's line because its needed for the volume required. your pressure is definately way too low even for idle. you should be around 6-7psi thats the sweet spot usually for holleys and the bg carbs are basically a glorified holley. same exact design he was sued multiple times by holley and lost. your issue definately lies in the fuel pump area though. on a heavy street truck vac secondary is the way to go no need for mechanical.

[Old Yeller 1970]

Thanks for the responses everyone. I did a tear down on the carb after the engine rebuild and thoroughly squirted every orifice with carb cleaner and compressed air. So I know there's nothing in the carb causing this. I spoke with two mechanics over the weekend, one said I may have something blocking the fuel line and the other said I could be sucking air from a leak. The first thing I'm going to do is figure out why I'm not getting enough fuel pressure and I bet that will solve everything else. My plan is to take the gas tank line off the pump, put on a short line and stick it into a can of gas and see how the pressure looks. I'm heading out the door to do it right now. I'll be back in about an hour with a report.

[cableguy0]

if it was sucking air it would also be leaking fuel. the pickup sock could be clogged also a fuel filter could be clogged but since im gonna assume everything is new i would be suspect of the fuel pump.

[Rodms]

You should be getting enough pressure,but if it falls on demand,Pump,fuel line,You will have to check pressure when in a load and see what it does.Carb just change jets!

[djracer]

Truck looks nice. Good luck with the fuel issue.

[Old Yeller 1970]

Originally Posted by djracer

Truck looks nice. Good luck with the fuel issue.

Thanks dj

OK here's the report.

I pulled the fuel tank line off the pump and installed a temporary line down into a can of gas. Still got 3 PSI. The problem is not in the line to the fuel tank.

Took the filter out of the carburetor fuel rail and with the line still in the gas can. 3 PSI. Problem is not a clogged filter.

Took off the fuel line between the pump and carb and blew through it. Air moves freely. Problem isn't there either.

Took the fuel pump off the engine and examined the pushrod. It shows no signs of wear.

Held the push rod on the cam with my finger while engine was cranked. Push rod moves back and forth like it's supposed to. Problem is not with the cam lobe.

That leaves only a brand new Holley Fuel pump as the culprit. What I don't get is this is the second one I've had that's done this. The original Holley was on the truck when it was stock and as I recall it never put out more than 4 1/2 PSI either. It didn't matter to the stock engine and was never an issue. It was an issue after the rebuild and so I put this one on thinking the problem should be corrected. I did have to take it apart to get the angle on the fittings to line up right with my fuel lines. I wonder if I screwed something up? I'm pretty meticulous and don't think I would have put something back the wrong way but I wouldn't rule it out at this point. And maybe Holley just sux at building fuel pumps.

[cableguy0]

pull it back apart make sure everything is in its place and that you didnt rip the diaphram. you probably figured out your own problem

[383Ram]

If you find it is the pump, try one of the Carter mechanical high performance pumps. I have had much better luck with them over the Holley pumps.

I also beg to differ about 3/8" line being needed. I don't know what GM put on trucks stock, but i have seenn plenty of people go 12's on 5/16 line---although i personally don't recommend it, because i'd rather know for sure fuel is high in supply and getting to the engine. Its just simple flow principles on the volume delivered vs volume needed to feed an engine. Just a FYI

[cableguy0]

a 350 will also run with a 300cfm carb but just because you can doesnt mean you should or that its proper.

[Old Yeller 1970]

Originally Posted by cableguy0

pull it back apart make sure everything is in its place and that you didnt rip the diaphram. you probably figured out your own problem

Yeah I'll do it tomorrow its gotten late.

Originally Posted by djracer

I would try a different pump next time.

Agreed!

Originally Posted by 383Ram

If you find it is the pump, try one of the Carter mechanical high performance pumps. I have had much better luck with them over the Holley pumps.

I'll give it a look.

[djracer]

I would try a different pump next time.

[Old Yeller 1970]

I disassembled the fuel pump this morning and there's nothing wrong with the diaphragm. I'll give Holley credit for making it thick and durable looking even if it is a POS. Since I don't see anything wrong with the diaphragm, I'm going to get another fuel pump. Based on 383Ram's suggestion I looked at the Carter fuel pumps on Jegs and the Jegs fuel pumps on Jegs. Knowing that Jegs re-badges stuff from other manufacturers I thought they looked remarkably similar. Have a look and see for yourself.
http://www.jegs.com/i/JEGS/555/15960/10002/-1#
http://www.jegs.com/i/Carter/180/M4891/10002/-1

The Jegs is $54.99 110 GPH @ 6.5 to 8 PSI with a 3/8" NPT inlet/outlet. And would reuse the 3/8 fittings I already have.

The Carter is $77.99 and rated at 120 gph @ 8 psi 1/4" outlet/inlet.

What do you think?

And one more thing. The Jegs has a pretty Chrome finish instead of aluminum finish like the Carter- you know that's an important factor for making HP.

[cableguy0]

I betcha 5 bucks all of those pumps jegs holley and carter and made by the same place. the carter pump is just an unfinished as cast. the jegs and holley are identical in specs and look.

[Old Yeller 1970]

Dang it you're right. The Jegs is a dead ringer for my Holley.

[383Ram]

Call Jegs and see if they can tell you whose pump theirs is.

But at this point, i'd still pay more for the carter based on my good experience with them and my poor experience with the holleys. Just my two cents.

[Old Yeller 1970]

Going by the cast, the Holley, Carter and Jegs all came out of the same mold. I looked at the Summit brand pump and it's also the same.
http://www.summitracing.com/parts/SUM-250020-1/
That doesn't mean all Carters and Holleys etc are from the same plant but these have to be.

Two more that are different from the above but just like each other are the Edelbrock and Mr. Gasket fuel pumps.
http://www.summitracing.com/parts/SU...1/?image=large
http://www.summitracing.com/parts/MRG-7716/?image=large

[383Ram]

I still vote Carter.

Let us know what you get.

[cableguy0]

for the most part there are very companies that actually make a lot of parts. for example a fuel pressure regulator from edelbrock is a holley regulator with the holley stamp ground off. edelbrock carbs are cast by weber.

[Marv D]

The one question no one has asked yet,, what fuel pressure gauge are you using that says it's only 2psi? The one common denominator here and I didn't see anything saying the gauge was verified. I will say this,, if it's an autometer with an isolator so you can read fuel pressure inside the cabin,, your kidding yourself if you think it is anywhere near accurate. But typically those show low VERY low when cold, and pressure increases as underhood temps rise.

OK, I'm going back to you have a CARB problem, not a fuel delivery problem. Without getting into a peeing match here, I will promise you that 2psi of fuel pressure in 5/16" will keep enough fuel in the float bowls to get you through 2nd gear. And backing up,,, I will tell you for absolute fact that you can run to nearly 1/2 track under WFO throttle with a 600HP small block before you run out of gas with the fuel pumps OFF. The BG float bowls are not any smaller than a Holley 4150 so at very WORST I'd say your at the 1/8th in high gear before it starts starving. Also think about this. A 5/16" line with 2psi of pressure IS fuel delivery. So your going to make it past 1/2 track pulling in high gear before it drains the float bowls. So,, running out of fuel pressure...... I'm not going to buy it.

WHY you have low fuel pressure?? I don't know and I wouldn't be concerned at this point till you have your carb issue straightened out.

Try this,,,, borrow a KNOWN working Holley and slap it on the truck for a few test passes. See if it's the CARB, or fuel delivery. I bet a dollar to a donut that although you do indeed have something showing low fuel pressure, that is NOT why it's falling on it's face in 2nd gear.

I hate to try and compare apples and orangutans, but I'm right in line with 383RAM and here is a FACT. I'm sure DJ and some of the other quicker guys that data log can verify the same scenario. My smallblock Nova dyno'd 797HP, runs 9.teens at 147 and I use a single Mallory 250GPH pump with an-8 fuel line. When I launch I drop to 1.5 to 2psi of fuel pressure. It recovers to 3+psi 2.5 seconds into the pass. It is not until 8 seconds that the fuel PSI ever recovers to 5.5psi or above. And I am NOT starving for fuel anywhere along the pass.

So... I again say. BORROW A GOOD WORKING HOLLEY CARB and watch your 2nd gear problem magically disappear.

[383Ram]

VERY good point about the gauge. I only use under hood type gauges and i rarely use any external gauge to see what its actually doing for a pass--unless there is a problem. I just always set it for idle and forget about it---mainly because if it MPH's good down track, i know its making power and getting good fuel to the motor. And i guess what i assumed about the gauge should have been asked.

I do know you are also very correct about the pressure dropping off the line then recovering down track. My experience shows a mechanical pump (typical holley or carter) will push 4-6psi by the end of track. Obviously there are always going to be exceptions.

But, while 2-3 psi at idle is fuel delivery as you say, and i also agree that you can get quite far down the track with just the fuel in the bowls, right now my belief is that the 2-3 psi is probably next to nothing by second gear. Its just my gut feeling and i have no proof, so i am not going to start peeing around here either.

So i guess my next question is to the OP, what are your next steps to figure this out?

If it were me, id plumb that gauge into something that has known good fuel pressure to see if its the gauge---of course this will work much better if you have a friend that has a working gauge in their car for comparison---or go buy a cheap check gauge from the store.

If possible, i second the carb swap. I never owned a BG carb, but everyone of the 5 i have touched to try and tune for others always still had issues--they look nice, but thats about it in my opinion.

I can only assume your gauge is near the carb inlet. If this is the case, and you tried the other things, then try a new pump.

Let us know the details.

[Old Yeller 1970]

Originally Posted by Marv D

The one question no one has asked yet,, what fuel pressure gauge are you using that says it's only 2psi? The one common denominator here and I didn't see anything saying the gauge was verified.
So... I again say. BORROW A GOOD WORKING HOLLEY CARB and watch your 2nd gear problem magically disappear.

I thought about the gauge and tested it but didn't post the results. What I have is an adjustable Summit fuel line with the gauge on the filter. All my readings are from under the hood right off the gauge. I took it off and drained my air compressor down to nearly nothing and used the rubber tip of my air gun to blow into it. As far as I can tell the gauge is working accurately. It will swing up to the max at 15PSI and looked to be the same as the gauge on my compressor below that.

I thought about throwing another carb on the the truck, specifically a Holley 750 VS but I can't afford to buy one except with my credit card. I asked the local drag racing guru if he had an extra one and he didn't. Keep in mind I live in a county of 900 sq mi with less than 8000 people in it so there's not to many people to go to around here. [Edit: Notice in the picture above there is absolutely nothing in the back ground. That's not some photoshop wizardry. There really is nothing here. ]

If it's the carb and not the fuel pump, then tell me why the carb ran great when it was on the engine when it was stock. It made a huge difference over the QJ. I didn't change anything in the carb (other than turning in the four corner idle screws) when I put it on the new engine. What is different is way bigger heads, way bigger cam and way bigger HP. This engine definitely want's way bigger gas and it's not getting it.

Curiously I noticed after I parked it that the fuel in the bowls was slightly below the bottom line. I had set it at the middle line. After cranking the engine it came back up to the middle line.

Originally Posted by 383Ram

So i guess my next question is to the OP, what are your next steps to figure this out?

I guess I'm going to buy a $60 pump or a $260 750 Holley if Marv talks me out of the pump.

One last thing. I was looking at a different brand pump last night and read through the installation instructions for that pump. After repositioning the body it said: "Before fully tightening these screws, the rocker arm must be actuated to and held in the “full stroke” position. This is done to ensure that the diaphragm will be pulled to and held in its maximum working (flexed) position while the retaining screws are torqued tight (20-25 in/lbs.). This procedure will ensure against premature diaphragm wear and subsequent failure due to over-stretching of the diaphragm material when in the full stroke position. Another by-product of an improperly set diaphragm is erratic fuel flow and pressure. NOTE: This procedure can be assisted by holding the fuel pump in a vise or appropriate fixture, and holding the rocker arm down with a pipe or similar tool."

I thought what the heck, pumps are pumps I'll try it on mine and see what happens. After re-installing it on the truck my PSI nearly went through the floor whereas it had been 2 1/2-3 it was now no better than 1 1/2.

[Rodms]

Might want to look at electric also,sounds like holley blue and reg would work fine with your stock lines and ajust the pressure.