Engine Starves for Fuel When I Hit Second Gear

[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.

[Old Yeller 1970]

Originally Posted by Rodms

Might want to look at electric also,

Choices, choices.

BTW, I lived in Ripley from 1994-1998 and Aberdeen/Amory from 1998-2006. Old Yeller and I have been through Olive Branch many times.

[Old Yeller 1970]

One more thought Marv. If a fuel pump isn't delivering any where close to its advertised pressure, why should one think it's delivering it's advertised GPH?

[Marv D]

First answer this... how much fuel per minute do you think a 5/16 line will deliver at 2psi?

[Marv D]

Second answer this,,, how long are you running the the motor at WOT before you feel it fall on it's face (Or in other words, how long does it take to pull through first gear if it's nosing over when you shift to 2nd)

[Old Yeller 1970]

Originally Posted by Marv D

First answer this... how much fuel per minute do you think a 5/16 line will deliver at 2psi?

That depends on whether it's free flowing or not. Free flowing should be a lot. But that's not how it works when attached to a carb so I don't know.

Originally Posted by Marv D

Second answer this,,, how long are you running the the motor at WOT before you feel it fall on it's face (Or in other words, how long does it take to pull through first gear if it's nosing over when you shift to 2nd)

I usually shift when I feel the engine start to fall off of it's torque which was around 5500 RPMS. It should be good for 6500 but I haven't taken it that high. I could do that in first and see what happens. I could also shift from 1 to 2 and wait a moment before nailing the throttle and see what happens.

[Marv D]

Now were gonna talk about break specific fuel consumption. I'm sitting here looking at two SBC dyno sheets, one my 666HP backup motor,the other the 797HP motor. Both have BSFC in the .47 to .50 range. (expressed in pounds of fuel per horsepower per hour)

Depending on the specific gravity of the fuel,, gasoline weighs roughly 6.3 to 6.5 pounds per gallon.


Here is a link to a wikipedia page on BSFC

Now you have everything you need to do the math but forgive me if I take a shortcut....

Go through the math and an efficient 800HP motor is burning roughly .1 pounds of fuel per second. Which makes sence,, I burn roughly a gallon of C-14 per pass.,,,, .1 gallon for 9 seconds not counting burnout etc.

Now lets reduce power to 400HP and make the motor horribly innefficient to a .6 BSFC

Still only going to burn about .05 pounds of fuel per second. or roughly 8 to10 tablespoons of fuel per second. HOW MUCH do the float bowls of that BG carb hold?????????

I wish you were closer, I have a couple of 3310's and a 4150 not in use, and a spare Mallory 140gph / deadhead regulator. In an afternoon we could positively find the culprite.

Now I want to know one more thing... what spark plugs are you running??? Do these heads require a 3/4" reach gasketed plug? Is that what your using?

[Marv D]

BTW, you can have fuel delivery with no pressure (as you said,, simply freeflowing out the end of the open tube) but you can not have pressure without delivery. Even at the car wash with the tiny orifice, the water is being delivered at high pressure, low volume, but delivery no matter. The same is true in your fuel system. If it's restricted with an orifice then sure, delivery would be WAY down. But the needle and seat is not much of a restriction. at least no more restriction at 2psi than it is at 10psi.

I'm gonna stand by my guns here and say even at 2psi you have delivery sufficient to carry a 400HP motor through 5 to 8 seconds. And more likely if the float bowls are full when you launch,,,, you have enough fuel to carry the motor WELL into 3rd gear and nearing the 12-13 second finish line before she starts to stumble.

Without a doubt I've been wrong before and could be very wrong here. But I think your 2nd gear issue is going to still be there when you replace the fuel pump. And don't get me wrong. I'm not saying 2psi is acceptable and that there isn't something wrong with your pump / fuel delivery. Just saying there is MORE going on than just fuel pump.

[Old Yeller 1970]

Thanks Marv, I'm glad to have the input. As for the spark plugs I don't know for sure how to answer your question. They don't have the tapered seat but have a flat seat with the washer. I'm unsure of the length. They are angle plug heads (not because I need them but because that's what was available.) The valves are 2.08/1.60. I've thought several times over the last year that the carb was suspect mainly because it does not fit the camshaft according to BG. The reason I got onto the fuel pump is because the PSI is obviously incorrect and I usually find that correcting something obvious fixes something less obvious. I'm leaving town tomorrow, and won't have any more time to work on it till next week. But I'll be here listening.

[Rodms]

Originally Posted by Marv D

BTW, you can have fuel delivery with no pressure (as you said,, simply freeflowing out the end of the open tube) but you can not have pressure without delivery. Even at the car wash with the tiny orifice, the water is being delivered at high pressure, low volume, but delivery no matter. The same is true in your fuel system. If it's restricted with an orifice then sure, delivery would be WAY down. But the needle and seat is not much of a restriction. at least no more restriction at 2psi than it is at 10psi.

I'm gonna stand by my guns here and say even at 2psi you have delivery sufficient to carry a 400HP motor through 5 to 8 seconds. And more likely if the float bowls are full when you launch,,,, you have enough fuel to carry the motor WELL into 3rd gear and nearing the 12-13 second finish line before she starts to stumble.

Without a doubt I've been wrong before and could be very wrong here. But I think your 2nd gear issue is going to still be there when you replace the fuel pump. And don't get me wrong. I'm not saying 2psi is acceptable and that there isn't something wrong with your pump / fuel delivery. Just saying there is MORE going on than just fuel pump.

Earlier you said it was not holding pressure,have you checked your fuel lines?If its any hole it can suck air as well,and your pressure will be low,I would think you should have 6 to 8 at the gauge before the carb.

[Old Yeller 1970]

Originally Posted by Rodms

Earlier you said it was not holding pressure,have you checked your fuel lines?If its any hole it can suck air as well,and your pressure will be low,I would think you should have 6 to 8 at the gauge before the carb.

In post #9 I experimented with pulling the gas tank line off the pump, installing a fuel line directly into a can of gas under my engine and still got the same low pressure.

[Marv D]

Let's go back to plugs for just a second. I looked up the heads. First they only list them with a 2.02 intake, not 2.08's but no matter. Everything I found says you need a 14mm gasketed plug w/ 0.72 to .75" reach.

The heads flow in the 230 range at 0.5" lift, with the cam let's assume your in the 375 to 400HP range. and have somewhere between 9.0 and 10.0 compression. (lot of assumetions but what else can we do)

You need a middle of the road heat range here. I'd HIGHLY suggest you use a Champion RC12YC plug (that's stock #71 for the parts counter jocky) or equavelent.

If Autolite is your favorite flavor,,, it's an 3923, or if you can find them the AC Delco FR3LS woulkd be the best plug IMPO, but it's all dependant on compression.

Too hot of a plug, or the wrong reach will cause symptoms exactly as you describe. I have seen too hot of a plug cause the motor to nose over and die at the top of 1st gear... just as using a short taper seat plug in a head calling for a 3/4" reach will not 'light the fires' when cylinder pressures come up (under WFO throttle) . I'd check those plugs for heat range and reach before you go any further.

If plugs are in order for the motor... THEN get back to why your registering such low pressure and what's wrong with the carb.

[Old Yeller 1970]

Originally Posted by Marv D

I'd check those plugs for heat range and reach before you go any further.

Roger WILCO.

You're correct about the heads calling for 2.02. But when we (my engine builder and I) assembled them, the 2.08s fit better so that's what we put in.

[Marv D]

and while were looking at the ignition... please tell me yuo don't have on of the MDS blaster2 coils the round stock looking coil painted red and made in mexico.

this one,,, http://www.jegs.com/images/photos/100/121/121-8203.jpg

if you do,, START by trying another coil

[383Ram]

Marv, i'll bite, whats wrong with those coils?

[Marv D]

I personally had 2 of them go over the hill and the first hint of a problem was a high rpm 'flutter', followed by spark scatter that drove me nuts. I would have just said I wasn't running a strong enough coil for the compression / cylinder pressures but we found the same thing in my buddy's 406. Around 5800-6000 it would start scattering, and dropping cylinders the rest of the pass. A new Mallory coil fixed his problem, I went to a HVC coil and not a hint of a problem since.

A little research and I heard many many stories of the same. I found the MSD Blaster 2 canister coil is made in Mexico, then shipped up here for the MSD packaging. It truly is a pig in a pretty dress.

Not that all things Hecho en Mexico has issues. Some of the most beautiful women in the world are from Latin America. Hell I should know, I married one! Wait a minute,, did I just say she didn't have 'issues' What was I thinking!!!!

[Old Yeller 1970]

Originally Posted by Marv D

You need a middle of the road heat range here. I'd HIGHLY suggest you use a Champion RC12YC plug (that's stock #71 for the parts counter jocky) or equavelent.

If Autolite is your favorite flavor,,, it's an 3923, or if you can find them the AC Delco FR3LS woulkd be the best plug IMPO, but it's all dependant on compression.

Currently the heads have Autolite 3923. Originally, I put in a set of Champion RC12YC plugs that fouled out while I was tuning the idle circuits. Then I put in a set of RC9YCs that fouled out while I was tuning the idle circuits. That led to the 3923s which fouled out once again while tuning the idle circuits only this time I cleaned them off with aluminum oxide sand paper and reinstalled them. I chanced to drive by an Autozone after church and they were out of the RC12YCs and didn't carry the AC Delco FR3LS plugs. I declined to buy more of the 3923s. If you think I need to, I can order the AC's or Champion plugs from my NAPA store tomorrow.
Edit: The few times I drove the truck before I had it painted, it was doing the same 2nd gear stall with the RC12YCs and RC9YCs. So I don't think that's the problem.

Originally Posted by Marv D

and while were looking at the ignition... please tell me yuo don't have on of the MDS blaster2 coils

I'm running the 50,000 volt coil that came in the cap of my distributor. It's a billet aftermarket unit manufactured in Australia, IIRC.

[djracer]

If the plugs got gas fouled they need to go!

[Rodms]

If [I] were you I would cross the plugs over to NGK[If you think its plugsthey are about the best to not foul.

[Old Yeller 1970]

As rich as my carb was running, nothing was going to prevent the plugs from fouling out. I ended up screwing the secondary screws all the way in and the primary screws are turned out only a 1/4 turn. The engine does die when I turn the primary screws all the way in so I figured there wasn't a problem with the power valve but it was incredibly rich to start with. I can at least stand to be in the garage with the door down without smothering in less than half a minute. It's fairly clean now for a Road Demon with such a relatively large cam profile and it burns clean enough it won't foul out again.

[383Ram]

If you have the secondaries shut and the primaries open a 1/4 turn, i am going to venture and say you have either a blown or the wrong size powervalve. Do you know what your vacum reading at idle is? and what size powervalve you have in there now?

Big overlap cams will "smell of richness" idleing, but that doesn't mean you need to turn the idle screws down so far as to possibly make it lean on the idle circut---unless the PV is just dumping fuel in, then obviosly its a tuning problem there.

Some engines like some plugs better than others, but you shouldnt be fouling any type of plug that quick.

[Old Yeller 1970]

The power valve is a 6.5 and the vacuum is 14. Everything I've read says you have to turn the idle screws ALL the way in and it still runs for it to be a bad power valve. It's the power valve that's not supposed to be able to blow out. Demon Carbs have a history of running rich at idle and the new ones have the idle eze baseplate to resolve it. I called BG about it and they said to run the ignition as far advanced as possible. Doing that also helped.

Like I said before it's not fouling the plugs now. Part of the problem was I was wanting it to idle at 600-700 RPMs and kept fiddling with it till the plugs would foul. When I finally decided to let it idle at 1000 RPMs I was able to get the idle circuit screws set right and haven't had a problem since. And BTW, when I turn the idle speed screw all the way in on either side it immediately dies.

I did get a set of NGK's ordered from my local NAPA today. They'll be in tomorrow.

[383Ram]

I know i said vacum at idle, but i forget not everyone runs a manual trans. So is that 14" at idle in park or idle in gear---either way, cam cant be that big to make that much vacuum. Either way it sounds your in the ballpark with the powervalve, i was just wondering---might be worth it to change it jus to make sure.

I haven't heard that Demons run rich at idle, of course i try to stay as far away as possible from them, they took a good basic design and really muffed it up IMO.

[cableguy0]

Demons are known for running rich. That thing should idle in park under 1k rpm.