Help with possible fuel starvation issue

[Will__L]

prostreet 68 c-10...with a 498 bbc...with 750 dominator...the issue i found is that from a dead stop if i mat the throttle (it just blows the tires off) but if i stay in it after a couple seconds (of blowing the tires off) it will die shut down. The first time i did it, it completely shutoff. The second time i caught it peddled it a few times and saved it from shutting down. If i go from a 20-30 mph roll it will not shut off. I just recently tuned the truck on a friends chassis dyno jetting through the curve is pretty close to perfect. Other than that the truck runs and drives very nicely. I was thinking maybe i need to move to long body main jets or maybe floats are a little low or both? i just found this issue because i never floor it from a dead stop...BTW i was doing this in a safe area...

[shortbed70]

Sounds to me like fuel is running out the vent tubes and flooding the motor. Jet extensions or vent tube extensions is my guess but I'm no carb guy.
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[Blue Rat]

What kind of carb? Floats to high on holley or too much fuel pressure. Just a guess.

[Marv D]

Who's carb? box stock Holley HP, QUick Fuel, CarbShop, Prosystems...???

There is a Holley guy that frequents the engine and drivetrain section, I'll go send him a PM and see if he will drop in on this... but I (not being much of a carb guy) would have to agree with what's been offered already.
BUT,, if you tuned it with the floats well below the site hole, you may find yourself looking for some more dymo time. I've always had issue with the holleys when the fuel level was too low. Once it's 'right' and fuel pressure / flow is 'right... the whole carb seems to be 'different' and you start from scratch with the jetting / pump shot / squirters / bleeds etc.

My 'always the best solution' resource is to put it in a box, send it to:

PRO SYSTEMS
1879 S. Wolf Lake Rd.
Muskegon, MI 49442

And tell Patrick to live test and let you know when it's all fixed up.

Buyt in th emeantime, why don't you lay out how the carb / fuel system is set up, (Squirters, jets, linkage, fuel line size fuel PSI etc....)

[Will__L]

Sumped aluminum fuel...holley black pump…screen type filter…-8 fuel line all the way to the engine…dead head regulator at 6psi holley dominator…74 main jets all the way around 71 idle bleeds 36 hi speed bleeds …40 pri and secondary squirters…only had to make 3 runs on the dyno afr was perfect across the board off the trailer
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[BigDan3131]

So what size hose from the sump to the filter/pump? Is that 6psi at idle? Do you have a fuel gauge inside the cab? I'm thinking that its sucking the bowls dry and or you need more pump shot. My idle pressure is much higher at 9psi but it doesn't overflow the bowls so at WOT its at 6psi. Is there no return/bypass in the system?

[Will__L]

Very short length of -8 from sump to pump…pump is at same level as sump…dead head system…truck ran perfectly on the dyno…af stayed rock solid through 6k…but that was on the the dyno with no inertia or g forces acting on the fuel in any part of the system…i can roll in to the throttle and it has no issues its just from a dead stop
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[prostreetC-10]

Ah yes.......the 750 dominator. I'm guessing it's an 80186? It's the Dominator that both Holley and I can't understand why it was ever made in the first place. Dominators usually start where the 4150s run out....which is 1050+ cfm. All I can do is a little arm chair on this over the computer. One thing we know is that chassis dynos do not simulate real world driving. You are in drive and you mash the throttle up against the chassis resistance. When you mash on the street, you go through 1st, 2nd, 3rd and so on......running through a few fuel curves. Someone help me out here but the mapped fuel curve in drive with a constant resistance is different is not like driving on the street. This is why carbs can run great on an engine dyno and then buck and snort when tested on the street.

Without riding in the rig, it's hard to tell if it's dying from too much gas (flooding) or running out of gas. Does this carb have a power valve(s)? Assuming you have the stock 50cc accel pumps, you are WAY TOO BIG on the shooters. IT should be 28 front and 35 rear. Stock jetting is 70 squared. That doesn't mean that your 74 is not right for your application but the squirters "should" be throwing it pig rich when you lean into it. If those float are adjusted just right and too low, it will hold in the dyno and run dry on a street mash.....especially on that big lung. Jet extensions will not cure this problem and are usually only used at the track when cars are leaving ultra hard and the G's throw the gas to the back. Granted, the subject and get quite technical of fuel fighting the effect if G's in the carb and line for that matter but that is not your issue.

Depending on the regulator, you really shouldn't be dead-heading that thing. Ideally, you run a return or bypass style regulator and you run it off to the side (like on the end of a log or something else like that). If this is a holley type 803 regulator, you need to realize that even running -20 lines, that fuel has to go through the restrictor in the reg which is about .220 just off my head. That's like running 1/4 fuel line!!! Combine that with floats too low and you will run 'er out of gas in no time. Let me remind you again I am arm chairing this and just giving you ideas to look at. By running a return regulator off to the side, it now acts as a turbo waste gate and only bleeds off pressure when the blades close and that fuel hits needles trying to close. Now under full throttle, the regulator is not a restrictor and the fuel gets to travel through the actual size of the fuel lines.

Hope this helps a little. Do you know if your linkage is progressive or not?

[Marv D]

500 inches is thirsty no doubt,, but it not running dry rolling into the throttle vs jabbing it at idle does seem a bit strange. Uncovering the rear jets seems the most likely suspect, but that should hit almost instantly after launch, not seconds downtrack.

2 things come to mind,, With a dedhead regulator and an-8 line you have a buttload of fuel that wants to sit still right there at the starting line. I log fuel pressure and the larger the line, the more weight that wants to rush BACKWARDS to the cell. With a Mallory 250 pump, an-8 to the vacuum boosted regulator and return,,, I see the PSI drop to 2psi for a good second.
The black pump is a 120GPH pump at carb PSI.,, it 'should' keep up with a 550-600HP motor easily unless there is issue with fittings.

If you feel the fuel delivery is good, only logical suspect is uncovering rear jets. It's wierd that it does it later in the pass, but ,, well if these things were easy....


I'd make absolutely POSITIVE fuel level is correct, double check fuel PSI with a GOOD gauge (not one of those little 1" on the fuel inlet things, I've seen them totally out to lunch both directions)
If so,, Add the jet extensions (and the correct float to clear them) . It's probably the cheapest.



Some of these carbs have been bastardized 10 ways from Sunday. Jetted square you either have NO powervalves, or PV's in both primary and secondary. 74 jets seem kinda small for no PV's. But if AF was 12.8 at WOT under load,, it is what it is and who cares what # they are.


{EDIT}
See I knew he couldn't resist a invite ona carb issue LOL,, he just typed a heck of a lot faster tham ne old pfhat finger.

[prostreetC-10]

Marv....I could be wrong but I didn't get the feeling it's a track truck. Maybe it is. Uncovering the jets is usually a pretty violent shutting down because the motor is pulling hard right at the time of starvation. I sure wouldn't want to drive any Holley on the street without a power valve. If they are plugged, the usually starting point is to jump up 6-8 sizes from stock. Altitude comes into play too. I'm at 3,500 ft so the already box stock rich Holleys are even richer where I am. For liability reasons, Holley will usually be a tad rich at sealevel just so they are not leaning someone's motor out right from the box.

[Will__L]

the truck is not a track truck...power valves front and rear they are both 2.5's and brand new

[Will__L]

the truck is not a track truck...power valves front and rear they are both 2.5's and brand new... anything less than 40 nozzles and the motor stumbles transitioning into the secondaries. i do agree that there is a difference between making runs on a dyno and real world street driving/runs. tuning on a dyno unless you speed ALOT of time on it looking at different variables and running through different scenarios is really just a good way to tune for WOT. which is all i really was wanting to see was if the WOT fuel was good the way i set it... which it was 12.8-9 solid across the board to 6k...with no lean spikes or lean tip in..or even a slight leaning out at the top...what im considering doing is since i have the carb off and apart anyway is to change to a set of fuel bowls with glass sight plugs so i can very accurately set float levels... throw in a set of jet extension in the rear with the proper float for them..change the current plumbing that consists of the pressure line to a deadhead that is attatched to one side of a "T" that then runs to the bowl to plumbing to the reg then out the reg with 2 equal length -8 lines going to each bowl...as well as uprading to a better reg and throwing a rebuild kit in the holley black pump i have at the moment for good measure...any reccomendations on good regulators or plumbing layouts are always appreciated

[Marv D]

The best article I've ever seen on fuel systems is Sam Solace's 'Fuelish Tendancies' over at centuryperformance.. Sam believes in overkill as do I,, but this is one of those thigs where it's cheaper to do it once, right.......

http://www.centuryperformance.com/fu...endencies.html

[Will__L]

That was a really great read…thanks for the link
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