[RocktimusPryme]

Took my 67 to the drag strip for the first time. Things did not go as planned. About the only positive thing that happened was I put down a 1.9 60’ on value section hard Futara street tires.

Basically the thing would run out of gas and fall flat on its face about 300 feet. So I never even got in a good 330’ time, let alone am eighth or quarter. It was disappointing. It would fall flat, then if you got back into it it would pull then surge again.

I made one change, and then got back in line. Told myself if it ran out of fuel again I would just coast it out so I didn’t hurt it. It did, and I did. Thus ended my day.

I have a RobbMc 550 pump. A 1/2 pickup, and 1/2 lines all the way up. Stainless up the side, and then -8 an to the pump and carb. No return line.

Also afterwards while I was troubleshooting my cruise was getting leaner and I could hear pinging pulling away from stops at light throttle. It has never done that before so changes need to be made for sure. The fact that it’s getting worse does make m believe that something is going bad. I’m going to call Robb and send him the pump so he can go through it. Maybe it’s that easy.

I started a siphon out of the pickup and it flowed out freely so I don’t think the pickup is cracked. Robb has mentioned that I might have air getting in a line when I asked him about the fuel draining back causing long starts. But I’ve looked everywhere and saw no evidence of leaks.

So I’m going to get the pump looked at. And I think I’m going to grab some 1/4 hose and make a vapor return line. It was hot, maybe vapor lock was a contributing factor. Is there anything in the Q-jet I should look at?

Also I’m considering adding a pusher pump on a switch just for the track and cold starting. What’s a good bang for the buck electric pump? I know a lot of you guys run both electric and mechanical.

I did get one suggestion that the factory steel line route has too many bends in it and can cause issues. But I feel the pusher would solve that if it was a problem.

[johnta1]

What fuel regulator?


Gas tank vented?

[RocktimusPryme]

Originally Posted by johnta1

What fuel regulator?


Gas tank vented?

Vented cap, no regulator. Robb’s 550 doesn’t require it. If I buy an electric I suppose I may have to plumb a regulator in.

[steve25]

You may have 2 issues going on here!

One issue is fuel pressure and fuel volume loss due to the G force of a launch at the track.

With a 2G leave from the starting line the fuel pressure will drop .3 psi for every foot of fuel line and since you have no pusher pump back at the tank your relying on the pressure from whatever amount of fuel you have in the tank being applied to a 1/2 hole in the pick up, and as you might guess that small 1/2 hole cuts back on the weight of the fuel and its pressure sitting on it a bunch!

Also if your running that crappy regular Blue Holley regulator just note that the neeedle and seat in that is smaller in flow area then the combined area of the needle and seat from the primary and secondary items in a Holley Carb!

Your pinging while accelerating from a stop could be a whole bunch of possibilities!

[RocktimusPryme]

It’s all new though. The problems I mean. I have launched from a stop on deserted roads and pulled hard easily through an eight using a GPS tracker.

It’s never pinged before. And the only other time it has lean surged like that was about a week ago after a U turn. So all recent. I didn’t think much of the U turn thing at the time. Now that I have some confirmation events I think that was the beginning of a problem.

Even the long starts I feel are newish.

That said I will solicit advice on a good part for the money on a regulator too.

[Scott65]

How much fuel was in the tank? If less than half a tank, easy enough to try it again with 3/4 full and see if the problem persists.

[RocktimusPryme]

Originally Posted by Scott65

How much fuel was in the tank? If less than half a tank, easy enough to try it again with 3/4 full and see if the problem persists.

It was probably somewhere between those two numbers. It was over 1/2 for sure.

[Chief of the 60's]

What carb?

[RocktimusPryme]

Originally Posted by Chief of the 60's

What carb?

800 cfm q-jet by SMI custom for my engine.

[Chief of the 60's]

Ugh

[Formulas]

Check your timing make sure distributor is tight

So many ignition issues are blamed on the carb and sometimes carb issues are blamed on ignition

Doesn't hurt to nail down the cheap and easy things so you KNOW what it's not

.

[HWYSTR455]

I've heard a number of people have issues with the RobbMC pumps, both the 550 and larger one too. Just saying.

Vented caps not only don't work well, but I've seen many that 'say' they are vented, and aren't, or aren't vented enough. To be sure, you HAVE to run a proper vent.

When you go to a 1/2" line, you can actually increase your chance of vapor lock, that 'column' of fuel in the lines is larger, as well as the surface area of the line, to absorb heat.

So, one principal of vapor lock is due to fuel psi. When that fuel in the line is under psi, there is less of a chance of vapor lock. The more psi, the more resistance to vapor lock.

Guess what? With a mech pump, the fuel in the line is under suction/vacuum, and that increases the chance of vapor lock.

Return line, they help tons. Sure you can reuse a vapor line, but it only 'helps', and you need a total solution.

Best way to handle a fuel system is to do it right, and you only have to do it once. Wish I had a dollar for every time I've heard someone fighting a fuel system. So many times people fight having to replace the lines or run new ones, and by the time they are done, have spent at least twice the money if they would have immediately gone to a correctly executed system, not to mention the frustration and some times, damage. Going thru lines, wraps, crappy pusher pumps, trying every mech pump out, you name it.

Long story short (yeah, I know, too late!), 1/2" feed and return, quality regulator as close to the carb as possible, and a good electric pump. I've seen since the tank isn't baffled, with the Robb pickups, you still have issues, and need to run a half a tank at the track, at least.

External pumps can overheat, even the best ones out there, so in tank pumps are better in staying cool (which also means they last longer). Aftermarket tanks have internal baffles, and accept internal pumps.

People whine about cost, but by the time they are done trying to make the original type system even 'just' work, it's more than if you would have went to the correct system right off the bat.

.

[HWYSTR455]

May want to check the filter too, but IMO, you've reached the point you realize you need to do the system right.

.

[Tom Vaught]

Originally Posted by HWYSTR455

I've heard a number of people have issues with the RobbMC pumps, both the 550 and larger one too. Just saying.

Vented caps not only don't work well, but I've seen many that 'say' they are vented, and aren't, or aren't vented enough. To be sure, you HAVE to run a proper vent.

When you go to a 1/2" line, you can actually increase your chance of vapor lock, that 'column' of fuel in the lines is larger, as well as the surface area of the line, to absorb heat.

So, one principal of vapor lock is due to fuel psi. When that fuel in the line is under psi, there is less of a chance of vapor lock. The more psi, the more resistance to vapor lock.

Guess what? With a mech pump, the fuel in the line is under suction/vacuum, and that increases the chance of vapor lock.

Return line, they help tons. Sure you can reuse a vapor line, but it only 'helps', and you need a total solution.

Best way to handle a fuel system is to do it right, and you only have to do it once. Wish I had a dollar for every time I've heard someone fighting a fuel system. So many times people fight having to replace the lines or run new ones, and by the time they are done, have spent at least twice the money if they would have immediately gone to a correctly executed system, not to mention the frustration and some times, damage. Going thru lines, wraps, crappy pusher pumps, trying every mech pump out, you name it.

Long story short (yeah, I know, too late!), 1/2" feed and return, quality regulator as close to the carb as possible, and a good electric pump. I've seen since the tank isn't baffled, with the Robb pickups, you still have issues, and need to run a half a tank at the track, at least.

External pumps can overheat, even the best ones out there, so in tank pumps are better in staying cool (which also means they last longer). Aftermarket tanks have internal baffles, and accept internal pumps.

People whine about cost, but by the time they are done trying to make the original type system even 'just' work, it's more than if you would have went to the correct system right off the bat.

.

Agree with all of above, engine mounted fuel pumps rarely, if ever work well on a drag strip application, without some sort of a pusher fuel pump at the fuel tank.

I ran a pusher fuel pump back in the 60s after seeing that a mechanical pump would not do the job for acceleration, with just the mechanical pump.

I also ran a dedicated gas tank vent as the stock non vented cap needs a large vent and the "vented cap" needs to be able to apply atmospheric pressure to the fuel tank fuel surface in order for there to be a fuel flow from the tank.

I would not blame the RM fuel pump totally, you need to FIX THE WHOLE SYSTEM.

Tom V.

[78w72]

im surprised you are having an issue so soon in the run & on street tires. i have almost the same fuel set up as you, only im using the 1100 pump & just recently added a mallory regulator. same pick up, same 1/2" line connected to -8 line to pump then -8 to carb. i run one of those "ugh" carbs too built by cliff...

on skinny drag radials & a very tight suspension set up more for road racing i have gone a best of 11.27 et & 123mph. & only randomly have the fuel starvation issue, maybe 2-3 out of 10 runs, & it happens at top of 2nd gear usually about half track, with a high 1.6 to low 1.7 60ft. will do it when its hot or cool out so its not vapor lock, & never any signs of vapor lock on the street. i run 3/4 tank of gas, ignition is rebuilt HEI from suntuned & no signs of detonation or other ignition issues. motor is a stock e-head 467, th400 continental 10" & 3.23 gear.

initially i ran no regulator with the pump dialed all the way down to 7psi, which is about equal to the 550. recently i added the ragulator & tried turning the pump up halfway to about 9.5-10psi & it still has the random cut out on hard runs. also the car has major traction problems due to less than ideal suspension so i have to launch at idle & gradual roll into the throttle, so that kills my 60ft but probably helps the starvation issue.

i plan to play with it a little more to see if i can get past the issue at the track, maybe get a bigger regulator, or try without a regulator & turn the pump up to 9-10psi since cliff said the q-jet can handle that with the bigger needle/seat for a short time. as HWYSTR mentioned, if i still cant figure it out & want to try & go faster i will convert to an intank pump & see how that goes.

if you send the pump to robb, consider having it upgraded to the 1100, he will do that for pretty cheap, & you can run it dialed down to 7psi, same as the 550, & not use a regulator. if you want to add a pusher for the reasons you mentioned, lots of people do that & one member here has a diagram for hooking one up with a bypass, may work for your situation.

[RocktimusPryme]

I don't disagree in theory with any of that. We all know a submerged pump is the best way to go. That's not really in the cards right now. I also know the pitfalls of external pump reliability, but I think at this point that is my best option. Along with running a return line, and adding a regulator.


Im also intrigued with the vent thing. I had thought to myself independently before I posted this if I should replace the cap, just because its easy. That said, Im curious what other options there would be for a dedicated vent without buying a new tank.


With all that said, i feel you guys are focusing on theoretical system deficiency. As someone who drives the car a lot. I really feel like a component has, or is failing. Ive made numerous hard pulls up to about 90-100mph from a stop without issue in the past. I wasn't running a sticky tire at the track, so it shouldn't be all that much different. Its never pinged before, its never cruised at ~14.8 before, never surged before. It is acting different. If it would have ran out of fuel at 1000' I wouldn't be all that surprised. But 250'?

Obviously when fuel supply is felt to be the culprit, look at the pump first. I couldn't find any leaks so I don't have any reason to suspect the lines.


I also considered timing too. I just checked it recently and it was stable at 36* or so total, but yes I intend to check it again. I have lines removed at the moment.

[68lemans462]

Put a fuel pressure gauge on it

[78w72]

yeah sounds like something may have failed if these symptoms never showed up before.

i considered the cap before too, bought a new vented cap & verified it is indeed venting by sucking through it. another trick is to drill an extra hole in the cap for even more venting, but if the tank is full you may get some sloshing of fuel on launch.

what HP is your engine? consider upgrading the pump for ~$100 if you can afford it & your engine needs it. the "550" rating is for an engine sitting still on a run stand with a short direct fuel line, once you put it in a car all that goes out the window & maybe you need a bigger pump?

best of luck!

[78w72]

Originally Posted by 68lemans462

Put a fuel pressure gauge on it

i plan to put a visible gauge on mine next time at the track to watch what the pressure does during the run. what is the minimum psi it needs to maintain on a run to confirm its not a fuel issue?

[TAQuest]

Originally Posted by 68lemans462

Put a fuel pressure gauge on it

X3
Then set up your iPhone to video the gauge while you are driving.
It's the only way to quit guessing. Guessing is not your friend.
When you know you have the correct pressure then you can move on to the next thing.
If you do anything other than this first you are wasting your time.