What caused this?

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7duster4

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For the first time last night I took my Duster to the drag strip. I was very disappointed. My first pass was in the low 18's. When I got to around 70mph it seemed like the car just didn't want to go anymore, almost like it was starving for fuel. So I just let off the gas way before I even passed the finish line. It did the same thing on my second pass. I wasn't too happy considering all the work done to the engine. Could my fuel pump be causing that problem of why it dosn't want to keep going after 70mph when the peddel is floored. It is just a stock replacement fuel pump on a rebuilt engine. Any help would be appreciated. Thanks
 
Check the fuel filter and see if its clogged, Check the fuel lines for kinks and pull the sending unit to see the sock is clogged up.
 
Sounds like fuel starvation. What has been done to the engine and what does your fuel system consist of? Once you get down into the 12's the car needs a lot of fuel.
 
Do all the normal checks, timing etc and MAKE SURE you are getting wide open throttle. Have a friend press the gas to the floor as you check the linkage at the carb.
 
The fuel filter looks fine, the last time I checked (which was about a month ago) the linkage goes all the way back when the peddle is to the floor. The engine has well over 1,000 miles since it was rebuilt. The major mods include:

-All new pistons, and brought to "0" deck clearence
-340 cam, lifters, and valve springs
-Block is bored .30 over
-Original 318 heads had 3 angle valve job, port-polish
-Edelbrock 500cfm 4-barrel, and performer intake
-ECU orange box

I still think I need to beef up the fuel pump and get rid of the stock replacement unit thats on it now. I have gotten on it a few times on the street and seems fine. It never acts like its starving for fuel, but then again I have never had the car floored from a dead stop going up to 70mph. The car ran fine at the stip until it hit around 70mph and thats when it started bogging and acted like it didn't want to keep on going.

When the engine was getting rebuilt the fuel line was replaced from gas tank to the carb. Just about everything else has been replaced as well.
 
Did you check the sending unit sock ?

If you buy a replacement mechanical fuel pump get a Holley. The Carters have been having a ;pt of problems

No that I think of it your stock replacement may also be a carter and could be bad too.
 
Pretty small carb on there, how far did you get before it was just plain slow? I have a 318, bigger cam and intake, stock 360 heads and am running a 650cfm. I swear the thing needs a bigger carb, thing drops out on the top end and is jetted up pretty well
 
With your setup you should not need to go to electric pumps but definitely get a high-volume mechanical before you do any more racing. Leaning out the engine because of fuel starvation can do a lot of damage.
 
Well I got oil/voltage/water temp/ tach and FUEL pressure gauges so I can see whats going on...You may want to do this later as you go down da track more and you wont be having nightmares of being overtaken by ricers...When staging...oil=45/water temp=180/tach 950 before burning out/FUEL pressure 7 psi.

Speedo pegged at 150 mph....oil 60psi/temp 180/tach 6000 and fuel pressure 7 psi other guy in lane behind me......ALL OVA....I win...12's. Its a pain to hook up all the hoses and wires...then the paranoya trying to look at them all at once...but then you get used to it and hopefully you get enough time to pull over before you hear something funny or if you notice something amiss in the gauge reading...Now if they only made a MSD FAIL gauge....my car just died and das when the gauges didnt help....
 
i would try the eddy 600 #1406. you are probably needing more cfm on the top end.
 
the carbs to small to start with whats the timing set at i've had stock 318's with 2barlls. run low 15's high 14's somethings a miss what gear ratio you got?
 
I dont think it has anything to do with the carb size. Yes it would be better with a 600 but the small carb isnt killing his power.
 
I have not checked the sending unit sock yet. I did 2 passes and it did the same thing. "2 Shelbys" - what kind of damage can fuel starvation do? I hope I didn't mess anything up. The edelbrock 500cfm carb has recently had larger metering rods and jets installed becasue it was running too lean. Felt better after that but I have yet to pull a plug to see if there is any change. I can't remember the jet size off the top of my head. I do have 318 manifolds, no headers. The only headers I would buy are tti's but im not spending that kind of money for 25hp. I know for a fact my rear end is really killing me off the line. It's a open 2.76 8 1/4. Something better will come in the near future. But taking off was fine, it wasn't until a little after the halfway point it started bogging so I let off the gas. If that didn't happen I think I would have ended up with a mid to low 16 second et. Im not sure what kind of fuel pump I have but I will get a new one, probably a holley. My goal now is to get that fuel problem straighten out and get some gears within the next few months. I'll be taking my car to the Mopar Nats next week and hopefully I can find what I need.
 
AdamR said:
I dont think it has anything to do with the carb size. Yes it would be better with a 600 but the small carb isnt killing his power.
Click to expand...

Two Words... FUEL STARVATION!!!

Does it cut out in 1st and 2nd or only in high gear?

Adam has the best suggestions as to your problems. Check the sending unit sock and fuel filter.

Carb size won't be an issue at this point. Yeah it's small, but I know cars that run 11's with 500 cfm carbs.

Bigger metering rods = leaner BTW. If you want richer you need to install thinner diameter rods.

If you feather off the throttle slightly and roll slowly back in will the car pick back up accelerating? If it picks back up = fuel starvation. Does it blow black smoke like a deisel? An excessively rich condition can cause the same type of situation, but, I don't think that's the likely cause. I think it's lack of fuel.

Nice call 2shelbys & Adam. :wave:
 
7duster4 said:
"2 Shelbys" - what kind of damage can fuel starvation do? I hope I didn't mess anything up.
Click to expand...
Leaning out to much greatly raises the temperature in the combustion chamber and can melt anything from plug electrodes to pistons. The good news is that if you had done it you would know.

Some good ideas are to install a pump that exceeds what you need and install a pressure regulator. Install the regulator as close to the carb as possible so it can react to a drop in pressure quickly and try to mount it somewhere other than on the body where vibration can lift the ball off of it's seat and flood the carb bowls. You also want to run the fuel line from the pump toward the front of the car and then turn it back toward the regulator so the G forces of acceleration supplies the regulator instead of starving it.
 
Top end lean out usually shows up as a serious bog like the engine is "cutting out" and then picks up again as the fuel bowls refill or you can sometimes hear it ping, did either of these things happen, 7duster4?
 
It did seem like it was really bogging until I let of the gas. But as I mentioned before it was running fine until that point around 70mph then it just simply didn't want to keep going. I figured if it wasn't getting fuel the car would just quit so I slowley let off the gas. I didn't hear any kind of pinging. But once I got to the end of the strip it was fine. I guess once I let off the gas and slowed down a little fuel was able to flow into the carb easily like any other time. I should have known better to put a stock fuel pump after all the engine work that had been done. A more high performance one is definetly in the works.
 
7duster4 said:
It did seem like it was really bogging until I let of the gas. But as I mentioned before it was running fine until that point around 70mph then it just simply didn't want to keep going. I figured if it wasn't getting fuel the car would just quit so I slowley let off the gas. I didn't hear any kind of pinging. But once I got to the end of the strip it was fine. I guess once I let off the gas and slowed down a little fuel was able to flow into the carb easily like any other time. I should have known better to put a stock fuel pump after all the engine work that had been done. A more high performance one is definetly in the works.
Click to expand...

Before you go blowing money on a new fuel pump, check the fuel sock in the tank.

You can put the biggest stinking fuel pump on it, like the ones on a top fuel car, but if the line has a restriction, the pump does no good. It's like trying to run a marathon breathing only through a straw, then to make matters worse, you stick a glob of gum on the end of the straw. Get the idea?

Make sure the only restriction from the tank to carb is the size of your line and not something like filters, OK. If you don't have a restriction, then go to a fuel pump. A stock pump should be able to at least handle your cars requirements at this point. I have a stock fuel pump on a 340 making about 390hp and it doesn't do what your car does. Car runs 102 mph in the 1/4 and it could use a fuel system upgrade at this point.

If your car sat for any period of time this is what the sock could look like:
pickup.jpg


Good luck and please check the simple things first.

pickup.jpg


pickup.jpg
 
How much gas did you have in the tank at the time? Are you sure you weren't just running out due to fuel level? Does the car come back instantly after letting up or does it run rough for a while after letting up on the gas? Hope you get it figured out. Probably alot harder to nail down since you have to hit 70 or so to see if it's gone. I would think a stock fuel pump would be fine on a mild build. There are members here that use them all the time and have no issues with fuel starvation.
 
that carb size is fine. it needs more fuel volume. It will run fine doing blasts on the street because it can use up the fuel in the bowls and play catch up. then a long full throttle blast is too much for it. Everyone always thinks they need a giant carb. The CI/rpm charts for carb size work well. I would get rid of the 5/16 fuel line and get a high volume mech pump and you wont have to worry about it again even with a few more upgrades.
 
I would definitely not stick with the stock 318 pump. My first car was a '74 Satellite Sebring Plus with a 318. I put 360 heads on it, put in a street Hemi grind purple shaft, and topped it off with a 600 Holley on an Edelbrock LD340 dual plane. It fell on it's face right after hitting 3rd gear. Fuel starvation. A high-volume pump and high flow fuel filter cured the problem. When it comes to fuel delivery you are better off knowing you have a little more than you need than you are hoping it will be enough.
 
I filled the car up with gas just a few miles away from the strip. It dosn't seems to run rough when letting off the gas and getting back on it. Seems fine. I don't know when i'll get time to check the sending unit sock. I'll be leaving for the mopar nats in a few days. But I hope it gets solved soon. Thanks for everyones feedback.
 
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