Hard right turn - engine stumbles and dies

Terry Stapley · #1 (**permalink**) 03-14-2007, 10:32 AM

I had my 418W dyno tuned last year to pass the emissions test and then took it back to be tuned for optimum performance after EM test was completed!
Since then when I make a hard right turn exiting the freeway @ 60mph onto another highway my engine will stumble and run rough for bit and if I have to stop about 1/4 mile after the hard turn the engine will die. I thought that I was having fuel slosh so I lowered the fuel level in the Holley 750 DP about 1/4" and it still did the same thing. I lowered it another 1/4" with the same results. The engine acts like it is getting too much fuel on the turn (runs rough for a bit but if I do not have to stop it clears up soon) but I do not want to lower the carb fuel levels too much. I am currently down about 1/2" from the sight holes!!
Engine has MSD 6AL Ignition with an MSD Pro Billet Distributor!
Any advice would be much appreciated!!

Rick Parker · #2 (**permalink**) 03-14-2007, 10:55 AM

Terry, you cannot lower the fuel level in a Holley as you have done without negative affects. The fuel levels should be at the very bottom of the threads of the brass sight plugs on the fuel bowls. If they are much below this the engine vacuum cannot "Pull" fuel (it is having to raise it additionally the amout you lowered the level). Do all the tricks including jet extentions and vent "whistles". You are currently "Way too low!" You have the level so low currently that the jets are being uncovered (fuel sloshing to side of fuel bowl).

Terry Stapley · #3 (**permalink**) 03-14-2007, 11:33 AM

That is what I was afraid of so I am going to adjust the fuel levels back up this evening. thanks for the heads up Rick!!

xlr8or · #4 (**permalink**) 03-14-2007, 01:19 PM

You were probably uncovering the jets as mentioned. To check you can try pumping the gas peddle when this happens to get gas out of the accel pumps. If it helps then the jets were sucking air. If it gets worse you may have been sloshing fuel through the vents.

Do you have center hung floats, they can help along with the jet extensions and vent whistles. The side hangars will sometimes get held in the up position by the slosh not allowing more fuel into the bowls effectively starving it on long turns.

Rick Parker · #5 (**permalink**) 03-14-2007, 01:25 PM

To make some nice jet extensions get a length of thin wall brass tubing (sold in 12" lengths) at hardware store or Hobby shop that fits snugly over the OD of the main jets. Cut 2 lengths about 1"-1 1/4" long and ovalize one end with some pliers or a vise. Slip them on the jets and go for it. Works great.

RedBarchetta · #6 (**permalink**) 03-14-2007, 02:20 PM

Quote:

Originally Posted by Rick Parker

To make some nice jet extensions get a length of thin wall brass tubing (sold in 12" lengths) at hardware store or Hobby shop that fits snugly over the OD of the main jets. Cut 2 lengths about 1"-1 1/4" long and ovalize one end with some pliers or a vise. Slip them on the jets and go for it. Works great.

Should also mention that Holley makes a float that has two indentations designed to clear jet extensions. Otherwise, for some they will never be able to adjust them properly.

-Dean

Terry Stapley · #7 (**permalink**) 03-14-2007, 02:48 PM

Thanks for the suggestions!!

XLR8R: My carb has center hung floats!
What are the jet extensions designed to do!! Keep the jets covered with fuel?
Would uncovering the jets make the engine run rich?? Or lean??
Please explain vent whistles!! I am clueless!!

Chaplin · #8 (**permalink**) 03-14-2007, 02:52 PM

Uncovering the jets, as you've discovered, will make it not run at all. I guess technically it would be lean condition because the carb will be sucking the same amount of air, except that it won't be drawing any fuel because the jets are no longer covered by fuel and in effect are sucking air.

xlr8or · #9 (**permalink**) 03-14-2007, 03:23 PM

Chappy is right.

The vent whistles are plastic breather tubes that vent the float bowl so the air has somewhere to go as the fuel level changes.
The extensions work best in the secondary side of the carb as the fuel sloshes to the rear of the carb the jet can become exposed on the metering block. The extensions simply extend the opening on the jet to the rear of the bowl.
You might also want to check the floats to make sure they move freely and don't hang up if held at an odd angle to simulate cornering/sloshing forces on them.

Rick Parker · #10 (**permalink**) 03-14-2007, 06:12 PM

Red Barchetta:
The notched floats are not necessary if using Brass floats and ovalized tubes as I described. There is enough float drop to allow the needle & seat to function properly.

RedBarchetta · #11 (**permalink**) 03-14-2007, 06:14 PM

Thanks, Rick. You learn something new every day!

392cobra · #12 (**permalink**) 03-14-2007, 06:21 PM

Does it happen on the left turns too ?

Maybe uncovering the fuel pick up in the tank ?

xlr8or · #13 (**permalink**) 03-14-2007, 11:17 PM

Quote:

Originally Posted by 392cobra

Maybe uncovering the fuel pick up in the tank ?

Doubtful as te bowls and line from the tank should keep the car running longer than that. When I forget to turn on the fuel pump in my car I can get down to the end of the street and around the corner before it starts to stumble.

spl310 · #14 (**permalink**) 03-15-2007, 05:58 AM

I haven't tried it, but you could check with Holley's tech service at http://www.holley.com/TechService/ - they may know an answer.

Roscoe · #15 (**permalink**) 03-15-2007, 07:10 AM

I installed the road race floats; tapered on both ends

Terry Stapley · #16 (**permalink**) 03-15-2007, 03:48 PM

Fred, the engine does not stumble when turning left, only right!!

My fuel pickup is on the drivers side bottom of the tank so a right turn would push the fuel to that side!

RedBarchetta · #17 (**permalink**) 03-15-2007, 04:09 PM

Quote:

Originally Posted by Terry Stapley

Fred, the engine does not stumble when turning left, only right!!

Terry, don't ask anyone from NASCAR to help you with this one.

-Dean

Terry Stapley · #18 (**permalink**) 03-15-2007, 04:12 PM

How True!! And Funny!!

Ron61 · #19 (**permalink**) 03-16-2007, 04:26 AM

You only started having this problem after the dyno tune if I am reading this correctly. Is this the first time you have gone through having it tuned and then set back after the smog check? If so, then I am guessing you never had any problems before after they set it back for maximum performance. Is your fuel pump mounted on the left side or near the center of the tank? It is possible, but not likely that it could have a little crap in the filter and on right turns not pull enough fuel into the lines to keep the car running for a while. If you have a fuel pressure gage watch it and see what it does.

Ron

JeepSnake · #20 (**permalink**) 03-16-2007, 01:11 PM

Terry - this sounds very familiar!

What material are your floats? Are they the old brass cans, or are they the foam composite material as shown in a photo on this thread? If they are the plastic/foam/composite type, they may be going "soggy" on you, losing buoyancy and causing a super-rich stumble.

Some of the foam composite floats that Carter used in the 1980's got a reputation for this. Over time, the gasoline & various additives attack the material, soak into it, and make the floats heavy. One of the first indications in many Dodge trucks & Jeeps with the Carter BBD 2-barrel carb was a flooding-induced stall during hard turns (I think it was left turns on that model carb).

Just a thought!