hard starting when hot!

[saltshaker]

I'm having 2 issues: frist ,the more I drive the longer it takes to restart and I have to give it more gas to start...then it starts and smells of gas.
second: still have slight bog if I want to tale off fast and when cruising and step on it there is a hesition before it takes off.
the motor is 428 w/comp 282s cam, ported heads,MR 2x4 w/450's (#63 jets, 6.5 pv,#37 squirters) 16 int 36tolal timing...could use a little help!
Jon

[Night Enforcer]

Sounds like good ol' vapor lock. I have a great deal of experience with this issue both with Cobras and other carbed rods that I own and my compatriots rods.

A couple of questions are in order. Are you using a mechanical or electric fuel pump? Return fuel line or no return line? What part of the country do you live in? Oxygenated fuel or not? Elevation where you live.

We have done extensive testing and found that certain oxygenated fuel mixes in Central and Southern Arizona will boil as low as 140 degrees F. Even some “Race Gas” is oxygenated and boils at lower than expected temps and can cause a bit of vapor lock after long hard runs and then letting the car sit and the heat to percolate. The low boiling point means that the fuel in your fuel log and float bowls may be boiling after the car sits for a while after a run, and the heat off of the manifold and engine in general, goes to work on the fuel. In addition the fuel in you fuel line running under your car to the mechanical fuel pump or to the carb can heat up enough to boil the fuel. In Tucson in the summer the pavement can reach 160F easy.

Keep in mind as you read the rest of my post that a mechanical fuel pump is basically sucking the fuel from the tank. This lowers the pressure in the fuel line thereby lowering the boiling point even further. (Boyles Law) An electric fuel pump is for the most part pushing the fuel and thereby pressurizing the fuel in the line and raising the boiling point of the fuel. (Boyles Law)

We have found several things and combinations that work to help alleviate vapor lock. The best is number (1). I have placed these in order of being most successful. (1) Electric fuel pump and return line to the tank. (2) Electric fuel pump. (3) Mechanical fuel pump and return line to fuel tank. (4) Holley aluminum reflector /diffuser plate and phenolic or wood spacer between the carburetor and the manifold. (5) Wrap fuel lines in reflective material and place reflective material over mechanical fuel pump.

Depending on where you live and the fuel you are using, the deflector and the carb spacer is enough to solve 80% of the problem. Let me know if you need any additional info.

[saltshaker]

I'm using the car in central NJ..not sure what type of fuel...no room for space under carb...mech fuel pump, how do you run a return line to the tank?
thanks,
jon

[PatBuckley]

If you are using an MSD distributor check the center terminal in the cap.

[Zoom This]

Sounds like you have 2 separate issues. Gas "drooling" into your intake when motor is hot and sitting after parked. Second is a bog due to an incorrect air to fuel ratio during throttle tip in. I was plagued with both of these issues when my 418W was new 7 years ago. Both our motors are completely different but the carbueration problems are the same. I was able to cure my gas drooling into my intake by drilling two anti-siphon holes in the metering block of the Holley 850 thus avoiding gas dribbling out of my main jets. I never could get rid of my off idle bog no matter how I modified my Holley 850. Since I swapped my 850 Holley for a BG 650 Mighty Demon I have no longer had carb problems. I wound up trading 15 hp at the top end for 18 lbs. of torque in the mid range. Not a bad trade. Also, the vacuum reading on the dyno with the 650 BG was .5 inches until 4k rpm, 1.5 inches from 4k rpm to 6k rpm. Good luck with the 2x4 setup Jon.

[Eljaro]

Before switching over to Webers (I would never, never go back) I also had problems with my 850DP Holley. It would diesel or run on when turning off the engine, it would stumble when taking sharp corners, it would die when breaking hard, etc. I think that the 850 cfm is too large for the engine, and that a 750 would have run much better in the 427 cid engine.
I had ordered a 750cfm Holley DP to do the change, bit never had a chance to try it on, because the Weber fever hit me and there is now way back now.

[jhv48]

Somehow, you need to make room under those carbs for a phenolic spacer. That will probably cure most of the hot start problem and is the cheapest/easiest way to start.

The fuel in your bowls is boiling after shutdown. I had to get a drop base air cleaner to clear my hood once I put the spacer on, but it was worth it.