Question About Fuel Starvation...

I think there's another thread on here somewhere about this.

We've tweaked my carbs, and that helps. Some claim to have completely solved the problem, which I don't believe.

Best solution? Downshift and stay on the gas!!!! At least that's what I do.

Here are a couple links:

http://www.ferrarichat.com/forum/showthread.php?p=135748634#post135748634

http://www.ferrarichat.com/forum/showthread.php?p=134595663#post134595663

On re-reading these threads, this is quite a little hornet's nest you're stirring. Fun to look at them again.

DM

 

MIke, Dave and all,
As you know I have lots of miles and do like to run hot on occasion. The left turn ..uuh.. really bugged me early on. Took the carbs apart and tried to come up with an explanation. Floats were fine, high G either side and no binding. Best place for floats is exactly where the book says to put them using the exact book technique. Ok, there is gas, the floats are happy with the carbs effectively tipped left or right. What if the carb is tipped forward or backward? Braking or Accelerating? In braking, liquid sloshes forward and floats (pivoted in the front) let a little more gas in. Not much but the effect is there. Going into a left turn should be no more of a problem than a right turn. No problem with right turns so fore and aft G is not significant. All that is left is left/right Gs. Well, I just tipped the carb left and right and tried to find out what happened to the gas in the tortuous path to the idle jets.
Bingo! Tip to the right and there is no gas running uphill.
Tip to the left and there is plenty.

Dinner time in Santa Barbara... To be continued in a little bit.

John

 

Ok, Nice dinner. Sorry for the interruption.

I have no way to prove or disprove this but I think that the following is happening: Car stops running after decellerating, turning sharply left at a relatively low speed (20-40 mph) and then accelerating in any direction. Acts like no gas at all for 1-2 seconds which seems like an eternity. I believe that the closed throttle and left turn effectively tips the carb 45 deg. to the right. Dino corners close to 1 G. Gas in the transfer lines goes 2" inches to the right, back into the float bowl. When you open the throttle to accelerate out of the corner, no gas to get started. Only thing you have is the burst from the accelerator pump. A second later the gas finally gets to the three sets of idle jets and revs build. Above 3000, the mains kick in and who cares about the low speed jets. Mains have a much shorter path to the float bowls so lag is not a problem. But mains don't work worth a damn below 3000.

Bottom line, Carbs were spec'd back in the days when the Dino V6 was mounted fore and aft in F1 and hill climb cars like the 206 SP. When the Dino was designed as a road car, the engine was twisted 90 degrees and the integral gearbox, rear end was added. Nobody remembered that the Webers were supposed to have the float chambers at right angles to the car centerline. Damn. But they got nearly everything else right!

The only carburator cure that has worked is the one Lancia figured out on the Stratos. Go to two tripple barrel webers, cut a hole in the rear deck to clear them and go like Hell. Floats are oriented just fine. Fuel injection also works but....

You live with the stumble. Keep the revs high so the main jets have enough air to work with. Learn to lead with the throttle so you keep some gas in the idle passages. With practice you can almost ignore the problem.

Welcome to the club. Don't worry too much about left turns, you can pass him easily on the next right.

John

 

P. S. Hot start problem has nothing to do with Dinoplex. A carb problem again. Engine hot is not a problem per se. Carb hot is the problem. 15 minutes is enough to boil out whatever gas is in the transfer line to the idle jets and some of what is in the float bowls. Turn key on, wait 20-30 seconds, press throttle half way down, crank and it will start eventually. Don't know why it starts instantly two hours after shutting down hot. Someone else will have to explain that.

John

P. P. S. Use NGK BPR7EIX plugs for great start, idle and everything else short of full race.

JC

 

I heard of a mechanic in Los Angeles who claims to have cured the loss of power on left turns. I believe he supplies a different float that allows more fuel in the float bowl.

The hot restart heat soak problem might be cured by checking into venting the float bowl to relieve the pressure.

The small amount of fuel that is pushed passed the jets on heat soak may vaporize after a few hours and the longer an engine sets the easier it is to start on a rich mixture.

 

I have a set of floats that are supposed to minimize the problem but haven't tried them yet.

 

Plant your foot and induce "torque steer"

 

You mean 3 dual barrel of course, Weber IDF.
I'm happy to see now the problem acknowledged, not so last time around...

 

Sorry, it was 3 each IDF with a special manifold for the 4 valve heads. I posted some pics a few months ago:
http://ferrarichat.com/forum/showthread.php?t=125099&highlight=dino+stratos
Bottom line is that the floats want to be in front or specially compensated. Learning to drive with the standard setup is not too bad. Problem only happens at low speed with heavy braking/closed throttle before accelerating out of the turn. Once the speed is up and you can use power through the turn, no sweat. Nothing more fun than 60-90 mph sweepers with the tires singing. Drives Porsche drivers nuts. Drive!

John

 

That's the key and what makes it manageable.