missing again, not fuel?

[MistressMotorsports]

Anyone ever heard of an ignition problem where the car misses while at part throttle, but not at light or wide open throttle? This has been happening at Willow Springs, while holding the car at about half throttle in the long corners. Once you get back to wide open, it goes away. I was convinced it was fuel, but after swapping fuel pumps, filters, even borrowing a carb, nothing changed. I'm now thinking the MSD has some goofy problem that only shows up in certain conditions. It does seem to get worse the more laps you run, so that also leads to ignition. Any thoughts?

Mike Eckhaus

[Aussie Mike]

The only clue here for me is the long sweeping corner so I'll take a couple of guesses. You may be experiencing fuel starvation as the fuel is pushed to one side of the tank exposing the pick up. Does it do it on the straights as well?

When you are under WOT you are probably sloshing the fuel around more so the pick up has a chance to catch some fuel.

If it get's worse the more laps you run, maybe the fuel level dropping every lap means less fuel around the pick up? Does it happen when you have a full tank?

A sump in bottom of your fuel tank for the pick would probably help.

I may be wrong here but it shouldn't be to hard to prove either way.

Cheers

[Randy Rosenberg]

I've had a simliar experience. I was told it is due to the fuel "puddling" in the mainfold, which in turn is due to the fuel slashing in the carb bowl and not evenly squirting into the manifold, and then due to the sideways "g" forces the fuel is being pulled into one side of the manifold, as opposed to the other side.

I've felt this during mid speed corners, both right and left, under medium throttle, at about 3000 RPM.

Now, I'm not running a race prepared carb, however I've got plenty of fuel pressure and good spark. I'm running a 750 Holley double-pumper on a dual plane Blue Thunder manifold sitting on a 2 year old crate 460.

I just kinda live with it, as it doesn't seem to upset the balance of the car thru the apex. As I transition thru the apex to the exit, I'm rolling on the throttle, and then the problem goes away. I was told that one solution is to carry higher RPMs thru the corner, however for me, that means go faster, and, frankly, I'm just not there yet...

Hope this helps.

Keep the rubber side down,
Randy R...

[Jack21]

Probably a silly question, but should you be using a vacuum advance distributor, it stacks up this way. 12 - 14 deg initial, plus 18 - 22 deg mechanical (all in by 2200 - 2600 RPM), plus 20 deg vacuum and you have 52 - 54 deg total adv at high vacuum. Engine will miss. Disconnect vacuum advance. If missing stops, that may be your problem.

[aeroace]

Mike,

The BG carb you have has the emulsion tubes driled too high in the float bowls. What carb did you try? A BG or a Holley? A fuel pressure gauge in the cockpit (with an isolator af course) could let you know if it's a pickup problem. I heard Mickey was pulling away from you at the end of the corners and on the straighrs at willow. Any truth/

[MistressMotorsports]

We put a Holley 850 on that had run perfectly in anothe car. The problem is not fuel. I'm going to try borrowing/swapping ignition components and see what happens. The car runs great at WOT, crappy at mid throttles, and just a little ratty at idle. Mickey and I never ran close enough at Willow for there to be a comparison, so I don't know where that info came from. On the front straight at the Streets a few weeks ago, we were dead even from a 2nd gear dig to midway through 4th.

[niles]

Mike;
Missing in long sweeps shouts "G"'s
Ignition and everything other than carb/fuel seems unlikely.
Thirty years ago in my Porche racing days yours was a common problem; either float level so low; causing a lean miss or flooding due to too much fuel; experiment with float height.
We solved it my setting the float dead on with the front jacked up around 6 inches
gn

[coyled]

Mike, sorry I missed meeting you at willow(tranny broke) maybe next time. By any chance are you running a crank trigger. Depending on how you route the coil wire, crank trigger wire and distributor wire, it can sometimes pick up a false signal. I had this occur intermitently at idle only for 1 year until I rerouted the wires. It felt tike and ran like a lean misfire under 2000 rpm.The car would run perfect WOT, so I was scratching my head on this one. This may not be it, but it happend to me. good luck, scott.

[RACER X #99]

Mike,
I had a similar problem this summer with my 351W,tried everything with fuel system, changed jets ,lowered fuel level, raised fuel level, advanced timing,retarded timing.Nothing worked.Friend suggested.Did you check you dist. cap? I dismissed him as a fool and went home and checked inside the cap. Loaded with moisture.I dried out the cap and dist. and car is running perfect. Guess I was the fool.
Cranky