High RPM@WOT problem

[ditch68]

Hello,

I have been sorting through some of the list of small issues with my car (there is quite a list). But this is something that needs to be addressed, and I want to properly diagnose it rather than just throwing parts at it.

What happens, is, when going up through the gears at wide open throttle, when the engine reaches about 5,300 RPM, it misses terribly, much like it has a fuel starvation issue (which it may). This continues and in fact worsens if I stay on the throttle.

I can get past that RPM range with a lesser throttle application, but of course, no power in that.

My thoughts were:

-Fuel starvation due to improper float adjustment, fuel pressure, or main jet sizing

-Faulty points

-Faulty coil

My setup is a 1969 911T engine with S cams (I am fairly certain), and Webers.

Anyone care to hazard a guess?

Jeff

[kidrock]

Jeff,

I think you're on the right track. My first remedy would be to clean & adjust the points (or R&R if necessary) and set the timing.

good luck.

[Christien]

The fact that you can get it to return to normal above the flat spot would make me think it's definitely not fuel, and probably something in the distributor that doesn't like spinning at that speed. Any chance you can borrow a distrubtor to swap and test?

[jstobo]

This is the same symptom I had after rebuiding my 69E. I had put in a MSD unit and had the plug gaps at .045. I reduced the gap to .030 and it solved the problem. Originally the 69's had pretty small plug gaps. Check your gaps it may help the problem. Good Luck.

[Craig]

+1 on checking the distributor first. Make sure the centrifugal weights are not frozen and able to move to full advance, and everything else is free to move as needed.

Good luck,

Craig

[ditch68]

Thanks, guys.

I was leaning more toward fuel, as the fact is the RPM is not the limitation, it is the wide open throttle that causes it. If I just rev it up slowly, I can reach 6,000+ rpm...but floored, it does stumble horribly. At first I thought I had a rev limiting rotor which was too low, but like I said, I can rev it higher, just not "mashed"

Rather frustrating, as it is still making gobs of power at 5,300, and in fact I believe the peak HP is higher still...I really don't know how fast my car can be.

I will definitely check the gap...that was one of the first things I did when I got it home (changed plugs).

Also will look into the distrubutor.

Unfortunately, I won't be back home where the car is until Sunday. I'm on TDY in Vegas, holed up in my hotel room watching "Top Gear" episode after episode. Great fun! (Not much of a gambler...though I did hit the Roulette table for a while earlier this week. Got spanked.)

Jeff

[ditch68]

Well, I took a look at the points, the mechanical advance seems fine.

I can easily rev to any RPM sitting still in neutral - the stumble only occurs under high throttle, high RPM full load situations.

I think it is fuel. I guess I need to find the tool to check my float levels. Or it there an expedited "backyard mechanic" method with common tools?

Jeff

[Goth]

I have seen this a few times over the years. Check the inside of the distributor cap for carbon tracks or general carbon build up. This can allow arcing under high RPM / full throttle conditions. Spark plug gaps too wide will affect this as well.

[70racing]

I chased the same problem for weeks - finally had the
Webers re-built with kit (gaskets, etc.) and problem was solved for good. It had been a few years on the Webers. I even replaced valve springs thinking they were weak at higher rpm. Good Luck ! Bob