Help required - engine breaking down at 6000+ rpm

Hey guys,

My race car has developed a habit of breaking down over 6000+ rpm. This has never normally been a problem in the past, however I did not notice that when I had the lights or wiper on when racing the problem occurs also.

It only occurs when the car has done a few laps and starts to get a little warm. Car runs on Webers.

I changed the coil, with no change to the problem.

I do run a small Odessey race battery.

Plugs are new and dual heat range.

My best guess is one of the following (what do you think!?!)
1. Altenator is not charging enough at higher rpm leading to a voltage draw
2. Leads are shorting out somwhere when under load
3. Electrical gremlin somewhere (even though car was restored 1 year ago)
4. Battery cannot cope with voltage required if slightly down on charge

The breaking down does not cut power all together but it creates a pretty good miss, so it does still spin out, albeit slowly and far from smooth. Motor has previously revved to 7500rpm with no problems.

you can see the videos at www.youtube.com.au/aewebster

Open to any thoughts, as our 1973 2.8 is also doing the same thing in certain conditions too!!!

Thanks in advance :)

Both cars? Bad race gas?

No I don't think it is Kenik, they both run on our BP Ultimate which is 98 Octane, and at seperate events, with different fuel batches. So fuel is not the issue. Good thought though! Thanks!

Are you using a Bosch CDI box?

I have had a few which did well in the lower RPM but acted up at the top end (above 6000 RPM). I had them rebuild and problem was solved.

Richard

Alex,

I think Kenikh might be on to something...

Your cars are well maintained and usually run like hell... so why all of a sudden...with both cars....?

I'm been looking at you guys great pics and video from 'down there' lately, and it seems you've had your share of crap weather... no?

I might be suspect of a little water contamination in the gas... or moisture weaseling into the electrics........

My .02 mate

Cheers,

Alex,
I have to concur with Kenikh & Chuck...

The fact that you've got two different cars doing the same thing tells me it's an "external factor", meaning;
1. You've gotten into a bum batch of gas - do you buy your gas by the barrel?
2. You might - as Chuck suggests - have a moisture issue common to both cars...Have you looked at both your distributors lately?
3. When was the last time both of your alternators got checked/tested?
4. A small battery like that, when they get older, will cause this too...I use a small, cheap lawnmower battery, and I change it constantly.
5. I know you don't want to hear this one, but; check every single ignition connection for surface corrosion, and tightness, if everything else seems to check out.

Hope this helps :D let us know what you eventually find.
Cheers
Thom

+1 to Thom's suggestion of checking every electrical connection.

My car started running really poorly over 4k rpm. I checked the spark plug connections and they were firmly seated. Still ran poorly. Pulled and cleaned the carb jets in my car, still ran poorly. After putting all the jets back in, I noticed a nut holding the ground to the coil had come a little loose. After I tightened it, the car ran perfectly.

So all that to say follow Thom's advice to check the grounds.

All great suggestions!!!

I'd add that you should be checking your car's fuel pump for correct pressure and volume. Weber's (or PMO's) need 3.5 psi and your pump should deliver a liter of fuel in under a minute to keep up.

Fuel filters????

System voltage????

Thanks boys,

will start the process!

The weird thing is that my car (1967S on Webers) does it when it warms up.

So one would assume that the issue be apparent from start up and not just when warm.

The yellow car (1973S 2.8 on MFI) also has done it on the odd occassion and not every time. I must admit that dad has been driving this car and I have not done as many miles in it so I cannot comment as to when it happens, hot/cold, lights on/off etc.

Will start to go over the leads, dizzy, rotor button etc and work my way through. Gives me an opportunity to clean it at the same time! Then will work my way to the alternator and check the output. I personally think it is simple as it has only just developed it since Phillip Island, which to me sounds like the moisture issue that many of your spoke of.

Chuck you are right, the weather was terrible down at the Island, however last weekend at Winton was sweet! 1st outright in the handicap race and 2nd overall for the weekend's 4 races! Stoked!!!

Thanks again guys, will report back once I have some news!