Hit the rev limiter and now running little rough

[Jay Laifman]

I hit the rev limiter on my 73.5 911T over the weekend. Now the car is running a little rough. I seem to recall this happening to me years and years ago too.

Is this a coincidence - or can the cut out on the rotor cause something else to go wrong? It was running fine immediately before, and running oddly immediately after.

Could the electric cut out cause some problem with the rotor? The cap?

This is the CIS car. I don't know if that matters. To be honest, it seems like it ran ages ago with a bad WUR that was causing the car to run too rich.

Thanks for any thoughts.

[Jeff Burger]

Jay,

You might have broken a valve spring or worse yet had the valves float and bent a valve from contact with a piston. Hope that is not the case. Visual inspection with the valve covers off and or compression / leak down might be warranted.

good luck

[CCM911]

If he hit the rev limiter on the way up, there is no way that he broke a valve spring or bent a valve. That is why there is a rev limiter. Now if it happened on the over-run, then it would be a different story.

Is the rotor on a 73.5 the one that has the rev limiter? If so, I would pop the distributor and take a look. Maybe even replace the rotor. That is probably the cheapest way to start.

[Jay Laifman]

Jeff,

Thanks. I think that is highly unlikely. I was right at the rev limit. I didn't fly over it. It was not like I downshifted and skipped a gear or something. This is a CIS T. So the rev limit is not all that high - and it wasn't crazy acceleration. I could be wrong in this analysis.

[T77911S]

hitting the rev limiter should not cause any problems. if you have the tools, personally i would do i leakdown and or compression test just to be sure.
not sure what ignition related would leave you running rough just for hitting the rev limiter.
might look at or replace plugs since i dont know that age of them or condition.
might consider checking for a broken valve spring.

if cap and rotor are old replace them.

if you have the rev limiter on the rotor thats just a very simple grounding device. even if the spring broke i dont think it would even run.

do easy stuff first

just saw other replies.
yea, bent valve if spring broke. you just dont know.
i bought a 3.0 from a friend that had a broken spring that he did not know about.

[Jay Laifman]

Christopher,

Yeah - the rotor has a spring with a tab that is the rev limiter. I'll take a look.

[kach22i]

The rev limiting rotors are a little tall, I've actually had to shave a few micro inches off the bottom of mine to prevent the stem built into the inside top of the distributor cap from becoming stuck in the up position.

Once jammed into the up position (by rev-limiter activation sometimes) it cannot do it's job and the rotor floats up, thereby allowing unwanted lateral movement and causing timing errors.

Take off your cap, un-stick the stem in the top of the cap, re-seat the rotor, put the cap back on and enjoy.

If the stem is not stuck in the up position make sure the spring action is working correctly, and re-seat the rotor as it still may have moved on you.

I have kept a couple of my old rev-limiting rotors just in case one of the inner springs or magnets fails. They come in handy when trying to eliminate other possibilities.

EDIT: for a typo in spelling.

[Jay Laifman]

Originally Posted by T77911S

hitting the rev limiter should not cause any problems. if you have the tools, personally i would do i leakdown and or compression test just to be sure.
not sure what ignition related would leave you running rough just for hitting the rev limiter.
might look at or replace plugs since i dont know that age of them or condition.
might consider checking for a broken valve spring.

if cap and rotor are old replace them.

if you have the rev limiter on the rotor thats just a very simple grounding device. even if the spring broke i dont think it would even run.

do easy stuff first

just saw other replies.
yea, bent valve if spring broke. you just dont know.
i bought a 3.0 from a friend that had a broken spring that he did not know about.

I was wondering if the shorting could cause carbon on the rotor, or when it kicks back in, if there could be an arch or something.

Truth be told, this was on the way to an autox! It ran fine during the autocross - and I certainly didn't redline it at the autox. It was just a fluke acceleration on the way there. Anyway, it was having a rougher time at idle and light throttle. I think it was marginally better after the autox. But I'm not 100% sure it is as perfect as it was before.

I did give the car a pretty full tune up in the last few months, including rotor and cap.

[Jay Laifman]

Originally Posted by kach22i

The rev limiting rotors are a little tall, I've actually had to shave a few micro inches off the bottom of mine to prevent the stem built into the inside top of the distributor cap from becomes stuck in the up position.

Once jammed into the up position (by rev-limiter activation sometimes) it cannot do it's job and the rotor floats up, thereby allowing unwanted lateral movement and causing timing errors.

Take off your cap, un-stick the stem in the top of the cap, re-seat the rotor, put the cap back on and enjoy.

Now that sounds like a decent explanation. Maybe too the autox afterwards gave it enough vibration and so forth to bring it back down by itself. I'll look tonight.

Thanks!

(Of course this is a good answer because I like it and it is cheap and it has a cause and effect - but that of course doesn't mean it is right this time).

[kach22i]

Originally Posted by Jay Laifman

Now that sounds like a decent explanation. Maybe too the autox afterwards gave it enough vibration and so forth to bring it back down by itself. I'll look tonight.

Thanks!

(Of course this is a good answer because I like it and it is cheap and it has a cause and effect - but that of course doesn't mean it is right this time).

Oh shat, I forgot to mention that I have a Pertronix magnetic pick up system in lieu of points.

Not sure if this changes anything.

It is the reason for the rotor "too tall" comment though, it's actually the hex magnet of the Pertronix which may be too tall.

[Jay Laifman]

Hmmm. So do I. And now that you mention it, yes, I too had to file off the bottom lip to get it to sit low enough.

[dicklague]

I was happy to get that damn mechanical rev limiter rotor out of there. My new CDI has a nice soft electronic limiter that you can set with a small screwdriver on the outside of the box. I set mine for 6500 on my MFI 2.7 and I love it.

I can just run up there and it reduces the spark voltage so you never hit a wall, but it just stops reving and further.

[Trackrash]

My new CDI has a nice....

Brand?

BTW, I occasionally hit the limiter when autocrossing. Never a problem.

[dicklague]

Originally Posted by Trackrash

Brand?

BTW, I occasionally hit the limiter when autocrossing. Never a problem.

The brand I installed in the Daytona-Sensors CD-1 kit that comes with a matching coil.

It is completely programmable and had data logging. In my 2.7 I am only using some of the features but I do love it. Puts lots of strong spark and makes the engine run really well.

[HarryD]

I periodically have a rough running issue.

I reseat my plug wires and the problem goes away until next time.

My theory, the vibration of the motor loosens the wires and I get poor contact. Takes about 1 minute to remedy.

[kach22i]

Originally Posted by HarryD

I periodically have a rough running issue.

I reseat my plug wires and the problem goes away until next time.

My theory, the vibration of the motor loosens the wires and I get poor contact. Takes about 1 minute to remedy.

That cannot be true with Beru connectors.

Or can it?

[Sunroof]

I drive a 1973.5T/CIS with a 6500 rpm rev-liniter and I have never had an issue despite taking it to the 6500 rpm limit and beyond! I did see one time that that black sealer material on top of the rotor was cracking so I replaced the rotor. At 6500 rpm the limiter does not quite bust up the spark that quickly so the revs will go higher. No damage so far........

I would check and reset the points first then if I had a spare rotor I would try that as well to see if you can get the roughness out. Check the distributor cap for any cracks next. Make sure the green wire is tight on its fitting.