Cuts out low gears, not high gears.

[vande17941]

When I go for max acceleration, I get engine cut out at about 4500 RPMs in first and second gear. However in 3rd and 4th gear I can pull all the way to Red Line no problem

Manual tranny
Pertronix (switched with another to make certain that wasn't the problem).
Wires & plugs good.
Linkage set perfect.
Timing at 30 at 3000. And yes I have listened to that idea that 35 is where it should really be. Tried it on two cars and almost blew them up...it pulls hard in 3rd and 4th so that's not it.

Runs absolutely great, pull's hard. It's like it hits a Rev limiter in 1 and 2nd gear.

Any idea.

[wayne R]

Hi  something you could check is the air flow at the front and in and
around inside your air cleaner, see at the lower speeds the air flow is
only half than at at say 80mph,it is critical, especially lower speeds.
Air is sucked in at front passenger side, only by about 6inch by 1/2 inch,
then widening around the air cleaner, as it swirls in , so its important to check.
Photos of mine a  while back when i checked mine. to paint my air cleaner.

[Benz Dr.]

When I go for max acceleration, I get engine cut out at about 4500 RPMs in first and second gear. However in 3rd and 4th gear I can pull all the way to Red Line no problem

Manual tranny
Pertronix (switched with another to make certain that wasn't the problem).
Wires & plugs good.
Linkage set perfect.
Timing at 30 at 3000. And yes I have listened to that idea that 35 is where it should really be. Tried it on two cars and almost blew them up...it pulls hard in 3rd and 4th so that's not it.

Runs absolutely great, pull's hard. It's like it hits a Rev limiter in 1 and 2nd gear.


Any idea.

I run mine at close to 40 degrees BTDC so I find it hard to imagine that's what your problem is. What was it that made you think the other cars you had were ready to blow up?

[vande17941]

Severe engine detonation in both cars at any setting over 30 BTDC @ 3000 rpms quickly convinced me. As well as the fact that 30 BTDC pulls hard and runs strong without ping in the later gears to redline wonderfully with lots of power. As well as three well known NB classic mechanics tell me I was crazy and should be willing to buy a new engine if I continue to run anything over 30. I understand your theory, but have nothing to to corroborate it from anyone have absolutely been dangerous to my motor when trying it.

[450sl]

I have had these rev.limiter symtoms with one of my bikes.   culprit turned out to be the coil...

[vande17941]

I think the coil is a good guess. But it pulls fine to redline in 3rd and 4th gears. Plus, we did change out the coil.

Based on what we see here, that matches the "little blue books", we see nothing that would say to set the timing at anything other than as indicated. Usually, in automotive engines, setting the timing to too much advance results in detonation which is exactly what happens here, as would be expected and timing reduction of a 5 degrees results in a loss of power but not the engine "hitting a wall" and cutting as if it hit a Rev limiter. Anyone else have any ideas?

[Bonnyboy]

Is everything up to snuff with your advance/retard mechanism.   Mine lost one of the bolts holding it all together and was horrible at low speeds but fine at high speeds.  take off the cover and see if anything moves when you poke about carefully with a chopstick (wood rather than metal)   

[vande17941]

Will do...it's driving me crazy. I've tried everything, including the deadly timing advance, proper plugs, proper wires, cap, rotor, adjusted FI linkage perfect, installed a pertronix (then another to be safe), new coil....etc etc etx

[wayne R]

Would you mind telling us  what brand and heat range sparkplug you
are using, your statement you just say proper plugs.
My reason is 40 years ago not in a merc but of all things a swallow Doretti sports car
basically a triumph TR2 engine , made for California, and it did the same thing,
those days i was not very good on mechanics,so took it to  2 workshops and ,first did not
fix the problem   second one did, it was the heat range plug was not correct  for that engine, to cold,
changed them on the spot, and car was great , i remember they were champion plugs.
This was in Invercargill NZ,a very cold wet place.

[wayne R]

I forgot to say  if a plug heat range fitted is to high, it can cause pre ignition,
and sounds like thats what you was getting  with timing up over 30,    regards Wayne.

[vande17941]

Thanks...NGK BP5ES.

Unlikely the plugs. Pulls HARD to redline in 3rd and 4th gear at 30btdc. Only cuts out in the 1st and 2nd gear.

I'm going to put a digital tach on it and make sure the recently rebuilt tach is able to keep up with the rapid rate of rpm increase in the lower gears. Maybe it's redlining before the tach has caught up with it. Will report back.

[450sl]

On my 70/280 i removed some microswitches on top of the gearbox ; dont know if the earlier models got them as well..

[vande17941]

Problem solved.....when using the Pertronix unit, Pertrnox specifically sates not to use solid copper low resistance ignition wires. So, we put carbon suppressor wires on it and the vehicle pulls to redline in every gear and runs stronger without any problems. The wires we used have a resistance of between 5000 and 8000 ohms. Pertronix told us this is a common problem.

[Mike Hughes]

Problem solved.....when using the Pertronix unit, Pertrnox specifically sates not to use solid copper low resistance ignition wires. So, we put carbon suppressor wires on it and the vehicle pulls to redline in every gear and runs stronger without any problems. The wires we used have a resistance of between 5000 and 8000 ohms. Pertronix told us this is a common problem.

Well that does make perfect sense!  When running with "old school" P&C ignition one should use "old school" copper core ignition wires that were the norm when our Pagodas were new.  But when converting over to "modern" electronic ignition it certainly is sensible to install the "modern" carbon core ignition wires that were developed to maximize the effectiveness of such systems!

Regardless of which type of system is installed every component of the system plays its part in the balance of performance.

[Benz Dr.]

Problem solved.....when using the Pertronix unit, Pertrnox specifically sates not to use solid copper low resistance ignition wires. So, we put carbon suppressor wires on it and the vehicle pulls to redline in every gear and runs stronger without any problems. The wires we used have a resistance of between 5000 and 8000 ohms. Pertronix told us this is a common problem.

What coil are you using?

[Atazman]

Good information!  Are "carbon core wires" to be used with the 123 ignition system?  I have never seen this discussed.

Thanks........

[mbzse]

.../...Are "carbon core wires" to be used with the 123 ignition system?.../...

No. The manufacturer states that normal copper ignition wires should be used together with the 123 ignition device.
Useful practice to exchange the ignition coil also, as you install the 123 ignition unit into your SL.
Make sure you secure the grounding of the the 123 unit to the engine block/head, do this by running a wire from the M4 threaded hole in the housing

[Benz Dr.]

I'm really scratching my head on this one. Carbon core wires add a lot of resistance which is something you don't want on a points and coil system that produces 13 KV. If you upgrade to the red coil, you still need to run metal core wires because that system is only 26 KV. Often times the coil wire will be carbon on a new set of ignition wires and that can lead to all sorts of poor performance so it's definitely not what you want near an early ignition system.

Unless you're running a 50,000 volt coil, I have a difficult time seeing where carbon core would be of any help to you.  Since I don't generally work on newer cars, I'm not as well versed on them but my '89 300SE still used metal core wires and it had a very hot coil. Like I said, I'm scratching my head here.........

[vande17941]

I'm running a Pertronix Flamethrower 40,000 coil ($25) and the Pertronix Ignitor ($95).

With supressor wires, and non-resistor spark plugs the car is absolutely amazing. It now pulls HARD to redline in every gear timed at 30 btdc at 3000rpm with the original 51 distributor.

In retrospect, it is quite simple why supressor carbon wires are required. The electromagnetic interference from solid wires without supression screws up the electronic ignitor unit when the wires aren't suppressed, just like in modern cars that require supressor wires to avoid interference with electronic ignitions and ecu's.