Curious tuning problem - new '70 S4

[Chrisrich]

I've got a '70 S4 with strombergs and pertronix that I'm trying to sort out. I've had the dizzy rebuilt. I'm running the timing at about 15 degrees at idle, no vac (seem to run more happily that 9 or10). The motor has a 'gallop' at idle, and while the first and fourth cylinders are firing (as observed with a timing light and a Colortune), I can remove both plug wires with hardly any effect. However, when I pull the 2nd and 3rd plug wires, the motor will shut down.

When I open the throttle the motor sounds pretty good, but I'm really not sure exactly how it's supposed to sound. I've driven around the block, and it feels like it's somewhat compromised, but hard to tell, frankly.

I have roughly 170lbs of pressure (cold/throttle closed) in each cylinder.

When I pull the plugs, they all look similar, quite carboned up, although the car's been idling in my garage, so I expect it to be quite rich.

Any suggestions on this? I wonder if my cylinder 1 and 4 problem is strictly an idle phenomenon, but if they're getting spark and it's sharing the carb input as 2 and 3, why would they behave so differently?

Welcoming any suggestions, and thanks in advance.....

Chris
Dobbs Ferry, NY

[CBUEB1771]

What configuration of inlet manifold do you have? Do you have the complete federal emissions system with cross-over to the exhaust manifold for preheating? Has the cross-over tubing been removed and the corresponding ports in the inlet manifold blanked off? It seems as though you have a balance problem with cylinders 2 and 3 robbing flow from cylinders 1 and 4. The ultimate solution would be to find a set of non-federal inlet adapters for Strombergs. This arrangement has a proper balance tube between the carburettors.

[bill308]

Russ,

You might also want to check your valve clearances.

Bill

[GordonM]

To me it sounds like you have a couple of plug wires crossed. I've done this before but I mixed up on 2 and 3. Creates same symptoms as yours but engine is only running on two cylinders. With webers you get occasional coughing out of the carbs.

[elan_fan]

If you seem to be missing a bit on idle and the car runs well but doesn't rev cleanly (it should sound quite crisp as you go up the rev range in first and second) it might be as simple as your carbs need balancing. On tickover particularly you might have 1 carb doing all the work but the engine runs because of the balance pipe.

regards

Mark
S4SE on strombergs
Plus 2S

[PeterDraper]

I had a problem with my webbers. I was not able to get the engine to idle. It turned out to be a small bit of brass on the edge of the butterfly. It was preventing one of the four butterfly's from closing.
Peter

[Chrisrich]

Thanks much, Peter, Gordon, Russ, Mark and Bill.
I do think it's a balancing issue. I put in new plugs (to give it a fighting chance) and found that it makes power reasonably well and generally felt very responsive, with a nice clean note. Cylinder 2,3 and 4 plugs were actually somewhat lean, while #1 was still a bit carbon'ed, so it seem that whatever is in play has the effect of richening that first cylinder.

As to the manifold, I think I have a very non-standard setup, as it's quite different from the shop manual: I see a blanking plate on the exhaust side where the crossover was, but on the intake side I see no provision for either a balance pipe between the 2 carbs nor a crossover tube. The intake manifolds are cast into the head, it appears. The throttle cable is held up above a bracket that runs across the 2 carbs.

I wonder if I've got some bastardized setup. I also have individual filters, and I've been advised by Ken at Dave Bean to go back to the stock airbox (I have that in a box of spares that came with the car....)

Chris

[CBUEB1771]

As to the manifold, I think I have a very non-standard setup, as it's quite different from the shop manual: I see a blanking plate on the exhaust side where the crossover was, but on the intake side I see no provision for either a balance pipe between the 2 carbs nor a crossover tube. The intake manifolds are cast into the head, it appears. The throttle cable is held up above a bracket that runs across the 2 carbs.
Chris

Could you post a photo of your inlet arrangement?

[Chrisrich]

thanks Russ.
I've actually got a new topic started at:

http://www.lotuselan.net/forums/viewtopic.php?t=15348

where I posted a few pictures, and I'm certainly getting somewhere. I'm missing the butterfly/intermediate intake with the balancing pipe, and that's causing some problems. Someone in Ohio is offering up that piece on the cheap and I'll grab it. I still have other issues, but at least I'm on track.