Brand New Engine, Rough Running, 123 Curves?

[FunElan]

Hi all,

After about 5 years, my father and I have gotten to the point in our restoration where we can start the fresh motor and run it in. Here are the specs:

69 S4 SE
Stromberg carbs, defederalized
B1Y needles
Aftermarket manifold crossover (from Union Jack Exotics here in the USA)
123 Bluetooth Distributor
Electric fuel pump

We've chased vacuum leaks and basically eliminated those. The carbs have come on and off too many times. We installed a fuel pressure regulator today (2 psi) to see if that would change anything, but I think it's time to look at our programmable curve in the distributor.

A fellow from the Elan group on facebook had created a distributor curve for a similar twincam stromberg engine and shared it with us. Their engine was tuned on a dyno/rolling road. This is the baseline we've been using, but I'm starting to think that maybe we don't have enough advance. Searching here yields little fruit when it comes to the combination of 123 distributor+Stromberg.

So, I'm attaching our current tune. I have the MAP curve disabled. Let me know what adjustments you think we should try. Thank you for any advice!

[h20hamelan]

have you verified fuel flow at carbs, and when lifting dashpot you see fuel

2psi at engine, measured?

123 set as per instructions

just asking, I was thinking of changing to 123

[FunElan]

have you verified fuel flow at carbs, and when lifting dashpot you see fuel

2psi at engine, measured?

123 set as per instructions

just asking, I was thinking of changing to 123

Indeed we have fuel to the carbs, the filter fills up (transparent) and the car actually runs and revs okay at standstill. Once under load things are different. 123 was set up per the instructions, but the curve it came with might be shite

[Andy8421]

There's a lot a bad data out there when it comes to Twinc advance curves, not helped by Miles Wilkin's book on rebuilding the Twinc being adrift. Lotus publications also confused crank rpm with dizzy rpm and whether static advance was added in or not.

There is a good thread here:

https://lotuselan.net/forums/viewtopic.php?f=31&t=47025

..that covers some of the recent thinking on suitable advance curves (understanding it is for Webers, but should give you a useful yardstick).

I had a quick look at your curve, and it doesn't seem far out, but see my comment below about setup.

A couple of personal observations. It seems to make sense to set the 123 to TDC on cyl 1 when fitting, and have static advance set in the app to zero. From then on, 'what you see is what you get' when it comes to the advance curve. It also allows some clever starting and tickover tricks to be added (details in the thread). It would be helpful if you could report back on what you eventually decide on.

Andy.

[mbell]

Have you got it timed at zero degrees, so no mechanical advance?

I'd except more advance that shown. Would expect way least 8-10 at idle and up to low 30's maximum to be safe.

Have you tried looking up the standard curve for the engine?

[661]

[Stevie-Heathie]

Sorry to hear you haven’t quite got the engine on song. Keep going - it’s worth it when you get there!

For what it’s worth here is my 123 curve, provided by my well respected engine builder. My car’s on Webers though. Good luck, keep the faith!

The 123 distributors are amazing. Imagine how much more of a pain this would be with timing light, burned hands and skinned knuckles

Best
Steve

[2cams70]

Do you still have the original distributor? If so I'd be re installing it and see how the engine behaves. If it runs well you can measure the advance curve from it.

123 distributors are only as good as the person doing the programming. Personally speaking they aren't a gadget I particularly lust after.

[ill_will]

I don't think it's been suggested already, but have you confirmed the valve timing is correct for your cams, using a dial gauge (not just the timing marks)?

Good luck!

[gus]

What does running rough mean?
Lack of advance will usually make less snappy in acceleration, but rough is not a specific term
I would also start with more advance, the emission numbers are for smog, not performance

[FunElan]

There's a lot a bad data out there when it comes to Twinc advance curves, not helped by Miles Wilkin's book on rebuilding the Twinc being adrift. Lotus publications also confused crank rpm with dizzy rpm and whether static advance was added in or not.

There is a good thread here:

https://lotuselan.net/forums/viewtopic.php?f=31&t=47025

..that covers some of the recent thinking on suitable advance curves (understanding it is for Webers, but should give you a useful yardstick).

I had a quick look at your curve, and it doesn't seem far out, but see my comment below about setup.

A couple of personal observations. It seems to make sense to set the 123 to TDC on cyl 1 when fitting, and have static advance set in the app to zero. From then on, 'what you see is what you get' when it comes to the advance curve. It also allows some clever starting and tickover tricks to be added (details in the thread). It would be helpful if you could report back on what you eventually decide on.

Andy.

Thanks Andy - will try some of the curves in that thread. Curious to see how differently it runs, even on a weber curve. Will report back, likely in 2024 "set the 123 to TDC on cyl 1 when fitting" - this is what we did, but when I try these other curves I can set static advance to 0.

Sorry to hear you haven’t quite got the engine on song. Keep going - it’s worth it when you get there!

For what it’s worth here is my 123 curve, provided by my well respected engine builder. My car’s on Webers though. Good luck, keep the faith!

The 123 distributors are amazing. Imagine how much more of a pain this would be with timing light, burned hands and skinned knuckles

Best
Steve

Thanks Steve - we'd definitley like to get it running with the unit, it's such a cool concept! I'll have to try your curve. The genius of it to me is that we can try as many different curves as we want, without touching the distributor and like you said, burning knuckles

Interestingly, the curve from the manual that @661 posted is very similar to the one we have loaded in.

I don't think it's been suggested already, but have you confirmed the valve timing is correct for your cams, using a dial gauge (not just the timing marks)?

Good luck!

I'm hoping the engine builder did but this is something we will investigate if none of the easy solutions (new curves help)

What does running rough mean?
Lack of advance will usually make less snappy in acceleration, but rough is not a specific term
I would also start with more advance, the emission numbers are for smog, not performance

This is a good point - "rough" is very subjective, here's a link to a video of it running up the street: https://youtube.com/shorts/j30_qrr7Wko?feature=share We've only been able to drive it a few hundred feet, it's stumbling and popping under load.

Thank you all for the guidance thus far, and to all, a happy new year

[gus]

Doesn't have the feeling of timing to me. Maybe if it was severely retarded
Still have the stock distributor? Might be nice to troubleshoot fewer things at a time.
HOw old is the gas?

[mbell]

Make sure your rev limit is set correctly.

I set mine down low (3000rpm) for shipping car and it made it run rough. Remember to set it back up and from quick fire up to pull it in to garage runs much better.

[FunElan]

Make sure your rev limit is set correctly.

I set mine down low (3000rpm) for shipping car and it made it run rough. Remember to set it back up and from quick fire up to pull it in to garage runs much better.

Interesting. We have it set to 4500 for break in. So we should move it to at least 6000 and see if something changes?

That would be a mind numbing solution to this problem after chasing it for 3 months

[mbell]

Yes setting it to 6000rpm is probably ok. Or bit higher and see.