Weber 45 DCOE tuning in WI
 

I know there have been quite a few threads for tuning a Weber 45 DCOE and jetting to use, but I was curious if anyone has had a 45 DCOE on a 12a tuned in Wisconsin and if so, where at, and the results? Currently my car accelerates pretty quickly, but as soon as I get to 4500 - 5000 rpms, it seems to fall on its face. I've verified my spark plugs are set correctly, currently running an MSD 6a with 3 blaster coils, 1 for each leading plug, and one for trailing plugs, running the full racing beat street port exhaust system, but the engine is still stock.

I'm looking to take the car in to have it dyno'd and tuned, but the tuning rates are 250/hour and I'm afraid I may not have the correct jets available to get the car tuned correctly. From reading other documentation, the symptoms I'm having is usually corrected with changing the size of the Air Correctors. I started with 160, and have gone down 3 sizes, to 145, but still having the problem. If anyone near the Slinger, WI area has experience with jetting and tuning the 45 DCOE and can at least let me know if tuning/jetting will correct the issues, it would be greatly appreciated. Otherwise, if you have taken yours to a tuner and had great results I'd love to know the place. The place I plan on taking it for tuning is Beyond Redline in Greenbay.

What size chokes are in there?

The current numbers for all:

Choke - 36
Venturi - 45
Main - 190
Emulsion - F11
Air Corrector - 145, but i have 140,150, and originally started with 160
Idle - 60F9
Pump - 45

also, not sure if it is typical, but in order to get the car to idle I did have to adjust the air bypass screw.

Any one else run into the problem with the Weber 45 DCOE where the acceleration is great, but top end completely lacking? I know it might not be possible to have the best of both worlds, but currently as soon as I get to 70-80 mph, 4500-5000 rpm, there isn't much power. I'm just not sure which jetting should be adjusted, and whether up or down in size, so if any one can give some advice it would be appreciated.

each time it idles? or just the one time to set it up? the Weber is designed to be used with 1 barrel for one or sometimes two cylinders. the rotary is almost like 3, so its moving a lot more air, and adjusting the air bypass is needed. with the IDA, we end up moving the throttle stop to add more air, and then we loose a transition port, which tends to cause hesitations.

190 jet might be too big. also what fuel pump are you using? it could be running out of fuel. its helpful to have a wideband oxygen sensor here, it will tell you if its too rich or too lean

The air bypass was adjusted the one time when initially tuning. I'm using the Mallory 4070M fuel pump. I do have a wideband hooked up to the leading exhaust pipe and numbers are looking good. When I rev the engine and monitor the gauge, it doesn't appear to be too lean or rich, but just doesn't really have a top end. Typically the number is around 12-14 regardless of the rpms.

WOT over about 4000rpm should be about 12.8:1 +/- about .5 of a point.

if it is, the carb is close enough, and you need to look elsewhere. ignition is important, wires can be checked, but cap and rotor should just be newish.

after that you just need more air flow, if you could up the venturi's to 38's that would help.

what are you running for exhaust?

For exhaust I'm running the Racing Beat Streetport Exhaust system. For ignition I have the MSD 6a with 3 blaster coils and MSD wires. I may just get a new cap and rotor as well as new spark plugs, they should be good, but it has been quite a few years since they were replaced. Any thoughts on the spark plugs I should run? I believe I'm currently running the NGK BR8EIX plugs. I'm also going to get the 38 venturis and see if that makes a difference.

in the trailing the GSL-SE, or FC/FD trailing plugs work fine. BR9EQ, or BR9EQP

for the leading i like the Rx8 leading plugs, they work better and last longer.

When you say the RX8 leading plugs, are you referring to the ones from Racing Beat, or is there a specific brand/model that you use? Also, when looking at the ones from Racing Beat, it doesn't look like the gap can be adjusted.

I run the 8 plugs as well, seem to work great. Haven't pulled em yet to see how they are aging, only been in there a few thousand miles so far.

More air sounds right and then you may need to do more tuning as it will lean out and change the mixture.

Sounds like you have it as best you can get with the venturis you have in there.

its the spark plug from the Rx8 car. its a better design than the previous plugs, Mazda Part number N3Y8-18-110A-9U, NGK is 6700, or RE7C-L

if you want to play with spark plug gap, and you have an MSD, try the Autolites. they need to be checked to make sure they are all the right number in the box, they also should be gapped, and then put them in the engine, and spin the engine by hand a couple of times, and make sure it doesn't hit stuff. once you do that though, the Autolites make power, and are cheap. they do not have quality control though, so you need to make sure they are ok.

Back when I played a lot with a 45DCOE I noticed a considerable high RPM improvement going from 36-38 chokes and very little difference in the lower RPMs. The rest of your jets look within the range of ones I had success with. The best change I ever did on mine was go with a different length pump rod. I forget if I went longer or shorter, but I'm leaning toward longer. Might be in one of my old posts.

Probably longer, this is a common mod on Nikkis AP as well.

Finally got the 38's in the mail, got them installed, as well as the RX-8 leading plugs, nice and tuned and full power now!!! Before it would barely get past 5k and after installing it, my wife helped me tune and she had no problem getting over 7k and went up to 8k. Still have the same acceleration at the lower end, but now it doesn't fall on its face above 5k.

Next step will be taking it to a dyno to fully dial in the tuning, but I am grateful for all the help the members on the forum provide.

Yeah actually and I live in Wisconsin too, just north of Madison and I'm running in to the same issues

Had the same feeling after installing the 45 DCOE, went from 36mm to 38mm choke, now also go happily to 7k rpm.

FWIW, I've been working with a 45 DCOE style EFI throttle body. Power curves we saw on the dyno may be relevant or at least food for thought.

A little info, my setup is a 45mm Jenvey throttle body mounted to one of those wrap around manifolds. There are no chokes or restrictions other than the butterflies since it's EFI. The throttle body is 90mm long and we tried 120mm flared horns and 40mm flared horns.

The '85 12a motor has a quite large street port and has been balanced for 10,000 RPM but we can't get it there. No air filter was used for testing and the hood was open. The 120mm (210mm total length) peaked at 6500RPM and started losing power fast after that. The 40mm (130mm total length) horns bumped the power band up to a peak at 7,000RPM and gained 11hp but still wouldn't rev much over 8,000. Peak power was 129hp but it was a dynapack and the operator said it has been reading low. Best guess is that it's making 160-170 on a typical dyno. They recently had a built Miata on the dyno and it only made 116hp when they were expecting 150+.

Anyway, it seems clear that either the manifold or the throttle body is restricting the motor. I've got plenty of spark with direct fire, the racing beat long primary exhaust, lightweight flywheel, electric fan, etc, etc, and there's no reason it should be peaking at 7k and losing power by 8 other than the intake is holding it up.

So depending on the overall length of your setup, and the size of your choke, it makes total sense that you are having trouble making high Rpm power. Shorten the air horns if you can, and run the largest chokes. And if you're looking to make power over 7k, run something else. I think the limits of the 45dcoe are somewhere between a stock port and mild street port.

Yep, the 45 DCOE just can't supply the air needed for more than a mild port job. This is why the RB prepped Dellorto was a 48 DHL:A. The wrap around intake also steals high end power in exchange for better low end torque. If you can go to a side mount short intake that hangs the carby just over the headers it will do better even for the 45.

a street port isn't going to make power that high no matter what intake you have on it

That's the current plan. I'm going to pick up the short manifold and make a run on the same dyno. It's an easy swap for me to try out.

It's not a basic templated street port, it's about as far as you can go without bridging. If I can get 9,000 out of it I'll be happy. Swapping in a Kia 4.77 soon.

if you can get it to peak around 7k you'd have a much more broad power band, net/net it would be faster

It peaks at 7k now, but falls off by the time it reaches 8k.