Need advice jetting 40s on a short stroke 3.2

[rory gallagher]

As the title says.
rebuilt 3.0SC w 98mm Mahles, big port heads, DC60 cams, lightweight rods
9.8 to1 and '82-'83 dizzy recurved for carbs.
Very young 40 IDA 3C carbs.
Looking for jetting and venturi help/info from personal experience.
3.0 info is easy to find. 3.2 ? .......my search skill may be at fault
TIA
Rory

[JackkTheMackk]

You should have 46mm carbs. 40s are too small for that displacement paired with those cams. I have a 3.2ss with DC60s and i’m even running 42mm chokes in pmo 46. My build thread has all my jetting info.

[porschyard]

Originally Posted by JackkTheMackk

You should have 46mm carbs. 40s are too small for that displacement and carbs. I have a 3.2ss with DC60s and i’m even running 42mm chokes in pmo 46. My build thread has all my jetting info.

☝️What he said, I know it’s not what you want to hear but unfortunately the 40’s are too small for the configuration

[snbush67]

Hi Rory, Subscribed. I think that it is worth experimenting. You need to be able to monitor your AFR’s and check your plugs frequently. I don’t know what the largest choke is that you can run in the 40’s, I think it’s a 38’s which is what I am running in my 3.2 SS, with 46 PMO’s, thats probably where you need to start. If that’s what you got then I don’t think your going to be limited.

I think that the major consideration with the 40’s vs the 46’s is that you have to figure out how to suck the same amount of air, through a smaller hole, at a higher velocity.



I’m pretty sure sure that if you want to make the most efficient power then your going to have to mix the same amount of fuel in less time because the air is going to be moving faster.

Likely your going to stick with the 55 idle jets. Hopefully someone will chime in with emulsion tube recommendations.

It would be good if you told us the current chokes, jetting, and e tubes you have, also what exhaust and ignition are you using?

Also, consider sharing your location, someone might be close and can help out.

Cheers, Shane

Who is the weber whisperer? 40 weber Ida, Largest displacement engine on 40mm

[rory gallagher]

Hey Shane
Currently the carbs have 34 vents, F3 emulsions, 170 air corrections, 150mains and 65 idles.
I'm in north New Jersey.
I had the engine running on a stand and it responded well to acceleration but did not idle well.
The response to mixture adjustment is weak coming from obviously lean to adequately rich.
It was pulling 6 -7 on my syncrometer on all cylinders but with fluttering and spitting back.
I have 36 vents and a good selection of jets on hand.
I suspect there is a problem with some contamination in the carbs as well. That's first to be
corrected.
Unfortunately, I cant do much for a couple weeks but want to gather input and be prepared
for when I can get back to it.
The engine is back in the car, it's a 914 6 GT replica with a 916 trans and suitable front oil cooler.
Thank you for your help
Rory

[snbush67]

I think that idles (65’s) are probably too big, try 55’s. Everything else seems reasonable. Try to get your Fuel pressure at 2.5 - 3 PSI and get your float levels at exactly 1/2 way up on the glass, there is a small dot that marks the half-way point.

A common cause of contamination is the black coating on the floats, little specs of “black magic” peel off and clog things up. A common way of curing it is to razor any hanging flecks and lightly sand the areas of the floats to smooth it out, be careful not to peel it away.

[rory gallagher]

Originally Posted by snbush67

I think that idles (65’s) are probably too big, try 55’s. Everything else seems reasonable. Try to get your Fuel pressure at 2.5 - 3 PSI and get your float levels at exactly 1/2 way up on the glass, there is a small dot that marks the half-way point.

A common cause of contamination is the black coating on the floats, little specs of “black magic” peel off and clog things up. A common way of curing it is to razor any hanging flecks and lightly sand the areas of the floats to smooth it out, be careful not to peel it away.

My carbs are NOS Webers....the later production ones ...from Spain ?
My float level (brass floats)is between the two upper lines on the old fashion Weber tool.
Fuel pressure is between 3-3.5 psi....too high ? with the EMPI / Carter fuel pump

[garment]

Subscribed as well. I recently went to 3.2 P&Cs and 964 cams but still running CIS. Definitely PMO-curious...

[snbush67]

Sorry Rory, I was thinking PMO’s with the black magic comments. Not sure about the psi but I think 2:5 -2.8 is a good range.

[Trackrash]

This is what you need. No way to do it right otherwise. You should go bigger with the venturis. I think 36 is the largest for the 40s. 38s would be best if that is possible.
Sounds like your jetting is in the ball park. FWIW, my motor won't run with anything less than 62 idles.
Paul Abbott
Weber service specialist
Performance Oriented offers to bore 40 webers to 44, I think. Might be work checking it out.
FWIW, I'm running 9.8-1 CR on my 3.0 with 40 webers with 36 vents. I'm using a GT2-102 cam and it's a good match for the 40 webers. It will be interesting to see how your motor behaves with that cam you have and the 40 webers.