Problems jetting my 2332 at low/mid rpm

[Speed-demon]

Hello. Yesterday I was at Jee-racing's Stuska Dyno to jet and adjust my 2332. Engine specs are:

JE pistons
84 x 94 = 2332
Street Eliminator heads ported by Udo Becker. 44x37,5 valves. JPM Oteva springs
Short Berg inlet manifolds
Weber IDA 51,5 Jaycee with 3rd progression hole. 42 mm venturis
JPM 406 cam (10,3mm lift at cam, 282 degrees 0,05 duration)
A1 1 3/4 exhaust
Approx 11:1 comp
Full MSD setup.

The engine is a blast. It dynoed 174 hp at 6200 rpm (did not try higher RPM) with fan belt at a very strict dyno. Another engine which dynoed 178 at the same dyno goes 11,8 at 402 (and dynoed 200 hp in a dynopack).

The problem is that it completely falls over at full throttle below 4500 rpm. The torque curve is falling fast and the engine is very rich below 4500. It happens almost whatever main and air jets we try, and whatever emulsion tubes we try (we tried F2, F7 and F11). At part throttle it has good torque also below 4500 rpm, and no problem with too rich mixture.

Can it be that it is "overcarburated" below 4500, and that we will not get it to run perfect at full throttle? The smallest idle jets we had was 55. So we have not tried smaller idles than that. Any ideas of what we can try?

The  ignition was set at 29 at full advance. The MSD is set u with "silver/silver" springs. We have not tried fiddling with the ignition timing yet.

BR

Jens Kristian (Oslo)

[ibg]

A lot of possibilities here: My engine is similar (bit less cam, bit less compression). 42 vents should work with F2's. I have had good success with 110 idle airs with 60 - 65 jets. I think 55's are too small (with 3rd hole drilled). Timing; my engine like lots of initial, close to 20 deg, all in by less than 3,000 rpm. 29 deg all in sounds good, but I don't know about the curve in the MSD with the springs you are using. Some one else should be able to comment.
With work on the dyno I got my engine to work across the transition (2500) and pull from 3000.

[Udo]

Did you try bigger idle jets ? I do not know about the cam but 282 sounds not too big .
I( would recommend F11 and 160 mains 180 air to try first
Udo

[Speed-demon]

No we did not try bigger idle jets. But how can bigger idle jets help a too rich mixture below 4500? Above 4500 it responded to changes in main and air corrector jets. And as I said, we tried both F2 F7 and F11 emulsion tubes.

The cam is maybe a bit big. The engine previously had a FK46/FK47 combo from JPM. Pulled strongly all the way to 7300!! The engine gives a strong impression now as well. Lots of torque on half throttle below 4500. But it gets extremely rich at full throttle.

Our theory is that the gas speed through these heads is huge (otherwise we would not get this kind of horsepower out of such relatively small ports). And that this draws too much fuel out of the idle circuit (since it has three progression holes). So we want to try smaller idle jets. How does this work in theory? Are idle jets important at all at 3500 - 4500 rpm? I suppose they du not "stop" delivering fuel at this rpm?

[Jesse/DVK]

Did you try changing the ilde air holders?

[Speed-demon]

No we do not have any experience working with idle air holders. I read on the web that IDA idle holders are usually 0,6 1,0 or 1,2mm. How do they work? Will the engine run leaner mid-range with larger idle holders or vice versa? What size should we try?

[Udo]

I do not remember the heads , but they should flow  .  A big cam makes it rich in that rpm range. May be you ask Johannes about this. I got now with 278 degrese @0,5  242 hp at my wifes engine . Pulls strong from 2000 rpm with full throttle . I have modyfied old VW 041 heads on it

Udo

[neil68]

I've experimented with a few jet changes on my simliar 2332 cc: 10.3:1 CR, JPM heads, JPM cam 274-degree/10.8 mm lift, full MSD, short manifolds, 1.75" header and ended up with the following:

F2 (tried F7's as well)
210 air
180 main
60 idles/120
42 vents (48 IDA's)

This engine has dynoed at 180.4 HP to the wheels and seems to work best at 32-34 degrees advance on 91 and 94 octane (Canada) which would be 95-98 RON in Europe.

[K-Roc]

Hi from what I understand about the 51mm modified Webers is that the signal on the booster venturi gets messed up when you bore the carb. I know thet when Geers performs this modification he also changes the booster venturi to a different one, perhaps this is a problem you are experiencing.
Do you have any un modified 48's you could try?

We have never really had great success with " just Bored out "  IDA's

As you mentioned you feel that you have a very strong signal due to the heads and this could be possible, every engine is different that is why no one can tell you what or how to jet the engine, you have to give it what it needs not what you think ( or what people tell you it needs)

Good luck with it.

K-Roc

[Speed-demon]

Thanks for all the help. I do not have any experience changing booster venturis either. Can someone explain what they do, and how they can be changed (what happens with larger/smaller sizes)?

BR

JK

[Speed-demon]

Turns out that I have 120 idle jet holders. I Will try larger. 130?

[ibg]

As the Idle airs get bigger you will need bigger idle jets. I tried 110, 115 and 130 idle airs. with 130's I couldn't get a consistant mixture accross idle to 2500 even with 70 idles. My 2 best combos were 115 idle air 65 jet and 110 with 65 jet.
The 110/65 pulled to higher revs (3000) with a fairly consistant 13:1 - 14:1. This may all be different on your engine but might help as a starting point. Remember the idle jet still flows when the mains tip in so it is good to have them sorted first, then look for an emulsion tube, airs and main to get the rest right.
I tried john C's advice of driving the car with no main jet stacks in the carbies to see what the idles really did. thats how I so settled on the 110/65 combo. http://vwparts.aircooled.net/    has some good carbie tech advice
Not sure of the length of the stax on your carbs but if they are very short the secondary venturies can be shortened to to increase the signal. (tip from Doug Berg that worked well for me)