Weber jets

[Vegard]

Ok, so my engine is now fitted with:

Idle jet F9 50
Main 175
Venturi 38mm
Aux Venturi 4.5

My RR dude says the car is to rich in the "bottom" bit didn't have any jets to fit.

Which idle jet should I get as a starting point?

[Worx_55]

I'm guessing its a hot/race motor?

I have always run 45F9 Idle jets in my race / extra mild engines and they give good mixtures down low, till the mains kick in! What air correctors and emulsion tubes are you running?

Regards
Rob

[Vegard]

It's a full race engine in fact. STR930 11.3: comp, 45DCOE etc.

The emulsion tubes are F2.

[Jack of all trades]

Going on the assumption that you run a 45 DCOE
Maybe this helps?

http://reality.sgiweb.org/mg/ahsdc/gobl ... webers.htm

And Vizzard suggests this;

Choke 40
Main Jet 200
Air Corrector 175
Emulsion Tube F2 or F9
Pump Jet 55 - 60
Idle Jet 50F11
Aux Venturi 3.5

[Vegard]

Going on the assumption that you run a 45 DCOE
Maybe this helps?

http://reality.sgiweb.org/mg/ahsdc/gobl ... webers.htm

And Vizzard suggests this;

Choke 40
Main Jet 200
Air Corrector 175
Emulsion Tube F2 or F9
Pump Jet 55 - 60
Idle Jet 50F11
Aux Venturi 3.5

Yes, it's a 45.

That setup does sem a bit "rich" for a 1293 at least

[Red1967]

I would highly recommend an AFR gauge with a wide band sensor. You can tune the weber yourself as you run the car through the RPM range. You can take it out once the the engine is running well.

I have the AEM Uego wide band gauge and sensor. Takes the guess work out of it. Saves on going to a rolling road as well. Hard to find a good rolling road over here.

My carb is running excellent. I hope you work everything out.

[Astro]

Hi,

We were always working with a wide band sensor. With a five port as well as with the eight port head. Up to 5000 you can control the mixture with the main jet, above 5000 with the air correction. For me, 200 main jets and a 40mm choke seems to be a bit much.

[ivor badger]

Going on the assumption that you run a 45 DCOE
Maybe this helps?

http://reality.sgiweb.org/mg/ahsdc/gobl ... webers.htm

And Vizzard suggests this;

Choke 40
Main Jet 200
Air Corrector 175
Emulsion Tube F2 or F9
Pump Jet 55 - 60
Idle Jet 50F11
Aux Venturi 3.5

It was the 70s when wizard wrote that and it was close to the std setup of the day. Petrol is now of much lower density with large amounts of ethanol, so the fuel jets have to be reduced to match current petrol. You would have needed to go down to 40/45 pump jets if using a full exhaust with silencer in the 70s.

[Worx_55]

When i first started racing and built my first race motor, i went and bought vizards race setup for a weber and it was a waste of money as i only used the emulsion tubes and thats it! It wasn't even close.

With my 1330 Group N Historic motor I run here in Aus I have the following on BP98 unleaded:

I only run BP 98, and get it direct from BP through a friend, as i have had issues with fuel quality from the service station, because there are too many handling variables involved once you get it out of the pump.

11:1 Comp
GR - 284mkII cam.
Choke 34mm
Main Jet 180
Air Corrector 160
Emulsion Tube F2
Pump Jet 45
Idle Jet 45F9
Aux Venturi 3.5

It pulls from 3000rpm to 8000rpm and lumps off 148hp f/wheel @ 7300rpm with 124ftlbs of torque.

Im in the process of ordering new pistons and bumping the comp up to 13-14:1 and running E85, after seeing what others have achieved with with hp gains.

[ivor badger]

When i first started racing and built my first race motor, i went and bought vizards race setup for a weber and it was a waste of money as i only used the emulsion tubes and thats it! It wasn't even close.

With my 1330 Group N Historic motor I run here in Aus I have the following on BP98 unleaded:

I only run BP 98, and get it direct from BP through a friend, as i have had issues with fuel quality from the service station, because there are too many handling variables involved once you get it out of the pump.

11:1 Comp
GR - 284mkII cam.
Choke 34mm
Main Jet 180
Air Corrector 160
Emulsion Tube F2
Pump Jet 45
Idle Jet 45F9
Aux Venturi 3.5

It pulls from 3000rpm to 8000rpm and lumps off 148hp f/wheel @ 7300rpm with 124ftlbs of torque.

Im in the process of ordering new pistons and bumping the comp up to 13-14:1 and running E85, after seeing what others have achieved with with hp gains.

Since you are using 3.5 aux venturis, so you would have come down to around 180/185 mains historically in the 70s. I see you are using 34 chokes and rev to 8k rpm. Have you calibrated your rev counter?

[Vegard]

When i first started racing and built my first race motor, i went and bought vizards race setup for a weber and it was a waste of money as i only used the emulsion tubes and thats it! It wasn't even close.

With my 1330 Group N Historic motor I run here in Aus I have the following on BP98 unleaded:

I only run BP 98, and get it direct from BP through a friend, as i have had issues with fuel quality from the service station, because there are too many handling variables involved once you get it out of the pump.

11:1 Comp
GR - 284mkII cam.
Choke 34mm
Main Jet 180
Air Corrector 160
Emulsion Tube F2
Pump Jet 45
Idle Jet 45F9
Aux Venturi 3.5

It pulls from 3000rpm to 8000rpm and lumps off 148hp f/wheel @ 7300rpm with 124ftlbs of torque.

Im in the process of ordering new pistons and bumping the comp up to 13-14:1 and running E85, after seeing what others have achieved with with hp gains.

Since you are using 3.5 aux venturis, so you would have come down to around 180/185 mains historically in the 70s. I see you are using 34 chokes and rev to 8k rpm. Have you calibrated your rev counter?

Have you calibrated your dyno?

[Astro]

what Group N please? The FIA Group N has to have the standard carbs and volume limits.

[Worx_55]

Here is the CAMS Grp N (Old APX J) Class Guide Lines...
http://docs.cams.com.au/Manual/Historic ... g_Cars.pdf
and car build sheet:
http://docs.cams.com.au/Motorsport/Hist ... -%20Nb.pdf

There is also a specific build sheet for Grp Nb Mini up to 1964 and Group Nc 65 - 72. We do have capacity limits which is 1330 or 1300 destroked and carbs are free to the period, so SU's, Webers and so on! In Grp Nb we also run up to 5.5" wide wheels, but we are stuffed when it comes to gearboxes we are only allowd 3 and 4 syncho boxes and thats it, No Dogboxes like your masters series and so on can run!

Ivor Badger, The tacho is brand new stack jobbie, and my stuff up it has 36mm chokes not 34mm, but still it will still run out to 9000 with 36mm chokes and the old GR 308/99 camshaft!

Vegard, the Super flow dyno engine dyno and Dyno Dynamics rolling road i use, gets calibrated on a quarterly basis. Which is more than your average back yard dyno!

Here it is on the the rolling road!

[cpr1]

you can tell it is correctly tuned by the exhaust sound,impressive, nice car also.

[Vegard]

Here is the CAMS Grp N (Old APX J) Class Guide Lines...
http://docs.cams.com.au/Manual/Historic ... g_Cars.pdf
and car build sheet:
http://docs.cams.com.au/Motorsport/Hist ... -%20Nb.pdf

There is also a specific build sheet for Grp Nb Mini up to 1964 and Group Nc 65 - 72. We do have capacity limits which is 1330 or 1300 destroked and carbs are free to the period, so SU's, Webers and so on! In Grp Nb we also run up to 5.5" wide wheels, but we are stuffed when it comes to gearboxes we are only allowd 3 and 4 syncho boxes and thats it, No Dogboxes like your masters series and so on can run!

Ivor Badger, The tacho is brand new stack jobbie, and my stuff up it has 36mm chokes not 34mm, but still it will still run out to 9000 with 36mm chokes and the old GR 308/99 camshaft!

Vegard, the Super flow dyno engine dyno and Dyno Dynamics rolling road i use, gets calibrated on a quarterly basis. Which is more than your average back yard dyno!

Just had my engine on a correctly calibrated "Land and Sea" dyno. If you manage to get 150bhp from that spec, please fly over here, and start building engines for a living

[Smiffy]

Ok, so my engine is now fitted with:

Idle jet F9 50
Main 175
Venturi 38mm
Aux Venturi 4.5

My RR dude says the car is to rich in the "bottom" bit didn't have any jets to fit.

Which idle jet should I get as a starting point?

Is it a 45dcoe 152 ? If so your gonna need to drill a extra progression hole and modify the emulsion tube. If it's a 13 you need to modify (drill extra holes) in the emulsion tubes. Same if its a 152G.

[CooperTune]

I too was thinking 34 s were a bit small. I think 36 s are small. My US vintage car 1293 ran 38 s and 165 airs over 195 mains. My engineer kept up with every drop of fuel Cam 2 110 we burned. We averaged 17 mpg ( US gallon ) using 8800 as a red line with a 3.9 CWP. Our EGT s were quite high but we never burned a piston. Steve (CTR)

[ivor badger 2]

Can't get this bit about 34 and 38 chokes. Longman used to machine out 40 chokes and I am sure they didn't do that if smaller chokes were better. 17mpg on a US gallon seems very economical, especially with 195 mains.

[Earwax]

I am a little slow out of the blocks,.

I have seen this mini in Group Nb ( and looked at Natsoft results), and it would be in the top 10 fastest Group Nb minis currently racing in Australia.... big claim but regularly in top 5 positions in big company. ( no affiliation- just envy from a beginning Group N racer)
Vegard - i would think the top 5 cars would be certainly over the 140hp mark at the fly,, and there is very little in it in terms of speed at this level, so Fly him over and he will indeed build an excellent motor.

The parts list in the build spec, doesn't show all the good bits... (- free crank, free cam, free pistons etc) and really well flowed heads, inlets and exhausts plus some secrets... well come on the top guys would all have some secretssss

Ivor - 38s would seem to be very common in Group N minis here, with some 40s in cooler climates but a number of these lads and ladies actually test 36 vs 38 etc whilst on the dyno in back to back comparison, and so know what works. The speed of flow it seems is just as crucial as volume,,, (this probably is a little different to the 70s (guess only) where bigger valves etc meant more power. Again fuel differences hard to gauge even our Race 100RON is discarded avgas, and the Group regs won't allow artificial octane boost products.

Anyway hope the OP got the jetting sorted.