jet advice again

[Rocket Ron]

Whats that rule of thumb which determines the size of the vents from the size of you intake valve? Doesn't the cam determines that also, say a FK 87 to a E110, in this case a K-8? I assume that would get you in the ball park, you could go up one size or down one size. Right? 

Determining venturi selection is based upon cylinder volume and rpm desired. An Engle 110 in a 2276 isn't going to make for an engine that needs 40mm+ venturies, let alone 48IDA Webers. Likewise, an FK10 in a 2276 isn't going to be setup to run on 28mm venturies in 40mm IDFs.

If you have engine "x" with a 320 degree cam in, and engine "y" with a 294 degree cam in it, all other variables (except CR) being identical, these two motors will make peak HP @ two different RPMS. The venturi size needs to match the RPM requirements.
The 320 degree motor might peak out @ 6800, the 294 @ 5500, so venturi diameter needs to be selected accordingly.

2276 Engine Y with peak HP @ 5500 would run w/ 37mm
2276 Engine X with peak HP @ 6800 would run w/ 41mm (I would err to 40mm)

Alrthough I haven't put the car on a dyno I would say fitting the 40 vents has raised the peak hp about 3-500rpm compaired with the 37mm vents

its just more willing to rev

[Jim Ratto]

Jim,how do you do your mixture screws ?
with idle jets,if you are out more than how many turns from seated until your jet is too small...2 1/4 ?
or too big 
thanks

If the idle comes on strong under 3/4 turns out from seated, when fully warmed up, the car will load up and run fat. (like with 70 idles )
If the idle comes on after about 1 turn out from seated, it's too lean. Again, fully warmed up. (Like with 55's!)

for fun, I've tried 55 idles in my car. It will not even idle, in fact it will barely fire up.

What's interesting, and why I stress "fully warmed up", is that before the engine gets to ~150F oil temp the carbs set up happy (temporarily) at much different settings, and once motor is up to temp, it all goes to hell in a handbasket. back when I was running IDF Webers on my car (and I have noticed this phenomenon on other cars with IDF Webers too) I noticed the "turn mixture screw out until highest rpm" process didn't finalize the settings. On the IDFs, I would open mixture screws until idle rpm was strong and solid, and then go back and by turning in each mixture, find a even stronger and more even idle. This would often mean turning idle speed screw back a bit to get idle down. Then going through and equalizing each throat with bleed screws, then again readjusting speed screws to suit. I have always thought this was interesting and hav never sat down and thought about "why."
On my 48IDAs, I've found, with the 60 idles, if I try and go back and sneak the idle up by turning mixture screw in, it will, initially clean things up and produce a stronger idle, but only works when engine isn't fully warmed. If I try this when engine is warm, the cylinder falls off, the "range of forgiveness" gets much narrower once the motor's warm. So once it's up on a nice idle, and the engine is at operating temp, I know it's right. Again this is with 60's.

where were we? 

[Jim Ratto]

Here's a good feature written by John Connolly on aircooled.net:
http://www.aircooled.net/gnrlsite/resource/articles/jetting.htm

quote from the aircooled.net article

" Turn the mixture screw back out until the engine idle smoothes out again, and then go out another 1/2 turn. Repeat for the other 3 cylinders. "

I can tell you, my car definitely does not like this setting. It will run fat and pig like.

[Jim Ratto]

quick update

I've changed the 55 idle jet to the 60 which helped a lot, then tried a 65 no real improvement so went back to the 60. then changed to 170 air and 165 main which feels much better higher up the rev range but has put a hole, all be it a smaller one than I started out with, in the transition area between idle and the main coming in so I'm going to try the 65 again or the 55 to see which way to go. I think Bruce said right at the beginning of this thread a 63 idle may be better.   

Jim and John you were spot on with the 160-165 main with the 170 air

BTW my original 125 air was drilled to more like a 170/180 

Ron, if you're getting the hole in transition, but car has a nice solid idle, with no pig richness (@ idle), I would try something besides going bigger on idle fuel jet. Are your mixtures screws about 3/4-7/8 turn out from seated?
I would try two things first:
1. see if you can give the motor more initial advance or a faster advance curve. Depending on rpm where the hole is, this may or mat not overcome the hole.
2. solder up your 120 idle airs (idle jet holders) and re drill to 100 and test. If car bucks (not hesitation) @ steady state rpm @ transition (say 2700rpm or so), it is too rich and you need to go up on air bleed hole size, so try 110

My car worked with combination of locked advance and going 110 on air bleed hole for idle. BTW my carbs have orig two progression holes.

[Brown-nose]

Jim,how do you do your mixture screws ?
with idle jets,if you are out more than how many turns from seated until your jet is too small...2 1/4 ?
or too big 
thanks

If the idle comes on strong under 3/4 turns out from seated, when fully warmed up, the car will load up and run fat. (like with 70 idles )
If the idle comes on after about 1 turn out from seated, it's too lean. Again, fully warmed up. (Like with 55's!)

Ok,thanks Jim...so i should be looking for 3/4 to 7/8s out from seated.cool
sorry for taking this off topic Rocket,but it's good to know. most things you read say 1 to 1 and 1/2 turns out which seems wrong to me as 60/65/70s all make for a different setting. good luck with your tuning and ps where would you get a drill bit to go 0.63 ?

[Jim Ratto]

Jim,how do you do your mixture screws ?
with idle jets,if you are out more than how many turns from seated until your jet is too small...2 1/4 ?
or too big 
thanks

If the idle comes on strong under 3/4 turns out from seated, when fully warmed up, the car will load up and run fat. (like with 70 idles )
If the idle comes on after about 1 turn out from seated, it's too lean. Again, fully warmed up. (Like with 55's!)

Ok,thanks Jim...so i should be looking for 3/4 to 7/8s out from seated.cool
sorry for taking this off topic Rocket,but it's good to know. most things you read say 1 to 1 and 1/2 turns out which seems wrong to me as 60/65/70s all make for a different setting. good luck with your tuning and ps where would you get a drill bit to go 0.63 ?

you're welcome. If the idle doesn't wake up until 1 turn out, go up on idle jet size, but remember engine has to be warm. If it comes on @ 3/4 turn out, you're good.

[Rocket Ron]

Well i thought I'd post a quick update

I haven't had much time to play of late but I did manage an hour or so on Sunday. 

Well it looks like I've settled on 60 idles 170 air and a 165 main jet. I was running OK on this setting but a quick check on the alternator showed up that I was getting about 12.4 - 12.8 volts from the alternator and not the 14-14.5v that I should be getting. A quick dig in the back of the garage and I found a new regulator which I fitted, not the most straight forward job but well worth it. The voltage is now back up and the engine is running really "crisp" and the little bit of smoke I was getting from unburnt fuel on really gunning it has gone.

The car now takes off like a scolded cat when gunning it and pull cleanly from 1500 rpm in fourth in town.     

Thanks for all your help, It has been a real education as it was my first trip into the insides of an ida, I cant thank all that helped enough, it drives like a different car now.

Got a few weeks to put some miles on before its time to tuck it up for winter. 
regards Ron   

[Jim Ratto]

Well i thought I'd post a quick update

I haven't had much time to play of late but I did manage an hour or so on Sunday. 

Well it looks like I've settled on 60 idles 170 air and a 165 main jet. I was running OK on this setting but a quick check on the alternator showed up that I was getting about 12.4 - 12.8 volts from the alternator and not the 14-14.5v that I should be getting. A quick dig in the back of the garage and I found a new regulator which I fitted, not the most straight forward job but well worth it. The voltage is now back up and the engine is running really "crisp" and the little bit of smoke I was getting from unburnt fuel on really gunning it has gone.

The car now takes off like a scolded cat when gunning it and pull cleanly from 1500 rpm in fourth in town.     

Thanks for all your help, It has been a real education as it was my first trip into the insides of an ida, I cant thank all that helped enough, it drives like a different car now.

Got a few weeks to put some miles on before its time to tuck it up for winter. 
regards Ron   

very cool. Almost identical jetting as my car. 

[DKK Ted]

Say Jim, Have ya ever ran an F-8, if so, how was tthat set-up? Or anybody else??

[Jim Ratto]

Say Jim, Have ya ever ran an F-8, if so, how was tthat set-up? Or anybody else??

Hi Ted, no have not. i know that is a popular tube amongst the guys that run DCOE's on Alfa, Lotus, etc.
I run F2's in my car.
Tried F7, F11, F4
sticking with F2

[Bruce]

Jim, I'm surprised you haven't tried the tubes (F14) Weber put in the 46 IDA (2bbl) carbs installed on the 2 liter 4 cam 904 engine.