48 IDA jetting at 400m altitude /1300ft

[1950split]

Hi,

I know that every engine is different but I'd like to have your opinion on the jetting I selected for my engine which has the following specs :

2276 (82*94)
10.5:1 CR
CB 2289 cam, advanced 4° (2° built in+2°)
Brothers Mid-D heads, 44*38 valves
CB 1.4 rockers
GB 590 manifolds
48 IDA (spain), 3rd hole, 3.00 Weber needle, 2.5 psi pressure
Mallory unilite
Timing advance: 8° BTDC

Gearbox : 3.875 3.78/2.06/1.26/0.89

As mentionned in the subject I live at about  1300 ft.

My current jetting is :

40mm Vents
60 idle/120 idle air
170 main/200 air/F2 emulsion.

I have no intake leaks/exhaust poping or accelerator pumps dripping.

So far I've just started tuning it but it is really too rich (measured with a LM-1).

At idle (1200 rpm) I was in the high 13/low 14, idling smoothly (messed with the idle mixture screws for a while)

However when I started driving in traffic (25 mph... yeah lots of traffic  ), my AFR fell to low 12 and I noticed that at traffic light the engine would die if I did not keep the idle at 1200 rpm.

I wonder now if my mains are not too big according to my altitude and I'm thinking of going down to 165 or 160 mains and reduce main air to 190 or 180 in order to have the mains coming in later. I also have 130 idle air stacks, could this help as well ?

Would it be better to switch to F11's ?

Thanks for your help,

Phil

[lawrence]

Your jetting does not seem far off. Make sure your ignition system is operating properly and grounded to the chassis. Solid, clean, electrical connections throughout the entire car are very important. Double check your fuel pressure setting. What pump and regulator are you using? I have always set my fuel pressure at 3 psi with a stock IDA needle and seat and never had problems with flooding. A larger needle and seat, such as in your case, will be more sensitive to fuel pressure changes. How many turns from seated are your mixture screws? Should be approximately 1-2 turns from seated.

It may be necessary to dial in a bit more initial timing, maybe 10 degrees BTDC, so that you can back the idle speed down a bit.

If these suggestions do not change drivability, proceed to change jets. Your idle jet combination should work and so should the emulsion tube. I have always liked the way my car ran with the f11 while others have tried the f2 and had great results as well. Try a 165 or 160 main like you suggested. That is a good starting point. The air corrector should be sized according to the main jet and the weber tuning manual says: main + 30 to 50=air corrector. So, with a 165 main, the air corrector should be from 195 to 210.
The weber tuning manual does not factor altitude into jet changes until 4900 ft, or 1500 m, so you probably do not have to correct for altitude. I could be wrong though since I live near sea level. Others may have additional insight.

Try these suggestions one at a time, make notes of the changes, and think conservative so you don't blow the engine up. It may take some time, but it can be fun, and afterward you will know a great deal about your car's tune-ability. Good luck.

[LGK]

Hi there,

The CB 2289 has quite a bit of duration,i would have set the compression more to 11-or even 11.5/1 ...
Cams like the CB 2289/engle FK87 needs at least an 65/110 idle to run,don't always follow your air/fuel monitoring,with that big cams your lambda is fouling you sometimes.
Like Lawrence said,more initial timing would be better too,at least 10-12° at 1050rpm.

Good luck Steve

[1950split]

Thanks for your replies guys !

Please excuse my ignorance. Why does a cam with more duration need more timing ?

Well I kept on working on the car yesterday evening.

What I reached is the following :

idle timing : 8° BTDC @ 1100 rpm.

Idle : 60 (approx. 3/4 turn out)
Idle air : 120

Main jet : 165
Air corrector : 190
Emulsion : F2

Did some launches (only up to  5500 rpm because the engine is brand new) and the engine behaves much better. I can notice a minimal stumble at about 4500 rpm if I remember correctly.

I noticed that if I go with the "lean best idle" procedure, my idle always ends in the low 12. I don't want to wash my cylinders before the rings are seated. Therefore I took the main stacks out to adjust the idle mixture screws by 1/8 turns 'til I reached an AFR in the hight 13 and low 14.

Although I'm quite pleased with the result (it still needs some tuning), I'm concerned of being too lean at idle. The engine does not fart from the exhaust and I have no backfire in the carbs though.

I wil drive a little longer now in order to seat the rings properly as this was impossible so far.

Thanks

Phil

[richie]

Down low that cam is causing alot of the fuel going in to go straight out again giving you a false afr reading,you should see some benifit from running more timing at idle and limiting it higher up,you quoted 8degrees advance at 1100rpm but this really isnt important,its the maximum advance thats important,as an example I run 32degrees advance on idle but only 26 at 2800rpm upwards,now with a distributor you can do that,but you can restrict the advance curve so you run 15 at idle and only 30maximum,then use the springs to control how fast it comes in.The extra advance at idle will really clean up the low afr and help loose the stumble as you go from idle to main circuits.

Also I am not sure what you mean by 

Therefore I took the main stacks out to adjust the idle mixture screws by 1/8 turns

why would you take the main stacks out to adjust the idle screws?

cheers richie

[1950split]

Hi Richie,

Couldn't this lot of fuel going in and straight out again cause a cylinder washing? This is the reason for which after adjusting with the "lean best idle" method I finished adjusting the idle mixture screws with the LM-1 til I was in the 13.7-14.2 range.

I took the main stacks out in order to see up to which rpm range the progression was going, in order to adjust my main air jets. Actually I noticed that I could easily rev the engine up past 4000 rpm. With this in mind I switched my airs from 200 to 190 and mains from 170 to 165.

I must say that with the main stacks out I had less erratic ups and downs while adjusting the idle mixture screws.

I have a Unilite which is set at 32° full advance with grey grey springs. It should be all in a 2400 rpm. (this I haven't tested so far).

[richie]

Hi Richie,

Couldn't this lot of fuel going in and straight out again cause a cylinder washing? This is the reason for which after adjusting with the "lean best idle" method I finished adjusting the idle mixture screws with the LM-1 til I was in the 13.7-14.2 range.

I took the main stacks out in order to see up to which rpm range the progression was going, in order to adjust my main air jets. Actually I noticed that I could easily rev the engine up past 4000 rpm. With this in mind I switched my airs from 200 to 190 and mains from 170 to 165.

I must say that with the main stacks out I had less erratic ups and downs while adjusting the idle mixture screws.

I have a Unilite which is set at 32° full advance with grey grey springs. It should be all in a 2400 rpm. (this I haven't tested so far).

I believe you are overthinking the cylinder washing thing,if it was in the 10.x afr then yes you could be worried but 13-14 "i" wouldnt even consider it,the fuel is going straight out the exhaust,not sitting in the bores

The engine will go to 6/7/8000 rpm on the idle jets,try going downhill in 2nd gear on light throttle,it will rpm,but there wont be much vacuum to pull on the main circuit,certainly from my understanding the mains and airs arent affecting what you are seeing,and they cetainly shouldnt have any affect on adjusting the idle screws,taking them out means if you created enough vacuum to pull on th emain circuit you really could wash the bores as the hole in the circuit is your only restriction

Your unilite will have an advance stop,changing this will allow you to run more initial advance and keep it to your desired max advance,but you may find you need to change one of those  grey springs for a blue or silver stronger one

cheers richie

[dragvw2180]

Looking at the numbers you posted for A/F ratios at idle they are definately not flooding your cylinders, you are close to Stoichiometric  which is 14.6 . I would look at the carbs and make sure the butterflies and shafts fit properly, consistantly close in the same spot. Any wear on the throttle shafts will make your idle inconsistant ( vacuum leaks at the shafts intermittanyly ) , if your idle drops down from the point you adjusted it I wouldn't be suprised if the A/F mixture went richer. FWIW 48 IDA's on the street are going to be a compromise of performance vs consistancy,  expect them to be finnicky. If I was going to drive it on the street I would probably have picked a differant carb setup, I love them on a drag car. I also would adjust the carbs with everything in place including air cleaners, Mike McCarthy

[lawrence]

I could never get my car to idle properly with the dual grey springs in the mallory unilite. They are very light and begin to advance at about 600 rpm. Mallory recommends the advance in the distributor to start at least 100 rpm HIGHER than idle rpm. If it works for you, cool, but I still think you would benefit from more initial timing.

My initial timing is 10 degrees with 30 total. Advance begins at approx. 1400 rpm and is all in by 2800 rpm. It is a street car 100%, so no need to go nuts. I may try swapping one brown spring for a pink spring. This will give me full advance at about 2500 rpm.

[1950split]

I went through the unilite spring kit instruction.

Indeed if I idle @ about 1100 rpm, the gray gray springs are not really the good choice.

I think that either brown/gray or brown/brown would be better.

Should I switch the springs?

[lawrence]

Try it out. The car may or may not run better. My car idles at 1000 rpm and I have used 2 brown springs since I bought the distributor. Another curve that looks good is brown/pink.