10/15 free HP

This weekend I installed an air fuel meter from CB. It's a three wire o2 sensor with a needle gauge that shows the mixture. I'ts funny as I when I hooked it up I thought I might be a little off with the mixture but nothing to be upset about. All I've got to say is I was way off and yet I thought the car ran great.

I got to tunning the car and I kept going down in jet sizes and the car sure seemed to like that. My idle jets are now 50 down from 60 and my main is 135 down from 145. The car is much more peppy and the engine seems to CRACK when I blip the throttle. Tunning is so much easier now as I can tell what and where the engine needs more or less fuel. As I adjust the idle mixture I can actually see the needle move on the gauge per 1/8 turn of the idle screws. The best thing about this gauge is it's not as spastic as some of the other LED type units, the needle on the CB setup moves nice and easy.

Once I get it all perfect @ 13-14 to one then I'll be appeased. I also can't wait to see what my mileage is after this. With gas prices out here at 2.35 a gallon I bet I could get the cost of buying/setting up the gauge within a couple thousand miles.

J-P

Not being real mechanically reclined, the adjustments you made with your new do-jigger, does that mean you were making the car run leaner or richer?
MM

50 idle and 135 main are 99.9% effective for a 44mm Weber as long as you run pump gas- no matter what the engine size is.......

Well, I don't know about 99% effective, Jake. It depends on what A/F ratio you want to run (power or economy), which may depend on your compression ratio - too lean may move the engine into detonation country. Leaner will certainly make acceleration crisper; just make sure you don't have pinging under any RPM and load condition. Leaner also means your engine will probably run hotter.

If pinging occurs under about 3,200 RPM (transition circuit) go larger 1/2 size on the idle jet; if pinging occurs from 3,600 on up go up one size on the main jet (main circuit).

Those are just ROTs - your engine might like a smaller air correction jet better to correct pinging on the main circuit.

Jake, whats most appropriate for idf 40's, on an 1885 type I stroker motor, with a mild cam?

Thanks for any reply

Gclarke

J.P., I gassed my 911 pickup (gashog) in Vancouver over the weekend. Because of the hot cam and high comp I have to use 94 octane and that costs...are you ready....$4.55 per gallon!!! True, our gallon is a bit larger (something like 20%), but still, $4.50 for a gallon of gas is hard to accept.
Ron
p.s. it's actually $1.01 per litre (for you metric types). Got some more yesterday. ONLY cost me $0.96 per litre.

I'm still messing with it a little and will continue to adjust the air/fuel mixt. as I go. I agree with watching out for the pinging, it could be a probelm in diff. altitudes. Anyway, for the first time I feel like I'm really getting to understand Webers. With this gizmo and to answer the above question, I'm getting the engine to run leaner. Now all I need is a couple days with a dyno to understand more about these motors.

J-P

Also I havn't gotten into the air correction jets yet, what do these do exactly?

J-P

Weber says the air correction jets act as a "brake" on the fuel in the main circuit system. For example, without them a main jet that is correct at 3,500 RPM would be too rich at 5,000 RPM.

Increasing an air correction jet three sizes (like from 185 to 200) makes the mixture leaner at higher RPM - it would be about the same as making the main jet one size smaller (like from 150 to 145). The difference would be that the main jet affects the mixture all the way from transition up, while the air jet has more of an effect at higher engine speeds.

The air correction jets act progressively, that is, when you first get on the main circuit from transition at around 3,300 RPM influence from the air correction jet exists but is negligable; as engine speed increases the air correction jet becomes more of a "leaning out" factor.

The combination of main and air jets should give the "correct" mixture from transition all the way up to full throttle maximum RPM.
(Message Edited 9/9/2003 1:53:30 PM)

So bassically the air jets lean the engine out on the top end. I'll keep an eye on the gauge and see how it goes, it's hard to look at the gauge and drive here in Southern Cal, to much traffic. Perhaps this weekend I can get more into it.

J-P

J.P.,
Can you tell me How many turns out (from lightly seated) your mixture screws are, and how many turns out your idle speed screws are set at.
Thanks

Dave

Dave,

I've since changed the idle jets to 55, seems the engine likes those better and the O2 gauge reads more steady. With the 55's in there the screws are rotated out about 450 deg. from the stops. Hope this helps.

J-P

JP -
I was running 55 idles, and 145 mains in 44 IDF's.
I noticed a flat spot at 1700 - 2000 rpm - I think this was an over-rich condition.
When I switched to 135 mains the flat spot went away at 1700 - 2000, but a new flat spot appeared at 3000 rpm. I think my mains are too lean now.
I'm going to drill out the mains to a 54 "wire size" (1.379mm)and see how that works; if they're still too lean I'll try drilling them out to 1.40mm
(Message Edited 9/17/2003 12:22:12 AM)

I tried the 1.379mm mains, and they seemed a tad rich, so I switched back to the 135s.
I also increased the idles up to .57150.
This combination seems better than anything else I've tried - no flat spots, and very crisp acceleration.

I think you may be right on the money. As I watch my gauge I notice all is fine until I hit about 2600 rpm or so and then the gauge reads lean for a split second and then back down to 12.5-13-1. I think my idles are a tadd small, will have to get some 57's also. God I love this gauge (don't mean to brag). I know it's not as accurate as a braodband type but it really gives me a good indication as to what to adjust.

J-P

If you are using F11 emulsion tubes in dual Webers and have a momentary lean spot in transition that can't be cured with an idle jet change try F2 emulsion tubes. F2's are the same as F11's except they are slightly skinnier (by .5mm, more reserve fuel in the jet well) and lack a row of holes at the top (a bit richer transition and mid-range but leaner on top end).

You'll have to rejet when changing from F11's to F2's - a good start would be one size smaller main and two sizes smaller air correction jets.

JP,
Instead of spending $20 on a new set of idle jets, you can buy a wire guage drill bit (size 74) for $1.50, and drill out your idles to .57150.

Dave

I'm almost there, I almost have the full collection of Weber jets. I know, it's pretty funny. The drill bits are a good idea it's just that one day I'm sure I'll want to change carbs. or up the vents. so I'll need to rejet again but first I want to be able to PERFECTLY tune these carbs. Anyway, I'll go get some 57 idle jets soon and see how that works out, after that I'll go to the emulsion tubes. Now as far as how the tunning is so far, the car doesn't hesitate it just has a very, very small flat area that pops up around 2K. I'm hoping the 57's work out. God, I love that gauge. I finnally can see the light.

J-P

JP,
I tried 185 air correction jets, and they seemed a little rich, so I switched to 200's. They work much better.

JP -

Where are you with your jetting combos?

Dave

Right now I'm at the same point I was before....I got into a house project that delayed me from driving the car for a couple weeks. I did drive the car around yesterday though, I definitely need to go bigger on the idles as I can feel a flat spot right aound 2500 rpm, also the needle on the O2 gauage shows a lean condition there. I think the weather has something to do with it as before the hesitation was almost not noticeable. The cold air might be adding more oxygen to the mix now. I'm going to go over to the carb guys today and see if they have some 57's.

I'm really currious about the CB horizontal spray bars. Has anyone here tried them. From what I've heard they improve throttle and add more rpms. Anyone know anything about these?

J-P

J-P:

I installed a set of horizontal discharge tubes (from CB) in my Dellorto 40mm DRLA's. Pretty easy conversion, taking maybe a couple of hours to complete both carbs. Unfortunately, I have no comparo info for you, as I did the conversion before I ever fired them up.

I'm running them on a 2,110 with an Engle 120 cam and 35.5 X 40 valves. I have not yet opened up the intake manifolds to match the head ports, so they're a bit smaller than they should be.

Overall performance is good, although they seem to be running a bit rich - I believe I have 140 main jets, but not yet sure (been 6 years since I put them together). I'll be pulling the carbs apart this winter and re-jetting, but am planning on installing a fuel mix meter to get it right (thanks to my high-tech son).

I'm running about 1,000 rpm at a reasonably smooth idle, (not a lot of shake) and I've noticed no real flat spots thus far. The over-rich mix tends to make them hesitate slightly when gently applying throttle at speed (any speed) in 4th with an occasional exhaust pop as they clear out (plugs are also a bit dark, too). I have been impressed with the low and mid-range torque of this engine and attribute some of that to the horizontal tubes. I didn't expect really good mid-range drivability with this cam, but I got it anyway. Can't wait to get them jetted right!

Hope this helps......Gordon

Thanks Gordon..

J-P

Put the 57 idles in and the car seems to love those. The O2 sensor shows a reading of 12.5-1 to 14.5-1 ratio when driving. The car has a nice pull all the way up to 6K. I may fiddle with the mains a little as it runs a hair rich after about 4500, or that might be the air correction jets. Anyway things are going well, can really dial the carbs in with the 02 sensor. Can't wait to see what kind of mileage I'm getting.

J-P

Jean-Paul: I have the horizontal discharge tubes from CB. My combo is a 2275 with Dellorto 45s. I found the change is comparable to stepping down about half a venturi size. Say from 38s to 37s. I couldn

That's interesting! I would think the update kit would add more on the top end of things. Just wondering Bruce, where does your engine like to be in the rpm range? My car seems to like anywhere from about 2500-5000 rpms, at 4000 rpms or so the car really picks up. I'm running weber 44's now and have been intrigued by the CB update kit as I was hoping I'd get a little more on the top end without sacraficing the bottom end. How difficult was ithe kit to install?

J-P

JP: The horizontal tubes have a bit better fuel atomization at lower intake velocities. So you should get better bottom end (similar to changing to a smaller venturi) but you won

Bruce,

Thanks for the advice, I'll have to look up what size the vents are in the Weber update, as it is now I'm running 36's in the Webers and the low end is great already. I would like to get more out of the engine so I was hoping the update kit would add a little without sacraficing the longevity of the engine, ie ratio rockers ect.. I've got to say though that I've finally got the carbs in a near perfect tune and the differance is pretty big as far as what it was before doing all this tuning work. Does the update kit use all the same jets ect. that the Delortos do? If not do you get a multitiude of jets
to play around with in the kit?

Bruce.....how do you like your 2275? Sounds like a good size engine for such a little car. I was also looking at this engine combo when I mae my engine upgrade but got scared off du to the 94 bore. How many miles do you have on the powerplant, how does the car feel when it powers-up? I imagine with the 94's in there with the 82 stroke your car rips pretty well.

J-P