Weber 46 Jetting suggestions

[seafeye]

Trying to get the Weber 46’s to run right on my car.
Motor is a twin plug 2.7l
Headers.

Weber 46’s
46/38 venturi Set
F26 Emulsion Tubes
175 Air Correction
145 Main Jets
55 Idle Jets
The car idles great. When I press on the gas the car stumbles. Pops. Spits. Once I find the sweet spot the car has amazing power. Like never before. But it isn’t drivable with just 100% throttle. recommendations?

[Walt Fricke]

Here's the setup I used on my 2.7 with nominal 10.3:1 Mahle factory race pistons:




Air density readings were from a Summit Racing meter - the kind bracket drag racers need. I used EGTs to find jets giving 1200-1300 F about an inch from the #2 and 5 exhaust ports. When I finally got on a chassis dyno, I found my jetting was as close as could be expected. Because they are Webers, I skipped the PITN of fussing with the air correctors, despite having a variety in my carb box. Home is around a mile high, but I raced at some lower elevations as well.

The specs charts shows both the '46 and also the '40 I ran in my sadly departed 2.3.

When I started out, I had a bad stumble coming out of corners. This was resolved by cranking way way down the accelerator pump squirt volume. You might try that.

Overall, I think the EGTs (the roller car came with a dual EGT gauge, so I used it)were the best. I've been less impressed with O2 sensor systems, although tuners swear by them.

[faapgar]

Just change to 155 mains and if you have any more issues around 3000 rpm go to 60 idles.Fred

[racing97]

The recommended injection quantity could be the problem measure it and cut it in half using the acceleration threaded rods by turning them in it works best at .5 cc. Also F4 emulsion tubes seam to work best but is not your problem at this time/

[seafeye]

Thank you all.
I’ve ordered the main jets.
I’m thinking too the squirrels might be pushing too much fuel. I’ll try dial them back.

Will let you know how I get on.

[seafeye]

Followup....

I had it in my head to change the Air Correction Jets from 175 to 155.
I didn't have 155's so I used 150's.

Then adjusted the pump linkage so I wasn't getting a squirt right away.

The car was drivable but still pops and spits. It likes full throttle but not anything less. When I was a kid I could drive like this but now id like to use 3000-5000rpms.

I just changed the Main Jets to 155's. Have not yet been able to go for a drive. But in the garage it still spits and pops.

Interestingly it seems to be more in Cylinder 5 more often. My old 40idas showed number 5 as having more black soot up the stack. Also my number 5 spark plug is very black. I have yet to pull the bottom plug to see that color. Im thinking the top wire was loose.

Could spitting and popping be an ignition timing issue? Should I retard the timing?

[racing97]

Popping through the tail pipe is rich usually and through the carb lean. Make sure you have the idle air screws roughly 2 1/2 turns out then crack open the idle jets themselves just barely and if the idle picks up or smooths out you will probably need to open them up just a small amount, then figure out a way to keep the throttle open at 2,000 RPM just off the stop and readjust the Idle air screws. Also make sure the throttle rods are opening the same on each side.
If air leaks by the throttle butterflies it can cause this type of situation no matter of making a fresh motor really cures it

Regards

[seafeye]

Ok thanks.
The tailpipe is clean. Everything seems to come up through the carbs.
I think the linkage is good. I’ve rebuilt the carbs but did not replace the butterfly’s or the shafts.

When I adjust the accelerator pump linkage... I’m assuming the nut out means fuel coming on later. And tighten the nut it cones on earlier?

Car seems to idle great. Just a couple fussy cylinders on acceleration.

[racing97]

Its not a early or late thing the longer the rod the more the fuel usually it needs to be cut in half from the published figures I believe .5cc or half of the registry on the quantity gauge is sufficient.
But if this is just a recent thing go back to what you have done, if for example you "boiled them out" or dipped them in carb cleaner and they are quite a few years old you have removed varnish the could possibly have added the seal around the shafts for the butterflies and that could be one the contributors to the popping. And if it cuts out on acceleration on 1 or 2 cylinders you could have some contamination in the squirters. Keep at it carbs are like painting a battleship by the time you get done its time to start again.

regards

[seafeye]

Thank you. Just went back to the 175 Air Correction Jets. I’m still getting flames coming up from number 5. I’ll run to the store and get some fresh plugs. It seemed to like the 175 AC Jets better though.
Pressing on the gas it looked like each cylinder was getting their fair share of gas from the accel pump.


Do you have a recommendation for spark plugs?

[racing97]

Bp8es

[racing97]

Ngk bp8es

[seafeye]

Ok Thank you.

Went for a drive, getting better each time.

It still doesn't like going from the idle zone to accelerating unless I'm 100% on the gas.
Also blipping the throttle make the car go BLAH. (Accelerator pump the culprit?)

But it is drivable, unlike earlier. All the help here has been priceless. Thank you.

[stownsen914]

As suggested you can try cutting the volume on the accel pump volume. Not a bad idea to measure their output, if you didn’t already do that. Measure each of them, since they can go off spec, get clogged, etc. You can even disconnect them entirely for troubleshooting. Heck, I know a couple racers who disconnected them permanently.

[seafeye]

Ok. I’ll try that. I bought new squirters and delivery valves. The lines were definitely clear. Carb cleaner went through all the lines. Plus I can see them squirting when the pump is operating.
If the carbs still backfire up the stacks... that’s still a lean condition? Would I need larger main jets then?

[seafeye]

Drivers side:




Pass side:

[seafeye]

Ok, tried 60 idles but that had a negative effect. The carbs like the 55's better.

Have everything pretty well balanced. But 1 thing I noticed. My number 5 cylinder is the one that usually pops or spits. And the idle mixture screws all have an effect on the idle. except #5.

Also when I check the suction with the synchronizer, they are all even but number 5 is low. I cannot raise or lower the value. With either of the adjustment screws.

The car drives much better than it did last week. So I'm just chasing the last 10% I guess.
Number 5 has me puzzled. Vacuum leak?

[Sebscst]

I had an issue with the syncing on my no3 I tried all kinds of adjustments and nothing helped. Finally I changed the manifold isolators and that did it.

[seafeye]

Was reading on Performance Oriented web site about the butterflies maybe not closing just right. Sure enough I had to persuade number 5 to close properly. Then I had better luck getting all the carbs to sync. Bit too late to take for a drive but they are all at least sucking the same now.

[stownsen914]

Sounds like an improvement, that’s good. Will be curious to hear results of another test drive. I’m suspicious that this fix won’t address the drivability issues you’ve described, but let’s see.