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Mon Aug 12, 2024 8:28 am

Hello everyone,

Bee away for a while and just trying to get back. I upgraded my 34 pict 3 to a set of dual Weber 40 idf. Trying to get up windy mountain roads up here in New England doing 35 in a 55 is just not safe.

The Weber keep clogging the idle jets and I have a crazy flat spot switching from idle jets to main jets. I have a afr meter and can see it spike to 19/20 to the mains. If I press the throttle I can bypass the flat spot so I know the squirter is working. But holding the throttle steady and slowly increasing speed it hits it. Getting kinda tired of going heavy throttle every time to get past this.

I've found removing the velocity stacks severely helped the flat spot but it's still there. Currently running with nothing for velocity stacks. The Weber manual says 16mms but if I have the flat spot here with nothing, then 16mms will make it worse.

I have an svda dizzy and tried a 010 and the power difference was amazing. But then it was popping at low rpms and cruising. Full throttle it was amazing. Switch back to svda popping gone.

Ive tried changing the AC jets from 170 all the way up to 240 and it won't solve the problem. I've tried main jets from 160-220 and the flat spot remains. Anyone have any help on this?

1641 cc engine
90 cam
Counter balanced crank
Lightened flywheel
Svda (have a 010)
Mains 120
Idle 50 (was running 47.5. Tried 55s but they were pig rich)
AC 200
Pump 55
Only run with 08 octane fuel
Fuel pressure under 3 psi

Thank you for your help!

Mon Aug 12, 2024 8:54 am

Correction 98 octane is the only fuel I run. We do have 10% ethonol here
Only way to get ethanol free is running 110 octane and I doubt the bug would utilize it or like it.

Sorry for any spelling mistakes. Typing this all on my phone

Mon Aug 12, 2024 9:27 am

Venturi size?

Mon Aug 12, 2024 9:30 am

Venturis are 28 mm. I tried a set of 26s and it didn't change anything. I noticed a massive decrease in power so I changed back to 28s. I've read 32s are too big for my motor and would probably decrease the flow through the throat making the flat spot worse.

Mon Aug 12, 2024 9:58 am

zombiebug wrote: The Webers keep clogging the idle jets
I would be willing to bet the farm you are running the screens that pass for air cleaners that are normally sold for Webers. Get or make a good set of outers for them and this problem will no longer to exist. My wife made these out of diaper material. Not one clogged jet in 5 years and I have to clean them about every month and a half so I know they are working!

This is what they look like in a few weeks. Most of that would have gone right through the typical Weber screens.

I am running 31mm venturis on my 1911cc engine so I would agree that 32s are too big for you. What are the float levels set at?

Mon Aug 12, 2024 10:03 am

Outside of the idle jet being blocked, is this a float or emulsion tube issue? Seems it isnt air or main jet issue?

Mon Aug 12, 2024 10:33 am

Opt, those are super interesting. I think I've seen this picture in the past on another thread I've been reading ove the past year while researching. You drive down a dirt road daily right? The dirty picture you posted is amazing. Your wife could make lots of money if she sold those! I am thinking of buying the foam outter covers since I'm not as crafty as your wife. Any thoughts if they will work as well?

I am using the air cleaners that are sold with the kit. I got the whole kit from CB performance over the winter of 2022. Installed everything spring 2023 and been fighting with them since.

Chris, I thought that. This is why I tried the F7 emulsion tube with no luck
I have the floats set to 10mms. I tried 11.5, 12, as well as 13 and 15mm float height. The 10mms seem to be the best setting so far. I even tried 9.5 but that had no difference so I went back to 10mm.

Mon Aug 12, 2024 10:36 am

What e-tubes are in now? What other have you tried with?

Mon Aug 12, 2024 10:41 am

Emulsion tube currently running is f11. I've tried the f7 but doesn't really have a change in the flat spot. On the f11 the light throttle on the highway will show 15/16s for afr. With the F7 light cruising is 12s for afr. This is the only difference I've seen.

I don't have any other emulsion tubes as they are super expensive.

Mon Aug 12, 2024 10:50 am

How many turns IN are your idle speed screws?. I.e. throttle plate screws.
And how many turns out are the idle mixture screws?
Are your carbs synchronized correctly.
What is your timing at idle?
I've been dealingwith tuning my idf's as well and these are
Things I'm fiddling with.
Make sure the throttle plates are not too far open revealing the progression ports.

Mon Aug 12, 2024 10:50 am

Maybe its related to the idle bleed jet size that sits in the carb body and feeds air to the idle jet. Make sure your air cleaner base/gasket has a clear path and isnt blocking it

Mon Aug 12, 2024 10:59 am

Where is the idle bleed jet? Is this in the base of the carb next to the idle mixture screw? If so, I have them a quarter turn open on cylinders 1 and 3. I've found those two back cylinders run higher cfm than the others. For example, when synching them cylinders 2 and 4 would be at 5 on the snail tuner and then 3 would be at like 6.5 and cylinder 1 would be at 7! I was working on getting them all in line over the past two years. Cylinder 3 is in line and cylinder 1 is still showing 6 on the meter. At one point I had this screw half a turn out and the volume never changed.

This throttle body screws that adjust idle are set at half a turn in. I made sure they were the same setting across both and even micrometered them at some point to ensure they were good. I don't remeber what my mixture screws are set to but I'll be removing the carbs today to clean the idle jets. I believe they are around 0.75 to 1 turn out all the way around. Each cylinder has different settings.

I've also had to

Mon Aug 12, 2024 11:08 am

Those screws near the carb base are for equalizing air flow between barrels. Normally they are closed. The jet i referred to is pressed in the carb body, just above the idle jet. You can see them with the carb top off. I think they are about 1.00mm hole.

Maybe alstrup can help, i think he knows about them more

You can see them at about the one minute mark:
https://www.youtube.com/watch?v=4gtDD8RIGrs

Mon Aug 12, 2024 11:36 am

zombiebug wrote: Opt, those are super interesting. I think I've seen this picture in the past on another thread I've been reading ove the past year while researching. You drive down a dirt road daily right? The dirty picture you posted is amazing. Your wife could make lots of money if she sold those! I am thinking of buying the foam outter covers since I'm not as crafty as your wife. Any thoughts if they will work as well?
I think they would. Haven't tried them because there isn't room, my air cleaners rub a bit on the body now.

Yes I have 1/2 mile of gravel to the pavement and 1/2 mile back home each time I drive it. We drive that part very slowly so as to limit the dust kicked up. Otherwise that is all blacktop driving you see on those dirty outers.
zombiebug wrote: I am using the air cleaners that are sold with the kit. I got the whole kit from CB performance over the winter of 2022. Installed everything spring 2023 and been fighting with them since.
Exactly what I have! After the first trip to the highway and back, 1 mile total, I pulled the carbs to change jets and was appalled at the quantity of fine dirt in the inside of the carbs! I got virtually nothing blowing compressed air through the air cleaner elements but the insides of the carbs had changed color to a light brown!

All those elements strain out is rocks, branches, low flying birds and curious woodland critters! Some guys run them off road as is. I cannot imagine what their cylinder walls look like! I suspect they were designed to be ultra low restriction for use on the race track.

Mon Aug 12, 2024 11:48 am

Did you disassemble carbs and clean them thoroughly before putting them on motor?

Start over using "Lean Best Idle Procedure".....

IF cylinders 1 & 3 are differte cfm the 2 & 4 it indicate a problem with butterfly's, possibly incorrect installed or bent shaft(s)...

Keep in mind dual 40 idfs are one carb barrel per cylinder, As someone once said tuning a VW motor with dual cards is like tuning 4 single cylinder Briggs & Stratton motors.....

https://www.piercemanifolds.com/category_s/313.htm

https://www.piercemanifolds.com/category_s/311.htm

https://www.piercemanifolds.com/category_s/317.htm

https://www.piercemanifolds.com/category_s/312.htm

IF you are having trouble with idle jets clogging , it's because you air cleaners are letting dirt and stuff in .... Recommend jet doctors and better air cleaner seal at base to prevent jet clogging...

Mon Aug 12, 2024 11:57 am

Thanks for your help. I just bought some new air filters that are K&N oiled filters. I'm going to do that and some grease at the top and bottom covers to help seal them.

Dale, when I got them over the winter I completely went through the top to bottom. Since I got them in winter and my car was under a few feet of snow I had nothing else I could do. I got a Weber manual and reset every aspect and cleaned it all to ensure I was 100% to the specs. I don't think it's a bent butterfly as they open the same each throat of the carbs.

I'll redo the lean best idle tonight after completely blowing out the carbs. I have to remove them from the intakes to get to the idle jets since I don't like cutting access holes in my car. I'll remove the idle jets and mixture screws to ensure I can blow it all out right.

Mon Aug 12, 2024 1:51 pm

What idfs are they?italian? Spanish?

Mon Aug 12, 2024 4:03 pm

These are Spanish Webers. I think I found the problems but I need you all to tell me how bad it is.

Here you can see the progression port slightly open on one butterfly. This is bank 3/4

But not in this one which is on the same bank of carbs

On bank 1/2 I noticed the mixture screw had a grove in the needle.

I started cleaning and noticed the other one cleaner wasn't coming out of the mixture port. Pulled it and found out why.

I was able to get it off and drop it back in the carb but it kept wanting to grab the needle. I got it to stay but I know I'm the future this will keep grabbing it and blocking that port. The part that confuses me is I can't get screw drivers in these and only turn them with the tips of my fingers fighting I between the body and the carb. No wonder I could t get this cylinder to adjust for the life of me.

Do I need new carbs?

Mon Aug 12, 2024 4:09 pm

I had a twisted throttle shaft where I could not see the twist. I didn't catch it until I looked deeper into not being able to balance the flow with the snail gauge. Pulled the carb that had one cylinder higher than the others and tore it down to the casting. Put two long bolts into the throttle shaft, threads matching the butterfly screws of course, one bolt into each outside butterfly screw hole (closest to the shaft ends) at the same depth. Then rolled the throttle shaft on my desk - one of the screw heads hit the desktop well before the other. They should have hit at the same time.

It's a good test if you need an easy one.

Mon Aug 12, 2024 4:13 pm

We posted at the same time.

One cylinder exposing the progression ports while the other does not indicates mis-drilled progression ports or a twisted throttle shaft. Use the test I just described.

You might be able to smooth out the mixture screw taper with fine emory cloth or wet/dry sandpaper and apply sleeve retainer to help hold the seat in the carb body when you tap it back in. Or knurl the outside of the seat by rolling on a coarse flat file.

Don't give up yet!