Twin Weber Problems

[WhoIsSea10]

-Twin Weber 45's w/ short trumpets to clear the brake booster (which I'm planning to delete in the future)

-Stock Cam (planning to upgrade which is why I went with twin dcoe)

-I'm not sure what jets as the car has had maintenance done and was told they switched out the jets to something more appropriate for the cam.

 

The car idles and drives okay, but I feel that it could be dialed in even more. When making any adjustments I usually listen to the exhaust. I want to hear it idle and purr smoothly without any pops in-between. The problem that's always stumped me lies in the fuel mixture screws on the carbs. The adjustment screws on the carb for cyl #3 & 4 work fine, in that the engine will rev higher/lower/smoother/worse when I make fine adjustments. But the carb feeding cyl #1 & 2 makes no changes. I can seat the adjustment screw or back it out completely and the engine barely cares. I bought the carbs new and have had them installed for almost 2 years.

 

I've checked for any/all vacuum leaks, and I even checked the plugs and replaced them.

 

How is it that this carburetor feeding into cylinders 1 & 2 doesn't actually adjust anything. Whatever the issue, it's clear that it has something to do with the carb as a whole. Has anyone had this happen to them. Please, someone, help me solve this.

 

Edited August 23, 2022 by WhoIsSea10
more info

[Schon '02]

Have you synced the carbs (either with a synchrometer air flow meter or other method to determine air flow is matched on the two carbs). This is the first step (along with idle speed) before adjustments to the idle mixture. 

[WhoIsSea10]

17 minutes ago, Schon '02 said:

Have you synced the carbs (either with a synchrometer air flow meter or other method to determine air flow is matched on the two carbs). This is the first step (along with idle speed) before adjustments to the idle mixture. 

Yes, I use a synchrometer when I make adjustments and I will also check the pinholes under the flat bolts if need be. As well as make sure my idle screw is set between about 1/4 to 1/2 turn after contact.

[Schon '02]

JIf you have Italian Webers with the short idle screw needle, your initial baseline should be 1 to 1.5 turns from initial closure contact… if you’re setting at 1/4 to 1/2 turns, then it sounds like your idle jet is too rich (large) and you have little turndown (or adjustment with your needle valve).

Edited August 23, 2022 by Schon '02

[mcmurb]

Maybe your throttle plates are open at idle on 1 & 2 and you’re sucking fuel from the progression circuit.  What throttle linkage do you have?  I had difficult time synchronizing my duals with the “erector set” type of overhead linkage.  

[WhoIsSea10]

54 minutes ago, Schon '02 said:

JIf you have Italian Webers with the short idle screw needle, your initial baseline should be 1 to 1.5 turns from initial closure contact… if you’re setting at 1/4 to 1/2 turns, then it sounds like your idle jet is too rich (large) and you have little turndown (or adjustment with your needle valve).

Don't think they're the italian ones. Got them from Ireland Engineering. Also, the 1/2 - 1/4 is according the Webers baseline specs. I may have to just pull the jets and inspect them, in order to get a better idea. But just seems weird that 3 & 4 effect the engine but 1 & 2 essential make no difference.

[Son of Marty]

Well, you have plenty of carb for a stock engine, it sounds like your running on the rear carb at idle but we need to know what jets and chokes your running and also your linkage set up. All Weber problems are solvable here if you give us enough info to go on.

[WhoIsSea10]

16 minutes ago, mcmurb said:

Maybe your throttle plates are open at idle on 1 & 2 and you’re sucking fuel from the progression circuit.  What throttle linkage do you have?  I had difficult time synchronizing my duals with the “erector set” type of overhead linkage.  

I actually have a linkage that I bought from an FAQ member. It's similar to the original ti linkage. I wanna say it was 2002Only, but I could be wrong. The kit has the interlocking link between the 2 carbs, so I can adjust them with the center linkage screw. I'm fairly certain they're aligned, based on what I can see through the pinholes.

[WhoIsSea10]

15 minutes ago, Son of Marty said:

Well, you have plenty of carb for a stock engine, it sounds like your running on the rear carb at idle but we need to know what jets and chokes your running and also your linkage set up. All Weber problems are solvable here if you give us enough info to go on.

Definitely agree that the carbs are a bit much atm (planning to upgrade cam soon). As far as the jets, I will need to take a look at them. I hate to guess, but pretty sure the venturi's are the same ones that came stock with the carbs when I bought them. That being said, I'm sure the stock venturi's paired with "short" stacks can't be ideal on a stock cam, but I still find it odd that one carbs seems to operate fine while the other is unresponsive. This car is basically my intro to carbs so I'm still learning. Will have to find more info on how to get to them and inspect them. 

Edited August 23, 2022 by WhoIsSea10

[Son of Marty]

Well the venturi's that came stock are most likely 36's and you'd be better of with 32's or 34's on a stock engine and while the jet setting would be nice to know, it really sounds like your carb's are out of balance to me.

[TobyB]

How are your float levels?  Fuel pressure?

 

While you're at it, get all the jet, venturi and emulsion numbers.

It's always worth making sure there aren't some fun features in there...

 

If the idle mixture isn't able to deactivate the cylinder, then the idle mixture's

not in effect, and maybe you're on the transition circuit.

Or maybe it's not working.

The 'idle' jets feed both the idle and transition circuits, and the needle just modulates

the idle fuel.

 

The warmup carb system is a classic idle leak, too.

 

One has to be both methodical and thorough with these things.

 

t

 

[norrinradd]

I ran into this exact problem! At some point ended up getting Hal Broyles s (2002s only ) linkage and switching the carburetors from front to back.  then I went after the idle jets. Bought a set of F8 and F9 and start  experimenting. I'm almost there ! Slight stumble at 2700 RPM. Everything is greatI 

[mcmurb]

10 hours ago, WhoIsSea10 said:

I actually have a linkage that I bought from an FAQ member. It's similar to the original ti linkage. I wanna say it was 2002Only, but I could be wrong. The kit has the interlocking link between the 2 carbs, so I can adjust them with the center linkage screw. I'm fairly certain they're aligned, based on what I can see through the pinholes.

I like those systems like that that use the interlocking link.  But I still think your front carb is feeding off the progression circuit at idle.  That’s why you can screw the idle adjustment screws all the way in and the motor keeps running.  They’re not really mixture screws, but rather metering needles.  The air/fuel ratio is governed by your idle jet under the top cover.  It sounds like in order to synchro the two together, you have to crack the throttle butterfly’s too far into the progression circuit on the front carb.  Have you fully closed your air correction screws on each carb?

[mcmurb]

27 minutes ago, mcmurb said:

I like those systems like that that use the interlocking link.  But I still think your front carb is feeding off the progression circuit at idle.  That’s why you can screw the idle adjustment screws all the way in and the motor keeps running.  They’re not really mixture screws, but rather metering needles.  The air/fuel ratio is governed by your idle jet under the top cover.  It sounds like in order to synchro the two together, you have to crack the throttle butterfly’s too far into the progression circuit on the front carb.  Have you fully closed your air correction screws on each carb?

I misspoke, I called the mixture screws (1 on each bore) the idle adjustment screws (1 per carb).  If you can screw the mixture screws on the top all the way in and the car doesn’t stumble, then I think its drawing fuel from the progression holes in order to keep running.  When you synched the carbs, did you raise the lower carb (opening the throttle plates) or lower the higher carb?

[Carlos_M]

I have a similar setup as you to include the linkage from @halboyles.  Everyone is correct in that you need to get the specs so everyone can help you more.  Venturi___, Main ___, Emulsion tube___, Air Corrector___, Idle Jet___   and make sure your float is set correctly.  Also... make sure the timing is correct before you start taking everything apart.

 

You'll also need to disconnect the carbs from the throttle down rod and from each other in order to balance the carbs correctly. My idle mixture setting is about 2 full turns out on each.  I'm happy to help if you want to chat on the phone or if you need me to send down some jets for troubleshooting purposes.

 

best,

 

Carlos...