Twin carbs, which ones?

[ozziedog]

I’ve still got the hex set up on mine and although I’ve not had any issues with it, I don’t think it’s that smooth or as smooth as it could be. Because I’m old and hanging I haven’t got around to changing it yet but I do have a CSP bellcrank ready to bang on. This is supposedly on my ‘To Do’ list and it’s in the
Next time the motor is out category
Just because I really suffer with cramps when I’m down in that engine bay and that’s a bar steward for banging your head when the cramp gets you :shock: :roll: :shock:

Ozziedog,,,,,,,,, but it’s on the list :mrgreen:

 

[mike202]

If you get the CSP bell crank linkage check if there is a spring included. When I got mine a return spring was an extra.
I found that the carb springs were not strong enough to bring down the revs at junctions etc and the engine surged. This seemed to happen only when the engine was hot. When the spring was fitted it solved the problem.


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[K@rlos]

If you get the CSP bell crank linkage check if there is a spring included. When I got mine a return spring was an extra.
I found that the carb springs were not strong enough to bring down the revs at junctions etc and the engine surged. This seemed to happen only when the engine was hot. When the spring was fitted it solved the problem.


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Combination of inadequate return springs and the carbs not being set up when the engines fully up to temp.

After working on many various combinations of carbs and linkages I’ve found the factory Weber spindle springs, CSP linkage/spring and the buttys pedal kit with return spring makes for a lovely pedal feel
Using a proper braided cable rather than 1 of those crap solid wire things makes a big difference too as it doesn’t drag in the tube.

 

[Low n slow]

Thanks so much everyone, I'll let you know how I get on.

 

[Low n slow]

I'm going to go for the Webbers with csp linkage, will I need to to change the mechanical fuel pump to an electric one? or is a just a case of suck it and see.

 

[tmcg]

Pressure output from mechanical pump will vary so you will need a pressure regulator as these carbs like to run at about 2.5psi. I run a mechanical pump with a malpassi pressure regulator. Some electric pumps can be set or give the correct pressure output so no need for regulator and less fuel pipe work in the engine bay.


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[ozziedog]

I’d go down the route of suck it and see :mrgreen: I’ve heard of lots of peeps having fuel over supply issues but I’ve run a few motors with stock pumps and twin 34s with no issues at all apart from one fuel pump worn out and a cheapso replacement lasting about two weeks. But the replaced replacement has lasted at least five years and that is a GSF cheapso one. If you got a stock pump, I can’t see you needing a reg, it’s when you start getting a super duper high powered pump that you might need a reg :mrgreen: But see what happens when you change to twin jugs, it’s fairly easy to test if your pump is pumping enough for them.:mrgreen:

Ozziedog,,,,,,, buy nuffink till you needs it :mrgreen:

 

[K@rlos]

I’d go down the route of suck it and see :mrgreen: I’ve heard of lots of peeps having fuel over supply issues but I’ve run a few motors with stock pumps and twin 34s with no issues at all apart from one fuel pump worn out and a cheapso replacement lasting about two weeks. But the replaced replacement has lasted at least five years and that is a GSF cheapso one. If you got a stock pump, I can’t see you needing a reg, it’s when you start getting a super duper high powered pump that you might need a reg :mrgreen: But see what happens when you change to twin jugs, it’s fairly easy to test if your pump is pumping enough for them.:mrgreen:

Ozziedog,,,,,,, buy nuffink till you needs it :mrgreen:

Suck it and see is not the way to approach things.. A stock pump will put out 7-8psi at speed, if the pump puts out too much pressure you’ll at least end up with a **** running engine or worse a fire when the carbs get overwhelmed, flood and puke fuel out the top over a hit engine. A suitable electric pump set up is ideal but If you really want a stock pump then you can lower the fuel pressure buy taking material off the pushrod.

 

[ozziedog]

Ozziedog???

 

[Dci_Carter]

King malpassi with faucet pump

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[SteveW4130]

Suck it and see is not the way to approach things.. A stock pump will put out 7-8psi at speed, if the pump puts out too much pressure you’ll at least end up with a **** running engine or worse a fire when the carbs get overwhelmed, flood and puke fuel out the top over a hit engine. A suitable electric pump set up is ideal but If you really want a stock pump then you can lower the fuel pressure buy taking material off the pushrod.

That’s incorrect, on a stock, original mechanical pump the fuel pressure is pre-set by the spring inside the pump itself. This specific spring gives a pressure reading of around 2.5-3 PSI regardless of RPM. What does change with RPM is fuel volume, the push rod stroke determines the volume and the float needle valve controls the push rod stroke. When you shim the fuel pump base you are reducing the amount of push rod stroke thus reducing the volume. The pressure will only drop when the volume has been dropped too much and the carb/engine is requiring more fuel than the pump can deliver. The correct way to change pressure (without an external pressure regulator) is to ensure the spring is the correct one, previously the rebuild kits contained the wrong spring and the pressure would be high. The latest rebuild kits from Wolfsburg West contain the correct spring and the fuel pressure is around 2.5 psi.

A stock fuel pump is easily capable of fuelling a bigger dual carb’d engine. I run dual carbs on my beetle engine using an original, rebuilt fuel pump without using an external regulator.

Reproduction mechanical fuel pumps are very poor in comparison to an original Pierburg fuel pump with fuel pressures wildly out and poor diaphragm material causing premature failure which I think has also caused a bad reputation for mechanical fuel pumps.

 

[Bluesnailman]

Awesome posts here and great learning! Thanks all. I've a pair of twin carbs in the garage that are a lot closer to being fitted because of this. This is what this forum us all about!

 

[Low n slow]

So the carbs are on and running. Had to get a new fuel pump as the old one couldn't supply enough fuel and also had to put a balance pipe on as the settings were spot on but the bus didn't quite run right. The spring on my foot pedal had broken too and the cable from the pedal to the carbs is too long. Do that somehow soon. Other than that, runs much better than with a blocked heat riser pipe or whatever you call it.

 

[ozziedog]

Suck it and see is not the way to approach things.. A stock pump will put out 7-8psi at speed, if the pump puts out too much pressure you’ll at least end up with a **** running engine or worse a fire when the carbs get overwhelmed, flood and puke fuel out the top over a hit engine. A suitable electric pump set up is ideal but If you really want a stock pump then you can lower the fuel pressure buy taking material off the pushrod.

That’s incorrect, on a stock, original mechanical pump the fuel pressure is pre-set by the spring inside the pump itself. This specific spring gives a pressure reading of around 2.5-3 PSI regardless of RPM. What does change with RPM is fuel volume, the push rod stroke determines the volume and the float needle valve controls the push rod stroke. When you shim the fuel pump base you are reducing the amount of push rod stroke thus reducing the volume. The pressure will only drop when the volume has been dropped too much and the carb/engine is requiring more fuel than the pump can deliver. The correct way to change pressure (without an external pressure regulator) is to ensure the spring is the correct one, previously the rebuild kits contained the wrong spring and the pressure would be high. The latest rebuild kits from Wolfsburg West contain the correct spring and the fuel pressure is around 2.5 psi.

A stock fuel pump is easily capable of fuelling a bigger dual carb’d engine. I run dual carbs on my beetle engine using an original, rebuilt fuel pump without using an external regulator.

Reproduction mechanical fuel pumps are very poor in comparison to an original Pierburg fuel pump with fuel pressures wildly out and poor diaphragm material causing premature failure which I think has also caused a bad reputation for mechanical fuel pumps.

Just for future reference, I am also a Steve W :shock:
This post however is not one of mine even though the thought process may have been identical, the delivery was far tooooo eloquent and precise. This is rather a scary thought boys and girls innit :shock:
I wonder if we’re related? Do you drink a lot of wine ? Or Stella ? :roll:

Ozziedog,,,,,,,two Steve Ws, don’t bare thinking about :mrgreen:

 

[SteveW4130]

Suck it and see is not the way to approach things.. A stock pump will put out 7-8psi at speed, if the pump puts out too much pressure you’ll at least end up with a **** running engine or worse a fire when the carbs get overwhelmed, flood and puke fuel out the top over a hit engine. A suitable electric pump set up is ideal but If you really want a stock pump then you can lower the fuel pressure buy taking material off the pushrod.

That’s incorrect, on a stock, original mechanical pump the fuel pressure is pre-set by the spring inside the pump itself. This specific spring gives a pressure reading of around 2.5-3 PSI regardless of RPM. What does change with RPM is fuel volume, the push rod stroke determines the volume and the float needle valve controls the push rod stroke. When you shim the fuel pump base you are reducing the amount of push rod stroke thus reducing the volume. The pressure will only drop when the volume has been dropped too much and the carb/engine is requiring more fuel than the pump can deliver. The correct way to change pressure (without an external pressure regulator) is to ensure the spring is the correct one, previously the rebuild kits contained the wrong spring and the pressure would be high. The latest rebuild kits from Wolfsburg West contain the correct spring and the fuel pressure is around 2.5 psi.

A stock fuel pump is easily capable of fuelling a bigger dual carb’d engine. I run dual carbs on my beetle engine using an original, rebuilt fuel pump without using an external regulator.

Reproduction mechanical fuel pumps are very poor in comparison to an original Pierburg fuel pump with fuel pressures wildly out and poor diaphragm material causing premature failure which I think has also caused a bad reputation for mechanical fuel pumps.

Just for future reference, I am also a Steve W :shock:
This post however is not one of mine even though the thought process may have been identical, the delivery was far tooooo eloquent and precise. This is rather a scary thought boys and girls innit :shock:
I wonder if we’re related? Do you drink a lot of wine ? Or Stella ? :roll:

Ozziedog,,,,,,,two Steve Ws, don’t bare thinking about :mrgreen:

Fortunately/unfortunately I don’t drink much alcohol!

 

[Low n slow]

Okay so I pulled the cable though a bit as it's probably the wrong one for the van. Once I did this the height of the pedal was correct but the springs on the carbs weren't shutting off quickly enough so I've put double springs on them and now they return fine. Any more trouble and I'll put a post with a spring on to the middle of the linkage and maybe look at re building the pedal connections as it's stacked with washers at present.

 

[sparkywig]

If you haven't already swapped the stock linkage out for a Butty's linkage then it's the best upgrade you can do.

 

[Low n slow]

If you haven't already swapped the stock linkage out for a Butty's linkage then it's the best upgrade you can do.

Doesn't that rely on your own linkage being in good/semi good condition though?

 

[sparkywig]

No, he sells everything to sort your linkage out.

https://www.buttysbits.com/product-category/bay-window/throttle-kits/rhd-1969-1972-throttle-kits/

 

[Low n slow]

No, he sells everything to sort your linkage out.

https://www.buttysbits.com/product-category/bay-window/throttle-kits/rhd-1969-1972-throttle-kits/

Link doesn't work I'm afraid