1959 Rapier Carburetor Idle

[beamdream]

Just an observation, the fast idle cam on the rear (?) carb looks rather odd. Can't see how the rear carb throttle plate could be set right at idle in that condition.

I'm thinking you need to upend the carbs on a nice flat surface, loosen the shaft joiner, back out the idle stop screws then, whilst holding both throttle plates closed, tighten up the joiner.

At least now you can be sure that both throttle plates can be adjusted from a known start
point.

 

[Chrisp Rapier]

Unfortunately I'm not familiar with Rapier manifolds. Ok, the interconnection is correct and original. Good, but did you check the synchronous butterfly movement before taking everything apart ?

Talking about the spindles your photo shows exactly the wear pattern which most of them suffer from. Wear occurs on the spindle and mainly on the non bushed side of the butterfly housing. If yours ons the 1688's are good though it's a good starting point. Wonder whether you can find the high idle idle root cause with everything taken apart, but would start with a careful inspection of the idle jets and clean ( the small bore tends to get blocked) the related fuel channels...

I did everything all over again. All I found in cleaning and inspecting is that I was missing a check ball in one carb and I had a particle in the mixture screw cavity. I put it all back together. No joy. Same high idle. Which leads me to my next attempt. Can I use two of these extra carbs I have? What is the deal with the air tube in the intake you can see in this photo?

 

[husky drvr]

What is the deal with the air tube in the intake

The tube is the bowl vent. The extra height and distance towards the center of the carb throat makes it much more difficult to splash fuel out of the bowl into the carb.

Just as a guess, it probably also gives a positive bowl air pressure where w/o the tube bowl air pressure may go negative.

Just a thought,

 

[Chrisp Rapier]

The tube is the bowl vent. The extra height and distance towards the center of the carb throat makes it much more difficult to splash fuel out of the bowl into the carb.

Just as a guess, it probably also gives a positive bowl air pressure where w/o the tube bowl air pressure may go negative.

Just a thought,

Interesting.

These carbs have different, much simpler linkage that directly engages the accelerator pump, rather than the roller, slider deal.

 

[husky drvr]

Interesting.

These carbs have different, much simpler linkage that directly engages the accelerator pump, rather than the roller, slider deal.

The cam and roller is the later design and is supposed to give a smoother pump shot (no backlash). It's output is adjustable, also.

 

[Chrisp Rapier]

The cam and roller is the later design and is supposed to give a smoother pump shot (no backlash). It's output is adjustable, also.

I see.

The older simpler linkage has less friction and resistance than the cam roller set up. Well at least with my rusty old linkage. I'll give the old one a shot and see if it will work for me. Thanks for giving me info on this version of the carburetor. I appreciate it.

 

[husky drvr]

The older simpler linkage has less friction and resistance than the cam roller set up.

Isn't that due to a stronger, internal pump return spring?

​

Bernd_st is the expert on the DD Zeniths. I just know bits and pieces from decades ago.

You'll need his help to figure out your parts in hand to see if you even have two matched carbs. If not, obtaining a smooth running engine will be a challenge because of firing order and manifold design.

WSM 124 indicates there are seven different carbs for Alpine series I, II, and 3, and more for Rapier sIII and IIIA.

That doesn't even include the pair for a sII Rapier.

All pairs have matched sets of different combinations of venturi diameter, main jet, idle jet, drilled air bleeds, all the way down to different size drilled progression holes.

YMMV,

 

[Chrisp Rapier]

Isn't that due to a stronger, internal pump return spring?

​

Bernd_st is the expert on the DD Zeniths. I just know bits and pieces from decades ago.

You'll need his help to figure out your parts in hand to see if you even have two matched carbs. If not, obtaining a smooth running engine will be a challenge because of firing order and manifold design.

WSM 124 indicates there are seven different carbs for Alpine series I, II, and 3, and more for Rapier sIII and IIIA.

That doesn't even include the pair for a sII Rapier.

All pairs have matched sets of different combinations of venturi diameter, main jet, idle jet, drilled air bleeds, all the way down to different size drilled progression holes.

YMMV,

The carbs I have been using are the set that was on the engine when I bought the car. When I bought the car, I also bought a parts car with it. I have the carbs that were on it and an additional set of carbs. They are no doubt pairs. For example one set of extra carbs has the following numbers:
C1629R
36 WIP2
P46290

These number are the same on both carbs in the pair. I believe this pair was on the second 1959 Rapier parts car as it had some proper linkage attached. anyway all of them have worn brass spindles on the front carburetors. I have soldered in brass material to attempt to tighten up the worn spindle.
I understand that the carb specs are not necessarily correct for my vehicle.

 

[Chrisp Rapier]

So which of the two holes does the check ball go into? It is hard to tell by the diagram.

 

[husky drvr]

 

[Chrisp Rapier]

View attachment 32778

Thanks for that. When I had a missing check ball, I had placed it in the wrong hole. and ran the car. Luckily, I removed the carburetors last night and the wrongly placed check ball was rattling around in the carburetor and fell out on the table. Could the missing check ball have caused a high idle?

 

[bernd_st]

Couldn't respond earlier, since we were out for a british car MTG (Rootes as special guest this time !) over the weekend .
Interesting spindle repair method...
Wonder where you mis-placed the checkball. It has to sit under the accelerator discharge nozzle mounting screw and acts as non return valve. Fundamentally without it you won't have sufficient fuel spray during acceleration (nothing to do with idle performance)...

 

[Chrisp Rapier]

Couldn't respond earlier, since we were out for a british car MTG (Rootes as special guest this time !) over the weekend .
Interesting spindle repair method...
Wonder where you mis-placed the checkball. It has to sit under the accelerator discharge nozzle mounting screw and acts as non return valve. Fundamentally without it you won't have sufficient fuel spray during acceleration (nothing to do with idle performance)...

Thank you that makes sense. I have now reconditioned my spare carburetors and installed them. I have not dialed them in yet but already my idle has dropped down around 950. It definitely sounds better, I even drove it around a little. Before I was stalling out coming to a stop sign. Now no stalling. So this clearly tells me there was some carburetor issue.

 

[bernd_st]

Ok, sounds as if you are fine now. Good luck for the dial in...

P.S. Proper idle should be set between 750 -850 RPM...

 

[Chrisp Rapier]

I did one stupid thing though. I set up the carburetors with the vacuum port on the rear carburetor. I guess a longer plastic vacuum line is not going to be an issue.

On the intake manifold for the Rapier there is an interconnecting tube running between the two halves. they are joined in the center with a tube of unknown material. looks like rubber a bit but I imagine it is some sort of heat resistant material. It is hard. It did not fit together very snugly when I installed it initially on the engine. When I was checking with carb cleaner for vacuum leaks, I also sprayed this union piece. There was no effect on the idle.

 

[husky drvr]

they are joined in the center with a tube of unknown material.

I think it is a section of reinforced vacuum hose similar to what is used on the later Alpines for the brake vacuum servo. Size and availability unknown.

I would seriously doubt the connector is more specialized than that taking into consideration 1950's technology, cost, ease of assembly on the production line, and it's not a big pain to service in the field.

Just a thought,

 

[Chrisp Rapier]

Ok, sounds as if you are fine now. Good luck for the dial in...

P.S. Proper idle should be set between 750 -850 RPM...

I have it down to 850 now but I am struggling a little bit with the corroded carburetor linkage. Thank you for all your input.

 

[Chrisp Rapier]

What is the connecting rod between the throttle and the upper strangler? What is it actually doing and if it does something how do I adjust it properly?

 

[husky drvr]

Chrisp,

Here is the link to the fuel section in the WSM124. The twin Zenith section starts on page nine of this PDF.

Your rod in question controls the throttle for the fast idle. Operation, adjustments, and troubleshooting are all included. (Starting from cold - page 12 of PDF)

https://sunbeamalpine.org/wp-content/uploads/2017/10/6-Fuel-System-C-part-1.pdf

The link for the page with the entire manual is (should be helpful but not specific since it starts with s III Rapier) :

Original Tech Manuals – The Sunbeam Alpine Owners of America

 

[Chrisp Rapier]

Chrisp,

Here is the link to the fuel section in the WSM124. The twin Zenith section starts on page nine of this PDF.

Your rod in question controls the throttle for the fast idle. Operation, adjustments, and troubleshooting are all included. (Starting from cold - page 12 of PDF)

https://sunbeamalpine.org/wp-content/uploads/2017/10/6-Fuel-System-C-part-1.pdf

The link for the page with the entire manual is (should be helpful but not specific since it starts with s III Rapier) :

Original Tech Manuals – The Sunbeam Alpine Owners of America

I guess since my fast idle at start up with choke sounds correct, that it is likely properly positioned. I just placed it as it was before the cleaning. Thank you for the links and info.