11 replies to this topic

[dklawson]

This is a generic question concerning the "initial" carb adjustments following the rebuild of an HS4 carb.

On traditional HS series carbs with a "standard" jet, you're supposed to lower the jet 2-full turns of the jet nut (down) from flush with the bridge to achieve your initial starting setting. I have a WaxStat carb I'm using on a non-Mini application. It's the first time I've worked with them. Do they have the same jet nut thread as the earlier HS series... or do they have a finer thread that requires more turns down to get the initial setting? I remember reading somewhere that later carbs used a finer thread and required more wrench flats "down" to get the initial setting.

Thanks in advance.

[Sherlock]

I've always used the 2-turns rule on waxstat jets & it works fine, although I don't like them because they react to engine bay temperature rather than the actual temperature of the engine, so we found them rather difficult to set accurately because as soon as you open the bonnet (hood) the air cools & the mixture richens. I replaced the stat part on mine by making up a steel spacer to fit in it's place.

[Dan]

although I don't like them because they react to engine bay temperature rather than the actual temperature of the engine

Quite fortunate really since that's what they are for! They compensate for the air changing density due to the weather not for the engine being cold at startup, that's what the choke does.

All the parts except the jet and its linkage are the same Doug.

[dklawson]

Thanks to both of you.

[ECG317W]

Sorry to hijack the thread but I've got a question about the different HS4 jets. I've got a LH and a RH HS4 carb which I'm going to use to make up a set of twin HS4s after I've rebuilt them, but one is waxstat, and the other is not. Are the throttle bodies a different casting or are the jets interchangable?

[jaydee]

On twin carbs its better using non waxstat type jets, surely not two different types.

[Asphalt]

Sorry to hijack the thread but I've got a question about the different HS4 jets. I've got a LH and a RH HS4 carb which I'm going to use to make up a set of twin HS4s after I've rebuilt them, but one is waxstat, and the other is not. Are the throttle bodies a different casting or are the jets interchangable?

Jets are interchangable. But the choke lever is different.
Just bung on a fixed jet choke lever - they'r interchangable too

[Dan]

Err, as written above....

All the parts except the jet and its linkage are the same Doug.

[Dusky]

On twin carbs its better using non waxstat type jets, surely not two different types.

why?

[carbon]

Other main difference between early and Waxstat carbs is the thread pitch on the jet adjusting nut :

- non-Waxstat jet nut is 26 tpi

- Waxstat jet nut is 40tpi

[dklawson]

 

On twin carbs its better using non waxstat type jets, surely not two different types.

why?

 

 

The argument is made that the wax capsule creates more problems with setting and maintaining the mixture properly than the earlier fixed jet.  Waxstats are not common here (in the U.S.) so I have little experience with them apart from the work I was doing back in 2009 when I started this thread.  Therefore, I cannot say how good or bad Waxstats are... I leave that discussion to others.  However, I really, really like the choke linkage more on the Waxstat jet than the earlier jet design.  Were I working on this application again I would either convert a questionable Waxstat to the early type using the "2 penny" conversion, or I would buy replacement early jets with the adapter bracket to connect them to the Waxstat choke linkage.  The 2-penny conversion is obviously cheaper if the inside of the jet is still in good condition.

 

As for mixing the two types of jets on a dual carb setup... I wouldn't.  For consistent and predictable tuning I would have both carbs set up with the same components (2 Waxstats or 2 early jets) so there were fewer differences between them that might affect tuning and running.

 

Carbon, thanks for the thread pitch info.  That was one of my original questions back in 2009.

[Dan]

Other main difference between early and Waxstat carbs is the thread pitch on the jet adjusting nut :

- non-Waxstat jet nut is 26 tpi

- Waxstat jet nut is 40tpi

 

  Sorry I don't believe thats the case.  The finer thread is used for bias needle carbs and the coarser thread for fixed needle.  The type of jet fitted into the bearing isn't relevant to that and they can be interchanged freely AFAIK.  Otherwise when converting a Waxstat carb to fixed jet you would have to swap out the whole jet bearing, which isn't the case.  The fine thread was brought in to allow finer adjustment as the swinging needle is more accurate, but the initial position (the 2 turns down position) is the same and the difference is taken into account in the jet bearing design I think.