30 replies to this topic

[JDImini]

Hi,

 

Is there a conversion for the HIF carb similar to the HS waxstat to pre-waxstat to remove/disable the bimetallic strip?

 

thanks

Darren

[PoolGuy]

There was a chap in the US who’d had some cnc alloy replacements made, I’m not sure if you can still get them. Another option is to disassemble the three metal strips and reverse them so that they work against each other to eliminate the auto adjustment. 

Edited by PoolGuy, 27 October 2020 - 09:39 PM.

[Turbo Phil]

Or make a solid one up from some stainless. It’s a common modification on turbo carbs.

Phil.

[croc7]

I took a Dremel to the two opposing bi-metallic strips, cutting them off as close to the rivets on one side and as close to the right angle bend on the other, leaving the center piece (the one that attaches to the jet) intact. Works great.

[luismx123]

why would you want to do this in the first place?

[Ethel]

To stop  it leaning out the mixture when it gets warmer.

 

I would like to see evidence it's a problem before trying to fix it. Unlike a waxstat jet, it's not sensing external temperature, just that of the fuel, that's being constantly replaced.

[ACDodd]

I have never seen the need.

Ac

[luismx123]

To stop  it leaning out the mixture when it gets warmer.

 

I would like to see evidence it's a problem before trying to fix it. Unlike a waxstat jet, it's not sensing external temperature, just that of the fuel, that's being constantly replaced.

yeah when the temperature rises, so does the air and the density of it drops too. less air, less fuel needed. Hence why it was made no?

Set up the carb to the right AFR at operating temperature and you shouldnt need to do anything if all is in working order. but yeah...as one pleases

[Ethel]

Hadn't really thought about it. It's usually described to be for fuel viscosity compensation, which makes sense if it's in the fuel. Interestingly, ethanol has more temperature/viscosity change than straight petrol - so if that's really true it'd be more useful than ever. You're right air density would be a bigger factor, too hard to figure out if an SU could compensate for that in another way...

 

damper oil viscosity, float chamber buoyancy    

[PoolGuy]

For transparency my findings are from an inline A series, which compared to a Mini is less affected by heat from the exhaust.

 

I've had an afr gauge fitted for some time. In the early part of the summer I suffered from varying idle speeds as the ambient temperatures increased. The numbers from the afr showed that the varying idle was coupled with changes in the afr at idle. Initially I corrected the idle afr to suit the increased ambient temps. As we had a dip in temps the idle changed again, so I adjusted the idle afr again. That lead me to look into what was causing it, this lead me to some threads on an MG forum, they were sure that the bimetal part was causing the problem. So I got a spare bimetal and modified it. Since then I've had a much more stable idle/afr.

 

Now I'm not saying that it's the solution to all idle issues as it could be that I inadvertently made a change that helped my erratic idle, and obviously the Mini suffers from more heat in the carb area than my van. 

 

I'm not passing this off as fact, just what I found in my particular situation. YMMY etc etc

[Turbo Phil]

It’s definitely an issue on a turbo A-series where the carb is directly above a glowing turbo.

Phil.

[Dusky]

Fitting a heatshield would be a lot easier.
Someone with more time than me could calculate if and howmuch the fuel in the bowl will heat up at idle, given an average consumption of +- 0,7 litres/ hour

[Turbo Phil]

Even with the heat shield fitted there can be issues, especially on a rolling road where airflow is reduced.

Phil.

[Ethel]

Have to admit it wouldn't be the first thing I'd think of.  It'd be an interesting experiment with an AFR gauge & an intercooler though.

[croc7]

As referenced by PoolGuy, chasing erratic AFR settings at idle is what prompted me to research/modify the bi-metallic temp compensator.  The type of camshaft installed in my car makes obtaining a steady AFR at idle a challenge but is much more stable with the bi-metallic strips removed.  Works for me.