20 replies to this topic

[lrostoke]

Here's a long shot ..

Is the jet a waxstat type... This type of jet does adjust the mixture depending on temperature.
I've replaced mine with a fixed jet...

Here's how I did mine (copied from a post I did on another forum)

I've been reading around and apparently the waxstat jet fitted to the later HS4 carbs may be good for emmisions and economy but isn't the best for power.
Basically how it works is a heat sensitive unit expands and weakens the mixture.
I'd also read that it can cause problems setting up carbs so with that in mind I've converted to a fixed jet, I can't take credit for the method
This is the site I found that explained it http://www.nireland....ph/waxstats.htm

But here's a few pictures

Complete unit



Cap removed, be carefull its spring loaded. Easy enough to do, 3 tabs prise back



remove metal button, this normally goes between the jet and the waxstat unit



replace waxstat unit with 2 one pence coins, keep the metal button in its original postion



After removing my jet assy, I did find that my waxstat unit looked damaged so this could have been causing the problems that led me to investigate
right unit is a good one, left is my original

Slight amendment, had confirmation from other people that they also have a waxstat with the dent in the bottom, so looks like some of them are made like that

[Minimininut's Dad]

Thanks Irostoke,

Good thinking, getting rid of the Waxstat/Capstat main jet is a good idea but unfortunately we have already done that !
I did it the lazy way with a kit from DSN Classics. That was back in the summer when we were having overheating and other problems.
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[Dan]

Where is the distributor ignition advance connected? To the carb, a spacer or the manifold?

[Minimininut's Dad]

Where is the distributor ignition advance connected? To the carb, a spacer or the manifold?

To the carb.

[Dan]

The problem may be induction pulsing and if that's the case then ironically it's caused by the engine being in the correct tune in terms of fuel and ignition. It's all to do with the port and manifold lengths of the exhaust and inlet resonating with the cam timing. If it was previously runing slightly rich at the trottle position in question then the pulses would have been damped. I asked about the vacuum takeoff because this being badly positioned exacerbates the problem by adding varying amounts of advance with each pulse. When Rover first built the MG Metro they had this problem on the majority of factory cars and because they had decided to hook the dizzy up to the manifold as part of the spec the problem was quite pronounced over a large rev range. Slightly de-tuning the cars and moving the dizzy hookup back to the carb (where it's supposed to be) cured the majority of the problems. If you have a manifold vacuum gauge fitted, or can get hold of one (Gunson's Lo-Gauge for example) then try to make note of the speed and manifold depression when you experience the problem and ask the rolling road operator to investigate the fuelling under those conditions. If you aren't happy with the initial results of the RR session he should be willing to continue investigating without charging you an extortionate price.

[Minimininut's Dad]

Thanks Dan for the induction pulsing information, it's certainly worth looking at and we will do so after this...

We are currently working on Minimininut's original feeling that the stalling problem was caused by the very cold weather i.e. Carb. icing. I, and others, thought this most unlikely and I dismissed the idea... but during several needle changes I noticed how very cold the carburettor felt, despite a run of 10 miles and the heated inlet manifold, and that there were beads of water (condensation) inside the carb. on the bridge and piston. There was no water in the filter or float chamber so it's not coming from the fuel. I read that icing/condensation can be worse at temperatures just above freezing as when it actually freezes that takes some of the moisture out of the air.

Today has been a little warmer and Minimininut reports much smoother running with less or no stalling at lights and roundabouts. So I think it will be well worth restoring a warm air supply to the air cleaner from around the exhaust manifold. A previous owner would have removed the flappy air valve, foil hose and warm air duct when he fitted his stage one kit.

I have some bits and pieces on order and will report again when they've been persuaded to fit and after there's been some more cold weather to test the theory.