21 replies to this topic

[skoughi]

I have a pair of HS4's that I have as a project to get refurbished for replacing the HIF44 that I'm using at the moment. It's been said many times on here that if you have an HIF that's working well then stick with it, and mine does work well. I've had the car on a rolling road and we spent a good while shaving down a needle to get a good fuel supply, it has a fast drop damper rod, sharp edges and been rounded off and it has an MED stub stack and ITG filter. However.......I now have these HS4's and I'd just like to learn about them, get them on and give them a try. If I decide to stick with the HIF then I can always sell on the twins. So if spent a bit of time trying to get the pistons to drop at the same speed, which they do for the majority of the time but it's not consistent. One thing I have noticed is my HIF piston drops far faster than either of the HS's. The damper rods that they have are the 8103 ones. Also one rod drops faster than the other, this has been confirmed by swapping components about. So I'm probably looking at buying two new damper rods so is there a fast drop rod available for these carbs? Or can I modify the existing rods to make them drop faster? Also I've read about swapping the the chamber and piston assembly for an ballbearing HIF setup. For an HS4 I'm guessing I'd use the HIF38 setup? Has anyone done this modification and how did it perform?

[sonscar]

To test the drop speed I thought you removed the dampers,bunged up the holes and timed the piston drop?If they are a pair and you have done this then the chamber and/or piston is worn(probably)Steve..

[skoughi]

Done that Steve, and one was slower. So swapped around pistons, chambers onto each carb body and it showed that whatever combination of parts I had had the "slow" damper" in it did just that. Even went to the stage of cleaning up the inside of the chamber and outside edge of the piston with wet n dry up to 1200 then a quick polish. Checked the dimensions of the end of the damper rods and they're both the same within a few hundredths of a mm. So that's kinda why I'm asking about swapping the chamber, piston and rod from an HIF. If there is some small issue with one of the parts then swapping it all for HIF parts could get a faster drop for both.

[PoolGuy]

. Even went to the stage of cleaning up the inside of the chamber and outside edge of the piston with wet n dry up to 1200 then a quick polish.

IMO 1200 is much too coarse for 'cleaning' the dashpot assembly. I'd use metal polish or 3000 grade paper at most. It sounds as if you may have made one or both of the components oval which is why you have the inconsistency of drop.

[skoughi]

 

. Even went to the stage of cleaning up the inside of the chamber and outside edge of the piston with wet n dry up to 1200 then a quick polish.

IMO 1200 is much too coarse for 'cleaning' the dashpot assembly. I'd use metal polish or 3000 grade paper at most. It sounds as if you may have made one or both of the components oval which is why you have the inconsistency of drop.

A good point to make Poolguy. I did have a look through the "yellow Bible" and Vizard said to clean up the inside of the chamber and outside of the piston with 400 W n D! Keeping with what you say in mind when I cleaned these parts up then the piston was mounted into a battery drill and turned whilst holding the Wet n Dry up against it so not to concentrate on one point and whilst cleaning the inside of the chamber I used as large sweeping strokes as possible, I did think about making some sort of mandrel to also mount it on a drill but didn't go that far. I would say that the inconsistent drop got no worse and certainly improved with cleaning but it's something that needs a lot of care to avoid making things worse.

[Fast Ivan]

use a thinner oil

[skoughi]

use a thinner oil

A big debate on that one Fast Ivan, I use the SU branded oil or 20/50. I'd rather use the thicker stuff to slow the rise of the piston to keep a more rich fuel mixture on acceleration. SU Burlen is stating a different damper rod for twins, I've got the 8103 and they say 8114 so that might help? As you suggest a slightly thinner oil could be interesting to try whilst they are sitting on the bench.

[PoolGuy]

I got the impression (maybe wrongly) that the inconsistency was without the dampers fitted? I'd try to get the drop similar before fitting the dampers, then the springs. It might be possible to detect what's causing the inconsistency by moving the piston by hand while turning it, a high spot may be noticeable, which can then be addressed, BUT you do run the risk of ruining the close tolerance of the assembly and making them expensive paperweights. Proceed with extreme caution.

[skoughi]

I got the impression (maybe wrongly) that the inconsistency was without the dampers fitted? I'd try to get the drop similar before fitting the dampers, then the springs. It might be possible to detect what's causing the inconsistency by moving the piston by hand while turning it, a high spot may be noticeable, which can then be addressed, BUT you do run the risk of ruining the close tolerance of the assembly and making them expensive paperweights. Proceed with extreme caution.

I started with just the pistons, with holes blocked up, in the chambers, swapped them about to check for differences then took to cleaning the inside surfaces to eliminate any issues there. Once I got them as close as I could I then added the springs to check to see what difference they would make then I added the dampers. The carbs are mounted on the inlet manifold and held at the angle they will be when on the engine. The piston is held in the one position whilst in the chamber and fitted to the carb body by the piston guide so turning it around makes no odds, any cleaning of the surfaces will only increase the gap between piston and chamber so should only make the piston rise or fall quicker if anything? If that gap is then too big then I guess the carb will not perform as it is designed to do? This can lead back to one of the first questions I asked regarding swapping the dashpot and damper for the HIF setup, thus replacing old parts that might have something very slightly wrong with everything! There is a few other things that Mr Vizard says about checking etc so will try these and see how I get on. I think I'll phone SU Burlen and see about getting a pair of 8114 damper rods as these won't cost too much and some new components will help. 

[skoughi]

I got the impression (maybe wrongly) that the inconsistency was without the dampers fitted? I'd try to get the drop similar before fitting the dampers, then the springs. It might be possible to detect what's causing the inconsistency by moving the piston by hand while turning it, a high spot may be noticeable, which can then be addressed, BUT you do run the risk of ruining the close tolerance of the assembly and making them expensive paperweights. Proceed with extreme caution.

I guess the wording of the topic is a bit misleading! One piston is dropping slightly slower than the other for the most part but it's more the slow rate of drop for both pistons compared to my HIF44 that's the main query.

[PoolGuy]

Ok, remember that HIF carbs have ball bearing dashpot mechanisms, so they move more freely. If yours are dropping in the specified time for HS4 then I’d not worry too much until you’ve fitted them. Any discrepancies between the dampers can be adjusted with oil weight as suggested by Ivan, then the dampers can be replaced once you’re happy that you’re going to stick with the twins?

[skoughi]

The yellow bible gives times for the piston dropping for all carbs so will check that as well, I'll try a few different oils as well. Cheers!

[cal844]

It's all well and good playing about with this on the bench, the car might need a heavy oil, or it might want a light oil, or a mix of both

[PoolGuy]

It's all well and good playing about with this on the bench, the car might need a heavy oil, or it might want a light oil, or a mix of both

I totally agree with you, if he can get it right on the bench then he should be able to do it on the car?

[cal844]

It's all well and good playing about with this on the bench, the car might need a heavy oil, or it might want a light oil, or a mix of both

I totally agree with you, if he can get it right on the bench then he should be able to do it on the car?

Yes indeed, I was simply meaning that the settings will need changed when on the road under load