25 replies to this topic

[woolfman]

Hello,

 

I am a long time reader in tjis forum on and offf.

 

MG Midget 1098cc driver with SU Hs2s.

 

I only recently dropped over AC Dodds work and recommendations, albeit they seem to be for Hiif carbs only. I have never heard of mods to damper pistons themselves. The literature I have is centered on the HS2/HS4, most popular for Midget/Sprites.

 

So I thought I post here, as there may seem to be people in the know:

 

Are there different versions of damper valves for the HS2s as well? Would it bring benefits to go over them on twin carbs? Part  numbers that may be relevant?

 

Tjanks for your help/opninions.

 

Cheers,

Wolf

[cal844]

AC Dodd will be along soon. He's a member of this forum

[nicklouse]

Yes there are. See https://sucarb.co.uk...assemblies.html

they are dampers just like a suspension damper (shock absorber) and they are valued differently.

 

you should be using the same. But even then they may require slightly different damping oil depending on how each carb works.

 

AC will, as mentioned above, be along with a more in-depth study on the matter.

[timmy850]

The HS2 uses the same damper type as the HS4. I believe the recommendation is the AUC8103

However:
Both carb pistons should rise at the same rate
Both carb pistons should drop at the same rate

The rate of rise determines the fuel mixture as the throttle is opened. A quick rise will be leaner than a slow rise

The rate of drop is also important - if it drops too slow on gear changes or changes in throttle the piston will be too high and cause a lean spot which gives bogging and poor performance

[woolfman]

Hello,

 

carb has been rebuild and new matching pistons/domes used. They drop with and without oil at the same time, also with dampers fitted. Needles have been polished and tested with lambda meter in tailpipe up to 5000rpm (the max I will ever spin it up).

 

What I saw in AC Dodds videos however were the modifications made to the damper valve itself, I haven´t seen that before and never heard of it being necessary. I always thought that the dampers are matched exactly to and for carb models.

 

How would I notice the damper valve not being good enough, too worn, too loose/tight or wrong? Would I see that on a lambda meter, how can I spot for that?

 

Just curious whether I need to sort smthg here.

 

Cheers,

Wolf

[timmy850]

He modifies them for a few reasons, and only if required after measuring the performance:
If the twin carb dampers act differently and they need to be evened up
If they drop too slow and cause a lean spot when changing gear

On your gauge:
When you are driving at a constant speed, then go full throttle the mixture should get richer and there shouldn’t be any stumbling
If it goes too rich under hard throttle you need a lighter oil
If it goes too lean under hard throttle you need a heavier oil

If you are speeding through the gears and get a lean spot when you engage the next gear it can mean the damper isn’t allowing the piston to drop quick enough. This is where modifying the damper to allow more oil flow under that condition is needed

[woolfman]

He modifies them for a few reasons, and only if required after measuring the performance:
If the twin carb dampers act differently and they need to be evened up
If they drop too slow and cause a lean spot when changing gear

On your gauge:
When you are driving at a constant speed, then go full throttle the mixture should get richer and there shouldn’t be any stumbling
If it goes too rich under hard throttle you need a lighter oil
If it goes too lean under hard throttle you need a heavier oil

If you are speeding through the gears and get a lean spot when you engage the next gear it can mean the damper isn’t allowing the piston to drop quick enough. This is where modifying the damper to allow more oil flow under that condition is needed

 

Do you mean  if the carb pistons rise not evenly in the first moment, that the damper is the problem here?

If so, then this might be he case here. Although they I did match tihem via drop test

 

-without oil and damper and spring

-without oil and damper

-without oil and spring

-without spring

-alltogether applied

 

After that procedure and refinements they perfectly dropped together.

 

I get them however not to equally on initial throttle. One of them always rises faster.

 

I dont want to use different oils, as this makes it too complex on the road.

 

Is it possible to only exchange the valve parts for example, so that I dont end up with dampers lying around?

 

What does filing away on the damper valve exactly do, as I've seen in Dodds videos?

 

Cheers,

Wolf

[timmy850]

As I mentioned you can modify them to:
Even the rate between the two carbs (so you can use the same oil). You can modify the damper to make it rise quicker by removing some material of the damper to allow it to pass the oil by quicker when it’s lifting

And/Or modify them to drop quicker. You need to remove material on the cone shaped seat to allow more oil flow when the damper is dropping. It has a one way valve which means it can be made to rise and fall at different speeds

You can go and buy new dampers and hope that the new ones are closer to what you want, but the tolerance is so specific between the damper and piston that there’s no guarantee that new ones will be better

But as always you need to:
Accurately measure what the engine is telling you
Know how you want the engine to perform
Know how to change or modify parts to make them work how you want
Verify the change with another measurement
If you can do all those things then you’ll be sorted - but this takes time, trial and experience

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[Lplus]

 

He modifies them for a few reasons, and only if required after measuring the performance:
If the twin carb dampers act differently and they need to be evened up
If they drop too slow and cause a lean spot when changing gear

On your gauge:
When you are driving at a constant speed, then go full throttle the mixture should get richer and there shouldn’t be any stumbling
If it goes too rich under hard throttle you need a lighter oil
If it goes too lean under hard throttle you need a heavier oil

If you are speeding through the gears and get a lean spot when you engage the next gear it can mean the damper isn’t allowing the piston to drop quick enough. This is where modifying the damper to allow more oil flow under that condition is needed

 

Do you mean  if the carb pistons rise not evenly in the first moment, that the damper is the problem here?

If so, then this might be he case here. Although they I did match tihem via drop test

 

-without oil and damper and spring

-without oil and damper

-without oil and spring

-without spring

-alltogether applied

 

After that procedure and refinements they perfectly dropped together.

 

I get them however not to equally on initial throttle. One of them always rises faster.

 

I dont want to use different oils, as this makes it too complex on the road.

 

Is it possible to only exchange the valve parts for example, so that I dont end up with dampers lying around?

 

What does filing away on the damper valve exactly do, as I've seen in Dodds videos?

 

Cheers,

Wolf

 

That might be due to unballanced carbs at idle, or the throttle linkages are not opening both together.  they need to be synchronised.

[woolfman]

They are perfectly balanced for idle and are matched @ 3000rpm as well, so that flow is equally good throughout the range.

[woolfman]

So has anybody clues on the parts that I might need for the dampers? I am somewhat overwhelmed by SUs new page, and since there are pictures missing from a lot of their offered parts it is hard to tell.

 

Also their customer support is of no help, as they keep me directing to standard replacement parts :-(

[PoolGuy]

I found this very helpful https://sucarb.co.uk...-catalogue.html

[timmy850]

So has anybody clues on the parts that I might need for the dampers? I am somewhat overwhelmed by SUs new page, and since there are pictures missing from a lot of their offered parts it is hard to tell.

Also their customer support is of no help, as they keep me directing to standard replacement parts :-(

What dampers do you have now?

Is the performance not what you want?

Changing things or modifying them because you saw someone else do it may make your particular engine run worse

[woolfman]

I have a lean spot on gear changes, which I spotted with my lambda meter (via logged/recorded graphs). I didn´t know until know that this can be resolved with the dampers, so I wanted to look into that further.

 

Since Austria doesn´t have a dedicated SU tuning scene - unlike the UK it is rather hard to impossible to find someone, so I have to do it myself.

 

This is the only "construction site" that is left over, anything else I have fully under control...

[Lplus]

I have a lean spot on gear changes, which I spotted with my lambda meter (via logged/recorded graphs). I didn´t know until know that this can be resolved with the dampers, so I wanted to look into that further.

 

Since Austria doesn´t have a dedicated SU tuning scene - unlike the UK it is rather hard to impossible to find someone, so I have to do it myself.

 

This is the only "construction site" that is left over, anything else I have fully under control...

Is the engine modified?  If it is standard. do you have the correct dampers specified, which were AUC8114?  Do you have the correct needles - GY for '62 - '63 or AN for '64?  Do you have the correct springs - Blue in this case?

 

I too have a pair of HS2s with a weak spot on intial light accleration as identified by an A/F meter, but mine are on a modified 1098 so I may have to live with it, or just drive it harder, which seems to help a lot.  I may play about with the pistons and washers in the future.