HD6 Question - on TR6

Hi guys,
I thought I would pose this question(s) here as I would probably get more valued responses since you are most likely more familier with the HD6 carb.

I bought "Jerry's" old HD6 carbs to replace my HS6 pair on my stock engine TR6. The carbs actualy fit very well and look fabulous, I had to cut the nice chrom connecter fuel line as the distance between the carbs must be about 1/4" wider.

So far I have the car running albeit a bit lumpy.
The jets are all the way up flush with the bridge, floats are as they came. The needles are standard "CV" and pistons seam to move ok.

On the front carb I am getting the occasional blow back "explosion" and it has a constant stream of vapour oozing out the entrance.
I have noticed the plugs seam very dry on it's side compared to the other side. However when I move the diaphragm lever plenty of gas injects out the top of the jet.

Is this a sign of richness ?

The back carb seams ok.

The car doesn't run well with the filters off.

The plugs are very black, however sliding the needles down(weakening) makes the car run very rough and hard to start.

Sometimes when I hit the gas the revs don't go up as if the Constant Vacuum is off or pistons haven't moved.

The idle is at 1000rpm with throttle stops backed off fully. (i am fairly sure I have no vacuum leaks )

What does the slow running valve do (spring loaded screw on top of carb body), where shoud this be adjusted. What happens when I screw the valve down or up.?

Float heights, should I lower ?

When I raise the lifter pin on one carb, should I be adjusting the other carb?

Any help appreciated. I will be able to take the car for a short drive tomorrow, so far I have just been fiddling with the idle.

Many thanks..

What was wrong with the HS6s?

Several years ago I put a brand new set of HS6s on a friend's TR6.
Once we dug through my boxes of SU parts and came up with the right combination of linkages, he was off down the road and never looked back.
Given the choice, I would use the HS over the HD type for the shear sake of simplicity.

Listen to THAT BS!
My Healey has a trio of 45 DCOEs

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Gary Pope:
So far I have the car running albeit a bit lumpy.
The jets are all the way up flush with the bridge, floats are as they came. The needles are standard "CV" and pistons seam to move ok.

On the front carb I am getting the occasional blow back "explosion" and it has a constant stream of vapour oozing out the entrance.
I have noticed the plugs seam very dry on it's side compared to the other side. However when I move the diaphragm lever plenty of gas injects out the top of the jet.

Is this a sign of richness ?

The back carb seams ok.

The car doesn't run well with the filters off.

The plugs are very black, however sliding the needles down(weakening) makes the car run very rough and hard to start.

Sometimes when I hit the gas the revs don't go up as if the Constant Vacuum is off or pistons haven't moved.

The idle is at 1000rpm with throttle stops backed off fully. (i am fairly sure I have no vacuum leaks )

What does the slow running valve do (spring loaded screw on top of carb body), where shoud this be adjusted. What happens when I screw the valve down or up.?

Float heights, should I lower ?

When I raise the lifter pin on one carb, should I be adjusting the other carb?
..<hr></blockquote>

Gary,

I'll see if I can give you some pointers while I'm at work. More detail will have to wait until I get home to my notes. (I need more memory! )

The HD carbs work a bit different than the HSs. At idle, the throttle plates should be completely closed. The slow-running screw provides the idle flow, bypassing the throttle plates.

The needles are set so their shoulder is flush with the bottom of the pistons and left there. Mixture is adjusted by raising and lowering the jets using the mixture screw (it's a small one on the side). There's also a fast idle screw that is used to adjust the mixture when the choke is pulled.

As a start, the jets start out flush, and the are lowered by turning the mixture screws about 3 turns.

Then loosen the throttle shart linkage between the carbs and make sure the throttle plates are completely closed on both. Then tighten the linkage between them. You can then adjust the idle with the slow running screw. Make sure you have the same flow through each.

If the plugs are very black but dry, the mix is too rich.

As for blow back, have you checked ignition timing? You really need to go through checking valve adjustment and ignition timing before the carbs, anyway.


John, BN4

Gary, Let me try as well to give you some help. My Ideas follow along with the previous post so I will just try to reenforce that.
I am assuming here that this engine ran rather well before you changed Carbs. Because you could have a vacuum or timing problem as well. But lets assume you don't and just try to get the carbs right because I think you need to dial them in.
-I'm going to make some quik comments in response to your comments then I will try to detail the adjustments to make.
-the jets are flush with the bridges, ok.
-engine running lumpy because the carbs are way off.
-blow back and vapour due to leaness in that carb, but here could be timing.
-you must clean the spark plugs really good. Black plugs will stay black no matter what you do to the carbs unless you put many many miles on them at pretty constant speed. It would be good to get new plugs so you can read them well.
-if you pull the jet down with the fuel pump energized you will get a stream of fuel through the jet.
-filters off and engine gets rougher tells me that it can't handle more air, at least one carb is lean, probably the front one.
-when you move the needles down to lean the mix and it runs rough & starts hard you are again telling me that the adjustments are too lean. At least on one of the carbs. (make the needles flush with the bottom of the pistons and leave them that way).
-the slow run screw is for the purpose of setting the idle 'speed'. It is controlling the passageway
which directs fuel mixture around and bypassing the throttle plates. This mixture is flowing from the main jet. So the adjustment of the main jet establishes the mixture ratio/quality for the idle passage and, the main bore when the gas pedal is depressed.
-you use the piston lift pins to test the carb you are adjusting.
---- Adjusting the HD Carb, Number 18 on the manual drawings is the jet adjusting screw, back it out till it does not touch its landing. the jet should be level with its bridge. turn this screw down till it just touches the landing of the carb body. Now turn it 1/2 to 1 turn as an initial setting. Remember this TR engine may need a much different jet setting than the healey. The jet should now be maybe 1/64 inch below its bridge. separate the link between the throttle shafts of the carbs so the carbs operate independantly. Back out the throttle adjusting screw of each carb so that the throttle plates are completely closed. With HD carbs these throttle plates will aways be closed when the engine is idleing. (unless the choke is on) Now turn the slow run screws all the way down and then back them out about 2 to 2 1/2 turns. Now with these settings the engine should start and run. If it runs at too fast of an idle, then turn in the slow run screw alittle at a time equally to slow the idle to where you want it. Maybe around 700 rpms to finish the carb adjustments. With the engine running now , let it warm up. If you had to connect the throttle shafts back together to get the engine started, then warm up the engine and disconnect the throttle shafts again. Now the slower you can get the idle the better for adjusting the main jet. If you can get it to idle near 600 rpms the better.
-Now for the main jet. Here is where you lift the center piston of the carb about 1/8 inch to see what the engine will do. Use the piston lifting pin or your finger. If when you lift the piston the engine just speeds up alittle then drops back to where is was then the jet on that carb is good.
If when you lift the piston the engine speeds up and stays up then that main jet is too rich and must be leaned out. So here you turn screw number 18, the jet adjusting screw, out a small amount maybe 1/4 or 1/2 turn to lean the jet.
If when you lift the piston the engine stalls or slows and all most stalls the the jet is too weak. In this case you turn the jet adjusting screw in a small amount. Then retest by lifting the piston. pay attention to what the engine is doing and continue to adjust till the engine responds with just a slight increase in speed momentarily when you lift the piston.
When this carb is right, do the other the same way. then connect throttle shafts back together and go for a ride.
Boy I'm sorry for being so laborious. I guess Basil will shoot me for using up so much space.
I hope this helps you get the TR running right.
Dave,

Guys, thanks for the replies.
I fiddled with it for about 2 hours yesterday and had to give up. From cold it starts fairly well but didn't idle well. Once hot, it was impossible to start unless I unscrewed the slow running screws all the way out and off the carb.
Then it started whilst hot but screaming air down the holes, it didn't run off idle .. idle was 1100 rpm. Laying the screws in the holes not tightening would cause engine to die.

I am really thinking of going back to the HS6's now as they are way easier to work with.

[ 02-23-2003: Message edited by: Gary Pope ]</p>