tr4 TR4 HS6 carb set-up

[TRnorm]

I'm trying to get to the point where I can sustain a running engine long enough to get hot enough to go through the Carb Balancing and the Mixture fine tuning.

 

I just cannot get it running other than on the Choke (at about 1500 RPM), but then any attempt to push the choke in results in an initial rise in RPM followed by a progressive loss of revs and final stall.

 

My HS6 carbs have the 0.1" jet and SM needle and Red spring. I closely followed the generally recommended set-up with the jets 2 Turns (12 Flats) down from the bridge level and with 1.5 Turns on the idle screw. The distributor is statically timed at I judge to be between 6 and 4 deg BTDC.

I also followed the instructions regarding setting the fast idle cam screw (and so far this has been the only adjustment that has had any marked effect on the running - more of that later)

According to everything I have read, this set-up ought to get it going sufficient to fine tune everything - the problem is in my case it won’t!

 

Initially I found that the engine fired instantly on full choke - but to a very high RPM in the order of 3000 RPM! I then did several systematic (and recorded) changes to try to get the choke-out speed down and allow the choke to be pushed in without the rise in revs followed by the decrease to stall.

To cut a very long story short (or just shorter) weakening the mixture (from the starting point of 12 flats) by up to 4 flats and/or similarly winding the idle screw from 1.5 to 1 Turns had virtually no effect.

 

The only thing that got the revs down (to about 1500) was by taking 1T out of the cam screw. In effect this meant that even with the choke fully “out” and cam at its maximum, the screw was barely touching the cam and consequently having little or no effect on the throttle position. This frankly seems all wrong to me, but it’s what I’ve found so far!

 

PS

I should mention that the plugs are incredibly sooty.

 

I can’t really say I expect someone will have an easy explanation and cure for what I have described, but can I just ask…….

 

Does it make any sense that pushing in the choke will result in a strong rise in revs (which then dies)? I suspect that if I could just get an explanation for that, then I might just start to make some progress fathoming out the rest.

 

Or more pragmatically, can anyone recommend an SU specialist mechanic in my area, Harpenden/St Albans?

 

Thanks in anticipation

Norman

[Tr4Tony]

Hi Norman

 

Sounds like you need a rolling road, but first a bit of a carb health check. It sounds to me like you have variable air intake, so those carbs aren't airtight ?

 

If you can get it running I recall that Southern Carbs at Wimbledon know their stuff. Ask for Peter if he's still there.

 

Regards

[Fireman049]

Yes I agree withTr4Tony ~

 

I strongly suspect that your carbs. are drawing in air from somewhere like the carb. to inlet manifold or inlet manifold

to cylinder head. Try spraying with carb. cleaner to see if it makes any difference.

A friend of mine had a similar problem with his TR and it turned out to be air being drawn in between the manifold

and cylinder head.

 

Hope this helps ~

Tom.

[TRnorm]

Thanks guys - optimism is being restored!

 

Certainly if I could get it going I would be heading Womble way - and when I do get it going, that is what I'll be doing.

If nothing else, I've realised that for me, the final carb set-up is something for the specialist.

 

I like the rolling road idea but its basically a new engine, so something for when its run-in.

 

So, off for some carb cleaner.

Thanks Tom and Tony.

 

Norman

[stillp]

I had something similar when first running my 4A. Managed to find an air leak by using the radiator overflow pipe stuck in one ear as a stethoscope. Turned out to be a leak at the manifold gasket, cured with some Loctite Instant Gasket.

[TR 2100]

Just a thought -

 

Initially, the choke acts on a cam that gives just a little bit

of throttle, before acting to enrich the mixture.

 

If this is wrongly set, and there is no initial throttle action,

then I reckon it could lead to the symptoms you descibe.

 

Tony - would that be right?

 

AlanR

[TRnorm]

If this turns out to be something as simple as an air leak I'll be well and truly jiggered - but delighted!

 

Alan, the funny thing is that when the choke cam is set-up to give the appropriate tweek to the throttle, that's when i get the high speed tick-over (choke out). And it's only when i readjust so that the cam does not contribute to the throttle opening that the high tick-over reduces to a reasonably sensible 1500 RPM. As I initially said, it doesn't really add up.

I have this kind of worrying feeling that in the end it will be a combinations of factors. Certainly the permutations of adjustments that you can make are legion which makes homing in on the culprit(s) less than easy.

 

As usual, airing a problem on the Forum inevitably gets the little grey cells darting off into completely different directions! What would most of us do without it?

 

Norman

[Chris Hubball]

Hi Norman

 

I have checked my records assuming your engine is in standard tune you should be using TW needles in HS6 carbs the SM needle was fitted to H6 carbs and is richer which would contribute to your sooty plugs, also have you checked the jets are centralised you can check this by removing the dampers lifting the pistons and letting them drop they should hit the bridge with a soft clonk.

 

Cheers Chris

[MRG1965]

Hi Norman, I struggled with this recently and it can be a pain. One issue (of many that frustrated me) was the jet on the rear cab stuck down, off choke, causing the engine to have the same issue as you as I tried to balance and set the mixture. Check the jets are fully up otherwise the mixture will be excessivly rich at wont idle at all.

 

Mark

Edited March 8, 2015 by MRG1965

[kob666e]

Have you checked the float levels, do the valves/needles close fully, if it's a new build any dirt in there?

 

Also check the throttle disc is closing off fully/centrally seated, even if the carbs are new it has been known to happen. This has been the cause of many an air leak!

[TRnorm]

More interesting stuff - many thanks

 

Chris - I'm now wondering why I thought SM was the needle. I need to review were that came from. Might be that because of the cam.

The engine is number CT20 thousand and something. It has BP270 cam (Piper I think) and the later exhaust header (cast iron 2 into 1 type). I forget exactly what the exhaust is but it was basically a Moss straight through(?) I've measured the head and reckon the CR might have been upped by no more than 0.5.

The needle/jet centralisation seems fine. With the jets fully in (lean), both pistons fall freely at the same rate and hit with that nice "clonk".

(Think I've just remembered why SM. When I sent the carbs away to Burlin 20 yrs+ ago for a full refurb (but only fitted last year) I asked for them to be jetted for a Fast Road set-up. They never confirmed the detail but because of the problems I'm now having I checked the jet dia (0.1") and the needle at 3 stations and concluded that it was a SM needle.)

 

Mark - interesting about what you experienced; similar symptoms yet as I indicated to Chris, I'm certain there is no binding twix needle and jet?!

I was puzzled about "checking the jets are fully up". Are you saying that your car runs with the jets fully up (lean)? Whilst I did raise them to bridge level to check the centralisation, I then lowered by 12 flats (2T) for the initial setting that I understand is the starting point that should allow the engine to run.

 

One other thing I have noticed that doesn't feel right is that with the dampers screwed in it takes quite an effort to manually push the piston up - real effort that I find difficult to think could be overcome by the suction in the upper chamber. Yes - its has Penrite SU carb oil in the pots and of course with the damper withdrawn, or with the oil removed , the piston rises with light finger pressure. (So no binding there i think.)

Recollections anyone on the force needed to lift the pistons?

 

Meanwhile - off to Halfords for some Wynn carb cleaner for a leak-test later today.

Thanks again

Norman

[TRnorm]

Thanks Justin - I have not checked the floats although it was in my mind that that should probably be the next move - now you've convinced me!

Although they looked good, I'll now give more than the cursory look at the throttle disk sealing.

Thanks

Norman

[peejay4A]

Also check that the needles are correctly positioned in the dampers.

[MRG1965]

Hi Norman, no I ment the jet had returned to the normal position when the choke is fully off. Also I found the 12 flats to be far too lean for my carbs, ended up using almost double that to get the idle to a point to start tunning from.

 

It is quite hard to push up the piston with your finger, but as long as they move freely without oil you should be ok.

 

Mark

Edited March 8, 2015 by MRG1965

[TRnorm]

Pete - the needles look located OK but I have not had them out - so that's another thing to add to, checking the float level.

 

And Mark - that's really interesting about 12F being too lean - cant wait to try it richer but double! How many gallons to the mile are you getting!

 

PS

Tried the carb cleaner routine earlier and nothing - so inclined to rule out an air leak.

 

Thanks also to Mike MD for the text - looking out for your email with details of your carb-man, near Cambridge

 

Thanks everyone

Norman

[MRG1965]

Hi Norman, don't really know what the mpg is now, was getting low 30's last year. Have had a number of issues with carbs (needle had fallen out of piston being the final issue). Only got a chance to take her out for a good run yesterday. I've proably moved the mixture back up to nearer 12 flats down, but did not count as I was sooooooo happy to get her running, I was pleased just to get the colour tune back to a nice blue I did not count, but with 12 she would Bearley start and would not idle. Will findout over the next few weeks what the mpg is.

 

Mark

[BlueTR3A-5EKT]

Any use?

 

http://www.rollingroadtuning.co.uk/

 

I know nothing of them save they came up in a search and are in Wellingborough, Northants

 

They at least mention SU in their ad.

 

There is also someone near Biggleswade with a Rolling Road that understands carbs - too many are ECU remappers these days due to current demands

 

Cheers

Peter W

[Kiwifrog]

After having endless problems with HS6's, now fixed thanks to the help on this forum I have this, mostly second hand advice but very helpful to me to pass on.

 

Have you checked that the gaskets and the air filters are not blocking the balance holes in the carbs, the two smaller diameter holes on the air filter side ?

 

I would also go through re-centering the jets to be sure then balance the carbs using a tube in your ear.

 

I am not fond of colourtune myself and tend to use the method outlined in the service manual of lifting the pistons, colourtune tends to leave a too lean mixture when checked after a few miles by chopping the plugs in my experience.

 

To be honest it sounds like the needles are to rich and you have an airleak I would order a new pair of needles to be sure they are cheap and you know where you are starting from. My SU guide recommends TW as a standard needle for HS6 carbs on a TR4A as TR4's were fitted with H6 carbs or Strombergs from factory. SM is the standard needle recommendation for a TR4 running H6 carbs.

 

I had a simular problem and it turned out to be a non matched pair of suction chambers found out by lifting up and watching the pistons fall many times till I was satisified this was the cause. Normally you need a rolling road and a few WOT sessions to watch to see if the pistons rise and fall together.

 

Also ring SU and order a carb parts book they are fantastic and along with mintylamb and SU Carburetters tuning tips and techniques from Brooklands books will give you everything you ever wanted to know about SU's

 

Cheers

 

Alan

Edited March 8, 2015 by Kiwifrog

[TRnorm]

Thanks Peter for the link to Lynx rolling road people, but what's more...

Looks like I'll be able to get there under my own steam!!

 

Frankly I didn't think that going richer as per Mark's experience was the way to go - all the evidence of sooty and wet plugs and plenty of petrol sloshing around suggested otherwise.

 

Nevertheless, I reset everything to the "standardised" starting point (12F,1.5T and fast idle screw just touching cam when the choke is just about to lift the jet).

Except I then made the jet richer by 2 more flats.

Oh Joy!

OK, the choke-out speed was still around 1600-1800 rpm, and it still rose to around 2200-2500 when the Choke was In. But...But...but.. the engine didn't die. This was real progress.

Emboldened by this; successive reduction in the idle screw from 1.5T to 1T, 3/4T,1/2T and 1/4T reduced the speed to 2000, 1800, 1700, and 1600 respectively.

Separating the throttle shaft for the final adjustment to the two slow speed idle screws got me a final 1500rpm - with equal Hiss.

Lifting the pistons by the requisite 1mm seemed to indicate that the mixture was correct - so no change to the jets position seemed necessary..

So in the end I have an engine that will get me to the SU specialist for a pukka set-up on a rolling road with gas analysers et al.

 

Obviously 1500 rpm is still a little high for a choke-In idle and it runs a little lumpy - a strobe light on the crank shows a regular fluctuation between about 6 to 0 degrees BTDC. Maybe I let the specialist work this out - but if anyone has an idea about this then Id love to know.

 

Thanks for everyone's contributions, all of which I took into account and which helped with the thought process..... but in the end the one I thought most unlikely proved to have been the most effective in my case - must be a lesson there!

 

Just seen your post Alan, so thanks for that. I was thinking about getting the Colour Tune but like you I think, found the Hiss method easy and I think effective. And I certainly don't want to be running lean. Also interesting that there's another vote for the rolling road.

 

Great stuff!

Norman

Edited March 8, 2015 by TRnorm

[Peter Cobbold]

 

One other thing I have noticed that doesn't feel right is that with the dampers screwed in it takes quite an effort to manually push the piston up - real effort that I find difficult to think could be overcome by the suction in the upper chamber. Yes - its has Penrite SU carb oil in the pots and of course with the damper withdrawn, or with the oil removed , the piston rises with light finger pressure. (So no binding there i think.)

Norman

.

Norman,

Aha! The air space above the dampers may not be vented. You may be trying to compress trapped air with a finger. The screw-top of the damper rods should have ca 1mmm bore drilling through them to atmosphere. If none, there has to be an internal drilling to vent the top of the damper-space air column into the under-dome air space, but I think this was only done in some 2" SUs. If you have neither you've found a problem: drill a 1mm hole off-centre in the screw-top.

Or the damper rods are badly bent.

Peter

Edited March 8, 2015 by Peter Cobbold

[TRnorm]

Thanks Peter - My caps do have the hole, but I'll certainly have a look at the straightness of the damper rods.

 

I'm beginning to feel I risk becoming a bit of an expert on HS6 carbs through acquired knowledge!

 

Which reminds me of that salutary definition of an expert...An expert is someone who knows more and more, about less and less, until he know everything about nothing.

 

Norman

[stillp]

An expert is someone who knows more and more, about less and less, until he know everything about nothing.

 

 

Or, as I was reminded the other day "An ex is a has-been, and a spurt is a drip under pressure"!

[Peter Cobbold]

Thanks Peter - My caps do have the hole, but I'll certainly have a look at the straightness of the damper rods.

 

I'm beginning to feel I risk becoming a bit of an expert on HS6 carbs through acquired knowledge!

 

Which reminds me of that salutary definition of an expert...An expert is someone who knows more and more, about less and less, until he know everything about nothing.

 

Norman

Norman,

Wish an expert could tell me exactly how an SU works !

The lift force should be equal to the force from the spring plus the weight of the piston. Piston is a few ounces, the spring rate should be a few more. There are two different red springs catalogued:

http://www.classiczcars.com/topic/42125-need-to-find-some-stiffer-piston-springs-for-my-sus/

I think yours should be 4.5oz at 2.5inches.

So roughly 10oz = bit over half lb =1/4kg to lift the piston.

If the finger lift needs more. then I'd sort that out.

 

The air flow lifts the piston by generating that lifting force. The choke tube depression acts on the outer annulus of the piston: so 0.5psi depression needs about 1.25 square inch to create lift of 10oz.

Peter

Edited March 8, 2015 by Peter Cobbold

[JFerg]

I've been wrestling with my 4A for years to stop it running on. A year or so I conceded defeat and gave it to the mechanic with a message to "fix it". He did. Sort of. Amongst a number of things that he did, one was to send the carbs away for a complete overhaul. It came back all lovely, and with new CIW (standard lean) needles fitted. It ran reasonably, no better than that, and was nauseatingly rich at idle, but it didn't run on.

 

Not satisfied, I re-tuned it myself from first principles using my colourtune. For a mug back-yarder, the colourtune is a brilliant device. I set the idle mixture and had a perfect, smooth, 800rpm, idle. It was almost undriveable, however, chronically lean everywhere off idle. Some years ago I'd fiddled with needles. I'd made a pair based on seat-of-the pants, went to the dyno, came back, worried a bit off here and there, back to the dyno, worry some more, back to the dyno, now too rich so make another pair and repeat. Over a dozen dyno visits all told. So I am not afraid of needles, nor of whittling them. I've made a measuring gauge, have a vernier micrometer, and the "feel" to use it.

 

Using "Haystack" as a guide and reference, I worried a bit off my new CIWs and found a very slight improvement. I drove a bit on some test grades, thinking and pondering. Once sufficiently thought and pondered, I abandoned the wise process of worrying a bit more off the needles, and went wholesale; I took a heap off, 4 thou (that's 40 ten-thou) at one station, progressively less at others simply as I saw the need.

 

The results are astounding and wonderful, even if very lucky. Performance is far better than ever before, it will pull smoothly from walking pace in third, and the economy is good, although I have not bothered actually measuring it. Plugs are perfect grey. Point is that it really should not run at all well on what is at face value a super-rich needle, but it does. The combination of extractors, cam, advance curve, compression ratio, port treatment and who knows what else (it had been given a "race motor" rebuild years ago) applicable to this specific engine mean that it works beautifully, on this specific engine. And there's the problem. When the car is 50 years old, no-one knows who has done what to what inside it.

 

As with many problems, the best approach is to begin with first principles. You've set everything else correctly, buy yourself a colourtune and you'll know with certainty that the idle mixture is right. Then satisfy yourself as to what it does when driving and use that knowledge to guide some needle substitutions. In Hertfordshire you can probably borrow some needles to play with, or judiciously buy some fairly easily and cheaply, two things not possible here in Oz.

 

cheers,

 

JFerg

[stuart]

You could use this to work out the needle requirements http://www.teglerizer.com/suneedledb/index.html

Stuart.