Advice sought on setting up HS6 Carbs on fast road engine.

[mikerf]

Can anyone provide some information on setting up a pair of HS6's on a fast road engine please?

Currently, my engine, although running is heating up very quickly and I feel this may be due to running too lean.

Firstly, let me explain that there is no issue with the cooling side. The block is clean, all hoses are new and the rad is re cored and pressure tested. I also have 2 Revotec fans on the front of the rad.

My theory re running lean stems from the fact that it takes about 6 or 7 turns of the key on full choke before it fires up and thereafter heats up to the extent that the exhaust manifold (a 4 branch s/s item) starts glowing red hot. Initial revs on choke are about 1800 and 800/900 warm but warm up, to my mind, is too quick particularly up here in rural Scotland.

I think the carbs were originally set up for a standard engine and may have incorrect needles.

Atm, I'm reluctant to let the engine run for too long as I feel the amount of heat generated is too high.

I certainly don't mind buying and trying a selection of needles to see if things improve but don't really know where to start so any advice would be appreciated.

 

Thanks in advance.

[Motorsport Mickey]

You gotta do better than that,

Have you checked for air leaks into the inlet manifold ? Sometimes the manifoild binds upon the dowels and stands proud giving a large air leak,

Spray some carburettor cleaner around the inlet manifolds (mask off the carb inlets so it isn't drawn in) see if the revs increase, if so you have an air leak.

you say it's a fast road engine 

what size are the pistons and what compression ratio are you running at ?

Have the SUs been on a car and running previously ?

What settings have you got on the SUs ? and pistons springs colour ?

Do you know how far down the jets have been set ? they should be set about 70 thou down from the bridge (nearly 2 mm) to allow enough petrol to be drawn through, otherwise they'll run weak. You can wind down the jets using the jet nut underneath.

Give us some answers and we'll have another go.

Mick Richards

[Drewmotty]

Where are you? Someone local may be able to help. 

[mikerf]

Ok, I'll do my best but don't expect too much.

 

I can certainly carry out the checks you suggest for air leaks.

 

The engine was bought fully rebuild from one of the main TR suppliers so I can't provide a huge amount of info on it. I do know that it has the 2.3 wet liner kit, what was described as a fast road cam (type unknown) unleaded head (no idea of compression ratio), a vernier timing gear but beyond that, I'd be struggling.

The carbs came from a guy that rebuilds SU's regularly. Or did, I bought these (and the engine) a good few years ago now so he may well no longer be in business.

I can strip the carb to check the spring and look at the jet setting but I did set it all up as per the SU manual prior to first firing it up. No idea what needle atm, but, again, can check.

 

Sorry to be so vague.

 

 

 

 

[mikerf]

Drew.

 

Perthshire, Scotland. Bit of a black hole for classic car fans, I'm afraid.

I did speak to a couple of the guys from the Register at a show last year and they suggested taking it to a local tuner, Mike Stewart but I really feel I should be able to get it at least sorted to run well enough myself. I don't mind getting it tuned properly later if needs be.

[Motorsport Mickey]

Ok, whatever you can give us helps.

No need to remove the carbs to set the jets, just remove the air filter and you should see the bridge (the alloy web that goes across the carb at the bottom from side to side.) the jet is in the centre and has the needle sticking down into it. You should be able to see the amount down from the bridge the jet is from outside, sometimes it's easier to wind the jet up (nut at the bottom) until it's flush and then wind the nut back down and you'll see the jet dropping, if you can measure how far down about 70 thou should get you there, if you can't measure it just guess about 2 mm. Count the turns down on the flats of the nut and make it the same on either carb.

Mick Richards

[AndyR100]

My first thought is to recheck your ignition timing - sounds very likely to be overly-retarded if you have a glowing exhaust manifold.

……….. Andy

Edited February 19, 2023 by AndyR100

[Motorsport Mickey]

"but I did set it all up as per the SU manual prior to first firing it up."

Just reread this, does that mean you know what the jets are set at ? or did you set them yourself ? and if so what at ?

Mick Richards 

[mikerf]

Hi Mick

Yes, I set them up myself by taking the jets fully up and then backing it off as instructed in the SU manual.

Then balanced them with a carb balancer. When running, the engine 'sounds' good, just very hot.

I'm also confused as to why I have to crank the engine so much before it catches and fires on full choke.

By way of explanation, I probably should mention that I have a fair degree of mechanical experience and, in the past, fully stripped and re-built the Essex V6 in my old Scimitar Se 5a. However, this is the first engine I've worked on that's run on SU's and, despite the fact they're meant to be 'simple' (ha) this has got me scratching my head. I'm so tempted to fit twin Webers, pity I can't afford them

I should probably have also mentioned that I'm running electronic ignition (123 Red) and coil with vacuum advance attached. 

[mikerf]

Andy, thanks for that suggestion. I have checked but not for a while now and not since I re-set the carbs. I'll do so again.

 

Thanks.

[rcreweread]

Hi - if you have a mechanical fuel pump with a priming lever, try priming the carbs first -  you should be able to hear the fuel going into the float chambers as you do this until the flow stops when the needle valves shut off and the resistance/noise changes when they are full.

Also, I shouldn't get too hung up about your tubular manifold glowing red hot when standing still - my stainless Phoenix manifold has always done this and the mixture and timing were spot on - there's very little draft of air through the engine compartment when the vehicle is stationary - just make sure you have a heat shield for your dynamo/alternator if you have fitted one

Cheers Rich 

[Z320]

Valve clearance too narrow?

One or more exhaust valves burned?

Edited February 20, 2023 by Z320

[Andy Moltu]

Firstly check the timing - if that’s out setting the mixture becomes impossible as you are tuning to suit an incorrect starting point. Check it is advancing freely. It is not unheard of to find the timing marks on the pulley are out as the damper deteriorates. Identify TDC and see if it ties in with the 0 degrees on the pulley. Then time to static of 11 to 13 degrees btdc or dynamically (with vacuum advance removed) to give timing figure of 30 to 32 btdc at 4000 rpm. 

Similarly, setting the tappers correctly is required. The use of a non standard cam may mean different gaps may be needed. This info should have been supplied with the cam. 

The way an SU works is that increasing airflow lifts the pistons to which the tapered needles are attached allowing more fuel to enter, matching the airflow to keep the mixture to keep to the optimum. The springs above the pistons and the dampers offer resistance to stop the mixture going too lean on opening the throttle and to maintain the correct piston height for the airflow. However the fuelling is generally matched to airflow so tuning an engine allows more air won’t make a huge difference to that, so often little change to the needles will be needed and assuming you have correct ones and the correct springs (for standard) your mixture shouldn’t be way out once set up.

Check fuel flow and float levels. Check for air leaks. If you have a servo this can be a source of air leaks in addition to the ones mentioned already.

Carbs that have been rebuilt are not all they seem. The previous owner of my 4A had had the carbs rebuilt. I was left scratching my head, struggling to dial out a tendency to kangaroo at low revs/throttle. I began to question whether I had gone too far with my engine tune. Eventually I noticed the carb springs were different in lengths and ultimately neither was the proper springs for the car! So check everything!

[mikerf]

Rich.

It's on an electric pump running through a Filter King.

Interesting to hear your manifold glows red hot too. Mine is also a Phoenix.

And I do indeed have heat shields for both alternator and carbs.

 

 

[Tr4aJim]

Another thing to check is to do a “drop test” to check that the pistons are matched to the air chambers. Basically it verifies that both pistons move at the same rate. There are several YouTube videos that show how to do this. When I first bought my TR4A I had trouble with idling/acceleration. After spending many unsuccessful hours fiddling with them, I did the drop test and found the pistons had been swapped at some point. Afterwards, the car ran great. Worth a try.

Jim

[mikerf]

Z320 - I hope not. Can't have run for more that half an hour since rebuild.

Andy - Timing was set up accurately. The cam has a vernier gear so it was relatively simple to set up and get the timing sorted.

I may have to have an in-depth look at the carbs just to check everything is in order.

I was kind of hoping that someone might suggest which springs and needles might provide a starting point and see if those correlate with what's actually in the carbs. Then I can start making small adjustments and changes to get to a more satisfactory point.

[mikerf]

55 minutes ago, Tr4aJim said:

Another thing to check is to do a “drop test” to check that the pistons are matched to the air chambers. Basically it verifies that both pistons move at the same rate. There are several YouTube videos that show how to do this. When I first bought my TR4A I had trouble with idling/acceleration. After spending many unsuccessful hours fiddling with them, I did the drop test and found the pistons had been swapped at some point. Afterwards, the car ran great. Worth a try.

Jim

Thanks, Jim.

I'll put that on my 'to do' list too.

[Z320]

Did you trust or check the valve clearance?

[AndyR100]

2 hours ago, mikerf said:

 

Andy - Timing was set up accurately. The cam has a vernier gear so it was relatively simple to set up and get the timing sorted.

 

Glad that the cam-timing is OK, what about the ignition timing? You added that you are running a 123Ignition, so I’d be inclined to double-check your static timing, the curve that has been created (if a ‘tune’ version) or the curve which you have selected  - then checking that the degree of advance is as you expect across the rev-range with a timing light.

As Marco has mentioned, always worth double-checking valve clearances to ensure nothing slipped as you nipped them up - it would be good if you knew a bit more about the installed cam because they usually have a valve-clearance setting that is different to the workshop manual.

[woodward]

When Revington were tuning my newly built engine they had to replace the needles with  AUD1291 RH needles to get the car to run well.  I didn’t have the issues you’re talking about but this info might be useful for you nonetheless.

Myles

[Peter Cobbold]

Red hot manifolds ! -I would check spark timing first. Ensure the crank pulley timing mark is still true, and then the 123.

Then buy a wideband exhaust gas sensor and meter (UEGO type) to insert into the exhaust and allow mixture to be read while driving.

Hot cams will tend to increase intake pulses such that at wider butterlfy openings the mixture will richen compared with a stock cam. But that condition does not apply at tickover or cruise when the butterflies are less than 30 degree open and pulsing does not reach the SU jets. IN other words at tick-over the hot cam is not going to demand a greatly richened needle.

 

Peter

[ianc]

A few years ago, I started to notice a tendency to pink in the mid-range under full throttle, probably caused by the changes which have occurred in formulation of modern petrol.

On the rolling road at Revington TR, Dan and Carl diagnosed a slightly weak mixture in the mid-range, changed needles to AUD1487, ran it to 4000 rpm and saw 90 HP at the wheels, and said "job done".  I asked whether I would be getting more than 115 HP at 5000, and the answer was yes, but no need to check.  I discovered that Dan had never had a ride in a Works' Rally TR4, so took him round the usual test route, where there's a long straight after a village.  Foot on the floor at 2000 and the car went to 5000 without any tinkling!  Marvellous!

Of course, one cannot say that a set-up on one car will suit another, but, with a trusted operator, I would recommend a rolling road as it's the fastest route to the optimum set-up.

My car has 88mm, HS6s, CR about 10.0, camshaft is the one installed in 1967 and Neil could only describe it as Rally Stage 2+ as no identifier.  Engine, which was installed by Gordon Birtwistle, Triumph's test driver in 1967, has all the mods to rods, head, manifolds etc. as described in Kastner's tuning manual, and has 4-branch exhaust.  Surprisingly tractable for a modified unit, so a delight to drive across country.

Ian Cornish

[Lebro]

AUD1487 = "RE"  (just looked it up)

Here is how it compares with the standard TR4 needles:

considerably richer from 2000 RPM onwards

Bob

[ianc]

Bob: certainly is richer, and much richer above 5000, but my TR doesn't rev to 7000, let alone 12,000 !

Ian Cornish

[Kiwifrog]

23 hours ago, mikerf said:

Z320 - I hope not. Can't have run for more that half an hour since rebuild.

Andy - Timing was set up accurately. The cam has a vernier gear so it was relatively simple to set up and get the timing sorted.

I may have to have an in-depth look at the carbs just to check everything is in order.

I was kind of hoping that someone might suggest which springs and needles might provide a starting point and see if those correlate with what's actually in the carbs. Then I can start making small adjustments and changes to get to a more satisfactory point.

For Needle comparison mintylamb has always been my starting point

http://www.mintylamb.co.uk/suneedle/