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4 pot Carburetter needles.


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I have a 3A with an engine spec. as follows:- 87mm pistons, Kent Sports 'R' cam (280° duration), CR 9.95:1. I rebuilt the carbs and during a rolling road session some time ago ended up with RH needles. These are the 'rich' spec. for the standard engine. I now have a digital AF meter and find that at low revs - say, tickover to 1600 rpm - it's running very weak, thereafter it is rich. This weak mixture accounts for the hesitancy when pulling away that I've been having - and the sooty plugs. - and running on.

 

Does anybody out there have a similar spec engine & if so what needles are you running on - assuming that you are happy with the performance?

 

All suggestions gratefully received.

 

Thanks in advance,

 

Phil.

 

by the by - for those who are aware of the mintylamb site - it's currently down as he's lost his host.

Edited by greasemonkey
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1 . Have you tried a heavier oil in the dash pot?

***That one worked for me on the pick up hesitation - I have a similar engine set up. with 87MM HS6 RH needles with red springs

2. or - Next try heavier dash pot springs with SM needles.

3. Finally - Rolling road for you then.....but who knows where to go TODAY, that understands the SU carbs and is not just a lap top jockey for injection systems?

 

Peter W

Edited by BlueTR3A-5EKT
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Hi Phil

 

i am running a TR4 with 87mm pistons Piper yellow cam not sure how this compares with yours Extractor Manifold and HS Carbs fitted with SL needles, good performance 32 mpg.Hopes this is of help.

 

Cheers Chris

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Funny thing about the RH needles. Even though they are the recommended "rich" needle, they are actually leaner than the standard SM needle at the first station. They are .100" (the same dia. as the jet)vs .099" for the SM needle. It would seem that the jet would have to be be adjusted lower to get the car to idle and cause the mixture to be richer above idle.

Berry

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Very similar to my engine. On a RR it is pretty much spot on SM needles. I too tried RH and found them to be over rich.

The only issue I have with the carbs H6 is the choke mechanism, which over time stiffens and results in the jet not returning properly. Fixed with lubrication.

 

Performance wise its pretty healthy,with correct mixture through the rev range.

Doc1.pdf

 

Iain

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I think that changes in petrol over the years (I used to use 4* leaded) have changed combustion characteristics for the worse.

In September, I had 4VC tuned by Dan & Carl at Revington TR. They changed the needles to overcome a slightly weak mixture in mid-range (3500-4500), and this fixed the tendency to pre-ignition. Afterwards, on the 5-mile "Revington road test circuit", the car pulled like a steam train all the way from 1800-5000 - marvellous!

And at Kop Hill, 10 days later, it performed excellently, as Wayne can attest (his video of the Saturday morning run appears in his report on the TRR site).

Ian Cornish

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Ian, you raise a good point, modern fuel is very volatile, in a matter of weeks it is going off.

 

Comparisons/tests on old fuel are therefore very misleading.

 

Iain

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I think that changes in petrol over the years (I used to use 4* leaded) have changed combustion characteristics for the worse.

In September, I had 4VC tuned by Dan & Carl at Revington TR. They changed the needles to overcome a slightly weak mixture in mid-range (3500-4500), and this fixed the tendency to pre-ignition. Afterwards, on the 5-mile "Revington road test circuit", the car pulled like a steam train all the way from 1800-5000 - marvellous!

And at Kop Hill, 10 days later, it performed excellently, as Wayne can attest (his video of the Saturday morning run appears in his report on the TRR site).

Ian Cornish

I couldn't agree more. The modern fuels have rendered the SU tables for needles nothing more than a start point. As a matter of interest, which needles did you end up with on 4VC?

Phil.

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Hi Phil

 

i am running a TR4 with 87mm pistons Piper yellow cam not sure how this compares with yours Extractor Manifold and HS Carbs fitted with SL needles, good performance 32 mpg.Hopes this is of help.

 

Cheers Chris

Thanks for that Chris. You engine spec looks close to mine so SL would be worth a try I think.

Cheers,

Phil.

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Phil,

 

If you decide to go for another rolling road session - and that's the best way to be certain about fueling and ignition setup - I can recommend Aldon Automotive at Brierley Hill. Roger their RR expert knows all about setting up carbs, whether SU, Stromberg, Weber etc. He's also good at optimising the ignition timing and advance.

 

On my GT6, he even went so far as to hand file the carb needles to cure a slight mid-range weakness, probably only necessary because of the limited needle choice for Strombergs. He certainly improved the performance of an engine that I had set up as well as possible at home.

 

No connection to Aldon, merely a satisfied customer.

 

 

Nigel

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According to Revington's invoice, I have 2 off AUD1487 Needle Carb RE fitted now in 4VC.

The car has 88mm pistons (2238cc), CR about 10.0, modified camshaft, head etc., and con. rods lightened. The modifications are very much as described in Kastner's excellent Competition Preparation Manual. Neil describes the set-up as being Rally Stage 2 (and a bit!). Gives about 115-120 HP at the rear wheels, but excellent torque, as can be seen from the attached diagram (Alistair's car was a standard TR4).

Ian Cornish

Annotated plots 4VC v Standard.doc

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According to Revington's invoice, I have 2 off AUD1487 Needle Carb RE fitted now in 4VC.

The car has 88mm pistons (2238cc), CR about 10.0, modified camshaft, head etc., and con. rods lightened. The modifications are very much as described in Kastner's excellent Competition Preparation Manual. Neil describes the set-up as being Rally Stage 2 (and a bit!). Gives about 115-120 HP at the rear wheels, but excellent torque, as can be seen from the attached diagram (Alistair's car was a standard TR4).

Ian Cornish

Ian. The standard car looks like it's torque is well down and decreasing from mid range revs.....was it sick. :-(

 

Iain

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iain - have a look at the torque plot in the attached figure. It's for the TR2 and we know that the TR4 produced a bit more grunt (partly because of the increased capacity). However, the 4-pot TR engine, in standard form was produced to give plenty of torque in the range where most drivers would use the car.

In the plot for the TR2, one can see that the peak torque is at about 3300 rpm, and then it dives downward quite rapidly from 3700 to 4700 - at which point Triumph ceased to plot further because that was where peak power was achieved. Allowing for the fact that the TR4 had a little more torque further up the range (and hence more power), I think Enginuity's plot of Alistair's engine, showing peak torque at 3800 rpm seems perfectly reasonable, and the decline thereafter matches the TR2's graph quite well.

 

I know that my old TR2, in the early 1960s had a lot of torque very low down - I could climb up the slope heading southwards in the 30 mph area towards Wandsworth Common having engaged overdrive top (3.7 axle) with the engine then pulling 800 rpm, and accelerate gradually to about 1300 rpm. Amazing, and I have never owned a TR4 which could manage that! Also, I never bothered to use much more than 4500 rpm as it seemed a waste of time!

 

Ian Cornish

post-4157-0-58951300-1510604490_thumb.jpg

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I've just found the TR3's graph in the Supplement at the back of my TR2 Manual.

In the attached plot for the TR3, one can see that the peak torque is again at about 3300 rpm, and then it dives downward quite rapidly from 4000 to 5200 - at which point Triumph ceased to plot further because peak power was achieved at 5000.

 

The VC Works' Rally cars were taken to 6000 (sometimes more!) by their drivers in 1962/3, and I know that my car is still pulling very strongly at 5500. However, in the interests of longevity (I don't have a team of mechanics available to re-build my engine!), I seldom exceed 5000 and have a personal self-imposed limit of 5500.

 

Ian Cornish

post-4157-0-07933800-1510605555_thumb.jpg

Edited by ianc
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Hi Ian. My 4 with 86mm pistons gives a comparable figure to 4VC albeit on Webers. A while ago @ Stanton Motorsports rolling road I got, over 3 runs, an average of 113 hp @ the wheels & an average torque of 145 both @ 4800 rpm (my self imposed limit!). After your kind ride up Kop Hill in 2016 I can agree 4VC goes well & I think both our cars are similar performance although mine appears to have a bit more torque probably due to the Webers? Of course all our runs do depend on weather, temperature etc!

Cheers.

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Monty - following the tune-up at Revington this September, 4VC is going better than ever with the new needles, which have slightly enriched the mixture in the mid range. I would not expect Webers to increase the performance until one gets beyond 5000, although I note that you have a self-imposed limit of 4800. After the needle change, Dan & Carl saw 90 HP at the wheels at 4000, which they said would be 115+ at peak revs - but they didn't bother to take it up there!

It's great that our cars perform so well and are such fun to drive!

Ian Cornish

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Monty - following the tune-up at Revington this September, 4VC is going better than ever with the new needles, which have slightly enriched the mixture in the mid range. I would not expect Webers to increase the performance until one gets beyond 5000, although I note that you have a self-imposed limit of 4800. After the needle change, Dan & Carl saw 90 HP at the wheels at 4000, which they said would be 115+ at peak revs - but they didn't bother to take it up there!

It's great that our cars perform so well and are such fun to drive!

Ian Cornish

Yes Ian considering they are over 50 years old, performance & fun indeed! Getting around 100 @ the wheels on SU's with my 4A too. Similar spec to the 4 but without the Webers, so that is quite good also!

Cheers.

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