2500 Carbs

[Mr Tiger]

Hi,
Does anyone have a (Vixen)2500 or 2500M with HS6 SUs, spring loaded biased needles and K&N filters? if so, please tell what jets and needles are suitable.
Many thanks,
Chris

[Slow M]

You will want to confide in your future benefactor if your engine is completely as per factory standard, and what iteration, as all variations will influence the applicability of needles. (Big or small port head should make a difference, here.)

Have you tried evaluating the existing needles? I.e. run it at a steady 2,000, 3,000, 4,000 rpm, and each time, pull over and do a plug check.

Best,
B.

[Mr Tiger]

Hi,
Thanks for your reply. The problem I have is that the car was running rich when I bought it a few months ago. Tick over was very lumpy and it chugged when pulling away or accelerating from lowish revs. Once it got to about 3000 it was ok. At 4000 it sounded lovely and went well. I didn't take it much beyond that as I'm unsure of the condition of the engine. All six plugs were black initially.

I've weakened the mixture gradually and now the tick over is improved but the car has lost its acceleration (too weak?) The back three plugs are now about the right colour. Front three still black. It's not as smooth as it should be. The front carb doesn't seem to respond to mixture adjustments. I've replaced the needle valves, checked the pistons rise and fall freely, topped up oil with 3 in 1, adjusted valve clearances, checked airflow with a carb balancer and checked compressions.

I think I should replace the jets and needles but don't know which ones to get. As far as I know the engine is standard and probably with a small port head - I should check this.

I was thinking a reasonable starting point would be to go for Triumph 2500S jets or even Dolly Sprint but probably with richer needles for the K&Ns. Just wondering if anyone is running a 2500 with HS6s and K&Ns?

Regards,

Chris

[thegamekeeper]

I have in my "museum" some boxed new or as new emission controlled original Strombergs from a 2500 Vixen. I will have a look tomorrow if I get time.



SU,s were not OE

Edited by thegamekeeper on Sunday 13th October 21:19

[Cerberus90]

If you can find a rolling road who know what they're doing with SUs, like a mini rolling road, then they should be able to tune the needles you have. It's done by maching/filing the needle.

I did see a sort of guide on how to do it yourself somewhere, but I don't think it was very comprehensive.

[Slow M]

Have a look at the front carburetor. See if the needle's position, in relation to the piston is the same as the rear carb's. They are raised/lowered via a set screw, in the piston, as I recall. If it's too rich, it may need to be lowered. If you tried to lean out the front three, by raising the seat, you may have to reverse that operation.

Please forgive me, If I'm wrong, it's been a long time.

Also, make sure the marking on the two needles is the same.

Also, look for a "Gunson's Colour Tune."

Best,
B.

[Hansoplast]

I do run a Triumph TR250 with SU6.
However with a sharper cam, so not the same as your set up.
But when 3 plugs are black and others white you need to equalize the 2 carbs (airflow)

Another thing is, have you greased the axel in the distribitor? Sounds stupid but sometimes helps to improve the pick-up of the revs.

Hans

[ATE399J]

Why not take it to a "traditional" garage and get them to set it up - timing and carbs together. At least it would give you a good start point. I did that with my MG and it saved me what would have been days of fiddling. They also discovered that valves in the butterflies were U/S and fixed that so l would never have been able to set it up without that being sorted.

[Slow M]

Do you have a carb synchronizer?

Best,
B.

[the other tim]

One ear and the overflow pipe off the radiator makes a very accurate synchronizer!!!!

Edited by the other tim on Tuesday 15th October 14:33

[Mr Tiger]

Thanks for all the replies - plenty of ideas to try here!

It would be nice to have a set of Strombergs for originality. I may be interested if the price is reasonable. The inlet manifold is original as far as I know. I think the SUs can fit the standard manifold with some sort of adaptor plates? There seem to be thick black rubber or plastic gaskets(?) in addition to the card ones between the carbs and manifold on mine.

I also read about machining the needles. I think it may have been in the How to Improve The Triumph TR5, 250 TR6 book. It's out of print as far as I know but much of it can be read on line if you have the patience. I'll get a copy one day. I think the book said to put the needles in a drill chuck and lightly apply some abrasive. This won't work with the spring loaded needles in mine though.

I haven't yet checked if the needles are of the same height in each piston. This could certainly explain the behaviour (or lack of) of the front carb. Also, I couldn't see any markings on the needles. I must look again.

I have a colour tune and gave up on it many years ago. The colours on the packaging are very distinct but in use I found it much harder to distinguish rich from weak. I'm pretty sure the front carb is too rich though with permanently black plugs. The ignition seems ok. The car starts well cold (with choke) or hot. I've got a set of 'Spark Plug Analysers' - short HT leads with filaments built in. They seem to flash with the same intensity from one plug to another. Not very scientific - but there's nothing obviously wrong with the ignition.

As for timing, lubing the distributor shaft, checking vacuum advance - I've done none of these yet. I will check them at some point but if any are not correct I would expect them to affect all plugs not just the front three.

The butterfly / throttle discs are the plain type without the valves.

I'd still be grateful if anyone with HS6s and K&Ns could let me know what needles they are using. If your engine has a hotter cam or big port head I could aim for needles weaker than what you are using but richer than standard.

Thanks again for all the replies.

Best regards,

Chris

[Turbo TVR]

Hi Chris,

my RHD 2500 has HS6 and now with K&N-Filters ...

I do not know which needles are fixed, but it was difficult to set the right mixture ...

My car has electronic ignition, OD and Engine Number CF9934 UE with CR 8,5:1

It did not stop instantly, when I put the ignition off - only with fuelgrade of 98+ octane

The six candles looks all brown ...

Best wishes Axel

[Mr Tiger]

Hi Axel,
Did you but the maroon 2500 from Rien in the Netherlands by any chance?
Best regards,
Chris