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good day all. 

I have recently reinstalled my fully refurbished triple webbers to my TR6. One thing that's very pronounce, which I dont recall in the past, is all the popping and banging when I let off the throttle. Its a lot, not just the odd pop. It sounds fantastic. Like I'm driving a race car, but at the same time I would like to know the reason. I am thinkung this is a timing issue. If it is, does this mean I ha e a problem and i need to advance or retard. The engine is not pinking. 

 

Thanks

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Leakage in the exhaust manifold close to the cylinder head?

I had these symptoms on my TR4 when the original (1962) SAH exhaust manifold started to fall apart at its brazed joints in 2005.  As the manifold was too knackered to be repaired once again, I replaced it with a copy of the original by Triumphtune/Falcon - but with welded joints!

Ian Cornish

Ian Cornish

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I haven’t experienced with 6-pot, however with a weber-equipped Spitfire I used to own this was simply down to richness on the overrun, as you say, it does sound great - never a problem for me.

...... Andy

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36 minutes ago, AndyR100 said:

I haven’t experienced with 6-pot, however with a weber-equipped Spitfire I used to own this was simply down to richness on the overrun, as you say, it does sound great - never a problem for me.

...... Andy

I know of a Spitfire 1500 which does that too, and it has a single DCOE carb which cannot deliver equally to the (4) cylinders due to uneven induction within each pair, rendering half of the cylinders either lean or rich. Others on the TRIUMPH EXPERIENCE forum had roundly dissed that arrangement. I too am sceptical of their application on anything but individual runner setups. 

A similar criticism is leveled at triple S.U. or Stromberg setups on inline 6 cylinder engines, pairing cylinders with different angular spacing. Not long ago I saw the claim that Jaguar used a different needle in the centre carb to compensate. AH only went with triples for a few months I believe, and Jaguar eventually went to (2).

 

Tom

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52 minutes ago, Tom Fremont said:

 

A similar criticism is leveled at triple S.U. or Stromberg setups on inline 6 cylinder engines, pairing cylinders with different angular spacing. Not long ago I saw the claim that Jaguar used a different needle in the centre carb to compensate. AH only went with triples for a few months I believe, and Jaguar eventually went to (2).

 

Tom

All XK150s, E type (early models to about 67 in US) all UK market and all MK10 Jaguars had the same needles across the triple SU setup they only went to two carbs on E types with the change to Stromberg for emission control. AH used triple SU on MK11 Healey from 61 to 64 and went back to two with the first of the MK111 as the US market emission controls started to come in and they stopped production in 67 anyway.

Stuart.

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I think tomorrow ill go through everything once more. Ballance, mixture and timing. These carbs are so tuneable I dont think ill ever get them 100%. 

So I'll do the nessesary in the drive, take it for a longish high rev drive. Pull over and take the plugs out to check the colour and adjust accordingly.

Without a rolling road and carb specialist, which is not available here in Croatia, its the best I can do. Maybe next year if I go back to work I will fund a place near Ancona in Italy that can do the business on the set up. 

 

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Just now, murrayarnold said:

I think tomorrow ill go through everything once more. Ballance, mixture and timing. These carbs are so tuneable I dont think ill ever get them 100%. 

So I'll do the nessesary in the drive, take it for a longish high rev drive. Pull over and take the plugs out to check the colour and adjust accordingly.

Without a rolling road and carb specialist, which is not available here in Croatia, its the best I can do. Maybe next year if I go back to work I will fund a place near Ancona in Italy that can do the business on the set up. 

 

You could always buy yourself a wideband sensor kit and then you have your own rolling road.https://www.ebay.co.uk/itm/UEGO-Air-Fuel-Ratio-AFR-Controller-Wideband-KIT-Bosch-LSU-4-9-Probe-With-Gauge/123931924568?hash=item1cdaeb1858:g:kvIAAOSwljFdudEy

Stuart.

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2 hours ago, Tom Fremont said:

I know of a Spitfire 1500 which does that too, and it has a single DCOE carb which cannot deliver equally to the (4) cylinders due to uneven induction within each pair, rendering half of the cylinders either lean or rich. Others on the TRIUMPH EXPERIENCE forum had roundly dissed that arrangement. I too am sceptical of their application on anything but individual runner setups. A

 

I ran a pair of 40’s so one throat per cylinder, to be honest I wouldn’t bother with a single 40/45, i’d stick with a pair of SU’s instead. I wasn’t bothered about the popping on the overrun, small price to pay for having the right fuel mix available on acceleration :) .

on the SU side, later models had a poppet valve in the butterfly to lean things off on the overrun which would help.... from memory,  I don’t think there was a similar option on DCOE’s

....... Andy 

 

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1 hour ago, murrayarnold said:

I think tomorrow ill go through everything once more. Ballance, mixture and timing. These carbs are so tuneable I dont think ill ever get them 100%. 

So I'll do the nessesary in the drive, take it for a longish high rev drive. Pull over and take the plugs out to check the colour and adjust accordingly.

Without a rolling road and carb specialist, which is not available here in Croatia, its the best I can do. Maybe next year if I go back to work I will fund a place near Ancona in Italy that can do the business on the set up. 

 

What idle jet are you using?

 

Tom

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2 hours ago, stuart said:

 AH used triple SU on MK11 Healey from 61 to 64

I could find no reference online to the triple S.U. fitment other than 1962 model year. The number of 355 recurs as a production total. There were a few notations about " the difficulty of keeping them tuned ".

As for the Jaguar, I thought it were to their credit to adjust for the induction anomalies via a different needle, but I've only ever seen one such claim ( and I think it may have been here ^_^ ).

 

Tom

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Hi

in my experience with Weber’s, it’s normally a fairly small air leak when the exhaust heats up and the joints open up. The favourite is the bottom manifold joint just behind the starter motor. There isn’t much you can do about it, but try a flexible joint with a long pipe overlap ie 50mm or more each side of the flexi. Stainless systems seem to be particularly prone.

if you had timing or mixture issues, you’d have a few more things happening like jets of flame out the pipe on a hot over run, grumpy running at idle, Smokey tailpipe etc. - again just my personal experience.

regards

Tony

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I had a Mk1 Lotus Cortina many years ago back in the ‘70’s and had a similar problem where the air would leak in past the rubber ‘O’ rings on the inlet manifold.

The twin 40’s were mounted using thackery washers. I removed the carbs, fitted new ‘O’ rings into the manifold and re-seated them. I tightened the washers more than I had done and it cured the popping. I’m not sure if yours uses either the washers or ‘O’ rings.

As Andy says they can be a pain in the butt and might be best to use a twin SU set-up. 

Kevin

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I followed a "sporty" TR4 on last years 10 countries run and it popped and banged loads on over run. I was a bit annoying but at night the flames in his exhaust really helped us follow him. Brighter than his tail lights!

 

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1 hour ago, Tim D. said:

I followed a "sporty" TR4 on last years 10 countries run and it popped and banged loads on over run. I was a bit annoying but at night the flames in his exhaust really helped us follow him. Brighter than his tail lights!

 

Our group leaders old TR2 on twin 45`s does just the same!

Stuart.

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13 hours ago, Tom Fremont said:

What idle jet are you using?

 

Tom

+1. The Weber 45s on my 3A used to do this and it would run on too. Took it to Tom Airey. He listened for 5 minutes. Opened the bonnet removed the idle jets and replaced with different ones. Instant improvement. He said the change was needed to address the use of ethanol in fuel. Another hour and a half fettling on the rolling road, etc., and it was like a different car. 

Miles

Edited by MilesA
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25 minutes ago, MilesA said:

+1. The Weber 45s on my 3A used to do this and it would run on too. Took it to Tom Airey. He listened for 5 minutes. Opened the bonnet removed the idle jets and replaced with different ones. Instant improvement. He said the change was needed to address the use of ethanol in fuel. Another hour and a half fettling on the rolling road, etc., and it was like a different car. 

Miles

smaller idle jets or bigger? 

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22 minutes ago, murrayarnold said:

smaller idle jets or bigger? 

You need some light reading to help Weber book

Stuart.

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5 hours ago, MilesA said:

+1. The Weber 45s on my 3A used to do this and it would run on too. Took it to Tom Airey. He listened for 5 minutes. Opened the bonnet removed the idle jets and replaced with different ones. Instant improvement. He said the change was needed to address the use of ethanol in fuel. Another hour and a half fettling on the rolling road, etc., and it was like a different car. 

Miles

I have looked at my idle jets. They are f9 x 45. I found another set in the hut, f8 x 50. So I will install these, redo the air/fuel mixture and see whats what's. I will check the ballance and tickle the timing and do some trial and error on the system. 

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51 minutes ago, murrayarnold said:

I have looked at my idle jets. They are f9 x 45. I found another set in the hut, f8 x 50. So I will install these, redo the air/fuel mixture and see whats what's. I will check the ballance and tickle the timing and do some trial and error on the system. 

Both of these are lean for the TR6 engine with CP cam or beyond, and very close to each other in that sense. Worth a try as it is so easy, but a 50F9 or 55F8 would be my suggestion.

The early 40DCOEs ( without the wings on the lids ) idle mixture screws should be ~ 3/4 turn open, and the later ones ( 151 ) ~ 2 turns open. More than this indicates a lean jet and vice-versa. These are mid-point values and small deviations are acceptable.

 

Tom

Edited by Tom Fremont
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53 minutes ago, Tom Fremont said:

Both of these are lean for the TR6 engine with CP cam or beyond, and very close to each other in that sense. Worth a try as it is so easy, but a 50F9 or 55F8 would be my suggestion.

The early 40DCOEs ( without the wings on the lids ) idle mixture screws should be ~ 3/4 turn open, and the later ones ( 151 ) ~ 2 turns open. More than this indicates a lean jet and vice-versa. These are mid-point values and small deviations are acceptable.

 

Tom

So maybe 3 and a half from seated you think should be good starting point. Well i have a colour tune and also the old school hoss and pop with the garden hose used to work well for me. As you said though, all the air/fuel mixture screw does is control the idle system flow. The mix is regulated by the idle jet. Its a science for sure. I will get it as close as I can. 

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5 minutes ago, murrayarnold said:

So maybe 3 and a half from seated you think should be good starting point. Well i have a colour tune and also the old school hoss and pop with the garden hose used to work well for me. As you said though, all the air/fuel mixture screw does is control the idle system flow. The mix is regulated by the idle jet. Its a science for sure. I will get it as close as I can. 

To clarify, the # of turns I posted above are from the seated/closed position. This refers to the idle mixture screw and not the throttle stop screw. Also, if you have the -151 carbs with the throttle bypass screws I would start with them all closed, and open them as necessary to perfectly synchronize them at idle, once the jetting proves satisfactory. 

Any idle jet can be made to work...at idle. All you have to do is keep opening or closing the mixture screw until it works. Off idle is another story.

 

Tom

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If you are really interested in weber there is a guy on the net called Keith Francks who did loads on getting them to work properly. Really really complex stuff. 

 

Edited by Tim D.
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