Weber setup?

[Guest ntc]

Chrome / steel trumpets by Weber should always fit. I use alumin(i)um ones in 18mm height because the 16mm steel ones can't be had that I know of. They fit like the steel ones but their bells are slightly wider which pose a little challenge when fitting the K&Ns.

 

I notice for both of you there may be a violation of the distance-to-nearest obstruction principle: this is found in Passini's book and I don't precisely recall what it is, but somewhere around 1-1/2 x choke diameter or 1x throttle size ( 40mm ) to, in this case, the filter housing. I use 2-1/2" deep filters with 18mm trumpets and they just barely qualify. Shorter filters therefore suggest to me no trumpets, and for Stan's 2-1/2" trumpets a 4" deep filter is probably recommended on that basis.

 

Tom

You are giving the usual good advise a few other forum user's are getting a lot info foc, if you can get a 4" rigid filter in a tr 6 engine bay something is wrong.

Regard's

Neil

[foster461]

Tom

You are giving the usual good advise a few other forum user's are getting a lot info foc, if you can get a 4" rigid filter in a tr 6 engine bay something is wrong.

Regard's

Neil

 

I'm giving you wrong information.. The trumpets on my carbs are 40mm, just over 1.5 inches and the filters are just over 2.5 inches so I have a little over an inch of headroom between the end of the trumpet and the lid of the filter but still short of the 1.75 inches using the 1.5x30 rule. Perhaps I'll just leave the filters off and drive naked.

 

Stan

[marvmul]

I'm giving you wrong information.. The trumpets on my carbs are 40mm, just over 1.5 inches and the filters are just over 2.5 inches so I have a little over an inch of headroom between the end of the trumpet and the lid of the filter but still short of the 1.75 inches using the 1.5x30 rule. Perhaps I'll just leave the filters off and drive naked.

 

Stan

Aerodynamics can be weird : if trompets are fitted to Webers or other carburettors, most of the air entering the trumpets, is coming from the engine side and only a small part is coming from the filter lid side or the inner wing side. It is proven by engine dyno work that the filter lids, or a sheet of metal can be held amazingly close to the trumpets before engine power is dropping. On the other hand, if a sheet of metal is placed between the carburettor inlets and the trumpets, the distance from this sheet to the outer rims of the trumpets must be bigger. So, if you have filter houses of 3 inch deep, I suppose that the trumpets should be rather 2 inch long than only 1 inch long.

[Guest ntc]

Aerodynamics can be weird : if trompets are fitted to Webers or other carburettors, most of the air entering the trumpets, is coming from the engine side and only a small part is coming from the filter lid side or the inner wing side. It is proven by engine dyno work that the filter lids, or a sheet of metal can be held amazingly close to the trumpets before engine power is dropping. On the other hand, if a sheet of metal is placed between the carburettor inlets and the trumpets, the distance from this sheet to the outer rims of the trumpets must be bigger. So, if you have filter houses of 3 inch deep, I suppose that the trumpets should be rather 2 inch long than only 1 inch long.

Spot on

 

Regard's

Neil

[Quark]

Interesting that the change in manufacturing location would have changed the way the units were cast. Good to know though if the setup of the later carbs is different from the earlier versions.

 

Thanks too for the snippet from the Dave Andrews (?) article. I have the full paper somewhere in pdf format and a quick web search yielded this link http://hometown.aol.com/dvandrews/webers.htm . Very nice writeup for the Weber novice.

 

 

Stan

 

As an aforementioned Weber novice, I looked at Dave Andrews page http://hometown.aol.com/dvandrews/ and found a handy little executable file for selecting Weber settings that was designed for a twin Weber setup on a four cylinder engine. Am I correct to assume that my triple Weber settings on the 6 cylinder TR6 engine should be the same as for a 1666 cc four cylinder engine (= 2500cc/6x4)?

Edited July 1, 2008 by Quark

[Tom Fremont]

As an aforementioned Weber novice, I looked at Dave Andrews page http://hometown.aol.com/dvandrews/ and found a handy little executable file for selecting Weber settings that was designed for a twin Weber setup on a four cylinder engine. Am I correct to assume that my triple Weber settings on the 6 cylinder TR6 engine should be the same as for a 1666 cc four cylinder engine (= 2500cc/6x4)?

 

This seems logical but the Lotus 1600 set-up won't work on the TR, just to cite one example. Head characteristics and bore/stroke ratio play large roles. Best bet is to try to match your engine spec to another TR6 already properly calibrated with Webers and use its settings for starters. Then either get to a rolling road or launch your very own trial and error process to dial them in.

[foster461]

This seems logical but the Lotus 1600 set-up won't work on the TR, just to cite one example. Head characteristics and bore/stroke ratio play large roles. Best bet is to try to match your engine spec to another TR6 already properly calibrated with Webers and use its settings for starters. Then either get to a rolling road or launch your very own trial and error process to dial them in.

 

One of the problems with the dyno trial end error approach is that it seems the only way to do this is to spend several hundred dollars more on jets etc only to eliminate most of them when you get to a final configuration. How do we narrow down the options to make this less hit and miss and buy the minimal set of stuff ?. If we look at all of the variables, can we fix a few of them (eg 30mm chokes) and focus on the few that we know are highly variable ?

 

Stan

[Guest ntc]

One of the problems with the dyno trial end error approach is that it seems the only way to do this is to spend several hundred dollars more on jets etc only to eliminate most of them when you get to a final configuration. How do we narrow down the options to make this less hit and miss and buy the minimal set of stuff ?. If we look at all of the variables, can we fix a few of them (eg 30mm chokes) and focus on the few that we know are highly variable ?

 

Stan

 

Stan

I would follow Tom's advice in his previous post, re choke's 30mm every time. Before you go to a rolling road for final setting's check that the brake servo is in perfect order if not blank it off, this has setup prob's on No.5 cylinder,another tip

Regard's

Neil

[Tom Fremont]

One of the problems with the dyno trial end error approach is that it seems the only way to do this is to spend several hundred dollars more on jets etc only to eliminate most of them when you get to a final configuration. How do we narrow down the options to make this less hit and miss and buy the minimal set of stuff ?. If we look at all of the variables, can we fix a few of them (eg 30mm chokes) and focus on the few that we know are highly variable ?

 

Stan

 

Not even 30s! I couldn't use these without a gas-flowed head. I started with 28s, and with the stock carb set-up Pierce advises 26s. I'm doing fine with 30s on my driver and 32s on my show car but both have stage @#$%!!%* heads, extractor manifolds and plenty of cam and c/r.

 

Here's what I'd say are given: 4.5 auxilliary venturis, weak pump spring/ short pump rod, 175 float needle valves. The rest vary from engine to engine. So, we're back to making an informed choice going in, with the expectation that some of them will survive the calibration phase

 

As for rolling roads: I'd have thought those fabled creatures found only in the U.K. to be flush with all possible jets ( like I am, now ) and that they would charge only for what you drive off with, or maybe do an even exchange... After all, they're not wearing parts. Returns to vendors have been refused traditionally due to the proclivity of many tuners to " solder up " and re-drill or just drill larger, a practice I abhor personally.

 

If you can develop a good relationship with a reputable TR specialist they may well share some anecdotal combinations...

[Guest ntc]

I think this is going round in circles now.

 

Regard's

Neil

Edited July 3, 2008 by ntc

[foster461]

If you can develop a good relationship with a reputable TR specialist they may well share some anecdotal combinations...

 

I have a good relationship with all of the US vendors, I have probably put most of their kids throug colledge and funded their retirements by now :-)

[Tom Fremont]

I think this is going round in circles now.

 

Precious little is conveyed in the telling; even less the first time round...

[Guest ntc]

Precious little is conveyed in the telling; even less the first time round...

I'd have thought those fabled creatures found only in the U.K.

We only built it in the first place ?

[foster461]

One thing that I notice while trying to get my carbs set up is that there is a relationship between the idle mixture setting and the idle speed and it seems to vary by carb. As an example, with all of the idle mixture screws wound out 2.5 turns, the rear carb is pulling a lot more air than the front two even though the idle adjustment on the throttle on thar rear carb is fully backed off and the throttles are closed. It seems that if the idle mixture is set beyond a certain point it will be difficult to balance the carbs and achieve an acceptable idle speed as the idle speed is not just determined by the 3 idle speed adjustment screws but also by the 6 idle mixture screws.

 

I'm thinking that I need to back off the idle mixture so that I have more control via the throttle idle adjusters.

 

Stan

[Tom Fremont]

One thing that I notice while trying to get my carbs set up is that there is a relationship between the idle mixture setting and the idle speed and it seems to vary by carb. As an example, with all of the idle mixture screws wound out 2.5 turns, the rear carb is pulling a lot more air than the front two even though the idle adjustment on the throttle on thar rear carb is fully backed off and the throttles are closed. It seems that if the idle mixture is set beyond a certain point it will be difficult to balance the carbs and achieve an acceptable idle speed as the idle speed is not just determined by the 3 idle speed adjustment screws but also by the 6 idle mixture screws.

 

I'm thinking that I need to back off the idle mixture so that I have more control via the throttle idle adjusters.

 

Stan

 

I don't see how the mixture screws can affect the air flow; this I believe to be absolutely controlled by the throttle stop screws - at constant rpm.

 

If it helps, on my driver the throttles were set with a Uni-Syn ( and it was necessary to add an additional spring and throttle lever on the far side of one carb to effectively close one of its plates, as one closes before the other on each carb, and in this case the nearside one closed 1st ). All mixture screws are set equally, and the result is it can pull a 500 rpm idle. This was all done 14 years ago with a few checks since ( not for years now ) and it may be over the top given the Cannon's balance tubes.

 

My other car has the throttles set an equal amount open ( <1 turn ) with mixture screws set equally. It has a perfectly acceptable 900 rpm idle like this but with only 170 miles on the engine it's so stiff that a super low idle is not realistic.

 

I'm curious to know about the idle mixture screw on new vs. vintage DCOEs. Both of mine are set to 1 turn open or less but everyone today says 2-3 turns is right

[Guest ntc]

Quote: as one closes before the other on each carb,

 

Impossible they are both on the same spindle ?

 

Over to you Tom

Edited July 3, 2008 by ntc

[foster461]

I don't see how the mixture screws can affect the air flow; this I believe to be absolutely controlled by the throttle stop screws - at constant rpm.

 

If it helps, on my driver the throttles were set with a Uni-Syn ( and it was necessary to add an additional spring and throttle lever on the far side of one carb to effectively close one of its plates, as one closes before the other on each carb, and in this case the nearside one closed 1st ). All mixture screws are set equally, and the result is it can pull a 500 rpm idle. This was all done 14 years ago with a few checks since ( not for years now ) and it may be over the top given the Cannon's balance tubes.

 

My other car has the throttles set an equal amount open ( <1 turn ) with mixture screws set equally. It has a perfectly acceptable 900 rpm idle like this but with only 170 miles on the engine it's so stiff that a super low idle is not realistic.

 

I'm curious to know about the idle mixture screw on new vs. vintage DCOEs. Both of mine are set to 1 turn open or less but everyone today says 2-3 turns is right

 

 

 

I'll have another go this afternoon now that I understand things a little better. The idle mixture does affect idle speed but I agree, if the throttles are fully closed I should not be registering large airflow in the trumpets. One of the many docs I have collected suggests:

 

<snip>

Finally, set your idle mixture. Maximize RPM with the idle mixture screws, then reduce idle speed to 850-1000 (lowest smooth idle speed) with the idle speed adjustment screw.

 

Tweak the idle mixture screws again at this speed. Repeat until no further idle speed increase is observed.

 

Your idle adjustment screws should be 1-1/2 to 2-1/2 turns out from full lean. If they are far outside this range, your idle fuel jet is the wrong size. Increase jet size to reduce the number of turns, decrease jet size to increase the number of turns out from full lean (all the way clockwise).

</snip>

 

BTW if I set my idle mixture to 1.5 turns it is obviously too lean as we are popping and banging. I have to go to at least two full turns to stop that. Ignition is 10 degrees btdc at 1000 rpm idle. Engine pulls strong below and after 2000 rpm, I have a bit of hesitation at 2000rpm that I hope I can iron out with the idle mixture setting. I think Neil suggested earler that the best way to evaluate this is to drive for 30 mins and pull and examine the plugs and I think that is a good project for this afternoon before the next thunderstorm rolls in.

 

 

Stan

[Guest ntc]

Pm sent

 

Stan

Regards

Neil

[Tom Fremont]

Quote: as one closes before the other on each carb,

 

Impossible they are both on the same spindle ?

 

Over to you Tom

 

It's a very slight amount, but registers with an air flow meter, and can also be detected if a throttle lever is fitted to each side: one hits just before the other with the screws completely out. Even with Weber accuracy perfect concurrence closing a chamfered disc into a round hole at a slight angle may be asking too much. Anyway it shouldn't matter unless shooting for that low low idle purr

 

I haven't checked with new carbs as fitted on my latest installation. Unless I get unhappy with its idle behaviour ( I'm fussier than most ) I never will

[foster461]

So here is where I am currently with these carbs.

 

idle mixture set to 2.5 turns from closed

Idle speed screws fully out

engine idles at 1200rpm

 

Since the idle adjust screws are fully out there is no opportunity to reduce the idle speed other than by messing with the idle mixture. I do register air is being sucked in through the trumpets. I am unable to force the throttles to close further, eg pulling up on the levers does not make the engine slow down.

 

Car starts easily from cold with a short assist from the cold start levers although needs babysitting for a minute until it starts to warm up. Engine pulls nicely through most of the rpm range but has some hesitation at 2000 rpm. For example in 3rd gear at 2000 rpm, press the accelerator, engine growls for a second or two and then responds to the throttle request. No other oddities between 2000 and 4000, have not explored further.

 

When shut off, I often get a backfire in the exhaust and the engine has a slight tendency to run on (I do have the anti run on valve connected). The backfire in the exhaust is different from the backfire in the carbs which I have experienced when the mixture is too weak.

 

I have about 70 miles on this engine so far.

 

Stan

[foster461]

I added the 2.5 inch k&n filters today, they only just fit. The front one is a challenge to just assemble as it is so close to the wheel arch but it does go together. The rear one is easy to get on but is just a whisker from the footwell. I drove around this afternoon and it does not appear to be touching.

 

Pulled the plugs tonight. Rearmost plugs look good, front most plugs indicate a weak mixture so I teaked the front two carbs 1/4 turn on the idle mixture and also tightened up the front carb soft mounts as I seemed to be able move that carb more than the others.

 

 

Piccies here:

 

http://photobucket.com/REDTR6

 

 

Stan

[Tom Fremont]

Since the idle adjust screws are fully out there is no opportunity to reduce the idle speed other than by messing with the idle mixture. I do register air is being sucked in through the trumpets. I am unable to force the throttles to close further, eg pulling up on the levers does not make the engine slow down.

 

Engine pulls nicely through most of the rpm range but has some hesitation at 2000 rpm. For example in 3rd gear at 2000 rpm, press the accelerator, engine growls for a second or two and then responds to the throttle request.

 

Sounds like progress

 

For the fast idle I'd eliminate vacuum leaks as it's quite fast even if your outboard throttles are not closing ( a gentle nudge with a wrench on the outboard nut will determine that ).

 

2000-3000 rpm is the range I've struggled with; idle jets governing here according to Pierce and others. A step to either side ( I suspect upward ) would bring it to the surface, or you might lean out your pump jets ( never saw 50s recommended 'til yours - mine was happier with 40s than 45s, FWIW ).

 

I suspect you'll be starting your own collection soon - unless some friendly soul nearby will share his If you were near to me we'd get it sorted with mine

[foster461]

I suspect you'll be starting your own collection soon - unless some friendly soul nearby will share his If you were near to me we'd get it sorted with mine

 

You are only a couple of days drive from me :-)

 

I do have a fellow club member (Bob Lang) who has messed with Webers in the past and has accumulated some jets so I'll see what he has and order anything else from Mike Pierce.

 

I thought that perhaps the Cannon supplied throttle levers (the ones that attach to the carbs) might be poorly made and keeping the throttles open but I tested one and that is not the case.

 

I'll go on a vacuum leak hunt. I dont have that many connections, just the servo and the anti-run on valve (and I am running on quite badly at the moment but the high idle might be provoking that). The servo connection is new with a new rubber sleeve at the servo end but it still looks/feels feeble.

 

Thanks,

 

Stan

[Guest ntc]

Hi Stan

Try 50/55 idle jets, ignition timing 12deg if you have 10.5 cp and don't get any pinking. Don't forget the internal's of the servo

Regard's

Neil

[foster461]

Whohoo !. Engine now idling smoothly at 900 and holding it there with the adjusters. No longer running on.

 

The fix ?. It was a vacuum leak but not the servo connection. The softmounts were not tight enough !. I put a few more turns on the nuts and it had an immediate affect on the idle speed (went south) and after returning home from a test run the motor shut off like it should.

 

Neil, I currently have 55F9 idle jets. I dont recall if I published my full spec so here it is:

 

9.6:1 Compression ratio,

Stainless valves with three angle valve grind.

1.55:1 roller rockers

Shorter tubular pushrods

 

Block zero decked with fire rings re-cut

Over bored .0020

Spit cam bearings

Goodparts GP2 camshaft, http://www.goodparts.com/shop/index.php?categoryID=9

 

 

Goodparts tappets and springs

 

Crank ground .0010 under

Tri-metal mains and big ends

Hepolite pistons +.0020

New timing gear, chain and tensioner

Everything balanced individually and as a system from clutch to damper.

 

Still running the stock header with the stock twin pipe SS exhaust

 

Cannon manifold and linkage with 3xDCOE Webers configured as below:

 

Chokes: 30mm

Mains: 125

Air correctors: 180

Accelerator Pump: 50

Idle jet: 55F9

Emulsion tubes: F11

 

Idle micture screws out 2.5 turns

 

The above initial carb settings were derived via a phone call with Mike Pierce at Pierce manifolds

 

The goal was a quick but driveable street car and I realise that the 3xdcoe's are overkill for this application but the bling factor is high.

 

The only outstanding problem I have remaining is that slight hesitation and growling at 2000 rpm. Once I get through that it is as smooth as silk as far as I have been willing to push it at this time. Just over 100 miles on the odo.

 

 

Really appreciate all of the excellent advice.

 

Stan