New SUs running very rich

[Peter Douglas Winn]

Has anybody had the following or can give me a clue as to what is happeneing?

My USA 6 has had a small conversion made, to up the power output from 100 HP to 125 HP.

 

2 SUs, PI Head, Spitfire exhaust, PI cam, Bored out to + 60 Thou., Vacuum on the distributor blocked off.

 

It drives OK but the petrol consumption is too high. Matching up with the high CO values. The Garage have set the sytem up for low CO values a couple of times. After a 600 miles the values are back up again. Any ideas.

 

I trust the garage as they have years and years of TR experience and even in the racing scene. They have too much to loose. The engine has now about 4,000 miles on the clock.

[BlueTR3A-5EKT]

Did the supplier of the SU carbs also give the correct needles, jets and springs?

 

Do you have thermostatic or 'Waxstat' controls on the jets? They are known to give problems.

The Waxstat system is designed to lean (lower CO) the mixture when the temp under the bonnet rises ie when idling in traffic. Usually causes lumpy tickover and rich mixture when running.

 

Best solution is to convert away to non thermo controlled jets.

Moss used to do a kit to convert. Part No TT1559

http://www.moss-europe.co.uk/jet-conversion-kit-hs6-tt1559.html

 

Peter W

 

PS

What type of jets do you have?

I know this is a Spitfire image. So the part nos are wrong.

see image http://www.moss-europe.co.uk/shop-by-model/triumph/spitfire/fuel-system-induction-controls/carburettors-manifolds/hs4-su-carburettors.html

Item 27 is NON thermo control jet

Item 28 is Thermo control jet. (also known as Waxstat)

 

PPS You can make your jets 'Non Waxstat' by removing the 'Waxstat' pellet at the base of the jet and gluing in a suitable sized coin.

[peejay4A]

With carbs you probably want the vacuum advance connected to help running at cruise, and therefore economy. Prof Cobbold will be along shortly...

[Peter Douglas Winn]

That is very intersting. Reading the Moss info it seems that when they go wrong the mixture gets weaker not richer. Or have I read it incorrecty?. I know nothing about SUs I was always a Stromberg man and could do everything with the Strombergs.

As it is a really professional garage I must assume they checked the contents for the SUs. Needle typ BCE. Ignition idle 12° advavnce 3000 rpm 30°

[Peter Douglas Winn]

I asked about the vacuum and they told me with this PI set-up there is no vacuum advance or at least it made no sence..

[Peter Douglas Winn]

I amnot sure about the jets I must go and have a look. The car is parked a long way away. Looking at the spitty parts I think the are the so called standard.

[Guest ntc]

A PI dizzy does not need vacuum , a none Pi does.DD can set the one you have.

Edited August 3, 2017 by ntc

[Peter Cobbold]

HS6 carbs? 1 3/4 inch.

 

 

With carbs you probably want the vacuum advance connected to help running at cruise, and therefore economy. Prof Cobbold will be along shortly...

Yes ....but that USA disy has only vac retard capsule so its best left disconnected.

Even without vac advance the engine with its 9.5:1 head should get closer to PI consumption.

 

The CO sounds badly rich. If the BCE needle is OK for that application ( someone will know) then I'd check the fuel level in the jet and ensure it is a few mm down the jet. Or is the fuel pressure too high and overloading the float chamber valve. Fit a pressure regulator and set it to 2 to 3psi.

 

Peter

[TR NIALL]

Engine 2.5 CP

Carbs HS6s from Dolly Sprint,Waxstats Removed and Coins put in place,BDM Needles with Yellow Springs,Dolly Sprint KNs with short RamPipes inside,Vac Adv connected as seen in Photo and all mounted on a 2.5s Manifold,goes like **** off a Shovel and ain't to bad of Fuel.

GT6 Dizzy with Vac Adv.

 

Edited October 26, 2019 by TR NIALL

[Peter Cobbold]

I asked about the vacuum and they told me with this PI set-up there is no vacuum advance or at least it made no sence..

Yes that's right, but you should get fuel consumption similar to PI.

 

However with the SUs at a later date you can improve economy by leaning the cruise mixture and fitting a disy with a vac adv capsule to give say 40-45 btdc at cruise.

 

Peter

[Peter Cobbold]

Engine 2.5 CP

Carbs HS6s from Dolly Sprint,Waxstats Removed and Coins put in place,BDM Needles with Yellow Springs,Dolly Sprint KNs with short RamPipes inside,Vac Adv connected as seen in Photo and all mounted on a 2.5s Manifold,goes like Shit off a Shovel and ain't to bad of Fuel.

Tks Niall, bookmarked ! Peter

[Guest ntc]

Simple as that,

[Peter Douglas Winn]

So where am I now? What can I say to the garage without insulting them.

[DRD]

That is very intersting. Reading the Moss info it seems that when they go wrong the mixture gets weaker not richer. Or have I read it incorrecty?. I know nothing about SUs I was always a Stromberg man and could do everything with the Strombergs.

As it is a really professional garage I must assume they checked the contents for the SUs. Needle typ BCE. Ignition idle 12° advavnce 3000 rpm 30°

I've got a similar spec engine and am running BAG needles. It's set to about 5% CO at idle and runs nicely.

[Peter Cobbold]

Find another garage that understands how to tune SUs and has the kit to do it.

Setting the tickover mixture at the jet is useless if the needle is wrong.

 

Cant you fit Niall's needles and springs yourself?

Peter

[dingle]

All of the needles are pretty much the same at the first station, so a change of needles shouldn't make much difference at idle. A good place to start is to make sure that the jet is full up when the choke knob is pushed in. Also, with the piston&dome removed, check the fuel level in the jet. It should be 1/8"-1/4" below the top. Some folks have had to fit shorter float chambers (AUD 2140) in order to lower the fuel level enough to prevent flooding.

Berry

[Alec Pringle]

If SUs could have been made to work sensibly with a PI cam . . . . . Triumph wouldn't have gone to the bother of fitting Lucas PI.

 

The more sensible answer might have been to utilise, for example, 2500S component as a known quantity . . . . . rather than trying to knock the corners off octagonal wheels.

 

I'm not sure why you're worrying about insulting the garage - if they knew what they were about then they wouldn't have wasted their time and yours with trying to adapt SUs to a PI head/cam/dissie . . . . . .

 

Find someone who knows what they're doing and start again.

 

Cheers,

 

Alec

[Ragtag]

I asked about the vacuum and they told me with this PI set-up there is no vacuum advance or at least it made no sense..

 

You haven't got a PI set up, you have SUs. This should tell you all you need to know about the garage you are using.

[Ragtag]

If SUs could have been made to work sensibly with a PI cam . . . . . Triumph wouldn't have gone to the bother of fitting Lucas PI.

 

 

I don't have the technical knowledge to understand why SUs wouldn't work with a CP cam, it isn't that wild but I was always under the impression that Triumph went with PI on the 5 and 6 as a marketing gimmick primarily, not for want of carburation options.

[Peter Douglas Winn]

The garage say they set the carbs up for 2% CO at idle and 3% at 3000 rpm. I have no reason to doubt. They even bought new measuring equipment after I complained. They said they were not 100% sure about the old equipment. They measure through 2 holes front and back in the exhaust manifold. I now have after 600 miles 9.3% CO at idle and 12.6% CO at 3000 rpm. One problem I have is, the garage is the other end of the country, but that's a long story.

I had with my strombergs with normal driving a fuel consumption over 28 mpg and now 20 mpg. The biggest problem will be the MOT next year.This is a standard sort of conversion they have been doing for years. That's why I don't undertsand what is going wrong or changing.

Edited August 4, 2017 by Peter Douglas Winn

[Peter Douglas Winn]

Compression 9 to 1. So as you say it is not a PI set but something in between. The increased consumtion matches the CO values. I have used 97 petrol and 101 Octan. If something is loading the engine during driving, like the brakes then when the car stops the values should go back to normal but they don't. Before I go back to the garage and complain again I am trying to find a Plausable answer. Like with a PI when the engine is new, the vacuum values will change a little, after putting miles on the clock and therefore a small change in the consumption. In my case the change is massive.

Edited August 4, 2017 by Peter Douglas Winn

[harlequin]

Peter

My car has the same set up as yours appart from the needles, as others have said BDM or BAG are what are normally used.

You can see the differences between needles using the Mintylamb tool http://www.mintylamb.co.uk/suneedle/. For what they cost its worth getting a pair of BDMs and yellow springs and give them a try

 

George

[PaulAA]

Engine 2.5 CP

Carbs HS6s from Dolly Sprint,Waxstats Removed and Coins put in place,BDM Needles with Yellow Springs,Dolly Sprint KNs with short RamPipes inside,Vac Adv connected as seen in Photo and all mounted on a 2.5s Manifold,goes like Shit off a Shovel and ain't to bad of Fuel.

GT6 Dizzy with Vac Adv.

 

Niall

 

At the risk of drifting off topic, what benefit does the 2.5S manifold give over the std TR6? Is there more of a difference than just the carb mounting angle?

 

Paul

[DRD]

Peter

My car has the same set up as yours appart from the needles, as others have said BDM or BAG are what are normally used.

You can see the differences between needles using the Mintylamb tool http://www.mintylamb.co.uk/suneedle/. For what they cost its worth getting a pair of BDMs and yellow springs and give them a try

 

George

BDE look far too rich right across the range, so as Peter has already said at anything other than idle it will be too rich.

[Peter Cobbold]

@ Pual,

The saloon engines were canted over to the the exhaust side, so I guess the saloon manifold on a 6 will slope down steeper to the head..

?

Peter

Edited August 4, 2017 by Peter Cobbold