Another Stromberg Carburettor 175 CD2 Question

[71 V12]

It looks like we are overwhelmed with Stromberg queries today!

Like a few others on the forum I have been taking advantage of the dry salt free roads and really loving being able to user the TR6 this time of year although a tad chilly even with a woolly hat on.

However, I have noticed the car does not run as well in cold ambient temps as it does in the summer. Slight misfire on acceleration even when warm. It has always run out of steam at around 4000RPM, even in summer. I have always put this down to the twin Stombies just not being able to provide enough fuel for such a large engine.

The car is 1974 California spec car actually first registered at Hollywood Sports Cars. I junked all of the ERG Valve, Carbon Canister and related stuff, replaced the head for 219016 UK head. Dizzy is a 41168 with vacuum advance.  Other than those changes as per original spec. Other than the slight misfire under load she runs like Swiss watch - really smooth even idle, torquey and responsive.

I am wondering whether there may be a Needle Jet profile that is better suited to cooler climes and the higher compression head? If anyone has a similar spec engine I would be grateful to hear about your experiences.

Happy New Year to all on this tremendous forum.

Kevin

 

 

[JochemsTR]

Kevin, there is no certain profile for certain climates.

I made my own needles and took an AFR Gauge to have a good balance. This worked in the French Alps and also on land. 

What is your spark timing, can you do AFR measurements? What cam and CR do you have?

Jochem

[harlequin]

Kevin

I suspect that your distributor advance module is moving at the wrong time, and messing with your timing

I dont know the details of why but I believe that the vacuum line for advance modules must come from above the butterfly, from your photos it appears that yours comes from the underside, which is the arrangement for vacume retard.

Try disconnecting and plugging the line to see if things improve,  you dont actually need the vacuum advance, PI cars have the module but it was never connected.

Geerge

[harlequin]

Kevin

Please disregard my previous post 

I have just seen that your line does go to the top of your carb

 

George 

[DaveR]

The head is from a 2.5S Big Saloon. The dizzy is from a Vitesse 2 Litre (Mk1). The standard CR for the S head is 8.5:1. It's the best breathing head and in may cases the head is skimmed to raise the CR.

 It is doubtful with this set-up there is over advance unless the springs in the dizzy or vacuum unit are at fault. The max advance on the weights is 18 deg on the crank, not counting the vacuum unit which should only work on light throttle setting but may be faulty. You either have a fault, ignition or weak needles are causing the problems. The first thing to do is check the dizzy springs and disconnect the vacuum unit, and then the ignition components. After that look at the needles. You could look at the needle charts and select richer needles. But as its not a standard set-up then setting up on a rolling road may be the way forward.

Dave

Edited January 3, 2019 by DaveR

[71 V12]

Hi Dave,

Thank you for your reply. I have checked the ignition components and they are functioning correctly.

It was a long shot to hope that someone had been through a similar setup and found Stromberg XXX needles gave good results. I am sure a richer running needle is required given the better gas flow through the head. Incidentally the cam is the standard CR spec cam of the period.

Anyone out there swapped Stromberg needles and obtained good results that can advise?

Regards,

Kevin

[JochemsTR]

Kevin, I addressed this is my post. You need to measure AFR, only then you know where a modification in the needle is required.

Jochem

[71 V12]

Hi Jochen,

It sounds like your technical skills are way more advanced than mine. I had to google AFR to know what it is!

But even now knowing what AFR is now I really don’t have the technical knowledge to understand the gauge readings even if I had a AFR gauge or fit Lambda sensors, never mind modify metering needles. So unfortunately it is not viable option for me.

Given how many imported US spec cars are in the UK and Europe now I was hoping someone had done the work and identified which needle spec would give good results?

I am sure someone on the forum must have had similar issues and improved performance by changing the needles.

Kind regards,

Kevin

[JochemsTR]

Hello Kevin,

unfortunately, there is no such thing as having similar issues, and by changing a needle it is all done. For us to help you, try to answer this

a) are the carburators overhauled if no, are they in good condition such as swimmer heigth, diaphragms, bypass and temperature compensation still ok ?

b) which needles do you currently have? The markings are on the needles. Open up the top cover, pull out the damper und needle. Should be like B1AF.

c) what ignition curve do you have? run the engine at 900 - 1000 - 1500 - 2000 - 2500 etc and have someone note the spark timing

d) can you go to a garage and have AFR checked?

Just as a side note, each engine behaves differently. I spent lots of time adjusting springs and needles in my carbs. The effort was however, worth it.

If you cannot or do not want to hassle with this, find yourself professional help.

Jochem

 

[Tom Fremont]

Hi Kevin,

You can get there without an AFR meter; seat of the pants will do.

These are fixed jet carburetors, and some have adjustable needle height ( have you played with this feature, assuming it's present? ). Make sure your floats are at the correct level, 5/8" if I recall correctly ( see Uncle Bentley for details ).

Some have retrofitted adjustable jet height bits from earlier Strombergs.

...Then there are other needles. I defer to others on this point but specialists in the 'States can point them out ( look this up on the 6-Pack forum www.6-pack.org ). I believe the camshaft dictates this, mainly - which one are you using?

Stromberg lovers will vigorously defend the twin setup as adequate for any TR6 application. Apparently TRIUMPH didn't buy that notion, fitting (6) throttles to their RoW offering. I'm with the latter camp, having found TR5/250/6 nirvana with triple DCOEs 22 years and 130,000 miles ago; I'll never go back! For the stock emissions controlled engines I think TRIUMPH made the right choice however.

I doubt the distributor is a factor here, and don't find the specific one in your photo in the TR5/520/6 original lineup. Anyway, the max advance is stamped into the weights.

 

Cheers,

Tom

 

 

[71 V12]

Hi Jochen and Tom,

Your experience and replies are greatefully received. To summarise the engine spec is as follows:

- 1974 US/ California CF engine. The EGR valve and all related components were removed. Vented fuel cap fitted.

- Full CF series engine rebuild approx 2000 miles ago to OE spec but +20thou cylinder bore and new pistons. Head replaced with a 219016 part from a Triumph 2500S for slightly increased compression at 8.5:1 and better breathing as Dave mentions in the post above.

- OE cam for a 1974 CF car which I believe is the same as a CR series PI cam.

- Vacuum advance dizzy with max 18 degrees advance at the crank as again mentioned by Dave. Timing set to 10 degrees BTDC static. Dynamic timing checked via strobe for idle and advance and all good.

- The Stomberg carbs were given a full comprehensive overhaul at the same time as the engine and give no trouble at all. I am not sure what needles are currently fitted but they will be as per OE spec for a 74 California car. I have tried to research what needles would have been fitted to Strombergs for California in 74 but so far not been able to find this. I will try the 6-Pack site as Tom suggests.

The engine runs really well, smooth idle good throttle response, nice torque however minor misfire when under load until throughly warmed up, which in the current cold weather I can not get. In summer the misfire disappears after 3-4 miles of running. The misfire can be eliminated by applying some choke.

When warm fully warmed the engine will run out of power at about 4000 RPM.

It really indicates to me that not enough fuel is getting to the engine.

Any thoughts?

Kind regards,

Kevin

[harlequin]

Kevin

Have you checked that the pump is delivering enough fuel ?  maybe a partially clogged filter

When you removed the Carbon Canister what did you do with the tank vent line?

If you have one of those glass inline filters throw it away as they can be rather restrictive 

My 6 has a similar set up to yours although I still have the carbon canister, I have disabled the temperature compensators and bypass which made things a bit simpler I also have a Facet electronic pump.

My carbs are new old stock CD175s that were ment for a Stag so I ran the car with the Stag needles for a while which was okish I have since replaced the needles with the standard TR6 needles and the car runs better and revs freely past 4k rpm. I spent a lot of time on the interweb looking for needle recommendations without success so will follow this thread with interest 

George

[71 V12]

Hi George,

Interesting feedback from you, I thought I might not be alone on this topic!

I junked the canister and pipe work and fitted a vented cap. The pump is a standard NOS AC pump, I have no way of measuring the fuel flow however when I have cranked the motor with the feed pipe to the carb disconnected plenty of fuel is coming through.

No glass filter but I did fit a clear plastic disposable item which did have some deposits when I replaced it about 1000 miles ago. I will check it again and I think I will check the filters on the needle valves as well.

Do you know the Stromberg reference number of the TR6 spec needles you fitted or where you found the spec?

Kind regards,

Kevin

[harlequin]

Kevin

B1AF is the standard needle 

I found this helpful when working on Strombergs http://www.buckeyetriumphs.org/technical/Carbs/CarbsI/CarbsI.htm 

I also have an xl spreadsheet for Stromberg needlesbut cannot attach it, I will PM you my email address  and if you want the spreadsheet send me an email.

George

[John L]

Kevin

Can you give us any reference numbers or tags on your carbs, usually attached to one of the 4 diaphragm screws, and also the code of your current needle jets, also the colour of the large spring in the dashpot.

  From this we should be able to advise a better needle if we know where we are starting from.

John 

[71 V12]

Hi John,

The carb ID tags are no longer present but I will get the needle and spring out over the weekend and report back.

Kind regards,

Kevin

[DaveR]

Kevin, If you have the 125 BHP cam, 311399, then this will run fine on carbs. It was also fitted to the late GT6 Mk3.

Dave

[71 V12]

Thanks Dave. I think the overall spec of components (cam, dizzy, head) is correct. I need to check again it’s all functioning correctly and what spring and needle is in the carbs.

George has advised the B1AF needle is good, so that’s the next check to see what I have got in my carbs.

Regards,

Kevin

[71 V12]

Well, I had a good look at the linkages and as George suggested they are incorrectly adjusted!

Managed to get a much better throttle opening by repositioning the arm on the pedal shaft and shortening the linkage rod on its adjustment threads.

Quite a difference in performance to say the least. The engines powers through to 5000 RPM with ease, general throttle response much improved. I still have a misfire until the engine thoroughly warmed up and on checking the fuel filter red deposits can be seen so I suspect rust in the tank.

Next job is to remove the tank and have it chemically stripped by an industrial cleaning company locally to remove all rust. I have done this previously on old motorcycle tanks and it is very effective. Once this is done I will clean the carb filters and fuel pump. I will check the needle type as part of this job.

I will also replace the O rings on the mixture adjustment again, needs topping up too frequently again.

I guess these O rings are standard Viton O rings. They are priced at about £2.00 each plus postage from the specialist suppliers. I can buy 10 for £2 if I knew the inside diameter, the outside diameter and the O ring thickness. Does anyone have the spec of these O rings?

Thanks again for all of the great advice, it really helps!

Regards,

Kevin

[dingle]

Kevin-The O ring for the carb piston rod is -010 (.070" csx.239"idx.37" od) The material can be viton or buna-n which is commonly available from most hardware stores. Leaks can occur even after replacing the O ring. This is caused by the little star shaped retainer for adjuster which has to be removed to replace the Oring. it scores the bore and leaves a path for a leak. The remedy is to polish the bore with emery cloth on a stick.

Also, the O ring on the float bowl plug is -114, available locally and can require replacement to fix a leak in that area.

Berry

[71 V12]

Hi Berry,

That’s really helpful. Do you think this is close enough?

https://www.ebay.co.uk/itm/Imperial-O-Rings-Nitrile-Rubber-to-BS1806-70A-Shore-NBR-O-ring-seals-Packets/113109265829?ssPageName=STRK%3AMEBIDX%3AIT&var=413430738978&_trksid=p2060353.m1438.l2649

Kind Regards,

Kevin

[dingle]

Kevin-It looks like the same #010. I just prefer to buy o rings locally, usually available individually, and no waiting.

Berry

[unclepete]

Hi Kevin

Been reading this thread with interest. I have a 1970 US TR6 which came to me with a set of TR4 Strombergs fitted to a short inlet manifold.

All ran fine but I was not happy with the set up, especially the throttle linkages and the Inlet manifold.

I managed to track down the later inlet manifold (same as yours) which has a much more even, smoother gas flow to the head, just looking at it made sense.

I also managed to find a set of almost mint Zenith CD175's from a mid 80s Range Rover, which the owner had swapped out for a downdraft Holley, after 18 months of ownership and had sat in a plastic bag on a shelf for 30 years!

These later Zeniths have a cable operated choke on one carb with a balance pipe to the other one. They also have a shorter piston with bias adjustable needles, which I changed to B1AF from Burlen, after stripping, cleaning and checking both carbs.

I also sourced, fettled and fitted a much neater and smoother throttle linkage (part TR6 CF, part my own)

I capped off the breather connections on the Carb bodies. Pulled out the choke and turned her over, Well! you could have knocked me down with a feather, she started first time!! Revs were a little high, carbs unbalanced and mixture a bit rich, but good enough to get her up to temperature. The carbs were balanced, linkage adjusted and the mixture set with the Stromberg tool (allen key type - yes, there are 2 types of adjusting tool!). I then bit the bullet and took her out for an enthusiastic test run. Ran Noticeably smoother and revved freely, so I am very pleased.

Now comes the fun part! I fitted a flame trap to the crankcase breather, removed the Carb breather caps and connected, via a T piece, the crankcase breather outlet. She will not even try and start! even being up to temperature? Putting the caps back on the carbs and venting the Crankcase breather to atmosphere she then starts and runs without problem?

Any ideas anybody?

[astontr6]

On ‎1‎/‎3‎/‎2019 at 5:57 AM, JochemsTR said:

Kevin, there is no certain profile for certain climates.

I made my own needles and took an AFR Gauge to have a good balance. This worked in the French Alps and also on land. 

What is your spark timing, can you do AFR measurements? What cam and CR do you have?

Jochem

You can use SU carb needles in Stromberg Snog carbs but you have to make up 2 small bushings and it needs some very accurate turning. These are best made out of brass using 0.250" material drill a 0.125" hole up the middle, this best done on a lathe. Carefully cut out a wedge shape portion out,1/3 of the diameter of the bush and cut the length of the bush. Trial fit to dash pot and deburr where required. having fitted the bush and needle into the dash pot, make sure that the cut out is facing the set screw. Mount the steel bearing shaft in a lathe chuck to check that the needle is properly centred, rotate at slow speed.

Bruce. 

[foster461]

If those carbs have temperature compensators have you checked that they are both working and operating to the same degree ?

Stan