Accelerator Cable for Dual Carbs ? Options

[cary]

Dang, I didn't know that there was quite this big of an issue with the carb linkage.
I guess I'll need to drive Mark's car a bit.
On the syncing. I was waiting till I install the 2.2 in my project car to figure that out.
But if we have any issues. I'll get some help. I have a 30 year Porsche tech that would probably make a house call.

[rgolia]

Get the tangerine racing cable system...what a difference. You will never look back.




and then get the CSP airbox

[somd914]

The KISS comment is aimed at CSP for bringing to market a product lacking 914 application or basic engineering forethought.

Don't even get me started on the empi/crossbar type linkage!

All these carb conversion linkages really are "the emperor's new clothes".

I've yet to see a properly engineered 914 carb conversion linkage for sale.

After reading your thread, your work is incredible, and thanks for sharing.

As for carb linkage and keeping it simple, in my many years of engineering I've learned budget, schedule, and market all play critical roles - compromises are a way of life and market share.

As for SA914, his system is easily remedied. Here are a few shots of my alignment - off a little (exaggerated by camera angle) but works fine, throttle response is good, pedal has a good feel, and easy to synch. First shot is idle, then approximately half throttle, and full throttle.

[SA-914]

Got it. Just need to shorten my bracket to get it closer and move it over to the other side of the block seam.

[Darren C]

Thanks for the kind comments.
I can understand your hope in making the CSP linkage you have “work to a fashion” which is a no cost option for you; but the title of the thread is accelerator cable related.
The fact of the matter is, the CSP linkage places the cable in line with the crankcase join, leading to having to re-route, bend and re-support the cable in an awkward way that will lead to length and binding issues. However “neat” you may think the CSP linkage initially looks, it isn’t a good product and will always have the inherent engineering faults that will cause issues.
As a very low cost compromise you could cut (hacksaw) off the short arm where the throttle cable connects, install the linkage and set the 45 Deg angle, adjust the rods to the carbs then weld the cut off short cable arm back on at a new angle in line with where the cable should run in a stock layout. You’ll need to make up a new small support bracket for the cable so that it can run at the natural angle it needs, to avoid all the issues.

RG,
The tangerine racing cable system is SHOCKING. Do you really think that that is good engineering??
Ok, you may go “ooooo” & ahhhhh” when you slap eyes on it, but really; its bloody stupid, over engineered and damn right dangerous.
Again your take off the Weber levers? Then fit pulley wheels with a counterbore in which to refit the lever retaining nut….so theres no provision then for the tab lock washer??
There is slotted brackets on which slotted brackets and eyebolts fit to hold the cable! This is BAD engineering and gives scope for the whole damn thing moving out of alignment.
You then link Carb A to B with a Bowden cable! So you are totally reliant upon Carb B’s return spring to keep the cable tension as well as return the throttle to idle when you lift off the gas pedal!!!
This in itself is plain stupid and dangerous as there is potential for not only imbalance in the control of the Twin carbs but also a chance that Carb B may stick open if the cable sticks or the return spring on Carb B breaks or weakens.
With age the Bowden cables will increase in resistance between the Carbs and to some minor extent suffer with heat expansion & contraction.
There is also a risk you run a cable off the pulley in a jam situation.
On rapid throttle operation the cable resistances will effect balanced “snap shut” responses between carbs. This will promote poor fuel balance and cause at best “popping” or at worst unwanted surge when you desire engine braking.
At least with a metal bar link rods you get positive shut off and proportional opening & closing between Carbs.
There is also the problem of running the accelerator cable to the first carb in this set up. The stock cable is either going to be too long or too short!

The whole Tangerine set up is intrinsically dangerous!
It’s a great example of “the emperors new clothes” engineering by someone without a clue of the big picture.

[ThePaintedMan]

The tangerine racing cable system is SHOCKING. Do you really think that that is good engineering??
Ok, you may go “ooooo” & ahhhhh” when you slap eyes on it, but really; its bloody stupid, over engineered and damn right dangerous.
Again your take off the Weber levers? Then fit pulley wheels with a counterbore in which to refit the lever retaining nut….so theres no provision then for the tab lock washer??
There is slotted brackets on which slotted brackets and eyebolts fit to hold the cable! This is BAD engineering and gives scope for the whole damn thing moving out of alignment.
You then link Carb A to B with a Bowden cable! So you are totally reliant upon Carb B’s return spring to keep the cable tension as well as return the throttle to idle when you lift off the gas pedal!!!
This in itself is plain stupid and dangerous as there is potential for not only imbalance in the control of the Twin carbs but also a chance that Carb B may stick open if the cable sticks or the return spring on Carb B breaks or weakens.
With age the Bowden cables will increase in resistance between the Carbs and to some minor extent suffer with heat expansion & contraction.
There is also a risk you run a cable off the pulley in a jam situation.
On rapid throttle operation the cable resistances will effect balanced “snap shut” responses between carbs. This will promote poor fuel balance and cause at best “popping” or at worst unwanted surge when you desire engine braking.
At least with a metal bar link rods you get positive shut off and proportional opening & closing between Carbs.
There is also the problem of running the accelerator cable to the first carb in this set up. The stock cable is either going to be too long or too short!

The whole Tangerine set up is intrinsically dangerous!
It’s a great example of “the emperors new clothes” engineering by someone without a clue of the big picture.

I'm not even sure why I bother responding to rants like this... but here it goes.

1) You're bashing the designs of a valued business member here, without much basis. I believe Chris has sold well over 100 of his linkages, and several of us have put them on race cars. Not one single failure thus far, as far as I know.

2) Like most people who feel that their opinion is the only one that counts, you have bashed two different designs, but as yet have not provided your own solution to the market. You know, the only "correct" linkage design. Congrats on being able to fab your own version, but unless you're selling it, I don't see why you're so angry.

3) Run a cable off the pulley in a jam situation? Oh, you mean like ALL modern throttle bodies before the manufacturers went to fly-by-wire? (IMG:style_emoticons/default/confused24.gif)

4) Chris's design does not only rely on Carb B's throttle return spring. If you took the time to understand it, both carbs still have their own return springs. I went ahead and added a second return spring to both as well out of my own choosing. But I never had any of the issues you describe before I did that.

5) The stock cable works fine. It is neither too long or too short.

Chill out. If you have no constructive criticism, or can't at least present it that way, then please just relax.

[Darren C]

The tangerine racing cable system is SHOCKING. Do you really think that that is good engineering??
Ok, you may go “ooooo” & ahhhhh” when you slap eyes on it, but really; its bloody stupid, over engineered and damn right dangerous.
Again your take off the Weber levers? Then fit pulley wheels with a counterbore in which to refit the lever retaining nut….so theres no provision then for the tab lock washer??
There is slotted brackets on which slotted brackets and eyebolts fit to hold the cable! This is BAD engineering and gives scope for the whole damn thing moving out of alignment.
You then link Carb A to B with a Bowden cable! So you are totally reliant upon Carb B’s return spring to keep the cable tension as well as return the throttle to idle when you lift off the gas pedal!!!
This in itself is plain stupid and dangerous as there is potential for not only imbalance in the control of the Twin carbs but also a chance that Carb B may stick open if the cable sticks or the return spring on Carb B breaks or weakens.
With age the Bowden cables will increase in resistance between the Carbs and to some minor extent suffer with heat expansion & contraction.
There is also a risk you run a cable off the pulley in a jam situation.
On rapid throttle operation the cable resistances will effect balanced “snap shut” responses between carbs. This will promote poor fuel balance and cause at best “popping” or at worst unwanted surge when you desire engine braking.
At least with a metal bar link rods you get positive shut off and proportional opening & closing between Carbs.
There is also the problem of running the accelerator cable to the first carb in this set up. The stock cable is either going to be too long or too short!

The whole Tangerine set up is intrinsically dangerous!
It’s a great example of “the emperors new clothes” engineering by someone without a clue of the big picture.

I'm not even sure why I bother responding to rants like this... but here is goes.

1) You're bashing the designs of a valued business member here, without much basis. I believe Chris has sold well over 100 of his linkages, and several of us have put them on race cars. Not one single failure thus far, as far as I know.

2) Like most people who feel that their opinion is the only one that counts, you have bashed two different designs, but as yet have not provided your own solution to the market. You know, the only "correct" linkage design. Congrats on being able to fab your own version, but unless you're selling it, I don't see why you're so angry.

3) Run a cable off the pulley in a jam situation? Oh, you mean like ALL modern throttle bodies before the manufacturers went to fly-by-wire? (IMG:style_emoticons/default/confused24.gif)

4) Chris's design does not only rely on Carb B's throttle return spring. If you took the time to understand it, both carbs still have their own return springs. I went ahead and added a second return spring to both as well out of my own choosing. But I never had any of the issues you describe before I did that.

5) The stock cable works fine. It is neither too long or too short.

Chill out. If you have no constructive criticism, or can't at least present it that way, then please just relax.

Like most heated replies to opinion, you fail to correctly read and understand my concise observations and retort at a tangent that is not constructive.

I fully understand the fact that I’m sticking my head above the parapet here by stating that all the commercially available carb conversion linkage kits for the 914 are flawed in one way or another.
However, I certainly don’t in anyway want to make this a personal attack on any individual. Again I understand that the guy’s who make and sell these kits have done it with all good intention.
Unfortunately I feel that they could be so much better, and in pointing out the flaws they may be taken onboard and resolved.
Little has changed since the 1960’s with the twin carb conversion kits. Empi etc must have sold 1000’s of the hex bar kits over the years. In the cold light of day we all know they’re not great, yet they still make them and folks will still buy them. The quantity sold is no indication that they're any good, just that they fill a gap in the market for which there's a demand.
This is a Forum…..and as such I’m just venting my frustration as an engineer at the worlds acceptance of a compromise when things could be made so much better, from which everyone would benefit.
I don’t know any of the vendors from Adam, and my observations and opinion is not an attack on the person, its on the flaws of their product. I have no intention of mass producing the utopic linkage or cable kit to compete with anyone, I just wish to vent my opinion and maybe let the manufacturers take some of it onboard and improve their products at best. At worst if a single person/owner says “Ah, I get what you say about this or that issue you’ve raised” I’ll be content. I’m not here for a fight just to maybe open others eyes to the complacent acceptance of these products and the fact the issues can be easily resolved to make a mediocre product great.

It's always a hard pill to swallow when some stranger says "Geez your baby's ugly"

[rhodyguy]

If YOU can build a better mouse trap do so. Let it go George.

You've made much of what MIGHT happen. None of which have occurred in my experience, nor others using the cable linkage as far as I know. First hand experience speaks volumes. Engineering posturing? Not so much. Btw, you came off as a prat with your ranting.

[rgolia]

Well sorry I chimed in and thanks for defending Chris's product boys. All I have to say is that I have put about 75k miles on my 914 with carbs on it. I have used the csp type linkage, the hex bar linkage, and now the tangerine set up. The carb syncing has never been so easy, the throttle response never so good......and no popping that came along with the other linkages. Did I add a spring or two, sure just like George did. (IMG:style_emoticons/default/beer3.gif)

[Darren C]

Ok, time out.

George,

Please change anger & rant you read in my posts for passion. I’m sorry you find my presentation harsh especially the way I express constructive solutions, but I’m a Brit and this is how we are (Cold). Our tongues can cut folk to ribbons when we are expressing praise or advice its a form of tough love.

Rhodyguy,

Please challenge the opinion, not attack the man unless you know him.

You seem like an intelligent guy, but we don’t know the first thing about each others experiences.
I’ve got almost 40 years experience with flat four engines and I’ve built many, many, street, track and drag strip VW & Porsche motors over the years. In my working career you may have briefly read in my Build-off Challenge that I lived in the US and worked on the Challenger Shuttle wreckage recovery and investigation in 86 thru 87. This gave me an obsessive compulsive outlook on engineering fault finding. This carried on in my work career with the work I did at EADS Astrium after NASA for the European Space Agency where we built military and commercial Satellites and developed projects for Mars Rover and Boeing to name a few. I then finally got my career in line with my passion…cars. I trained at Bentley Crewe in 2000 and now work at Rolls-Royce Motorcars Goodwood designing, developing and analysing complex engineering projects. From concept to design and now 10 year evaluations.
My engineering opinion and natural ability to just look at something and see potential fault/failure and remedy is highly respected by R-R, Bentley and Jaguar motorcars (who I did some freelance work for). I've been doing just that for so long, 30 years + now and can't help myself.
Here’s a small window into my working environment. This is the ONLY personal moving film footage that has ever been allowed by R-R to be published outside of factory approved filming in Area 51 deep within the R & D department; such is the respect R-R have for me. (I'm the guy at the end in the lab coat getting out of the car) This was the very first mule Wraith prototype car that was mocked up as a pre-production car. with pre-launch alloy design wheels and one of the 1st six interior trims to be built to the new design. No BS here check the dates I made the film that UK format for 5th March!

https://www.youtube.com/watch?v=2pcCBJiSFDg

I have a large collection of classic cars that I’ve been extremely fortunate to acquire along the way. I’m active in numerous car clubs (and offer advice worldwide as the "spares and technical officer" for the RREC,..... http://www.chichesterweb.co.uk/rrec/rr05officers.htm I'm also a renown and respected world concours judge with an eagle eye for detail. I once awarded poor marks to Arnold Schwarzeneggers car!) and run a small business from home called D.C. Shed Industries, (a little like Mark does at 914rubber) making unobtainium parts for classic cars and new improved parts for several marques that I’m passionate about. This I all do voluntarily and ALL income from the sale of the parts I donate to charity.
This gives me the knowledge to make constructive comments and have opinion on bringing products to the open market “half cooked” and to welcome all criticism, good, bad or indifferent with open arms that may lead to a better product for all.
Just today I’ve finished a new batch of parts for one club.
Link (go to page 16) and you’ll see this is not BS.

http://www.deloreaneurotec.uk/viewtopic.ph...;p=70293#p70293

I’m currently working at R-R on the finishing details and infrastructure for manufacture of new models to be launched in 2018 (to be confirmed)

So I think I can justify my experience which allows me the freedom to rant on the simple throttle linkage and cable issues of aftermarket 914 kits!

Rgolia,

I truly appreciate your experience, but you have just re-enforced my whole point.

By saying that you needed to add a few springs here and there as George has, it’s proved my point that the kits (made by whoever) just aren’t right and need modifications.

All,

I’m not seeking anything here, just acceptance that I have an opinion based upon experience, I’d never shoot my mouth off about something I know nothing about. If any of the vendors visit this site or if any of you know them, please get them to PM me, I’d be only too pleased to help them develop their products, free of charge.
Just please don’t attack me for airing my opinion. I'm a Brit, we mostly moan about stuff, that's what we do!

[rgolia]

Darren,
All good here. I understand where you are coming from. Continuous improvement is a good thing. (IMG:style_emoticons/default/beerchug.gif) Cheers...and if you do some engineering for 914 parts I would be happy to be one of the first to try it.

[rhodyguy]

So, your bluntness can be acceptable and explained/justified due to nationality? You seem to interpret my bluntness as anger. I'm American by birth and Irish by genetics, but I still have to watch my tone and tenor. Or not. Depends on my mood.

[Darren C]

So, your bluntness can be acceptable and explained/justified due to nationality? You seem to interpret my bluntness as anger. I'm American by birth and Irish by genetics, but I still have to watch my tone and tenor. Or not. Depends on my mood.

Sounds like my ex-wife...

:-)

Can we just kiss and make up now?

[rhodyguy]

Of course!

BUT, considering the other linkage offerings available for carb conversions, Chris' functions better. You'll have to trust us on that one.

[Darren C]

I'll give you that one.

But genetically you know you're 50% banana.

[cary]

Is it me, or is the bar style dual carb linkage pretty stiff? Finishing up Mark's car this am it just seems like it takes quite a bit pressure to push down the gas pedal.
Cable itself is silky smooth. I did convert to a lighter spring. Helps a little.

It feels like a drive to Medford would wear out your leg.

[somd914]

Is it me, or is the bar style dual carb linkage pretty stiff? Finishing up Mark's car this am it just seems like it takes quite a bit pressure to push down the gas pedal.
Cable itself is silky smooth. I did convert to a lighter spring. Helps a little.

It feels like a drive to Medford would wear out your leg.

I recall the hex bar on my silver car was a but stiffer than my CSP linkage, but not as you describe.

The Revenna green car also a hex bar system but is extremely stiff. I removed one of the two return springs and now has a tendency to stick. Cable seems to run freely, and also note this system has the cable connection at the passenger side of bar next to the carb, not a center-mounted cable. So, the cable runs the factory path except for the left-hand bend towards the bar which is a large radius.

[cary]

I'll retract that statement/question. I didn't have a point of reference.
I just went out and tried the D-Jet in my DD. Its about the same. The carbs may be a bit stiffer, but not significant.

[Darren C]

Cary,
Sometimes you have to go with your gut feeling. The DD is a good but not fallible reference.
You need to consider several things in our 40+ year old cars.
Starting at front.
1, The gas pedal.
I’ve changed several of these over the years in my various 911’s and also in my 914 and got a whole new feel.
The metal hinges inside the pedal rust and go stiff so can affect the resistance and feel. The hinges can also wear and even break inside the rubber and you wouldn’t necessarily know. The pedal design also relies in part to the rubber moulded around the hinge to act as a natural return to the upright position when you let your foot off.
If you replace it, buy GENUINE Porsche, for a few dollars more you get a thicker steel inside and better quality hinge than the aftermarket copies.
2, Pedal set bushes.
If worn these will cause issues in smooth operation and increased friction.
3, Cable route at the pedal end and chassis tube.
It is possible to cross over the accelerator & clutch cables inadvertently when replacing them so one runs across another. You can’t see easily inside the tunnel and this can happen especially if the accelerator cable tube breaks free at the pedal end. Corrosion is an issue here as it causes friction and closes down on the cable if the tube is rusty.
4, Cable.
ALL cables wear. Most owners carryout a Carb conversion and use their old accelerator cable thinking it’s ok. Bowden cables wear the nylon sheath on the inside radius of any bend and the outside radius at each end of any bend and cable outlet from each end of a sheath. Over time if a cable is undisturbed you don’t really feel any difference as you get used to it and the change is so infinitely small. It only becomes an issue if the nylon sheath breaks somewhere (usually where the steel ferrule fits at the bulkhead) wears through, the cable sheds a wire or jams and the sheath external spring rusts out.
Cables also pick up dirt and dust and fray which can give resistance. I've had cables out of a car and they run free (making you think they're fine) refitted them and they bind under operational tension or when asked to lay in awkward routes.
The worst thing owners can do is oil these accelerator cables in good faith. This can swell the sheath, attract dust/dirt to quickly clog up and although you think you've solved an issue temporarily, long term its just made things worse.
The cable is a cheap item (in Porsche terms) and easy to replace, so if you're unsure how old your cable is and what condition it's in...just change it for peace of mind.

When owners carryout a FI to carb conversion, one big issue is moving an old cable around the engine bay to the new linkage mounting point. Just doing this itself can create a binding as the old worn cable is now bending/laying in a different position so any internal wear from where its “worn in and settled” over the years can be an issue
Cary, its difficult to have a good reference unless your reference is a car with all new parts down the chain. If you jumped in the car and thought “hey this pedal feels stiff” then 9 times out of 10 I’d say go with your gut feeling. Comparing it to an “unknown quantity” another DD is a starting point but certainly not to be relied upon.
Looking at it logically, on FI you have only one throttle body, one butterfly valve and 2 springs (dependent on year, there’s a coil on the shaft and a secondary emergency spring introduced a little later). On a carb conversion you have 2 spindle, 4 throttle butterflies, two coil springs, and additional springs that come with your linkage, and maybe more springs owners have added to get the throttles to return. Plus most linkages have friction points and odd mechanical advantages thrown into the equation.
It’s for this reason that I’d question your comparison with the DD against your gut feeling here.
If anything I'd say the DD with FI has an issue if its got the same heavy pedal feel/resistance as the carb conversion car!

Regards
Darren

[yeahmag]

RG,
The tangerine racing cable system is SHOCKING. Do you really think that that is good engineering??
Ok, you may go “ooooo” & ahhhhh” when you slap eyes on it, but really; its bloody stupid, over engineered and damn right dangerous.
Again your take off the Weber levers? Then fit pulley wheels with a counterbore in which to refit the lever retaining nut….so theres no provision then for the tab lock washer??
There is slotted brackets on which slotted brackets and eyebolts fit to hold the cable! This is BAD engineering and gives scope for the whole damn thing moving out of alignment.
You then link Carb A to B with a Bowden cable! So you are totally reliant upon Carb B’s return spring to keep the cable tension as well as return the throttle to idle when you lift off the gas pedal!!!
This in itself is plain stupid and dangerous as there is potential for not only imbalance in the control of the Twin carbs but also a chance that Carb B may stick open if the cable sticks or the return spring on Carb B breaks or weakens.
With age the Bowden cables will increase in resistance between the Carbs and to some minor extent suffer with heat expansion & contraction.
There is also a risk you run a cable off the pulley in a jam situation.
On rapid throttle operation the cable resistances will effect balanced “snap shut” responses between carbs. This will promote poor fuel balance and cause at best “popping” or at worst unwanted surge when you desire engine braking.
At least with a metal bar link rods you get positive shut off and proportional opening & closing between Carbs.
There is also the problem of running the accelerator cable to the first carb in this set up. The stock cable is either going to be too long or too short!

The whole Tangerine set up is intrinsically dangerous!
It’s a great example of “the emperors new clothes” engineering by someone without a clue of the big picture.

To be frank... You have no idea what you are talking about.

The throttle levers stay on and are "pinned" to the pulleys.

The cable connecting the master to the slave is ideal as it doesn't change with heat or expansion. Once the slack is taken out you are more or less done.

All the standard springs for the carbs stay in place, so you are no better or worse than with a linkage. If one carb hangs open with either system you have a potential problem.

This setup is WAY smoother than my PERFECT CB hexbar set up. My balance and feel is perfect with this setup. Something I could never achieve no matter what I did with a hexbar setup.

I race the stuff Chris builds and appreciate his engineering greatly. Not a fan boy, just a user.