CIS or PMOs

[chris_seven]

LJK Setright who was the Technical Editor of CAR magazine once wrote 'A carburettor is an instrument that has been specifically designed to produce the wrong mixture under all conditions'.

LJKS was a firm supporter of Fuel Injection and made some very valid comments.

Carbs, however, make it relatively easy to modify engines and to tinker at weekends without the cost of a bunch of expensive tools and computing.

As technology has become more accessible and the programming tools needed have reduced in price many of the arguments in favour of carbs have become less significant.

Historic Motorsport is one area, however, where EFI systems, at least in FIA Sanctioned events, won't encroach.

It is also useful to understand the basic needs of the ignition/fuelling requirements of an engine which remain constant regardless of how we decide to provide the fuel and the spark.

We still have interest in both systems as well as for a sound conversion of a CIS into a single I

Don't think there is an 'absolute' solution it all depends on the real needs of individual owners.

[Omegaman]

I have spent many weekends "tinkering" with carbs. Trying to obtain steady AF ratios at multiple throttle angles using carbs is a nightmare. Idle jets, main jets, air correctors etc.

Using wideband O2 measuring equipment is a must during setup, you soon realise carbs are blunt instruments compared to electronic fuel injection.

Saying that, CIS when setup correctly will be tough to beat if using a standard engine on normal road conditions.

[safe]

I'd say tuning EFI is cheaper. Almost everyone has the tools, a laptop. Even an ipad will work with some systems. With carbs you need a bunch of different neck rings and jets.
With electronic ignition you can change the ignition curve with a few button clicks instead of sending away the distributor for a recurve/rebuild.
Assuming a CIS system in Tip-Top condition (with a bunch of n/a parts) its still a very boring engine...

[chris_seven]

I don't think a carb is a blunt instrument -it is just what it is and it used to all that was available.

You have to understand that setting up carbs was usually done by ear and by road testing.

When we started Rallying we had a screwdriver, a rubber hose and little else.

Wideband lambda sensors, rolling roads and all the other fancy kit just hadn't been invented.

We seemed to manage and I think it should only take about half a day to set up carbs virtually from scratch.

Everyone had a stock of jets, needles and the like in the same way that everyone has a lap top and a set of jet reams was obligatory.

It really isn't that difficult.

[winders]

It isn't all that easy either.

A carb is a blunt instrument compared to modern EFI. The difference between pad and pencil versus a calculator is similar! There is no situation were carbs out perform EFI. None. Nowhere. Nohow.

Carbs are less efficient. Carbs don't even come close in tuning granularity. The only place carbs are equal to EFI is possibly no throttle and at full throttle. Anywhere in between EFI is vastly superior.

[Tippy]

^Agreed. For the cost of PMO's, you can buy, have installed, and tuned EFI.

[Omegaman]

Compared to EFI they are. Even large car companies like Audi couldn't get the mixture right when they had carb fed engines.....they were pig rich under heavy load.

I'm sure lots of people "tuned by ear" but then how long did the engine last with the oil being washed from the bores by an overly rich mixture or burnt valves from it being lean.

Anyway....carbs look cool and on some old crappy British "sports car" , then they are acceptable.

It's the same argument with distributors....sure you can set the max advance the same but the curve or trimming odd spots out in the midrange is better left to EFI.

I still look at the condition of the plugs and the colour of the exhaust tail pipe as a guide of a cars overall running though.

[Mark Henry]

You guys must have all been really lousy at tuning carbs.

97% of all carb issues I see are owner/novice induced.

Originally Posted by winders

The difference between pad and pencil versus a calculator is similar!

NASA put a man on the moon with human calculators... pad and pencil. Many were black women mathematicians like Katherine Johnson and Mary Jackson.

[chris_seven]

Originally Posted by winders

The difference between pad and pencil versus a calculator is similar!

How about a slide rule?

I think you miss my point completely.

I just don't think it is a contest.

We run carbs on Period FIA race engines, there is no alternative, we use Solex 40PIs as they are mandatory. We have had to develop an expertise and learn how to make them work.

When you have engines on carbs and make them run well it is rewarding and enjoyable.

I am equally sure that a good EFI will be superior in every respect expect perhaps WOT.

Equally rewarding but why does the comparison have to so black and white.

Some of us old farts still like them

[Pork Chops]

Originally Posted by chris_seven

LJK Setright who was the Technical Editor of CAR magazine once wrote 'A carburettor is an instrument that has been specifically designed to produce the wrong mixture under all conditions'.

LJKS was a firm supporter of Fuel Injection and made some very valid comments.

Carbs, however, make it relatively easy to modify engines and to tinker at weekends without the cost of a bunch of expensive tools and computing.

As technology has become more accessible and the programming tools needed have reduced in price many of the arguments in favour of carbs have become less significant.

Historic Motorsport is one area, however, where EFI systems, at least in FIA Sanctioned events, won't encroach.

It is also useful to understand the basic needs of the ignition/fuelling requirements of an engine which remain constant regardless of how we decide to provide the fuel and the spark.

We still have interest in both systems as well as for a sound conversion of a CIS into a single I

Don't think there is an 'absolute' solution it all depends on the real needs of individual owners.

I used to read him all the time when he was alive. Things have gone downhill since his departure.

[3literpwr]

https://www.youtube.com/watch?v=bripeGzQJ_4

https://www.youtube.com/watch?v=2kcaq6eUQgI

First start?

https://www.youtube.com/watch?v=2kcaq6eUQgI

[Dpmulvan]

Which triumph throttle bodies are you guys using?

[Mark Henry]

The newer 2000- something 3 cylinder TB's. There a couple of threads in the tech forum on it if you do a search.

[3literpwr]

I've got the 45mm set you need if you want to explore that route. I was aiming for this direction before I went PMO. This CAD is built off the Triumph parts and was going to use water jet aluminum adapters and off the shelf aluminum tubing.