Why block cold start valve on Weber IDF's?

[RHough]

I been searching and reading for over an hour and have not found an answer.

Why does everyone block off the cold start system on the Weber's? In most applications the correct settings for good operating temperature drivability do not allow an engine to start and idle when cold without a choke/fast idle system. I suspect the Weber's get set up too rich and or people put up with poor cold drivability?

Another way do ask this is "Has anyone made the cold start system on the Weber IDF's work on a VW?"

I did find one reference that advertised the cold start block off kit to "prevent dirt getting into the carb". Could it be that the buggy guys had dirt problems that were solved by disabling the cold start system and now it is just common practice? Is adding a choke cable more hassle than it is worth?

The reason I'm asking is that even the road race engines I've built had better drivability/throttle response with a carb setup that was too lean for good cold start. I'd like to have the operating temp performance as crisp as possible.

Can anyone say something like "We block the cold start valves because they are prone to fail and effect the mixture." or "When the carbs are setup properly the cold start makes the mixture too rich and fouls plugs." or "The cold start enrichment is used for applications where fuel pooling in the manifold is a problem, VW's don't have that issue."

Not trying to say that anyone is wrong, just trying to understand why the VW/Porsche community disables a system the Weber designers included.

Thanks for any insight and or a history of Weber's on VW's

Randy

[miniman82]

2 reasons: nearly no one knows how to 'tune' the warm up circuit, which is because it's typically not needed. Remember, it's an air cooled engine so it gets up to a temperature where it idles smooth a lot faster than a water pumper. I doubt anyone would invest the time on something so trivial.

[sideshow]

Have you considered the linkage hassle? Manual chokes are great, unless you forget to turn them off.

[RHough]

Have you considered the linkage hassle? Manual chokes are great, unless you forget to turn them off.

Manual chokes are usually better than no way to provide cold enrichment.

miniman does have a point that air cooled engines warm up quickly. Many British motorcycles of the 60's and 70's had no chokes, just a button to depress the float and flood/prime the engine for starting. They ran well enough to ride in a minute or two. They were also pretty rich all through the range. Later model air-cooled engines in motorcycles had working cold enrichment systems, leaner mixtures (EPA standards were looming) and better fuel economy. These tended to be unridable when cold.

Some air-cooled engines rely on a rich mixture as part of heat management. Do VW's respond to lean mixtures with overheating and detonation? That could be a reason to run mixtures that are rich enough to not require a cold start system?

After some more digging I found that Porsche did not provide chokes or fast idle cams on the Solex equipped 356's. That is pretty close to a VW with 40mmIDF's ... so if the Porsche factory didn't bother, I won't worry either ...

[Piledriver]

The throttle pedal is more than sufficient to provide cold start fuel, warm up enrichment and "fast idle".
Perfect? No. Works, yes.

Example:
I ran CIS for ages, and I eventually ditched the basic fuel meter for -E meters as they work better, have a wider range, and can be remotely controlled electrically.
The described setup lacks the warm up regulator setup that makes warm up theoretically better.
(except when it doesn't, it has it's own issues)

I had a push button i would tap to fire the cold start injector, and perhaps a few more taps to keep her going for the ~30-45 seconds it took to get the heads warm enough to idle by itself when it was 20F outside.

I DID use the CIS idle air valve for cold//fast idle,is operated by an internal 12v heater, provided gradually decreasing bypass air for fast idle, works well for what it is.

With Webers, you have an (hopefully) intelligent closed loop cold start and fast idle control system right behind the steering wheel. Sometimes less is more reliable.

As noted, aircooled engines get to a happy place much faster than watercooled motors with a huge thermal mass to heat.

Thought of an additional reason folks generally do not run chokes on IDFs:
The aftermarket (as opposed to OEM on Alfas etc) carbs almost ~never came with chokes, and sometimes (I have heard) the required passages are not even machined. (never bothered to try, personally)

[sideshow]

Shrug, I've done 100,000+ miles with duals in snow/summer/altitude and I have never missed the choke

[buildabiggerboxer]

Some air-cooled engines rely on a rich mixture as part of heat management. Do VW's respond to lean mixtures with overheating and detonation? That could be a reason to run mixtures that are rich enough to not require a cold start system?
]

They do assuming we are talking carbureted race motors pushing a Beetle, for circuit racing we run very rich indeed, those that don't and run 'ideal' and near stoich just go slower and yet slower as just a few laps are run, such motors often run small power pulleys in the search for hp, compounding the problem, about 10/12 mpg on the BBT 1641s with a single centre mount 40 dell, gives an idea of the jet sizes required to keep them alive, seizes were not unheard of for the unwary, my 2.5 ltr race Beetle on dual 2b carbs returns about 7mpg at races.

[Marc]

I agree with the spirit of the above remarks. Cold enrichment just isn't needed when the carbs are right above the heads (unless you're in a truly cold climate, of course). To me, it's better to put up with a little balkiness for a few minutes rather than take the risk of a possible failure which could cause horribly rich operation which washes down the cylinder walls - or worse, an external leak leading to an engine fire.
K.I.S.S. - parts left out cost nothing and cannot fail.

[Slow 1200]

...all that, plus with some manifolds they hit the fan shroud