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Re: [T3] Dual 40 DCNF Carbs


On 19 Sep 2002, at 22:07, Keith Park wrote:

> Uh Oh... one of those rare moments that I differ from Jim..

That's okay, I don't mind.   ;-)

> I have the L Jet on my Opel... and for the first 170K or so it was flawless,
> although my father tweeked things a bit when it was new.  The air meter, with
> the vane, was used well into the 90's at least and is quite well designed and
> seems to have a very long service life, there is very little issue with wear
> if nobody messes it up.  There is no pressure sensor with brass bellows to
> have the solder seam fail on. 

Yes, but there will always be people who can take care of any system, and 
those for whom nothing last for long. It's for those in the middle that the 
comment applies.  

I've never seen a bellows seam which has failed. That doesn't mean that it 
doesn't happen, just that the parts were well enough designed that such 
failures are rare. While the brain and PS are often viewed with suspicion, 
they are seldom the problem.  

The air meter with its pivoting vane and rubbing potentiometer contact is a 
much larger source of wear and abuse problems than the D-Jet PS ever was. 
Any rubbing or sliding contact will always be less reliable than a properly 
engineered flexing part. The D-Jet system, however, was the leading edge of 
the FI revolution, so it took the brunt of the critisism.  

The L-Jet air vane's biggest problems came from damage from backfires and 
from mechanics who thought the way to deal with them was the same as 
with a carb choke: ie, jam a screwdriver down its throat. I'm sure that Keith 
was always careful with his. 

> Fragile wiring?  the connectors are MUCH improved with a positive snap lock
> and better sheilding against water and dirt, and the rubber covers seem to
> hold up better. 

The point I wanted to make is that ANY electrical wiring in an engine 
compartment is bound to be vulnerable. Yes, the L connectors are better 
designed, but the wires are still there and mechanics still 
feared/hated/misunderstood them. They felt the same about the brain which 
the L also had. It is the misunderstanding which leads to abuse and 
destruction of the harness. If people had just treated these parts with a 
normal amount of care and respect many of the problems we have today 
would have been avoided.  

The K-Jet system, at least in its first introduction, had very few wires. Instead 
there were fuel hoses which mechanics "understood." The K-Jet system was 
extremely interesting and there is very little about it which is intuitive or 
obvious, yet it was accepted much better. Part of this acceptance had to do 
with the lack of a ECU and wiring harness, and part was simply because the 
FI revolution was already somewhat accepted by the time it came out.  

> Perhaps the biggest plus is the lack of trigger contacts to get dirty and go
> intermittant. 

This is true, but in most cases it is rather easy to do a bit of occasional 
preventative maintenance and avoid almost all of these problems. Dirt in the 
trigger points can be minimized by keeping the dist clean, lubricated, and in 
good working condition. Actual failure of the trigger points is extremely rare.  

-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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