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Re: [T3] Crabby Carbs



Yea, that's what ive used for years.  They are called 7902's now if I recall
right and the Russian version are inked in black instead of green.

Keith


Top Notch Restorations
topnotch@nycap.rr.com 
http://www.a383ina68.addr.com/radiorest/main.htm
71 Squareback "Hothe"
65 Notchback "El Baja Rojo"
65 Squareback "Eggcrate"
87 golf "Winterat"
93 RX7 "Redstur"


-----Original Message-----
From: type3-vwtype3.org-bounces@lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces@lists.vwtype3.org] On Behalf Of B Fye
Sent: Wednesday, September 25, 2013 10:16 PM
To: type3@vwtype3.org
Subject: Re: [T3] Crabby Carbs

I like the w8ac when the weather goes cooler on my 1600s

Brian Fye

> On Sep 25, 2013, at 5:42 PM, "Keith Park" <topnotch@nycap.rr.com> wrote:
> 
> Very interesting Jim,
> I pulled the Brazillain Bosches out (I think they are called 7902 today)
and
> the insulators were quite white and clean, the inside of the plug was
black
> with carbon otherwise but not crusty or anything, they only have about
1500
> miles on them and 18 miles to work and back since it was really bad.
> 
> I put the new Russian Boshes in there, Ill see how it runs with them
> tomorrow for comparison.
> 
> Thanks
> 
> Keith
> 
> 
> Top Notch Restorations
> topnotch@nycap.rr.com 
> http://www.a383ina68.addr.com/radiorest/main.htm
> 71 Squareback "Hothe"
> 65 Notchback "El Baja Rojo"
> 65 Squareback "Eggcrate"
> 87 golf "Winterat"
> 93 RX7 "Redstur"
> 
> 
> -----Original Message-----
> From: type3-vwtype3.org-bounces@lists.vwtype3.org
> [mailto:type3-vwtype3.org-bounces@lists.vwtype3.org] On Behalf Of Jim
Adney
> Sent: Wednesday, September 25, 2013 10:15 AM
> To: type3@vwtype3.org
> Subject: Re: [T3] Crabby Carbs
> 
>> On 24 Sep 2013 at 20:30, Keith Park wrote:
>> 
>> I think the plugs may have gotten fouled... when I was restoring this car
>> with the stock jets It would start running crappy rather quickly if all I
>> did was move it around, unlike the FI 71 which just didn't care.  I put
> the
>> 2X Richer jets in and It ran poorer than the 1X, then I drove the car
down
>> to the neighbor kids house several times without warming it up and that's
>> really when things went downhill.
> 
> Here's my guess: You're running a bit rich at low speeds and loads. 
> This allows carbon to build up on the SP tips because the SP ceramic 
> never gets hot enough to clean up. It may be that the mixture is 
> fine, but it's just that the engine never gets warmed up enough.
> 
>> What I don't understand though is how it can run so nicely at light
> throttle
>> and have a perfect idle if the plugs are fouled and only have problems if
> Im
>> stepping on it a bit... and it would start perfectly too, I always
> remember
>> fouled plugs making an engine hard or impossible to start.
> 
> When our cars were new, gas had lots of tetraethyl lead. That stuff 
> would accumulate on the SP ceramic, and everything else, after the 
> gas burned. SPs that got enough lead deposits on them were "fouled." 
> The lead deposits had the unusual property of becoming conductive at 
> some temperature, so the engine would start, but would quit once it 
> warmed up a bit. (BTDT) There was no cure other than bead blasting 
> the SPs or replacing them.  
> 
> Lead deposit buildup occurred any time the engine was run mildly and 
> also during warmup. Deposits of any kind get cleaned off slowly once 
> the SP ceramic reaches what's called the "self cleaning temperature" 
> (SCT.) SPs come in different temp ranges for different engines to try 
> to assure that the SP insulator temperature is normally above the SCT 
> and below the temperature where it's hot enough to ignite the 
> mixture, the "preignition temperature" (PIT.)
> 
> So you want a SP that rises above the SCT quickly without ever 
> reaching the PIT under any circumstances. SP Makers control the heat 
> range of a SP by changing the length of the heat dissipation path 
> from the hot end of the insulator to the cyl head, where most of the 
> heat goes. The main heat transfer paths are thru the threads and the 
> crush washer.
> 
> We don't have lead in our gas any more, but similar things happen 
> with carbon buildup. Carbon deposits don't have the same temp 
> dependence of conductivity as lead, but an insulator that has some 
> carbon buildup just behind the ceramic tip might be a good insulator 
> for "low" voltages, but if the spark voltage got higher, it might 
> jump along the surface of the ceramic to the carbon deposits and 
> short to ground instead of jumping across the SP gap.
> 
> If you manage to get more of the insulator above the SCT, you clean 
> off more insulator, making it harder for the spark to short to 
> ground.  
> 
> When you jump to wide open throttle (WOT) the combustion chamber 
> pressures go way up, and this requires more spark voltage to jump the 
> gap, so that's when a marginal carbon situation might turn into a 
> "miss."
> 
> Gary Forsmo drove up here yesterday for me to look at his front end. 
> He had been experiencing similar "miss" problems, but they went away 
> once he got the engine up to speed and up to temperature. I suspect 
> his problem was similar to yours.
> 
> Cars that foul their plugs frequently may need hotter heat range 
> plugs. Cars that are run very hard may need cooler plugs to keep them 
> from reaching the PIT. Modern plugs have a pretty wide range between 
> the SCT and the PIT, so choosing the right plug is usually easy.
> 
> I've always used Bosch plugs, which seem perfect for our engines. 
> When our cars were new, these were Bosch 145s, then they became 
> W145T1, W145T1.1, W7A, W7AC (copper core), or W7AP (platinum.) Early 
> Type 3s, like Keith's notch may have taken something different, I 
> don't have any experience with that era Type 3.
> 
> If you're curious about heat ranges and self cleaning temperature, 
> you can check out this site:
> 
> http://tinyurl.com/ksnbzyj
> 
> but the best explanation I've seen is in this very old booklet, which 
> I bought in the early '70s from JC Whitney.
> 
> Bosch Electrical Systems for Automobiles
> published by Interauto Book Co., Ltd., London, England, 1972
> ISBN 0 903192 06 3
> Adapted from "Service-Fibel fur die KFZ-Electrik"
> published by Vogel-Verlag, Wurtzburg, 1971
> 
> -- 
> *******************************
> Jim Adney, jadney@vwtype3.org
> Madison, Wisconsin, USA
> *******************************
> 
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