The volume demands may be higher then stock at lower RPMS where the butterfly in the throat of the carb is partially closed further reducing the amout of air entering the carb....In addition you need to consider the velocity demands of your new configuration. Check out this link http://www.4secondsflat.com/Carb_size.htmlDan --- On Thu 03/20, Bob_Kai Wongthanavimok < [EMAIL PROTECTED] > wrote:From: Bob_Kai Wongthanavimok [mailto: [EMAIL PROTECTED]: [EMAIL PROTECTED], [EMAIL PROTECTED]: Thu, 20 Mar 2008 19:18:50 -0700 (PDT)Subject: Re: [vintagvw] Stumble engineThank you for your help.Just a thought though. If the carb cannot keep upwith larger cylinder volume, shouldn't it have problem during high rev aswell? It only stumbles during low rev < 2k rpm.----- Original Message ----- From: "dan moy" To: Sent: Thursday, March 20, 2008 7:52 PMSubject: Re: [vintagvw] Stumble engine> Sounds like the addition cylinder volume is theproblem. The carb cannot > keep up with the demands, have you thought aboutdual kadrons? You will > more then likely have to change your exahust if youmove to a larger carb > setup. --- On Thu 03/20, Bob_Kai Wongthanavimok <[EMAIL PROTECTED] > wrote:From: Bob_Kai Wongthanavimok [mailto:[EMAIL PROTECTED]: [EMAIL PROTECTED]: Thu, 20 Mar 2008 00:59:33-0700 (PDT)Subject: [vintagvw] Stumble engineBy way of introduction, I'm anew old listee (been with the list few times many years back) from Bangkok,Thailand. I have a 71 RHD Super with recently mod as follow:Existingstuffs:o 1,600 standard single port AS case engine with 30-Pict3 carb - nowreplaced with belowo 009 dizzy with Pertronix magnetico Bosch blue coil butrecently changed to Hitachi Red (my mechanic said it is compatible)oAircono 831 trannyo Old standard muffler Newly put in (~3 months):o New single34 Pict 3 Solex (but I think made by Bocar) on> dual port (was single port before)o New 76mm CBperformance crank! o New > 88mm Mahle piston set The two should put me to a1,850cc engineo New > 044 CB Performance heads (I think 40X37mm valves).On 34Pict3, I have made > some mod according to Nate from AirCooledTech.com byplugging the throttle > by-pass hole to boost the vacuum so that 34pict canwork with 009 see > link: http://www.aircooledtech.com/34pict3_modification/Here is my > problem, whilst running nicely on high rev, theengine stumbles on low rev > (below ~1,800 - 2,000 rpm). Situations like thisnormally occur:a) > cruising along the road, turn in to cross street,shift down to 2nd, push > gas pedal while releasing the clutch, stumble almostthe engine is going > to stop.b) cruising along, slow down, shift down to2nd, same to a)c) > cruising, stop on standstill traffic on neutral, theengine stumbly idle. > However, after a while, the engine came back to(almost) normal with > slight hiccup every minute or so. The symptom is a!> s> if the gas does not come through sufficiently. Ona) & b), I have to > push gas pedal a bit (to keep rpm up) together theclutch to hold so not > to go too fast. Any idea? My mechanic suspects on 2things, (1) bad carb > (he is kind of not trusting Mexico or Brazil madecarbs), or (2) stand > muffler cannot cope with such a large engine. thought that exhaust cannot > come out fast enough. Oh, BTW,"sometimes", there were some > backfire like single firecracker too. Hope it is nottoo long. Appreciate > everyone comments. Bob/Bkk/71 RHD Yellow Super ---------------------------------Never miss athing. Make Yahoo yourhomepage._______________________________________________vintagvwsite [EMAIL PROTECTED]://lists.sjsu.edu/mailman/listinfo/vintagvw>> _______________________________________________> Join Excite! - http://www.excite.com> The most personalized portal on the Web!>--------------------------------------------------------------------------------> _______________________________________________> vintagvw site list> [email protected]> http://lists.sjsu.edu/mailman/listinfo/vintagvw ____________________________________________________________________________________Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
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