synchro my carbs


Asked by Oct 31, 2010 at 03:05 PM about the 1974 Volkswagen Beetle

Question type: Car Customization

im trying to synch my dual solex 47's and its not going to well!!! Im running a 1641 w110 cam, and it runs like crap! it starts easy... it idles smooth at 1200-1400 rpm. if i adjust the air flow down to lower the rpms to 900-950 it looks like the motor wants to take off walking as in unbolt itself and waddle down the road!!! lol!

am i running to big of a carbs?
or are they junk?

any advice or solution would be freakin awesome!!!!

thanks, A

5 Answers


first thing is i've never heard of solex 47's! i've seen all the stock solex's, plus the 35's and 36's, but never a 47!! but hey, i've only been messing with these things for 25 years. anyway, what kind of synch gauge are you using? a snail or a unisych? the unisynch's are a pain in the butt and usually will cause more problems than good. so make sure you use a good gauge (SNAIL)!! high idle can be caused by alot of different things. first thing to check would be for vaccum leaks. if you have a vaccum leak it will cause the symptoms you describe. high idle rpm, and when you try to lower it with the carbs the motor will cut out and do all kinds of crazy things. second: are these carbs SINGLE barrel carbs or DUAL barrel carbs? if singles, do you have a balance tube hooked up between them? the balance tube (while not necessary) will allow a smoother idle, but really has no affect once above idle. third: when adjusting carbs, your linkage is DISCONNECTED correct? it must be. and last: make sure the engine is completely warm, adjust the high carb down to the low carb. once this is done, recheck, and redo. never adjust up, always down. RECHECK FOR VACCUM LEAKS, oh, have you checked the timing on the car? what distributor is on it and what's the timing set at?


the carbs were from jc whittney scat solex carbs 47mm throat.... im using a snail sychro, my timing is set at 28 degreed full advance, distributor is a 009 w/ a petronix ign. i checked for leaks everything was good/ no leaks! yes pulled linkage off before sychro. i did get it to idle smooth around 950-1000 rpm now im getting popping out of the exhaust.... heres a pic of one of the carbs.. single barrel. BALANCE TUBE? the only line going to the carbs is the fuel line....I'll go check to see if somethings been plugged off...


hey chris i think im just gonna bend over and take one in the a** for stupidity! BIG TIME STUPID! For some strange reason don't really know why, i was looking at my distributor, so start to look at wires and freakin "BAM" "NUTS AND BOLTS THIS IS SCREWED" wires all wrong im still scratchin my head how could this thing run or even idle??? it was late so i quit!


if those are truely 47mm carbs, what size venturi is inside them. hope its 28mm if not, they probably will never run right. a 47mm carb would work well on engines in the 2017 or larger size. way to much air to run right on a stock size engine. anyway, popping out the exhaust could be jetting, or exhaust leaks. check for leaks first because it's easy. just feel around the joints and where the header bolts to the heads. as for jetting, what idle, main, air correction jets are in the carbs, and also will need to know what venturi size is. i run kadron 40mm single barrels on my 1641. i run a 50 idle, 130 main, 180 air correction. just a rough guess with 28mm venturi's. balance tube runs from intake manifold to intake manifold. it helps balance out the reversion between the cylinders with single barrel carbs. not needed on dual barrel carbs, and really isn't needed on single barrel carbs except for a smoother idle


chris you're absolutely right!!! i pulled the manifold off the right side, i could see where it was sucking in from...used the spray yesterday to see if it was leaking but i didnt get any change in the motor so i assumed there were no vac. leaks... WD-40 dont work!! Guess i should've used B-12!!! But any ways the carbs jets-- 160 air correction 52.5 idle ?????? main just have to re-adjust the timing a lil and she'll be good to go!!! Thanks Chris!!!

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