Hi, I have a timing question re my L bug 1600 dual-port. I have re-built it and using advice from Air-cooled Tech and others have set timing, adj.valves etc and it has started ok, idling adj. went fine as according to Tech notes. So it runs and idles fine but when I give it heaps it starts missing and the timing seems to be up the creek. My question is regards the vacuum advance, would this be the culprit as when I suck on the adv. tube it only moves a few mm. The dizzy has a number 114905205Z and is the stock single vacuum hose type, seems to be in good nick but I am far from an expert. Can anyone see any obvious fault from these symtoms? I set it at TDC as I cannot find any reference anywhere to this particular dizzy, not on the oldvolkshome website anyway. Any advice gratefully received!

I would advance it a bit more than TDC..
try 7 1/2 or 10 degrees...

I have a similar distributor here and it also only moves a few mms when sucked on...

maybe thats normal???

cheers

Lee

when you suck on the vac advance tube put yr toungue over the hole and see if the advance mechanism stays put which it should if it creeps back then the diaphragm is stuffed

time for an electronic ignition module

Well that's good about the hose, I thought it might not be doing anything so I will try adv. it and try that. So will that bring the spark in a bit later at higher revs?

set it at 10 deg at idle but check the sucking first

Just read your post vw54 re putting tongue over hose, no haven't done that so will try that too tomorrow. What brand/type module is the go?

I'll try that, set at 10 deg and see how it goes.

Well today I checked the diaphragm on the vacuum and it passed the suck and tongue test, held vacuum ok but after setting the timing 10 deg btdc it still is not smooth at higher revs, idles ok but tramp it and it starts missing an a bit of black smoke comes out. Maybe the dizzy is crook? Would the rotor be suspect too?

The carby is stock 34pict3 and the vacuum hose is new, leads plugs and points all new, I haven't got a spare dizzy except one from a 1500 single port, would that do for a test? Would electronic ignition solve this or not? I will get a timing light today and do a test.

Yes the dizzy from the single port will work u need to make sure the drive locates correctly before u tighten the holding clamp, I have had a few instances in the past where they idle fine but under high revs it misses and farts, under driving conditions its even worse..... it ended up being a fouled spark plug! black smoke normally means unburnt fuel and if the plug is not causing correct ignition will casue fumes and slight backfiring. The vacuum advance distributors can happily run without the vauum canister due to mechanical advance being inbuilt.may not be as quick in advance curve but will still operate happily. Be intersted to find out what it is????? A quick change of the coil with a spare may be on the cards too?? At least its a quick swap over!!

Thanks Pete, an update: I replaced the coil, got hold of a timing light and re-timed rather than static, and this time it had improved heaps but still not 100%, still slight missing on revving but a lot better. I am still suspicious of the dizzy and have ordered a new vacuum advance one so will wait till that arrives and go through it all again. Hopefully will resolve it or end up with a motor which has lotsa new parts!

did u check the point gap this is most important 0.016 "

if it aint right then the rest is not going to help

I didn't apart from when I initially fitted the new points, so I guess I have a mission tomorow, will get back tomorrow after I have done this

Well points gap is fine, while I am waiting for new dizzy to turn up thought I would check carby again. I have a spare and have been using both to get one good one: i.e. one body has tighter throttle shaft etc, anyway one thing I hadn't swapped was the main jet which I did and now there is a big difference, on cold start itis good then when it warms up it seems to starve and stalls. One big difference is that on higher revs the missing it had before isn't noticeable! Maybe my diagnosing is up the creek and the carby might be the problem, I could have sworn the advance was not working. How can I check the size of main jet and what should a stock one be? I don't fancy buying another carby. There are so many interelated things to check, Before I changed over main jets it idled fine but now it's erratic and won't idle no matter which way I turn the bypass screw. Maybe a previous owner died in this bug and his ghost is having some fun!

If the accelerator pump is blocked or leaking, the engine will not want to rev...
it needs the extra fuel pumped in with the accelerator pump..

starving for fuel and flooding can both stop an engine...

You may have a fuel and not an electric problem...

either can be frustrating....
especially when you install the new dizzy and it still plays up

cheers

LEE

i had a friend who had no end of strief with the same thing you describe
i said have you cleaned the carby jets and galleries answe no so we took the carby off and unscrewed everything than using a compressor blew air into all holes
and guess what a bit of rubber popped out must have come of the degraded rubber tube so all tubes were replaced they looked like the ones that it had when leaving the factory looked but in side crap

Yep think a huge clean is in order and check accelerator pump circuit, again! I was reading a tech article about soldering up the hole in the throttle butterfly-plate to increase vacuum at idle, apparently helps to match with 009 dizzy, has anyone done this and has it helped?

Further update to this: I have thoroughly cleaned carby and filled the hole in the throttle butterfly plate (as per article in Aircooled-tech) and put it back on and now I can get it to idle, not entirely perfect but not bad and it doesn't miss on accelereration, this is with the old dizzy so that's good BUT (there's always a but!) when I was checking timing with the strobe, momentarily the timing would fluctuate and it would run rough then regain it's composure and run smooth again. This is for only a second or two and only now and again, does this mean the dizzy is crook or something more sinister? Another question: In the attached pic of the carb the accelerator pump adjuster gadget interferes slightly with the side of the alternator, is carving a bit off the alternator the best solution? Thank you for your assistance so far I'm actually progressing with this.

thats a generator style carb
the alternator ones have the accel pump adjuster facing the other way

quick fix i use is use a shifter and gingerly bend the adjuster away from the alternator
and also shave about 4-5mm off the alternator in the interfernce zone

i would be looking for leaks on manifold or carb. it easy if you get some carby cleaner or even WD40 (abit messy) and spray it all over the carb and manifold joints if the revs drop you are sucking the stuff in and it dont burn to well OR use some Aero Start ( Start you basted by Nulon) and if the revs increase you have a leak. if you do have a leak it will effect timing with a vac dizzy and also you fuel air ratio

Good Luck

Thanks Thinker and Davo, I did check the points and they spot on .016", not sure re leaks in the manifold, when I did the re-build I hummed and haaard about changing the rubber joiner bits but used the old ones so they could be suspect. Check tomorow

Another update: I did as thinker suggested and sprayed some aerostart around the manifold joints and carb. near the throttle shaft, seems no manifold leaks but when I sprayed the throttle butterfly shaft especially on the right side where the accelerator pump adj. is there was an increase in revs, I did it about ten times to make sure so the shaft is not as tight as it needs to be. As a quick fix I took the linkage and adjuster off and put an o-ring (fat one) on the shaft and refitted the linkage an adjuster and re-timed and retuned carby and even just doing that makes it idle heaps better, still fluctuating a little bit but definately improved. The o-ring appears to reduce the air getting sucked in there but it is amazing how small these amounts are to affect idling, I think I need a better carby