im not sure if im having the same problem as the other 2 backfiring/flatspot problems on this forum in the last week, so i'll tell you whats happening.

ive got a 1600 beetle with a 40dcn webber, and it got its timing adjusted last week and was running sweet... during the day.:thumb

come night-time i get this lurching popping (like backfiring) drop in power in the mid-high rev range in 2nd, and again in the mid-high rev range in 3rd. sometimes it will even get backfiring in 2nd.
and no matter how long i drive it for, if its nighttime (and therefore cooler) it does the same thing. and the webber is always really really cold.

gave the carb a little tune-up but it still does it, and it didnt do this weird lurchy thing in 2nd and 3rd before i got the timing adjusted.

i let my car warm up for at least 2 mins every night before i drive off so i dont stall it and it doesnt backfire all the way home.

so is this what a flat spot feels like? (i thought if you had a flat spot you would have a flat spot wether it was cold or hot?) and even if it isnt, is what is happening bad for my car, because it sounds bad and feels bad and im getting a bad feeling about it. she runs fine when its warm, but i hate to hear her bitching about the cold.

im also thinking about dual webbers sometime in the near future, so will i be having to deal with twice this amount of webber-ness in winter?

any ideas, help or sympathetic swearing is much appreciated!

Have a look at
http://www.aussieveedubbers.com/forum/viewthread.php?tid=8899 
in particular the part where Grey57 suggests icing as a possible problem.
This is especially applicable to single-carb, modified-inlet VWs as:
- the inlet tracts are relatively long and
- the original heat function may not be implemented.
hth

Flat spot = put your boot into it and nothing happens. I've got a progressive weber on my 2l kombi and it has more like a hole than a flat spot when you move off in first. It's definitely worse when cold, but I now always let the motor warm up for a few minutes b4 attempting to move on cold days. Dual carbs should be significantly better in this regard because of the shorter manifolds. I would like to test this theory but $$$ hold me back!

Is there an angel of flat spots rampaging around Australia taking the first born of the like? Quick, everyone paint your VW's in lamb's blood and the flat spoting angel will pass over you!

If your engine's fine when its warm then you may be running a little rich when its cold. The choke is already making the mixture rich remember... I used to put the choke in when i was accelerating and only pull out the choke at the lights when the engine was still cold (not saying i mash the right foot when the poor engine's cold).

So yeh, maybe lean out your mixture a bit and check your timing again, hell while you're at it, check your coil too.

You may have to get an aftermarket manifold heater blanket if symptoms persist... or go see a doctor and only use as directed....


Good luck dude

IF it didnt do it before - go back to what it was.

Do you know how the timing is set now??

Strange - i wouldnt have really connected the 2.

I take it it is a single DNC?

You could have a blocked idle jet. Might want to chect there.
IF it is only doing it at night i would say you are leaning out. Popping rather than backfiring

But timing shouldnt effect this.

Did they do any thing else???

Adjust the mixture screws??

Even if you were to advance you would run hot and get pinging and run on

to retarded - sluggish

hmmmm......... confusing

mnsKmobi, if you mean a hole like it gets to a certain rev range, sputters and bitches, then if you keep putting your foot down it gets over it, then im guessing thats what ive got.

Im not sure about the timing, mechanic fixed it all up for me during my monday of hell 2 weeks ago. as you say blue74, its probably not the timing, its just strange that it started happening after the timing got adjusted.

Yup, its only the single dcn, and its already running pretty lean. My mechanic wont touch the webber, and ive had a pretty good run of tuning it myself (which is helpful!) I'll definitely try everything out.

Thanks for the help guys