How do you adjust the mixture on a 34 pict3.
i have a backfire until the engine is really warmed up(too lean?).Living where i do and only driving about 10km to work in the morning is a pain in the butt as it is so cold in the mornings. Thanks in advance for your help

http://www.angelfire.com/tx2/ntnb/Carb_Instructions.htm 

Thanks Daimo. Adjusted and running a bit better but i checked on saturday morning and there was ice on the manifold under the carb, i guess i will be changing it.

backfire on coasting? backfire/splutter when you take off?

what distributor you running?

mixture screw adjuster only for when there is zero throttle (ie: idle).

check your timing too. it might be too retarded. You could advance it a little and this helps (be careful though, not too far)

I get condensation under my carburettor, if cold enough i spose it could turn into an ice. Natural with fuel evaporating into a vacuum, it absorbs the surrounding heat energy (similar process of cooling in an 'evaporator' of an air conditioning system).

Are your heat riser tubes working properly??
That will cause icing if they are blocked

Also make sure the large and small O rings on the adjusting screws are good

it may be sucking air as well

i am running a single vacuum advance distributor with a Pertronix ignitor and matching coil. The backfire is only happening on acceleration although there is a slight miss on idle.
definately ice on the manifold as i stopped and checked. Are the heat risers able to be cleaned they look like it would be a pain because of the bends.

i have tightened the manifolds and exhaust. Maybe i should check the o rings on the screws.

i have some acid i got for a science project of my daughters. i will get the car through its pink slip this week then try cleaning them.

be sure there are no splits/cracks in the manifold boots too.

The crazy sensativity to vacuum leaks on these motors is like a red head in the sun. Only takes a little to cause trouble and it gave me plenty of grief in the past. The 'spray aerosol around the manifold components' trick works well. just listen out for a substantial 'rev up' to know the aersol is passing through manifold joints and boots to know there is a vacuum breech present at that area. Deoderant works good, smells ok too

i will give that a go.

i will have to try a different supplier this time round.

also 4 got to say there are CHEAP crappy air screw O rings around

that just DONT work

i have 2 big boxes of assorted o rings at work. they are wurth brand which are supposed to german

It doesn't matter about the brand (well it does) but there are different types of rubber.

most rubber o-rings are not fuel stabilised. It has to be a 'fuel specific' o-ring. Just like injector O-rings, there are made of a special specific rubber that can handle exposure to fuel without degregation (fuel acts as a solvent).

I learnt the hard way, replaced a pinched injector o-ring with an o-ring (automotive one mind you) from a mixed packet at super cheap, lasted 4 months before i had to replace again as after following the fuel smell i could see fuel leaking out of the rail from that injector. The rubber just gets eaten away. So i went to a local fuel injection specialist and got the proper stuff; fuel stabilised rubber o-rings.

Its just like how silicone or gasket maker goop gets dissolved away by fuel. same thing happens to the o-ring. turns sticky and gets eaten away.

Hi

I worked on a twin port 1300 once that had a hole in the inlet manifold going into heat riser, some brain surgeon had fitted a 150 main jet to compensate, so when you take the manifold off have blow through it, followed by a beer.

The later intake manifolds preheats were larger in diameter and seem to resist blocking a bit more.

Is it a dual vacuum carby, as in a vacuum port facing out the back of the car? What jets are you running?

Your heat riser should sizzle when you lick your finger and touch it after the motor is warmed up.

Steve

I'm not sure if its a dual vacuum carby and do not know what jets are in it. as far as i am aware it is all standard for a 74 beetle.

Tried the deodorant and there was no change to the engine speed. i will take the manifold off now that the car has passed the pink slip and unblock the heat risers and i will check the timing and replace the manifold gaskets and seals.

blocked heat risers aren't so hard to clean. use a 6mm drill for the first 3 inches and then get a thick wire coat hanger. Cut a 6, 9, 12 inch and full riser length piece and use a hammer to flatten one end of each into a sharp flat end.

Place each bit in order in a drill and the flatted end will cut the carbon out fairly well. Once you've made a hole you can carry one with the lengths of wire and make coils of wire or try some pool acid down the hole. That should eat into the carbon pretty well too

Does sound like an air leak somewhere aswell. Flatten the inlet manifold faces with 180 wet n dry, some wd40 and a flat piece of glass. Do the same to the inlet manifold face and the bottom of the carb. Check your rubber boots. If still misfiring after new gaskets then either dizzy or carb issue.

i will give that a go.

I have removed the inlet manifold and it is not blocked. The heat riser outlets on the exhaust are blocked up with rust. I guess thats what happens when you buy cheap stuff.

I dug the rust out and it turns out the exhaust has not had the holes for the heat risers put in it when it was made but has the flanges on it. I suppose you get what you pay for. I will have to see if i can make a hole but it is not a straight tube.

I believe you can get electric heaters to go around the manifold for acting like a pre heater when heater risers are either non-existant or the flanges are not present.

I think i recall Joel talking about em' at one stage many moons ago on here ??

Permanent bandage fix?

The holes are in the flanges but not in the pipe. I dont think its meant to be like that.