Weber carb woes

[big_wig_074]

I have just spent all day fitting a Weber dmtl to the Rocco and all was going well until, after five minutes of driving, the car started spluttering and lost all power, then died. I got under the bonnet, fiddled a bit with the 2 adjustments, got it just about going then went home where I used some instant gasket to make sure no air leaks, then I took it out again, all Good for 5-10 minutes then again, lost all power. When it does this I can limp it home on the choke but what's going on? I can't follow the Weber set up instructions as it just won't idle low enough. It had always wanted to idle at 1000-1100, even on the pierburg but the Weber was supposed to be an upgrade, it was running better on my bodged together manual choke pierburg, at least it would get to work and back every day and run the same all the time on that. Any clues? Thanks

[james butler]

sounds like crud in the jets or the jets are loose.
take the airbox off and you will see 4 brass screws on the top in the centre of the carb.
unscrew them one by one strip and clean then replace them in EXACTLY the same hole you got them from.
then you will need to set up the carb again.

[bengould]

First of all, the weber isn't an upgrade. It is a simpler carb and easier to set up, not better.
Having said that a well set up weber will run a lot better than a tired worn out pierburg.

Did you buy the weber new or 2nd hand? If new did you buy the right "kit" for your car i.e. correctly jetted for your engine size and with all the correct adapters to fit the standard air box.

Are you using the standard air box or a "bolt on" filter? If your using a bolt on, don't. The standard air box with the warm air flap will stop the carb freezing, it is still cold enough for this to happen and possibly is what you are suffering from.

From the sound of what you have described I would say, if it's not freezing up, one of your jets is getting blocked by rust from the tank.
You can get the jets out easily there is a gap between the 2 halves of the carb that they just unscrew from. Even if you cant see anything in them blow through them hard to clear anything.

Take off the inspection panel under the back seat and have a look in the tank. If there are any bits in there at all, stick a magnet in there to catch them, replace the fuel filter and also put a temporary one after the swirl pot on the engine to catch as much of the crap from the tank as possible.

If there is anything in the tank it is likely to be from the filler neck. If you haven't replaced this already, do it.


Before I swapped my engine I had a weber and found it ran much better without the swirl pot. I used a t-piece with a welding tip screwed into the return to restrict the flow back to the tank a bit.

As far as your idle issues if you can't get it down it would suggest the idle jet is too big. Check the size on the chart on the back page of the manual and it will tell you what size all of the jets need to be. Even if it was supplied new as the right kit for your car I would double check all the jets just to make sure.

Good luck, hope you get it running.

Ben.

[james butler]

looks like this from the top so you can see the 4 brass screws i told you about.
https://www.google.com/search?q=weber+j ... KZw-9rM%3A

these carbs are super sensitive to dirt and debris blocking the jets but are easy to get to and clean.

[Nate]

There is also a filter on the inlet to the carb, which most people neglect at service. 17mm nut directly under the inlet. Be prepared for some slight fuel escape when you remove it. Inside there is a small gauze filter. Clean carefully with carb cleaner spray then refit. If there is any white furry stuff in there, it's a pointer towards water in the fuel system

[big_wig_074]

its a used carb, came with an adaptor plate, but only one gasket, under the plate to the manifold, I used instant gasket paste on top (im thinking this is my problem)I took out the 4 jet screws on top one at a time and got carb cleaner in each hole and the emulsion tubes etc, although one of the outer jet screws was difficult to get back in, the jet seemed to have fallen over in the hole,it took a few tries to centre it to allow the screw back in, could this have damaged it?im planning to go to fastroadcars in Newport today after work to get a gasket and potentially some new jets too.
I only meant its an upgrade as in its supposed to be more reliable, which is the important thing, and it will be running the standard airbox

[big_wig_074]

bit worried ive damaged something now. and have I read correctly that some people are using cereal box to make gaskets for the carb flange? just a dry bit of card cut to size?

[big_wig_074]

Ok, special k box cut to size, jets removed and cleaned with a sewing needle and carb cleaner, advance retarded a little bit and she is running like a beauty!!! Thanks for all the help. I hate unanswered questions in forums, so thought I'd reply with how it went.

[big_wig_074]

well,it seems I solve one problem, only to be presented with another!!!!!
now I can get the car to idle and run ok with the special k gasket, MOST of the time! but ive had to richen the mixture up MASSIVELY! the mixture screw is out about 4 turns, but doesn't seem to make any difference to the idle speed from 2 turns onwards. however, it runs far too lean at this point, causing the car to eventually run like a bag of spanners until I richen it up again or use the choke, but then it has a 3000rpm idle!. Also, I have now noticed the car hits a brick wall at 4000rpm, in any gear.which im guessing is fuel starvation? ive had the top of the tank off and the fuel looks really clear and clean, the filler neck looks fine, there was a little bit of crap in the plastic fuel pick up pipe but ive blown that out.the fuel filter is also clean and clear, fairly new too, I blew through that yesterday, no issues.theres no pump in the tank is there?just the level indicator. im clutching at straws now. ill drive the car and all is well, I give it back to my mrs and she drives to work, it loses all power and struggles to drive!!!
ive ordered a new gasket from fast road cars now, so ill try that, ill also reinstate the fuel separator and put a restrictor of some description in the return line. then I suppose its onto new fuel lines?when its running and I have it set up rich it will run ok up to 4000rpm, then it falls flat on its face, the power just stops, but the engine doesn't die, all the vac lines seem ok, I have played a little bit with the timing but its where its happiest at idle. could this now be a carb AND ignition problem?

[Nate]

Have you used a logical approach to getting it running right, or just twiddled things to see what happens?

[big_wig_074]

Nate
the jets are all correct, ive checked and rechecked, ive set the base idle mixture at 1.5 turns out from fully in (out seems to richen the mixture?) then I let it warm up. I then turn the mixture screw anti clockwise until it stops changing the idle, then another 1/4 turn, then I set the idle speed at approx. 900-1000rpm. it will then idle with a very slight lump,so slight that the rev counter stays still, but the back box has a slight blow so it could be related to that. I then take it out for a drive, it all seems ok at low revs (sub 4000rpm), but when you hit 4000rpm its as if someone has covered the top of the carb with a rag! just no power at all!
I have driven the thing again and again, checking the plugs, readjusting base mixture, drive again, check plugs, repeat, repeat. and it will all seem to be spot on, then ill take it out again and it will fall flat on its face again at 4000rpm.
I had it working yesterday through to 5000rpm where it felt a little flat, I made a tiny adjustment and suddenly the 4000rpm limiter is back, and no amount of readjustment will bring it back!
the plugs are now mainly black with a white tip on the end of the electrodes so theyre ok. it was driving fine at low engine speeds yesterday, but im waiting for a call later from my mrs where she will no doubt tell me its driving like crap again!
when I initially start the car ill set the idle, then as it warms up it will raise about 1-200 rpm,then I readjust, it warms a little more, back up again, we are talking 1200 rm vs 1000rpm. is this right?i have to keep retuning it down until its warm, then I can start doing what I said above.
starting to think maybe the dizzy is crap? or ive got a vacuum leak that's nearly undetectable but is enough to throw things off?i have new or nearly new vacuum lines everywhere, im running direct from carb to dizzy too so I can discount the brake vacuum line.
hmmmm....puzzling

[Nate]

Spray carb cleaner over all vac lines and gaskets while engine is running, listen for the engine note changing. It will complain if it sucks in carb cleaner.

Black plugs doesn't sound right? Should be a sort of sandy colour http://www.v6z24.com/mods/howto/images/ ... lugs19.jpg

Part of me is wondering if you scratched a jet when you poked them out with the needle. But I'm not convinced on that one yet.

Have you got a rotor arm with the built in speed limiter? Could be the spring gone soft in that so it's killing the spark too early.

For checking the ignition timing, line up the notch on the crank pulley with the little pointer. You should then see the rotor arm roughly lines up with the little notch in the rim of the dizzy body. From here, I'd recommend the advance timing until it pinks under load, then back it off a touch method.

Also, if you've got a vacuum gauge, stick that on it and see if it gives you any pointers...

[big_wig_074]

haven't got a vacuum gauge annoyingly, timing was set by the mark and pointing the rotor arm at cylinder 1, then rotating the dizzy left to right to where it idles nicely, and leaving it in the middle there. this worked ok with the old pierburg.

[big_wig_074]

right, I thought id put this to bed, it seems to be running right consistently nowadays! I stripped the carb and cleaned it out completely, fitted a new gasket set and filters etc.. and also adjusted the float level. carb cleaner, toothbrush, lots of scrubbing and rinsing.thanks for all the help