weber carb problems help needed

[hillelson1]

I always wanted a Porsche with webers and I finally got one. It kind of fell into my lap. I don’t know much about the carbs and I am having a problem. The car pops really bad on start up and when it warms up it clears a little but not much. It sounds like unburned fuel igniting in the exhaust manifold. After the car warmed up I pulled the plugs and the #5 and 6 were black. I changed all the plugs and nothing changed some problems. Any advice would be very helpful. I don’t know were to start. Also I noticed that there are no vacuum lines hooked up to the advance on the distributor. Is this common for carb motors? If it should be hooked up were do the vacuum lines run? I attached a pic of the engine bay it may help you guys not sure but I did it any way. Any help is very appreciative and I and thankful for a website like this.

also the motor is a 2.4 with a 2.7 big bore kit. high duration euro spec cams and high compression heads and pistons

[unimog406]

am i correct in saying those are weber 40ida 3c's?
check your plug wires. also try leaning out those cylinders some [the screw on the bottom with the spring] watch out, they are very sensative
the same sh** was happening to me, turned out my plug wires and ignition system were both shot. if yours is set up the same way mine is, cyls 5 and 6 both run off the same float, if nothing else works , check to be sure that is set right and the needle valve is not sticking. my best bet is its just tuned wrong, but dont listen to me, i still cant get my car to run well...

[T77911S]

sounds like it is lean, without the vacuum hooked up to the dist, the timing at idle will be advanced, (the vacuum retards it). advanced=a lean mixture. timing needs to be retarded (vacuum hooked back up) or you have to richen the mixture, which is a bandaide for the timing problem.

[hillelson1]

cool thanks for the info. how do i know if the floats are set right?
how much should i turn those adjustment screws?
how do i know if my plug wires are any good?

[hillelson1]

also does anyone know where the vaccuum lines run to the distributer?

also one guy says its running rich the other lean i am confused the plugs are black so i think its rich? right?

[JP911]

popping in the carb = lean
popping from the exhaust = rich

To lean the carbs you turn the screw in. Turn by 1/8 increments. But, before you do all of that, do yourself a favor and read this post: Weber rebuild

[2.7RACER]

Since 5 and 6 are both black, this is a great clue.
5 & 6 share the same float bowl. Likely the float is set too high.
The float height is extremely important with webers.
There are guages or a sight glass attached to the bowl to properly set the level.
PMO carbs have a built in glass in which to see at all times what the floats are doing. The folks at PMO knew what they were doing.
With modified engines it will take some work to fine tune the various jet sizes for optimum performance.
This leaves you with 2 choices. Get busy learning about Webers or find someone with the knowledge.
I have a similar engine 2.7L with a solex cam and high comp pistons. The difference is I'm at 5000 ft.
My info is: Mains 140, Idles 45, Airs 200, Emulsions F3, Venturi's 32mm.
While I was optimizing the jets I found new idle jets marked anywhere from 45 to 55 that weren't as marked.
So check the jet sizes to be sure they are as marked.
I'm thinking 33 or 34mm vents might be better. I'll try 'em early next year.
If you are near sea level, I would start out with the following:
Mains 150, Airs 180, idles 50, emulsions F3, and 32mm vents.
Others at your elevation and with the same motor may have dialed in the jets already.
To really get it right, you'll need to check it out on a dyno with someone that know's Webers.
Back to your original question, get the 5 & 6 float set correctly.

[Cordts]

I have webers and recently had the same problem..

After weeks of trying everything else..

I adjusted the timing
Put in new NGK plugs
Put 55's on the idle jet circuit and cleaned out the carbs
Properly adjuste the carbs

And voila! She runs like a champ..

[hillelson1]

cool from what i read so far that seems the best choice to start with. the car is a supposily a retired race car from lime rock and was tuned properly but the owner i guess passed away and it sat for a few years i am thinking the float may be stuck open? what do you guys think? also any ideas how to or if i can hook up the vacuum advance on the distributer?

[unimog406]

in my limited experience, when the float gets stuck open, it just dumps fuel in those cylinders, till they cant run at all. if you just pop off the tops [6 nuts around the velocity stacks, 4 screws in the bottom] then you can get at the needle valve, they're located under the big brass nut. take them out, clean them, blow air through them, see if the one sticks, then switch them. the only other way to get trouble with floats is to have the tab on the float itself bent too far, and this does not very often occur. i can get you a write-up to see how to check them using feeler gauges and a depth gauge. what had happened on my webers, was when they got rebuilt, the guy put in the floats UPSIDE DOWN. yeuch.
there is a way to avoid all this though. sight gagues. instead of paying a million dollars for custom ones, just take some clear tubing [not quite sure what dimension, but small probably about 1/4"]. unplug your fuel pump and run the car till it stops to drain the float bowls. then take out the drain plug on the bowl, put in the tube, and tuck the top end into the hole near the top of the carb. plug in the fuel pump and fill the bowls. I forget the actual measurement for what the level should be [i can check later] but you probably dont have a problem unless it fills all the way up and your float bowls get pressurized. you can do this to all 4 floats at once. one piece of advice. if you stick the tubing too far into the whole, it jams the float down. compare your levels.

[unimog406]

i guess i would add to that advice: if the car has been sitting, or you have never rebuilt the carb, there could be all kinds of junk and crap in there. i reccommend just rebuilding it. its rather intimidating the first time, but it really doesnt need to be. just have a system. start by taking the carb off [undo the throttle linkeage by prying it with a small [8-10 mil] open end]. you can look at some weber books if you have questions, but in general things look unlike other things, so you wont get mixed up. i would say, just take 5&6 apart, and if you have any questions look at 4 to see how it should go together [because you know that cylinder works. hit everything with carb cleaner, and blow compressed air through them. many components have a holder and then the actual jet, even though it looks like one piece, it can be taken apart. blow air through the manifold after everything is off, then reassemble, making sure not to rip the gaskets on your volume control screws [with the springs, grease them before putting them back]
you may also want to compare your two floats next to each other to see if the tabs are bent differently.

once youve done it once, it is not really a big deal.

[hillelson1]

the guy i bought the car from is a porsche mechanic out of ct and he said he rebuilt the carbs for me and that i just needed to do the fine tuning. he told me it just needed the idle mixtures adjusted, but i have a feeling it may be more. but ill look them over i've rebuilt other carbs before i'll have to buy a good book on these is there any out there that you know of?? also any ideas on the distributer?

[kucharskimb]

not to throw a wrench into your troubleshooting, but not all weber castings were drilled the same. on mine, and half of the other pictures i have looked at, 4 and 5 are paired, and 6 is by itself...

i will second that you need to go completely through the setup procedures, and then troubleshoot from that known starting point. picking up halfway down the road is wasted time.

ask me how i know...

[Cordts]

If the guy is a Porsche Mechanic, nd it wa his car, then you should contact him for advice and maybe try to get him to assist,, considering he told you that it was something relatively simple and it may not be..

[unimog406]

its easy to tell if its 4 and 5 or 5 and six. just look at the side, and see where there are holes, but no jets/adjusts.
its possible the guys right, these carbs are very finicky. you could just be a turn off and get all this trouble. these carbs react to even sixteenths of turns suprisingly much.
if you do decide to do a rebuild, write down the position of each mixture adjust, its easiest if you have a starting point

[marlinaness]

Does anybody know where to connect the vacuum to the distributor? I have the same issue with a 72 2.4T.