I was terrified. Flashbacks from my childhood haunted me. My mother would bundle us up for school in the early January winters in Minnesota. My brother insisted on riding his flippin Scorpion snowmobile. I was forced to put my brand new gloves over the carb intake so he could load it up with fuel and get it to fire. That thing freaked me out! And, ruined my gloves…

Now, 20 years later my carbs are acting up on my 69 Porsche 912. Was I afraid? Yeah. I don’t know why but carbs kinda scare me. I refuse to take it in to a shop and pay through my nose to have somebody else spend 30 minutes on my car doing a temp fix.  Although it took me ALOT longer than 30 minutes there’s nothing better than the feeling you get when the engine is back into great running order. Symptoms- I brought the car down from MN January 3rd. The car was running excellent for the first few days then suddenly, I was driving over a bridge and heard a backfire. Black smoke billowed out of the tail pipe for a few seconds and then the car would not keep a steady throttle feel. It would surge and then stumble, pop and boom. As I’ve been learning more about carbs I knew certain sounds were the carbs getting starved of fuel and then BOOM, they loaded up and exploded. I’m running dual Weber 40IDF Made in Spain model carbs on the 4 cylinder Porsche motor. Diagnosis 1- Carbs: First off remove your air cleaners/filters. Be careful not to drop anything into the intakes (the holes ontop of the carbs). These are where your engine sucks in filtered air to mix with the fuel in the carb and send it into the intake to ignite in the cumbustion chamber via the spark plug! Once you’ve got the aircleaners off you’ll see two brass flat head bolts ontop of the carb. Don’t worry. These are threaded in all the way and are not an adjustable device in regard to tightening and loosening. These are #47-50 on the Diagram below (click to enlarge). This is commonly called the main jet. The jet itself can be changed out but to my understanding that’s not a concern unless you’re setting up new carbs or re-jetting current ones.

Once you’ve unscrewed #50 pull it straight up and out. You will see the small ports that could possibly be plugged with gunk. You can pull the emulsion tube (upper part) apart from the lower parts and blow them out with compressed air or carb cleaner. Once you’ve confirmed these are clean you can reinstall. Again, don’t drop anything into those holes! Now look at #22-24. These are the idle jets. The brown line I drew in show’s where the idle jets thread into the carb. When you remove these be careful as there is one small O-ring that could either come out with the jet or stay in the hole or… fall down into the abyss. So watch it closely. I’d remove one close to you first so you can see what I mean. Then you’ll know what to look for on the back where it’s dark and hard to see. Procedure for cleaning the idle jets is the same as the main jets. They pull apart and you can see how easy it would be to change out your jets for different sizes on the Webers. They are truly a tuner friendly carb. The Maestro states it takes almost 2 hours to change jets in Solex’s! I’ve never had a pair so I wouldn’t know! Here’s a pic with the Idle Jet pointed out. It’s the top orange arrow! The bottom arrow is the pump rod. Don’t touch it. There are 2 idle jet screw’s like the one pointed out in this picture. The other is directly behind that hex head you see. It’s tucked in back there basically symmetrical to the front so feel around for it. The idle jet is where I found a small piece of rubber similar to a fingernail clipping. This was completely restricting fuel flow to the #1 cylinder! Once I got that cleared I had to re-adjust the idle and mixture settings.

I also blew out the fuel lines with carb cleaner. Start by having a small pan or empty water bottle along with some rags/towels handy in the engine bay. I remove the fuel line going into the pump first. Most of the time there’s a filter inline with this hose. Unscrew the clamp and have that bottle ready to set the line into to catch the fuel that comes out.  You can let it sit in the bottle while you remove the next hose inline which is the outgoing side of the pump. This one will have fuel in it too so be ready to catch it. This line should go up to a T located somewhere behind the fan shroud. Now’s a good time to check and see that you have a good T (metal not plastic) in place. The fuel line runs behind the carbs and into them on the back side. It’s easiest to access these with the air cleaners off. Once you have your lines free you can inspect them to see if there are any cracks or weathering. I blast them out with carb cleaner into a clean bottle. See if anything comes out. The one going back up to the tank I blast out too. You’ll hear it sort of Gurgle up in the tank when you spray carb cleaner into it. I drop about 8oz of K100 fuel treatment into the tank after this. K100 is the best stuff I’ve found and believe me I’ve tried alot. Being in the tank cleaning business (large scale 8k gallon +) I’ve had my share of additives thrown at me. I’ve tested alot of them and K100 has proven to be good. You can buy it straight from their website.

Once I’d done all of this the left bank still wouldn’t fire. I decided to remove the carb which is held on by 4 13mm nuts. If you haven’t noticed by now there is ALOT you can do to your 912 with a 13mm and 10mm wrench and a flat head screwdriver! Well, my carb wasn’t being held on by 4 nuts. One was gone! Since I had already used my magical magnet to fish out my bonus prizes from the lower quadrants of the engine tin I knew I wouldn’t find it floating around in there. But it had been a while since I went fishing and I couldn’t remember exactly what I caught. Since I was working on the car at my dads place I didn’t have access to my stash of stuff I’ve found in 912 engine bays. The VW shop down the street had some really neat shiny 13mm nuts and washers he spotted me along with the previously mentioned spark plugs! I cleaned up the carb and re-installed it using the new nut/washer. The nuts that were in place when I removed the carb were definitely not tight, hardly snug. This could’ve been my problem!

The nut

And here are the miscellaneous items I’ve pulled out with my magnet. The two shiny nuts at right are the replacement nuts the VW shop gave me. Luckily when I got home I found the 13mm nut that had fallen off the carb/manifold mount in my pile! Thank God because I didn’t want those shiny things glaring in my eyes when I tried to work on my car.

Diagnosis 2- Electrical: So I thought I tracked down the problem with cleaning out the carbs which eventually did end it. But, Intermittently I was having misfiring on the left bank, both cylinders!? After going through the fuel issues I realized it must be electrical. I put in new plugs which definitely helped but it still had an intermittent hesitation and backfire. I cleaned the connections on the wires and still had a problem. I decided to swap out the ignition coil from my bus and see what happened. At the same time I put in K100 fuel treatment and checked the valve adjustments (which were good) before starting the car. Good thing- the misfire was GONE! Bad thing- I did 3 things and I’m not sure which one fixed it? I ended up ordering a set of new wires, distributor cap, coil and rotor. The cap and rotor don’t fit my Bosch 050 Brazilian distributor… They’re too big? Anyway, Problem fixed. I got the idle set in and it’s running VERY well. Dave’s bringing over his new Syncrometer for us to really get the carbs dialed in. Here’s a video of the car running now.

Tags | 356, 912 Weber Carb, Carburetor Cleaning, Jet Cleaning, Porsche, Problem