Drove the 914 to turkey time yesterday, about 50 miles of backroads. Seemed to be runnin' about normal with the usual symphony of only-occasional random backfires and pops. It was, of course, ridiculously fun.

Car sat til I left around 10 PM, and by then it was around 40 degrees outside. Lots of popping and stuttering at part throttle. Full throttle and it was the usual fun excitement.

The ride home on the freeway was unpleasant because the 2.7L doesn't need much throttle to keep my little car moving. Could this just be temperature related? Idle jets sized for Los Angeles (where I bought it.)?

Otherwise I assume I'm looking at checking for gunk in the idle jets, I assume.

This is my first carbed porsche, so I guess it is time to really "grok" them. Is there an obvious "start here carb newbie" direction? Book and/or web site? Googling turns up tons and tons of random stuff.

Thanks.

pretend you have an early 911 and search web acordingly. there are many early 911 triple weber info sites.
yes, I think you idle jets are dirty. this is common. clean them out

Years back... early one morning in the spring I was driving to an AX. Temps were in the mid 40s, I figure. It started running foul. Pulled over to the side of the road & opened the lid. The carbs were icing up. Let it sit (without running) and warm them up for a bit then off we went. Sometimes the isolators work too good,me thinks.

That said, I wouldn't bet against a clogged idle jet. You run on the idles below around 3200-3500rpms.

I could be wrong, but I don't think being 300 miles north of LA is gonna affect the carb jetting. Generally speaking, altitude is measured in feet above sea level, not in miles north (or south) of the place where the jetting was done. Of course, looking at a globe could be confusing, what with north being up and all.

The Cap'n

Cleaned the idle jets with compressed air and carb cleaner, took it out and got it good and hot.. no dice. Still popping and sad at part throttle.

What's my next most intrusive cleaning option? and/or troubleshooting? Some of the "o" rings are a bit chewed up on the idle jets, but squirting some cleaner at them while running didn't seem to have any impact.

Rain coming, so at least I won't be sad I can't go drive it.

Your first post told me it wasn't running right from the git go....no farting/popping allowed when warm.

I would suggest you go buy yourself a syncrometer (if you don't have one) then go to the bird board & search for Weber tuning. There are some good ones there & some kinda shakey so don't settle for just the first one that pops up....do some comparison shopping. I'm way to lazy to type out how to do the Weber dance but it has been done there.

I will tell ya that Webers NEED an MSD set up (or something similar) to perform properly these days ......but first, learn the dance, get em' right and go from there.

Webers are also intolerant of mis-set float levels, excessive pressures, improper jetting, and vacumm leaks.

It took me 6 mos to finger out how to get everything right on my 2.7L....but I'm kinda slow & was on my own. You aren't.

Gud luck.

I've spent the last 24 hours reading tons of threads, ordered a couple of books and the synchrometer tool.

So I'll go into "larval digestion mode" and come back later.

Thanks for the encouragement.

Get the float setting tool while you're at it....cheep enuff.

No need to eat magots that I can see.

Pulled and clean the idle jets.. no change.

Pulled the mixture needles AND idle jets, blasted some air and carb cleaner through, and replaced the deteriorated O-rings with some new Viton size 008 o-rings.

SUCCESS!

At least, it runs as well as it did before.. I will still do the full weber dance, because I am suspicious of the mixture screw settings. They varied from 2+ turns out to 3/4 turn out. I put them back where they were for now.

Ok, I bought 5 books and googled a lot.. bought the synchrometer (hereafter called "the snail" because synchrometer is hard to type.)

I took a whack at adjusting today, and some oddities I don't understand:

Many procedures say to start with the mixture screws 5.5 turns out. My car won't start/run 5.5 turns out. So I started at 3.5 turns. What's the logic of starting at 5.5 turns out?

I did several rounds of snail/idle level screw/mixture screw/air correction going 'round n 'round until things seemed pretty well set EXCEPT...

Two of the idle mixture screws (#5 and #6) did not seem to have much impact on idle quality. If it was roughly 1 turn out it would start bogging a bit.. but between 1 and 2 turns it didn't seem to have any impact, other than popping up through the carb.

I left those out a bit so I wasn't getting popping (well beyond where it was impacting idle.) I am, of course, terrified of running lean.

After all that, I drove it and still got some backfires. Seems to idle smoother though.

Any other thoughts or tips?

Thanks.

You seem to be getting on the right track. Several things to consider to help with carbs that were never made to use the gas we try to suck through them now: First is to drive the car every few days and get it hot so the carbs will keep clean. Otherwise you'll get that snot stuff inside. Noew even race gas can develop that stuff if allowed to sit. Next to to use some Marvel Mystery Oil now and then to add some lube and help keep them clean. Next is to make sure there are no air leaks such as base gaskets, insulator blocks, cracks in the intake manifolds (especially if they have been ported and modified) and as you saw those pesky o-rings. If one cylinder seems off from all the others when you are adjusting or checking then there is something wrong, usually an air leak. Finally budget the cost every 2 to 3 years to have the folks at Pierce Manifolds do a full blown overhaul which is not cheap but they will be like fine running Rolex watches when they get done!

If you have radical cams such as 908s or other wild high revving grinds, the carbs will pop and thet is due to the wild cam overlap that is used. To cure this many race cars will idle at 1200 to 1400 RPMs which while irritating on a street car is okay for a racer.

Before you get too deep into the carb settings, when was the last time your valves were adjusted?

If your valves need adjusting, nothing you do to the carbs will ever get it "right" ...

I try to drive it to full operating temperature at least once/week, plus I run Seafoam in the gas which does seem to help.

No cylinder was off more than 1 on the airflow meter, but that may have been already compensated for. I am suspicious of the 2 cylinders that don't respond much to the mixture screw - maybe I'll blow some carb cleaner or propane around there and see if something is leaking air.

Valves & timing all checked 2K miles ago, pretty confident those are good. Also running Crane XR700 electronic ignition.

Just drove it a bunch more, and it is definitely much better when warmed up than it was before, or maybe it is just the placebo effect of spending 2 hours turning screws 1/8 at a time.

Do you mean 5.5 half turns out or 5.5 full turns?

It's 5 HALF turns out from all the way in (gently seating with 2 fingers on the screw driver).

Oops, that may have been it. That's what I get for reading 5 books.

In any case, I ended up around 2.5 full turns, so one way or another I'm in the ballpark.

The inside of the engine doesn't care how many turns out the idle screws are, it cares if the mixture is right. There will be differences between cylinders. 2 1/2 turns is a good starting point but once you've started it you need to adjust the mixture. Turn each screw in 1/8 turn at a time until it begins to fall on it's face, screw it out again until it purrs, plus 1/8 turn. You're a beginner, that 1/8 turn extra may save you a ton of money, pistons aren't cheap.
Any cylinder that doesn't respond to the mixture screw has a problem, usually a clogged idle jet, sometimes O rings as you've learned. All those O rings have to be in good shape. It's not uncommon to foul idle jets several times in a row because there's probably more than one little piece of junk floating around in there.

A really important tool that everyone one should have is a wideband O2 meter. Damn cheap insurance when messing with a high buck engine.

You can get a DIY JAW kit for under $100 and an entry level Innovate is less than $200 off of ebay. I know instantly if my can is running lean and I can jet/adjust carbs on an engine to within a frogs ass hair in no time flat.

Hell of a lot cheaper than a hole in a slug.

Here's a site I ran across that may help you....I also have the PMO instructions that came with my carbs....As this site suggests, turn all the idle air correction screws in until they hit their seats and lock them down....PMO suggests 1/8 turn out to start...I had better luck with them all in, then taking the barrel that is pulling the most, using "snail", and match others to it opening the air screws...that helped mine run better....also, lightly oil the mixture screw "O" rings every time they are re-installed....Hope this site helps.... http://www.huskyclub.com/porsche40ida3cweber.html

Thanks everyone for the tips - I took the car out on my official test drive loop (~40 miles, stevens creek canyon-highway 9-skyline-84-280 for the bay area locals) this morning and it is much much improved.

I only THINK I heard a couple of pops up the intake, and a few minor backfires on deceleration going downhill. Actually I think it is less chatty than my old '74 2.0 with FI and my old '83 911SC with CIS.

I am still going to give it one more round on the mixture screws, after cleaning the idle jets & passages with air and carb cleaner on the 2 cylinders that didn't respond very granularly and then using the "higher RPM" method recommended in a few procedures (1400-1800 RPM instead of barely-idling) - Thanks PK for your detailed procedure.

Some other random things noted here:
Air correction screws - I have one bottomed on each carb, the rest adjusted to equalize.
O-rings - I replaced them all with Viton. CA gasoline seems to turn the rubber ones to mush.

Thanks again everyone.

Side to side balance is adjusted with the down link on the carb linkage. After the end to end balance is correct I use the pass side for a base, then adjust the other side to it using the barrel nut...it expands or contracts the down link when turned. I back off the driver's side idle adjuster and let the linkage "rest" on the pass side only.
This gets the slop out of the linkage. When right, your "snail" should read the same
on all throats from idle till it goes off the scale.

That takes care of balance. Then it's time to do the mixture screws again.....then check balance....again. Once done, it will stay set for a years....baring catastrophe. The Tango is a piece of cake by comparison

Ok, this reply made me laugh, thanks Cap'n!

Dem, I'm a little late here.

I struggled with my IDA3C carbs that popped and spit and would never quite run right. This went on for years. I cleaned and rebuilt them several times, including twice under the watchful eye of skilled 914world members.

Finally after frustration that spanned years, I sent them off to Oregon for a complete overhaul. Actually, remanufacture is more descriptive to what happened to them. No leaky throttle shaft bushings. All the tolerances very tight. Cosmetically, they look new.

If your shafts are severely worn, no amount of valve adjusting, timing setting, or carb adjustments are going to make up for it.

best of luck.

One thing I learned about keeping the carbs clean is that you have to make sure you have good air filtration. Some say to use a film of grease between the air filter and air cleaner. I have heard that k&n air filters dont keep carbs clean enough (yet I still run them ). Also run plenty of fuel filters.