Carpokes Porsche Forum

As an old schooler who has been a 914 enthusiast since the early 70s, I tend to prefer visually stock iterations of the car (with a few exceptions) and all of my previous 914s have been stock. Under the bonnet I'm generally fine with just about anything that anyone wants to do to increase basic horsepower on their crate (but I draw the line at V-8 conversions since far too many tend to be a bit rushed and amateurish in their execution), I also tend to prefer FI fuel systems, meaning well maintained original 914 FI plumbing. All of my other 914-4s have had their standard, OEM FI. [My '70 vintage 914-6 had, naturally an OEM carb-equipped engine, but like a damn fuel (sic) I rashly sold that beautiful specimen some years ago for a pittance!]

My present 914 has a flat-four, 2.0 liter engine, but it had been converted to a twin, dual-throat Weber 40-IDF by its prior owner. Throughout all of my 914 owning years I have heard the oft-repeated admonishment, "Leave the car FI'd: don't convert it to carbs" repeated by Those Who Know, since older 914s with original injected fuel systems tend to be problematic and in poor condition (due to wear, aging and lack of proper engine maintenance over the years) and tricky to keep the OEM FI operating properly.

There are, of course two equally valid opinions on this contention but since I no longer have a choice in the matter, I am now faced with gaining the necessary Weber carb knowledge and acumen to properly adjust and tune my car's 40mm IDFs. I even have the Haynes Weber and Weber/Dellorto carburetor tech books in my Porsche library. That said, they contain a hell of a lot of precise material and detailed information on proper carburetor adjustment (too much!) and it's all a bit overwhelming for someone like me, who has had to cope with 'undiagnosed ADD' since childhood. If you need some clarification on this last point, let me explain that ADD makes intense concentration and single-minded focus for sustained periods quite challenging! Ditto for anything requiring prolonged study, such as educational courses and programs (but I've made it this far, despite a lot of lost sleep and chronic mental fuzz throughout my degree programs and writing efforts).

So there it is. I suppose I'm asking anyone out there who is a carburetor whiz of the Weber/Dellorto kind to kindly share some opinions on what I should do to be assured my car's carbs are spot-on-the-mark, adjustment-wise. I am, as a VW owner past & present, already somewhat familiar with such beasts as the SOLEX 30PICT carb, but Webers and Dellortos are a whole new type of fish in my frying pan.

My car seems to have a mild and intermittent tendency to experience pops and slight backfiring after the car is warmed up and moving at close to speed (say on a highway, accelerating to about 70 or so). Given what little I know about carbs, this suggests to me that the carbs may be running a bit lean...that the idle and/or main fuel jets may be slightly too small, requiring a larger set of jets for a slightly richer fuel mixture. My car's plugs do not appear to have excessive carbon deposits on the tip, but I haven't yet pulled the idle and main fuel jets to note what size they are.

Given all of the above, and the fact that the car has recently had a valve adjust and 'supposed' tune-up at my local Porsche shop, I would welcome any shared insights on how best to go about further 'drilling down' into this minor but irritating anomaly, so as to make running operation smoother.

I'm sure some will say "If you aren't satisfied with how your carbs are presently adjusted, get your shop to take a look and make any required adjustments." Easily understood advice, but I thought that instruction was complied-with on my last visit (perhaps it was not adequately done). I wish I knew a good local shop that could do carb adjustments on Weber IDFs on the car, but I am a bit flummoxed in trying to find a shop anyone recommends for this purpose. Another small problem is that although we have several Porsche-specialist shops in town (who will work on 356s, with their similar carb set-ups), these shops deign to NOT work on 914s! The old '914 bastard child/almost a REAL Porsche but not quite' syndrome again, we 914 owners have always had to contend with, sadly.

Anyway, feel free to pitch any ideas this way, concerning the subject. I'd be grateful for any inputs by those with real knowledge and experience in coaxing Webers to perform properly (whether on 356s or on 914s! Thanks, folks!

914PUTSCH

[My '70 vintage 914-6 had, naturally an OEM carb-equipped engine, but like a damn fuel (sic) I rashly sold that beautiful specimen some years ago for a pittance!]

Don't feel bad. I had an Italian car that I bought from and sold to (in that order) the same person for the same price as he had put a lot of time and energy into the car so I looked at the transaction as more of a paid borrowing of the car. I got to enjoy it for a several years so no harm no foul......years after I sold it back to him, I saw it on a dealer site for 20+ times the amount that exchanged between us....I had another Italian species that I was completely redoing, ran out of time and space, and sold it to a friends brother at $0.15 on the dollar.....it went to more skilled and mature hands....C'est La Vie!
I've never really looked at my interesting vehicles as investments but a purchase to enjoy....they are not a business decision but a decision of the heart....
You probably sold the 914-6 for the going price at the time.....who knew their value would expand at such a level.....

@914PUTSCH

Enjoyed the read! Excellent! However, I cannot assist in your quest for answers since I'm in a "let someone else handle this for me" kind of life.

BUT, I love 914s very much! I'd have one if I hadn't become quite risk-averse to working on vehicles that I haven't a clue how to dig into. I blame that reluctance on many other things that have little to do with an acknowledged lack of skill, such as non-normal/non-stock cars over the past decade+ such as a C2 Corvette roadster, a C6 Corvette race car, an ancient M35A2 deuce-and-a-half (an RVN vet 1967 Kaiser that I had no idea what to do with), etc.

I am, however, am hoping for only the best for your little darlin'! Someone here will have a bit of knowledge to share, I'm sure.

(If no reply, we'll give your post a bump!)

@914PUTSCH
Hello,
I am a certified Carb nerd! Dellorto is my favorite flavor but Webers will do as well. I do have some thoughts. First know that these carbs have three circuits, Idle, cruise and main. The mixture screws control the idle, the idle jets control the cruise and the main jets control the high load areas. Your job is to determine where it is not running right and adjust the area of concern. Popping at idle means it is lean, you need to unscrew the mixture screw a bit till the popping goes away for example.

One thing that has helped me a ton is to install a wideband oxygen sensor and gauge so you can see what the engine is doing. You can get them for sub $200, AEM and Innovate are good choices. You will need a bung welded into your exhaust and even if you do a temporary install just so you can drive around and see what is happening will be very insightful.

Let me know as you get to specifics.

Jeremy

A big second on the wideband suggestion. I put one in my old CIS-injected Mercedes and was able to make it purr (and pass smog) with a fraction of the trial and error, and effort, of doing it without one. I take it out most of the time and really just use it for smog tests these days. As for carburetors, I literally haven't touched one in 45 years, so I'm not much help there. For inspiration, here's a picture of how I installed the wideband in the old Mercedes.

J-Dub wrote: Wed Nov 06, 2024 5:16 pm @914PUTSCH
Hello,
I am a certified Carb nerd! Dellorto is my favorite flavor but Webers will do as well. I do have some thoughts. First know that these carbs have three circuits, Idle, cruise and main. The mixture screws control the idle, the idle jets control the cruise and the main jets control the high load areas. Your job is to determine where it is not running right and adjust the area of concern. Popping at idle means it is lean, you need to unscrew the mixture screw a bit till the popping goes away for example.

One thing that has helped me a ton is to install a wideband oxygen sensor and gauge so you can see what the engine is doing. You can get them for sub $200, AEM and Innovate are good choices. You will need a bung welded into your exhaust and even if you do a temporary install just so you can drive around and see what is happening will be very insightful.

Let me know as you get to specifics.

Jeremy

G'day Jeremy and thanks a heap for those insights into the mysteries of these carbs. As previously stated, supported by your remarks, I suspect a lean fuel scenario, so I will try the tweaks you suggest and see what transpires in the immediate short term.The idea of adding an 02 sensing system is a good one. That's something that wouldn't have normally occurred to me in approaching this problem from my stance of having deficit carb expertise. That should provide exactly the sort of informational feedback I need in the longer term. Most appreciated! Cheers, mate!

Tom wrote: Wed Nov 06, 2024 5:59 pm A big second on the wideband suggestion. I put one in my old CIS-injected Mercedes and was able to make it purr (and pass smog) with a fraction of the trial and error, and effort, of doing it without one. I take it out most of the time and really just use it for smog tests these days. As for carburetors, I literally haven't touched one in 45 years, so I'm not much help there. For inspiration, here's a picture of how I installed the wideband in the old Mercedes.

That's a great image, Tom of your install on the Merc and also most helpful. Back in my 'Fix-It-Again-Tony' days, I used to absolutely hate air-injector and 02 sensor installations, given that they worked so drastically against me at smog-time, here in Californica (sic), but in a purely helpful diagnostic context they're pure genius! Being able to make my Jezibel purr smoothly, rather than sound like a bowl of SNAP-CRACKLE-POP cereal would be Heaven-sent! Vielen Dank!

Subsequent to both Tom's and J-Dub's inputs on carburetor adjustment possible 'fixes', if the idea of fabricating a commoniser pipe with a sensor fitment port ('bung') is a bit too much work, there are some innovative 'clamp-on' type-02 sensor bungs that require simply a hole drilled into an existing pipe and fitment of a stainless steel 'clamp-on' bung. Since all such 02 sensor bungs are of an automotive standard size, such a quick-fix approach will accommodate any wide-spectrum 02 exhaust gas sensor you care to use/install. One such accessory may be found here: https://www.glowshiftdirect.com/1-3-4-2 ... g-adapter/ and it is a reasonably priced thingie, too. Then, you may install your 02 sensor of choice, hook it up to a gauge (mounting it remotely, such as on the car's instrument panel, if preferred) and Bob's your Auto Mechanic! (NOTE: for the non-Anglos amongst us, look up 'Bob's your uncle' on WIKI, if unfamiliar with this term).

I've seen those advertised and assume they work. They may leak a tiny bit, but probably no harm done. Assuming you have no catalytic converters or thermal reactor thingies, and no exhaust leaks, you can also just put the sensor up the tailpipe -- like they do on smog tests -- for a 'good enough' reading. A coat hanger could probably do the trick, but they also make fancy tailpipe fixtures like the one below. No need to make any changes to the exhaust that way.

Tom wrote: Thu Nov 07, 2024 9:42 am I've seen those advertised and assume they work. They may leak a tiny bit, but probably no harm done. Assuming you have no catalytic converters or thermal reactor thingies, and no exhaust leaks, you can also just put the sensor up the tailpipe -- like they do on smog tests -- for a 'good enough' reading. A coat hanger could probably do the trick, but they also make fancy tailpipe fixtures like the one below. No need to make any changes to the exhaust that way.


o2 hanger thing.jpg

Good to know about, Tom. Beats drilling a hope in some exhaust pipe and clamping a bung on. Thanks. Just hope my Jezibel doesn't resent having something gracelessly shoved up her...er, ahem..posterior extremity! Gives a whole new meaning to the expression 'bung hole.' Jez is already somewhat resentful of my occasional reference to her having an air-sucker tucked away, up that extremity, LoL, but I am guessing I'm not the only 914 owner who has a sensitive car!