Printable Version of Topic

Posted by: Next GenRacing Sep 6 2004, 03:50 PM

Okay i have been working on my dads 914 for some time now, it has a freashly rebuilt motor, it ran good for about a year after the rebuild. but now it wont start, i suspected air flow meter/sensor. replaced it w/ the same symptoms. it wont start unless the flapper thing on the inside is like half way pushed in. then it will run while i hold the flapper to keep the a/f ratio's happy but when i let go it dies instantly. i have been through it many times w/ no luck. i am contemplating just swapping to a carb setup. i have seen numerous 914's w/ carbs on them, but it always seemed kinda stupid to put a carb on a car that was fuel injected.

also what kind of costs am i looking at to do a complete RELIABLE conversion?
also is there any performance gain to doing this?

just some info on pros and cons of doing the swap would be nice as well as anyhelp w/ the problem i am having cause that would definatly be the best solution

sorry if i am rambling
Danny

Posted by: Next GenRacing Sep 6 2004, 03:56 PM

oh yeah, it doesn't have any intake leaks or low fuel pressure, it will idle fine if i disconnect the plug that goes into the mass airflow meter. also it is a 75 1.8l

thanks again, and let me know if you need any extra info i will be happy to find it out if i dont already have it
Danny

Posted by: jr91472 Sep 6 2004, 04:00 PM

this is gonna be a great thread!!! The bullets will be flyin

Posted by: jr91472 Sep 6 2004, 04:21 PM

One thing I will offer is that switching to carbs is not as easy as pulling off the FI and bolting on a carb. Performance will suffer unless a "carb friendly" cam is installed as well.

I think most here will tell you the FI is superior to carb (period). I switched over carbs many years ago when my FI harness desintegrated in my hands during a engine rebuild. I have been completely happy with the setup.

IMO

Posted by: lapuwali Sep 6 2004, 05:08 PM

Sounds like you have L-Jet. This injection system was fit to MILLIONS (literally) of cars and has proven to be very reliable. There are a great many people out there that can offer all kinds of advice on exactly how to diagnose and fix the system. It's not particularly specific to the 914. As for your specific problem, I'd start to isolate the wires that lead to the airflow meter, since you say the car will run w/o it. There's a switch in there that's supposed to cut the fuel pump when the flapper is completely closed. Try jumpering the fuel pump to run straight off switched +12 and see if that clears it up. If so, your problem is somewhere in the circuitry connected to that switch.

Swapping to carbs, honestly, just trades one set of problems for another. Search on this board and look for all of the people having problems with getting their carbs working properly. If you bother to learn how to properly diagnose the L-Jet system, you'll be able to fix it w/o the expense of the carb swap (which can be considerable). Carbs on the 914, even very well set up, also give really crappy gas mileage (like 8-12mpg less than a functioning EFI 914 gets). The normally available carbs have no choke circuits, so cold starts (and by cold, I mean engine cold, not cold outside) are more of a hassle, and warm-up idle control has to be done with your foot. I have carbs on my car, and I'm switching back to EFI as soon as I can make it happen.

Posted by: rhodyguy Sep 7 2004, 08:53 AM

when the engine is cold, do you push the gas pedal all the way to the floor and then release it, before you try to start it?

kevin

Posted by: Jake Raby Sep 7 2004, 09:53 AM

The post concerning carbs getting less gas mileage than EFI is too broad and generalized. I get the same fuel economy with my EMS system as I got with my Dual Webers.

The only problem with carbs is that few people really understand them, and even fewer know how to tune them correctly.

The reason there are so many issues with the carbs on the engines on this site is that most were never set up specifically for the engine thay are installed on, and even fewer are running at full capability.

I went 59,000 miles with my carbs on the 912E before I switched to the EMS. I had one dirty idle jet and synched the carbs twice.

D Jet, and L jet are my two least favorite systems because I have seen somany issues with them that have literally killed engines. The Kit Carlson EMS on my 912 now runs many stock components(Injectors, throttle body, plenum, runners) and has performed great. A stock system (D jet or L jet) would not feed this engine at all! It was built for carbs!

Don't slam carbs until you figure out the intricate works and manipulate them to do what you want. I grew up working on carbs and old school point style dizzys, so carbs to me are like cake walk.

Posted by: SirAndy Sep 7 2004, 10:05 AM

i hate carbs!
Andy

PS: i guess that means i just don't know how to work them ...


back to the question at hand:

if the car runs with just one wire disconnected, i think it would be way overkill to go through all the hassle and expense and convert a motor to carbs that wasn't build for them. to get any improved performance out of a carb conversion, you'll need at least a CAM that is more suited for carbs. more $$$ ...
figure out what's wrong with that one wire, fix the FI and be happy with it.

btw. IF i stick with the 2.1L /4 it'll be converted back to FI, which means you are more than welcome to buy my carbs!

Posted by: Mueller Sep 7 2004, 10:09 AM

sounds like you have a vac. leak.....the L-jet is very sensitive to vac. leaks, even a bad oil fill cap o-ring can cause problems...when I was trouble shooting my L-jet, I disconnected all of the hoses that went into the large tube that is in between the AFM and the throttle body, I made plugs that went into the holes.

switching to a is one of the worst things to do....switching to dual is a little better, but there are no guarantees that you won't have problems, they too need to be setup correctly in order to run right, with carbs you are more likely to run too rich or run too lean (and ruin your motor) unless you know what you are doing.

Posted by: fiid Sep 7 2004, 10:19 AM

To my mind the FI argument is quite vague between carbs and the L-jet or D-jet. The bosch systems are difficult to diagnose because they use analog circuitry - which basically changes physical mechanisms to electrical voltages and resitances.

Get to digital fuel/spark management and the world changes completely.

Heres what I would do:

Find a good guide to the L-jet system. One that makes you take a multimeter and check various components of the system in various ways to test that everything is functioning correctly. Inspect your wiring very closely, and do a lot of systematic checks. Only change one thing at a time. Do check all the temp sensors and warm start stuff - since the cold-start might be interfereing with your normal running.

If you can't get your L-jet to work, consider going with something like a megasquirt, KitCarlsen FI, Tec-II or something. You will be able to use most, if not all of the existing L-jet kit. Something like a Tec-II will take you a lot less time to build, figure out, and debug, but will hurt your wallet a lot.

With a megasquirt, this kind of stuff is easy to diagnose, because you can tell what all the sensors are reading just by jacking a laptop into it and reading the numbers. If it's a cool day, the temp sensors should all read "cool day" before you fire it up. Easy.

Getting a numerical report out of carbs is significantly harder, although if you have prior experience with setting them up - it may be a good way to go for you.

Posted by: lapuwali Sep 7 2004, 10:27 AM

Jake, not everyone has the ability you do. I would be very surprised if your 912 had a completely stock engine in it, so your using it as a basis of comparison isn't very sound. If one simply takes a Weber IDF kit and puts it on in place of EFI with no other changes, mileage will suffer. This has been shown many, many times. Since that was the specific question being asked, that's the answer I gave. Saying that putting carbs on an engine specifically built for them is better is true, but means nothing to someone with a stock engine that wasn't built for carbs.

If, as is very likely with the original poster, you don't know how to diagnose either system, than simply slapping on a pair of carbs will not solve the problem, but simply change the problem. The carbs problem is no easier or harder to solve than the L-Jet problem, but it does cost a good bit more.

I'm not trying to say carbs are universally bad. I'm saying they're not going to solve this problem without a lot of other expense.

Posted by: type47 Sep 7 2004, 10:54 AM

consider 2 things: 1) to quote the factory workshop manual "L-jet is the modern FI system....", 2) if you have to buy a carb system, consider that investment to be, what,.... $3-400 or more? you should be able to repair your FI system for same $. i have some links to L-jet troubleshooting manuals & such if you need them.

Posted by: otto Sep 7 2004, 12:12 PM

Take tension out of the flapper box spring until it runs then spray starting fluid to find your vacuum leak. Repair vacuum leak then set the CO by adjusting the spring or the mixture screw.

Posted by: Root_Werks Sep 7 2004, 12:21 PM

Take Otto's advise on this one. I would say work with what you have. A good FI system that is already in place will be easier to correct and tune than a new or used carb set up. I have done lots of the 2k rpm idle fixes, or won't idle cold or won't idle warm fixes on 914-4 FI cars over the years. I really haven't seen anything too hard to track down. Once set, you really don't need to touch it.

I am a carb man myself. I like things simple.

Posted by: Mueller Sep 7 2004, 12:26 PM

I wish I knew that little trick when I was still running an L-jet...no big deal, the car ran great without all the vac stuff, the only issue I had was that I had to run an oil-puke can like on carbs, no big deal.

Posted by: joes Sep 7 2004, 12:51 PM

Just to add my 2c worth also. A dual carb set up is very sensitive to the compression of each cylinder. If you have a wore out engine tuning carbs becomes that much tougher where as a single carb (or FI) helps even out the bumps. l- jet is a good system spend some time figuring it out and you'll like yourself better in the morning. Go the bookstore and get "how to tune & modify Bosch FI systems" by Charles Prosbt.

Posted by: lapuwali Sep 7 2004, 12:58 PM

There is a book by that title, and there's a great book on Bosch EFI by Probst, but they're two different books. IMHO, get the Probst book, published by Bentley, titled "Bosch Fuel Injection and Engine Management". It covers ALL Bosch EFI in detail, and is aimed at learning both the theory of EFI systems in general, as well as practical blow-by-blow testing to fix common problems on the various systems.

The Tune and Modify book is by Ben Watson, published by Motorbooks Int'l, and isn't nearly as good as the Probst book.

Posted by: morphenspectra Sep 7 2004, 02:36 PM

carbs work just fine.
if you know what youre doing with them.i switched from injection to carbs and been happy every since.so its not impossable to have a relaible smooth running car with carbs.

Posted by: SirAndy Sep 7 2004, 02:45 PM

to quote a seasoned porsche mechanic:

"Carbs belong into a Museum. They're 50's technology that doesn't belong in a car driven in the 21st Century."


Andy

Posted by: morphenspectra Sep 7 2004, 05:28 PM

he was prob talking about a newer car too
i wouldnt recomend a carb conversion for my 3.3 l intrepid either.that would be taking a step backwards.but for a air cooled motor that was concieved on a drafting table in 66,thats close enough to 50s technoligy for me.and besides i would recomend that the person who asked for help,to fix his fi.its a good system,simple too and very easy to understand.
i just prefer carbs,there simple.and not because i dont understand fi systems.i drove my 73 for almost 10 years with fi (d-jetronic)
i rarely post on carb vs injection due to the strong beliefs that people have.

Posted by: Jake Raby Sep 7 2004, 06:13 PM

The only solution either way comes from understanding either system that you choose.

If you don't understand it, its impossible to work with it!

I have a thorough understanding of carbs because I never gave up on them. I never had that luxury! When something kicks your ass and you are forced to make it work it has a way of force feding you with its understanding.

I shoot for simplicity, these engines were made by VW a company known for simplicity and practicality. Me definition of simple is effective, BUT only having as many components as it MUST.... Thats why I like the EMS system, it gets rid of alot of crap the stock system needed because its ancient.

Carbs may be ancient, but you'll appreciate that when you can patch it up on the side of the road and save a tow bill. These cars are all I have ever driven (aircooled VW and Porsche) and never once have I had to walk! I have had to patch things up many times but never had to walk.

Someone mentioned above that not everyone has my ability. That may be true, BUT each and every soul here has the capability to learn it(its not rocket science and I don't have a degree nor the first day of formal training in automotive engines! It can't be too hard if a dumbass like me can figure it out!

challenge yourself! Put out! No pain no gain!

Posted by: gregrobbins Sep 8 2004, 12:56 AM

[ "It can't be too hard if a dumbass like me can figure it out!" Jake Raby, 2004]

This quote is from somone who has probably forgotten more about air cooled motors that I will ever know? I am sure that will make my repair shop owner happy.

I think the next generation of computerized FI systems will be the ticket. In the next couple of years a lot of carburator folks may re-evaluate as will a lot of D and L jet owners.

That is why we keep on keeping on

Posted by: Jake Raby Sep 8 2004, 01:06 AM

I am lucky.... When the good lord was thinking about me he gave me a little bit of an edge..

Due to this I haven't really forgotten any of what I have learned... A few years into school my teachers noticed that I never forgot anything. They gave me some tests and found out that I had a photograpic memory..

when I spell I don't sound words out, I remember where I saw them and then spell them! I don't type normally either, I just have the key positions memorized but not in the conventional manner....

All my combos are in my head, I have 43 camshaft grinds memorized to the digit, carb jetting, timing and the works...... I did get lucky!

Posted by: Next GenRacing Sep 8 2004, 11:47 AM

well i am definatly more comfortable w/ FI believe it or not, i am 20 years old and have a 423WHP neon (believe it or not) i am using a product called SMT6 built by perfect power (its similar to mega squirt, it has pretty complete fuel and ignition tuning ability's) anyway i just didnt want to pay for another full session of dyno tuning $$$$. i am just stumped on this one. the worst part is that it worked for about a day all the sudden, then it stopped working again. i dont want it to be that unreliable, it would be worth it to me to have the reliablity of the carbs. otherwise i think i may just try and start replacing the FI system till i get it worked out (problme is w/ this the cost could be much higher then a carb setup)

also the carb kit i was looking at was on ebay, it was a progressive weber setup, it was also a single carb kit.

thanks for the replys i'll keep everyone informed.
Danny

Posted by: Next GenRacing Sep 8 2004, 11:48 AM

also how do i adjust the spring in the air flow sensor? i used to mess around w/ some electronic stuff under the black cap, but my new one has the black cap glued on and i dont want to loose a warrenty cause i took it apart.

thanks
Danny

Posted by: lapuwali Sep 8 2004, 12:55 PM

The progressive single carb setups suck. Tuning them so they work under all conditions is very difficult. I tried for several weeks and ultimately gave up. I don't know of anyone that's managed to get one working acceptably. If you're not at all picky about drivability, they're a cheap alternative, but if you're used to EFI drivability, it will drive you nuts.

The L-Jet airflow meter can be opened, and once you see the spring, it's pretty obvious what needs to happen. There are several adjustment notches, and the looser the spring, the richer the mixture. You REALLY need to buy one of the books mentioned above. It sounds like the L-Jet is very close to working. It's also possible the "old" one still works, since swapping to a new one didn't fix it. Try adjusting the old one. If you approach it systematically and eliminate all possible problems, you'll eventually stumble across the problem. Sounds to me like it's something really stupid you're overlooking. Happens to everyone.

Posted by: Mueller Sep 8 2004, 01:02 PM

.....from who???

do a search here for L-jet info, I know a few good links have been posted in the past...the L-jet is so simple it's not even funny once you figure out what does what......basicly, the engine during it's intake stroke creates a vac, opening the flapper door, when the flapper door opens, it turns on the fuel pump and engerizes the injectors (when the key is on)...if you have any vac leaks, the engine will have a harder time "sucking" in the air in order to open the flapper valve.......

find the vac leaks either with the method Otto mentioned or I mentioned (disconnect the hoses going the air intake tube, and plug or cover the holes in the tube)....

Posted by: Jake Raby Sep 8 2004, 05:04 PM

The Weber progressive is not classified as a Carburetor.

Its a piece of shit that should be recycled and used to make new Hondas with.
Pure junk

Posted by: Andy Sep 20 2004, 04:51 PM

Talk about a definitive answer!

Funny thing is I haven't been lurking around much lately and missed this thread, just did a search for "progressive weber" since it sounded like an easy cheap way to get my type IV off the garage floor... I guess not...