OK all of you pro trouble shooters I have a live one for ya that is turning my hair grey! I have a 1.7 that was rebuilt before I got it, all cylinders have great comperssion and everything looks to be done right. When I got it it had a weber 32/36 on it with a .003 distributor... yes a 3.. I was told it was a 9 but it wasn't. I was not happy with the way it ran because it had a big flat spot in the middle so I put on a freshly rebuilt 38/38 and had the same problem. I have since replaced EVERYTHING on the topside I now have 40 empi's, a dual advance svda distributor with compufire, plat plugs 8mm wires, supercoil, carter fuel pump/ pressure regulator and on and on. I know everyone is gonna say it is the empi's but it isn't they came off of the factory's test engine and worked perfectly. I still have this damn flat spot at all timing ranges , it is quite a bit smaller now, I can drive through it easy but it is annoying! any idea's on what else could cause this??

Ok, don't know what a dual advance svda dizzy is. (mechanical + vacuum with a single vacuum diaphram advance?)

1.) accelerator pump on carbs giving to big or to little a shot in transition (to much air or to much fuel)

2.) Mechanical advance is hanging up or rate is to slow

3.) Cam profile

where does the flat spot occur? 2500, 3000, 3500, etc, rpm? can you see the venturi size (usually the # can be seen looking down one of the throats and the # is on the top edge. oh, engine off while doing this)?

k

your right about the svda, its just as you described. I don't think it is the distributor, but the carbs maybe... not so sure though, I have tried all adjustments on those things including pump squirt. I'm far from an expert on them, its a learning process. The cam though that is a possibility I NEVER wanted to consider... I don't have the resources right now to go deep into the engine... I looked through the old reciepts and can't find one for a cam so it is probably the one she started out with, which is pretty old since this car is # 610 off the line...

the flat spot is variable usually between 2500 and 3500

Whats strange to me is all the symptoms point me toward the carbs, it is always at about 1/4 throttle that I hit it, but I'm on my 4th set of carbs with this problem..

goes on its nose, or just a hesitation? you're going from the idle circuit to the main at some point in that rpm range. i *think* the 40s are pushing the ceiling, from the fact venturi spcs, size wise, for a 1.7. low air speeds thru the carbs at low rpm?

now the usuals. what type of pump, what type of fuel press regulator, if any?

k

All things considered I would have to agree with Ron on the cam diagnosis.

Install the platinum plugs where they belong, in the trash. Replace them with Bosch W7CC or NGK B6ES. The Cap'n

Is that only under load? Will it still give the same indications by slowly depressing the accelerator when in neutral? I don't know what Empi 40's are; they the same as Weber 40's? I'd first look at the idle circuit and make sure you're not too lean. It would be easy to richen it up and try it out. People tend to overlook the idle circuit. Are the carbs (assuming these are duals) balanced (Uni-Sync), and is the throttle linkage adjusted correctly so that both carbs open in unison? Will the motor rev if you stab the throttle when in neutral? A lean accelerator pump jet or linkage adjustment will usually reveal itself if the motor responds poorly. Timing is correct? Perhaps it is slightly retarded? Have you checked the obvious stuff; vacuum leaks, etc? I'm no 914 expert, just old school (had a '73 with dual 40's 30 years ago).

Andys

from tomlinson's book, enjoy.

"Venturi Selection

The use of a venturi that is too small will stifle the top end performance. A venturi that is too large will cause bottom end stumble mid range flat spots." this preceedes the text and chart for venturi selection.

Bob Tomlinson's Weber Tech Manual (from cb performance) is invaluable.

k

Ok let me ask this, could it be a valve problem? When I first got the car the valves were terribly out of adjustment and it had been run like that a few times by the former owner at high RPMs, I'm wondering if I may have burnt or intermittently sticking valves? What do you guys think?
As far as the timing, it is a little bit advanced, I have a carter 4060 pump with a regulator and pressure guage set at 2lbs. Not 100% on what jets I have they were set up for me by the QA guys at EMPI, I do know that the problem has been consistant over all 4 different carb set ups.
BTW I have 28mm venturi's on the properly adjusted dual setup...

not the jets, venturi. if the epmi (who are they) guys sent a specific jetting setup, leave it alone for now. turn the fp up to 3.5 lbs. you need to have the valves and timing as spot on as possible.

i take it you don't have a weber book.

k

I've got a weber book, went throught it with a fine tooth comb... the EMPI corp are the guys that own the part of the Weber corp that make the IDC type carbs. They are relitively new at making their own and have picked up a bad rap because they look like knock off webers.. I think I may roll the timing back a touch, but I'm still curious about the valves... guess I may have to get off of my oh so thin wallet and work that angle..

one more thing I forgot, if I'm really in it WOT or even just on a strong accel there is almost no flat spot, but if I am cruising along at about 1/4 to 1/2 throttle I get a light popping and sputtering. The engine has the same symptoms with and without a load.

I think you said your dual were properly set up, but just in case...double check your linkage geometry.

You might have them perfectly sync'd at idle, but if one side opens the butterflies faster (i.e. at a different rate) then they will be out of sync under open throttle conditions. That could cause a stumble, etc.

In my experience with dual carbs, my tuning issue wasn't caused by just one problem: Timing a little off, valves just slightly out of adjustment, and a vacuum leak where the manifolds meet the heads, yada yada.

There's a thought for you: a vacuum leak b/t the manifolds and the heads would exist across all the carb combinations you have tried.

just thinking out loud....good luck.

Thats a great thought, unfortunately I had the same one early on... made triple sure there were no vac leaks around the manifolds. You are probably right though saying it is a combination of things, probably dosen't make a whole bunch of difference adjusting the timing if the valves are out of whack...

That is a really early car you have there, take good care of it.

What about the distributor. If the advance was hanging up that may cause some problems. Some guys forget to oil the felt in the top of the shaft on the original dizzy's, not sure if yours has that. It may also have a bad advance curve.

Well, the distributor is brand new, from aircooled.net, and the engine was doing the same thing with the old distributor in it so not so sure about that...
I plan on keeping this little guy, I want to get it in the best shape I can, when I get the scratch together I'm gonna paint it the original orange.

One other thing it could be is the dist. you are talking about is in the family of the

009. They were the "Smog" dist. and with a lien mixture could cause a flat spot.

From hardly noticable to torturous. Try retarding your timing to 4 degrees more

than sudjested, and check your mixture on the carbs. Maybe post a pic of your

plugs and size of your mains.

I've been thinking on this. 1600 CC 912s with Webers mostly never run all that well, not even as well as with wornout solexes. As I recall, Webers use the idle circuit as part of the main system, and consequently tend to run on the fat side whenever you're at cruise. Popping can be traced to cylinder condition, variations in cylinder vacuum, plug and wire condition, valve adjustment, linkage angles, and incorrectly balanced carbs. Not only do they need to be balanced at idle, they need to have equal movement throughout the range of motion. That means the rod lengths and angles need to be the same. Use a synchrometer, not a Unisyn. Good luck. The Cap'n

Well, I just went out and reverified my linkage, it is just as it should be, equal all the way from idle to WOT, I've retarded the timing just a hair and the same thing. This is what has me frustrated, I've tried all timing settings from too far retarded step by step 1 degree at a time to too far advanced. On the last set of carbs I spent over $350 in jets trying to figure it out (that made the wife happy ), then finally swaped the carbs out with a factory test set directly from EMPI that was proven to work perfectly. I have a hard time thinking it is the new distributor because the problem existed before it was put in. As far as leaning out, I'm actually running a little bit rich if anything. I don't want the problem to be something deep in the engine but damn... At least I can drive it fine, it is more of an annoyance than anything, as long as I punch it everywhere I go I'm fine lol

Okay, so multiple distributors: no change = probably not ignition
multiple carburators: no change = probably not fuel
wide timing settings: no change = probably not timing

I've pretty much established it is not the original engine, case anyway. Hard to know what was done inside. We are well aware of the problems of flat cams from bad lifters. Check your oil filter, section it and inspect for fine magnetic particles. What is your valve clearance history? Is it changing in one direction only? Too bad that Jake is on the road.

What exhaust and what intake manifolds do you have? Also how OLD is the linkage. I ALWAYs had a bog of unballance about 3500 until I replaced the linkage. I got the best performance with longer intake manifolds (builds more torque but loses top end). Also, per Jakes advise, I got a Mallory diz and whoooo-weee it is smooth now. But the linkage did not have any apparent slop, I just knew it was 18 years old. The replacement stuff I got with cast aluminum parts is really a great improvement in appearance too.. Lastly, you can add some velocity stacks. I've got little short ones that fit under the air cleaners. I got all the stuff from Aircooled.net.

Well lets see, going in reverse, I have the short stacks, it has a new hex linkage I got the full 914 install kit with manifolds and everything. As far as valve clearance I have no clue what the history of it is or what it currently is so that is my main focus right now. I have a monza pipe being fed by skinless exchangers (just the pipes)

I went back a read your first few posts. Are we working under the assumption that your motor has a stock FI cam?

I am not sure of the specific implications of this, but that is generally considered a no-no. The real experts here will have to tell you what kind of performance you can expect from a carburated stock cam'd motor.

I bummed for you man, this stuff can really drive you crazy. Hang in there.

Yeah... I have to assume it is a stock FI cam, I can't find any receipts for another cam, but have them for everything else... I thought I found the problem this morning, maybe it was a contributing factor because it is a little bit better. I pulled the dizzy out and noticed that the mounting bracket was a little bit bent keeping the dizzy from going all the way in, I was thinking that the drive cog may be rising up a bit advancing the timing a touch... I don't know I'm grasping at straws now . I'll have to wait until I get back from vacation and look into going deep into the engine. I have never really worked on a 914 block, do I need to split the case to change out the cam? Guess I had better break out the ole Haynes manual again..

Well guys, thanks for your input on this, I think I figured it out. It was a 2 part problem, pump squirt, and more importantly WIRING!! I had not even considered that some of the ignition wiring may be faulty, until I noticed the tach jumping eratically during the flat spots. Turns out I had some seriously bad splices in my ignition leads. I went in and soldered all of the wet lines and what do ya know, she runs pretty damn well Now all I need to do is finish the body and paint her! Oh.. forgeting about the hundred other little things that go with all teeners..