why does my 912 always run rich...

[Touque]

I'm getting more than a little frustrated at my carbs...

Car runs rich at idle (can smell it, and when I rev the engine, it dumps black smoke out)

switched to smaller idle jets, thing started to backfire and hesitated when I hit the gas

car used to run VERY cool (when i picked it up). The only difference is that I swapped a 009 dizzy for a new 050). Now it runs REALLY hot (3/4 or more past the gauge when doing 4000rpm on the highway). The timing has been set to 33 degrees so i don't think that's the problem.

so... if it was lean all the time, i'd expect a hotter engine

I can't make it non-rich on the low end without hesitation and then it still smokes black. (couldn't get rid of the black smoke and burning eyes and smell)

i have a synchrometer, and have adjusted the idle mixture and air-bypass screws with no success

could it be that my main air jets are too large or small?

my biggest 'worry' is my webers - they are weber 44 IDF's. I know i've read and heard that they are 'too big' for a 912 engine... does this sound like the case?

thanks in advance,

Troy

p.s. what do your temperature gauges read?

[Duke]

I have heard the 44s are too large for the 912. You need the 40s.

[Touque]

right, but what does that actually mean?

[Griznant]

You can pretty much make any carb work on any engine if you try hard enough. I've seen 48 IDAs running on a VW 1600 before!

What size are your venturis? Air correction, main, and idle jets? What emulsion tubes do you have?

You can probably make them run on the 912, but it might take you some trial and error to get it right. The high compression of the 912 engine should lend itself to running fine on more carb than a bigger low-compression engine. 40s maybe more ideal out of the box, but I think you can make do with what you've got.

Tell us what you have, and maybe someone can help you out.

As for why it's running hot, I don't know about that one. What condition are the tin and seals in? How clean is the engine itself (gunk and crap on the fins)? Too rich and it should actually run cooler (then again you might be washing down the cylinder walls, thinning out the oil, and causing more problems).

Later,

G

[Morrie]

I run Solex but....

If Webers have accelerator pumps like solex do, then too agressive feeding of the pumps will run you too rich and suck gas. The books spec about 3 times what you really need. Today's fuels are better than the old stuff.

Morrie
67 912 Coupe

[Touque]

hmmmmmm

What size are your venturis? Air correction, main, and idle jets? What emulsion tubes do you have?

good question - really good question. Since the P/O put them in and i've only had the car since September, I don't have a clue other than the idle jets are .055

is there an easy way to find out the sizes of everything without taking the carb apart?

as far as the heat - the tin is all in place, but there is a gap that runs around the tin and where it meets the body. The engine has less than 2k miles since it's rebuild and it's clean with no crap anywhere (that I know).

thanks for all your input!!

[Griznant]

First thing: There should be no gap between the body and the tin. There is a rubber seal that needs to be in place. Without this the engine will just keep sucking it's own hot air back into it over and over again. Make sure you get that sealed up for SURE!

Second, no need to disassemble the carbs to see the other jets. On webers, changing jets is simple as cake. To find out the jet sizes, you need to pull out the emulsion tubes. These are the two brass "towers" that stick up in the center of the carb between the two barrels. They are removed with a regular flat blade screwdriver. Pull them out. In the end of them is the main jet, and it can be checked by pulling it out of the body, or just reading the side of it. Then, the bottom section of the brass tube can then be pulled from the top section of it. Inside this should be the air correction jet. Number will be on it. The upper part of the brass tube should have a number on it (probably F7 or F11), that's the emulsion tube.

The vents can be checked by shining a flashlight down the barrels and looking for a number stamped into the venturi. No idea what size you will have, but probably 30-something. This one may be hard to see, and you may need to remove the carb to see it in there. Check both carbs to make sure they all match!

Find out this info, and hopefully we can put you through to the right people, or give you more info. 55 idles might be too big for a 1600, you may need a 50. Let us know what you find.

Later,

G

[Green 912]

Almost everything about the 44s are incorrect for a stock street 912 and you might well be experiencing the effects of just that. The simple reason is that the 1600 912 motor doesn’t pull enough air through the carbs. This causes the velocity to be too low for it to work correctly. Some folks have been able to make then “work” but it is a compromise on many levels without any gain for using them.

There are flow and sizing charts for setting up a carb for a motor and Webber 44s are simply not recommended for a mild 1600 912. Period. It is not a mater of what I like or what my uncle likes or what we did in the past or what the Maestro sez. It is pure physics. Your car will not run better or be faster or make more HP with 44s over 40s If you have a gas analyzer and a dyno and a selection of ventures and emulsion tubes and jets you might be able to get it to run OK but by the time you do that you could have just installed correctly setup 40s and it will run better. There are plenty of folks that feel that bigger is better and I bet that someone has a recipe that will get you running OK with the 44s. The only one I can find is for a flat out full race 1720 and it makes little power under 4000 but goes like stink at 7000. You are already on the right track by changing of the 009. Did the PO build this motor up to a total full race track motor? That might explain the 009 and the 44s. Either that or he was a Bug guy.

G has it right, let us know what you have as far as the jets, E tubes and ventures. Morrie is on it too. It would also be good to measure the accelerator pump amount. If it is to high it will go too rich and soot up when you rev it up. That coupled with too small a main jet could lean things out and explain the hot cruising. I might recheck the timing as well.

The good news there is an easy fix to your drivability problems assuming the motor is sound.

Get 40s.....

[Touque]

anyone want to swap a pair of almost-new 44's for some 40's

you guys have some great detail - unfortunately, i'm away on business and can't check anything out. My tin's in great shape, but there is a gap between it and the rubber...hmmmmm - wonder why...

Did the PO build this motor up to a total full race track motor? That might explain the 009 and the 44s. Either that or he was a Bug guy.

well, he put a different cam in (not crazy, but yes a step up from standard), and he was also a bug guy and built tons of extreme dune-buggies. I'm embarassed to say that yes the bottom and top-end was re-done (have the work orders for most of them), but I honestly don't know if it's the standard 1600 (don't think so), or the 1720. why would he put a race cam, 009 and 44's (he said he wanted to race it), but not the larger P and C's... In the Porsche engine manual, the section on the cylinder sizes, he had written in pencil just under all the measurements 85.9... this would lead me to believe that it is the 1720 because they use 86mm pistons for the big-bore. He only put about 3 marks in the whole book so I think it wasn't just idle thought.

sheesh, I guess I could always call him!

so after the long story, I have new 44's, 1720 (i think), rich and lean symptoms, and gaps in my tin... on the whole, the car is great EXCEPT for the smoke/overheating. Timing is good (33 degrees at 3000rpm). New dizzy, new wires, new plugs.

thanks for your help

Troy

[Touque]

oh, and I do have the rubber seal, but there is still a gap

my tin hangs an inch or more lower than where it should meet up... perhaps it should go over instead of under?

any way (as I wonder outloud) to get something in there to 'plug' it up (dynamat or something)?

one more clarification - the black smoke is after I rev the engine (when revving it), and when it is coming back down to idle - it'll then stay that way for a few seconds until it finally cleans itself up

[adot]

Hey Troy

Can you stick the old 009 back in to see if cools things down?

Brett

[Touque]

did that already and no, it didn't help

I checked my tin gap just after I got home from the airport, and it's not terrible, but there is a 1" gap on each of the sides, but the back is relatively sealed.

obviously, in my quest to 'optimize' things, I took a cool-running, non-smoking (don't think so - not as bad anyways) machine and messed it up - timing, valve adjustment, and distributor are the main things I changed.

question regarding my points and dwell - is it right to assume that the dwell angle is more important than the points gap (even though you change the dwell by adjusting the points)?

[adot]

question regarding my points and dwell - is it right to assume that the dwell angle is more important than the points gap (even though you change the dwell by adjusting the points)?

The dwell is just a electronic way to measure the gap. IF the gap is right , then the dwell is right. I THINK

Wish I could do my valves with a dwell

Also Troy, Dumb question. How are you timing the car? Whats the idle timin at? Maybe pull the total +33 down alittle (28) and see if that make an diff. in how hot it runs. MAybe your using the wrong marks ??

Brett

[Touque]

just had the chance to check the dwell and it's at 52 degrees... right within spec

[Touque]

ok, weber's taken apart (washer fell down SOMEWHERE, HOPEFULLY not inside the carb...)

Then, the bottom section of the brass tube can then be pulled from the top section of it. Inside this should be the air correction jet. Number will be on it. The upper part of the brass tube should have a number on it (probably F7 or F11), that's the emulsion tube.

emulsion is an F11
air correction jet is 200
number at very bottom end is 115 (whatever it is - guess i'll have to go read my weber book)

[Green 912]

F11 is a rich E tube and the 115 main jet seems way small. I run a F7 with a 200 air and a 135 main on a 1720. (this is for 40s, I have no data on 44s) I have a hunch that you have too small main jets and too much accell pump. That would run too rich on spin up but lean out when driving steady. If had F7s and 135 around I might try them.

Contact PMO, they know carbs! You will get a message but they call back. to order you gota send a fax, a pain but the service is well worth it. (310)393-5423

Per Adot... you timing from #1, right? What do you start with at idle. 4 to 6 deg? what did you set the valves at? Did you do them cold?

[pokemon]

I have 36mm DRLA dellortos and had the same rich hesitation (engine dies for a moment) problem when accelerating.
Turned out to be the accelerator pumps giving too much gas.
You can reduce the amount of gas by reducing the accelerator pump jet (what else)
For the actual size of the accelerator jets for your motor? Go as small as possible without the car backfiring (too lean) on acceleration. Don't start measuring the actual cc of gas that are pumped for each two full strokes as i did after reading one porsche manual. It's a waste of time.
Regarding dwell and gap. Change the gap and you change the dwell. Both are directly related.
Important here is that when you change the gap to adjust the dwell, the ignition timing will also change.
Therefore you have to adjust/check the dwell AND the timing a few times till you get them both right.
In other words, dwell is adjusted by the gap and the iginition timing (3-5 degrees before TDC) is adjusted by rotating the distributor.
If i remember correctly, dwell is the time the points are closed. During this time current will flow trough the ignition coil and built up a magnetic field. This has to be strong enough to produce a strong enough spark when the points open. Too short a dwell angle will give a weak magnetic field in the coil and the spark may be too weak to jump the plug gap.

BR,
Patrick

[Touque]

Also Troy, Dumb question. How are you timing the car? Whats the idle timin at? Maybe pull the total +33 down alittle (28) and see if that make an diff. in how hot it runs. MAybe your using the wrong marks ??

nah, not a dumb question at all. I actually have the Craftsman timing light which has the little knob at the end - I can set it at 33 and then i just have to align TDC with the notch. the idle is at 15 degrees (lining up TDC with the notch, then adjusting the knob until they line up). I may try to 'lower' the timing and see - good idea

just figured out a few things - now (not when I bought it), the second I start the car, the temp gauge jumps to about 1/4 of the way (wonder if I can re-calibrate it?), so maybe my temp problem is not really a problem at all.

put duct tape on the gap of my tin and rubber seal and it seems to make a slight difference - that's a good thing

I'm going to go and pick up some different main jets and then go from there - my venturi's are 32, and the other things are withing spec - my Weber book also says that 135 is a good starting point for the main jets

also, i'm going to check out my accelerator pump/amount - I am starting to think that it's dumping too much fuel

[adot]

Hey Troy

15 at idle sounds way to high. Not sure how the car starts that high. Try setting the idle 3-5 at idle and then check the top. Maybe bad dist.

But then again, Whats your Idle RPM?

Also, the gap. Maybe this pix will help fix that. two springs and two cotter pins. The cotter pins were bent to form a 'T'. Not sure if the 1/8 hole at top is factory , but I think the one in the tin is.

GoodLuck and glad to hear you got the washer out.
Brett

PS if you use Green912's motor removal guide, ADD: remove tin springs or you will have some new 3 foot springs, dont ask

[Griznant]

Ok, now I am not a weber master by any scope of the word, but the jets you have sound about right for that engine. Going to a 135 might get you too rich. My friend runs a 135 main on a 2270 Type 4 (very hopped up) with 44 IDFs, and it runs just about perfect for that.

You may be on the right track for the accel pump, but I think that changing the jets before then might be premature.

Also, the distributor is not working right if you have a total advance of only 18 degrees, and it starts at 15. That sounds as bad as what a 009 will do! My 050 runs about 7 degrees at idle to a max of around 33 degrees at high rpm for a total of 26 degrees total.

If nothing else you now know what's in your carbs so you can make an educated guess on it. You can always talk to John Connolly over at Aircooled.net about your carbs. He might be able to give you a good idea of what your jets should start at. If you need to buy new jets, it'd just be common courtesy then to buy them from him. He has been just about spot-on for several engines I know of.

Later,

G