911pcars

I'd start with a basic compression check just to verify the engine is basically sound (normal compression pressure).

Typically, if fuel consumption is an issue and the carb jetting is to spec (yours looks fine), I'd suggest checking the fuel pressure and the float level. Fuel pressure should be 3-3.5 psi. Float level should be verified w/engine running. Use a PMO float level inspection tube that attaches to the float bowl drain.

One quick check is to remove the air filter housing and look down each carb throat. With the engine idling and off-idle, you shouldn't see any fuel dripping from the discharge nozzle. The idle circuit provides the fuel up to and including part-throttle operation.

Sherwood

randomhick35

Well, compression checks out, leakdown is normal, pressure is a constant 3, float levels are good, and using a mirror, i cannot detect any fuel leaking down in the throats. Thanks for the tips though. It being such a nice day up in NH [about 80!] I plan to take the car on a loop today, and see if I can have any more luck with tuning. perhaps I just need to appease the porsche gods with an offering, anyone have a spare fuch to sacrafice? "and with this fuch, and this torch, I do hearby cleave my wheel in sacrafice!"

randomhick35

I do have a syncrometer and a [hacked up] sight glass, but I may just go ahead and try different idle's and perhaps mains. I plan on going for factory settings [unless he advises otherwise], any other suggestions?
the engine is a 2.0, and i'am pretty sure [but not confidant] that compression and cams are stock. The last owner was a real whack job [put 6 kill switches hidden throughout the car among other things] and could have done anything to it. to the best of my knowledge this is not the case.

911pcars

I think your jetting is fine. Surely not so far off to earn just 5 mpg. I had the same setup when my flat six was a 2 liter T.

Since the idle circuit continues to operate well into part-throttle, it could be the adjustment of the idle mixture screws. You've got six and they're fairly sensitive to their adjustment. Borrow or purchase a Gunson CO meter (~$100) and use that, along with the Synchrometer, to adjust the carbs. It doesn't take much to change the mixture from lean to rich.

Another common cause of low mileage is the weight of your foot on the gas pedal. Are you driving delicately or aggressively? Start and stop driving conditions? Using the lower gears more than the high gears? Do you downshift to lower gears instead of coasting in the same gear? Hill climbing vs. level roads? Do you idle the engine for long periods of time?

Sherwood

Jay Laifman

You may want to post what float level you are using. I bought a 356 that had its share of creative maintenance over the years. When I first started trying to get it all up to snuff, I found that the Zenith carbs float bowls were set perfectly! Perfectly to Solex heights that is! :-)

There are lots of other bits that I had problems with on those Zeniths before I got them right, like that modern rebuild kits' accelerator pumps are no good. But, in the end, it was a dream.

randomhick35

I can post exact float height's when I get home, [at work now] but they are set according to a weber manual. I am not driving like a maniac, but I am having to give it a good amount of throttle because my midrange is soooooo bad. In general I am having to run my rpms up to around 3.5k to avoid horrendous lurching. I do not expect to get great mileage, but I am not driving in any sort of extremes, in general just cruising between 35 and 50 in third or 4th gear.
I did try an interesting experiment yesterday though. Because my tuning was bad anyway, I just decided to start from scratch. But before I did this I took all of the adjusts and screwed them in to seat, and then back out about 1 half turn. Driving the car there was an occasional pop, and a noticeable loss in power under all rpms and throttle positions. Beyond that, the behavior was almost exactly the same. Once the engine had cooled [I can only get it up to about 175 even with bp4es plugs!!] I pulled all the spark plugs to check them. They were all black, but not wet, except for 1. One plug was completely lean, looked new. I think That just means I shut the fuel off to that one. I didn't drive it long enough to get any sort of an accurate fuel mileage, but on an estimate, I think it stayed about the same. Has anyone tried one of the CO2 gauges? My next thought is just to start swapping jets. Any thoughts on what I should change first? thanks for all the help so far!
-Bob

Jay Laifman

Here's one more thought. With the 356, there was this procedure you could go through to figure out what carb or throat was causing the problem. You'd to an isolated area, stop, and disconnect the linkeage to one carb, then try to drive it. The car wouldn't go great. But, it would move with some acceleration. Then, you'd go back and reattach that side, and disconnect the other side, and do it again. If you got the same result, the problem was not the carbs. If you got the bad carb, it wouldn't move and it would bog down.

Then once you had a carb id'd, there was a way to check which throat it was. But, I'm not remembering what that was. Perhaps it was idleing and pulling the spark plug wires on that side to see what happened. But, I don't remember for sure. Note if you do that, use a spark plug wire pliers!!! And, yes, I learned that one from experience!

Droops83

I'd advise against pulling a live secondary ignition wire while the engine is running, especially since he seems to be running pretty rich (fuel vapors + secondary ignition spark=BOOM!). A safer way to do a power balance test is to put a short section of vacuum hose (~2 inches) between each cylinder's ignition wire and where it plugs into the distributor. Sounds weird, but it'll run this way. Then, using a test light or jumper wire with one end connected to a good ground, touch the other end to each cylinder's vacuum hose and see how much the RPM's drop. If they don't drop much or at all on one cylinder, you've found your problem.

That said, randomhick's problem seems to be an overall running condition, not a dead cylinder; if this were the case the engine would run crappy and miss under all conditions. I'm scratching my head, seems all the likely possibilities (float levels, jetting, etc) have been suggested. Might be time to give up and take it to a professional who is good at setting up these things. Let us know what you find!

---Chris A.

911pcars

Chris,
I haven't run across that method of shorting cylinders before, but I'm open to new ideas. I'd think a 2" air gap as a result of the vacuum hose is a bit much and would stress the ignition system. Perhaps a 1" hose (air gap) would be less stressful. I've always momentarily pulled the plug wire at the dist. cap. Adquate airflow from the fan doesn't allow gas fumes to collect, especially if the air filter housing is installed.

Sherwood

mo_gearhead

Bob,
The fact that you have 5 "black but not wet" plugs and 1 that 'looks white/new" seems to point towards a problem with THAT particular cylinder. I would certainly focus my attention on the carb. (fuel supply) and spark to that cylinder.

randomhick35

well, attempted a couple of these shutting off ignition tricks, and all cylinders respond approxamately the same. As for the cylinder that the "clean" plug came out of: turns out I just had the fuel shut off during my little "experiment". cracking the adjust just a little, and the plug came out about the same as the rest of them.
My next step is to talk to a friend of mine who has many many weber jets, and see how the engine responds to replacing the main, and perhaps idle jets. [providing he has the correct ones...] If not, my next step is to send a fax off to PMO and get some advice on, and buy, a few new jets. I wish I could find an intermediate step, but that seems to be the next logical option. I've tried taking it to a professional, but the only local specalist is too busy for the next couple of weeks to take a[nother] look at it. I know this guy well enough that I'll just try to take care of it myself in the next few weeks, and take it to him If i cant fix it, rather than go out of my way to find someone else.
Thanks for all the great responses so far!
-Bob

911pcars

There's an off-chance the jets (correctly marked) could have been drilled to a larger size. Starting with new idles, mains and air corrections is one way to begin from a known reference point (or compare with a drill jig set, if available).

Sherwood

randomhick35

oooh, good idea!
I don't have any really small metric drill bits, but I know where I could get some to compare with...
That's exactly the sort of sneaky thing the P.O. might've done; redrilling without re-labeling [or just warning me...]
I'll try and check that this week, it also looks like I might be able to borrow some jets from a friend to try.
I'll be sure let you guys know how it works

One further question, for the weber guys: what sort of gas mileage do you guys get around town? not on the highway, not city, but on some backroads, maybe a few stoplights. I'am not really sure what to expect out of this car, so it's kinda hard to know what to shoot for. Also, do you get much of a flatspot? if so, how bad?
thanks for all the tips
-Bob

kblume`

Hello, Can you tell me where to obtain the glass tube gauge?
Thanks,
Kevin

r911

18 mpg is common

flat spots can be from a lot of things, progression hole issues is one

try finding Paul Abbott for the gauges or other parts - or he will (or used to) rebuild the entire units
http://www.performanceoriented.com/

for Richard Parr, you fax him your phone # & a time to call, then he calls you back - see his web site for parts

both guys are getting old, just like the carbs...

with a manual, you can tear them all the way down, but carbs have lots and lots of tiny parts...

- everybody should do it once in their life - it builds character