Webber Tuning

Long Nose · 05-25-2007, 02:45 PM

All of those webber experts...

So I sent my Webber 40 IDA off to Bieker Engineering, came back beautiful. I have installed them, set the floats, tuned them, etc. New distributor, new ignition wires, new rotor, new SSI heat exchangers, new OEM muffler.

The car now idles beautifully. However, it seems to be a bit starved for fuel at higher RPM. What do you think is the most likely scenario:

1) Car has not been driven for 2 years, although I would turn it over and idle it every couple of months, so maybe there is just a carbon build-up.

2) Valve adjustment? Valve adjustment was completed about 2 months before I parked it two years ago. Could the valves go out of adjustment just from sitting?

3) Timing - ditto. Should I go thru the valve adjustment and timing again.

4) Two years of dreaming about driving the car and my expectations are elevated (unlikely, since it seems to have trouble getting over 90 mph, whereas before it had no problem going 100, 110 mph.)

Does all of the ballancing and tuning you do on the webbers only affect the idle, or does this have an affect the top end as well.

I don't think that Hary changed the jets, so I have no reason to beleive that it is jetted any differently. It used to run really rich, ran great over 3000 rpm but idled horribly.

Any sugestions?

911pcars · 05-25-2007, 03:33 PM

"However, it seems to be a bit starved for fuel at higher RPM. What do you think is the most likely scenario:"

Does it run out of power at higher revs? This symptom usually indicates a borderline fuel pump and/or blocked line/fuel filter. Check pressure and volume. It's around 3-3.5 psi and at least 1 liter/min.

Sherwood

Long Nose · 05-25-2007, 03:42 PM

As I was posting, I was thinking about how I set the floats. I used the universal float guage and added shims under the needle valve, but it was very tricky.

Ended up that the top of the meniscus was at the mark, however the level was actually slightly below the mark on the float guage.

Do you think that could be causing it?

I did replace the fuel lines in the engine compartment with Auto-Pro rubber 5/8" line, as the Porsche OEM fuel line was a lot of money. Could that be inhibiting flow?

911pcars · 05-25-2007, 09:43 PM

Yes, if the float level is too low, that will delay fuel introduced via the main jet. However, the float level isn't so finicky if you're a miniscus or two off. Does power drop off drastically, as in engine almost dies until you let up on the throttle?

The fuel line should be fine unless it's kinked somewhere.

Sherwood

randywebb · 05-26-2007, 11:36 AM

Weber or Webers - nobody will find this thread on the search engine unless spelled right...

LM-1
I don't think you need to spend a lot of $$ to fix this problem...

The fuel filter replacement Sherwood mentioned is cheap & needs to be done periodically anyway. I'd start there if floats & pressure are right.

Grady Clay · 05-27-2007, 09:21 AM

I hate to be too repetitive but always suspect is the filter screen in the gas tank.

Best,
Grady

john walker's workshop · 05-27-2007, 12:13 PM

starving for fuel at top end can often be corrected with a smaller air corrector. liken it to a drinking straw with a hole half way up the side. the bigger the hole, the harder you need to suck to get the kool aid. it fine tunes the main jet.

shbop · 05-27-2007, 05:01 PM

How's the fuel preasure?

Long Nose · 05-28-2007, 09:38 AM

Thanks for your replies:

It has a new fuel filter in the engine compartment.

What happens is as you are accelerating, at around 4000 RPM you can feel the power curve just back off. It doesn't stall or anything, just doesn't pull as hard. But going around a left hand bend or going down an incline, and it feels a lot better.

John Walker - do you actually change the air corrector, or do you just dial in less air as you do the air correction adjustment during fine tuning. It draws in around 3 when it idles at 1,100 RPM.

kent olsen · kent olsen's Garage

Ok I'll bite. What is an LM-1?

Kent Olsen
72t upgraded 2.7
soon to be 3.0

911pcars · 05-29-2007, 11:21 AM

Quote:

Originally posted by kent olsen
Ok I'll bite. What is an LM-1?

Kent Olsen
72t upgraded 2.7
soon to be 3.0

It's one brand of wide-band O2 sensor. Accurately measures A/F ratio throughout rpm range. Kinda pricey for just checking one time ($400). However, to constantly monitor A/F ratios, that or or an equivalent is kinda necessary.

Sherwood
(no affiliation)

shbop · 05-29-2007, 11:47 AM

I bought one of these, (LM-1's), earlier this year. I added the rpm sensor, and while it is pricey, I've found it to be a valuable tool. I'm more comfortable seeing data that either confirms, or helps me go in the right direction, sorting out carbs. This discussion is probably good for a whole other thread.

304065 · 05-29-2007, 01:26 PM

I talked to Harry the other day, he doesn't change the jets as a matter of practice. "Modern jets aren't as good."

Do you happen to have any photos of the restored carbs?

Long Nose · 05-29-2007, 01:49 PM

I'll take some tonight and post tomorrow - they look great, and it idle's nicely, just as I mentioned the fuel starvation at high RPM.

304065 · 05-29-2007, 01:54 PM

Thanks for the offer of photos. My 40IDAs are en route to Harry right now.

Most fuel problems are ignition problems. How is the advance at 4000? I would check that before suspecting the carbs, if you didn't change the jets. "New Distributor" what make and exact model? For a 70T you would be replacing the Marelli with a Bosch, right?