Baby steps

Charlie Chops 1940 · May 12, 2008, 05:27:23 PM

I finally got the track roadster out of the trailer from Cobo and into the front garage on Saturday. I Have never been able to get the side draft webers to start well or idle well. I spent about 3 hours over the weekend reading the Weber tuning book I have and reviewing all of the other data I collected on the web over the last few years. This time around it started to make more sense...gotta do more than lead me to water sometimes.

So, the first thing I did to day was get it started and checked with starter fluid to see if I had any leaks in thed intake system. None evident.

Next I removed the air cleaners and the throttle cable and set everything back to zero so to speak. Went through all the adjustments and got it to start and idle fairly well. Then I got the air flow meter out to see how well I had synchronized the two carbs. I must have a tin ear cuz I sure missed. Back to the books and the screw drivers, and I finally got both carbs to read the same and the idle down around 800-900 rpm.

Took it for a spin around the block and it actually moves out pretty well. Still at issue is the throttle not returning to idle well - return spring problem - and a bog off idle. So, one issue at a time. Maybe a little more improvement tomorrow.

I want to get it running well enough to start doing plug cuts at steady state speeds - 35/45/55/65 to see where it's running lean or rich and then start rejetting, etc until it gets better.

The Weber guys say they are infinely adjustable but they require learning how the carbs work and a willingness to experiment. A steep learning curve - one that I'm definitely just approaching the upward slope.

I want to drive the car to OBT's soirée in a couple weeks and take it to Indy next m onth, so my work is cut out for me.

Charlie

HotRodLadyCrusr · May 12, 2008, 05:59:41 PM

Good luck Charlie. I'm anxious to see it running down the road.

Dave · May 12, 2008, 06:01:23 PM

Charlie I have found that when ever i learn something new its a good day but I need time to myself to really read and have hands on time with the new project.. Now that all the other stuff is done maybe its the right time for the fuel system where before there were just too many little things to get finished. Yup baby steps.
Dave

moose · May 12, 2008, 06:17:44 PM

Charlie,
It will be good to hear when you get it running as good as it looks! And congrats on all the press coverage..

Tim

Bruce Dorsi · May 12, 2008, 07:01:00 PM

Quote from: "Charlie Chops 1940"The Weber guys say they are infinely adjustable but they require learning how the carbs work and a willingness to experiment. A steep learning curve - one that I'm definitely just approaching the upward slope.
Charlie

Good luck, Charlie! .......It's doable, but it is frustrating as hell.

What model carbs are you using?

The challenge seems to be from the TOO many variables which can be tuned. ....Each part change seems to affect another portion of the fuel curve where changes were not wanted.

I went nuts and spent a fortune in jets, gaskets, emulsion tubes, etc, trying to tune a single 45DCOE on a turbocharged Lotus 4cyl. .....The Weber and turbo was my idea, so there were no factory guidelines.

I did so many on-the-shoulder-of-the-road plug readings, I thought I would wear out the threads in the head!

I also used an on-board exhaust gas analyzer, but all that did was indicate if my changes were heading in the right direction.

I read everything I could get my hands on (pre-internet days) pertaining to Weber tuning, to no avail. .......Local Weber "experts" were unable to help me get this sorted.

The two best Weber books I found at the time were written by John Passini, and published in the UK.
........"Weber Carburetors - #1 - Theory" ......(orange cover) ISBN number 0903192403 ........approx 60 pages
........"Weber Carburetors - #2 Tuning & Maintenance" ......(green cover) ISBN 0851130607 .......approx 120 pages

These two books were published in 1973, so I don't know if you ever came across them. .......Perhaps info available on the 'net is just as good.

I'm embarassed to say, but in sheer desperation and frustration, I replaced the Weber with a single Stromberg Constant-Depression carb, and my problems were solved. .......One simple metering needle modification was all it took.

Charlie Chops 1940 · May 12, 2008, 08:32:59 PM

Thanks guys for the encouraging words.

Bruce - I have a pair of current production DCOE45's - bought in 2002. I will take note of the books you mention and see if either are available anymore. The one I have seems fairly comprehensive and the tech. info out on the web seems supportive/in line with the Weber books. I have gathered a number of articles off some owner blogs where the guys put a lot of effort into their experimentation and went so far as to also tell what didn't work out too.

Like a lot of new ground, it takes a while to get comfortable with the terms, which seem to be backwards from all I ever learned about Holleys - for instance.

After supper I came back out and took another look at the carb linkage and it suddenly dawned on me why the return springs weren't doing their job. Fixed, I think. As everyone says these carbs are infinitely tuneable, but it would appear that it requires small changes. And all the prior adjustments must be done at a high perfection level.

I could have went with a single small 4 barrel but these things look so good with the air cleaners hanging out through the side of the hood.

It's good to learn new things and I have fully come to the realization that I will have to stumble through it.

Charlie

Jbird · May 12, 2008, 10:23:08 PM

Make sure your ignition system is spot on, or your carb tuning will spin you in circles. Are you using a unisyn type synchronizer or a manometer(a bunch of mercury filled glass tubes)? Get the synchronization as close as you can by adjusting the linkage before you start screwing screws.
I've played with a few dual Weber setups, the component changes are pretty easy to make, just make sure you only make one change at a time. Once you figure them out, they won't be so confusing (duuuh?).
Jbird

Charlie Chops 1940 · May 12, 2008, 10:52:19 PM

Jbird - thanks.

MSD 6A box and coil, stock dist. with a Pertronix conversion now. I went through that a couple years ago when I first got it running. It was so rich from poor ignition that it ran me out of the shop That was the first impediment to running well.

I have a unisyn type tool which seems to work pretty well. The synchronization seems pretty much right on now - and you are correct - it was all in the linkage adjustment. I had to do that a few times to find the cause and effect from carb to carb.

Each time I work on it the bulb gets a little brighter....

Charlie

1FATGMC · May 13, 2008, 12:07:13 AM

Have you thought about getting a air/fuel meter like the LM-1 we use? With it and a TPS you could make you could data log the air/fuel and see what it is doing under different throttle conditions. You can't beat it and you can get the idle right on. The nice thing is weld a bung in any vehicle and take the LM-1 to it.

How many exhaust pipes you running. I can't remember :cry: ,

Sum

Pep · May 13, 2008, 01:40:27 AM

Some times a day at the dyno will save weeks of frustration....

Fast.Fords · May 13, 2008, 03:00:42 AM

Just this from an old Multi-carb bike guy.... The Mercury filled tubes are dead on accurate for setting carb sync. Ya, i know 4 and 6 carbed bikes aren't the same as Webers, but in theory all carbs are designed to do the same thing....

The balance tubes I have are the big ones, 18" long with incrementation reading down to .10" vacuum.... If they're good enough to keep my 6 cylinder, 6 Mikuni carbed Honda balanced and synched I sure don't see any reason they wouldn't work on Webers. With one tube measuring manifold vacuum, and one each tube to the idle vacuum port on each carb synching should be easy.

Anyways, because the tubes have Mercury in them, all the shops have had to dispose of them.... I was nice enough to help the shop I worked at the time "dispose" of their set by putting them in my garage. The best thing I like about them is that they are long tubes, and even a very minor change in vacuum is readily apparent...

If you have any friends in your area who do Multi-carbed bikes, see if you can borrow his balance tubes. Not saying it's a cure all for the Weber blues, but it would certainly help with the synch.

For the off idle to WOT checking is a bit more difficult. The shop we chassis dyno cars at has the regular exhaust gas analyzer, but also has one of the old 4 gas analyzers robbed off an old Sun Engine Analyzer.... Probably another tuning tool that is out of production now in the EFI era, but IMO worth checking around for....

You're right though, the challenge of getting them right makes getting them right just feel that much better!!!!!!

papastoyss · May 13, 2008, 08:41:00 AM

Back in the 70's I ran a VW powered drag car w/2 48ida Webers. The idle jets control fuel mixture past idle speeds up to app 1500 rpm at which the main jets take over. Air correction jets control high speed mixture. We normally used a 20 spread between jet sizes ie a 170 main , 190 air correction.Webers don't like a lot of fuel pressure, seems like we used 4 lbs max. Until I found that my idle jets were way too rich we had problems with loading plugs up during staging and return road. Hope this is of some help .

Charlie Chops 1940 · May 14, 2008, 11:21:10 AM

Sum - I may take a shot at an analyzer of that nature...but not yet.

Papastoyss - I've got a regulator and in-line pressure gauge in the fuel system. Set at 2.5 psi which is sort of an average of recommended pressure.

I'm taking everyones suggestions under advisement. Anyone with some Weber experience is a lot of jumps ahead of me.

Didn't get much done yesterday or yet today. In my quest to move the foot feed closed to the firewall I screwed up my throttle cable. Had to go out and order another one this morning. Gonna work on the mechanical part of the pedal this afternoon.

Charlie

slocrow · May 14, 2008, 08:49:03 PM

I wana ride.......................

wayne petty · May 14, 2008, 09:40:57 PM

i have always been interested in carbs.. i have rebuilt hundreds over the past 30 years... not so many lately... i was following along and also think a wide band oxygen sensor with a gauge to display the fuel mixture..

i have been known to drive around with my long test leads hooked up and my digital volt meter on the dash watching the O2 voltages..

i seem to recall that jc whitney has a 30 buck gauge that can piggyback on the 02 sensor.. if you have a bung..

?? i take it that you don't...

http://www.jcwhitney.com/Air-Fuel-Ratio-Gauges/600002105.jcw

i randomly googled and this unit popped up..
http://www.performancetrends.com/wide_band_uego.htm

a few years back there was a great article in air and space magazine about the fuel injection mixture problems on flat 6 aircraft motors... somebody figured out what needed to be fixed ... changing the fuel injector flow rates to the position in the motor... another guy came up with a 6 postition air fuel ratio gauge with exhaust temps built in... all in one gauge... (for each motor)

i am thinking about tuning the weber... and my thoughts are to put a throttle stop... and tune it for part throttle first... agenst the stop... so you stick to low speed circuts, mid speed circuts and then high speed circuts..

i would almost think you would ... with the temporary throttle stop... plug off the jets for high speed and work on the low and part way through the mid speed tuning...

red line out here in walnut or compton is the importer of webbers here...

i wonder if they have a series of charts of what each differnt emulsion tube does to the fuel mixture.. and what the idle and high speed air bleeds do to...