Webers.....
 

I have been using the wealth of information from this site for the last 4 years. Finally my ride is running and on the road. Building this car was a gas... So here I am looking for some help from some of the weber guys. I built a Ford 408 (stroked 351), please see engine specs below. I topped the Ford off with Webers from Carbs Unlimited. The engine runs OK but is running really rich, plugs are black and it has a stumble around 2000RPM. Once past that point it pulls pretty well. It starts good and runs pretty good (with an occasional pop or fart) but seems to go down hill after it warms up. Once warmed up I am getting a loud backfire from the exhaust when backing off the gas and sometimes while at idle. The side pipes are flanged as well as the headers so I doubt that I have an exhaust leak. One odd thing, I installed the small air filters (one on each stack) and it ran awful, almost undriveable. Removed the filters and it went right back to running OK.
I have not yet changed anything in the carbs,
Main Jet 135
Air correction Jet 120
Emulsion Tube F7
Choke 37
Idle Jet F10/70

Engine specs.
Ford 408 (stroked 351W)
10.5-1 C/R
Alu Heads
Hyd Roller cam: Gross valve lift .603 (Intake) .608 (Ex)
Druation @ .050 230 (Intake) 236 (Ex)
Lobe separation 114.0
Timing set @ 16 deg at Idle with an 18 deg bushing for total advance 34 deg. Full advance at 3200 RPM.

Any and all suggestions are welcome, I really think that the issue is in the jetting.
Thanks

What is the idle air holder size. This plays a big part in the idle and up to about 2700 RPM area.

Tony,

As Rick has asked, the idle jet you have is 70F10.

All IDA holders are designated "F10".
What size is the air hole in the side of the tube? 0.60mm, 1.00mm or 1.20mm?

Looks like the carbs are jetted "Stock" which means your Idle holder should be 120. I have a 294 C.I. SBF with a cam that is not quite as healthy as yours. Here is what I ended up with...
Idle Jets 60F10
Idle Holder 110
Main Jet 140
E Tubes F7
Air Correctors 100

Make sure you set the floats at 5.5mm. Get the float gauge tool from Gene Berg. If you want to save some money, get some drill bits from McMaster Carr & start soldering & drilling your your jets until you find what works. Then buy the correct jets once you get it all figured out. Start with the Idle circuit & work your way through to the air correctors. Many of us here have done it with success. It can be frustrating, be patient & settle in for a fight! :3DSMILE: One piece of advise I can give... Don't skip a size in jets. I had 135's (Main Jets) in the car & it stumbled. I put 145's in & it stumbled. I put 140's in & stumble disappeared. Webers are very sensitive.

Thanks Guys,

I will need to pull the jets to confirm the size. I am guessing that I will need a set of small drill bits to use for measuring. Busy tonight but will have at it on Wed.

Thanks again, this gives me a good starting point

Tony

They should all be clearly marked.

Thanks #13, getting the drill bits on order today from McMaster. I have played with a ton of Holley's over the years but I have to admit, I need to learn alot about the Webers...

Tony

Good suggestions, but before you change any jets, try just a little more advance first. I was surprised how much difference an additional 2 degrees made on ours. 36 degrees was recommended to us.

A little carb theory goes a long way with webers. If you understand the theory you will have a lot better time of it. & as above, timing does help. I have mine at 18 deg initial right now.

Thanks, I'll try twisting another 2 deg advance out of it.

Tony

Chances are its not going to clear up your plugs, but it will get you at the correct starting point. Once you get it a little closer you will want to check total advance.

Thanks #13, my thought exactly. I will add the timing and it may help with the exhaust backfire, but the plugs will still be black.

Hey Dallas, can you share your jet sizing with me? You have a few C.I. on my 408 but I am thinking it may give me a better starting point.

thanks
Tony Loz

I don't know if you've seen this yet? I have been thinking about starting a new thread to update the spreadsheet. Ideally I'd like to get all of the info from everyone that I can to have a comprehesive list. If I was a web guru I'd set up an editable list...I'm pretty webtarded, unfortunately...
http://www.clubcobra.com/photopost/d...G-SURVEY-1.jpg
As you can see there are 3 identical lists. The highlights were to point out similarities & overlap was to read "Lobe Separation"

Tony, idi you come up with the idle holder number yet? There's a big chance you have to move up to 120 as Rick says. As it look you have a rich low-end it might also be a acc-pump setting, although I've not done any work on the IDA's I'll have to loook it up in a book!

Your mains and airs look OK (although they might not be ideal for your setup- testing & measuring will tell).

The puffing & popping might not be caused by fuel. The carb sync need to be 100% spot on; always... The tendency for nuts & bolts in the links to move slightly made me move away from the webers in racing applic.

Get the timing up as adviced as well.

It will run good in the end, so spend your time fiddling with those carbs.

Thanks for the note. The idle holder is a 120, I am picking up a set of small drill bits tonight, I am thinking of changing it to a 100 (or 1mm I think)... I sync'ed the carbs and they should be good, I will check them again. Rechecked the timing and added another 2 deg, 18 deg at idle and 36 deg at about 3200RPM.

I read an old stream about the popping, figured I would give it a try, opened each of the idle mixture screws about 1/2 turn. Popping is now gone, I am thinking this is just covering up another issue. I will play with jetting a little and hopfully can go back to the orginal 1 turn at the idle mixture screws.. It seems to clear out at highway speeds 55-65 MPH... This is the first time I had driven a Cobra, total of about 60 miles on it now, what a friggin blast....

I did order the float level gauge and will confirm settings as soon as I have the tool

Thank you everyone for the info, I will follow up with my finding.

Later and thanks again
Tony Loz

One item that is illustrated but not discussed when setting the IDA floats is a 3" long piece of 3/16"-1/4" wide clock spring. It is used to hold the float in a stationary position while taking measurements. I went to a clock repair shop and the guy had cigar box full of broken springs, he cut off a piece. This little item is a big help.

Hyde: What is the significance of the "Yellow Bars"?

I had originally put those in to draw comparisons between jetting setups.
Here is the new chart with jetting updates that I have received...
http://www.clubcobra.com/photopost/d...g_Database.jpg

Rick,
I made my own float spring and do not like the way it pushes the float to one side. I think I get a better adjustment using a screw driver to pull back the vert. tange to raise the float. That connection on the screw/shaft is loose. I got quite a bit difference with the two methods. Using the spring did you have to change the adjustment?

I had it push the float opposite from the needle & seat instead of at the side.
IE at the opposite end/side of the float bowl.

I finally got out to my garage last night wth my float gauges from Gene Berg. All four carbs where set quite high. What a difference... The idle changed from about 900 RPM to 1300 RPM and the engine behaved very well around town. Now I have stumbles at higher RPM. I starts to act up around 3500 RPM and seems to carry on up to 5000 RPM where I shift. Its a new motor so I havent been running it up to 6000RPM (yet). I am thinking a main jet change may fix this??

Gaining on it

Tony Loz