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MOTORHEAD 04-16-2013 06:30 AM

running rich
 
Initial tuning my weber set-up on 452 FE with jets from inglese seemed rich. When adjusting idle mixture rpm picked up when leaning, but engine overheated at idle ! Installed A/F meter and confirmed rich running at all eng speeds up to 4k rpm(didn't run it faster) Initial timing 17-18 deg, max 38 deg all in by 2800.
Tuning should start with idle circuit, but leaning seems to increase heat too much. Any ideas?

dallas_ 04-16-2013 08:04 AM

When you say rich, how rich? What is your AFR at idle?

MOTORHEAD 04-16-2013 08:36 AM

Dallas; 10-11 pretty much through the whole range from idle to 4k. If I lean out idle mixture I can get 12.5, but no more and heat is rising, which is normal going leaner, but it shouldn't o'heat. Idle mix screws are at about 7/8-1 turn out at the 10-11 afr which is pretty normal.

*13* 04-16-2013 08:44 AM

I'll second the mixture screw read. If you aren't in the acceptable range you likely have the wrong jets. If you are rich, you will know just by the fumes coming from the pipes. Make sure the engine up up to temp before adjusting anything. My car sounds like a drunk hippo til' it gets up to temp.

MOTORHEAD 04-16-2013 08:51 AM

13: yeah, my first clue was my eyes burning. Never any black smoke.
I'm going to try a larger idle holder.

carmine 04-16-2013 08:58 AM

Motorhead

What idle jet and holder you running?

MOTORHEAD 04-16-2013 09:05 AM

carmine:idle holder: 80, jet : 70. 80 holder seems very small, as most BB guys on the weber survey are running 100's or 120's. The 80 was inglese's recomendation based on my engine specs. There were 120's in the carbs when I bought them (used from a fellow CC menber), so I will put them back in and see what I get for A/F reading.

Rick Parker 04-16-2013 09:22 AM

A 70 jet with 100 holder will get you very close.

carmine 04-16-2013 09:37 AM

I would say 75 idle, 125 holder for the cubes your running.

If any transitional stumbles you might try 80 idle with 130 holder.

Buy yourself pin-hole guage to check that idle and holder hole sizes are actually as marked.

MOTORHEAD 04-16-2013 04:38 PM

Put the 120 holders in with the 70f10 jets. A/f 13.5 with idle mix screws 1&1rch out. idle ok but not as smooth as 1& 1/2 turns out which gives me 11.5 and teary eyes. This engine likes a rich idle, makes no sense to me!

Rick Parker 04-16-2013 06:07 PM

I repeat:

Quote:

A 70 jet with 100 holder will get you very close

zrayr 04-16-2013 08:27 PM

Quote:

Originally Posted by MOTORHEAD (Post 1240120)
"..........Initial timing 17-18 deg, max 38 deg all in by 2800..........."

before changing any jetting, I would try 20 to 24 initial timing with the same total timing of 38. If you need less mechanical advance than the msd bushing offer (the18 degree bushing is at the bottom of their selection) then these folks have 10 and 14 degree:

Tuning MSD Distributors

nice write up at the bottom of the page...

If you have access to a start retard box, running that much initial timing is no problem. I use a msd digital 6+ box, it has a 20 degree start retard feature. It's amazing to see how fast the starter can spin the engine with the timing retarded 20 degrees.

I've had some success experimenting with timing first, before I start changing jets.

Z.

*13* 04-17-2013 03:08 AM

Have you looked at my comparison spreadsheet in an earlier thread? There are a lot of variables In there. Everything I've heard about Inglese is that he usually will get you pretty close, jet wise, if he baselines the carbs for you.
How does the car run through the throttle range driving down the road? I assume you are adjusting the idle screws by ear? If the jets are too big, the motor will still have a "best" setting & will still run rich. I suggest you buy a set of pin drills from McMaster Carr & work your way up from about 60. Solder them closed & drill one step at a time. Once you find the right size you can buy a new set... Or just leave them.
I went through the whole process with my carbs from a stock setting. You need to use your own logic to get where you need to be. The more you read online the more confusing & conflicting information you seen to get. Inglese wrote a piece online which has some useful information but, more often than not, it was confusing. Start from the beginning. You you have the right sleeve size? Does the idle jet & holder seem about the right size? The one thing about these carbs is that they don't work if something is 1 size off. When I was changing out main jets I went up two sizes because I had a stumble & I though I was too small. I still had a stumble. I said WTF & put the size between in & it was gone. It's a game of patience with a methodical mind that will get you there. Isn't that was life is about?

Gaz64 04-17-2013 03:22 AM

Quote:

Originally Posted by MOTORHEAD (Post 1240185)
A/f 13.5 with idle mix screws 1&1rch out. idle ok but not as smooth as 1& 1/2 turns out which gives me 11.5 and teary eyes. This engine likes a rich idle, makes no sense to me!

If you have a fairly wild cam, you'll get high hydrocarbons and teary eyes from the high valve overlap and late closing inlet.
The rich idle shows up as unburnt fuel since all the available oxygen was already used up in the combustion process.
Getting the A/F ratio to read chemically correct may make it lean in the cylinder. Unfortunately, this is where sequential EFI wins.

MOTORHEAD 04-17-2013 07:53 AM

Rick: I heard you the first time, but I don't have any 100's handy so I tried the 120's but those seem too rich. So, if 80's are too rich, as are the 120's how could a size in between the two be anything but rich also? Not trying to be a SA, just trying to learn .

MOTORHEAD 04-17-2013 08:03 AM

13: Oh yes, I have spent much time pondering you spread sheet ! There is only one BB there with same c.i.d. as mine, 452. (427 with 428 crank) and he is using 37mm chokes, all larger 482's are using 40's. My carbs came with 45's which I though might be too large, but Inglese thought they should be ok, so based on that, my main jets are 180's, while larger displacements are getting by with 150-170 main jets.
to be cont.

MOTORHEAD 04-17-2013 08:15 AM

Cont: I'm making my posts short as I type slow and have been having trouble connecting to this site.
My first runs with the jetting the carbs came with had a good idle, but stumble in the transition area. No AF gauge at that time. I called Inglese and he sent me a jet package based on my eng specs. Trial run after installation showed improved idle, but still stumble in transition. Called Jim with results and he said I should set the initial timing up to around 18 deg, which I did but then the stumble was just at lower rpm.
After that I bought and installed the AF gauge so I coul see if it was going rich or lean.
cont;

MOTORHEAD 04-17-2013 08:27 AM

Gaz: My cam was spec'd for webers by Barry R. I don't consider it wild at all. It's a hyd roller for street with some track time. I'll have to get the specs.
What you're saying is that due to the cam overlap it may not be possible to get a good idle at best a/f ,and for best performance it will have to run rich, at least at idle ?
I was thinking that might be the case, but I'm still rich over the whole rpm band.
When I mentioned A/F meter to Inglese he said " do you want it to run right, or do you want to chase numbers?"
I want both, as much as possible. I realize there exceptions and trade-offs.

MOTORHEAD 04-17-2013 08:32 AM

13: I have not had a chance to drive it since I changed the holders. Going to try that later today . I hope the A/F gauge will let me know if the stumble is from too rich or too lean. I do have a new set of 40mm chokes if that might be more appropriate.

MOTORHEAD 04-17-2013 08:38 AM

3 Attachment(s)
just for grins:


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