Need Help with tuning Webers

[priobe]

Hello All,

I have been trying to figure out these webers for awhile now. Of course the more you play with them, the more you will understand them.
My questions is, I installed a fresh set plugs NGK # 7 in my 427 SO engine and ran the motor for about 3-5 minutes at idle and plulled the plugs and found that they were black carbon. Here are my specs:

Main Jet - 160
Air Corrector - 210
Emulsion tube - F-7
Chokes - 37
Bypass - 55
Idle Jet - 55 F10
Idle Jet holder - 120
Pump Jet - 45
Aux Venturi - 45

I also noticed that my mix screws are about 2 to 2 1/2 turns out. Whats funny is I am using an LM-1 to tune the carbs and I set it lean to about 17.1 -18.1 and it still runs rich.

I read the articles on the web from inglese and it states that it should be 3/4 turn on the mix screw. I am suspecting that I need to change the value on my my Idle Jet and Idle jet holder.

Any suggestions

[jay bentley]

Turning your mixture screws to 3/4 turn will put you in the ballpark.

Jay

[ERA 626]

Running your motor at Idle then pulling a plug will result isn a rich mixture, the best way to do that is to get the car up to speen approx. 60mph then clutch in turn key off pull over to the side of the road then check it. This will give you an accurate reading.

[priobe]

Jay,

If I turn in the mixture screw to 3/4 it will lean out even more. I was thinking that I had to change the value on the Idle jet holder and Idle jet.


ERA 626,

If I move the car wont the other circuits change the read of the plug?

Are your plugs black when you pull them out?

[Gun Doc]

priobe

I don't have much experience with Webers, but I have read about them and have plenty of experience with Harleys and other bikes with similar problems.

When "reading" plugs, you should always start with a fresh, properly gapped set...For each run. Webers run on the idle circuit up to around 3000rmp, so you should make a run from a start up to 3000rpm, then like ERA626 said; clutch in, engine off, coast to a stop and pull the plugs. They should be light tan. Black (sooty) indicates an over rich condition (too much fuel).

If the 3000rpm run checks good, but you still foul plugs, you should do another run (fresh plugs) up to 5000rpm, or so. Same thing start from a standing start then put in clutch and shut off the engine. Problems here could be with your mains, as the idle circuit does nothing after about 3000rpm.

Jay is right on when he states that you should be at 3/4 turn on the idle mixture. You should never have to go more than 3/4 of a turn to get it right. If you have to go past that, you probably need to go up in idle jet size. Your problem sounds more like your jets may be too large, or the mixture screw is too far out.

Like I said, I am no expert but the above are pretty basic tuning tips when it comes to Webers.

Gun Doc

[priobe]

Update:

I spoke to pierce manifold and they recommend to lower my idle jet to 50 and then if that does not work change Idle holder to 60.

I will give that a shot as well as the above mentioned. At this point I will try anything.

Maybe FI is the way to go?

[Gun Doc]

priobe,

Don't give up!!! That 427 NEEDS those Webers!!!!

It looks great, and once you get it dialed in, it will sound great, as well!

Gun Doc

[priobe]

Thanks for the words of encourgement.
Its just that every time I try to post a problem about these webers, I never seem to get a response to my questions.

Here is a pretty simple question that I can not seem to find an answer to.....

I am experiencing a problem as well as others on CC, that when you start your motor with webers the fuel pressure starts to fade.

Anwsers
1. Is this normal
2. Is this a bad pressure gauge
3. Is it a bad fuel pump
4. Nobody seems to know the answer


what should the pressure be set too if it fades after the motor warms up. the cold setting or the warm setting. If you set it to the cold setting, how do you know if you are getting the correct pressure when it is warm? And vice versa.

[G.R.]

Originally Posted by priobe

Thanks for the words of encourgement.
Its just that every time I try to post a problem about these webers, I never seem to get a response to my questions.

Here is a pretty simple question that I can not seem to find an answer to.....

I am experiencing a problem as well as others on CC, that when you start your motor with webers the fuel pressure starts to fade.

Anwsers
1. Is this normal
2. Is this a bad pressure gauge
3. Is it a bad fuel pump
4. Nobody seems to know the answer


what should the pressure be set too if it fades after the motor warms up. the cold setting or the warm setting. If you set it to the cold setting, how do you know if you are getting the correct pressure when it is warm? And vice versa.

Priobe,
I think the gauge pressure fade is more common than not. I've set mine with both the engine cold and warm I've found in my case that the warm engine setting, 3lbs, increases to about a 6lbs reading upon a cold start until the engine warms up and a rich mixture, lots of smoke out of the exhaust results and over time it drops to about 2lbs. I finally went back to a cold engine set of 3.5lbs and have left it at that, as long as I have fuel the engine runs well, the pressure will also show a drop to about 2-2.5lbs after being run for awhile. I'm using an Aeromotive 0-15lb "dry" gauge. I think if the fuel pump was bad you'd develop erratic pressure readings .

Gary

[427Aggie]

Ok lets ask some basic questions

1. Was the a new set of weber..IE manufacturered in 2005?
2. The only way I found you can accurately tune webers is to put the car on a dyno for a day and just keep tweaking....when you dyno tune it you can plainly see what idles, mains and air correctors you need.

basic 427 setup should be 37MM Chokes, 120 Idle Holders, 60 Idles, 160-65 Mains and 200-210 Air correctors with a .50 - .55 bypass in the float bowl.

3. Did you ever set the floats? you can't assume that they were correct.

4. What pressure are you trying to run the webers at? I ran mine at less than 3lbs usually around 2-3...I set mine when the car was warm and then just forgot about it...if I had fuel I was good.

5. ARE YOU RUNNING SOME TYPE OF FILTER ON THE CARB!?!
bad bad bad...I could absolutely NEVER get mine tuned if I had any type of filter on the carb...theres a really good air flow analysis over on the GT40s.com website that shows how much these things like air and how anykind of disruption changes the complete characteristics.

I spent 3 years learning how to freakin tune these things and still have serveral thousand dollars in jets and parts....THE DYNO really taught me how to fine tune a set. Once I got mine tuned in I NEVER>....NEVER had to either sync them or tune them again..they just ran and ran and ran.

And yes they will ALWAYS smell like you are running rich even if they are tuned correctly and you really can't read the plugs.

matt

[aldersonjames20]

Originally Posted by 427Aggie

5. ARE YOU RUNNING SOME TYPE OF FILTER ON THE CARB!?!
bad bad bad...I could absolutely NEVER get mine tuned if I had any type of filter on the carb...theres a really good air flow analysis over on the GT40s.com website that shows how much these things like air and how anykind of disruption changes the complete characteristics.
matt

So you run your webers open, no filter of any kind? I have velocity stacks on my efi that I am thinking of running with no filter, but everyone I talk to says that it will be fine, till I suck a rock in there or too much dust. I have actually picked rocks out of my current filter so I have to say it does scare me. How do you prevent this type of thing?

James

[ENTDOC]

is it possible that you have a header leak that is giving you a false reading on the LM-1? I just orderd several sets of jets and got an LM-1 so I can try to get mine running better also. Aggie has much info on these things and will tell you some issues that pop up on 427 slanted manifolds. These things are frustrating but fun.

[Randy Rosenberg]

Originally Posted by ENTDOC

is it possible that you have a header leak that is giving you a false reading on the LM-1? I just orderd several sets of jets and got an LM-1 so I can try to get mine running better also...

LM-1's seem not to like being at the end of a sidepipe. I don't have one, but when a trusted expert tried to use one on my SPF, it didn't accurately at all. Others in our BACC have had the same problem, and they have installed O2 sensor plugs (ports) in their collectors in order to get the O2 sensor closer to the source and away from the end.

Hope this helps,
Randy R...

[Terry Brown]

I am the lucky recipient of one of Traindriver's laser cut plates. I had mine chromed and it simplified my linkage setup. Works much better than the side pull linkage. I think you are getting the DISCOUNTED price!! Better get it now before he raises the price!




Terry Brown SPF 930

[dwblaine]

I'm listening here because I am in the process of installing my webers right now. 48IDA's on a 351 Stroker.

I just ordered the individual air filters that go on each velocity stack. You're saying this is a bad idea?????

Dean

[priobe]

1. Was the a new set of weber..IE manufacturered in 2005?
No this is an older Italian system that I purchased used Everything was tight

2. The only way I found you can accurately tune webers is to put the car on a dyno for a day and just keep tweaking....when you dyno tune it you can plainly see what idles, mains and air correctors you need.
My setup basic 427 setup should be 37MM Chokes, 120 Idle Holders, 55 F-10 Idles, 160 Mains and 210 Air correctors with a .55 bypass in the float bowl.
4. What pressure are you trying to run the webers at? I ran mine at less than 3lbs usually around 2-3...I set mine when the car was warm and then just forgot about it...if I had fuel I was good.
My pressure is 3 PSI when it is cold then I readjust it when it fades

5. ARE YOU RUNNING SOME TYPE OF FILTER ON THE CARB!?!
bad bad bad...I could absolutely NEVER get mine tuned if I had any type of filter on the carb...theres a really good air flow analysis over on the GT40s.com website that shows how much these things like air and how anykind of disruption changes the complete characteristics.
Open no filters at all

Thanks Aggie for chiming in.

ENTDOC,

I verified my exhaust and it is sealed.

Thank you for suggestions


Dwblain,

I hope this thread help you also, and we all get a benefit from this thread. I know I will

[ENTDOC]

what does 50 (or whatever number ) mean on the exaust jets? do 50's allow more or less fuel through the squirters than 55's? I get a lot of black smoke when I goose the throttle; I have 50's

[traindriver]

EntDoc

The exhaust jet is a bypass jet, basically in parallel with the pump jet. It's the only gas jet in the IDA where the SMALLER the number the MORE fuel is supplied. So a 050 (actually .50mm dia) puts more fuel thru the pump jet. Try a 055 to reduce the pump shot a bit. For those with lots of $$ and patience..you can play with the pump jet along with the exhaust jet (aka drain jet) to affect the shot volume and duration..the exhaust jet mainly affects the volume of the shot whereas the pump jet mainly affects the duration. I haven't ventured there yet.

Chuck

[427Aggie]

Oh its all about cubic dollars..especially since you spend everything times 4 or 8.

Entdoc did you get yours fixed?

The problem of the old Italian vs the new cars is in the pump jet. The old ones us a ball at the bottom of the pump jet that is screwed in...the new ones push in and unfortunately inside the jet itself they put a brass fitting that is flat!...so when you cant the carbs 10deg the ball doesn't always fall in the hold and stop the fuel...IT DROVE David and I NUTS!!! to the point he was ready to just sell the car...he finally figured it out..you have to remove the brass fitting in the bottom and then ream out the hole to have a dish so the ball always!!! falls in and stops the fuel in the squirter..check that and make sure yours aren't press it but screw in..one of these days I will take a picture of what i'm talking about.

I never ran filters on my car...I changed my oil much much much more often and the rocks were a concern but..this is to give you an idea of how much is screwed up my tuning. WIthout filters I ran 170 Mains! with them I got down to 105's and was still running pig rich! Now this was before the dyno that we now have access to but you can see the difference now in how they normally run and rich!

Ok the one thing your going to have to do is just step back and do one thing at a time or your going to go NUTS. Your not getting popping so I'm not going to go into CAM issues.

Really is there a dyno close that you can rent for about a half a day to tune the car with?

Its really neat watching what the jets do...the idles will hold you up till about 2500-3500 and you can watch on the graph where they change to mains up to about 5500 then you can watch how the air corrector changes it from about 45-5000 up...its really kind of cool when you see it graphed out..the only problem that your going to have is your going to want to make sure you have enough jets to change about 20 up or down from where you are Thats where it gets expensive. Send me an IM and i'll give you a number to call me at and we can talk.

CalMetal has forgotten more about Webers than I'll ever know but he took the time to teach me stuff and get me pointed in the right direction and for that I will be eternally grateful and willing to pass on the knowledge.

Matt

[427Aggie]

Oh and Dean here is the suggestion I'm going to give you. I volunteer my jets to Rob at Keith Craft Motorsports in Plano. The rule is if anyone does a tune with Webers I come up with the kit and he just replaces the last set of jets that he used so you and he don't have to keep (what is about $3000) worth of jets and parts on hand..I went a little nuts.

Robs going to be in Austin this weekend so talk to him about setting up a time to bring the car up and tune it...you can do it with and without the filters then and see the difference it makes..your going to want them to be setup anyway and when he does it and I'm there I can show you how to do everything on the carbs so you don't have to worry about it going forward.

matt