Need Help with tuning Webers

[ENTDOC]

easy to make a pattern out of cardboard and trace it onto a piece of aluminum flat stock, cut it out with a jig saw

[Gun Doc]

ENTDOC,

Did you ever solve the rich condition on your BB? Are you now running Webers on the GT40? If so, how does it run?

You may have seen my posts over this past weekend regarding my linkage problems. I think I have that part fixed, at least for now, but my engine is running pretty rich on the idle circuit. Like you and your BB, when I punch it, it looks as if a Mac truck just pulled out!

I am running a 351W with 185AFR heads, cam has 573 intake lift, 244 duration, 568 exhaust lift, 230 duration. Timing is 32 deg, emulsion tube F7, 145 main jets drilled to.058/120, 120 low speed air bleed, 70 idle jets and 120 high speed air bleed.

The engine runs great once the transition to the main circuit is made. No stumbling, except right near 2000rpm, which I think may be caused by flooding.

Any help any of you Weber experts can provide would be greatly appreciated!!

Thanks,

Gun Doc

[ENTDOC]

your bypass jets will largely control the amount of fuel when you punch it, what size are they? They are usually 50's so you may need to go to 55. Having said that, mine got really better after going to 40mm chokes,no black smoke anymore

[traindriver]

Gun Doc,

Yes I do have some, in fact i have a complete SPF centerpull linkage kit for a 351. email me at cbdesignengineering@wi.rr.com.

[tommyboy]

Gun Doc,
There are a few things you should address given the engine/carb specs off your last post. Some things free and easy some thing can be more expensive. So let's start with the free and easy.

1) Float level and fuel pressure properly adjusted.

2) Carbs synchronized.

3) Timing - Try 14-16 degrees initial timing with about 20-22 degrees advance for a total of 34-38 degrees all in by 2500rpm.

4) Idle mixture adjustment - Try getting your idle speed down around 650rpm when adjusting the mixture screws. You want to make sure the throttle plates are closed as much as there allowed. With engine off lightly, carefully turn the mixture screws(clockwise) all the way in ( I remove the idle mix screw springs for this so I have a good feel). Once you have determined the fully seated position index the screw(12 o'clock) for future reference using a yellow paint marker or something that will last while. You now have a nice quick visual for where your idle mix screws are set. Reinstall the idle mixture screw springs and set all 8 mixture screws at 1/2 or 3/4 turn out. You now can turn each screw one cylinder at a time in/out (lean/rich drop) to achieve best idle. Too lean you will have a slight pop out the side pipe. If so tweak it a little rich until no popping is heard. End result should be idle screws between 1/2 and 1 turn out each. If over one turn you can try going smaller on your idle jet then tune with your idle jet holder. You should move down to a 55-60 idle jet from your 70 idle jet. As for idle jet holder try 90 through 120. (to save money on idle jet holders I have purchased the smaller size and precisely drilled out larger until I am where I need to be. Also you can solder the orfices shut then precisely redrill to the I.D. you want to try. Just make sure you cleanup any access solder on the inside bore of the idle jet holder without removing any original brass. Once you get to your final and proper jetting size purchase that particular size). Once you get your idle mixture and idle speed circuit tuned you can increase your idle speed to where ever you feel comfortable.

5) Your F7 emulsion tube is rich. You should achieve better midrange (pickups, 2000rpm to 3000rpm range) by going to a leaner (larger diameter) F16, F15 emulsion tube. Above this rpm you will be tuning your main circuit with your main jets and air correctors, although you can affect your midrange driveability by tuning with the main jets some. Remember this, changing a main jet richer or leaner will affect the main circuit fuel mixture throughout the entire rpm range. Changing the air corrector jet will affect the main circuit fuel mixture in the upper rpm ranges.
What I have done to reduce the midrange stumble is to lean out the midrange by installing the leaner emulsion tubes then leaning out my main jet until the stumble disappears. Then do some full throttle passes (hold in the clutch and cut the igniton) and check you spark plug colors. Tune the high end by changing the air corrector jets richer/leaner until your mixture is just right.
Remember, if you change one area of your jetting you will most likely have to tweak another.

Goodluck.

[ENTDOC]

where did you get your idle jet holders?

[Gun Doc]

Thanks to all for great insight and advice on tuning these carbs. I guess my first step is to purchase to the Weber tuning manual and the synchrometer, then I can look at what parts need to be replaced to get this thing running correctly. Do any of you know of a good source for chokes, jets, etc?

Thanks,

Gun Doc

[ENTDOC]

EBAY is where I have gotten most of my parts. Weber carbs direct is good