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Wed Jul 15, 2015 3:23 pm

These are the modified venturi that Doug was referring to.

Wed Jul 15, 2015 4:31 pm

A set of chokes like this for our 58's went into Flemming's Super Street engine,,, (making close to 300hp) Gained 17hp @ 8500rpm's,,, The road racing mazda,,, Gained 8 mph on the straight away (13b single58) Which is around 30% increase!!! Anton (my buddy in Reno) that has been helping me develope these for the last couple yrs. He went from 42 choke to Grooved 40 choke & gained 7 hp topend,,, and move peak torque down 1000 rpm's and increased it !!!! They come in different sizes Doug...

Wed Jul 15, 2015 5:28 pm

That could make all the 37's floating around more usefull.

Dan

Thu Jul 16, 2015 8:27 pm

Doug Berg wrote: A set of chokes like this for our 58's went into Flemming's Super Street engine,,, (making close to 300hp) Gained 17hp @ 8500rpm's,,, The road racing mazda,,, Gained 8 mph on the straight away (13b single58) Which is around 30% increase!!! Anton (my buddy in Reno) that has been helping me develope these for the last couple yrs. He went from 42 choke to Grooved 40 choke & gained 7 hp topend,,, and move peak torque down 1000 rpm's and increased it !!!! They come in different sizes Doug...

This sounds super interesting. Would you say this technique is only helpful for race engines or would street engines also benefit?

Thu Jul 16, 2015 10:52 pm

On our flowbench we have 2 meter's,,, 1 read's the volume,,, the other read's airspeed,,, Most flowbench's only read volume!!! We modify the IDA's to set screw the booster in!!! (secondary auxillary) this allow's us to rotate the booster 180 degree's in the carb,,, And run the airspeed probe in the booster,,, So we can read the vacuum on the E-tube (main jet) The grooved 40 chokes Anton is using,,, Had the same signal on the booster as a 38 choke,,, And the total volume was very close to the straight 42 choke!!! Mark @ GBE has a flow simulator on his computer @ home,,, He said this shape hole flowed over 15% more than a round hole of the exact same size !!! Doug...

Thu Jul 16, 2015 11:31 pm

That's way cool. Thanks for sharing this, I will try it too!
Oh, and don't worry I won't tell anybody if it works or not, LOL

Thu Jul 16, 2015 11:52 pm

The guy w/ the road racing Mazda( a lot like a Super Vee) He was complaining about how hard it was to drive thru the pit's @ pit speed even in low gear,,, We moved him from a 50 mm straight choke to a grooved 46 choke,,, He is very happy w/ the drivability in the pit's now,,, They figured it @ 30% increase in power because it's up over 160 mph down the straight away now!!! I believe it work's on all engine's!!! A greater volume of air @ a higher velocity is what we all dream of!!!! Doug...

Fri Jul 17, 2015 12:38 am

Hi guys! Where can I get a set of 38mm vents?

Fri Jul 17, 2015 1:12 am

I have a set here,,, they're just 37's opened up on the lathe!!! Doug...

Fri Jul 17, 2015 1:21 am

Doug Berg wrote: I have a set here,,, they're just 37's opened up on the lathe!!! Doug...
How much? Can you post a clear pics?

Fri Jul 17, 2015 11:53 am

I'm pretty sure I can arrange to have your's cut @ GBE,,, Not sure on what kind of price??? They have a 4 day work week (closed on friday's) The shop is in Orange Cal. off of Ball Rd. Let me know!!! And "no" I can't do picture's yet!!!! Doug...

Fri Jul 17, 2015 12:59 pm

Doug, I'm interested as well. I'd like to get my 40mm vents modified. Please keep me in the loop.
And possibly my ida vents prepped for my race carbs. Those are 44s.

Fri Jul 17, 2015 2:19 pm

Another berg inovation!!! Nice to see it happening again. Like to know how much it will cost for the mod. I will call GBE on monday.

Doug for a engine that likes size X standard type, how many mm smaller choke would you need to start with for the mod to achieve the same HP but the better low end or a split the difference?

Dan

Fri Jul 17, 2015 2:23 pm

The other thing not mentioned here is "Profiling" the carb's,,, We swap the fluted butterflies for "non" fluted,,, and knife edge them,,, (swap to our throttle shaft's) or modify yours,,, (ours has adjustable squirter ramp) It's anywhere from 20 to 35 cfm improvement!!! which is about 15 to 18 hp increase!!! (on Johnny Loctite's)(John Schurger) I went up 20 some cfm and no change on the dyno!!! went back more mods to carbs up to 35 cfm improvement!!! and no change on the dyno!!! Sitting there smoking a cig staring @ the dyno,,, (In my head I heard Gene say... "Cant get it in if you cant get it out"!!!) Change to 1 7/8 header from 1 3/4 and "BOOM" 21 hp gain!!! Doug....

Fri Jul 17, 2015 7:08 pm

Dan,,, the # of grooves is odd (7) so that the grooves are not opposed,,, so the cross section remains small,,, all of the math is based on the radius,,,, If say you have a 40 mm choke,,, And you start w/ a 37 choke for grooving and then cut a 42 mm groove in it,,, That gives you a 39.5 choke which out flow's the original 40,,, while still having the velocity closer to the 37 choke you started with!!! (18.5 + 21 = 39.5) I like "middle of the road".... When it comes to rod length,,, not too long & not too short,,, valve/port size,,,, not too big & not too small!!! It's funny "they" call it a "HAPPY MEDIUM" !!! (or just right!!!) Doug...

Tue Aug 11, 2015 10:48 am

Okay I'm doing some fine tuning. My current jetting is f11 65/120 idle 155mains 200airs 37 vents. The car runs smooth as butter from idle to 6k but I think it's still rich . I changed the idle to 60/120 and now there some hesitation on transition :x so I know it's running lean. What should idle airs should I get 110or 115? Please I need your help so I can buy today thanks !
timing is 28* full advance / 8*idle

Tue Aug 11, 2015 11:36 am

2 or 3 progression holes? The solution is to bring the mains in sooner, not keep the progression longer, UNLESS the carbs only have 2 prog holes. The problem is so large, that's why tuners and eventually Weber went to the 3 prog hole on the IDA. 2 is insufficient IMO.

vwsb74 wrote: Okay I'm doing some fine tuning. My current jetting is f11 65/120 idle 155mains 200airs 37 vents. The car runs smooth as butter from idle to 6k but I think it's still rich . I changed the idle to 60/120 and now there some hesitation on transition :x so I know it's running lean. What should idle airs should I get 110or 115? Please I need your help so I can buy today thanks !
timing is 28* full advance / 8*idle

Tue Aug 11, 2015 11:46 am

[email protected] wrote: 2 or 3 progression holes? The solution is to bring the mains in sooner, not keep the progression longer, UNLESS the carbs only have 2 prog holes. The problem is so large, that's why tuners and eventually Weber went to the 3 prog hole on the IDA. 2 is insufficient IMO.

vwsb74 wrote: Okay I'm doing some fine tuning. My current jetting is f11 65/120 idle 155mains 200airs 37 vents. The car runs smooth as butter from idle to 6k but I think it's still rich . I changed the idle to 60/120 and now there some hesitation on transition :x so I know it's running lean. What should idle airs should I get 110or 115? Please I need your help so I can buy today thanks !
timing is 28* full advance / 8*idle

John, they have 3rd progression holes .

Tue Aug 11, 2015 2:07 pm

vwsb74 wrote: [email protected] wrote: 2 or 3 progression holes? The solution is to bring the mains in sooner, not keep the progression longer, UNLESS the carbs only have 2 prog holes. The problem is so large, that's why tuners and eventually Weber went to the 3 prog hole on the IDA. 2 is insufficient IMO.

vwsb74 wrote: Okay I'm doing some fine tuning. My current jetting is f11 65/120 idle 155mains 200airs 37 vents. The car runs smooth as butter from idle to 6k but I think it's still rich . I changed the idle to 60/120 and now there some hesitation on transition :x so I know it's running lean. What should idle airs should I get 110or 115? Please I need your help so I can buy today thanks !
timing is 28* full advance / 8*idle

John, they have 3rd progression holes .

Why when I changed the idle jet I'm now having hesitation on 3-3500k rpm
Before it did not? I have hesitation also below 2000rpm and it smooth out until 3-3500k rpm and smooth again .
My understanding is stumble below 2000rpm small idle jet, stumble 3k-4000k rpm small main jets is this correct?

Tue Aug 11, 2015 4:30 pm

Pulled the 60 and put back the 65 , while waiting for the 110 air holder from Italy . Update you guys in few days. Right now the 65/120 combo is like butter with a hint of gas :lol: