IDAs, Venturis and intake valves...
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Re: IDAs, Venturis and intake valves...
So, I removed one of my IDAs and decided to look inside.... What a cluster. By all means NEVER assume that the shop that you spent hundreds of dollars having the carbs rebuilt and replacing a float would actually set the float height. I flipped the carb upside down and the float was hanging nearly twice the setting called out for in the book. So I'm starting from scratch. I have set the needle and seat to 25mm by sanding the gasket to achieve this measurement. I fortunately have the Gene Berg tools to set the float height.
I hope that going back and ensuring the float height is correct will improve my ablity to tune these carbs with effective results.
I hope that going back and ensuring the float height is correct will improve my ablity to tune these carbs with effective results.
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Re: IDAs, Venturis and intake valves...
Bummer
better luck with round 2
better luck with round 2
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Re: IDAs, Venturis and intake valves...
So I completed the work required to get my IDAs back to spec. I started with a leaner idle jet stack, but the engine just likes the 100/65 idle jetting. My main jet stack started at 200 air correction, F2 emulsion and 145 main. it ran much better! It is rather lean on the top end. The wideband shows high 10 to 11.4:1. I installed a bigger air correction jet (210) to see if it would lean out just a bit, but it didn't seem to help.
Any of you have any more insight to help clean up the top end of my main circuit???
Any of you have any more insight to help clean up the top end of my main circuit???
- Marc
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Re: IDAs, Venturis and intake valves...
You mean rich, right?ecksrash wrote:... My main jet stack started at 200 air correction, F2 emulsion and 145 main. it ran much better! It is rather lean on the top end. The wideband shows high 10 to 11.4:1. I installed a bigger air correction jet (210) to see if it would lean out just a bit, but it didn't seem to help...
- Piledriver
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Re: IDAs, Venturis and intake valves...
Put the F11s back in, all else same.
Addendum to Newtons first law:
zero vehicles on jackstands, square gets a fresh 090 and 1911, cabby gets a blower.
EZ3.6 Vanagon after that.(mounted, needs everything finished) then Creamsicle.
zero vehicles on jackstands, square gets a fresh 090 and 1911, cabby gets a blower.
EZ3.6 Vanagon after that.(mounted, needs everything finished) then Creamsicle.
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Re: IDAs, Venturis and intake valves...
Yes Marc, I made a mistake typing... It is rich on the top end, which I tried to correct with a larger air correction jet. I may try a smaller main jet. I'm at 145 with the main now... if I can locate a set of 142 mains I'd be ecstatic!!!
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Re: IDAs, Venturis and intake valves...
Your trying to fart threw a straw, ,
That 1 5/8 header is chocking it
beg barrow or steal a 1 3/4 header
really wakes them up been their
That 1 5/8 header is chocking it
beg barrow or steal a 1 3/4 header
really wakes them up been their
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Re: IDAs, Venturis and intake valves...
I am really glad I stumbled on this thread. I'm about to make the switch to IDA's from 44 IDF's and this info is invaluable. I am also upgrading my motor. Here are the specs when I get it running:
2275
10.2:1 cr w/ SLR Cams EXR 310 (@ .050" 268 deg. dur., .417" @ cam, w/ 1.4:1 rockers .584" lift at valve)
1 5/8" merged exhaust
Performance Workshop (Tims) Stage 3 heads
Stinger S4 ignition
I'm hanging onto my 44's until after I know the motor will run right w/ the 48's.
ecksrash - Keep us posted on this. When/If you get it running "perfect" I'd like to know what your jetting/timing/etc. solutions were. Thanks!
2275
10.2:1 cr w/ SLR Cams EXR 310 (@ .050" 268 deg. dur., .417" @ cam, w/ 1.4:1 rockers .584" lift at valve)
1 5/8" merged exhaust
Performance Workshop (Tims) Stage 3 heads
Stinger S4 ignition
I'm hanging onto my 44's until after I know the motor will run right w/ the 48's.
ecksrash - Keep us posted on this. When/If you get it running "perfect" I'd like to know what your jetting/timing/etc. solutions were. Thanks!
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Re: IDAs, Venturis and intake valves...
Hey britegreen, I ended up with 37mm vents, 100 idle air, 65 idle fuel, 210 air correction, F2 emulsion and 140 main jets. The AFRs are real good in the idle circuit and the main circuit is a bit rich. I'm at about 11.4 to 12.1:1 at cruise. If I flog it hard the AFRs are in the low 13s.
You need to know some things about your particular carbs before you get started. Do they have the third progression holes? Are the float heights set per the Weber Manual? Are they new? All of these details make a difference, plus more details.
I am by no means a pro with these carbs. I can say that they have humbled me and sent me on a great adventure. I have learned from mistakes and gained knowledge to help me in the future. I must say that the contributors to this thread have helped me figure out some things and enlightened me with their experiences. Keep us posted with your developments.
You need to know some things about your particular carbs before you get started. Do they have the third progression holes? Are the float heights set per the Weber Manual? Are they new? All of these details make a difference, plus more details.
I am by no means a pro with these carbs. I can say that they have humbled me and sent me on a great adventure. I have learned from mistakes and gained knowledge to help me in the future. I must say that the contributors to this thread have helped me figure out some things and enlightened me with their experiences. Keep us posted with your developments.
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Re: IDAs, Venturis and intake valves...
ecksrash - They do not have 3rd prog hole, they are not new, they are Italian Webers. I'm am going to be setting the float bowl levels when I get to that point. For a starting point I'm going to be using 100 idle airs (recommended by Jack Sachette to make up for not having 3rd prog hole), 60 idles, 200 main airs and 160 mains.
In your case, with that much fuel at cruise have you tried going to a bigger idle air? Smaller idle fuel? Messed with timing? How does the AFR read when you slam it wide open and the engine goes through the RPM sweep?
In your case, with that much fuel at cruise have you tried going to a bigger idle air? Smaller idle fuel? Messed with timing? How does the AFR read when you slam it wide open and the engine goes through the RPM sweep?
- FJCamper
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Re: IDAs, Venturis and intake valves...
Gentlemen,
I hope you get your 48's right, and please don't construe my opinion on them more than that, just an opinion but backed up with a lot of field experience.
48's were never meant to be a civilized street carb. Lots of users try and make them streetable, and the 3rd progression hole is clear evidence of that. The 48's are pure racing carbs and making them streetable is a hobby in itself. It means you like to tinker with your carbs.
You'll hear from some 48 users that they have theirs dialed in, and run to the market or go on in-town errands with them as easy as you please.
The gray area is what each user thinks is acceptable performance. Some ignore flat spots, hesitation, etc., as normal and are oblivious to it.
Setting 48 jets (actually, Weber 40's and 44's) with a wideband is better than guessing, but widebands are more for fuel injection. You will not see smoothness of transition with jets like you will with injection. The only way to see a real world representation of your jets is on a road test or on a dyno where you can match up manifold vac with RPM and spot when a transition actually occurs.
Every time you shift your intake velocity changes, and the jets get momentarily confused as intake velocity drops, then resumes, and for a moment, your carb's jet-feed fuel passages have air in them.
Like Ecksrash discovered, a smaller venuri improved power. More intake velocity meant a stronger vac signal to the fuel passages. Air fuel mixture was improved.
Weber 48 veterans will usually tell you to run smaller vents on the street, and change it all out on race day.
Those 48's are the big guns of our motrorsport. They are not easily tamed.
FJC
I hope you get your 48's right, and please don't construe my opinion on them more than that, just an opinion but backed up with a lot of field experience.
48's were never meant to be a civilized street carb. Lots of users try and make them streetable, and the 3rd progression hole is clear evidence of that. The 48's are pure racing carbs and making them streetable is a hobby in itself. It means you like to tinker with your carbs.
You'll hear from some 48 users that they have theirs dialed in, and run to the market or go on in-town errands with them as easy as you please.
The gray area is what each user thinks is acceptable performance. Some ignore flat spots, hesitation, etc., as normal and are oblivious to it.
Setting 48 jets (actually, Weber 40's and 44's) with a wideband is better than guessing, but widebands are more for fuel injection. You will not see smoothness of transition with jets like you will with injection. The only way to see a real world representation of your jets is on a road test or on a dyno where you can match up manifold vac with RPM and spot when a transition actually occurs.
Every time you shift your intake velocity changes, and the jets get momentarily confused as intake velocity drops, then resumes, and for a moment, your carb's jet-feed fuel passages have air in them.
Like Ecksrash discovered, a smaller venuri improved power. More intake velocity meant a stronger vac signal to the fuel passages. Air fuel mixture was improved.
Weber 48 veterans will usually tell you to run smaller vents on the street, and change it all out on race day.
Those 48's are the big guns of our motrorsport. They are not easily tamed.
FJC
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Re: IDAs, Venturis and intake valves...
and what goes in must come out, , I see so many guys using to small exhaust
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Re: IDAs, Venturis and intake valves...
madmike, since my heads are 42X37.5mm valve sizes and I'm running a 1 5/8" exhaust do you think I'm choking out my engine??? My exhaust is already larger than the exhaust valve... too much more would improve flow but decrease velocity on the outbound gasses... right?
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Re: IDAs, Venturis and intake valves...
I do whole heartedly agree with FJC. IDAs are racing carbs and not designed as an every day driver carb without keeping in mind that there will be GRAY areas. I've come to the conclusion that I'll have to settle for "close enough" rather than "perfect". These carbs have humbled me in so many ways...
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Re: IDAs, Venturis and intake valves...
When I ran my 2332 with the same 1 5/8 & 48 IDA's it would only rev to 6500 or so ,then swapped header to 1 7/8,
didn't change anything else and the thing zinged to 8000+ made me a beliver
wish u were closer I'd loan u mine
didn't change anything else and the thing zinged to 8000+ made me a beliver
wish u were closer I'd loan u mine