48IDA problem with idlemixture -> progression circuit (transition) NOW SOLVED!!

[Rasser]

Hi

I have my new 1971ccm engine up and running, and I have been tuning and testing the last few days. I have one problem that I can´t figure out how to solve, and I really need your help.

Engine is 1971ccm, heads with 42-36mm valves, webcam 494 (280 degree) and 1.3 rockers, 9.1:1 C/R, 1½" Merged header and 2½" "straight through" exhaust. I have bought new IDA´s (made in spain), and they have the 3. progression hole (aligned perfect). Jetting: 34vents, 135main/F11 emulsion/180air, 120idleair/60idle.
I have mounted a wideband air/fuel ratio device (in the merged part of exhaust).
Carbs are in 100% perfect sync, at idle and all the way to full open throttle. All the throttle plates are 100% perfect aligned in the bores, and no twisted/bent axles - everything works smooooth. And yes, the carbs are 100% clean and all channels are also clean and free of any debris.
Float height is set by the book, and then further fine-adjusted by looking at the fuel level, took the emulsion and jets out and measured to be 100% sure.
Fuel pressure is 3.25-3.50psi.
carbs are neither boiling or freezing.
No leaks anywhere on manifolds/carbs/heads.

Problem is:
If I adjust the idle and idlemixtue, then I can adjust the mixture so the engine runs perfect at idle(just like I always do on a dual carbed volkswagen), but when I start to open the throttle just a little bit and hold it in that position (I mean just a little little bit - a few millimeters or so, probably right when the progression holes should start to kick in) then it starts popping up the carbs, and I can see on my air/fuel ratio meter that the mixture is way to lean (idle shows mixture is good).
I have tried with 60/65/70 idle jets, but the problem is still there - but it is a little bit less with the 70 idle jets.
Problem is the same with both cold and warm engine, but offcourse a but more noticeable when cold.
Then I tried to open the throttle to the point where the engine had the biggest problem with popping and running lean (obviously related ;-) ), , and then holding the throttle in that position. I then adjusted one idlemixture screw at a time, to richen up the mixture (turning the screws out). I could then make the problem dissapear by turning the mixture screws excessively out, but it is now running waaaay to rich when on idle and is really rough at idle.
The engine now drives extremely well with no hesitation and really really good throttle response, but it has terrible idle because I must turn the mixture screws out this much. I am cheating my engine to run better - and I hate it!
The air/fuel ratio meter also tells me that the engine is now happier.



I am turning the idle mixture screws so far out that I let the engine get enough fuel from the mixture screws to overcome the lean transition from mixture screw to the (first) progression hole, but since this is not the right way to do this, I would really really like a better way to get around the problem.
I am thinking that I either have to open up the first progression hole a bit, or perhaps make another (smaller) progression hole beside the first one, or slighty closer to the throttle plates. This is to help the fuel easier start coming from the progression holes.
What do you think - should I try and enlarge the first progression hole to 1.1/1.2/1.3/1.4/1.5 or something else (it is now 1mm), or is there another way to help the fuel being pulled out of the progression holes earlier/faster ?
Does the air-idlejet have any effect on the transistion from the idle to the progression holes, or does it only have effect when the mains are about to kick in ?
Now, with the throttle plates in closed position (without the idle adjusting screw holding it), then the first progression hole is just above the throttle plate, and I can just get a 1mm drill through the hole, and it is just barely touching the top (backside) of the throttle plate. I am just trying to explaing where my progression holes are positioned in relation to the throttle plates.


ANY HELP IS MUCH APPRECIATED -Because I KNOW that it is possible to make these "race carbs" fully streetable.

Please give me your comments, and tell me what you have done to overcome similar problems (If you have ever experienced anything similar). Regardless of experience with IDA´s, please let me know what you think before I start modifying my IDA´s.

Thanks Rasmus

[Jim Ratto]

I guess I would need to ask you a few questions to make sure I understand what the engine is doing. I am reading that despite idle jet size, you have to open mixture screw too far open and the idle suffers, but car runs good. Am I right?

First since changing the feul jet in the idle circuit doesn't seem to be affecting how it runs, I'd ask what size holes are in idle jet holders (air jets), and don't go by what's stamped on holders.... use a gauge or wire drill bit to jugde size. If it has been drilled out, then yeah, even the 070 idle is going to be lean in progression, unless you overcompensate by cranking mixture screw too far out.
Stock size is 120, which should work with 060 or 065 if everything else is in order. It can be changed to improve things, however. I went to 110 in my carburetors to enhance transition and went down to 060 idle to clean up idle.

next, when you talk about mixture screws.... how far out are you turning them? To get a nice, even, hard edged idle, you shouldn't be too far away from 3/4 to 1 turn out from bottom. If the idle is still rough and choppy, and you get the pop and thudding from muffler @ 1 turn out, then the idle jet is small or plugged. If the car idles good for a moment right after you set mixtures but then begins to get soft and lazy, you can try turning mixture screws in 1/8th of a turn from your initial setting and it should clean up and you'll hear idle increase 200rpm or so... if you do this and it gets lazy again, then the idle jets are too big. But if you get the idle consistent, and it fires up clean and crisp when cold (it might sneeze and crack a few times up thru carbs when cold and adjusted correctly), BUT it still has the lean hiccup nose dive thing at transition (when warmed up) then you should look at richening the idle air circuit by going smaller on air hole. This is what got me out of my quandary of "ok it runs good off idle, but it loads up" or "it idles clean but it hiccups on acceleration". Jim 'Sarge' Edmiston and John Rayburn taught me this and they were right on the money.

Sounds like you know which way is up and you should be able to figure out how to make them happy. Good luck,
Jim

[Rasser]

I guess I would need to ask you a few questions to make sure I understand what the engine is doing. I am reading that despite idle jet size, you have to open mixture screw too far open and the idle suffers, but car runs good. Am I right?
Yes, you are right!

First since changing the feul jet in the idle circuit doesn't seem to be affecting how it runs, I'd ask what size holes are in idle jet holders (air jets), and don't go by what's stamped on holders.... use a gauge or wire drill bit to jugde size. If it has been drilled out, then yeah, even the 070 idle is going to be lean in progression, unless you overcompensate by cranking mixture screw too far out.
Stock size is 120, which should work with 060 or 065 if everything else is in order. It can be changed to improve things, however. I went to 110 in my carburetors to enhance transition and went down to 060 idle to clean up idle.
I will try to measure today, but 120 is stamped on it and it´s new - it has 4 bigger holes in the top for air inlet.

next, when you talk about mixture screws.... how far out are you turning them? To get a nice, even, hard edged idle, you shouldn't be too far away from 3/4 to 1 turn out from bottom. If the idle is still rough and choppy, and you get the pop and thudding from muffler @ 1 turn out, then the idle jet is small or plugged. If the car idles good for a moment right after you set mixtures but then begins to get soft and lazy, you can try turning mixture screws in 1/8th of a turn from your initial setting and it should clean up and you'll hear idle increase 200rpm or so... if you do this and it gets lazy again, then the idle jets are too big. But if you get the idle consistent, and it fires up clean and crisp when cold (it might sneeze and crack a few times up thru carbs when cold and adjusted correctly), BUT it still has the lean hiccup nose dive thing at transition (when warmed up) then you should look at richening the idle air circuit by going smaller on air hole. This is what got me out of my quandary of "ok it runs good off idle, but it loads up" or "it idles clean but it hiccups on acceleration". Jim 'Sarge' Edmiston and John Rayburn taught me this and they were right on the money.
Yes exactly as you say, if I turn them out where the engine is idleing perfect, then it is 3/4-1 turn out. But I still has the "lean hiccup nose dive thing at transition (when warmed up)"  as you describe. If i then turn the idlemixture screws more out (and richens the idle), then I can make the car run perfect, but offcourse the idle suffers badly.
Sounds like you know which way is up and you should be able to figure out how to make them happy. Good luck,
Jim

I will try to solder the idle airjet and drill a 100 hole, and if that runs then try a 110 and see what. Thanks.

[Stoo the worm Simpson]

i had a similar problem with the progression from the idle circuit transition to the main circuit...after takeing some of jims and sarges advice...changed my jet set up..mine is a very similar engine to urs..2017...but very similar spec..i was running 37 vent, 160 mains, 120 idle air, 55 idle and 190 air correctors...i changed to 160 mains, 110 idle air, 60 idles and 200 air correctors....this helped alot, and the car is now drivable completely through the rev range, it has transformed the car from a bear to drive, to a smooth ride ( until i put my toe down )....
have a search through the threads...it was only a week ago...there might be some good advice on it.
cheers for the help jim and sarge... .

and i hope u find a solution to your problem soon Rasser.

Stoo

[Rasser]

i had a similar problem with the progression from the idle circuit transition to the main circuit...after takeing some of jims and sarges advice...changed my jet set up..mine is a very similar engine to urs..2017...but very similar spec..i was running 37 vent, 160 mains, 120 idle air, 55 idle and 190 air correctors...i changed to 160 mains, 110 idle air, 60 idles and 200 air correctors....this helped alot, and the car is now drivable completely through the rev range, it has transformed the car from a bear to drive, to a smooth ride ( until i put my toe down )....
have a search through the threads...it was only a week ago...there might be some good advice on it.
cheers for the help jim and sarge... .

and i hope u find a solution to your problem soon Rasser.

Stoo

Thanks - but my problem is the transistion from idle mixture to the progression holes - not the transistion to main, all is good there!

[Rasser]

I guess I would need to ask you a few questions to make sure I understand what the engine is doing. I am reading that despite idle jet size, you have to open mixture screw too far open and the idle suffers, but car runs good. Am I right?
Yes, you are right!

First since changing the feul jet in the idle circuit doesn't seem to be affecting how it runs, I'd ask what size holes are in idle jet holders (air jets), and don't go by what's stamped on holders.... use a gauge or wire drill bit to jugde size. If it has been drilled out, then yeah, even the 070 idle is going to be lean in progression, unless you overcompensate by cranking mixture screw too far out.
Stock size is 120, which should work with 060 or 065 if everything else is in order. It can be changed to improve things, however. I went to 110 in my carburetors to enhance transition and went down to 060 idle to clean up idle.
I will try to measure today, but 120 is stamped on it and it´s new - it has 4 bigger holes in the top for air inlet.

next, when you talk about mixture screws.... how far out are you turning them? To get a nice, even, hard edged idle, you shouldn't be too far away from 3/4 to 1 turn out from bottom. If the idle is still rough and choppy, and you get the pop and thudding from muffler @ 1 turn out, then the idle jet is small or plugged. If the car idles good for a moment right after you set mixtures but then begins to get soft and lazy, you can try turning mixture screws in 1/8th of a turn from your initial setting and it should clean up and you'll hear idle increase 200rpm or so... if you do this and it gets lazy again, then the idle jets are too big. But if you get the idle consistent, and it fires up clean and crisp when cold (it might sneeze and crack a few times up thru carbs when cold and adjusted correctly), BUT it still has the lean hiccup nose dive thing at transition (when warmed up) then you should look at richening the idle air circuit by going smaller on air hole. This is what got me out of my quandary of "ok it runs good off idle, but it loads up" or "it idles clean but it hiccups on acceleration". Jim 'Sarge' Edmiston and John Rayburn taught me this and they were right on the money.
Yes exactly as you say, if I turn them out where the engine is idleing perfect, then it is 3/4-1 turn out. But I still has the "lean hiccup nose dive thing at transition (when warmed up)"  as you describe. If i then turn the idlemixture screws more out (and richens the idle), then I can make the car run perfect, but offcourse the idle suffers badly.
Sounds like you know which way is up and you should be able to figure out how to make them happy. Good luck,
Jim

I will try to solder the idle airjet and drill a 100 hole, and if that runs then try a 110 and see what. Thanks.

I measured the idle air jets, and they are 120 spot on (all 4 of them). I got hold of another idle air jet set, and they are also 120. I will try to solder the second set i got, and see what the engine does (will drill to 100 and then 110).

I tried to run 55 idle jets today, but that did NOT work. 60 is spot on, the AFR is good when cruising with the 60´s - but idle is still rough because I have to turn the mixture screws so far out.

Will get back with updates next week, when I will try the smaller idle air jets. If that does not work, then I will try to enlarge the 1. progression hole....!  but i sure do hope that a smaller idle air jet is all it takes!

[67worshipper]

when redrilling whats the drill bit sizes to make say a 110 or 120

[Rasser]

when redrilling whats the drill bit sizes to make say a 110 or 120

I have bought new drill bits in 0.1mm steps. I plan on soldering the exsisting hole, and then drill a new hole in a different position. This should not cause any problems, since it is the idle air jet.

[Torben Alstrup]

Yes, your problem is definitely too large idle air jets. Best way to get them corect sized is ti drill them 0,05 under and then ream them to correct size.
T

[Lanny Hussey]

I did the 110 conversion 10 years ago, great results.

[Bruce]

(will drill to 100 and then 110).

I wouldn't bother with the 100s.  I tried original Weber 100s one time (for an extended distance) and found it would load up in the transition so bad the car started to run rough.  A change of 5 is big.  Try a 110, then a 115.

[Rasser]

Thanks guys - that´s what I wanted to hear!

[63 ripper]

roughly when do you need to go bigger than a 120 holder ? 40mm or bigger venturi ?

[Rasser]

roughly when do you need to go bigger than a 120 holder ? 40mm or bigger venturi ?

I would say that it has nothing to do with the vents, since the throttle is only very little open. my best guess is that cam, heads and ccm are the things that has the biggest influence. . . .

[Jesse/DVK]

According to aircooled.net

'The Idle Air Jet Holder is TIG welded closed, so that it can be re-drilled to the size needed. In Art's experience, the Idle Air Jet Holder is one of the keys to unleashing the IDA's tunability. The Idle Air Jet Holder should be sized to the application and engine size. Sizing makes a HUGE difference in idle and off idle performance. Try a 110-115 on small engines, and 130-135 on large ones (they come with a 120).'

[63 ripper]

roughly when do you need to go bigger than a 120 holder ? 40mm or bigger venturi ?

I would say that it has nothing to do with the vents, since the throttle is only very little open. my best guess is that cam, heads and ccm are the things that has the biggest influence. . . .

sorry, that was a lazy way of saying would an engine (worthy of) 40 mm (or bigger) vents...for example a 2276,FK87 with 42 valves need the enlargement ? or is 120 big enough ?

[63 ripper]

just reading through some old posts and found John Rayburn saying he used an idle jet holder sized 113. this is on a 2332 motor,86c cam and 46 by 36 Jeff Denham heads.the IDAs have 42 mm vents and no 3rd progression hole.
somewhat different than the aircooled.net article suggests but perhaps the difference is in the extra hole...

[DKK Ted]

Can you still get the 110 Idle jet holders?? If so, where??

[Bruce]

Can you still get the 110 Idle jet holders?? If so, where??

Ted, you have to get them custom made.  The only sizes from Weber are 60, 100, and 120.  Art Thraen can set you up.

[DKK Ted]

Thats right! I forgot about Art, will give him a buzz tomorrow. Thanks Bruce.

[Rasser]

Thought I would share my R&D on my IDA´s with you.

I have now tried almost every possible jetting setup, but it never fixed the dead spot i had when just opening the throttle (leaned out the mixture). I decided to drill another progression hole closer to the throttle plate (0.8mm drill)!

Right now it runs perfect, with excellent throttle response - amazing difference!!!
But my A/F ratio meter tells me that the mixture is a little bit to rich when cruising, so perhaps I will have to close the original progression holes, and then redrill them to 0.8mm instead of the std. 1mm size. Or I could close the 2. progression hole (the one that original was the 1. hole), and redrill the current 1. hole to 1-1.1-1.2mm. I am guessing this will help the engine run a bit more fuel efficient, because I think the engine sucks to much fuel out the holes right now (just a little bit - but to much ;-).
If I did not have the A/F meter, then I would just have run the car as it is right now. It drives soooo smooth now. But the A/F meter still tells me there are things that can be improved.

So next time you are out buying repro IDA´s, check that the 1. progression hole is RIGHT on the edge of the throttle plate. You should not be able to see it with the throttle closed and the idle screw backed out, but as soon as you touch the throttle you should see the 1. hole right away.

Hope this helps others to make their junk repro IDA´s run perfect.

[Peter Roberts]

Better to have repro IDA's , that can be sorted with fiddling and tuning , than relying on a limited number of original worn ones , in my opinion .

[lawrence]

What A/F ratio are you getting and are you reading it at idle or partial throttle? Im curious.

[Rasser]

What A/F ratio are you getting and are you reading it at idle or partial throttle? Im curious.

I´m reading it at cruising speeds (partial throttle). WOT is all sorted out, and it gets the right A/F.

At steady cruising speeds (50-70mph) I am reading 11.5-12, and I am barely just touching the throttle. I would have liked to have it near 14.0 - but if I try to use smaller idle fuel jets or bigger idle air jets, then it doesn´t have good throttle response etc. - so right now it´s a compromise between running right and running fuel efficient (Guess this is why someone invented fuelinjection ;-) )

Anyone else have some A/F readings with IDA´s?

[BeetleBug]

What A/F ratio are you getting and are you reading it at idle or partial throttle? Im curious.

Anyone else have some A/F readings with IDA´s?

Yes.

2332 / 51,48 Jay Cees
Idle; 12.85 - 12.95 (0-3000)
Full throttle; 12.90 - 13.05 (3000-8200)

190/190/65 F7 + 45 venturis - no filters

Only issue is a small hesitation between idle jets and full jets where the AF jump a little to 14.4 - 15.0. Can probably be tuned away but I dont care, it is hardly noticeable.

And yes - I totally agree with what you`re saying about the quality. The repros are crap.... a long with most other stuff we use in our cars.

[Rasser]

What A/F ratio are you getting and are you reading it at idle or partial throttle? Im curious.

Anyone else have some A/F readings with IDA´s?

Yes.

2332 / 51,48 Jay Cees
Idle; 12.85 - 12.95 (0-3000)
Full throttle; 12.90 - 13.05 (3000-8200)

190/190/65 F7 + 45 venturis - no filters

Only issue is a small hesitation between idle jets and full jets where the AF jump a little to 14.4 - 15.0. Can probably be tuned away but I dont care, it is hardly noticeable.

And yes - I totally agree with what you`re saying about the quality. The repros are crap.... a long with most other stuff we use in our cars.

Did you have 3. progression hole, and have you tried with other emulsion tubes than the F7 ?

Did you do the readings yourself?

And let me get this right - you are between 12.85-13.05 all the way from idle to 8200, regardless of whether you are cruising or WOT?

[BeetleBug]

What A/F ratio are you getting and are you reading it at idle or partial throttle? Im curious.

Anyone else have some A/F readings with IDA´s?

Yes.

2332 / 51,48 Jay Cees
Idle; 12.85 - 12.95 (0-3000)
Full throttle; 12.90 - 13.05 (3000-8200)

190/190/65 F7 + 45 venturis - no filters

Only issue is a small hesitation between idle jets and full jets where the AF jump a little to 14.4 - 15.0. Can probably be tuned away but I dont care, it is hardly noticeable.

And yes - I totally agree with what you`re saying about the quality. The repros are crap.... a long with most other stuff we use in our cars.

Did you have 3. progression hole, and have you tried with other emulsion tubes than the F7 ?

Did you do the readings yourself?

And let me get this right - you are between 12.85-13.05 all the way from idle to 8200, regardless of whether you are cruising or WOT?

I do have 3 progression holes and no, I did not try other tubes than the F7 since I`m quite happy with how the engine work as is. And both yes and no regarding the readings, I have dynoed/tuned the engine two times, first at JPM and second time at a local dyno. Last time with the AF sensor both in the plunge (collector) and out of the muffler. One reader inside the car and one for me standing behind the car.

And no. I do not have 12.85 - 13.05 all the way because of the little lean spot mentioned above. Apart from that - yes.

Changing the air jet to a 195 leaned the engine to 13.90 - 14.00 - not what I wanted.

[Bruce]

The repros are crap.... 

They aren't repros.  They are made by Weber.

[JS]

What A/F ratio are you getting and are you reading it at idle or partial throttle? Im curious.

I´m reading it at cruising speeds (partial throttle). WOT is all sorted out, and it gets the right A/F.

At steady cruising speeds (50-70mph) I am reading 11.5-12, and I am barely just touching the throttle. I would have liked to have it near 14.0 - but if I try to use smaller idle fuel jets or bigger idle air jets, then it doesn´t have good throttle response etc. - so right now it´s a compromise between running right and running fuel efficient (Guess this is why someone invented fuelinjection ;-) )

Anyone else have some A/F readings with IDA´s?

On the SCC bus (82x87mm 1950cc) we have 13-13,5 at full throttle from 2000-5500 and cruising mid 12´s.
48´s with 37 venturies, 60/155/210 jets. No extra progression holes.
Not in your league performace wise of course as it dynoed only 108hp last weekend, but I thought I´d share the numbers anyhow. 

2276 engine is on it´s way into my car this weekend, looking forward to tuning it!

[Rasser]

What A/F ratio are you getting and are you reading it at idle or partial throttle? Im curious.

Anyone else have some A/F readings with IDA´s?

Yes.

2332 / 51,48 Jay Cees
Idle; 12.85 - 12.95 (0-3000)
Full throttle; 12.90 - 13.05 (3000-8200)

190/190/65 F7 + 45 venturis - no filters

Only issue is a small hesitation between idle jets and full jets where the AF jump a little to 14.4 - 15.0. Can probably be tuned away but I dont care, it is hardly noticeable.

And yes - I totally agree with what you`re saying about the quality. The repros are crap.... a long with most other stuff we use in our cars.

Did you have 3. progression hole, and have you tried with other emulsion tubes than the F7 ?

Did you do the readings yourself?

And let me get this right - you are between 12.85-13.05 all the way from idle to 8200, regardless of whether you are cruising or WOT?

I do have 3 progression holes and no, I did not try other tubes than the F7 since I`m quite happy with how the engine work as is. And both yes and no regarding the readings, I have dynoed/tuned the engine two times, first at JPM and second time at a local dyno. Last time with the AF sensor both in the plunge (collector) and out of the muffler. One reader inside the car and one for me standing behind the car.

And no. I do not have 12.85 - 13.05 all the way because of the little lean spot mentioned above. Apart from that - yes.

Changing the air jet to a 195 leaned the engine to 13.90 - 14.00 - not what I wanted.

Ok.
I would like to know what A/F ratiosyou have when CRUISING the streets (not WOT), have you measured that ?

If I where you then I would try different e-tubes (perhaps F2 or F11), that might be able to cure your flat spot, and this will gain HP and ET ;-)

Please share your cruising A/F data if you have measured that, because thats what I find hardest to tune/jet/adjust properly.