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Posted by: Elliot Cannon Apr 26 2015, 04:09 PM

Ya' think? 175 air jets. 130 main jets. 44idf Webers. I'm thinking of going to 180 air jets to maybe lean it out a bit.


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Posted by: tomeric914 Apr 26 2015, 06:20 PM

Idle jets get you to about 2500 rpm

Main jets get you from about 2500-4500

Air jets get you from about 4500 on up

Exact RPM ranges will vary depending on the engine setup but these are a good rule of thumb.

How black the spark plugs is dependent on what RPM range you predominately ran in before shutting the engine off.

I would guess that the idle screws need to be turned in a bit before changing the airs. FWIW, you're wasting your money going from 175 to 180.

Alternatively, get one of those clear spark plugs from Gunson, called the Gunson Colortune. Then you can dial in your idle settings by sight. If you were closer, I'd let you use mine, I think they're about $30 off eBay.

Posted by: Elliot Cannon Apr 26 2015, 06:36 PM

I have never heard of these before. Would the adjustment on the Webers be made with the idle adjustment screw? It looks like I'm going to have to have one of these. https://www.youtube.com/watch?v=xEZ0-uN0NA4

Posted by: tomeric914 Apr 26 2015, 06:53 PM

Be warned, the colortune high tension wire isn't well insulated. You can guess how I know.

Before you get the colortune, try turning in the idle screws a 1/4 at a time and listen to the engine RPM. Keep track of where you started from so you don't get all crossed up. If the RPM goes up, you were probably way rich at idle. If it stalls out while driving, you've leaned it out to far.

Back to the original question, somewhere around 180 is good for air correction jets on an air-cooled motor. I'd rather be a bit rich at the high end.

Posted by: Elliot Cannon Apr 26 2015, 07:17 PM

That's the technique I used but it seems the colortune might be a bit more precise. Does the cooling tin get in the way when using the colortune? I flew this thing a lot. It had big radial engines and I would lean the mixture out at night by the color of the exhaust.


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Posted by: 930cabman Nov 1 2021, 10:56 AM

I have had a Colortune on the shelf for a year or so, .... Finally had the need to find out what's going on in the combustion chamber. Wish I would have used it year ago. Simple, effective

Posted by: Shivers Nov 1 2021, 01:01 PM

Can you see in well enough through the cooling tin spark plug hole? And how fun was it to screw that extension on?

Posted by: 930cabman Nov 1 2021, 01:40 PM

If I can do it, anyone can. I have only done cylinders #1 and #2, will go for #3 and #4 tonight. A little tricky, but very doable. I did wrap the "glass plug" with blue tape so a 5/8" socket would grab it. I was impressed with the results and assume the information gained is mostly accurate.

Posted by: r_towle Nov 1 2021, 08:23 PM

Elliott? You rang?
Get 40mm carbs
Venturi size?
Timing?

Rich

Posted by: r_towle Nov 1 2021, 08:27 PM

A "hot" spark plug has a longer insulator that prevents heat transfer into the water jackets. It keeps more heat in the tip of the spark plug, which helps burn off combustion chamber deposits. But if there's too much retained heat, the engine will experience preignition. A "cold" spark has a shorter insulator and retains less heat at the tip end—but if it's too cold, deposits accumulate and eventually the plug will short out (known as "fouling").

https://www.motortrend.com/how-to/10-factors-that-affect-spark-plug-heat-range/

Posted by: rfinegan Nov 2 2021, 08:00 AM

I did not catch your engine displacement in the post of the set up..
Im running a fresh 2056 with early weber 44
HERE is my set up:
55 Idles
200 Air
F-11 tubes
150 mains
36 venturis
This was my out of the gate first swing and ran very well. I May need a little dyno tune to optimize

My 2.0 run well with weber 40
130 main
F11
200 air
55 idles
32 venturis
this was a daily driver with a mild street cam and headers and no issues

NOTE:
Fuel pressure and float height can effect settings so remember to base line before you make any changes

Posted by: 930cabman Nov 2 2021, 01:58 PM

I brought a six years old thread back to life with our 1.8 twin carb'd Weber 40IDF as purchased from Redline. History of the engine is unk, but was running ok with a Holley 2V carb as converted by PO. I had a set of 40IDF's laying around and thought I would give them a try. Fuel pressure is 3.5, floats unk, jetting unk

Rick, did you get your current build sorted out with piston/valve clearances?

Posted by: VaccaRabite Nov 3 2021, 11:15 AM

Elliot. hasn't been on in over a year, and the thread is from 2015.

Though admittedly when I saw this thread pop up I hoped he had decided to come back.

Zach

Posted by: 76-914 Nov 3 2021, 11:22 AM

Rick or Elliot?

Posted by: VaccaRabite Nov 3 2021, 12:59 PM

Elliot. Oops! Not sure WTF I was thinking.
Zach

Posted by: r_towle Nov 3 2021, 06:41 PM

I’m a bit slow in responding, and I may have gone into dark mode for a few years.

Someone go find Elliot and get him back, he was funny.

Posted by: GBX0073 Nov 3 2021, 10:44 PM

More Carb talk is always Appreciated by me

Posted by: 930cabman Nov 4 2021, 05:20 PM

Our 1.8 with twin 40IDF's idles best with the mixture screws 1/2 turn out from seated. I will check the float levels and fuel pressure again, maybe go more lean with new idle jets.