Dave's Duh / Doh, Carb / Plug / Exhaust Questions????

[SpecOps13]

The plugs in my 89 are now running the same color, but very little color on the insulator.. Just a tinge of Tan on the Insulator after 18 miles, How lean is too lean???
I set the sync at 3,000 rpm and it's apparently right on as I shut the bike down from 3,000 rpm and coast into the driveway. Outer ring is black but not to an excess. Tip is tan.

A/F Screws, I believe I know the answer to this but want to confirm. Farther in, Richer? Farther out Leaner? I'm currently at 2-1/2 turns out.

If I free up the intake to breath better, It Leans the total mixture?
If I free up the exhaust to breath better, it Richens the total mixture?


Kerker with 2" core, K&N, 147.5 Mains. Stock needles shimmed 0.034, all other jets stock, AF Screws as mentioned 2-1/2 turns out....

Thanx for answering my Stupid Questions....:ummm:

 

[gamorg02]

a/f screws are opposite. they are 'fuel passage' screws. the more you unscrew the more fuel is let into the idle circuit.

right on with freeing up the intake
i'm not sure on freeing up exhaust.

go as lean as you can as long as its not popping or stumbling, then you are too lean.

 

[PATMAX]

Hey Dave, I always remembered A/F screws and diapragm needles acting in the same way. They have that tapered end fitting into an orifice. The deeper toy sink the tapered end into the orifice, the smaller the space for fuel to pass through. Smaller the space, the fuel allowed to pass hence less is leaner. I have some excellent technical articles I wish I had a way to electronically send to you. One is from a jet manufacturer, one from Paul's Shims which is available on his website and another from a carb tuner. My little pea brain took several readings to comprehend it but you may do better than I. Maybe I can scan and send your way. I also thought a less restrictive exhaust was making things leaner not richer hence the need to rejet bigger but what do I know...

 

[PATMAX]

Sorry Dave, I was not ask clear as I should have been but it looks like Gamorg jumped in there. The farther IN you drive the A/F screws, the less fuel you are allowing to pass hence leaner. I may be wrong but I don't believe you can actual stop fuel flow all the way to "0" turns out. It still allows some fuel to pass. I think one of the tuning tricks was to quick twist the throttle. If it seemed to bog down then slowly catch up, you were running rich on the low circuits of the carbs. A fast advance of rpms with no stumbling and you are on the right track. Cylinder head or better, EGT or exhaust gas temperature was another way to monitor leanness. Lean is of course hotter. Some meters are out there using infared sensing. Even model engines use this for optimal running without burning something up. Of course this is all theory to me. I have not used it to tune my bikes nor could I tell you what temps you should be looking for. Maybe/probably Sean would know.

 

[maleko89]

The a/f fuel screws are both....control pilot mixture of air and fuel.

 

[SpecOps13]

Reason I asked all these dumb questions is: My A/F Screws are in very good condition and only 2-1/2 turns out. The bike starts and warms up best with no choke, Turn the throttle just off the stop while starting. Blip the engine ever so lightly and it settles into about 1,000 rpm's until warm. Not a problem for me to accept, although I don't fully understand it.

Sounds like I can richen the mixture to a point by turning the A/F Screws out to 3 or 3-1/2 turns. May even make the bike easier to start? The plugs are running whiter than I consider good practice. I like a little more color. I'm jetting for mileage, that's my primary concern. I'd like the bike to run like Strafer which is just a tad, tiny bit tanner on the plugs. It however will not start without the choke,,, period.:ummm:

My tuning is very close to being satisfactory, I just need to Tweak it a small amount. That was the reason for the rest of the questions. Looking for what would be the easiest thing to do. Also, I did several full throttle runs on the interstate and in lower gears. She runs like a Raped Ape.. Letting off the throttle slightly or applying small amounts of choke doesn't gain anything... So, I believe overall, my jetting is good.

I'm running Non-Ethanol as always until there is no more....


Thanx for the answers..
I'm more confused on some solutions now than before though...:rofl_200:

 

[[email protected]]

Plug reading info:

http://www.4secondsflat.com/Spark_plug_reading.html

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

Check out the comments in this one about the porcelain color.
http://www.wallaceracing.com/plug-reading-lm.html

 

[hawkeye]

Hey Dave,
With regards to the free-flowing exhaust I always thought it leaned the bike out as more air was going through the engine (same as opening up the intake) but maybe I'm missing something with the Vmax carbs.

Also, it seems you might be running rich at idle if you can fire it up without the choke. Again, I was under the impression that if the bike is lean it'll run better when the engine is hotter and if the engine is rich it'll run better before it has reached operating temps.

Someone correct me if I'm slinging misinformation!

 

[SpecOps13]

mabdcmb: Best I've seen on the subject, Thanx...


hawkeye: I'm no expert on intake and exhaust theory by any stretch of the imagination. I have a couple friends who talk about ballistic theory of various AR-15 Rounds with different powders. They go way over my head in a hurry too.:rofl_200:


My thoughts were that freeing up the intake and leaving the exhaust the same would allow more air but limit the fuel because of the still restricted exhaust making the engine leaner.:ummm:


In the opposite direction, freeing up the exhaust and leaving the intake alone would allow more burnt gas to escape and create more vacuum at the carbs, making the mixture richer to the engine.:ummm:


Maybe those thoughts are totally Blonde though..:confused2::confused2::confused2:

 

[hawkeye]

Dave, that is a totally higher level of thinking!

I think what makes me a bit unsure is that these bikes are carburated... and air flow is what sucks the fuel out. From my experience with FI bikes it's easy - if you open it up you just need more gas to compensate for the increase in airflow.

Most often exhaust and intake are done together (known as "uncorking") so I just assumed you'd need more gas for the change.

I'll talk to some of my friends who are more versed with carbs and see what I can turn up!

 

[hawkeye]

I always assumed that an individual jet was functioning at max flow, so if you increased the air flow (which is what pulls the gas through) you'll need bigger jets to let in enough fuel.

I've never differentiated between either mod - intake or exhaust, but I imagine exhaust has the largest effect. It seems to me that that would be the limiting half.

 

[sdt354]

I'll be comparing plug color after my run today with stock exhaust, and 1st run with soon to be installed Marks 4/2. I will have pics.
I could have sworn I read a post that opening the exhaust up reqires smaller jets. Sean?
Can ya help us out on that?
Steve-o

 

[maleko89]

Opening up exhaust side richens, opening up intake leans it out.

 

[SpecOps13]

I had to flip back and forth several times between my post and Mark's but I think I'm not Blonde in my original thinking...:rofl_200:


Yeah.....:biglaugh::biglaugh::biglaugh:

 

[hawkeye]

Haha I learned something today! Sorry to throw a wrench in a good train of thought.

 

[gamorg02]

Opening up exhaust side richens, opening up intake leans it out.

why is that on the exhaust again?

 

[maleko89]

Combination of scavenging and back pressure if I remember right. I remember learning about after reading about someone drilling their stock cans out. Fuel consumption went up and plugs were darker.

 

[SpecOps13]

Freeing up the exhaust makes it easier for the engine on exhaust stroke to empty the cylinder and push the burnt gasses out the exhaust. When the engine transitions to the intake stroke, the cylinder being emptier allows this additional vacuum to pull extra fuel into the cylinder in relation to the air that wants to flow at the same rate it always has through the air box... Creates a richer condition of the mixture..

On the other side, say we shim or remove the "Y" and leave the exhaust the same. Back pressure keeps the cylinder from fully emptying the of burnt gas. When the engine transitions from exhaust to intake, more of the burnt gas remains. Less vacuum is available to pull new fuel in because the intake breaths more easily through the more open air box... Creates a leaner condition of the mixture..


This is be an exaggeration for example but I hope that's a reasonable explanation..:ummm: My dad taught me this but it's been almost 50 years ago so it's all from memory..