Yz 144 sputtering

ahrma479 said:
Hello.

All the above suggestions have merit.

Here are some of my suggestions you can try.

1) Unless you did a throttle specific chop IN the throttle position/fuel circuit you are testing plug reading is suspect.
Simply removing the plug and looking at it is not an indication of AFR plus, you need to look at the spark plug base ring to determine AFR. Plug reading is complicated.

2) Ambient air temperature/air density have been super high lately, this causes a rich condition. Are the needles you have/tried the same p/n?
If not, use a micrometer and write down the diameter top to bottom of the two.
http://www.sudco.com/Carburetor/MikuniCatalogPg32.jpg
Larger diameter = less fuel = leaner.
Smaller diameter = more fuel = richer.
The I.D. size of the needle jet vs the O.D of the needle is the amount of fuel that can flow through the needle jet to the main jet.

3) I would do a throttle specific to fuel circuit test to determine the exact fuel circuit to change.
0 ~1/4 = air screw/pilot circuit.
1/4 ~ 3/4 = needle position.
3/4 ~ WOT = main jet.
BUT,,,, ALL fuel flows through the needle jet to the main jet (not counting off idle where the slow speed circuit comes into play) so don't forget that the main jet DOES come into play in the 1/4 ~3/4 throttle position.
The needle plays a HUGE part in tuning which is why there are so many variations of needle/clip position (s).

4) Do you set the sir screw each time riding? On both 2 and 4 stroke (although 4 strokes have a fuel screw and the slow speed metering system is completely different) you do need to set the air screw or fuel screw each time you ride to the
highest smoothest idle once the machine is up to normal engine temp, then re set the idle to where you like it.

5) Pump fuel is always suspect if you are looking for stability. I did dyno testing when I was at SuperTrapp/Kerker using different local fuels and found a huge difference in quality and performance.
A dyno room is supposed to be temperature/humidity controlled and have a high air change rate per hour thus a stable testing atmosphere to give consistent results.
I have done allot of testing in poor dyno rooms where the exhaust gasses remain in the room giving false powercurve readings making fuel re calibration a nightmare. You also get a nice headache.
Sunoco was the best pump fuel batch to batch.
Additives in todays pump fuel make it harder to get a proper AFR than 100% race fuel.
ALWAYS use race fuel if possible, race fuel is consistent batch to batch, pump fuel is NEVER consistent batch to batch in quality and additives. Always, always test ANY fuel for water.
I use Kolor Kut:
http://www.grainger.com/product/KOLOR-KUT-Water-Gauging-Paste-8UNU1

6) Keep a log of carb circuit settings per track and note the ambient air temp and water grains. Sand tracks/muddy conditions are of major concern. Sand/mud taxes the machine increasing engine temperature and throttle position.

7) Crude ways to check AFR: do a more air less air test. Simply taping over the airbox inlet will show a quick result.
More air = less fuel =leaner.
Less air = more fuel = richer.
Hot ambient temp/high water grains = more fuel = richer.
Cold ambient temp/low water grains = less fuel = leaner.
For all the 4 stroke racers: Innovate has a fantastic AFR you can use to keep tabs on your machine. Summit racing has them.
http://www.innovatemotorsports.com/products/MTS.php
I have a AFR on my drag bike combined with a weather station I can predict how my machine will run in different ambient conditions.

8) 2 strokes not only have to pass fuel through the fuel circuits but they also have to pass the lubricating oil through the same fuel circuits.
A change overnight in oil manufacturer can change the AFR.

9) Usually, once you set up a fuel system (2 or 4 stroke) you normally do not need to make huge changes spring, summer to fall. The setting of the air/fuel screw is the exception.
So, if your machine is running poorly it is probably something else you did to the machine and not the fuel system.

10) Dirt bikes are not racing where TIME is measured in your 60 foot, or your elapsed time or index. Your set up in the morning may be totally different than the heat of the day where a weather station and AFR monitoring
allow you to make changes to your dial and or fuel re calibration so you can meet your prediction or index. Dirt bikes are forgiving, we do not "feel the difference" in minor ambient changes.

Good luck and I hope this helps.
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I would like to hire you as my mechanic but I don't think I could afford you...lol but seriously that is some great information!!!!
 
john lilly said:
I would like to hire you as my mechanic but I don't think I could afford you...lol but seriously that is some great information!!!!
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I can attest to his mad skills at correctly jetting two strokes. He taught me a lot on the subject many years ago.

Glad to see him jump into a post here and there to spread some of his knowledge.
 
sturd said:
A nit to pick



Air temperature has been super high and air density has been super low. Still causes a rich condition
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Looking at the average August daily humidity numbers I stand corrected.
I guess Ive been playing too much Star Wars on the computer.

John, my pleasure. Dont b afraid to ask info is always free.
Thanks Mike I wish I could be more active in racin with y'all.

Thank gosh for EFI, no more fuel soaked hands, just hook up a lap top move a few numbers here and there and presto !
OR use Dobeck Performance AFR plus, set the AFR you want and the box keeps it there no matter what.
http://www.afrplus.com/AFRplus-feature-descriptions.asp
 
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hershey said:
Is it popping or missing ? 2 different things. If you were jetting dead on before the heat and it is popping then you are rich on the needle and pilot. It is hotter this past month than it has been all year.

If it is missing or going flat then you are lean and have an air leak issue from putting it together wrong.
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Was running great at briarcliff in the same heat the week before.

We will see if I can get it straightened out.....
 
Ahrma ( 479 ) If I was standing next to you with a Corona in one hand while you were telling this long winded question.... I would of thought you said....Just get a " 45 and an a shovel". LOL Kirby.
 
mx527 said:
Ahrma ( 479 ) If I was standing next to you with a Corona in one hand while you were telling this long winded question.... I would of thought you said....Just get a " 45 and an a shovel". LOL Kirby.
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Piston Kirby !!!!
I'm sorry Sir, your beef is with the dealer, he's the one who bored you in the first place.
 
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after bike was put back together hour meter flashes and shows svc. Can't find much info on this except that it means the bike Need's serviced according to yamaha.... ??
 
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premix said:
I'm not overly familiar with the Athena kit but if it's doing it under load as you're describing it could also be detonating from not enough octane or timing being off. I would call Athena and get their recommendation for each. And spend the extra money on quality race fuel. Pro car in Akron sells it very reasonably. But once again without seeing or knowing what else is done to the motor, I'm just throwing out potential solutions.

Start with the seal first. Pull the left side cover. Let the bike run and spray contact cleaner on the seal, if it revs up, you've found your issue.
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Doesn't rev up.
 
theres probably a service interval on the meter that can be adjusted / reset / cleared or something. that meter doesnt know when your bike needs serviced its a reminder for people like you to change their oil and stuff =P all that meter is doing is picking up your spark to log hours
 
Yea i figured that much. Trying to figure out how to reset it.

Im gonna call athena today and see what they recommend for jetting etc.
 
Before you tear the motor apart, does anyone up there in your hood have a setup to leak test the engine? Basically plug the intake and exhaust, put some air pressure on it and see if it will hold the pressure. weve done this with succes. This tests for base/intake gasket problems, as well as crank seals. Can even be done without removing the engine. If it doesnt leak, at least you can rule out the evil air leak. Just a thought. Good luck.
 
I think it's all jetting related.

Did some adjustment at OIR and now im pretty close to perfect. No more sputtering and she's pulling hard out of the corners. I'll get a miss every once in a while when I land or going hard through rollers. Which leads me to think the float might not be perfect.

Started at 430 main, 42.5 pilot.

Now I'm at a 410 main, 37.5. Considering a 400....


Gonna run one oractice at cliff this Saturday see how she's doing. Then pop a 35 pilot in. I'm confident it'll be a rocket ship by Sunday morning.
 
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