Runs like choked all the time

[PorP]

I would get the carburetor sorted out then see what happens.

Funny you say that,  the pin was 1/2 way out of the float,  that's why it looked so weird.

It's all apart now including the choke I broke this morning.

It's got 50 pilot,  needle is 2nd slot from the bottom and the main is 168.

[broken1]

Both mine are on straight race gas but I could get away with 50/50 mix race/non-eth super.

[PorP]

Both mine are on straight race gas but I could get away with 50/50 mix race/non-eth super.

You had my attention for a minute.  Race gas isn't readily available at hayfield mccoy, I gotta be able to run super at most.

And the way hayfield is set up with the ability to ride paved road into town,  the truck (or hotel)  is start and end,  you get gas and food in the different towns the trails take you to.

[The norm]

Shoot I'm running 48/178 on my son's mildly ported cylinders with the needle in the middle.
Loren

[PorP]

I must have not messed with the needle before....

Ps, when i was in the slide,  i found 2 clips on the needle,  i don't know if this is a common pj thing,  i never heard of it.

Between that,  the floats and the broken choke,  i just bought a 38mm air striker. It's supposed to be here Friday so I will update next weekend....

[PorP]

Shoot I'm running 48/178 on my son's mildly ported cylinders with the needle in the middle.
Loren

What altitude (out where do you live), Loren? I can explain the pilot I think?  A lot of racers ran rich on the pilot to prevent detonation.  A lot of racing is WOT and no throttle and on the binders. Being rich in pilot helps lube the cylinder when you have a hand full of clutch and a foot full of brake.

On the 168? Can't explain?  It was 10 years ago... so with a grain of salt.... i feel like I must have done a 4th gear plug chop? It would be abnormal for me to not chop the main.

[The norm]

Oops sorry I forgot to mention my elevation and I didn't notice where you are riding.  We ride from sea level to around 3,500 feet. I understand the big pilot for sure. I have had a few MX two stroke dirtbikes and they always have a rich pilot circuit. Which is not the best for trail riding in my experience. But for MX racing it makes sense like you said you don't want detonation!
Loren

[PorP]

Oops sorry I forgot to mention my elevation and I didn't notice where you are riding.  We ride from sea level to around 3,500 feet. I understand the big pilot for sure. I have had a few MX two stroke dirtbikes and they always have a rich pilot circuit. Which is not the best for trail riding in my experience. But for MX racing it makes sense like you said you don't want detonation!
Loren

Thanks for the reply Loren!

Now that I had some time to think on it,  the other thing that makes jetting so complicated are riding types,  when i do go to hatfield, my dad rides a ute so I almost never see the main in 5th or 6th.... when i race,  I'm mainly 2nd, 3rd and maybe some in 4th. If you plug chopped in 5th or 6th... (or if i did)  I'd probably end up leaner on the needle and richer on the main.

[Jerry Hall]

Oops sorry I forgot to mention my elevation and I didn't notice where you are riding.  We ride from sea level to around 3,500 feet. I understand the big pilot for sure. I have had a few MX two stroke dirtbikes and they always have a rich pilot circuit. Which is not the best for trail riding in my experience. But for MX racing it makes sense like you said you don't want detonation!
Loren

Thanks for the reply Loren!

Now that I had some time to think on it,  the other thing that makes jetting so complicated are riding types,  when i do go to hatfield, my dad rides a ute so I almost never see the main in 5th or 6th.... when i race,  I'm mainly 2nd, 3rd and maybe some in 4th. If you plug chopped in 5th or 6th... (or if i did)  I'd probably end up leaner on the needle and richer on the main.

You are missing or misunderstanding a very important and basic fact about carburetor tuning.  The engine and the carburetor does not know what gear you have selected while you are riding.  Anytime the throttle position is in the range of approximately 3/4 to wide open, the main jet is the circuit that is metering the majority of the fuel flow into the engine at that instant.  When you position the throttle wide open in any gear the main jet is being used.  A carburetor is throttle position sensitive not transmission gear sensitive.

My most common error I find when tuning Keihin carburetors for customers is:  They have too large of a pilot and the diameter of the straight portion of the needle is too large and or the slide cutaway is too lean.  This error in carburetor tuning theory or lack of a large needle and or slide selection causes them to keep increasing the pilot jet size to take the lean bog or hesitation when suddenly opening the throttle from an idle.  This error in theory by oversizing the pilot will overlap into the throttle positions where the slide cut a way and straight diameter portion of the needle should be controlling the fuel flow at less than about 1/2 throttle position.

Moving the clip on the needle cannot affect the fuel metering until the tapered portion of the needle is changing the fuel flow area between the needle jet and the needle.  On most Keihin carburetors, on two strokes, the start of the taper is not exposed until about 1/2 throttle opening. 

Another common problem guys have when recommending jetting specs. on Keihin carbs with buddies that have similar engine packages is: The needle jets and needles are made of brass/bronze and they ware rapidly.  This ware causes the need to use a different needle to get identical fuel metering.  I wish Keihin aftermarket needles used the hard anodized aluminum needles like they supply to the OEMs for their CRs, YZs, etc.  It has been my experience that using similar metals for the needle and needle jet or in any design of parts that contact each other is a common engineering error of freshman engineers or intentionally controlled by the marketing departments to limit the life of their products.

[PorP]

Jerry,

I think i understand (didn't know the needle part)  i'm aware the atv doesn't care which gear.

But what I think i also understand (or maybe not? ) is rpm and time.  Because this is not a sealed environment,  i believe venturi effect is impacted by piston speed.  To say i believe venturi is maximum at max rpm. And the time piece is that window of max venturi effect in 4th gear is pretty short.

[PorP]

Installed the air striker with 50 pilot, 175 main,  needle 3rd clip and floats adjusted.  Same problem.

So other things I think might cause this.

I installed a dynatehc cdi, it sparks during the kick. Oem cdi sparks after the kick is done,  like .25 or .5 seconds after the kick is finished.  Oem spark is louder and shaper, but it won't start on this cdi.

When i dropped the counter balance bearings,  it broke the CB holder.  I replaced it with a boss racing adjustable timing holder.  I got no instructions,  so I set it to 0 degrees advance assuming that it correct.

Do I need to advance the timing and run the oem box?

[Jerry Hall]

I installed a dynatehc cdi, it sparks during the kick. Oem cdi sparks after the kick is done,  like .25 or .5 seconds after the kick is finished.  Oem spark is louder and shaper, but it won't start on this cdi.



Do I need to advance the timing and run the oem box?

I have had a lot of problems with the Dyna tech CDI boxes.  They typically act like the main jet is too rich.  I have also had a few OEM CDI boxes act real rich and will kick back real hard when kick starting.  The Honda CDI boxes that kick back real hard have a timing curve malfunction and have the ignition firing around 45 to 50 deg before TDC.

Have you removed the ignition flywheel and checked for a sheared flywheel wood riff key?

You should not need to advance the timing if the wood riff key and OEM CDI box are good.

[2ndmoto]

0 degrees should be fine. Something is up with your cdi, I recall mine pulling spark through the kick. Would be nice if you could get your hands on a known good one.

Let's start checking things off the list. Did you do a leak down test? Grounds are good? Low resistance between points? Check the spark plug cap and coil.

[Jerry Hall]

Jerry,

I think i understand (didn't know the needle part)  i'm aware the atv doesn't care which gear.

But what I think i also understand (or maybe not? ) is rpm and time.  Because this is not a sealed environment,  i believe venturi effect is impacted by piston speed.  To say i believe venturi is maximum at max rpm. And the time piece is that window of max venturi effect in 4th gear is pretty short.

I am not sure what you mean by venturi effect.  Are you saying that the suction of the main jet is at a maximum at the maximum RPM?  If so, the suction or what many guys call the signal strength, is at a maximum when the air speed flowing over the needle jet shroud is at a maximum. 

The maximum velocity over the needle jet shroud is a function of where the torque and power peak occur.  Maximum air flow through the carburetor usually occurs very near the torque peak.  On narrow power band two strokes, the torque and power peaks most often occur at about the same RPM, so signal strength is at a maximum at the power peak.  On a 250 cc single cylinder two stroke that is designed to produce maximum acceleration, the torque peak will often occur 1000 RPM or more before the power peak.  Air flow at maximum RPM (in the over rev RPM range) is seldom very high because the engine is loosing torque and power rapidly after peak power occurs. 

[PorP]

Jerry, 

Ya the engine is a complete rebuild including the crank,  woodruff key is installed. My problem is primarily on the main,  it seems to idle fine. I've read what you said on the dynatech cdi, the oem vdi issue is new to me though.

Ya, venturi is the air flowing from large opening to a small opening and then to a larger than small opening,  it creates the vacuum on the jets.