82.5 c500 carb tuning

[silverstreakNZ]

i plan to stick with the vm44 when i rebuild the cr500 . will prolly make a carb wing . on the air box side

bike currently has a #2 slide . however i see vmx/cycleworld rekons a #3 was the go .
only other mods are boyesen reeds and the muffler is slightly bigger bore .

bout 20 deg and sealevel riding . bp 98 and maxima full synthetic at 40/1

the bike would kickstart if it had to and i thought it ran alright .

the chrome is worn off the slide currently so ill prolly replace the whole carb

also is it possible to tune a 2 stroke with a wideband 02 sensor in the exhaust ? as i have one and could back pack a battery etc . what ratio would you aim for ? 12.5 /13 :1 ? or os that too lean ?

 

[jo360]

you can always go with a pwk set up for a honda cr500 these have the bigger pilot and leaner main already installed, you will have to make up a manifold spigot but long term should be easier to live with than the vm which has the heavy round slide.

 

[fran...k.]

you can always go with a pwk set up for a honda cr500 these have the bigger pilot and leaner main already installed, you will have to make up a manifold spigot but long term should be easier to live with than the vm which has the heavy round slide.

A pwk 38/39 will force into the rubber for a 38mm stock carb. I wasted a lot of time making/adapting what you describe to adapt something similar. It still is short for the dual shock application.

silverstreakNZ The dual shock application carbs are longer don't forget to make sure you order what is correct.

 

[Bigbill]

I installed a mikuni 40mm on my 81/390. I went to the smaller needle jet. She ran awesome. The 390 was a beast.

 

[Kartwheel68]

Husky went away from the 44mm to the 40mm because it was a nightmare to jet correctly. There was a "secret" needle jet and/or needle that is no longer available that supposedly fixed the problems with the 44mm but the simple fix is a 40mm carb.

I installed a mikuni 40mm on my 81/390. I went to the smaller needle jet. She ran awesome. The 390 was a beast.

There was no 390 in '81, the last year was '80.

 

[86 400 XC]

I still have the 44 on my 82 500, its runs really good. Zero complaints.
I never did open it up to look at the sizes of jets, slide or needle and right now its tucked away for winter, sorry as i would help you out.
In my part of Alberta its around 4k feet above sea level, so we have crappy thin air here.
At first when i bought it had an external flywheel and it ran great, i assume it would stall too easy unless you dump the clutch hard.
Most likely because the 4 speed box, 1rst was really 2nd gear to other bikes.
I put the internal motoplat on it and it revs even faster and its just as crisp all the way through the RPMs.
I would try a 40mm when i find one for cheap just to see how it gains someday soon.


~Steve Sept

 

[evcross0]

All I ever did to my 82.5 500 was cut the slide to about what a standard 3.0 would be. always ran perfect.

 

[dartyppyt]

I still have the 44 on my 82 500, its runs really good. Zero complaints.
I never did open it up to look at the sizes of jets, slide or needle and right now its tucked away for winter, sorry as i would help you out.
In my part of Alberta its around 4k feet above sea level, so we have crappy thin air here.
At first when i bought it had an external flywheel and it ran great, i assume it would stall too easy unless you dump the clutch hard.
Most likely because the 4 speed box, 1rst was really 2nd gear to other bikes.
I put the internal motoplat on it and it revs even faster and its just as crisp all the way through the RPMs.
I would try a 40mm when i find one for cheap just to see how it gains someday soon.


~Steve Sept

Plus how many guys have the cool factor when someone walks up and says: what's that?

That's one bad husky that uses a Mikuni coffee mug to fuel it!

 

[SteveJ]

[QUOTEalso is it possible to tune a 2 stroke with a wideband 02 sensor in the exhaust ? as i have one and could back pack a battery etc . what ratio would you aim for ? 12.5 /13 :1 ? or os that too lean ? ][/QUOTE]

Using a wide band O2 (A/F sensor) to tune is an interesting idea, and I understand there are a few people doing so. From my automotive background where these sensors are commonly used I would say there are many factors involved. Just as an example, the sensor cannot be inserted into the end of the exhaust as air aspirated into the silencer or stinger will cause lean readings. So, a bung may need to be welded into the exhaust either for the sensor itself or to install a port for a remote sensor. Air fuel ratio will still be a matter of experimentation since it will be different for idle, part load, heavy load and wide open throttle and will likely need to be varied dependent upon state of tune of the engine (mild or wild), etc. Probably works best for engines that see a more limited RPM range, like high strung two stroke road racers or snow mobiles with auto clutches. In the case of our 500's, we go from at times lugging down to almost idle in a tight turn to a wide open white knuckle blast down a straight. So I suspect for most of us, the conventional means of tuning is easier. Just my two cents, others may feel free to disagree in a friendly manner .

I run the Mikuni 40mm on my 83 500. It lugs right down to almost idle and then pulls cleanly away with a twist of the throttle. Good luck on your project.

Steve

 

[Bigbill]

What about adding the UFO to the bottom of the round slide. I put them in my 38mm and in my 40mm carb too. It smooths out the gas flow obstruction that's under the round slide. It does allow it to throttle up much smoother.

 

[silverstreakNZ]

cool thanks guys .
yeah the wide band sensor would have to go a fair way up the exhaust to ensure its only reading exhaust .was thinking about the ufo on the bottom of the slide also . will see what happens

 

[justintendo]

you usually see people tuning microsprints (cr250 powered) or snowmobiles by exhaust gas temp, never seen a a/f ratio setup on a two stroke. i would think it would get fouled up with oil