Two Cr500's Help!

are you still running very light oil mix ratios?

Ok gents, ive been following this thread in silence.

For 35 years the only dirtbikes ive cared to own and ride have been husky 500s and 4ts, for their character, ability and speed.
All of the problems mentioned in this thread have been encountered.

In 2012 i started to focus on topspeed runs and that is where the worms crawl out of the can enmasse.

Oct 2016 i clocked 127mph at an official event on a stock 83 500xc.
Smooth, sorted and fast. 4 engines later with all bugs resolved.
One run with top speed at 7900rpm, achieved in less than 700metres from standing start.

There is a procedure to sort and optimise. To build a husky engine that runs proper for just about any application. One mainjet change between 0 to 2000 metre altitude. One timing setting. Starts on 1st or 2nd kick hot or cold.

Maybe a new thread alltogether.

Recently I read a VM Mikuni tuning manual. Would love to hear your sort and optimize procedure to carb tuning. A manual typically lacks what real world trial and error teaches. Also, in the late 90's I figured out that retarding the ignition a degree or two on my 600 Husaberg made it easier to kick start, giving up a little performance was worth it.

Without writing a thesis:

Mikuni tuning manuals are general and apply to carbs attributed to machines with baseline jetting and components already sorted.
The following is actual info which elucidates the functions and methods; these boys wrote the manual...
http://www.klemmvintage.com/mikuni-tuning.htm
Husky VM40 baseline is perfect and if sorted theres no need for alternatives. With a 35yr old carb you dont know what the previous owners got up to, if the carb is varnished up inside passages etc. Get new brass to start off with and have carb sonically bath cleaned.
Needle 7DH3, centre groove good starting point
Emulsion tubes AA-5 and BB-0
Slide cutaway 2,5
Airjet in bell of carb 0,7
Idle fuel jets 40-55
Mainjets have a kit 370-430
Important; 3,3 3hole needle and seat is marginal, go for 3,5 6hole as found in YZ and IT 465/490 38Mikuni.
No airleaks at choke, top cap, cable inlet.
The finer points of optimising vacuum signal, air velocity can be covered later. Important is reed valves, Dual stage Boyesens are a no go!! Stock reed setup in good condo or my favourite the Mossbarger reedblock and petals work real well.

More than adequate fuel supply has been covered in this thread. To affirm: Karcoma fuel taps will never supply a howling 500. Clarke sells a nice 20$ fueltap good enough flow for general use and it bolts right up to plastic tank.
For speed trials i have a 8mm i.d. setup with inline ballvalve and enlarged carb inlet passage to needle and seat.

No amount of tuning will work if engine build is not up to standard.
http://www.klemmvintage.com/airleaks.htm

In Fact, study all they have to say
http://www.klemmvintage.com/
I can provide list of all the areas Husky bigbores develop airleaks and the finer points of sorting it.
Pressure test on husky bigbore should hold 10psi for 5 minutes and youre good to go for many hours on engine. Viton and ordinary rotational shaft seals will hold 5-7psi at best and when engine hot and youre going hell for leather, as engine loads up its likely to leak and nip sooner than later.

Timing; I run orig SEM and Motoplat mini6 as i have stock. Never ran MZB, HPI or Electrex, would be nice to try.
These ignitions are individual. 2-2,5mm BTDC is the starting range.
Retarding a tad helps with starting kickback.
Ultimately the uphill test will determine. Im fortunate to have a asphalt track for testing and tuning. Fast righthand sweep exit in 4th, hammer uphill in 5th and see how quick i can get into 6th and still accelerate before cresting.

Cheers for now

All great points! Also don't forget to take recordings of weather conditions and log down the temperature, barometric pressure, humidity. And calculate the corrected altitude and air density ratio during each test session. This way you can make accurate jetting changes as the weather/altitude and conditions change and don't change the fuel mix ratio. This way you won't seize up a motor!

I have a long straight 3/8 mile uphill dirt road I estimate is 7-8% grade that I use for carb/jet testing and tuning. I will get into the highest gear as fast as possible and put a real load on the motor and at the end of the run I will cut the motor clean the turn around and cost back down the hill and then pull the plug for reading. Also at that time record weather conditions and make jetting changes as needed. I do this for each 1/4, 1/2, 3/4 and full throttle position. My throttles on each of my "riders" are all marked.

Marty

Wow, klemmvintage looks like a great source of practical tuning information. Can't wait to read it all. Thanks for posting husqyhamm!

The bit about the shortened CZ intake was interesting based on the improved starting and throttle response. For the last few years my interest has been in late 60 and early 70 big bore huskys and they can certainly use a shorter intake, especially the owners who mount a 38VM Mikuni to the end of the stock intake with a rubber boot. The distance from the slide to the cylinder has got to be pushing 120mm.

And what about the way the stock Bing carb clamps onto the intake with only a metal to metal seal? That seems like a leak source to me.

not one picture of either bike in this whole thread !

Here you go. Sorry it is not a CR but this is my 83 500XC
Marty

Damn good looking big bore not to mention its probably a blast to terrorize the desert with. Very nice.

Jetting on the 44mm carb was tricky but worked well/ 40mm better but 38mm best.
Simple fix make and put screen around main jet damn things shook so bad the harmonics from vibration aerated fuel in float bowl so bad felt like running out of fuel. Did the fuel flow drill back in 1982 on the Silver Streaks bigger NJ and leaner needle modified did the trick along with screen on main jet. Figured it out 37 years ago with no computer or internet. Haven't forgotten everything as yet.
Later, George

To much advance will take your leg off or worse break the cases. 2.0 max.
Later George

Can i ask why not boyesen reeds ?

George do you remember the NJ size and needle size you found that worked best for the 44 Mikuni on the 500's? If you do it would probably help a lot of the 500 owners out if you could share that info.

Marty

Thank you! I need to build a 83 500WR. I know Husky didn't do a 500WR in 83.... they should have! Yes it is a rush to ride it!

Marty

no 32 :1 castor 927. the kato dealer closed so im off the motorex.. i now believe the engine man bored the job too tight as he honed it said it measured well. feels better actually.

i see, was just curious..that will do it!

1st stage petals too light, really confound jetting. Also they dont last long, furl and dont seal properly in no time at all.
2nd stage actually restrict airflow at higher rpm.

Always enjoyed reading your comments. I have a question have you found a main lower seal you like. I seen you have found the most main seals leak on testing after 7 pounds
I have been using SKF main seals and having great luck with these on my rebuilds and also found a more hefty , and noted by supplier to be the max seal
name brand not know by me to try. It looks heavy duty. Note all are double lip viton seals I was shocked to find a couple well know suppliers , selling us new/but old stock than was , get this 20 years old !!. I had to replace one of those. Skf s are all less than year old. Thanks for any feedback

Also please note on reed material. Mossbarger has been supplying newly cut brand new reeds to me. They even have some options too on material Had them make up a few custom shorter cages for 430s to help fit the rear airboots better.

Oh I wish somewhere I could find a Dyno chart on 81 82 430 Huskies, never have found one and I think I have just about all the old mag tests

Why bring this up ? because Husqyhamm has done some nice dyno work on the 500