Reasons why 500's ping, Now 2-stroke porting idea's ;-)

[John Orchard]

Well done John. I discovered something similar with my then '74 CR250M . There are 2 different length pilot jets for the early Keihins. One about 10mm longer than the other. When I first got my CR, I couldn't get the thing to pull cleanly off the bottom for the love of jets and jet drills. The thing was like a light switch and pinged with the DG head. Then I found longer PJ's at a dealer in Taree NSW. Grabbed a couple of different sizes and then set about trying them. Even with a too lean PJ the bike stopped pinging! I used a #60 PJ and then drilled that bigger again. I ended up with an Elsinore that actually had bottom end response 

That's awesome, I don't know why I haven't seen more info about this?

[John Orchard]

I just ripped the bowls off my PE & PJ carbs, the PJ is on the left, you can just see the shroud around the pilot jet.



This is my make-shift extension that fixed the problem out at the track, just a bit of fuel hose pushed in with a wedge cut out of the end so it doesn't seal on the bowl bottom..




I'm looking at stuffing some foam in there somewhere, plus I'll raise the float level another 1mm from 16 to 15.

[sa63]

Good stuff! I'll look at the  PE on the 480 tomorrow although it hasnt really pinged until it gets really hot. Seems like a good little upgrade. Planning to ride it on Sunday. I guess there is more likely hood of the jet blocking though.

[FourstrokeForever]

Well done John. I discovered something similar with my then '74 CR250M . There are 2 different length pilot jets for the early Keihins. One about 10mm longer than the other. When I first got my CR, I couldn't get the thing to pull cleanly off the bottom for the love of jets and jet drills. The thing was like a light switch and pinged with the DG head. Then I found longer PJ's at a dealer in Taree NSW. Grabbed a couple of different sizes and then set about trying them. Even with a too lean PJ the bike stopped pinging! I used a #60 PJ and then drilled that bigger again. I ended up with an Elsinore that actually had bottom end response 

That's awesome, I don't know why I haven't seen more info about this?

I didn't see any info about it either. I just stumbled onto it when comparing jets at the bike shop and thought there had to be a reason for the longer jets. The '75 and '76 CR's came out with the longer jet which might help to explain why they run so much smoother than the '74....

[80-85 husky]

"I wonder what carb was on Jeff Leisk's CR500RE back in the day when he won Mr Motocross?!!"

Jeff Leisk doesn't use a pilot or needle jet.......the slide is out of the carb and the throttle just switches the ign on or off.....

[smed]

  I wonder what carb was on Jeff Leisk's CR500RE back in the day when he won Mr Motocross?!!
[/quote]

Jeff rode a pre proddy or semi factory air cooled 500 in 83 to some moto wins in MR MX, But won the title on a watercooled job the next year;)

[John Orchard]

Was it in '83 I saw pics of the rear disc air-cooled CR500 at Broadford?

[smed]

 I was wrong JO, It must have been 85 when he rode the watercooler, This sticker on Ebay shows an aircooler & it says 1984 MR MX 

http://www.ebay.it/itm/Jeff-Leisk-1984-Mr-Motocross-Honda-Australia-sticker-CR500-Moto-X-motorcycle-/121463482050

[Tahitian_Red]

Interesting stuff!  I knew there was another reason, besides being fast, that I have you as my factory rider. 

The CR500RE has a different crank balancing than the CR480, maybe that is why it might vibrate more?  This makes me wonder about the infamous YZ490 and it's pinging problems.  I think vibration is almost always mentioned in the YZ490 tests.

[Slakewell]

I would be interested to what difference a probably balanced crank made to the pinging?
Frank did my 84 495 crank.

[John Orchard]

I guess with regards to balancing a single cyl, it can only be balanced for smoother operation at a certain rpm, and not balanced either side of the rev range?  Need some input from Lozza, he would have an idea.

[bigk]

The hose on the pilot jet thing was a common "fix" for the big flat spot bog that Honda XR's had when landing from jumps or going over a long stretch of rough ground. Never seen in on a CR till now though.
K

[John Orchard]

I wonder also if the tin baffle plates in the fuel bowl help contribute to the frothing fuel from vibration?

[John Orchard]

The CR500RE has a different crank balancing than the CR480, maybe that is why it might vibrate more? 

Jay the 500 has a longer stroke also, which would also help contribute to the vibration.

[80-85 husky]

there is a bloke in qland who cured his husky from vibrating by balancing and matching his crank halves. it was a 250 and he milled a scary amount of metal off the crank cheeks before he panicked and stopped but the result was superb.