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Old November 25th, 2018, 03:17 PM   #1
corksil
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Tuning the CR500

My project is finally gathering some momentum. It's a CR500 engine swapped into a CR250 aluminum frame, and it's quite a handful. The decompressor on the head really helps, but it's still a chore to start.

I've got it back to stock jetting, with all the jets that Honda recommends. I've got a richer needle, and two leaner needles in addition to the stock needle which is in it now.

Have a leaner main jet, and three richer main jets in addition to what's in it now.

Also have a leaner and a richer slow jet as well as the stock/installed jet.

Took it to the track for the first time yesterday -- first ride on dirt with dual sport tires. 3rd gear will take the bike up above 80mph, and it's got 5 gears. It has a 45t rear instead of the 51t rear sprocket that Honda called for. Seems smart to gear it back toward stock -- I don't want to go faster than 90 on that bike because it has a bit of headshake and it's mighty twitchy at speed.

I'll be using this thread to document my changes to jetting etc and hopefully get a bit of feedback/advice about the direction that this project is moving in.

Next thing to try will be leaning out the bike -- I'll probably raise the clip on the needle, and then going one size down on the main jet. The bike was running rich, because it was smoking for most of the time, and at WOT it was hesitant to fully come online. It would pull hard and then start 4 stroking and bogging a little before it would "catch" and really light up and take off the way it should. Think that these are signals of a rich mixture. I didn't do any plug readings.

It has an aftermarket FMF gnarly pipe, and an FMF powercore 2 muffler on the back. The pipe has a minor dent, and a 3" long crack in the second bend on the left. Surely neither of those things help -- but I don't have the $ to replace the pipe right now so hopefully it won't make my tuning much more complicated.

Anyways, that's the latest. Dear diary.
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Old November 25th, 2018, 03:57 PM   #2
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You giving that the supermoto treatment or staying dirt?

If you go Sumo, it would be pretty easy to get 120 mph out of it with the right suspension tweaks to add some stability.
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Old November 25th, 2018, 09:40 PM   #3
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The general idea is to get the bike dialed in and comfortable on dirt before figuring out if re-configuring it for street riding is feasible.

I suspect that it's going to be a long process
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Old November 25th, 2018, 11:15 PM   #4
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Corksil, you take on the coolest projects!
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Old November 27th, 2018, 10:15 AM   #5
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Just a quick thought. You can buy a "Dent puller" for about $20 at Autozone or Pep boys (most likely cheaper on the internets) and easily pop out most dents in the pipe. Also if the crack in the pipe is not too wide, flowing some solder into it can seal it up and you can use "Liquid Metal" EPOXY as a temp patch but it will need to be redone after a few rides as the heat usually breaks it down. Anyways, Good luck with the tuning I am so jealous of your project
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Old November 29th, 2018, 05:57 AM   #6
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As far as the jetting, get it running at WOT first. Don't worry so much about how it gets there just how it runs when you are WOT. Dial the main back until you get it running well. Then work on leaning out the needle clip and moving to a leaner needle all together if you have to. Then the idle - 1/4 shouldn't be too much of a PITA to tune. If you are running the stock carb. 38mm PJ i believe, they are not the best carb but they can work good enough. Most people opt to a PWK. I had a 39mm pwk on my 500, and boysen rad valve. It took a ton of jetting tests and changes but i eventually got it dialed in and it was electric.

As far as the pipe. Weld the crack then make 2 plugs, a solid for the exit and one with a shrader valve for the intake. Pump ~ 20psi of air into the pipe, then heat the dents with a torch, nothing too hot that you will burn through it. Handheld torch with MAP works. The heat will expand the 20psi of air already in the pipe and increase the PSI and force out the dents. If you get the dent nice red and hot and it is still going nowhere after awhile, pump a few more PSI into the pipe in small increments until it does.

As far as going fast on the 500, you are entirely correct, they get scary at high speeds, the chassis isn't designed for that kind of speed and the front gets so light very subtle unwanted inputs into the bars can cause big problems.

Here is a picture of my valve pipe plug for blowing out dents. Pretty simple, i just used couple pieces of angle and a piece of wood to create a clamp, cut a patch out of an old tube with the valve stem. Just sandwich it all together and it is good to go.

Good luck and have fun.
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Old December 4th, 2018, 02:49 PM   #7
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I had a 1984 CR500 (air cooled). Was a beast to start. Often had to tip it to the side to flood the transfer ports then start it. I remember a gal who wanted a CR500 back in 1985. She came to the shop with her boots and said if she can start it she'd buy it. She started it and she bought it.
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Old December 5th, 2018, 05:46 AM   #8
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#1 rule for starting any big bore dirt bike is always start immediately after you rotate past TDC.

Push the kicker and feel the compression build, go slow, and after it releases rotate the kicker a tiny bit until it clicks. Then return the kicker to the starting position and give her a good solid kick the whole way through. Repeat until it starts.

This is not a bad practice on any bike that uses a kickstarter as it helps takeaway some of the initial stress that is put on the kick start mechanism and you are less likely to break things. I use this method on all my dirt bikes when they are cold.
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