300r air cooled build, need some help

[jaykup]

I'm building a 1981 ATC 300r but I need some help...

I was able to find:

• 300r Hondaline big bore cylinder
• Sleeve & piston for the 300r
• Exhaust
• 38mm PWK flat slide carb

Got it assembled, but...

• The rubber boot that connects the carb to the reed cage is far too small. Where can I get a larger one? Will one off a newer 85/86 work? The OD of the carb on the intake side is ~46mm
• Where should I start jetting? I have a bad habit of running 2 strokes too lean and don't want to make that mistake with this build.
• Why does my damn swingarm keep cracking? I've welded it but it just cracked around the weld...

Stock carb jetting: 50/165
PWK carb jetting: 55/160

I'm hoping taking it out this weekend

Pics:


Frame


Engine


PWK vs Stock


Running lean


Not gonna happen

[fabiodriven]

If your swing arm won't stay together, it may be because of inferior welds. That's not always the case though. Sometimes it doesn't matter who welds the break or how. If it's a spot that's susceptible to breakage, it just may not hold.

[jaykup]

That's entirely possible, I tried to mig it where it cracked and it was hard to get the industrial sized welder I was working on to go low enough not to burn through.

I thought I remembered something about these early model 250r swing arms cracking, and wondered if there was a solution (maybe its just a better weld).

[D-dub]

I think you need to get yourself an Fl350 intake off ebay

[jaykup]

I found this

http://www.3wheeler.org/vb/showthread.php?t=10112

Which some guy thinks the 81 is the same as the 86 as far as bolt patterns so I got this:

http://cgi.ebay.com/ebaymotors/230644554241

because otherwise I'd have to get this:
http://cgi.ebay.com/ebaymotors/110642356138

which is cracked and I'm not sure if a 38mm would fit...

or this

http://cgi.ebay.com/ebaymotors/370527399233

which is expensive

[hillbilly 200x]

This may fix your swingarm http://cgi.ebay.ca/HONDA-ATC250R-AFT...item45fbe557ee

[laidout2times]

that swingets not for the 2nd gen inless it eliminates the linkage.

[jaykup]

I ran into an issue with the new 300 sleeve, it was too long and was leaving a 1/16" gap where the base gasket sits. I had to have the skirts on the sleeve machined down .100" (used a surface grinder).

Now it fits up nicely.

The machine is fully assembled, the boysen RAD cage is a bit of a tight fit because of the angle and the size of the new carb, but it will work... I hope.

Anyway, going to start it up tomorrow and drive it around for a break-in.

What do you guys recommend I start at for jets? Anyone with a 300r and a ~38mm carb let me know what jet sizes you are running with...

[jadleybray]

The 81-89 250r reed cages are all the same bolt pattern. V force reeds and cage will fit the foolers. I do know that the 85-86 width swinger will fit into the 83-84 frame opening although not a direct bolt in. Pic is an 84 with my 86 swinger and rear end on it

[gotballs 250r 82]

the swing arm will fit on a 82 set up you would need a 82 axel and a 82 rear disc brake to make that swing arm work it will not work for a 81 set up drum brake and axel is not the same as 82

[jadleybray]

Oh , good call Balls. I looked too quik and thought that was a trx swinger. Those are hard to come by for the first gen R's.

[gotballs 250r 82]

ya i have one on my trail 82 R but that is not the swingarm in the first pic the drag R has one almost the same but biger and longer