Jump to content
Sign in to follow this  

1983 YZ 490 Jetting (IT 465 hybrid)

Recommended Posts

I was wondering if anyone on here has experience jetting the 82-83 yz 490's. I just got done rebuilding my IT 465 with a YZ 490 top end. Jetting wise I'm running a 45 pilot, and 420 main jet. I purchased a carb from eBay as a spare, and it was labeled as a yz490 carb but definitely seems like it came from a it 490 due to the jet needle being a 6f39. Anyways....

I am pretty sure the 6f39 needle is far to rich of a needle seems to be really blubbery from 3/8-3/4 throttle. The needle clip is in the highest/ leanest position which did help some. I see the yz 490. Is supposed to run a 6f16, should I get one of those jet needles or something else all together different?

Tha me for your input!

And a picture of the money pit!

IMAG0433_zpswcnpy1jt.jpg

Edited by 79yamdt
  • Like 2

Share this post


Link to post
Share on other sites

Well what I found what I was looking for at another forum! I'll post my findings in hope it'll help someone else.

CARUBURETOR

Pilot 40 @ 1 3/4 turns out

Needle Jet R-0 (series 247)

Needle 6F8

Needle clip position 3 (middle)

Main 430

Slide Cutaway 3.5

The stock slide is a 3.0. I have never been able to find a 3.5 slide for sale so I modified my 3.0 slide into a 3.5 slide. Use the illustration below to modify your 3.0 slide to a 3.5 slide. I am interested in

Edit:

My testing tonight has me running a 45 pilot, 410 main and everything else the same as above.

Edited by 79yamdt

Share this post


Link to post
Share on other sites

Heh-Heh, didn't Eric Gore make a small fortune on this exact topic!

Yeah he probably did. The head reshaping services are like 35 bucks through him though, not really a small fortune for some machine work. I guess he'd also suggest a slightly different needle jet then the one I have in currently, in conjunction with the head mod. I see no need to send mine in to be done at this moment. I have no pinging or the like currently. It may have already been done, I'm not sure.

Share this post


Link to post
Share on other sites

I had a near unused 82 yz490 back in 94, before the age of the interweb. I didn't know of E.G. and tried my best to jet that thing. Then I understood why it was unused when i got it.

Share this post


Link to post
Share on other sites

I had a near unused 82 yz490 back in 94, before the age of the interweb. I didn't know of E.G. and tried my best to jet that thing. Then I understood why it was unused when i got it.

Well maybe mine has already had work done to it. It could probably still use the needle clip moved to the next leaner position.

I can't imagine finding out almost anything I've researched on my bike without using the interwebs since I was born in the early 90's

Share this post


Link to post
Share on other sites

Here are some other pics for those interested! IMAG0495_zpsqwyhh1ks.jpg

Here it is as of last night, IMAG0953_zpslzr4rclk.jpg

The only thing that's really bothering me is the seat! I had to add some foam and didn't quite shave it perfectly so the seat has wrinkles in it that in can't seem to get rid of.

Next weekend I'll be racing it in a vintage hare scramble, that should be fun!

Edited by 79yamdt

Share this post


Link to post
Share on other sites

i found a 3.5 slide................cant remember where.........but they are out there

 

 

mine already had the mod done when i got it

Share this post


Link to post
Share on other sites

i found a 3.5 slide................cant remember where.........but they are out there

mine already had the mod done when i got it

I bought a it 490 carb just for the slide ! They came with a 3.5 from the factory.

And yes if definitely flies! It needs some more slow to go with all the go

Share this post


Link to post
Share on other sites

as far as i know they came with a 3.0 slide from factory..........but good that you have a 3.5 

Share this post


Link to post
Share on other sites

I just picked up a 82  IT465 and was doing a bunch of research on the Yamaha IT forum AU. There is one thing you should be aware of on the 465 and the early 490's. The kick start gear and shaft is weak and if the slide on gear fails it will be disastrous. You can use a newer IT/YZ 490 one but you need to change the kick start lever as well. Here are a few links so your can read them your self.

 

http://www.yamahait.com.au/forum/index.php/topic,16128.0.html

 

http://www.yamahait.com.au/forum/index.php/topic,15864.0.html

 

And here is a pic of my 465 I just picked up.

 

 

photo A4 Large.JPG

Share this post


Link to post
Share on other sites

Here is another Link on the Kick start shaft problem and the pic shows when the kick start lever returns to far.

 

http://www.yamahait.com.au/forum/index.php/topic,16128.0.html

 

Here is the best price I found on one.

 

http://www.partzilla.com/parts/detail/yamaha/YP-57H-15661-00-00.html

 

 

 

And here is a few links for a push button Decompression to save the Kick start shafts.

 

http://www.yamahait.com.au/forum/index.php/topic,16459.0.html

 

http://www.yamahait.com.au/forum/index.php/topic,15762.0.html

 

http://www.jackssmallengines.com/Products/HUSQVARNA/Decompression-Valve

 

http://vulcanworks.net/catalog/Compression-Releases-orderby0-p-1-c-1.html

 

 

 

Here is a some good reading on Different reeds for the 465/490!!

 

http://www.yamahait.com.au/forum/index.php/topic,18214.0.html

 

 

 

I think my kick start shaft gear is cracked as my kick start is returning to far forward.

 

 

 

photo F3.JPG

photo F4.JPG

Share this post


Link to post
Share on other sites

Thanks for the advice. I May be misinformed about what a IT 490 came with from the factory carb wise. I'll keep the kick shaft in mind,maybe find a complete used assembly. If it hasn't destroyed itself in 30 some Years I don't think its an urgent matter.

I'm also on the it forum and have a thread on there following the rebuild of the bike.

So anyways back to the jetting the beast...

Today I continued to test it and played with the needle clip position and ended up going with what I started with. So as of now I'm running a R-0 needle jet, 6f8 needle with clip in position 3, 3.5 slide cut away, 45 pilot 1.0turn out, and a 410 main jet. This is all on 93 octane 32:1 (amsoil dominator) at around 550ft above sea level .

Edited by 79yamdt

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×