YZ 490 Help/advice needed

[LWC82PE]

the bearings were ok its been recently rebuilt i reckon. they had used grey 3 bond

The stator plate looks like its still got the one set of standard adjustment slots and hasn’t been modified.
I read some of the Bell 2 stroke book and he reckons to start using an extra 3 – 5 degrees advance with methanol.

Any one know what the biggest mikuni main jet available is?

This engine has a 43 or 44mm mikuni on it is this a stock 490 YZ fitment?

[lms6201]

 vm 40 ss is std  ,      the jet might have to be drilled ,  try a 3/16"!!

[LWC82PE]

yeah that really should have all been done but i want to check everything before i run it again. my info says that the biggest hex mikuni main is about 720 and on one bit of info i found, the 490 has about a 440 std and with methanol jets about 2.3 times as big should be used so a main over 1000 would at least be needed i reckon as well as a bigger needle and seat

[LWC82PE]

had some progress today. Had to buy a universal Carbon Tech reed and cut them and drill them my self. It took a while but I got them so good that is hard to tell they were not hand cut.

Now with the timing. Looking at the stator there are 5 marks on it. 1 long mark in the center and 2 short ones each side. Is the timing mark the center long mark correct?? I assume it is as its the center on the suzukis.

I set the stator where it was before and checked the timing at 2.7mm BTDC and the rotor mark lined up with the first short mark to the right of the center mark so I don’t think that’s right as it was too retarded. I can see that there is 2 key ways on the rotor. This is not standard??? Should it only have one? I’m thinking that it has had a another key way machined to move the rotor to give correct timing with the YZ 250 internal rotor set up and still run it with a key other wise with no key the rotor could spin.

So guess all I need to know is if the long center mark is the timing mark I have to set it to 2.7mm. And once its set up as std I might advance the timing a little for the slower burning methanol

it would be good if i can get an answer on this before tomorrow. thanks

[LWC82PE]

i just had another idea. is the center mark the mark to indicate top dead center?

[LWC82PE]

got this machine going today. bit tricky to push start it with not much space, but got the owner to help out and drive it as he was used to driving these things and started it in 3rd gear.  We set the timing at around 2.9 deg btdc which is a .2 degrees more advanced for the methanol which i hope will be ok. Before it was way too retarded which probably caused the meltdown along with not enough oil, and used the middle mark on the rotor so hopefully that is right. we mixed some methanol with shell M at 20 to 1 but there didnt seem like much smoke out the back so we have recommended to go to 18 to 1 when he takes it out to a race on the 14TH of dec. It was very loud so we suggested repacking the muffler. I had never heard a YZ 490 before but this one sounded too loud. By the way the onwer blasted up the track sideways it looks like it is a very quick machine. Hopefully it goes alright at the races.

If it holds together well we will be looking for some spare YZ 490 engine parts as the barrel is on last oversize, but may consider a re-sleeve if anyone can recommend some one good to do stroke sleeves as this barrel has already been ported and strengthened for methanol.  Serco perhaps? Also the carburetor body has had a repair around the float pin area so will be looking for another 44mm roundslide carby.

I put in custom made Carbon Tech reeds so after the first race I will ask the owner what he thought of them.

[LWC82PE]

well this had its first race since the rebuild and a quick note came in with payment from the onwer and he said it went well, but im not sure what place he got. at least it held together with the methanol and 18 to 1.