Building a 1981 Yamaha YZ465 Factory Replica...

Discussion in '2 smokers' started by FJ_Kevin, Mar 11, 2012.

  1. wfopete

    wfopete Suffer Fools; Gladly!

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    Kevin,

    I just received my 2013 AHRMA Handbook. Under section 3.3 Technical Inspection sub section 3.3.2 it states that Snell M2010 helmet are required for ONLY road racing and dirt track. All MX, PVMX and Cross Country must meet Snell M2005 or equivalent standard.

    So in those respects you are good to go. Unfortunately, you modified your helmet and in the same section it also states that ALL helmets will be closely inspected for ANY damage OR modifications to the shell and inner liner. Any damage or modifications (to include non-OEM visors) to the helmet found will be grounds for immediate denial or disqualification from any AHRMA event.



























    ...just kidding about that last part :lol3
  2. FJ_Kevin

    FJ_Kevin Been here awhile

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    Haha, lucky for me I saw your last sentence first before reading the first part. Otherwise, with the way things go these days, I would have believed!

    BTW, I had a good time at the York PA swap meet a couple of weeks ago. Seemed to be a good turn out with lots of parts and bikes up for sale. They had an auction for the first time too. I was too busy to watch much of that but it looked like fun and folks were bidding. There were bike for sale out in the parking lot too.

    This Montesa looked pretty good,

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    Here are some Hondas out in the parking lot.
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    Some top notch show bikes were on display indoors,

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    This Elsinore was in the auction as were the bikes behind it.

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    My understanding was that all the following bikes, with number 46, were from the same family

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  3. FJ_Kevin

    FJ_Kevin Been here awhile

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    With the motor back together and back in the bike, attention was turned to the carburetor. The YZ/IT 465's and early 490's sported a 38mm Mikuni carburetor with left side idle adjustment screw. Later 490's came with a 40mm carb so be careful when comparing jetting across the model range.

    It is important to note the side of the adjustment screw because replacement slides are available in left and right hand versions. If you choose to buy a replacement slide, say with different cut away,you will want to make sure you get the correct one for your carburetor.

    It's alway good to get things cleaned up before starting a carb rebuild. Like others, I have been moving away from using harsh carburetors cleaners (when possible!) in favor of something safer.

    I had good luck with Pine-Sol on some Goldwing carbs I rebuilt a couple of months ago and so that's what I chose to use here.

    The following photo shows several carbs going into a tub I picked up from home depot. These tubs come with a handy top that helps keep unwanted items from falling into the solution while the carbs are soaking.

    Using the top also keeps the smell from being over powering.

    I used pine-sol at full strength and soaked 4 (added one more after photo) disassembled carbs for about 12-14 hours.

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    And here they are after soaking,

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    The carb in front had a bit of corrosion in the top of the float bowl area but it should still work OK.

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    Here is one that's easy to miss.

    The bell of the Mikuni accepts an air correction jet (see hole at 12 o'clock position) for some applications. The IT490 uses a jet here but it is completely left out for the YZ465. Aways a good idea to check this if you dont know the bikes history.

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    I already has some baseline jetting combinations in mind from experiments on the IT490. Before going forward I had to see what parts I already had on hand.

    The main jets are along the top with values of 350 through 460. The needle jets are in the center Q2, Q4, Q8. It looks like I had 2.0 and 3.0 slides on hand. Pilot jets are mostly in the 35 to 50 range with one flyer at 80.

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    More to come...

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  4. D.T.

    D.T. Difficult but useful

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    Cool stuff man. Thanks for sharing!
  5. wfopete

    wfopete Suffer Fools; Gladly!

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    I've had problems with discoloration when using the Pin-Sol method however I found if I follow up with a little soda blasting things really start looking nice. SB is cheap, EZ but a bit messy. Also, due to the wear and tear over 30+ years of use I often opt out for a new carb with nice fresh jets/slides/needles. Kevin, you might want to get a 3.5 slide to play with at some time too. Another option is using a good proven carb (a good thing instead of dealing with a mystery carb). Remember these bikes were originally designed to run on Yamalube R @ 32:1 but Yamaha also recommended Shell Super M or Castrol R30 mixed @ 20:1. Oils have advanced 10 fold over the years and who still uses those ratios? These are a few pieces of the puzzle to consider when getting ready to jet/tune. Your approach to jetting/tuning the bike can vary but some guidelines when tuning the motor are:

    GOOD, fresh high octane fuel and oil
    Decide on what oil/fuel ratio to use (probably what you want to race with)
    Plenty of time (you don't want to rush this process)
    One change at a time (don't change the PJ & MJ at the same time)!
    A logical sequence of test events (Don't jump back and forth between jetting and timing changes)
    A good, safe test area that offers hard packed dirt and deep loam (helps load the motor)
    Many, many new spark plugs
    Paper/pencil

    Doesn't hurt to have a knowledgeable friend help around to lend a hand & tell you how they see the bike running. I also like to have some compressed air handy to blow any dirt/dust off the carb before disassembly. A 2 stroke tuning book to helps you keep your mind straight during the process too. YZ 465/490s are known for problems in tuning so don't make it any harder on yourself than you have too. If you have all the pieces in place tuning the motor can be a lot of fun instead of a frustrating ordeal. Do what you can to make it fun.
  6. FJ_Kevin

    FJ_Kevin Been here awhile

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    Pete,

    Yes, I'd say you covered it pretty well and saved me some typing too!

    I will add a little information that I found in my own searches that might be helpful to others too.

    First, there is the Mikuni VM Tuning Manual available here,

    http://www.mikuni.com/pdf/vmmanual.pdf

    I also found Pats Small Engine Parts to be an excellent source for Mikuni jets. The web site is not the best but the prices are the lowest I have seen and shipping is reasonable and fast. If you are buying several jets for experimentation than you will really appreciate the low prices.

    Here is a link to the PSEP carburetor parts page,

    http://www.psep.biz/store/mikuni_carburetor_part.htm

    I found a jet needle change to be necessry. For an explaination on needle tapers and how to compare them, go to the sudco page here,
    http://www.sudco.com/CatalogJPG/114.jpg

    I also changed out the needle jet. The sudco needle jet chart is here,
    http://www.sudco.com/CatalogJPG/117.jpg

    Before tuning the 465, I had spent considerable time jetting the IT490.
    At that time I did some searches on the Yahoo YZ490 page, the Yamaha IT forum (Australia) and some other sites.

    While there was no universal agreement, there did appear to be a general concensus that the YZ/IT's were jetted too rich in the low to mid rpm range. Several identified good results with a change in jet needle, needle jet and slide.

    The jetting I wound up with in the IT490 is as follows,

    Pilot Jet= 40
    Main Jet = 380 (it pinged with a 370)
    Slide = 3.5 (I took a 3.0 slide and hand filed the cut away to 3.5 specification, the stock IT slide is 2.0)
    Needle = 6DH4 (stock was 6F16, also tried a 6F8 but not as good)
    Needle Jet = R0, 247 series
    Premix = 40:1

    I found the change in slide and needle to make a big improvement on the 490. Its a real fire cracker now and lots of fun, starts pretty easy for a big bore.

    I ordered the same needle and needle jet for the yz465 but started experimenting with the jets I had on hand before the parts arrived.

    Thats where having the mikuni charts proved handy. It turns out that the 6DH3 needle is pretty close to the 6DH4. And the Q8 needle jet is only 1 step off the R0. So right now I am running the following combination in the YZ465 with good throttle response and no pinging thoughout the range.

    Pilot Jet= 50
    Main Jet = 380
    Slide = 3.5 (also a hand cut 3.0 slide)
    Needle = 6DH3
    Needle Jet = Q8, 247 series
    Premix = 40:1

    I should mention that both of these bikes have DG pipes with FMF universal spark arrester silencers. I did drill out the spark arrester cone on the 465 however.

    Regarding the hand cutting of slides, I'll post up some more details on this but this is necessary as the 3.5 slide for the left hand idle screw carburetor does not seem to be available new. Or at least I could not find anyone who listed this.

    More to come...

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  7. FJ_Kevin

    FJ_Kevin Been here awhile

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    Thanks DT.

    There are so many great street and dirt projects going on in advrider, lots of variety and creativity... its a good bunch here!

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  8. D.T.

    D.T. Difficult but useful

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    Cool pictures. All the cool kids had YZ's growing up and all I had was a DT.

    I have had my 1985 XT torn apart about 10 times (3 on the motor) and it's getting old trying to keep it up. Modified the shit out of it (TT pickup and flywheel, wiseco piston etc). It's leaking from the fork and engine now since I have only ran it once in the last year. The piston rattles pretty good so I should find a stock cylinder and have the piston fit, but I may just sell the old thing. :cry
  9. FJ_Kevin

    FJ_Kevin Been here awhile

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    Mikuni offers different slides with varying degrees of cut away for the VM38 carb on the YZ465 / IT490.

    They are identified by number (2.0, 2.5, 3.0 etc) stamped on the underside like this (see 3.0 at about 10 o'clock),

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    The amount of cut away and air flow increase with the slide number. The IT490 came with a 2.0 slide and the YZ465 came with a 3.0 slide.

    The 3.5 slide for my bike was made by increasing the cut away in a spare 3.0 slide to 3.5 specification.

    This diagram from the yahoo yz490 group shows the difference between 3.0 and 3.5 slide cut aways,

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    One way to cut the slide is on a milling machine (yz490 group photo)

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    As the slide is made of brass, hand filing is pretty easy to do also.

    Here are a couple of photos showing how the slide was marked before hand cutting.

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    From the earlier drawing you can see that the highest point of the arc should be 7/32" from the bottom.
    An easy way to test for this is with a 7/32" drill bit. That is, file the arc until the drill bit slides through the arc with the bottom of the slide on a flat surface.

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    Here's a cool picture of Tony D.

    I remember having a pair of those Full House Mx pants. My exhaust pipe cooked some holes in them!

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  10. mxscot

    mxscot n00b

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    Hi again!
    You kindly posted the rear spring page from the manual showing the spring rates and the markings a couple of pages back and it has been most helpful. I am hoping now you could do the same for the front fork springs, please. It is the YZ465H 4V4 I am interested in. The springs I have are soft to match the rear - too soft for me.
    I don't know if the ones I have are Yamaha OEM or not. They have two saw marks for identification on the end, no paint.

    Also I see you posted that the standard rear rim size is 2.50. Was the front a 1.60?

    By the way I did manage to get entry for both Hawkstone Park and Farleigh Castle events this year so its all looking good so far....just need that bike sorted up! :wink:
  11. FJ_Kevin

    FJ_Kevin Been here awhile

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    Welcome back!

    I am afraid I don't have a yz465h manual but do have the G manual as well as several 490 manuals. I also have a copy of the Yamaha Race Preparation and Tuning Manual from which I found this,

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    From above, it looks like the standard spring is for 155-165lb rider weight. Better lay off the chips!

    Here is the page from the yz465G manual. It seems the two saw marks may indicate you have the stiff springs already (0.357kg/mm). Maybe they have sacked out over time?

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    Next is the data from the '82 YZ490J manual. It only lists the standard spring.

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    Here is the 1983 YZ490K. It too shows the double slit spring as being heavy duty (0.325kg/mm).

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    Finally, the IT490 sheet,

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    I believe that the spring and preload spacer length vary across the model years.

    I seem to recall the Racetech site offering the same length spring for the 465 and several years of the 490 even though the original spring lengths differed. I am not sure what to make of that.

    Anyway, please let us know if you come up with a favorable front spring solution (preferably for someone weighing 180 or so :evil).

    On the rim, your are correct in that the rear rim is 2.50 (not 2.15 like that girly 250) and the front rim is 1.60.

    Thats great news about Hawkstone and Farleigh Castle. I just watched the Farleigh Castle GP from 1982 this past Saturday. It looks like a spectacular track.

    I hope you will post some pictures as you get your 465 setup and especially of you at the races!


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  12. anotherguy

    anotherguy Long timer

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    I run the race Tech 3 rate kit at full stiff in my 465 w/'82 forks as well as emulators. Works well.
  13. FJ_Kevin

    FJ_Kevin Been here awhile

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    This section will deal with the repair of several broken cooling fins on a very special cylinder, one that came to me from a source with close ties to former Yamaha factory team mechanics. It has led a tough life but is definitly worthy of repair.

    What makes it special? Well, that will take an explaination all on its own.

    So first I will will go through the repair and then I will disclose what makes it is so unique.

    Now before starting work, I practiced on a scrap cylinder so as to determine the proper heat range and refine my welding technique as I have gotten a little rusty.

    I then turned attention to the so called “factory” cylinder.

    This first photo shows one of several broken fins to be repaired.
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    You can see I have already removed most of the paint and have cleaned and sanded back the affected areas. The plan was to weld up the fin by making multiple passes with the tig welder rather than weld on a fin from a donor cylinder.

    Next the cyliner was pre-heated in an oven. Aluminum is a very good conductor and will quickly draw heat away from the weld and into the surrounding mass. This can affect penetration and the time and energy required to puddle the aluminum at the weld site.



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    Another concern was the rod compatibility. But good results were obtained with a general purpose aluminum rod I already on hand.


    This next photo shows the first run of aluminum bead made with the tig welder.
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    After 3 passes it looked like this,

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    After several more passes, there is more than enough material to shape the repaired fin.

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    Next is the repaired fin after a little shaping with a grinder and hand file. There is still some work to do but I was pleased with the weldability of the cylinder and the overall result (after a little more work).

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    So now, what is so special about this cylinder?

    Here is the first clue...

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    Now, it is well known that the Yamaha team riders had factory and production bikes at their disposal to use both in practice and to race with. As the factory OW41 racers were expensive, a lot of practice time (and some race time) was spent on the production bikes. However, the stock production bikes had significately different characteristics campared to the full OW’s, especially in power delivery.


    To close the gap, Yamaha developed special 465 cylinders with OW41 style porting. These were denoted OW41 P (P for production based or production prototype). These cylinders had special markings as shown above.

    So what we appear to have is an OW41 P cylinder with a displacement of 476cc.
    But what does R X mean?

    To help answer this, I turned to the book Legendary Motocross Bikes,


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    We find Rex Staten identified as one of the factory OW riders at that time.

    It is said that, due to personal preferences, it was common to ID cylinders with rider initials to accommodate a riders preference for a particular porting configuration.


    Can it be concluded this rare OW41 P cylinder was for ReX Staten’s production based YZ465 racer?


    Comments?







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    Keith Mann at Unadilla
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    More to come...
  14. anotherguy

    anotherguy Long timer

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    Care to share a portmap of that cylinder?
  15. mxscot

    mxscot n00b

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    Thank you very much!

    I certainly will be posting photos........and laying off the chips! :rofl

    The wife got me a Go-pro for Christmas so hopefully I can get some video of the events too.

    Here is an advert for the 2012 Farleigh Castle event http://youtu.be/PVPSTDZZPYs
  16. ctune80

    ctune80 Been here awhile

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    Yeah, what he said! What a cool piece of history to have.

    I am a Facebook friend of Rex Staten, do you want me to ask if he remembers anything about the markings?

    Anxiously awaiting more posts on this project, Very interesting stuff!
  17. ctune80

    ctune80 Been here awhile

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    Hopefully this isn't a repost, but here is a link to a Cycle News article on Marty Moates' USGP winning YZ. It actually displaced 493cc, I hear it was due to a longer stroke, not just bored to the 490 sized bore. I would like to know for sure, but haven't found anything in print.

    I lived in Waukegan for a while, a little after the LOP era. I knew a couple guys from that crew. I wish I could have got some parts for my 465 from them!

    http://www.cyclenews.com/articles/friday-flashback/2010/07/09/friday-flashback-27-07-09-2010/
  18. wfopete

    wfopete Suffer Fools; Gladly!

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    For sure way up there on the coolness factor & just what a replica bike needs! Perhaps the best way to judge what type of punch the porting may give is to know how Rex liked his 465 power served up. For your average racer it may be dang near unridable...or great. I recall Bob Hannah stating at one time when he was trying to get a 250 setup for SX. He wanted lots of low end power and told the factory guys "You can't give me enough low end power!" Turned out that the factory gave him so much low end boost he could hardly ride the bike. Although very cool and the latest for their era, think of some of the things that have been abandoned in motor and suspension beliefs of that time. The factories were all over the extremes of suspension, power and handling; some of it was "over the edge". It's funny when some of the factory riders talk about the old bikes (or even better ride them years later). They often come away saying something like: Man how did we ride those things back then! I think the factory riders generally hated the corporate marketing people. Marketing would to come up with some goofy bling (remember boost bottles?) :rolleyes to sell bikes and the poor factory guys were supposed to show how well the stuffed worked.
  19. anotherguy

    anotherguy Long timer

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    So....uhm.........no portmap?
  20. brucifer

    brucifer Long timer

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    Wow, that engine is (was) impressive! 4th gear starts?! :eek1
    But the suspension set-up; man that sounded more like suspension for a tight woods bike with lots of roots, rocks and ruts to deal with at slow speed rather than a motocross track. I guess maybe they just didn't have the optimum valving, so soft was better than hard.