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BergDonk's DR650s

Discussion in 'Thumpers' started by BergDonk, Dec 20, 2010.

  1. BergDonk

    BergDonk Old Enough to Know Better

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    Hmmmm, depends on priorities I guess. If its an adventure bike that has to get there with a load and have ultimate reliability I'd stick with a well setup 650. If its a fun bike, the 790 is more fun. The 790 is also a better highway bike when higher speed cruising and overtaking comes into play.

    I haven't played with HC pistons or cams, but have seen a couple of DRs that blew up with those components aboard. Top end fails, cams shedding hard facing and cracked pistons, and a broken rod. Caused by parts not as good as stock, or poor assembly/maintenance, or both, dunno.

    If you want a lightweight fast bike, its not a DR in any of its incarnations. If you want a lightweight adventure bike that will take you almost anywhere, then it is a DR. However I've ridden with well setup WR250Rs and they cover the ground we travel on just as fast as the bigger 650s for the most part. But they are more work, and have to be ridden on the gear lever and rpm. I prefer less frenetic torque.

    I'm very happy with my 790 conversion, but I'm also very happy with the latest version of my wife's stock engined DR too.

    So what do you want? I want a reliable fun bike that will take me most places. Absolute speed isn't a big deal, but the 790 is more fun for a few % of the time when the extra torque and power kicks in. I may also be an outlier, but based on my 790 experiences, they do generate more heat, and in hotter climates, I think that needs to be managed in some way over and above the stock cooling system.

    I do like the Nova gearboxes, and reckon they're key to having a DR that you'd have no concerns about. Although I'm not aware of any 790s with gearbox failure, I wouldn't build one without a Nova box. There's been too many failures with stock top ends and the 790 must add to the gearbox stresses, and at times, I can be a long way from home in remote places, albeit still in Oz.

    $s? No idea if its worth it, only you can answer that. And a very expensive DR is still cheap in absolute terms. I reckon HE650RS has cost about $15kOz which still doesn't get a KTM690 off the showroom floor here, then it still needs setting up. I do like the look of an AJP PR7, and have test ridden them too, and my wife might now be keen on a RE Himalayan....

    My 790 is a keeper though, its been an enjoyable ride to get me here, almost 9 years, 117 pages and > 400k views.

    How about, "If it floats your boat...."

    So a rambling answer that probably doesn't help....

    :beer
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  2. JagLite

    JagLite Long timer Supporter

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    I think your rambling answer is the best answer. :thumb
    There is not a "yes or no" answer, only different ways to look at "is it worth it".
    Which is what you said. :ricky
  3. Dalmatino

    Dalmatino Been here awhile

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    Exactly what JagLite said!!

    This build is more for street use, so yea, leaning more towards the fun bike aspect.
    In my mind I figure, what's really the point in doing the big bore and cam if the valves aren't big enough to process it. Although I can see doing just the 790 kit simply for that extra displacement/torque.
    Got some thinking to do lol.

    BergDonk, got to say big thanks for all your input on here! You along with some others provide a wealth of information here that make life a lot easier for many! :beer
    Hivernaut, BergDonk, JagLite and 2 others like this.
  4. joenuclear

    joenuclear Still here....

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    Thanks BD!
  5. Eddieb

    Eddieb Long timer

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    I've run 25000 km on a high Comp piston and love it. No issues so far, touch wood.
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  6. BergDonk

    BergDonk Old Enough to Know Better

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    I did some more back to back riding on HE650RS and HI790S. I've also only ridden one other 790 to date and that was the @procycle bike with the other WRB box at LaSal. I don't recall the specs, but I think, TBC, that Jeff said it had stock valves with a port clean up, and a cam. Mine has a stock cam, but big valves. His bike is also lighter than mine, stock tank etc. Hard to be definitive this far apart, but the PC 790 felt to have a bit more snap off the bottom than mine, but didn't rev out as far.

    Comparing my two, bearing in mind my 790 is geared a bit lower than the 650 in top by <> one tooth on the back, the 790 is happy in 5th at 75 kph whereas the 650 wants to be closer to 90 kph. The 790 also easily pulls away from the 650 over 90-100 kph in 5th, or 4th. It revs harder, and is smoother too, less buzzy. They both have solid mounted footpegs and tapered bars and the same Protaper grips.
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  7. Eddieb

    Eddieb Long timer

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    Interesting. My 650 with Hi Comp and fcr is comfortable down around 70.
  8. BergDonk

    BergDonk Old Enough to Know Better

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    Final drive gearing?
  9. Eddieb

    Eddieb Long timer

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    15/41
    airbox has a 10cm square hole with tl1000 32mm exit exhaust for great bottom end and mid range.
    Some home done exhaust port work.
    BergDonk likes this.
  10. BergDonk

    BergDonk Old Enough to Know Better

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    So geared about the same in 5th overall, interesting. My impression was much the same when my bike was new and almost stock as it is now, so maybe our feeling of happy is different?
  11. Eddieb

    Eddieb Long timer

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    Mine is 'will hold the speed smoothly on a flat road without juddering and will accelerate from that speed without doing it also'.

    I had a 40mm outlet gsxr600 pipe on the bike originally but going down to the 32mm tl1000 pipe made a big difference down low. Obviously breathing better than stock but not overpiped.

    If you believe in dynos it clocked 41hp and change at the rear wheel.
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  12. Dalmatino

    Dalmatino Been here awhile

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    Thanks for this...great info!
    In process of placing another large order with PC (cam included), but I cant get the motor apart for cores (away with work and than real cold weather) so the big bore and head must wait till than. This will be at least May. Man It really sucks having all these goodies and having to wait so long!
    Winters in Canada suck and they're getting worse :(
    JRowland and JagLite like this.
  13. BergDonk

    BergDonk Old Enough to Know Better

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  14. Dalmatino

    Dalmatino Been here awhile

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  15. Bugga Me

    Bugga Me n00b

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    Looking at the adaptor now. Just wondering if you may have any pictures of what you machined.

    Thinking of adding a small radius but also making it eccentric to better match the position of the throat.....am I making sense?
  16. BergDonk

    BergDonk Old Enough to Know Better

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    [​IMG]

    This is my first FCR39 with MXRob sleave. Lower right is a bellmouth insert I machined up that made the low speed running impossible, so I removed it. Lower right in the above pic.





    [​IMG]

    Latterly I use a straight taper that enables access to the MAJ and PAJ, machined in Delrin and is an interference fit onto the carb. Works OK, and much easier to sort than the bellmouth.





    [​IMG]

    My adaptor also has a lip on it to seat the airbox boot.




    [​IMG]

    I also machine the head side of the carb so its the same as the BST, one groove at the correct diameter instead of two at a larger diameter.
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  17. Bugga Me

    Bugga Me n00b

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    That's really interesting.

    Cant quite see in the picture. In your last delrin adaptor, did you machine the taper in the centre of the delrin rod or match the bore of the adaptor to the offset throat of the FCR?
  18. BergDonk

    BergDonk Old Enough to Know Better

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    4 jaw chuck etc. As mentioned, the venturi was a fail, stuffing up low speed running, but looked good, the straight tapered one is fine, not offset to allow easy access to the jets.
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  19. Bugga Me

    Bugga Me n00b

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    Yep got it. You saved me putting a bellmouth/radius on the adaptor....!!

    Thinking about it a bit more it sorta makes sense. The airflow from the airbox is already reasonable directional and uniform (as opposed to when you would usually use a bellmouth/trumpet - in an open volume of air which has no particular flow/direction). The already uni directional airflow caused by the airbox would see 'right angle face' of the bellmouth adaptor as a flow restriction. The adaptor with a taper however is effectively/simply an extension of the carby throat - hence perhaps why a taper works better in this instance.

    Still curious about the possible effect of the bottom 'lip' with the two jets tho.

    Anyway you saved me some work/effort. cheers
    BergDonk likes this.
  20. DR Steve

    DR Steve Been here awhile

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    Yes, you are making sense and that's the way I made mine.
    I'll have a look and see if I can find a picture - lost a hard drive recently that had most of my DR stuff on it.

    If you look at most FCR equipped bikes rubber intake horn they have an eccentric bell mouth with two access holes for the MAJ and PAJ.

    edit. Found a pic. FCR39 on the left and FCR40 on the right.
    DSCN2473 (1024x768).jpg
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