DR650 790 Big Bore Installation and Review

Thank you. I haven't seen any installation guides and I'm sure meany people want to get this kit but aren't sure what it is going to take to do. I love my DR, and I'm sure its going to be in the garage for a very long time.

I didn't replace the cam, so I don't know if it has to bed in at all. Check out one of the above posts about the timing. Like you said to me, it was not difficult at all . I'm going to do a modified motoman break-in. basically the same thing, but not as rough. I did a lot of down shifting to put pressure on the rings. During the first few times doing it, i felt a strange shake, not sure what that was, but it went away after a few minutes. Could be the clutch, could be the engine about to explode .

Thanks for the tip, I'll keep this in mind should I do this again. A friend of mine is thinking about getting a DR over the summer and converting it.

EDIT: This is my 650th post... time to get that count up to 790!

Great write-up!!!! Thank you very much! Now I'm wishing my own bank account had the funds in it RIGHT NOW to order a kit. :)

A few questions... given 29k miles on your bike, did you replace the head bolts? I'm guessing you did NOT replace the timing chain? I have 25k on mine and figure I'll have closer to 30k before I open it up for my 790 kit, and had been planning on replacing those parts as a precaution. I wonder how necessary it is. I know on car motors, it's considered standard practice to replace the head bolts whenever you remove them.

'Course I'm also (tentatively) planning to pull my motor and split the case and check out the transmission, replace all the bearings, and consider the billet 3rd gear if I can spare another $500. I'll have to wait and see how yours holds up. :)

Anyway, great job, and we sure do appreciate the write-up and photos!

Rob

nice! congrats!

but, i don't understand why the rpms would not be exactly the same if you didn't change gearing. if you were at 4700rpms at 74mph before, changing the engine displacement alone shouldn't affect that... you should still be at 4700rpms at 74mph...

doug s.

If my third gear goes, I'll eventually get another motor when the time comes and replace this. Ill move the kit over to that engine should it not be destroyed . I don't think I'll have a problem though. (Fingers crossed). I didn't even think to replace the head bolts or timing chain. They looked alright, but maybe I should have...

Even though the gearing is the same, the bigger engine works less to obtain that speed. At least that's my theory

Yeah, sorry 'bout that. Sometimes my reading comprehension ain't too good. I was thinking about doing the big bore and the stage 2 cam, but I think I'll just do like you and do the 790 kit first, and then maybe sometime this summer swap out the cam.

Couple questions: Why did you change the placement of the carb needle. I know you mentioned your carb was set pretty lean; did you guess at that change or did PC recommend a different setting. I've got jetted stock carb and open airbox, and my bike runs great. I'm just trying to anticipate if I should plan on making some jetting changes ahead of time?

Are you running a stock or over-size header? From the pix it looks like a stocker.

The only thing different I plan to do on my build up is to do a base-line dyno run of what I have now, and then another dyno run after to see the difference each modifications makes. There is a dealership with a dyno 7 miles from my house. They also use an exhaust gas analyser, so I can see if I need to make some carb/jetting changes as well.

Thanks again, you pushed me over the edge on this one....

No way I'm going that far into the motor and NOT doing the cam.

My first big bore will be the 351 kit on my KLX250S... hoping to do that in another month or two. BUT, sadly, there are no cams for it yet, so all I can do is the big bore. There IS a big-valve option which I will do, though.. it's $400 extra. They're supposed to be working on cams for it (it takes two) but nothing out yet.

Rob

Man this is an exciting build, I don't even own a dr650 haha (klx250sf) I love the idea of big bores on bikes, its so simple and easy power!!! I come from working on big block trucks and such, you want a bigger bore? tear down and send to machine shop, what a pain...this is so simple I love it!!!

Congrats on a great project and way to wrap it up with the 650 count

that's my problem. and then no way i wanna do it w/o doing the head. so then you're looking at $2300 plus having to install it. and do yo really wanna do the cam w/o replacing the lifters?

doug s.

Lifters? Good point, will add those to the parts list if I can't come up with the money for the head. I'm hoping I can, but I dunno. It'll depend greatly if I'm able to pick up the extra work over the next few months that I'm hoping like heck I can. It'll make all the difference between doing it the way I want versus doing it on a tight budget.

Rob

does the new head include new lifters?

doug s.

Dunno... for what they're charging it sure as hell better. :)

Rob

Any idea of how much power the $1200 ported head with big valves would give vs. the stock head? Assuming you went the full-boogie with the 790 kit, stage 2 cam and so on...?

If it's only 5-8hp...? That's a lot of dough for little gain. I don't know how much hp it would end of giving over the stock head, but it had better be a bunch otherwise that's some expensive HP.....

From talking to Jeff (ProCycle), and from what I remember, the big valve head is worth at most 2-3 hp. Definitely NOT a bang for the buck item.. BUT, the DR650 motor, even in stock form, has really small valves compared to other 650s, so it's definitely a worthwhile mod. I seem to recall the dyno result of the 790, cam and head being in the 53-55 hp range.

Rob

Thanks for the write up! That makes this 650 seem like a exciting road biased dual sport! I'm wondering if it rides at all similar to the DR800? I used to ride one of those a bunch as a mechanic I used for my KTM LC4 had it as a loaner bike when he worked on the KTM.... which was all the time!
I preferred the DR800 on the road - much smoother!

Sorry to hear all that stuff on your 1st post re: the trails being closed! To be honest I'd rather have a crappy bike and amazing places to ride than the reverse...

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That's also my plan for the cam, probably next winter. I'll probably do the stage 2 as well. I just want to ride and this snow is killin me!!!!!!! We just got another inch last night. <o></o>
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As for the carb: When I did the Hayabusa muffler I had to change my set up to accommodate it. My first ride at 50mph+ I couldn't go full throttle without a major bog. I went with one step up on both the main jet and the pilot jet. I left the needle in the 2<SUP>nd</SUP> notch down. Went riding, and it worked well, all around better acceleration and nice sound. I felt good till I got to the pump. 42 mpg. This was a 6 mpg drop. Could be the colder weather, winter gas, or riding harder, never-the-less, I never see mileage that low. So I did some research and read that If I raise the clip a notch, I can get better mileage. I also changed the pilot jet back to the stock setup from procycle. I did that but I noticed on some rides I would have a surging at 30-40 mph. I also adjusted the fuel screw on the lean side, and starting was pretty hard. (one of the reasons it wouldn't start right away) <o></o>
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When I got this kit all together and started it, I let it idle for a while at a higher rpm, and I noticed my header was glowing red. I read that this was a symptom of being too lean. So I put the clip back to its original position and left the jets alone. I adjusted the fuel screw as well to 2 turns out. Now is seems fine, and only time and some riding will tell if it's okay... and that brings us back to the original problem.. this snow needs to melt!!!!!!!<o></o>
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I'm really interested to see the mileage I get with this kit now…

Forgot to mention: I have the stock header. I would like to find a dyno now and see what I'm running, but I never got a base line.

What's a stock 650 DR have for HP?

About 36hp

Did you notice any increase in engine vibration with the 790 kit installed?