DR750 & DR800 owners thread

Discussion in 'Thumpers' started by MCmad, Jul 14, 2008.

  1. robmoto

    robmoto Long timer

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    RAY maybe for that extra little bit of air and still using the snorkle , you can drill some holes in the remaing part of the triangle bit all these little things add up in the end , and allso did you file or grind the head so it lines up perfectly with the inlet manafolds .
    The bike I am doing now these were 1.5mm or about 1/16th out of allignment, but only on one side.
  2. Ladder106

    Ladder106 It's a short cut, really

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    Intake boots and cylinder head castings lined up very well on this bike.

    I always check for this.

    It wasn't up to a professionally "ported" head standard but pretty close with no large gaps or lips for the gasses to trip over.

    I also check the welds between the head pipe and the attachment ring that mates to the head as I've found that some bikes have a significant restriction at this point.

    Have a few chores this morning, then will give my "Unequal DR" a run back to the shop for the correct bits.

    One this I did notice while riding yesterday was a very slight sideways slip int he rear tire when accelerating away from a corner apex. Twice to the left and once to the right.

    I think this means that the 800 engine is pulling just a bit stronger than the 750 since the 750 engine never spun the rear wheel like that unless is was a conscious effort to do so and usually only on gravel or dirt.
  3. Ladder106

    Ladder106 It's a short cut, really

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    Jetting update.

    Well..another day....another test ride.

    The two different jets (1-120 and 1-127.5) ran OK but no real improvement in top end.

    I've done a bit of research and discovered a few points. These things are likely obvious to the more experienced Big owners but a bit of interest to me still so I'll share.

    Reading the service manual I discovered that the main jets for the SR41 were 120. When the SR42 (800 cc engine) was put in using the same frame and airbox as the SR41 the standard main jets used were 117.5.....so actually leaner.

    This certainly supports Robs statement that when I put the 800 into the 750 frame (using the smaller airbox) that the bike would need smaller mains.

    The other fact I discovered while searching the DR650 sites regarding the GSXR 1000 silencer was that the STANDARD main jets on the DR650 should be made SMALLER (leaner) if the GSXR silencer was used on the 650 with no other mods to the airbox or carbs. This supports what Bluesman has been saying all along that you have to have a large volume silencer for this bike. What complicates things for me here in the western US is that I MUST have a spark arrestor on the bike to ride anywhere off-road. The GSXR pipe supports the spark arrestor nicely so I'd really like to keep using it.

    So now I have an engine that wants smaller mains and a silencer that wants smaller mains.

    I have 125s in now and am thinking about going right back to standard jetting for a SR42...that being 117.5. I think I have those jets in the box.

    I'll play with it tomorrow and see what happens.

    So, even with you lot beating me over the head with information, it's still taken me over 3 years of Big ownership to learn stuff. :dhorse
  4. KilgoreTrout

    KilgoreTrout adventure flyfisher

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    Another day another test ride Ray... it must be nice! When I went to work this morning it was -38C with wind chill:eek1 However they are forecasting +7C by Saturday....heres hoping The question I am posing is whether the side panels from the 89 750s and 90 800s are interchangeable and are the colors the same ( Marble Dynamic Blue ) Figured if any knows the answer it would be here. Thanks in advance for any help with the puzzle. Cheers BA
  5. robmoto

    robmoto Long timer

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    Pigs ass they need a big silencer, they just need a big hole at the end .:ear.
  6. robmoto

    robmoto Long timer

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    The shape is the same . but as for the colour I have only seen red 89 ones down under from memory.
  7. mait

    mait Been here awhile

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    Now that was funny, made me spill my coffee :rofl
    I have the same silencer from GSXR1000 as Ray and I am pleased with the sound, too. No idea how it performs, due to snow I did not do any field testing before I tore the engine apart. The gas flow is definately easier compared to stock muffler. If the hole is big enough will be seen in the spring.

    Ray, I am watching your jetting progress with interest because I will have the same way to go when the pistons arrive.
  8. Ladder106

    Ladder106 It's a short cut, really

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    Rob,

    Hole at the end of the can is 37mm (with spark arrestor installed)

    It's 45 mm with spark arrestor removed.

    I took the spark arrestor out and did one test ride with essentially no change in performance other than just a bit more noise.
  9. Ladder106

    Ladder106 It's a short cut, really

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    KT,

    I posted a reply in drbig.info.

    Bob answered your question there. The short answer is the 800 came in blue but a different shade and color name.

    eBay perhaps??
  10. KilgoreTrout

    KilgoreTrout adventure flyfisher

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    Thanks Ray, I saw it and figured as much I will go with white and keep an eye out for a spare:wink:
  11. robmoto

    robmoto Long timer

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    Ray 37mm is good size should be fine, I was thinking it may have been smaller like the GPR ones 25mm
  12. Rik Le Ray

    Rik Le Ray VAT FREE FISHING

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    ok guys i have a set of Marboro decals for sale 1 only the same as the pic please email me sales@tackledirect2u.co.uk if your interested £125.00

    [​IMG]
  13. Ladder106

    Ladder106 It's a short cut, really

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    When I first started riding my "transplant" bike (1993 SR43 engine in the 1989 SR41 frame) I noticed that it felt like the gearing was different.

    Noticably taller.

    Since I also changed the rear tire for a brand new knobbie I put this off at being the result of the tire change.

    Yesterday I was able to put in a much longer 80 mile ride and spent some time on the motorway for the first time. Here I really noticed that the gearing had changed. I was at 4550 rpm and 70 mph. Before the transplant 70 mph had been just under 5000 rpm.

    Why the difference?? And also (and more importantly) maybe this was the real reason the bike would not pull to redline in top gear. :hmmmmm

    So I took a careful look at the service manual.

    Final Drive ratios:

    The manual lists 15/48 as the final ratios for the SR41 and also for the SR42.

    The SR43 gets a 15/47 final. So when the 800cc engine gets the larger air boxin the SR43, it gets more effecient. The main jet size goes from 117.5 to 130 and the final gearing gets a bit taller.

    When I first got my bike it had a 47 on the rear. I've kept that and didn't think that much about it.

    The final drive ratio I am using is: 15/47. (3.3333) and this is about a 4 % increase in ratio (which is just about equal to 1 tooth at the rear sprocket...smart men those Suzuki guys) from the 15/48 that I SHOULD be using per the service manual....so I'm already a 4% overgeared.

    Took a look at all the internal transmission ratios......no change across the board for any model DR750 or 800.

    Why the big change in the way the bike felt? :huh

    I kept looking through the manual and found......AHA !

    When the bike got built into the SR43 (with the larger airbox) the PRIMARY DRIVE also changed. :deal

    The primary went from a 62/32 (1.937:1) on the SR41 and SR42

    To a 61/33 (1.848:1) on the SR43

    This is about a 4.5% increase

    This gives me a total increase of about 10% in final drive rations.

    You are all saying .....

    "THAT'S WHY THE BIKE WON'T PULL TOP REVS IN 5TH GEAR...DUMMY !" :bash

    Yes, I've been quite insensitive and while I'd like to think that I'm a rider much more attuned to his bike, I have to use the excuse that the bike was out of service for the better part of 6 weeks during which time I've spent a lot of time getting retired from my job, wading through retirement system paperwork and getting muddy on my DRZ400 to relax. The transition back to the "big bikes" is always a bit of a change to my riding.

    And I mistakenly wrote the difference off to the engine transplant (for some magical reason) and the new tire (except that the tire would have to be GIANT to account for this much gearing change)

    At least THAT mystery is cleared up.


    Now for the latest jetting (cause I know Mait at least is watching this)

    First thing yesterday I installed a Laser Pro-Duro silencer (that I got when I bought the SR43) It's the one that states : "Not for road use". A test ride with that silencer made no difference (other than more noise) than the performance with the GSXR silencer. This data using only top speed figures and my butt-dyno.

    So at least I know that the GSXR silence was not being overly restrictive (or maybe that the Laser is just equally as restrictive).

    Then.....reasoning that Suzuki used 117.5 mains in the standard SR42 AND that my internet searching showed the GSXR silencer actually needing smaller mains when used on the DR650 bikes.....
    ..... I went back to the standard recommended jetting for the SR42 (800cc engine in the 750 frame with smaller airbox) which is:

    Using 117.5 mains. and the rest of the standard jetting listed in the manual for the SR42.

    There was actually improvement with this:

    The bike will now pull quickly to just above 6200 rpm in top which is the best I've done so far. (The richer mains kept the revs at about 5500 and would slowly climb to about 5800 from there.) There is no lean surging and no detonation (atleast none that I can hear at that speed or when running through the lower gears at large throttle openings)


    My goal is not to have the bike go as fast as it can, rather I was using top speed as an indication of correct jetting with the engine transplant and the addition of the GSXR silencer.

    What have I learned.......

    (a) If I want the bike to have a bit more power (like the standard SR43) I have to improve flow into and through the SR41 airbox.

    (b) When adding the GSXR silencer you PROBABLY do not have to change jetting. I'm adding the word PROBABLY here because I do not have any scientific evidence that the bike is running as well as it can right now.

    Essentially, it's taken me a week to discover everything the Suzuki engineers found in about an hour while updating this machine.

    I plan to still do a bit better. I've been talking with "Motolab" here. He has a dyno and all the super scientific gadgets necessary to evaluate fueling and is about 80 miles away from me.

    So the next step is a trip to him for the final assessment.



    For now......I'm going to leave the bike alone (to the relief of my wife) and just ride it.

    I rather like the tall gearing. 1st is still low enough for most off-road stuff that I get this big bike into. The bike runs easily with the taller gears at road and motorway speeds (4000-5000 rpm which it where it seems like it likes to run anyway). I do not need a bike that will go over 100mph for any reason.

    It remains to be seen if mileage will improve over the 42-45 (mpg) I was getting with the 750 engine. I've rather burned though a half tank of fuel doing testing so I'll assess mileage figures later.

    Apologies for this being so long but there is some information in it that was a revelation at least to me and I hope others find this helpful.

    Thanks to Rob and everyone who has offered suggestions and advice. Now it's time to start work on stripping the SR41 engine....lots to do
  14. Bambi

    Bambi Been here awhile

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    Hello guys,
    may I ask you to step a bit closer and would you please line up? Cause I'm going to tell you a little secret: It's Lars' (evildent resi) birthday! Ok, in Germany the day's nearly over now. So would you please join the international chorus of Big-riders around the world:
    For he's a jolly good fellow, for he's a jolly good fellow, for he's a jolly good fellooooooow - which nobody can deny!
    Which nobody can deny, which nobody ...
    Thanks, guys, and a big applause for your (nearly :rofl) nice singing :clap:clap! And I can surely tell you, that he is a jolly good fellow, trust me.
    So kind regards and congratulations to him and Mela, his beautiful lady, hopefully from all around the world, lead by Iris (my beautiful lady) and me, Bambi
  15. mark618

    mark618 n00b

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    Hello to all interesting forum. I have recently become the proud owner of a 1988 DR 750. Bit of a project so I don't have to endure appaling TV. The bike has a tank form a 450 I think anyway it is split and looks far too small. Need to replace it but not easy to find in the UK. Is there an aftermarket tank that will fit, such as the acerbis on NAVE's lovely looking bike. Any help gratefully received.
  16. Ladder106

    Ladder106 It's a short cut, really

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    HAPPY BIRTHDAY LARS !!!

    :happay:happay:happay
  17. Puddle

    Puddle Been here awhile

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    Happy Birthday Lars...and if we missed it, celebrate it again!
  18. Resi

    Resi Been here awhile

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    *blush*

    Many thanks guys!

    Cheers,
    Lars
  19. mait

    mait Been here awhile

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    From me, too!
  20. robmoto

    robmoto Long timer

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    HAPPY BIRTHDAY Lars,
    Bambi can we stop singing now my throat hurts, :lol3.

    Ray good to see that you have now come to some sort of a conclusion .
    I will post some air box mods I have done in the last 6 months when time permits, I am busy doing the blue 750 at the moment and need a couple of weekends to finish it.