Ahhh life...

Questions regarding the DR750

Re: Ahhh life...

Postby H_Lime » Tue Aug 13, 2019 12:06 am

Being planning to further interfere with her in the shape of an extended carb fiddle so thought Id plant that here.
But first off Nug, bummer the cdi shit the bed. Bet tracking that down as a causation was one of those sherlock holmes scenarios "when all other possibilities are eliminated..." craic yea?
Major saviour in the shape of the Bobcat carrying a spare. A two minute fix! :D how many pints ya buy him that night :clap:

Back in April i bought a set of bst36 that "OR" on here had dissected and mounted on a dr carb brackets. The idea being the + 3mmm or roughly 19% extra volume once jetted correctly = well more in some regard. O.R. has done this for a fair few Dutch riders and the consensus seems positive. With my hit and miss carburation i said in for a penny.

Tried them but the idle settings were off for my bike. OR had best guessed the my jetting but she was choking. Left them there and swopped some bits with another set of stock BST33's I also bought from him and I've been there since.

With a date with my dyno dude tomo and a day off work booked i took a gamble on at least one removal of the carbs (i suspect there may be many lol) and swapped the idle jets from 37.5 to 45 and main jet from 135 to 127.5. Fairly standard and maybe a good starting place. I'm a complete amateur in regard jetting but am a willing student shall we say:)
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So armed with my bag of spares and three sets of carbs I'm hopeful he's an understanding sort lol
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Anyway, the plan is a ride home on a mostly "finished" bike tomo evening all going well. Lol, as if.

Our Dave22 wisely recommended rigging an aux fuel bottle so tank ripping and install drams be limited so that will be done, and I've rejigged the toolkit with all the necessary bits (i hope) ya regularly reach for when ripping carbs out. This same fellas good. With my moriwaki system he eeked 145 horse from her. Doesn't say much but knows much!

Here was the last run, which saw the engine develop its knock on the ride home:( Hopefully no re runs of that drama.

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Of any bike Ive ever owned a wot run as above will say the least in terms of rideability and enjoyment than with this machine, outright power is not what she's about but a fat crisp delivery just on the right side of rich will make Harry a happy boy.
Will report back :tup:
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Re: Ahhh life...

Postby BigBob » Tue Aug 13, 2019 8:54 am

But first off Nug, bummer the cdi shit the bed. Bet tracking that down as a causation was one of those sherlock holmes scenarios "when all other possibilities are eliminated.

In the normal course of events you would be absolutely correct, but as I always carry a spare CDI as well as spare cables etc, on the grounds that if I have them I won`t need them, it was the first thing we tried. Happy days when she sprang into life immediately :tup:
I don`t drink so it was a cheap fix for Nathan and he still has the CDI as a spare.
We`ve had to help each other a few times when we have had problems on trips, that`s what mate`s are for.
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Re: Ahhh life...

Postby nug » Tue Aug 13, 2019 10:03 pm

Yes Bob, I remember a few events in our past trips......Hunt the brake pad was a fun game! Not sure my eyes would be good enough now to spot that tiny pad miles up the road :clap:

Much tinkering going on Colum. I hope the Dyno tune yields some positive results for you. Rideability is everything as you mentioned mate. Plenty of thump should be released with the right tune :tup:
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Re: Ahhh life...

Postby dave#22 » Tue Aug 13, 2019 10:41 pm

Well...how did it go, the suspense is killing me. :tup: or :tdown:
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Re: Ahhh life...

Postby H_Lime » Wed Aug 14, 2019 7:35 am

Yawn :yawn: god mornin:)
Got in last night at nine o'clock. Wrrrrecked lol. Was too wrecked to post lol.
We did not have time to rejet 36's from the ground up so I will revisit them later in the year, but we had fun with the stock 33's.
Tbh if i were to post a WOT dyno chart for the days work to compare against the one above it would tell you very little, outright hp is the same but there's a very big improvement, more power on part throttle everywhere is the biggest thing, cleaner pick up from a closed throttle and the bike is way more rideable.
I'll bang up a better description of the in's and outs later as I'm out the gap to earn my salt in the coal mine :P
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Re: Ahhh life...

Postby H_Lime » Wed Aug 14, 2019 10:41 pm

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He drilled the header and installed a rivnut just before the link to get an accurate afr reading. Smart! Screw in a small domed allen with copper washer when done.

Despite the needles having been dropped a notch 350 miles ago by yours truly she was rich everywhere. On wot up top there was a puff of black even :wtf:

Out with carbs and with space limited i made do :D

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Stock jets 120 were swopped

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Net results was an improvement but we reckoned on smaller again. He tried swopping the jet with carbs in situ but engine bars and a hot engine made it impossible so out with them again. While in changed the needle with some minor or visible wear.

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115 is what gave her the best results

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On the dyno on wot she shows a bit rich pre 4k but its acceptable. Deffo want to be on the rich side of the 12.9afr.
Again like I said earlier and Nug mentions what wot doesnt show is part throttle improvements. On these bikes thats where you use most. Bike is far livelier on the throttle and feels more snappy. Coming home from the dyno in the mixed weather i felt i had better control of her in and out of bends. Clears off lovely with a great pick up.

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With the baffle out she made more hp and torque low down but under load was more prone to stutter due to a lack of back pressure. I guess there is a limitation of the cans design here. I'd like those gains but not at the expense of the noise and loss of rideability. Down the line that cans for the shelf. Bobs words about devil cans ring in my mind... whats the internal structure like ya know Bob?

Can anyone elaborate on what makes a can good for us? Obviously that goldilocks setting of improved flow over standard but some labyrinthine structure to give enough backpressure that she needs to scavenge efficiently.
Mulling over a twin exhaust system or a custom made exhaust. Our Mabuse has a very interesting custom made gazelle (iirc) system and cans on his bike and I'd lay a bet the are in the goldilocks area as are fruity but not barking so improved flow but with back pressure.
Something to be fussing over during winter as shes as ready for road now as shes ever been and cannot wait to get out again on the weekend. Despite being tired and having ridden nearly 250k in the wet on shitty slimy backroads I had a ball, especially on the way home. I do not have nor ever owned another bike that could do that;)
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Re: Ahhh life...

Postby BigBob » Thu Aug 15, 2019 8:08 am

Some interesting comments there.
I don`t think we can ever set up these old girls perfectly due to the fact they are a firkin big single so gas flow will always be compromised.
Best exhaust I ever had in terms of performance was the original set up which felt crisp and responsive throughout the rev range.
Shame it weighed so much, was pig ugly and rusted as you watched.
I`m not so sure that changing your exhaust will make any difference as I seemed to have tried them all and there doesn`t seem a lot in it apart from noise, the only exception being a Predator which had a very narrow downpipe which strangled the motor.
Best bhp I`ve seen on a road bike was 45bhp on a 750 and 48 on an 800, so you are a bit on the low side but not much to gain.
I`ve found all Bigs run on the rich side even when new and always thought they should run 117.5 rather than 120.
One of my 750s runs standard jetting and a Marving exhaust and runs really sweet and clean and gives 55mpg despite doing a zillion miles
Another 750 with a Devil was only doing 35mpg and the plugs were black and sooty and ran really fluffy till I dropped the main jets to 115 and the needle one notch.
Now it runs fine and 50mpg though it rattles a bit as the motor has clocked up over 120k miles.
My SR43 is standard jetting and a Devil exhaust and runs sweet as with 68k and gives 48mpg.
Trying to make sense of the carburation on these bikes seems to be a black art and very hit and miss indeed and I feel you will be chasing your tail for ever on this one in pursuit of perfection when it`s almost unattainable. I think these old girls are a bit too agricultural to be fine tuned to our liking.
As for your comments on riding in the wet. The Big is the best bike I`ve ever had for wet roads and no amount of flooding or wet mud bothers me any more, I always feel safe.
Reminds me of the time I went out with a friend on his Busa through lots of twisty lanes and B roads and I had to stop every few miles so he could catch up!
btw Mark Lawes who lives just up the road from me raced in the British single cylinder championship for years on a Tigcraft framed DR800 and was getting 96bhp at the back wheel
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Re: Ahhh life...

Postby nug » Thu Aug 15, 2019 5:27 pm

Sounds like a good result then :tup:
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Re: Ahhh life...

Postby H_Lime » Thu Aug 15, 2019 10:05 pm

BigBob wrote: Some interesting comments there.
I don`t think we can ever set up these old girls perfectly due to the fact they are a firkin big single so gas flow will always be compromised.
Best exhaust I ever had in terms of performance was the original set up which felt crisp and responsive throughout the rev range.
Shame it weighed so much, was pig ugly and rusted as you watched.
I`m not so sure that changing your exhaust will make any difference as I seemed to have tried them all and there doesn`t seem a lot in it apart from noise, the only exception being a Predator which had a very narrow downpipe which strangled the motor.
Best bhp I`ve seen on a road bike was 45bhp on a 750 and 48 on an 800, so you are a bit on the low side but not much to gain.
I`ve found all Bigs run on the rich side even when new and always thought they should run 117.5 rather than 120.
One of my 750s runs standard jetting and a Marving exhaust and runs really sweet and clean and gives 55mpg despite doing a zillion miles
Another 750 with a Devil was only doing 35mpg and the plugs were black and sooty and ran really fluffy till I dropped the main jets to 115 and the needle one notch.
Now it runs fine and 50mpg though it rattles a bit as the motor has clocked up over 120k miles.
My SR43 is standard jetting and a Devil exhaust and runs sweet as with 68k and gives 48mpg.
Trying to make sense of the carburation on these bikes seems to be a black art and very hit and miss indeed and I feel you will be chasing your tail for ever on this one in pursuit of perfection when it`s almost unattainable. I think these old girls are a bit too agricultural to be fine tuned to our liking.
As for your comments on riding in the wet. The Big is the best bike I`ve ever had for wet roads and no amount of flooding or wet mud bothers me any more, I always feel safe.
Reminds me of the time I went out with a friend on his Busa through lots of twisty lanes and B roads and I had to stop every few miles so he could catch up!
btw Mark Lawes who lives just up the road from me raced in the British single cylinder championship for years on a Tigcraft framed DR800 and was getting 96bhp at the back wheel


You know me Bob/Nug I'm not happy unless I'm unhappy:lol: Think I will investigate a custom made can this winter.
How in the name of god he got 98horse from it is beyond me :shock:
Had another spin there and yeah, it's really nice, still pops a little on decel but i should be able to sort that as theres a small leak at the link/header join. Biggest improvement is the responsiveness and the way it happily shoots up the revs. Am chuffed.

Time to own up to owner stupidity...dyno man John O'Grady noticed as i was getting ready to drive off that i had overadjusted the lever on the rear drum. He was looking sideways at it as i throwing on the jacket and in literally one second i realised why be was staring at it. Had done it a week ago at a petrol stop as lever travel was annoying me.
With the bike on the centre stand we adjusted it and lo and behold a far free'r wheeling wheel in ten seconds. With the dyno all locked up and the man paid i knew there wasnt another run to be done but it explained why she wasnt pulling past the 40 hp mark she did last time on his dyno, despite now no longer being excessively rich as she was then!!

Question for ye lads...
Anyone know if the stock oem suzuki filter is freer fowing than the wee moto equivalent?
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Re: Ahhh life...

Postby dave#22 » Fri Aug 16, 2019 5:20 pm

Hi Colum, glad to hear the DR's running well, you didn't mention if the 45 idle jets were an improvement.
My carb settings....
DR 750 (SR41), +0.10 oversize piston, 43 camshaft, foam air filter on std filter frame inside std airbox, no snorkel with domed stainless mesh, short aluminium Devil silencer.
Idle LH 50...main jet 130.
RH 40...main jet 125.
DR 800 (SR43) 750 engine +0.05 oversize piston, 43 camshaft, airbox as above. Twin aftermarket silencers (opened up), middle collector replaced with stainless Y piece, larger dia exhaust pipe.
idle LH 45...main jet 115.
RH 45...main jet 120.
DR 750 lightweight, twin K&N filters on plenum tubes. Laser Produro silencer with mesh baffle removed.
idle LH 50...main 140.
idle RH 40...main 130.
Never dyno tested, just tuned by the seat of the pants. :lol:
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