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 Post subject: Re: BST magic
PostPosted: Tue Jul 24, 2012 10:04 am 
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Adventure Rider
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Joined: Wed Apr 11, 2012 10:29 am
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Location: N39° 9' 0.4" W107° 4' 58.4" (WGS84)
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I was just browsing Nc Ricks website . Good stuff Rick . Love the photo gallery . Saw a familiar photo of Yellow Jacket at Balsam Lake in NC . That old 5 time national drag bike champion is tougher than tough . It's good to hear he is back riding . Last I saw he was requestiong a rider chaperone to ride to Ohio with him . What an amazing story of tragedy and recovery .

Here's Nc Rick's site if you guys are interested http://www.motocd.com/cd/

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 Post subject: Re: BST magic
PostPosted: Tue Jul 24, 2012 11:36 am 
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Adventure Rider
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Location: N39° 9' 0.4" W107° 4' 58.4" (WGS84)
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Sorry Rick .I just gotta do this . And I'm not one real big on revelling in another man's misery ............. BUT ! ! !

:rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:

:old:



nc rick wrote:
When I was a kid... I was tuning a vm mikuni for my hopped up two smoke and came to the conclusion that clipping just a bit off the bottom of the needle would give me the full throttle boost in fuel I wanted. It did. The bike ran great. One afternoon our local cop was back to prevent me from riding in that spot so as I exited stage left, a nice wheelie seemed to best express my feelings of the whole situation. The needle did not follow the same path into the jet because of the more acute angle of the bike and wedged open the throttle causing a bit more of a show than I had intended. After landing on my back, I also learned that two stroke motors don't really need a spark when running at about 20,000 rpm and that a furiously spinning bike making its own donuts won't respond to the kill switch. When you remove the spark plug wire ( hoping to save the motor from what seems like a faulty kill switch) I found that the 20,000 rpm motor is very efficient at developing suprisingly (shocking actually) high levels of voltage. Anyhow, the cop let me go partly because he felt sorry for me I think.

Another thing I learned over the years is that modified needles will not last as long as a factory anodized job, particularly in a bike that vibrates more. The this anodizing adds a good bit of wear resistance to the aluminum part.

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Our adventure begins where the rest of the world finds themselves lost !
Trip reports are created in the mind, committed in the heart and
finalized by sharing . Let's see some trip reports .

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 Post subject: Re: BST magic
PostPosted: Fri Oct 05, 2012 12:57 am 
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Adventure Rider
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Posts: 580
Location: brisbane, australia
Some have asked for an update. Others are looking for information. Since my last posting I have video of my slide movement with the air box off and the bike reving slowly and then quickly. What I noticed was a significant misting of fuel during a fast roll of throttle with a drilled slide compared to an undrilled slide. This led me to compare it with an accelerator pump from the FCR. Interesting!

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"Sold" 2011 DR650 GSXR #24, drilled slide, cut spring, modified stock needle, with cut air box, air assist forks, lowered pegs, stock tank,15-41. Still love working on them!


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 Post subject: Re: BST magic
PostPosted: Sat Oct 06, 2012 7:01 pm 
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Adventure Rider
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Location: brisbane, australia
Pumper carb vs. the BST.

Pumper carb controls the air supply with just the slide. Fuel supply controlled with flow by needle unless the throttle is whacked then accelerator pump squirts in extra. Result is finely controlled by multiple circuits. Especially on acceleration. Fairly easy to tune with great results.

BST carb controls the air with the butterfly valve attached to the throttle cable. Fuel is supplied by flow around the needle and needle height is adjusted by a diaphragm with pressure differential on the top supplied by a hole or holes in the bottom of the slide. The quicker the butterfly is opened, the greater the vacuum above slide to raise it allowing extra fuel.

I think this is all right so far, of course dis-regarding the pilot circuits that I will get roasted for.

So when the pumper carb is accelerated hard, fuel is sucked and sprayed in in large quantities to satisfy a temporary lean condition to stop a stumble. The slide is controlling the needle height.

So when the BST is accelerated hard, fuel is only supplied by slide height allowing x amount of fuel by. So why not get the slide up as quickly as possible and this can be done by drilling an extra hole or drilling the existing hole bigger. Seems to me that higher vacuum, quicker, is a good idea. In practice this has worked great for me. I am now at two 1/8th.(slightly bigger than 3mm.) holes in the slide and will keep drilling until I get a rich stumble. The BST would have to supply a lot of extra fuel to equal a pumper carb in my opinion. Because the slide moves independent to the butterfly throttle setting who cares where the slide is as long as it can supply enough fuel.
Steady throttle fuel supply is controlled in each carb by the jets and needle position so both need to be close.
The DR is not a fast revving 450 and I feel the BST set up properly can supply adequate fuel at the right time for all dirt riders. Street riders can use all the acceleration and power they can get.

Has anyone drilled a slide too far to see just how much is too much??
People will question whether surging will become a serious issue. My bike has never surged at steady throttle, I feel because my air box has not been fully opened and I keep the secondary filter well away from the air box opening.

I am now running a KTM needle shaved to be similar to the DJ and a 155 main.
Comments??

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"Sold" 2011 DR650 GSXR #24, drilled slide, cut spring, modified stock needle, with cut air box, air assist forks, lowered pegs, stock tank,15-41. Still love working on them!


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 Post subject: Re: BST magic
PostPosted: Sat Oct 06, 2012 11:43 pm 
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Adventure Rider
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Joined: Sun Aug 14, 2011 6:44 am
Posts: 511
Location: Melbourne, Australia
Auscanvet wrote:
Pumper carb vs. the BST.

Pumper carb controls the air supply with just the slide. Fuel supply controlled with flow by needle unless the throttle is whacked then accelerator pump squirts in extra. Result is finely controlled by multiple circuits. Especially on acceleration. Fairly easy to tune with great results.

BST carb controls the air with the butterfly valve attached to the throttle cable. Fuel is supplied by flow around the needle and needle height is adjusted by a diaphragm with pressure differential on the top supplied by a hole or holes in the bottom of the slide. The quicker the butterfly is opened, the greater the vacuum above slide to raise it allowing extra fuel.

I think this is all right so far, of course dis-regarding the pilot circuits that I will get roasted for.

So when the pumper carb is accelerated hard, fuel is sucked and sprayed in in large quantities to satisfy a temporary lean condition to stop a stumble. The slide is controlling the needle height.

So when the BST is accelerated hard, fuel is only supplied by slide height allowing x amount of fuel by. So why not get the slide up as quickly as possible and this can be done by drilling an extra hole or drilling the existing hole bigger. Seems to me that higher vacuum, quicker, is a good idea. In practice this has worked great for me. I am now at two 1/8th.(slightly bigger than 3mm.) holes in the slide and will keep drilling until I get a rich stumble. The BST would have to supply a lot of extra fuel to equal a pumper carb in my opinion. Because the slide moves independent to the butterfly throttle setting who cares where the slide is as long as it can supply enough fuel.
Steady throttle fuel supply is controlled in each carb by the jets and needle position so both need to be close.
The DR is not a fast revving 450 and I feel the BST set up properly can supply adequate fuel at the right time for all dirt riders. Street riders can use all the acceleration and power they can get.

Has anyone drilled a slide too far to see just how much is too much??
People will question whether surging will become a serious issue. My bike has never surged at steady throttle, I feel because my air box has not been fully opened and I keep the secondary filter well away from the air box opening.

I am now running a KTM needle shaved to be similar to the DJ and a 155 main.
Comments??



I have to admire your perseverance, and I think you have a point about the slow revving nature of the DR motor, and it's resulting fuel requirements.

FWIW if you have an FCR setup properly, you can remove the pump rod all together - totally disableing the acc pump, and it will run just fine. It will be very difficult to induce a lean cough while road riding, more of an issue offroad when you want to loft the front over something. It's the best way to tune a pumper, so the acc pump doesnt cloud the results of the other circuits.

The fact that your not fully opening the airbox means you will never equal the performace of an opened airbox - pumper or otherwise.
The real benefit that I like from having an FCR is the ability to gear up. While I still had a tweaked BST I was running a 14t sprocket - flicked that for a 15t as soon as the FCR was tuned properly, and am fitting a 16t shortly.

I have a fellow rider with a dyno-jetted BST, with the full airbox cut out, and it performs fine with no surging at all. I could easily be happy with a well sorted BST, but I like to mess with things !

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 Post subject: Re: BST magic
PostPosted: Sun Oct 07, 2012 12:28 am 
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Adventure Rider
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Location: Eastern Ontario,east of Belleville,Canada
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I'm impressed by your relentless research and obvious knowledge . As convincing as your results appear to be I still don't believe that a "fine-tuned" BST would equal a "well-set-up" PUMPER . --- Not that it would matter to me but a "performance-freak" would be more satisfied with a PUMPER . --- What small difference there would be , it would be to the PUMPERS advantage . --- IMHO ---

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 Post subject: Re: BST magic
PostPosted: Wed Jan 16, 2013 6:01 pm 
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Adventure Rider
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Joined: Sat Jan 07, 2012 4:59 pm
Posts: 580
Location: brisbane, australia
Results update for my modified BST carb. Still running great, getting 23km/l, about 52mpg (USA). No issues with surging or any other bad habits. Thank you to the three Aussie's that just bought mid-pipes for their GSXR cans. In many others and my opinion the GSXR conversion should be "Step 1" on the list of performance mods. "Step two" (always just my opinion) is the free mods to the air box, slide, plastic spacer and needle. This will release about 90% of the stock DR's potential. "Step 3" another 5% with bigger main jet and ground header pipe, again very cheap mods.

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"Sold" 2011 DR650 GSXR #24, drilled slide, cut spring, modified stock needle, with cut air box, air assist forks, lowered pegs, stock tank,15-41. Still love working on them!


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 Post subject: Re: BST magic
PostPosted: Thu Jan 17, 2013 5:54 am 
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SuperMoto Dude
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Joined: Fri Jun 29, 2012 6:50 pm
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Location: Sydney in OZ
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What you have watch is that the slide doesn't start lifting too high or too quickley that it intrudes into another jet systems operation like the needle jet or pilot jet, all these as well as the slide are controlled by vacuum(as you know) but work & stop at different vacuum values so that one transitions into another so we get a smooth power response(well thats the theory), when we drill holes & cut springs the working vacuum value for the slide starts to drop down towards the working vacuum of the jet systems lower than it, this then allows the carb to get fuel/air from two systems at the wrong time richening up the mixture from two jet systems at the same time instead of the usual flow from one to the next with the required overlap inbetween them.
Just be careful you don't run over rich, big single's & v-twins handle richer mixtures better than multi's, but the excess fuel washes the cylinders down & creates a lotta carbon build up & wear. good luck with it! :bumps:


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 Post subject: Re: BST magic
PostPosted: Thu Jan 17, 2013 9:54 am 
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I clipped my spring and drilled the slide, all was going very well so I clipped another coil and stared getting stalls with a quick blip of the throttle and if I was riding very rough trails with a few little jumps within a few seconds. So I put a couple of washers above the spring and fixed the problem.


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 Post subject: Re: BST magic
PostPosted: Thu Jan 17, 2013 11:51 am 
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Adventure Rider
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Joined: Sat Jan 07, 2012 4:59 pm
Posts: 580
Location: brisbane, australia
Guipago, what you described would possibly occur more likely with a slide controlled carb where the slide is forced to maintain a high position relative to rpm (high gear low rpm, hard acceleration) allowing too much fuel in over a longer time, especially with an accelerator pump! With a vacuum slide carb the slide may initially allow more fuel than necessary (sound familiar?) but would return to the proper height relative to rpm much quicker. My bike is getting 20% better fuel mileage (18.2 stock, now 22-23 klm/l) so I feel there is likely a much less chance of fuel washing. What you described would result in a very poor running bike, certainly not mine.

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"Sold" 2011 DR650 GSXR #24, drilled slide, cut spring, modified stock needle, with cut air box, air assist forks, lowered pegs, stock tank,15-41. Still love working on them!


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