|
SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Mikuni BS40 vs BS40SS Carbs /cgi-bin/YaBB.pl?num=1496430849 Message started by Andy RN on 06/02/17 at 12:14:09 |
|
Title: Mikuni BS40 vs BS40SS Carbs Post by Andy RN on 06/02/17 at 12:14:09 When looking up our carb, I found this: https://www.oldjapanesebikes.com/mraxl_GT_Resource/manuals/suzigtcarb/index.php So the BS40 carb was used in the Suzuki GT750, and it looks similar to our carb, but it definitely has differences. It's hard to keep all this straight as a beginner :-? |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by Dave on 06/02/17 at 12:20:51 The GT750 was a 3 cylinder motorcycle with a 2 stroke engine. It has no need for a TEV valve, and the jetting requirements are far different than the Savage. You could go crazy trying to sort though the different variations of Mikuni carbs, as they are also used on snowmobiles....and I suppose could be used on any engine. |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by IslandRoad on 06/02/17 at 13:38:16 I spoke with the guy who supplies jets for the Mikuni carb here in Australia. He gave me an unsolicited opinion: " The best thing you could do to get the most out of the Mikuni carb is pull it out of the bike and tie it to your fishing line, halfway between the hook and the rod! ... now which jets do you want?" |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by Andy RN on 06/02/17 at 13:54:30 Sentimental moment: This forum is an endless source of wisdom. Much appreciation. Thanks guys :) |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by Dave on 06/02/17 at 14:19:05 774D525F505A6C515F5A3E0 wrote:
I am not sure I would agree with that - Mikuni carbs have been the standard replacement for lesser carbs and winning races for how many years?.....I can remember that the Mikuni carb was the choice back in the late 60's as replacement for the Bing and Amal carbs - and they still are. There may be more modern carbs that are as good and maybe even better....and big four stroke bikes do like accelerator pumps - but they are not as popular and likely don't have as many people who can get you parts. |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by batman on 06/02/17 at 15:56:31 I believe Dave is right our stock carb works fine on the bike ,with a bit of work it can become better, changing jets ,the white spacer mod ,are both good examples of what can be done, I've also gone to a tuned intake 18 " long ( that you can't see as it's inside the stock air box), and drilled my vacuum ports in the carb slightly oversize( which kills most of the throttle lag normally seen in CV carbs) .That combined with a Dyna muffler ,puts me at an estimated 34-35 hp , Speeds in the 60-72 and 80 -92 range in 5th gear, gains can be found elsewhere (lower gears) due to increased EV of 4% and 7% ,that are dependent only on rpm. With an internally stock motor,a top speed a few ticks past 90,with a minimal investment of time and money the bike runs as strong as I could hope for.At rpm ranges outside of 3822 to 4686and5096 to 5860rpms , the motor runs as normal ,running at 55 or3503rpm ,I'm getting 48 mpg that's been my norm for years. |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by IslandRoad on 06/02/17 at 17:22:49 Yeah, I didn't take his advice 8-) I don't know enough about carbs yet to have an opinion ;) |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by Andy RN on 06/02/17 at 23:37:54 I contacted the guy who posted the old suzuki carb guide link I listed above. I was asking him about the differences between the BS40 and BS40SS. He seemed like a knowledgeable guy, so I'm posting his email response to me, including some pics he sent. ... begin message ... Hi Andy, No idea what the nomenclature means. They have VM for round slide, BS for CV carbs with round slides. They added SS on the end of some BS carbs and on some VM carbs too. Some BS(T) carbs have flat slides just to confuse the issue. The 40 refers to the carb throat diameter and in the case of GT carbs it is the outlet diameter. Carbs on a GT750 have a ramp in the throat which is probably there to increase gas speed through there so that the slides will lift. 4 strokes have stronger suction than a two stroke so the 2 stroke needs ways to speed up air flow especially at low speeds. early 4 stroke BS series carbs tend to have a more open throat and use "bleed" type emulsion tubes/needle jets compared to the Primary type in a 2 stroke. In Bleed type, air is mixed with fuel to create an emulsion ie smaller droplets to burn better. Remember that liquid fuel does not burn. Odd but true. It is the vapor on the surface of each bubble or drop od fuel that burns and here's the trick. For the same volume of fuel, smaller droplets have greater surface area and therefore burn faster and more completely. That's also why modern fuel injectors have more (smaller) outlet nozzles to better break up teh fuel into smaller droplets. So back to your bike and 4 stroke BS carbs. A version of those have been used on most 4 strokes from Suzuki for years including GSXRs and most other street bikes. GSXRs use a flat or semi flat slide for better throttle response. Most earlier carbs use a round slide with rubber diaphragm similar to a GT750. That way the slides rise as gas velocity increases and that makes for a much smoother road bike. Almost the same idea as modern fly-by-wire but without the computer control. The slide rises in relation to engine load, so it adjusts to the engine needs. Attached is a cross section of an XS650 carb and you can see the difference in the throat under the slide. That same basic design is used on many Suzuki and Yamaha twins from that era. Yours has a few differences. The choke (enricher) is the same idea but is cross mounted rather than vertical and it appears to have an accelerator pump on it. Do a quick google search for Suzuki Savage carburettor and you will find a lot of useful leads. I'd also recommend getting a Factory Service Manual. It looks like there are some downloads and maybe one on ebay too. Cheers http://i.imgur.com/I0ePZze.jpg http://i.imgur.com/cMyMYYZ.jpg http://i.imgur.com/bRyLBSG.gif |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by batman on 06/04/17 at 09:14:54 What he's calling an accelerator pump ,is our TEV valve, which only opens when the throttle is closing ,to add fuel after the butterfly valve to keep the motor from stalling,and control after firing /poping something we need due to having a thumper.which is why changing to a different carb is harder ,with out a TEV you have to close the throttle slower or not completely to calm after firing. |
|
Title: Re: Mikuni BS40 vs BS40SS Carbs Post by hotrod on 06/04/17 at 10:02:53 Would like to help, but have problems of my own, like trying a 36mm Dellorto . |
|
SuzukiSavage.com » Powered by YaBB 2.2! YaBB © 2000-2007. All Rights Reserved. |