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Buell Forum » THUMPer Forum » Buell Blast Thumper Knowledge Vault » Engine - all topics related to the Motor » Engine - Carburetion & Intake » Rejetting question... » Archive through March 04, 2006 « Previous Next »

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Manomako
Posted on Wednesday, March 01, 2006 - 06:08 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

hey all,
new bueller here, been doing alot of reading on your threads and was wondering...what the heck is rejetting?
what are the jets? and what kind of maintenance should i do on them?
thanks in advance!
dave in maine
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Marijane0569
Posted on Wednesday, March 01, 2006 - 10:12 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Jets are in the carb.
Fuel flows through them on its way to the engine.

The larger the jet the more fuel flows to your engine. The smaller the jet the less fuel.

Rejetting is when you remove one size jet and install another size for performance, milage, etc... reasons
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Naustin
Posted on Wednesday, March 01, 2006 - 10:17 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

the jets are small components inside the carburetor that control how much fuel gets sucked into the air stream. There are two of them, one for slow speeds, and one for high speeds. They work together along with several other parts of the carburetor to keep the air/fuel mix at the proper ratio across the rpm band. Since there is no computer control, the carburetor must achieve all this mechanically and carburetors are really pretty amazing when you think about the job they are performing. This means that they can be pretty delicate too, and you don't wanna mess with it if you don't know what you're doing. That said - the blast has a very simple, basic carburetor and anybody should be able to work on it if they have even the most basic understanding.


If you change how much air your engine can move by installing a less restrictive intake, exhaust, or do some head work, you'll need to change the jets or adjust the other parts of the carburetor to compensate.

Basically, when you "re-jet" you are fine tuning the carburetor for your specific set-up, altitude, temperature, etcetera.

The bike is fairly lean from the factory, so many people will "re-jet" as soon as they install a different exhaust to keep the bike running correctly.
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Jackbequick
Posted on Wednesday, March 01, 2006 - 04:35 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Dave,

Check out this link:

http://www.bcrider.com/blast1.html

Looks pretty simple to me. You can probably get the jet at Central Maine H-D or maybe even John's over in Hancock.

I did a similar jet change (slow speed jet only) to my M2 and it made a miraculous difference in low speed smoothness and the lower speed ridability. If it is like the M2, the slow speed jet will help even if you don't change the high speed jet too. And if the plug looks okay now (tan to light brown color) your high speed jet should be okay.

Jack (in Ellsworth)
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Ezblast
Posted on Wednesday, March 01, 2006 - 05:08 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

LOL - see the Carb section for jetting recomendations.
GT - JBOTDS! EZ
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Manomako
Posted on Wednesday, March 01, 2006 - 05:11 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

thanks everyone, mystery solved!
jack, great site. what did you change your slow speed jet to? what number jet?
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Ezblast
Posted on Wednesday, March 01, 2006 - 05:16 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Stock - 44 or 45 - with 44 prefered primary - no change to the 170 main.,
Exhaust change - 45/175 except for Kerker and Pro-series which should be 45/170.
GT - JBOTDS! EZ
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Jackbequick
Posted on Wednesday, March 01, 2006 - 08:54 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I went with the #48 which is a commonly used size for the M2. I think everyone who ever used that #48 slow speed jet on a CV-40 carb on a tuber had nothing but nice things to say about it.

The high speed was a #200 if I remember right and I left it alone as the plugs look fine. The plugs continued to look fine after I changed to an AFT (Sportster/spam can style) air cleaner.

Jack
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Ezblast
Posted on Wednesday, March 01, 2006 - 10:19 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Yes, however, we are talking singles here - lol
GT - JBOTDS! EZ
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Gearheaderiko
Posted on Wednesday, March 01, 2006 - 11:12 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Yeah, you'll drown a Blast with those jet sizes!
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Jackbequick
Posted on Thursday, March 02, 2006 - 08:37 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Ezblat & Gearheadriko - You guys might be wrong about the jets being too much for the Blast.

Think it through, you have one 500cc cylinder sucking on a carb that looks to be about the size of a CV-40 (I'm guessing, I don't know for sure). The M2 has two 600cc cylinders taking turns sucking on a CV-40.

I've never worked on a Blast but that link I posted above recommends a #45 and #170 combo. A good combo for an M2 is #45 or #48 and #200 or so on the high speed. Sounds to me like the carburation setups are very similar as far as fuel flow needs.

Jack

(Message edited by jackbequick on March 02, 2006)
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Gearheaderiko
Posted on Thursday, March 02, 2006 - 09:40 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I'm confused.
If the link you posted recommends a #45 & #170 for a Blast why would you say a #48 & # 200 is also good for a Blast? Or did you mean that 48/200 combo was only good for an M2?

My Softail runs a #48 & #195.(1450cc)
The Blast, which has been dyno'd twice,
is now running a 45/155 combo.

Similar as far as fuel needs, means they can both use the same carb. 100cc extra, different head, piston and cams will also change things.With the extra cylinder it also changes the exhaust scavange effect along with pulses to the carb.
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Blake
Posted on Thursday, March 02, 2006 - 09:42 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

What Jack said.
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Ezblast
Posted on Thursday, March 02, 2006 - 11:44 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

180 too rich, been there - dynoed that - Blake research the topic - you will see what I'm saying - overlap of a twins fuel system needs means more air enters the system, meaning more fuel for the same effect, why a single is more fuel efficient than a twin.
GT - JBOTDS! EZ
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Jprovo
Posted on Friday, March 03, 2006 - 12:15 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

They might be wrong, but they might be right. Both Erik and EZ have had A/F checked on their bikes, and they both know Blasts. Erik's bike pulls nice and hard with the 155, I know I've ridden it on the racetrack for the last four months, but it's nowhere near stock. On my bike I run a 45/175 and it's a little rich on the Plug read with the Pro-Series pipe and air filter.

Just a thought, A stock Blast has a 42/170 or a 42/165 jetting (depending on the year), what did the M2 come with stock? A 42/195??
Both have CV40's
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Light_keeper
Posted on Friday, March 03, 2006 - 09:30 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Dave
Mine is at 45 and 170. If you are going to do it your self there is tons of info on this board about it. mine was done after the first season with it. I replaced the fibre gaskets at the top end cleaned the air passages a bit, added the pro exaust, redid the carb and added the Buell sparkplug. It is a much different bike now. I have a friend in Union who just got theirs last summer and is making the same changes this winter.
Sandy
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Jackbequick
Posted on Friday, March 03, 2006 - 03:46 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

My 2000 M2 had a 42 and 200. It now has a 48 and 200 with the low speed mixture screw set a 2.5 turns. The change from a 42 to a 48 and using the adjusting screw (it had been blocked as stock) made a wonderful difference.

I didn't mean any harsh criticism of anyone, and was speaking in generalities on carburation. And I did not mean to say that 48/200 was good on a Blast. But it might work.

I did not agree with the statement that those jets were grossly oversized for a Blast. The jet numbers are fairly linear, a 170 is a little smaller than a 200, a 210 is a smaller amount larger.

You start somewhere and go up or down. As a guy who has fouled a lot of plugs (too rich) and melted hole in one piston (too lean, and that was not on a Buell), I would much rather have my first attempt be too rich.

Jack
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Ezblast
Posted on Friday, March 03, 2006 - 04:52 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Have done both as well on a Blast - that is why I recommend the jetting I posted, and that is why I'm the Thumper Moderator - lol - twins have overlap - that is why they need more fuel, a great example of this - the Ninja 250 gets only 1 mpg better than the 500cc Blast - See recent Cycleworld for comformation - lol
GT - JBOTDS! EZ

(Message edited by ezblast on March 03, 2006)
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Jprovo
Posted on Friday, March 03, 2006 - 07:21 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Jack, I agree with you on your tuning methods and your accounts...

Keep in mind though, that although jet sizes are fairly linear (in the range we're talking about, they're 5-6% larger per step)

A 175 jet is 6% bigger than stock (170)
A 200 jet is 38% bigger than stock

I don't think that the average street Blast with an air filter and pipe is going to like a 200 jet, but I've been wrong before. Frankly, I'm suprised that Erik's bike runs as well as it does with a 155, but the Dyno and seat time tell us that's what that particular motor combo likes.

Us Blastards just get a little defensive sometimes...

James
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Jprovo
Posted on Friday, March 03, 2006 - 07:38 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

EZ,
I think that the Ninja's poorer fuel consumption has more to do with what RPM it's turning. A Blast is going to cruise pretty pleasantly at around 3500 RPM at 55 MPH, an 250 Ninja is probably turning 7500 in fourth beacuse it can't pull 5th (but I'm guessing)

500cc * 3500 rpm / 2 revs per cycle =
14.6 liters of Air/Fuel mix a second

250cc * 7500 rpm / 2 revs per cycle =
15.6 liters of Air/Fuel mix a second

James
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Ezblast
Posted on Friday, March 03, 2006 - 07:48 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Still that wouldn't explain why a twin needs more gas/larger jets - last I read it had to do with intake overlap making for more air going in, thus more fuel. Please correct me if I'm wrong.
Anyway - I know the dyno doesn't lie and 180 drowns a Blast.
GT - JBOTDS! EZ
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Jackbequick
Posted on Friday, March 03, 2006 - 10:55 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I'm sorry I mentioned the M2 and #200 jet now. I was not recommending it for or trying to say was a good idea for the Blast. I certainly defer to you guys that are working on them and know them.

But I'll bet I know how you can get a #200 jet to work on a Blast. You just have to leave the air cleaner and the muffler off. :>;)

I'm hoping to get together with Dave once the riding season returns since we're almost neighbors. I've never seen a Blast up close and am curious about them. Big four stroke singles have always had an allure for me.

Jack
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Ezblast
Posted on Saturday, March 04, 2006 - 12:37 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Thats cool having Dave for a neighbor! Enjoy! I came close to stepping up to those jettings, but I was running a hot non resist 6R12 with an extra high po coil ignition set up - and I was at 14.5 to 13.5 on the AF - in fact Blake sugested I go higher to 48/180, however, the boot ripped, causing an extra lean condition and 'melt down' - lol - in the middle of a 1200 round trip - lol - so (on the cheap I could have gone new stock cyl and hi comp piston) I went with the 515cc kit and hi po extras for the new needed head and some head work - low - now especially with the Dial A Jet secondary - I had really quick response - but am jetting at 45/150 with a max of 13.5 AF - good enough for the changes here in Coastal altitude - lol - the new piston is now designed for the head and higher comp - so less gas than the off the shelf sporster is used - lol -
GT - JBOTDS! EZ
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Manomako
Posted on Saturday, March 04, 2006 - 01:18 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Boy did i start a great discussion or what? and such a simple question....haha
ok, here's another one, when i give it gas there is a 1 second delay before i feel the power, like a hesitation...could it be the jets? what do you think?
thanks again guys!
dave
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Jprovo
Posted on Saturday, March 04, 2006 - 10:17 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Manomako,
The Blast carb isn't as snappy off the trhottle as a carb with an accelerator pump, but you can get some better response if you adjust your low speed mixture screw to 2 to 2 1/2 turns out from a light bottom. There should be some good links in the carb section.

http://www.badweatherbikers.com/buell/messages/20164/6812.html?1137733442

James
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Jackbequick
Posted on Saturday, March 04, 2006 - 01:25 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Do the Blasts have to have a cap over the low speed screw that has to be drilled out and removed so you can adjust the screw like the CV-40's on the tubers?

If so, then I'm guessing that if Dave goes to the larger slow speed jet and plays with the mixture screw, it will improve the roll on from idle. It might create the same miracle a lot of found when we did that on the tubers.

Dave - I'm right off of Bayside (SR-230) about 3-1/2 miles east of Ellsworth. Give me a call at 664-0782 if you're out and about and going to be in the area.

My Duece is down in the basement now, up on a Centerstand and with the wheels off. The wheels are going in Monday for a set of new Metzler Z6's. A little bit more on clean up and detailing and I'm ready for the spring roll out.

Jack
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Jprovo
Posted on Saturday, March 04, 2006 - 01:51 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Jack,
Yup, the Balst has the same cap over the low speed screw...
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Ezblast
Posted on Saturday, March 04, 2006 - 05:24 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Just got back from a little loop of a 100 miles from 35 to 85 to 1 back to the beginning of 35 to home - sweet and I beat the rain to boot! Us Cali folk ride all year except for the occasional rainy day - our bikes never look as good as most of the rest of the other bikes in other states - too busy riding - lol
GT - JBOTDS! EZ
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Ezblast
Posted on Saturday, March 04, 2006 - 05:37 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Note: This dialog will be moved over to the Carb section soon enough - so you'll know where to look - if you don't find it here - lol
GT - JBOTDS! EZ
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Manomako
Posted on Saturday, March 04, 2006 - 08:50 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

awesome, thanks guys.
so where exactly is this low speed mixture screw?
jack, my info is on the riders' assistance network as well...getting my permit on monday so i'm sure i'll be out and about all next week, gotta try out the cold weather gear. i ordeded up some of those inexpensive grip warmers, if i can i'll install them next week too. good small project for the boy and me. what time to you get off work during the week in case i'm in the area?
thanks again guys, good stuff.
dave
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