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Discussion Starter #1
Anybody here have any experience with HD sportsters? I would like to know how much top speed to expect from a bone stock 883 sportster.

Mine seems to top out at around 80. Pulls well to there then just doesn't have anymore. Heck, my CB360 can do 80mph in 6th.

Thanks,
Jack
 

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Carb size on the bone stock 883's is pretty restrictive....probably just can't breath enough to go much faster than that.
JohnnyB
 

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quote:probably just can't breath enough to go much faster than that
Johnny,
If you up the size of the carb by 2mm what do you do with the jetting? If the head is bored to 22mm and you put a 24mm what effect does it have on runability?


JS
 

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Champ....doesn't sound like you are talking about an 883, sounds more like a Monza Junior.

Depending on the condition of the ports...ie smoothed, stock, shaped etc. It's quite possible a 22mm port will flow more than a 24mm carb. I'd start around one jet size larger.

Now if you put a 24mm Delorta SS carb on there....it's going to reduce your low rpm power some, but help up top. I wouldn't think 2mm would make a substantial change in ridability...since most OEM carbs are so undersized anyway. For comparison a Honda CB100 circa 1972 used a 22mm carb, and would probably handle a 24mm with no change in ridability, 26mm and you'd start to see some hesistation in off idle throttle response.
In general I'd think going 2mm larger on a Junior would make it MORE ridable.
I would suggest matching port size to carb size if possible...don't think the Ducs use an insulator so it might take a little dremel work. You just don't want that step down into the port to be abrupt...try to get a few mm of taper in there so it doesn't disturb flow too much.

Typical of bikes of that era, the carbs are undersized and the main effect of this undersize is ease of use for a beginner and lack of top speed. Go a few mm larger and sometimes the top end really comes alive with an almost imperceptible change in off idle response to an experienced rider. In other words...it would go faster...but would be just a tad easier to stall for someone with ham fisted clutch habits.
JohnnyB

PS. Might require some fiddling with the idle circuit, small displacement bikes use so very little fuel at idle that a carb change can make substantial adjustment necessary. Remember...it's not using that larger carb until it gets up in the rev range, so you want to try to duplicate the idle conditions of the stock carb. Not unusual for the bike to have to idle a bit higher.



Edited by - jbranson on Aug 27 2007 10:31:30 PM
 

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Thanks, good info. It's for my Motobis and from what you are saying it seems to be right as I upped my 125 to a 24mm and went 4 sizes on the main and it likes it up top!!

JS
 

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Sorry about the thread hijack...but have you posted a collection of pics of that Motobi yet? It is one of the little four strokes right? I don't know shit about them, but I know they make a freakin beautiful lump of metal for an engine. Is it one of the horizontal engines or vertical?
The attention to detail they gave those little engines is really impressive....probably the closer to an MV in quality than most any other vintage bike I've seen.
Not to dis Duc's because they are cool too...but it always seemed to me that a Duc is to a Motobi what a Japanese bike is to a Duc....if you see what I mean.
JohnnyB
 

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I like the Ducati much better. It does everything better than the Motobi. Power and handling being the most important factor. The Motobi def. has STYLE points but it is nothing but an in expensive for the masses road motor bike. Very simple compared to the Ducati, heck I can even work on them with not to much "HUH" effort. The 125 was built by the late Lance Weil and he installed an "S" cam. It REALLY goes well. I should have no problem keeping up with the 160/175's in the Giro.


JS
 

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quote:I should have no problem keeping up with the 160/175's in the Giro.
we'll see.

d.
 

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Since it's only an inexpensive bike for the masses....I'll trade you my Hodaka for it:)
Very pretty bike....buy yeah, could use a Duc type tube frame.
JohnnyB
 

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there's something about those motors that to me say forward motion russian rockets . . .
 

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nice bike champ....one of these days i gotta see your collection. did you ever get the brake switch?

tex

p.s.- fyi....i washed all the old italian grunge out of those cases!
 
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