A bit more oomph.

MacMcMacmac

MacMcMacmac

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Thinking of adding some Uni-filters to let the old girl breathe better. I am hoping to get a bit more top end, as my bike only pulls 140km/h (80mph) in top. This is most likely due to the rather large gearing change on the back sprocket where I went from the stock useless 36 tooth to a 31 tooth. I suppose I could rev out in 4th, but that does not seem optimal. I wouldn't mind livening up the whole powerband actually, as the power output is really the only thing I would want to change on this bike besides the horrid front end.

I don't mind chucking some jets at it to get it to run right. Anybody have a baseline to work with? I have Commando "style" pipes on it, probably Emgos. They have XS650 actually stamped into them. I'm not sure if they are considered free-breathing pipes or not. I know the proper route to power is porting and boring, but I am starting off slow, and I have learned the mistake of taking up most of the riding season with wrenching, so I am not really interested in going whole-hog right now, just planning some mild and well thought out upgrades. Are EX500 carbs worth the effort? What are the benefits? Help me before I slap on a set of RS36's like I did to my Bandit!

As an aside, I was thinking Sportster springs might help my front end. The new Progressives sure didn't.
 
You probably should have re-jetted a little already. Many claim the BS34s perform better on a totally stock bike if you up the mains a size. You've changed the exhaust already so I'd say for sure you want to bump the mains. As far as exact number sizes, I can't say because you're in Canada and may have Canadian spec BS34s. Besides the adjustable needles, they may be jetted slightly differently than the U.S. models were. But, I can make a recommendation on the number of sizes to go up. If you install the UNIs too, I would bump the mains 2 above what you've got now, and the pilots one.

Yes, I think your high gearing is a big factor in your limited top speed. These are only about 50HP bikes and that's not enough power to pull to redline in 5th if you gear too high. I'd change that sprocket again, to a 32 or 33 if you have a 16" rear wheel, a 33 if you have an 18" wheel. Now, you may not think one tooth difference in sprocket size would matter much but it really does on this bike.

I have no issues with my front end, in fact I think it works quite well. I have the MikesXS springs, have done the Minton Mods, and use about one ounce more oil. The springs help a little but the major benefits came from the Minton Mods and the extra oil.
 
5twins said:
Many claim the BS34s perform better on a totally stock bike if you up the mains a size.
Click to expand...
I did that simple change on mine out of curiosity and the supposed leanness they have stock. I can't tell much difference, in fact if anything the stock mains might have felt more powerful. But the plugs with stock mains were scary light colored before and now they're more normal.
 
Xjwmx, sorry to chip in, but were the scary light colored plugs with or without the stock air boxes on the BS34s?

Thank you.
 
Everything is stock on it, even the plugs are still over the pilot screws. Stock airbox and I think the filter elements are stock as well; I give them a good washing every couple of years. I really noticed the light color after a rebuild. I think traces of oil had been darkening them.
 
Thank you Xjwmx. I am on all stock with the SH but have not yet established whether or not my plugs are correct color because I rebored the bike and only have approx. 1000 miles on them. May still be burning a tiny bit of oil on one side. Will post the pictures of the plugs at some stage.
 
Oil burning in a new rebuild or in general seems to be highly dependent, maybe singularly dependent, on the pressure of the rings against the wall. That varies a lot with rings and seems to be a very important thing that isn't spec'd anywhere for the bike or on the rings (as far as I know). So I did some intensive reading about it on 2M's suggestion. Bottom line, use tight rings.

And now back to our regularly scheduled topic...
 
Both my 80SG Oceania model and Canadian 83SK have the Adjustable 51X11 needle and 132.5 Main Jet and 130 Small Main air jet. These are not a MikesXS Canadian needle kit, these are Factory or at least set up before Mikes XS was selling the Canadian Needle Kits.

Factory BS34 Carb with Factory Adjustable needle and non caped Pilot screw, (air mixture screw), Factory size's/settings..............
4E3-3W6-3U6 TEXT.jpg
 
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I'm showing that going from a 36T to a 31T makes your new 4th almost the same ratio as your old 5th. Consider your new 5th as an overdrive...
 
Well I also think your bike is too highly geared, the motor is not making enough power at the RPM it is doing at 140kph. Experiment try using 4th or third and see what if it will pull a higher speed.
If you decide to gear down a 16 tooth sprocket is available from Worldsend motorcycles and this opens up a whole new range of ratio options.
 
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