Shorty Mufflers and Uni Filters Rejetting??

Samuraiace

Samuraiace

Workin from the shed
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I just swapped over to Shorty mufflers and Uni filters, I'm trying to see what jet sizes are working for people. I'm not really looking to buy alot of jets just to keep swapping them out and trying others. So if someone's running the same setup I'm curious what jets worked. Thanks
 
Usually one up on the pilots and two up on the mains will get you close. But no two bikes are the same.
My shorty muffs will have different flow than yours. My engine may have higher or lower compression than yours. I may live at a higher altitude than you. My fuel may be blended differently.
All these as well as many others effect jetting. The only way to know for sure is to let the bike tell you what it needs. Test it the way it is, make one change, test, make a change, test. The only way to get it right for your bike.
Leo
 
XSLeo said:
Usually one up on the pilots and two up on the mains will get you close. But no two bikes are the same.
My shorty muffs will have different flow than yours. My engine may have higher or lower compression than yours. I may live at a higher altitude than you. My fuel may be blended differently.
All these as well as many others effect jetting. The only way to know for sure is to let the bike tell you what it needs. Test it the way it is, make one change, test, make a change, test. The only way to get it right for your bike.
Leo
Click to expand...

That's what I did and its perfect for my bike:bike:. I'm not worried about the dino tester,, Just want to run rich enough not to burn anything up.
 
XSLeo said:
Usually one up on the pilots and two up on the mains will get you close. But no two bikes are the same.
My shorty muffs will have different flow than yours. My engine may have higher or lower compression than yours. I may live at a higher altitude than you. My fuel may be blended differently.
All these as well as many others effect jetting. The only way to know for sure is to let the bike tell you what it needs. Test it the way it is, make one change, test, make a change, test. The only way to get it right for your bike.
Leo
Click to expand...

I understand what you mean about the differences between bikes.
Makes sence there would be more back and forth testing I was just hoping to get in the ballpark of where I should be.
Right now I'm running one up on both my pilots and mains, I'll try two up on my mains and see where that puts me with a bit of finagling.
Thanks
 
What head pipe stock or 1 1/2 . A 135 main jet should be close. I ran 1 1/2" with mikes short cones stock air box 135 main. The plugs were tan a little rich. I'm doing some jetting on mine from the cones to the commando muffler. I have to start over the jetting not even close you wouldn't think it would change that much. I have the adjustable XS John needles. I have to find the 135 and give them a try. A good starting point. With the stock needles my 750CC motor ran good there was a little lean condition a bigger pilot jet might have cured with the 135 main.
 
I have the stock headers. Right now she doesn't run very well, stumble and inconsistent idle. If I put it into gear it will die out, and if I leave it idling it will die out. The mixture screws are to stock setting.
 
The mix screws on the BS34s were set by the factory to meet E.P.A. specs, not for best running. You shouldn't be running them at the stock settings, especially if you've done mods. Also, any time you change pilots, the mix screw settings need to be checked and usually re-set. Set them to 3 turns out from (gently) closed and fine tune from there. The BS34s usually run best with the mix screws somewhere between 3 to 3.5 turns out. The mix screws control your idle mixture so setting them correctly should cure many of the problems you're having.

As far as main jet size goes, with your mods I think you're going to need at least 2 sizes up (137.5), maybe even three (140). One size probably won't be enough. Only actual testing will tell you for sure. I would get and install the 137.5s now and eventually try 140s. Trying 140s will tell you for sure if the 137.5s are correct.
 
This is an interesting thread. My recently finished bobber is running open baffled pipes and foam unipods. I am part way through setting the BS34s I have. So far the best running I have achieved has been 1 up on the pilot to 45. The main have tried different sizes from 135 to 145 and the stumbling at WOT gets worse. Pop the stock 132.5s back in there is a barely noticeable stumble at WOT. However, it runs up to 70 mph, returns 50 mpg and the plugs look spot on. The next step is potentialy purchase the canadian needles and needle jets from Mikes and try upping the mains whilst dropping the needle but I am not convinced that expense is going to be worthwhile. I may try lowering the float height to allow more fuel in the bowls.
 
If your pipes are very short, like cut off right by the footpegs, you might try extending them 6" to 8". That may make tuning easier.
 
How do your plugs look? When dialing carbs you should check your plugs every time you change anything, before and after.

BTW, I read that from 5Twins at some point and its been invaluable info ever since. gotta give credit where its due
 
Alright finally got some time and a nice day to do some tinkering.
I'm now running 137.5 mains and 45 pilots with the mix screws out 3 turns.
She starts up and idles alright but taking off it has trouble and at 2/3 throttle it bogs like crazy. Also the left exhaust is popping alot and is pushing more exhaust, almost twice the pressure as the right. ???
 
Was it a running bike before you started and/or did you fully rebuild the carbs before? I have started replacing all needles/seats/jets etc if it wasn't running when I started the project. The crap that comes out of ethanol fuel these days really screws up the brass, plus I have had several deformed needles from them sitting in the seats for years.
 
Now that I think of it, I haven't synced them yet. I've had them synced before my engine rebuild but not after my tear-down of the carbs and engine. The bike was running before but really poorly, hence the top end rebuild. Since then I've been replacing and upgrading parts, this is the first time I've had the bike together. It's alot of new things all at once.
Sounds like I have a pair of carbs to sync tomorrow. I don't know why I didn't think of that sooner.:doh:
 

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