Carb jetting

Ok so i live in denver co about 5200 feet so the bike i have is a 79xs with I believe is bs38 carbs i got the bike from way up north and the kid i got if from had no filters on it it runs .... but after it gets worm it just wants to die when i cold start it and have it warm up for a min and i try and snap the throttle it just cuts out completely but i can roll on the throttle fine
Im going to be putting uni pod filters on it any help would be amazing thank you guys
 
Well yes put filters on for a start, As carb guru grizld1 just said today Got a free xs2 today Any time you buy a gas motor more than 10 years old expect to do some carb work, you will seldom be disappointed.

This may prove helpful after the carbs are gone through and all issues dealt with. http://www.jetsrus.com/FAQs/FAQ_rejet_elevation_and_temperature.htm
Not to mention that an engine run in a sandy or dusty area with no filters for very long is unlikely to have much compression.
 
You'll need to take a look at the jetting you have in there now. There's no telling what the P.O. may have done/changed. Here's a chart showing stock jet sizes .....

7wbHkpb.jpg


Normally, for mods like you plan (pods and different exhaust), you would go up one or two on the pilots, 2 to 4 on the mains. Your higher altitude location may require the low side of these increases (one on pilots, one or two on mains). Carb re-jetting for mods is all about experimenting and finding what works best. No one can tell you for sure the exact sizes you'll need, actual testing will tell you that.
 
Well yes put filters on for a start, As carb guru grizld1 just said today Got a free xs2 today Any time you buy a gas motor more than 10 years old expect to do some carb work, you will seldom be disappointed.

This may prove helpful after the carbs are gone through and all issues dealt with. http://www.jetsrus.com/FAQs/FAQ_rejet_elevation_and_temperature.htm
Not to mention that an engine run in a sandy or dusty area with no filters for very long is unlikely to have much compression.

it definitely feels like it has good compression lol i do have some white smoke coming out of the exhaust i dont know if thats from being way to fat or something els this is what my plugs look like (if i was sitting on the bike) Left side IMG_5518.jpg
right sideIMG_5515.jpgim going to get into the carbs this weekend.
 
thats what i was thinking do ya think i just need to check the torque specs on the head or is it if its only one side its rings ?... this is not the place for this lol ill start posting in my build thread about this
 
Question: Im trying to set my mixture screws, but it starts to "stumble" with the mixture screws 1/2 turn out from fully seated and i can not get it to stumble at all when turning the mix screw out further. It runs and idles good, it feels rich when revving from idle. And plugs (smoke ring) looks rich when its been running on idle.
Should i try stock Pilot 42.5? Or will adjusting the needle leaner work?
My first try would be the leaner pilot 42.5, but i would like to hear others opinions aswell =)

EDIT: Or maybe increase an Air Jet?

Setup:
Minor cleanup porting
277 rephase
700cc
uni pods
free flow exhaust with cone engi mufflers.

BS34
Adjustable canadian needle (2nd slot from top) with needle seat.
Main 137.5
Pilot 45
Air jet 130
 
The pilot air jet can be changed for fine tuning, but you have a bigger pilot mixture imbalance than that. The first thing I'd check is float valve function and fuel level. If that checks out, right, drop PJs one step to 42.5.
 
Heads up: this is a new BS34 question, NOT the OP!
ebb0tk Thanks for posting your set up details right away!
"Setup:
Minor cleanup porting
277 rephase
700cc
uni pods
free flow exhaust with cone engi mufflers.

BS34
Adjustable canadian needle (2nd slot from top) with needle seat.
Main 137.5
Pilot 45
Air jet 130"

Stock
Main 132.5
Pilot 42.5
Air jet?? would have to go look, what's the stock air jet?
What grzld says; BS34's set up and working right, just won't run rich at idle, usually not happy much less than 2-3 turns out on the idle screw. There are 3 ports the screw only affects one of the three. So we are thinking something else is causing extra fuel to go in at idle.
are the rubber caps on the pilots?
The float valve/carb body o-rings are always suspect, unless recently changed Do you have brass floats, did you do a dip in hot water leak test? Even foam floats can get fuel soaked. Are the springs in the float valves free moving and strong? I would want to do a clear tube fuel level check. The fine points of setting BS 34 float level have confused a few. Basically the floats should LOOK level when set right.
Carb synch done?
How's it running above idle?
The fine points of setting BS 34 float level have confused a few. Basically the floats should LOOK level when set right.
 

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Uh, Gary, I have to quibble just a little bit with you and my old partner in crime 5twins. The proposition that the mix screw afffects only one nozzle out of three isn't quite right. When the screw is turned out, more vacuum is applied to the PJ, pulling more fuel and richening the mix through all pilot nozzles. Nice job of clarifying fuel level issues!
 
Thanks for the correction! My only excuse is that it's been awhile since I played with a BS34 (or any vacuum diaphragm carbie, for that matter). Currently running a pair of rescued Mikuni 33 mm. flat slide 4-stroke pumpers. Lots of refurb and fabrication involved, but the results are worth it.
 
Heads up: this is a new BS34 question, NOT the OP!
ebb0tk Thanks for posting your set up details right away!
"Setup:
Minor cleanup porting
277 rephase
700cc
uni pods
free flow exhaust with cone engi mufflers.

BS34
Adjustable canadian needle (2nd slot from top) with needle seat.
Main 137.5
Pilot 45
Air jet 130"

Stock
Main 132.5
Pilot 42.5
Air jet?? would have to go look, what's the stock air jet?
What grzld says; BS34's set up and working right, just won't run rich at idle, usually not happy much less than 2-3 turns out on the idle screw. There are 3 ports the screw only affects one of the three. So we are thinking something else is causing extra fuel to go in at idle.
are the rubber caps on the pilots?
The float valve/carb body o-rings are always suspect, unless recently changed Do you have brass floats, did you do a dip in hot water leak test? Even foam floats can get fuel soaked. Are the springs in the float valves free moving and strong? I would want to do a clear tube fuel level check. The fine points of setting BS 34 float level have confused a few. Basically the floats should LOOK level when set right.
Carb synch done?
How's it running above idle?
The fine points of setting BS 34 float level have confused a few. Basically the floats should LOOK level when set right.

Ill start from the beginning on the carbs.

They have been rebuilt, ive ultrasonic cleaned atleast 3 times and blowed air through every hole i could find.
Ive set the floats to 21.5-22mm (plastic ones) and done the fuel level check with a tube on the bike. I'll do that again today and post pics here when im done to see what you think.

Carb sync is done, first benched then used that home made with oil in it. Almost spot on, maybe a 1cm-1,5cm between them.

Float valve is stock mikuni, cleaned with a quetip and with a new needle. New o-ring on the float valve aswell.

New rubber thingies for the pilot jets aswell.

Bike is running awesome above idle. Just the idle that keeps showing rich.

I'll EDIT here aswell: ive gone through cam chain tension, valves, ignition timing.

So everything is good there aswell =)
 
Yeah indeed. Ive been running the mix screws at 3 turns out until. I noticed before it was a bit rich but the mixscrew respond was about none.

I can get a hold of 42.5 PJ's, but would be a week before i could give them a try. I'll do the level check with a tube and post in a few hours. Swim easy so long =)
 
ebb0tk, if others were as careful to do the whole job and give all of the relevant information as you are, they'd have a lot less grief. Well done!
 
Hehe thanks man :) Id rather not post before i actually went through other systems first :)

Here you have fuel levels. Both Side almost identical, first picture is left carb, second right.
I was making sure i had No air in there too. Petcock on, bike level (as you were riding it)

Even made a nice mess on the floor (forgot to close the drain screw on one bowl :)
 

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