WTF? I'm so tired of this game....

[terry]

Well considering the collective experience here, this is probably a silly question, but when you reinstalled the OEM air box, did you refit the OEM filter? CV carbs are super sensitive and while the bike will idle fine and rev out on the center stand with no air filter installed, under load it'll run like crap.

I installed a new foam filter in my GS1000S airbox (I don't know why people use pods, it must just be for looks, the OEM airbox flows plenty of air) and it ran way, way too lean, until I coated it in lots of foam filter oil, which reduces air flow considerably.

If you haven't re-installed your OEM filter yet, do so, and I bet all will be well. Cheers, Terry.

 

[PAULYBOY]

Okay, so reading this thread, and accessing a couple of the links therein, has me wondering (riddle me this) some mention turning the screws out to richen the mixture, some mention turning them in. It can't be both, so which is it? I thought turning the screws clockwise (IN) meant more fuel to less air, and turning them out (counterclockwise, or anti clockwise for the Europeans among us) meant more air in the mix.

 

[Nessism]

Okay, so reading this thread, and accessing a couple of the links therein, has me wondering (riddle me this) some mention turning the screws out to richen the mixture, some mention turning them in. It can't be both, so which is it? I thought turning the screws clockwise (IN) meant more fuel to less air, and turning them out (counterclockwise, or anti clockwise for the Europeans among us) meant more air in the mix.

For BS/CV carbs, the pilot screws control how much gas/air emulsion enters the engine - out is richer. This is not to be confused with VM carbs which have separate fuel screws and air screws.

My advice for the OP is to verify everything in the intake system is stock: jets, properly sealed airbox (foam needs to be intact), filter in place, etc. Running a stock bike at 4500 will richen up the mixture which should be close to perfect since the bike was set up quite lean from stock.

If you still get the lean surging, try playing with the needle height; lowering the clip raises the needle which will richen up the mixture. Move a couple of notches and see how it goes.

Good luck.

 

[C.V.]

I got my experience and info from Sudsco/Mikuni 4th Edition tuning manuals.

http://www.lambretta.net/shop/shopexd.asp?id=3996

Here is a Mikuni tuning guide for the VM Series
http://www.mikuni.com/pdf/vmmanual.pdf

A quick how to guide for the Mikuni CV Series
http://vmaxoutlaw.com/tech/cv_carb_tuning.htm

Here is a write up on the ST series of Mikuni carbs, go to the thread with all the pictures...
http://www.gixxer.com/forums/showthread.php?t=159718

In any case, there seem to be a lot of opinions on how to get something done.

Hope some of this helps in getting ya'lls jetting straight...

Great links! These should be posted up here permanently, the mikuni guide really offers a lot of insight into how carbs work, very usefull.
Lambretta Huh? You an old scooter guy? My first ever solo ride, and subsequent first crash, was on an Vespa primavera 125. Started a long career of scooter crashes!

 

[flyingace]

I'm confused about what the poster is trying to do at this point. Going back to stock makes sense. To me, that means going back to exact stock settings, not trying to rejet for altitiude and continue to get frustrated when it doesn't work. Remember, the airbox, filter, manifolds and carbs were designed and set to work as a unit.

I'd go back to box stock carb settings and see how it runs. At 4500', there may be no altitude effect. My bike ran fine stock at 6000'.

 

[Smokinapankake]

Thanks for all the replies folks, this is what makes this forum so great.
I wanted to return to stock because 1: It's stock - this gives a solid baseline to make assumptions from, i.e., It will run, because the factory designed it to. 2: I had the same line of thinking - airbox, filter, manifolds, carbs and exhaust were designed to run as a unit with little trouble. Eliminating as many variables as possible. See reason 1.
3: Stock looks way prettier (to me anyway) than some bastardized 4-1 with noisy pods. Because that's what it would have to be since virtually no one makes a decent 4-2 replacement pipeset for this motorcycle (excepting the UK).

Thanks for the tip Terry, I don't know how but the air filter completely slipped my mind. I'll put it in and see what happens.

BTW, I have verified through the forum at www.katanacentral.co.uk that my carb settings are factory. See thread topic 2900.

 

[terry]

Thanks for the tip Terry, I don't know how but the air filter completely slipped my mind. I'll put it in and see what happens.

No worries mate, I hope that fixes your problem, it certainly did for me! Cheers, Terry.

 

[jetta90]

Smokinapankake - Ive been doing some carb work on my 1984 GS 750E lately myself.
Privious owners had a 4 into 1 and pods. When i bought it came with original exhaust and foam filter in stock air box.
Someone else metioned this before - the CV Mikuni carbs are EXTREMELY sensitive.
If your going back to stock make sure your foam element is in good shape and not overly oiled and that the air box is totally sealed.
This is what i've got running now but I don't think I'm there yet..................
Main jet - 120
Needle jet - Y7
Jet needle - 5D10
Pilot jets - 40
My fuel/air mixture screws are ONLY turned out 1/2 turn and not the usual 2 turns plus. Note that my pilot jets are 40's and not 37.5's like the factory, this probably is why it is running fine at 1/2 turn out.
The above gives you an idea where you could need to be.
No two ways about it ................... make sure your valves are adjusted. Don't go any further until you are sure your valves aare adjusted to spec.