[737mechanic]

Just installed a Powercore 4 on my 2010 tee dub and am enjoying a pretty noticable increase in midrange power. It seems to idle alright, and for the most part runs ok. However, if the engine goes from a heavy accelleration or 3/4 throttle to full closed (getting off a highway) it blubbers and pops. If you pull the clutch lever in it goes to the idle circuit and seems to correct itself. How can I smooth her out? I reckon I need a little bigger main jet in the carb. It's a Mikuni. I have not modified the intake at all and want to adjust one carb item at a time so I can keep stuff close to being right. Any other thoughts?

 

[RodneyReed]

Just installed a Powercore 4 on my 2010 tee dub and am enjoying a pretty noticable increase in midrange power. It seems to idle alright, and for the most part runs ok. However, if the engine goes from a heavy accelleration or 3/4 throttle to full closed (getting off a highway) it blubbers and pops. If you pull the clutch lever in it goes to the idle circuit and seems to correct itself. How can I smooth her out? I reckon I need a little bigger main jet in the carb. It's a Mikuni. I have not modified the intake at all and want to adjust one carb item at a time so I can keep stuff close to being right. Any other thoughts?

Sounds like your bike is running lean.



Qwerty's got it all figured out. See his post below.



http://tw200forum.com/index.php?/topic/647-carb-tuning/

 

[qwerty]

One change at a time is the way to go--main, needle, pilot, in that order. You'll have a better tune in less time in the long run.

 

[737mechanic]

Thanks for the fast reply all. I confirmed my suspicions and your suggestions about running lean by pulling the plug this morning after I got home from work. It just looks hot and dry. Most plugs are a little more interesting looking. This one just looks well, lean. I have a #130 main jet on order, and will start my adventure into carburetors in 7-10 business days.

 

[737mechanic]

Just installed the number 130 main jet. It still wants to blubber with a load on the engine and the throttle closed. So do I just get a 132, 134, etc. until the blubber is straightened out? Or is this just the nature of the beast?

 

[pgilles]

Does it blubber while holding it wide open? Or only when you suddenly, quickly close the throttle after wide open? If it runs well at speed but not when you close the throttle immediately after then you may need to richen up the needle & pilot to keep it from blubbering at closed throttle in those conditions. Try shimming the needle some. Then adjust the pilot.

 

[737mechanic]

No, it runs great wide open. In fact, I think with the mixture more rich with the bigger main jet it runs better than the stock 126 jet. It only blubbers if the throttle is suddenly closed at just about any speed. More notable if at a higher speed when the closing of the throttle occurs. No blubbering as soon as you pull the clutch lever and take the load off the engine. After reading the write up qwerty did on this subject I think I am either going to try a 132 main jet the shim the needle, or is it worthwhile shimming the needle now?

 

[pgilles]

You'll probably find that the main jet will end up being a 130, but you could go trying larger ones to be sure. I'd say shim the needle and adjust the pilot where you are at, if you are satisfied with plug chops and the way its running with your current main.



It will run better with more fuel, as you found out. Most come lean.

 

[RodneyReed]

I would try shimming the needle first.

 

[qwerty]

Is everything else right with the bike?



Occasionally, after a fast stretch of highway and some decel, Tdub will bog at roll-on. Seems to be worse with E10. Seems to be common on TWs.



If you can tell no performance difference at wide open between the 130 and 132, I'd stick with the 130 and try messing with the needle height next.

 

[demarko69]

The newer carbs are not my thing but on the early model carbs they have an anti-"blubbering" circuit. There is a little vacuum diaphram pump that on decel it gives a little shot of fuel to keep the engine from "blubbering"



Does the newer carbs have this and if so check for a vaccum leak

 

[demarko69]

early model carb

 

[737mechanic]

Update: I am running the 130 main jet with .030 washer under the needle. Seems to have smoothed out the blubbering when closing the throttle while bringing on some great low and mid range throttle response. I feel like it will still pop a little bit when the throttle is closed off while at a loaded condition and high rpms but don't know if it can ever be perfect with a slip on exhaust. Would it be advisiable to go after the pilot jet now that the other items have improved or should I try another .010 washer under the needle. This whole project is so much fun, and super easy!!

 

[737mechanic]

The newer carbs are not my thing but on the early model carbs they have an anti-"blubbering" circuit. There is a little vacuum diaphram pump that on decel it gives a little shot of fuel to keep the engine from "blubbering"



Does the newer carbs have this and if so check for a vaccum leak

Just a side thought, the newer carb doesn't have this extra diaphram but it has a decelleration enrichment circuit that is kind of a mystery on paper.

 

[qwerty]

It would be cheapper to raise the needle a bit more. You can always go back.