[PalmStateCrawler]

I want to try to clarify this. When adjusting the pilot screw, turning it clockwise will lean out the mixture. So turning it counter-clockwise will richen the mixture allowing more fuel to enter the cylinder. So if there is a surge at low speed when opening the throttle quickly it needs to be leaner. Correct?



And is there a sweet spot where it will be easy to start and not surge or is it a trade off?

 

[pgilles]

Counter-clockwise = more fuel. You are metering fuel with it, not air.



Surge is usually a lean condition, meaning you need to give it more fuel (counter-clockwise). The carby sticky has the procedure on how to tune this circuit properly, but most find somewhere in the neighborhood of 2.5 turns out works best...screw it in (clockwise) until it just stops (don't torque it down), then back it out 2.5 turns.

 

[PalmStateCrawler]

I have done this and i'm thinking that maybe I need to remove a washer or 2 from my needle. The issue occurs when I rev up let off and then immediately rev it back up. There is a small hesitation which makes it hard to pop the front end up over obstacles.

 

[pgilles]

I think you're on the right path. That doesn't sound like the idle circuit, that sounds like the midrange and too many washers would cause it to run fat/boggy.

 

[PalmStateCrawler]

Hmmm I took out 1 then 2 washers and the low throttle miss is fixed but now I have it at mid/high range and when I rev it all the way out, it smokes a little

I now have it set with a 130 main, 3 .01 shims and 2.5 turns out on the pilot screw. It was at 130, 5 and 2.75 turns out. And i'm usually running at about 475ft above sea level.

 

[PalmStateCrawler]

I am about to head out to the garage to mess with it some more. Any suggestions?

 

[pgilles]

What color is the smoke? What does it smell like? Is it just vapor from built-up moisture in the muffler? Does it smoke when driving wide-open throttle at high rpm or just when revving it in neutral? Is it continuous or just a puff? Are your valves in spec?



What's your float height measurement?



When figuring out carbs, you are supposed to start the main jet, then the midrange (washers), then the pilot. Basically, make sure you are starting off with the correct main. When that is correct, move to the midrange and make adjustments, then end with the pilot.

 

[Gerry]

Hmmm I took out 1 then 2 washers and the low throttle miss is fixed but now I have it at mid/high range and when I rev it all the way out, it smokes a little

I now have it set with a 130 main, 3 .01 shims and 2.5 turns out on the pilot screw. It was at 130, 5 and 2.75 turns out. And i'm usually running at about 475ft above sea level.

PalmState, it is not my intent to be/seem critical. I had recently been involved in a discussion concerning what was termed a "lean surge". In order for posts to be as helpful for the reader as the author, sometimes additional information needs to be secured. If I understand your situation correctly, you had a bit of a miss at some low rpm (transition point). Can I assume this occurred after you changed your stock carburetor settings?





Seems the general rule of thumb is, one goes from the stock carb adjustments to; 130 main jet, idle jet turned out around 2.5 turns and needle raised an additional .03 (thirty-thousands). Again, I don't want to back anyone into a corner. What was your thought when you raised your needle .05 (fifty thousands) ?





Should we have an issue that we need help with, it will not only help you, but all that follow if you share as much detail as possible.... Again, when we talk of washers/spacers, it is clear that the measurement matters a lot. In my opinion, we need to give those numbers. To say adding or subtracting some, or two does nothing but create confusion.......... I would say you are likely on track PalmState. Remember, it seems a new (stock) sparkplug does wonders in smoothing out a 'very' minor hic-up in running or starting. Gerry

 

[PalmStateCrawler]

I am an eternal optimist and take anything that may be seen as critical, as another suggestion/opinion that should be considered.



Yes. The bike was running fine when stock. It was popping under decel (lean) so I opened the pilot to 2.5 and it ran fine but I feel it is better to run a little rich through the whole throttle range especially since I do a lot of sustained wot. I went back to 5 washers today and ran it for a while with minimal problems. I will pick up a new plug on monday to see if that helps. Any suggestions for a better plug than ngk? Or should I stick with them?

 

[Gerry]

Appreciate the fast reply. So as far as the needle height is concerned, you went from stock, to .05 ( 5 x .01 washers). You then stayed with the same 130 main jet, 2.5 turns on the idle jet but lowered the needle down to 3 ten thousandths washer (total .030). Today you went back to five washers which puts you back to .050 (5x.01). This was done to maintain an intentionally rich mixture for prolonged high speed riding to keep the engine a bit cooler.



I believe for the myself and the other two guys that mentioned putting in a new plug netted them a smoother engine, the new plug was indeed another stock NGK. Thanks, Gerry

 

[PalmStateCrawler]

Put in a new plug today. No change... Did a plug chop and it was white but I ran it through all the ranges so i'm not sure where it is running lean. So I guess I am going to undo everything i've done and start over. Back to the 126 main and no shims and try this again.

 

[dubstep]

following this thread with interest since it describes my symptoms well.



( ie hitting the gas after just letting off the gas gives a "lurch" before power comes on )



just cleaned carb - and its minorly better...



altho my gasket was fubar'd so I'm committed to going back in..



my main is a 132!!!!! altho my exhaust is a low slung supertrapp stubby.. ( the way I say my makes it seem like my bike - its not - its the wife's! )



cant tell what the pilot is?



I'm at sea level and its often 90% humidity here.. ( that affects it right? )

 

[Gerry]

I suspect that there are a lot of things that have impact on engine performance (perhaps an understatement). Fuel quality, ambient temp, engine temp etc. Now you have a modified exhaust and that may make your situation different (in a significant way) than those posting above.



We have some esteemed members that have adjusted their needle shims (hobby washers) by smacking them with a hammer. Others have indicated that our carburetors are set by Yamaha to represent a happy medium and as a result, should run reasonably well in most situations. When new, my bike ran fine. No hic-ups or issues. My problem followed my moving to a bigger main jet (130 I recall, I turned my adjustable idle jet out 2 1/2 turns and raised my needle up to .036 +/- .003).



Seems we are still not seeing the 'big picture'. What I resisted doing and still seem reluctant to make the investment in is, sitting down and spending an entire weekend, perhaps more in tweaking then testing, then tweaking again. I make a change, if the bike starts, I test it down the driveway. If it seems to run 'ok', I am off on a 40 mile adventure only to find myself wondering what the hell this studder is during some light load, load speed transition. I have done it to myself and am intrigued as to what the future holds for us 'Carb Clods'. The finger that I may seem to be pointing, is aimed squarely at myself. Gerry

 

[dubstep]

yes a process I was about to undertake,, but was interrupted,,..



- and as someone with an easy to type name ( no not asdfghjh

) has mentioned



should be doing the main jet - then the needle shim's and lastly the pilot..



I have found a post stating that in the hot hot and at sea level then a 132 main jet IS appropriate.. ( by that guy again!

) ( we are usually over 30 degrees celcious - its certainly sweaty here! )





now it seems to me that the main is correct- high end is excellent -

the idle was ok



the only glitch was if I have the gas on - take it off - then pull the gas on hard I get hesitation!





so why was I interrupted,,,?



well I had one day undisturbed to do this and a bunch of other task.. was planning to take carb down to shop to make sure I bought the right jets,,,



loose exhaust downpipe manifold bracket - so put in a new gasket and replaced the bolts ( no choice! they had jumped ship! )



I adjusted the valve clearances - seems the clearances were in the double range..



clean carb cos it had been hard to start sometimes recently.. ( there was a piece of black crub in the pilot ( gasket?) )





well power was definitely improved! noticeable so!



unfortunately what I hadnt noticed was that the exhaust baffle screw ( spark arrester on the supertrapp??) had come off too..



so I blew the baffle out going down a highway when I was giving her some welly!



of course the car behind ran it over

after that I understand why the supertapp is referred to as a megaphone exhaust!

 

[pgilles]

Can I ask why you guys are grabbing the gas, letting off, and grabbing it really quickly again?? If you want to pop the front tire, just slip the clutch and goose it (if there's any goose left

). Don't worry about letting off first.



You can watch my youtube video in my signature and I never left off the gas a considerable amount during shifting. Now, maybe because I was a commuter and not an offroader I have a misunderstanding of the gas on/off/on concept.



It's a CV carb, meaning the slide doesn't open when you crack the throttle open. The slide moves when the vacuum is strong enough to draw it up and against the pressure the slide-spring exerts on the slide (the slide-spring is trying to keep the slide closed). Therefore, when you are cruising at speed then let off the throttle the vacuum diminishes, the slide starts to return to closed position (couldn't tell you how far it actually moves), then you crack open the throttle again and the slide must move back up before you have true "full throttle". MAYBE, the time it takes for the slide to move back to "full throttle" is the hesitation you feel.



I'm one of a few that have enlarged the hole in the slide that allows it to move a little faster. Maybe that's why I never experienced the hesitation you guys are speaking about.



Also, the hotter it gets the less jet you need. The probable reasoning the hot hot climate TW's get the 132 is for COOLING not wide-open performance. Nonetheless, if the 132 works then go with it. But start with the main, then the needle, and finally the pilot.

 

[dubstep]

well for me - Im WOT - change gear - and WOT again on the roads on the TW.. but I'm real quick doing it...





interesting point about the vacumm



I was wondering if that was it - becos that one of the scenario I suffer it in..



car in front slows to turn - I'm off the gas.. then back on it hard to accelerate.. ( hard = WOT )





exhaust is off - getting baffle welded back.. - but I'm pretty sure if I wound on the the gas more gently.. it didnt do this...





bent needle? or the vacum rubber? or that spring in there?



I took the vacuum cover off but couldnt see anything unusual.



thanks - i may try a 130 as we are riding from ground to say 500 meter ( I actually live on a mountain top - but only 10 mins ride to the beach! )



mart

 

[atleastbehandy]

Clean the carb.



Mine was doing the same thing. Pulled the carb and found black sediment all over the place! Source (I think) was the foam air-filter. It had degraded and bits were coming off.

 

[PalmStateCrawler]

I ride single track trails with lots of twistys and whoops so a responsive throttle is a must.

 

[dubstep]

thats a +1 from me..



looking at the exploded parts carb diagram.. to the right of the "main jet holder" is a rubber seal... I'm not sure I saw that when I cleaned my carb... is something missing? or did I miss cleaning a part of it?

 

[pgilles]

Gotcha.



Throttle response above idle is gonna be the midrange circuit (duh, right? haha)....Anyways, dirty emulsion tube could create issues for that quick response, make sure all those tiny holes are cleaned and you can see light pass through them....A slow moving slide would also affect it, and drilling the slide is an option.



If you're running a lower rpm but the throttle is wide-open, it doesn't mean the slide is wide-open. At that point, if you let off and crack it open again you are starting on the low-range circuit to get back to the midrange circuit. To a degree, it's the same circumstance with being at high rpm, letting off, and cracking it open again...when you crack it, you are starting at the low/midrange circuit.



You may just be asking more than what is capable of the TW carb with just shims and larger main...it's doing the job but not quite the response you need on the trail. That's why you may want to research the slide drilling option. Here's an old thread on it http://tw200forum.com/forums/39803/ShowPost.aspx. Xracer uses a 3/32" bit with success. I had used an 1/8", but I had a cam and opened intake. Remember once you go too big with the hole you can't make it smaller...so start small and test!