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Discussion Starter #1
I'm curious what size main jet you guys running in colorado. I'm in Denver. Figure I'd ask before buying a jet



Thanks,

fletch
 

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What ever you do, dont do the following:

a. Ask Qwerty

b. Search this forum

c. Read the pinned post on how to tune a carb.



Save your money, Denver is the mile high city. Stock will be very close. Maybe even perfect for the newer tw'2.
 

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Discussion Starter #4
OK, I was just looking for what others had found to work best for them in Colorado. I just figured someone could say "oh yeah, I tried a 115, 120, 130 and a 135, but the 120 worked best for me in Colorado". Since, several people on the site live in Colorado. I was just looking for a better starting point then buying 5 different jets.



1) I have read defiantly enough not to ask Qwerty, or get slammed




2) I have surfed the forums of this new site and the old one Google brings up. This site is why a bought a TW in the first place.



3) I have read the pinned carbing by qwerty under technical help (which is great)



Anyways the engine pings and pops on deceleration and it has the stock 125 in it, so it is lean I assume?
 

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AH-HA! Now we have a sympton to diagnose. Popping on decel is too lean. However, if no other symptons are present, you might not even need a jet in Denver, especially if you often head uphill from there. Maybe go ahead and put a washer under the needle and open the pilot screw 3/4 turn, then let us know how the bike responds to those changes.
 

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x2 qwerty, as usual he is spot on



decel meaning the throttle is closed- indicates pilot 'idle' circuit- could be dirty/clogged or needs adjustment

do the simple first, adjust the pilot screw, and run a few onces of seafoam in a tank today and report back,
 

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if the pilot screw has not been previously adjusted you will have to remove the little plug.

if you can get to the pilot screw I would turn it closed then couunt three full turns open. ride for awhile.
 

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Discussion Starter #9
I tried 4 different jets, all could find is Precision (AB) jets that are marked by cc. Well, the one that felt really good was a 120, would this make since due to being higher in altitude to go down a jet size? A new plug looked the best with this jet as well. I put one shim under the needle and it seems the surging is still there just alittle. I then opened the screw under the small metal plug by one turn. The factory it was set to one turn out, so now it is at 2 turns out. It starts very easily and doesn't die if I bump the gas when it is cold. Would this bea goo spot to call it good? I am going to keep an eye on it over the next couple days and do some more plug chops when more plugs come in in a couple of days from the auto part store.



Thanks for the help
 

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Plug chops are a waste of time and money and money. Twisting plugs in and out of a hot aluminum head is begging for messing up the threads.



I don't give advice on non-Yamaha jets. You are on your own. I would expect a #120 Yamaha jet to be a bit lean at 5000 feet. If the bike has a rideability problem due to carb tune, fix the rideability problem. If there is no rideability problem, no sense fixing what isn't broke.



Tune one thing at a time. Which of your changes affected the surge problem? If you tune one thing at a time, you know. If you mess with all at once, you don't. That is why it is so important to do one thing at a time. Main jet first. Needle second. Pilot last. Yes, it is a pain in the ass. Most people are too lazy to tune by symptoms, but every racer does. Therefore, most people never learn to tune a carb.



If you still have surge, there is room for improvement. Keep tinkering.



At what cruise speed does your engine surge?
 

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Discussion Starter #11
I just wanted to do some plug chops so people wouldn't say "hey, did you do any plug chops?" it is a pain in the butt.



I did do each one at a time. I changed the mains out one at a time, since the bike comes apart really easy.



Once I got the main where it felt best I then shimmed the needle to get the surging out. Then when I thought the surging was gone I adjusted the the pilot screw to help with idle.



The shim is when most of the surging stopped, but after riding it for a while I could still feel alittle bit of surging. The surging is around 30 mph in 3rd gear. If I do add another shim how will I know if I put in too many?



Thanks
 

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I just wanted to do some plug chops so people wouldn't say "hey, did you do any plug chops?" it is a pain in the butt.



I did do each one at a time. I changed the mains out one at a time, since the bike comes apart really easy.



Once I got the main where it felt best I then shimmed the needle to get the surging out. Then when I thought the surging was gone I adjusted the the pilot screw to help with idle.



The shim is when most of the surging stopped, but after riding it for a while I could still feel alittle bit of surging. The surging is around 30 mph in 3rd gear. If I do add another shim how will I know if I put in too many?



Thanks


Good info and good question. Now we are getting somewhere.




If you put in too many shims, you'll get a bog at midrange when the throttle is whacked open. Whatever you did to make the improvement you felt, do it more.
 

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Excellent. One step at a time. If there is further improvement, go one more shim. Keep adding one shim at a time until signs of too rich appear. Then back off half way between that setting and the setting with the last bit of problem with lean. Some of the shims people use are so thin the difference between too lean and too rich may be 6 or 7 shims. Once you find the happy median, you will have completed Carb Tuning 101.



On to Carb Tuning 102. If most of your riding is short trip, moderate throttle, cool weather, you might consider just one shim more than lean symptoms to maximize fuel efficiency and avoid plug fouling. If most of your riding is high speed, step hills, and hot weather, might want to run one shim shy of rich symptoms to keep the engine cooler.
 

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Discussion Starter #15
I havent written here for awhile, due to starting the tuning process over. I took the Qwerty's advice and just ordered and waited for Yamaha jets. I have finally got it dialed in (how I feel) right. When the Yamaha jets can in I just started from square one. I have settled on a 128 jet, one shim and 2 3/4 turn out on the mixture. It is running great no surging at all and the carb is nice and responsive. I just wanted to update this post and say thanks to those lending their knowledge.



fletch
 

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Tdub likes #128 once she gets up to 5-7k. Lower she likes a #130.



"Feels right" is the best way to tune a carb. Did you find the improvement in rideability worth the effort?
 

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hey junk munk, i just got back from the riding in the green mountains of vt. not as high of elevation as denver but still up there in some spots. i had no issues with my tw running a #130 main jet with a DG slip on exhaust. i also got the needle shimmed with two .020 shims. the higher elevation did not cause and popping on decel even when i was in cooler more dense air.
 

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High elevation won't cause popping on deceleration. Higher elevation results in a richer mixture, and popping on deceleration is a lean symptom. Now, if you get way too rich, it's possible to load the muffler with fuel vapors that can get set of, but that sounds more like a shotgun than a popgun, often resulting in a split muffler if not shrapnel.
 

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New to the forum, which has been most useful in helping me choose a new TW 200. I live in the San Luis Valley, 7500+ feet, and the local Yamaha dealer installed a 118 main jet in the TW. Performance seems fine, but I have not yet had it to high elevation, 10,000+ ft. By the end of the summer I will have a better sense of performance with this jet. Anita and I winter on the Baja at sealevel, so I will need to rejet (back to 128?) for the winter. Thanks to all of you for putting together and maintaining a most useful and interesting forum.
 

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118 main? That's really small for a late model carb. Tdub was fine up to about 12000 feet with a 125. Tdub likes a 125 when in the Salida/Buena Vista/Leadville area--7,000 to 11,000 feet. 5,000-9,000, she likes a 128. 0-7,000 she runs fine on a 130, but when the heat is cranking, she gets a 132 at low altitudes.
 
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