timer
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1#
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From: Canada 
Registered:12/08/2008
Time spent: 0 hours
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Re:Need tuning help on project racer.
(Date Posted:03/14/2009 07:31:47)
HI
I still have the same air filter but run a supertrapp. only way i know of telling if you are runng too lean is the spark plug colour. Give it a good rip down the road & shut it down. Running at idle will not tell you what you need to know. Pull the plug & look at its colour. White= too lean, black=too rich. use this to guage which way to move you c-clip. I actually had to lean 1 pos from stock. I found too lean made the motor a hard start when cold. I was able to change the c-clip without removing the carb from the bike. Timer
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nh141
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2#
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Rank:none
Score:101
Posts:101
Registered:01/29/2005
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/14/2009 09:37:47)
I would go with a 38 mm Mikuni, they can be picked up cheap on e-bay and than you can purchase the needed slides, needle and needle jet to make it work. Even with a stock engine the XL gets some life with the carb and pipe.
I think a XL350 with a 1 5/8 inch exhaust pipe is easier to tune than a 1 3/4 inch - I say this after having done both. I really struggled to get the 38 mm to run clean (it was always lean at the bottom) in all throttle settings. It would probably make a difference if on the 1 3/4 inch pipe there was a slight size reduction right where the exhaust pipe bolts to the cylinder head - reversion cone.
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zucker
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gride2
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3#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/14/2009 09:53:45)
The only thing I done to the carb is move the clip up a notch, since the site says it runs rich at the stock setting, one up from center. It starts easy, idles great, but when you go to take off it wants to fall on its face. It will not open up at when going down the road, like its starving. The plug is showing signs of being lean. It will slightly pop out the exhaust at idle as well, lean condition. Is there a way to make the stock carb work, like up the main jet a couple and the pilot one or two #s. If not, I have a 76 XL350 header I may swap out to see if that makes a difference. I do have a small exhaust leak where the header attaches to the head, I may have to give the pipe more of a mounting surface to seal with the gasket. The 76 header would also fix that. Keep it coming guys, I'll have time next week after work to try out your ideas. Thanks.
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timer
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4#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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Re:Need tuning help on project racer.
(Date Posted:03/14/2009 15:17:22)
Sounds like you have to move the c-clip the other way to richen. Dont forget you can also tweak by adding/removing discs from your supertrapp. From the sounds of it you will need to remove discs. Positive thing is less discs= quieter=more back pressure=torquer bottom end=( i would expect(not sure) a richer condition)
What ever you find that works please share with us so we can all learn from your experience
Timer
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350s
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5#
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Rank:none
Score:381
Posts:381
Registered:01/04/2007
Time spent: 0 hours
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Re:Need tuning help on project racer.
(Date Posted:03/15/2009 09:27:46)
Fellas, A carb has 3 systems for fuel delivery. Pilot, slide cutaway and air or fuel screw are the idle parts. Needle and needle jet, stacked on top of idle system is the midrange. Main jet stacked on top of idle system is top end. The needle and needle jet are not in play when on the main jet, provided the needle and needle jet are not too small for the main jet your trying. i.e. the hole between needle and needle jet is NOT as big as the main jet. Get the pilot system right first, then the intermediate[1/8 to 3/4 throttle], then the main[WOT]. Pat Orman.
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gride2
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6#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/15/2009 16:34:08)
350s, I agree, I believe it's going to take jet changes to cure this problem. I had to do the same thing on my 1998 WR400 whenever I changed the pipe, I had to up the main jet a few #s because there was a dead spot whenever I gassed it. If I don't have any extra jets laying around, I'm going to stop by the local bike shops and see what they have. I'll keep you guys posted.
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350s
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7#
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Rank:none
Score:381
Posts:381
Registered:01/04/2007
Time spent: 0 hours
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Re:Need tuning help on project racer.
(Date Posted:03/15/2009 18:49:04)
OK, but a dead spot when you gas it is probably NOT the main jet. Until your about 3/4 throttle or more your on the needle, needle jet. Put the needle all the way to the top and then all the way to the bottom. See which way works the best and go from there. Pat.
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gride2
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8#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/16/2009 18:59:05)
I'm in the process of making a wider flange on my pipe to improve the header to head surface to fix my exhaust leak. I moved the needle clip all the way down and I took 4 of the 9 plates off the supertrap. I'll let you guys know by the end of the week what the outcome is. I'll post some pics then to. Thanks!
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Disco_enduro
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9#
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From: USA 
Registered:12/01/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/16/2009 19:14:44)
Thank you pat! You really cleared up some carb tuning q's for me. Now I think I can figure out jetting for a pipe and filter. So you are saying if I change pipe and filter, first make it idle rock solid then part throttle then I'll know if main jet is close after full throttle run? Thanks, I was wondering how to know when to tweak the various ways to go rich or lean!
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gride2
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10#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/18/2009 18:49:37)
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gride2
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11#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/20/2009 20:59:43)
Picked up a 140 main jet and a 50 pilot jet today. I'll let you know if they make a difference.
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timer
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12#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/22/2009 15:39:00)
I LIKE IT
I assume it has a CR tank & seat? That tank really suits the bike. Why not try Cr side panels?. They would have the oval # plate incorporated in them. That rear sproket should enable you to do wheelies like crazy. Mine has a 14/45 set. Proper for dirt??. My Bike also hesistates, If i crack the throttle off of idle. Anything above 1/8-1/4 its spot on. Interested to see what diff your pilot jet makes.
Kevin
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gride2
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13#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/24/2009 17:05:41)
Kevin,
Are you running stock jets? I believe the pilot jet may be to big now because I can screw the fuel mixture screw all the way in and the motor actually pics up some RPMs, instead of dieing. It was raining today so I didn't get to take it out. The motor wants to almost die if I gun it at idle. This is getting frustrating.
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gride2
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14#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/24/2009 17:07:41)
Where do you measure a Mikuni carb to see what size it is?
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timer
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15#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/24/2009 17:32:31)
HI
Mine does the same from idle. The pilot jet acts the same as yours although i have not tried screwing it in all the way. I believe i have the stock pilot jet but unsure. I dont know how to measure the 38mm. I asked the very same question on my c-clip page. I will look to see if i got an answer. One kind fella mentioned also switching to a xl 250 flywheel. I only assume its lighter & thus should help with throttle responce. Whatch my other page xl250 vrs xl350 hope he adds some more details. Back to my earlier question. Is the seat & tank both off a cr 250? was it a big deal to install them? have you decided on side panels yet?
kevin
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gride2
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16#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/24/2009 18:31:09)
Kevin,
The seat is off a 73/74 cr250 and the tank is off a 76 CR250. I relocated the tank front mounts forward and down from the stock XL mounts. I also have about a 2"spacer holding up the rear of the tank. The stock XL tank mounts do work after trimming them, but the front of the tank sits up pretty high off the frame. I agree with the side panels you mentioned, but with the way the intake is and the left outlet exhaust, I'd had to cut up any of my good pairs of side panels to make them work. For now I might zip tie some aftermarket maier # plates to the sides. Question, how many plates did you leave in your supertrap exhaust? Thanks, Keith
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nh141
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17#
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Rank:none
Score:101
Posts:101
Registered:01/29/2005
Time spent: 0 hours
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Re:Need tuning help on project racer.
(Date Posted:03/24/2009 21:02:44)
The XL250 flywheel is lighter and gives quicker throttle response. I have heard the TL250 may be lighter yet. The location of the air (or pilot) screw dictates whether you richens the mixture are lean the mixture when turning the screw in. On the off road VM type Mikuni carburator the air screw is located on the air cleaner side of the throttle slide which means the screw controls the amount of air flowing though the passage the draws fuel through the pilot jet. Screw in less air more fuel, richens mixture. On the stock XL carburator I think the pilot screw is located on the intake valve side of the throttle slide. This means the screw controls the actual mixture, screw in leans the mixture. Sometimes changing the float level can have an affect on the air screw setting. Last year I built a bike similar to yours for vintage racing and I used a early side panel off of an CR250 Elsinore. I have an angled K&N filter on my 38mm carb and to my surprise using heat on the side cover enabled me to form the cover around my air cleaner
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zucker
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timer
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18#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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Re:Need tuning help on project racer.
(Date Posted:03/25/2009 18:08:59)
Thanks Zucker.
If i get a chance to pick up a flywheel from a xl 250 ( i assume 72-75) i would like to try it. You know Keith, Zucker has a good point about the flexibility of covers. As an example i used tin snips to cut a UNI rectangular # plate to make oval. Soft/pliable . Also have seen Aftermarket side panels on e-bay for $75 (early cr 125/250) I expect it would make more sence to butcher aftermarket panels as opposed to OEM. Softer as well , i would expect. 12 discs in my supertrapp. its loud, just the way i like it. Hey Zucker whats a chance on seeing a pic of your bike
Thanks
Kevin
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gride2
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19#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/25/2009 18:21:48)
I agree with both of you. I'm all for making this thing look like a factory racer, but first I have to get it running like one. I believe I made some progress tonight. After messing with the stock carb for the 100th time, I finally got feed up and took it off. I grabbed a Mikuni that came off a KX420 and put in a 270 main and a 35 pilot. The bike fired right up and I noticed a big difference when taking off down the road. It feels like it could open up little more at WOT, would that be the main jet? The needle clip is in the middle position. I think with a little tweeking it's going to be the bike I imagined it would. I also put 12 plates in my supertrap. Good idea on the flywheel, I wonder how much lighter it is?
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nh141
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20#
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Rank:none
Score:101
Posts:101
Registered:01/29/2005
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/25/2009 20:31:39)
Below is a picture, XL350 in an XL250 frame - current mod. planned is a XL350 swing arm. Currently it wants to wheel stand to easy I have to be carefull when opening the throttle. Hopfully with the longer XL350 swing arm this will help. 
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zucker
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timer
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21#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/26/2009 15:19:34)
Hi Zucker
Thanks for the pic. Its a sharp looking bike. I dont know what Keith thinks but i know that pic just inspired me.
Where can i get a pipe like that? I have tried to buy one on e-bay but they are not on there that often . this could be a money maker for a young go getter. Im sure there is a demand, especiallly after seeing the price of the rusted out one on e-bay. Keith, keep me posted on the carb progress. Although my carb does not work bad Im open to performance mods. Zucker, is the 250 frame the same except the 350 except for the swing arm?
I think im going to have to buy some repo side covers myself.
Kevin
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gride2
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22#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/27/2009 18:38:51)
Nice bike Z! Any chance of getting a pic of the left side? I can see now I'm going to reroute my exhaust, because the way I have it, it's sticking out on the left to far and it's in the way of a possible side cover. I think I'm going to bring it closer to the center down tube and exit it out the left side, like Zucker's exits on the right. Kevin, all you need is a mig welder and old headers that you can pick up at auto swapmeets, they already have the bends you need. I'm going to pick back up on her tomorrow. I got a 290 main jet i might try to see if that helps WOT. Where do you guys get your front sprockets. All I can find is 15 tooth with a 530 chain. I'd like a 14t w/520 chain. Also in the hunt for a xl250 flywheel. Anybody know the weight difference? Later!
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XL_2Fidy
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23#
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From: Australia 
Registered:08/06/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/27/2009 23:53:44)
Here's a couple of other ideas for pipes and sidecovers? This is on a 250 but would be the same for the 350? The right side was easy as it still uses the original airbox There was a real nicely setup XL250 on the 250 forum.....but it's disappeared.   I just made up a cover from a scrap of aluminium 
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'74 XL250
'76 Z900
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timer
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24#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/28/2009 04:55:24)
XL-2fidy
Nice ride & thanks for your input. I like your exhaust set up as well as Z's. I definitely like the front fender on the 250 as opposed to the fender on the 350. Id also lke to put a 250 tank on it as the 350 looks huge. Whats involved i dont know. Keith, talked to a guy at work. he says 38mm is measured on the motor side of the carb, not the air filter side. He also mentioned a little weight on a flywheel is a lot of throttle responce. He raced newer 4 strokes & spun his down on the lathe. Took something like 1/8" off od & it was a completely different bike. Keith looks like you & i have some work to do. My 1st priority is exhaust.
Kevin
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timer
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25#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/28/2009 04:58:26)
Keith
Someone in the group mentioned bikebandit.com for parts. I have looked them up & lots of parts there , at fair prices. I have never delt with them so thats all i know
Kevin
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gride2
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26#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/28/2009 05:27:02)
I was kicking around turning the 350 flywheel down on a lathe, I may just do that if a friend of mine can't come up with a 250. It's raining, so no test runs today, but I can work on the pipe and flywheel.
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nh141
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27#
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Rank:none
Score:101
Posts:101
Registered:01/29/2005
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/28/2009 05:44:25)
I mention the XL250 flywheel as a replacement for the stock XL350 because you can get one on Ebay and you have no extra cost, just a bolt in. The XL250 & XL350 flywheels are the same except the XL350 has an additional plate on for added weight. Not sure how easy it would be to separate the plate.
The side part XL250/350 have a triple clamp with a three bolt attachment for the fender which makes it difficult to bolt a after market fender on. The center port XL250/350 have a triple clamp with a 4 bolt fender attachment which makes it nice to bolt the CR Elsinore fender on.
On the exhaust it has been my experience to try to shoot for a pipe that is not longer than 32 to 34 inches before the silencer. You can get all sorts of angles pipes from a company that makes headers – the one I have ordered form is Stahl Headers located in York, PA http://www.stahlheaders.com/Frame%20Tubing.htm. The exhaust pipe I have on mine is a Torque engineering pipe form the 70’s. If I were to make an exhaust pipe today I would start with a header pipe from a YZ400/426/450 fourstroke and make modification as required.
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zucker
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gride2
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28#
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Registered:07/24/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/29/2009 09:25:11)
I revised my exhaust yesterday to allow more room for a number plate. I also switched back to the stock xl front tank mounts. This closed the gap I had between the seat and the tank, and this eliminated the rear spacer. The tank just sits higher off the frame, which is OK. I also eliminated the choke cable, since I'm using a Mikuni now. Everything is still in the ruff stage, still tuning, painting and smoothing is next. I might go with the K&N 20 degree angle air filter as well, I believe that's what Zucker is using. Will look into flywheel options as well. Here are some pics.  
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timer
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29#
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From: Canada
Registered:12/08/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/29/2009 18:02:09)
Keith
You have been busy. It rained here all day so i had time to kill. I read all interesting posts (23 pages of them) Its a good read & i would highly recommend it. I learned so much & feel almost embarrased as most of our questions have been answered in past posts. I read that the xl 250 flywheel weighs 1 lb less than the 350. You have to tell me the difference in perfromance . Also learned you can expect an increase of 15% with a pipe & carb. Going to work on my exhaust this week
Kevin
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XL_2Fidy
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30#
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From: Australia
Registered:08/06/2008
Time spent: 0 hours
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RE:Need tuning help on project racer.
(Date Posted:03/30/2009 01:09:25)
Just been reading the paperwork that came with my Supertrapp. For the XL350 it suggests 1.625" or 1.75" clamp on model silencer plus Acc. pipe (32" for max. peak power).....stock engine?
1.75" core insert with 16 discs for racing use and 7 discs for trail use.
Also claims up to 30% increase over stock exhaust.(generally)
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'74 XL250
'76 Z900
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