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Engine jerk or miss @5k-5.5k rpms cdi issues?

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Hello, I'm John, new to Thumper talk, and I'm looking for info on a recent running condition. First off, I've got a '99 XT350, stock internals w/11k mi, uni filter in the o.e. box with the door drilled and snorkel removed. Removed the spark arrestor and installed a restrictor with a 1" hole, ngk d8ea. I opened up the jets one size larger, but that was all that was done to the carb. The bike was running fine through town and on the highway. I have a 45mi commute through small mountain passes and then flat area. I usually run @60 when it's flat. Let's be realistic this is only a 350, but I wanted a light bike. I have a Bonneville that gets most of that commute time put on it, but I like to run the XT from time to time. So, to the meat of this, I've been keeping a eye on the plug and found it to be pretty lean so I pulled the carb and put two small spacers under the pri and the sec needles. The spacers are @ .5mms thick ea. I 5 - gassed the bike before and after and took if from @ 15 down to @ 12.5-13.5% of stoch. I then started to notice this very quick jerk or miss @5k-5.5k in 6th @55mph, it was very intermittent. That was after I had gone about 20mi through town and then started to cruise. I have felt it in lower gears at simliar engine speeds. Feels like ignition, but the coincidence has me puzzled. The plug though, now looks great. I've seen cdi's fail and they usually go to crap and stay that way until they cool, not miss like that. I have pulled the carb again to make sure nothings in the bowl and it is clean. I don't want to throw parts at it. To be honest, I will deal with it if it means not melting the engine. Sorry for being long winded, but I was trying to be thorough, Just looking for some insight. Thanks in advance for your time!

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I'm not familiar with "5 - gassed" . Please , expound .

 

You might check that your stator pickup coil is as tight to the wheel as possible and insure all connections are clean and scratch tight .

I had some missing when I ran a standard NGK plug , but that has not happened since I installed an iridium spark plug .

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Hello pd350, "5-gassed" is an exhaust analyzer like they use at the emission station. It's a quick way to find out how rich or lean the mixture is by the exhaust. I knew it was lean, just not how lean. I'm going to be changing the plug too to be sure. I'll double check the stator and connections too.

 

Thanks for the info!

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Thanks for the education on 5-gassed . Learn something new every day . ;)

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this bike likes to run hot.  i have mine jetted too ritch on the pilot and when i higway cruse it needs the choke on or it stalls.  just leave it a tough lean and you should be fine.

 

mine also has the buck at 5500rpm and i just do not ride it at that rpm any more.  tried a bunch of stuff and nothing really got rid of it.  around here my crusing speed is right at that rpm with 19/54 gearing.  i am going back to 19/55.

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Hello Maim, I leaned it back out some yesterday, and so far it's been much better. I'm going into work this morning and I'll keep ya posted. Thanks for the response!

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Update on the bike, It's pretty good at this point! I'm not going to mess with it. I've put about another 200mi on it and it has only bucked maybe a handful of times. I also had revelation , more like a duh, when it was running the worst I was @5k ft of elevation. In Tucson and home it's @ 2300k ft. It obviously was too rich and it was being finicky. So at this point I have 1 spacer under each needle, and the jets have been opened one size. Thanks again Maim and PD350 for your input!

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Hi John, welcome. I'm a relative newbie myself- I have an 89 XT and was wondering how much of a difference your mods make. I also have stock internals but run a uni-filter in the stock airbox.

Stupid question but what are the advantages of drilling holes in the door-I know it obviously has greater flow but does it make a noticeable difference?

Also the snorkel removal too?

Lastly I've seen a few people mention an iridium plug. Are they superior to a regular NGK?

My bike is running fine but I wouldn't mind getting a little more oomph out of it.

I also have a parts bike that has a 50 tooth gear vs the 47 on the bike now- will that make a big difference lowering the rpms? I do almost 100% street riding

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Going from a 47 tooth sprocket to a 50 tooth sprocket won't lower the RPM's it will raise it . These bikes came stock with 19/55 gearing . A easy way to remember gearing changes is bigger numbers on the  back sprocket equals more RPM's and less top end speed and smaller numbers equal lower RPM's and more top end speed .

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Going from a 47 tooth sprocket to a 50 tooth sprocket won't lower the RPM's it will raise it . These bikes came stock with 19/55 gearing . A easy way to remember gearing changes is bigger numbers on the  back sprocket equals more RPM's and less top end speed and smaller numbers equal lower RPM's and more top end speed .

Woops-got it backwards- asking about going from a 55 to a 47 tooth sprocket

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Howdy Bigred, I think the mods make some difference, I hope! The holes in the door, and the snorkel removed just give it the ability to more air on accel. When I got the bike, it had some issues that I had to get sorted out. I was told the bike sat for a long time and was then put back on the road. Then the jug gasket then started to leak. So he then pulled the head and jug to repair it. I traded another bike for this one and right away I thought it was kind of a dog. It just didn't have the power I thought it should, so I was looking for info for getting more power. The air box mod was the first thing I did, then I had the carb off and opened the jets 1 size. Still it was not great, so I removed the spark arrestor and made a restrictor for the stock pipe. That helped a little, but still I just felt it should be better, like maybe the timing was off...something! I also figured out that the rear sprocket was not stock it was a 51 tooth instead of the 55. I upgraded the chain and sprockets to 520 with the stock gearing. The 428 kept stretching! There's a guy on ebay selling a 520 kit, and he's got a ton of info on the conversion to the 520 and the ratios you can get. Then at the same time I pulled the valve cover off and found the intake cam to be late by a tooth. So I retimed the chain, and replaced the chain and sprocket, and then the bike was running pretty good. It would barely do 50-55 in 6th. It was like what's the point of 6th I can't pull it. Now it's better, it still is not a speed machine, but It pulls hard up to 60-65, cruises good @55-60, and gets @48mpgs. Opening up the air box makes it louder on accel too, you can hear the intake pulses. You've got to be careful that you don't drive it too lean in the mods, it can damage the engine.

 

The iridium plug is a harder plug so its just going to last longer, that's why they're in cars that only need plugs every 100k mi. The 47 tooth sprocket maybe a bit tall, but if you're not having engine issues it may pull it. You could give it a try, you've got nothing to lose. You'll have to shorten the chain, but if you keep the links you could put it back in with another master link.

 

So I hope that helps! If you have any more questions i'll try to help! Be safe!!

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Is 65 MPH as fast as it will go ? That is very low in terms of it's potential . Have you done a compression test on it ? My bike is completely stock except for being bored .020 over and I can do 83MPH wide open though I do not hold it there for very long because it is screaming for mercy . Lol. 

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Hello rzxt350! Yea It'll go faster, but as you said, it screaming! At 60mph it's probably taching about 5500rpms. It seems to like that speed, and plus the speed limits only 55. My ride in is very hilly and then flat. About 20mi of mountain foothills, and 25 of flat with a grade. Pulling the hills can be pretty much wide open when trying to go 55-60 in 6th, but down shift to 5th and it takes right off. When I'm on flat ground it's no sweat. I just try not to kill it. Today on the ride in I think I lost a valve seal, started to get wicked smoke on decel and idle. Had oil dripping out of the pipe. Dang, something else to fix right! Going to check it out tomorrow.

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Update: Got the cams out and found the valve seals in pieces for both exhaust valves. Got 4 on order, will keep ya'll posted!

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