Help! '03 YZ450 snapping and popping under power?


16 replies to this topic
  • JSJ17

Posted October 25, 2004 - 10:22 AM

#1

I'm not quite sure what to make of this -- I've done a search on TT and so far the only hits I get are for "popping on deceleration". The problem I am having is that my bike snaps and cracks under heavy throttle.

The trouble first appeared very suddenly. Took my bike out for a 45 minute ride and it was running great (the gas in the tank was from my last ride). I added some fresh fuel that I had just bought (a 50/50 mix of super and 110 octane), and went out again -- just a few minutes into the ride it started snapping and popping whenever I would get on it. The power still felt good, although I thought it might have been just a little off (that might be me being paranoid, though!) I thought at first that I maybe had some bad gas? Drained all the gas, re-filled with a completely new supply -- same problem. I then tried replacing the sparkplug (properly gapped). Next I checked to be sure that the packing in the silencer wasn't blown out (it was fine). I gave up on the ride, took the bike home, and THOROUGHLY cleaned out the carb (completely took it apart and blew out all of the jets), thinking maybe I got some goop sucked into a jet. I tested again yesterday and it is still snapping and popping under a load! :cry:

I had the valves checked at the shop about a month ago (I know I should have done this myself but I was pretty intimidated by it!), and they said everything was in spec.

Help!! Any thoughts or suggestions? :cry:

  • moto2000

Posted October 25, 2004 - 10:44 AM

#2

Only time my bike would pop under a load is when I had the needle set too lean. Maybe raise the needle one clip position and try it. Weather getting cooler?

  • SureBlue

Posted October 25, 2004 - 10:47 AM

#3

Are you sure it gets enough fuel? Remove the petcock hose from either one end and see if fuel flows out or if it is partially clogged.
Air leak?
Electrical: Stator has overwarmed and givin up or then you have a faulty ignition box?
Kill switch?
:cry:

  • motocrosschump

Posted October 25, 2004 - 10:49 AM

#4

that would mean its too rich? is it hot wear you live?

  • Ga426owner

Posted October 25, 2004 - 11:22 AM

#5

I'm not quite sure what to make of this -- I've done a search on TT and so far the only hits I get are for "popping on deceleration". The problem I am having is that my bike snaps and cracks under heavy throttle.

The trouble first appeared very suddenly. Took my bike out for a 45 minute ride and it was running great (the gas in the tank was from my last ride). I added some fresh fuel that I had just bought (a 50/50 mix of super and 110 octane), and went out again -- just a few minutes into the ride it started snapping and popping whenever I would get on it. The power still felt good, although I thought it might have been just a little off (that might be me being paranoid, though!) I thought at first that I maybe had some bad gas? Drained all the gas, re-filled with a completely new supply -- same problem. I then tried replacing the sparkplug (properly gapped). Next I checked to be sure that the packing in the silencer wasn't blown out (it was fine). I gave up on the ride, took the bike home, and THOROUGHLY cleaned out the carb (completely took it apart and blew out all of the jets), thinking maybe I got some goop sucked into a jet. I tested again yesterday and it is still snapping and popping under a load! :cry:

I had the valves checked at the shop about a month ago (I know I should have done this myself but I was pretty intimidated by it!), and they said everything was in spec.

Help!! Any thoughts or suggestions? :cry:



First drain all gas Tank and from carb/float(COMPLETELY clean carb and all jets if you have not) and only use 93 octane gas to start. NO 110 Octane! No race fuel!

Here is some help/tips:
You have JD Jetting kit - you live in Oregon are you using the blue or red needle jet? Where is the clip? #2 from top or #3?What did you change your main to 165/168/170?
I would go back to completely stock jetting from your manual with clip in 3rd position. Fuel Screw 2 turns out to start...see what results you have - if it is detonation during throttle engagement - you may have TPS or CDI issue - hopefully not - plug TPS in if out.

If you solve the issue going back to stock jetting - then add your Blue needle clip in 2nd position - main jet for your altitude or ask JD - I believe 168 or 170 - but please verify.
Do not ever use 110 octane in this bike - I do not care if it is premixed - if you want race fuel use VP U4 but try to solve the issue before adding complexity with JD kit & fuel.

Hope this helps

  • SureBlue

Posted October 25, 2004 - 11:28 AM

#6

I can no way be a question of needle and jetting; it started suddenly when riding, gotta be something else.

  • JSJ17

Posted October 25, 2004 - 11:59 AM

#7

I can no way be a question of needle and jetting; it started suddenly when riding, gotta be something else.


Yeah, I don't think the jetting is the issue because there was only about 10 minutes between when the bike ran great and when it suddenly started acting up. Just to fill you in, though, I have been struggling with the jetting recently, so I HAD gone back to the stock needle at the #3 position, with a 170 main and everything else stock. I've also since learned that mixing in some 110 octane fuel doesn't really help, so I've stopped doing that. When I drained the gas and re-fueled (on the day it first started giving me trouble), I used some super that I just bought from Chevron (no race gas mixed in) and it still acted the same. Under heavy throttle it snaps and pops, no matter whether I am at 1/4, 1/2, or WFO throttle ...

I'm starting to think that maybe it is electrical, but I sure hope not. When I cleaned out the carb, I checked the TPS connection and everything seemed fine there, so I left it plugged in, but I still get the same results ... :cry:

  • Ga426owner

Posted October 25, 2004 - 01:08 PM

#8

agreed on the jetting after rereading your post a couple more times. - You either have some bad gas or CDI is acting up. Any chance of water from airfilter coming in? Check the head pipe for tightness - does it detonate at all rpms or just above certain point every time? Water in tps connection?

weird....

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  • JSJ17

Posted October 25, 2004 - 03:37 PM

#9

agreed on the jetting after rereading your post a couple more times. - You either have some bad gas or CDI is acting up. Any chance of water from airfilter coming in? Check the head pipe for tightness - does it detonate at all rpms or just above certain point every time? Water in tps connection?

weird....


I tried all new gas after draining the tank (from a fresh gas can, even!), while I had the carb apart I looked over the TPS plug before re-connecting it, and I also very carefully cleaned and re-oiled my filter so that I wouldn't have any water or excess oil in it. Heck, I even spit-shined the whole airbox/boot connection, so I don't think anything in there should be part of the problem. It's looking like something electrical or maybe an air leak? I'll check the head pipe for tightness and inspect for an air leak, and if that doesn't do it, I'll look into the CDI.

Thanks for all of the suggestions -- if anyone thinks of anything else, please pipe up! :cry:

  • WR426madness

Posted October 25, 2004 - 05:14 PM

#10

Have you changed plugs? Sounds like your ignition is breaking down under a load.

  • mxcowboy

Posted October 27, 2004 - 05:40 AM

#11

Check your fuel screw. Mine was running great and then started popping and backfiring on acceleration. After research I found my fuel screw was missing (vibrated out)and causing a lean condition. Good Luck

  • tboned328

Posted August 01, 2005 - 09:16 PM

#12

Installed a new pipe lately? Or did this start happening around the time the weather changed perhaps? Adjust the fuel screw and you should be fine, start with a half a turn in, better/worse....then go half a turn out. If that won't work, if it's stock piston, don't run race gas. That's what I did to make my popping stop.

  • Chills

Posted August 01, 2005 - 09:44 PM

#13

I am struggling with the same issues on my 426. Mine was more of a progressive process over time. I live in AZ, ran a Jan series without any issues, and a couple of months ago my cousin started noticing that my bike was running rough, like is was missing at steady throttle, whether it be 1/4, 1/2, or 3/4 throttle or anything in between. I guess I didnt notice it because I grew acustomed to riding it. Finally, after a couple of people mentioning the same thing, I took it out for some test riding, rather than focused riding. And wow, I was completely blown away at the fact that I didnt pay more attention to how crappy it was running. We felt as though it was due to a lack of rebuild since it was a 2001. So that afternoon I got the parts from my local dealer, and rebuilt it that afternoon. Once everything was back together, the problem still existed, and we were baffled. I tore the carb apart like you did, blew the entire thing out, double checked the valve clearances and timing. Everything checked out OK. I have riden the bike for a year now, and havent messed with the jetting, but since the temp has soared over 105 degrees, there has been a lot of discussion here in AZ about bikes performing this way under these heat conditions, and contributing it to jetting. I wasnt totally sold on the jetting, but at this point, I was exhausted with my troubleshooting capabilities. We did however mess with the TPS position, and it seemed to help, but not completely solve the problem. It was at that point we decided to go ahead and take it to the shop and have them put it on the Dyno and check out the Ignition System, TPS, Jetting, or anything. There was another post about a guy having the same problem, he has replaced, the CDI, Coil, Coil Source Pick-up, and still had the same problem. He stated he had a TPS on order, and would let me know the results. Like I said, I would much rather have a shop that has the equipment to check out the things I cant, rather than spedning $$$ playing the guessing game as to why its running the way it is. I will let you know what they say. They are supposed to have it back to me by the end of the week....

  • mxaction

Posted August 02, 2005 - 10:45 AM

#14

I added some fresh fuel that I had just bought (a 50/50 mix of super and 110 octane)


your using 110 octane in your 450, i dont care if it is mixed with premium or not. no matter what, if you have any high-octane race gas in your four-stroke it will lose horsepower (and not run correctly). every manufacturer tunes their bikes to accept 91 octane pump gas. any higher than that and you are not only wasting money, but losing horsepower.

drain the fuel and go back to running 100% pump gas, and if money is just burning a hole in your pocket, spend it on vp u4 race gas. its not high-octane but instead contains a 6% oxygen content. on the dyno it can give a 450 up to three horsepower.

  • kmier

Posted August 02, 2005 - 02:41 PM

#15

I had a problem very similiar to this on my 03' 450. Bike ran great, until I put in a fresh tank of gas. Went through three plugs in one day of riding. Bike would pop/very short hesitation when under load at the worst times, my boys still hurt just thinking of it! :D When I would pull the plug it would be covered in what looks like suet. I replaced the plugs till I ran out and resorted to cleaning them with some ether, either way seemed to last just as long. Cleaned the filter, careful not to over oil, good gas flow from petcock, went through carb, no hoses pinched, no bad wires or connections, etc, etc, etc, this went on for a couple months. What the problem boiled down to was where I live there is a different blend of gas for summer and winter. It was October and all the stations were switching to their winter blend. My bike did not like the winter blend. My fix was to run a mix of 50/50 race fuel/92. I still run this mix just to be sure and this problem has never reoccured. This may not be your problem, but it sure sounds like a fuel problem. Try gas from a different station.
My buddies, one on a 426 the other cr450 had no problem on the same gas. Go figure.

  • intothumpin

Posted August 03, 2005 - 09:48 AM

#16

Check your hot start valve. I had the same problem with mine and it turned out the hot start was worn and sucking air. It ran strong at higher revs but would barely run at idle or just off idle. I went through everything just like you, even had another mechanic go through it. after cleaning and re-assembling the carb 3 or 4 times i finally replaced all the rubber in the carb. The only thing I found that showed wear was the Hot start valve & O'ring. Now i am back to stock carb settings and the thing fires first kick and runs like new.

  • mxaction

Posted August 03, 2005 - 06:38 PM

#17

your using 110 octane in your 450, i dont care if it is mixed with premium or not. no matter what, if you have any high-octane race gas in your four-stroke it will lose horsepower (and not run correctly). every manufacturer tunes their bikes to accept 91 octane pump gas. any higher than that and you are not only wasting money, but losing horsepower.

drain the fuel and go back to running 100% pump gas, and if money is just burning a hole in your pocket, spend it on vp u4 race gas. its not high-octane but instead contains a 6% oxygen content. on the dyno it can give a 450 up to three horsepower.

Ditto.





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