03 wr450 missing/skipping/sputtering.
Posted May 29, 2012 - 09:15 AM
now for my issues. #1 it starts hard, if i choke it and hold the throttle at 1/8 turn or so, it fires up and idles second kick. otherwise im kicking for a while. #2 at any throttle position, 1/4, 1/2, 3/4, or full, as soon as it gets to the max rpm at any of those postions in any gear, it starts stuttering. what ever it is its kind of hard to tell. almost seems like a misfire. i have checked everything, exhaust leaks, tps, timing, pulled the carb apart, etc. all things i have found searching. i pulled the plug and the entire thing was black. last time i knew that ment it was rich but the symptoms make me feels its lean. what do you all think. could it be a fould plug or an electrical issue? also, with the jetting setup the was it is it ran fine for two short rides and numerous rips around the house so im having a hard time thinking its the jetting but i am no pro so it sure could be. any help would be great.
Posted May 29, 2012 - 11:54 AM
Posted May 29, 2012 - 12:46 PM
As far as starting the pilot jet and fuel screw along with the pilot air jet control idle and therefore starting (most people don't mess with the pilot air jet, and most of us have found nirvana with 45-48 pilots and roundabout 1.5 turns on the fuel screw, give or take) (great sticky on choosing pilot and air screw adj).
The needle is the main control for 1/4-3/4 throttle, god knows what the dynojet needle is, again if it ran good before should be ok.
The main jet only controls the 3/4 to wide open but 140 sounds waaaaay lean reguardless of the needle so recheck that while your in there... Most folks seem to come in around a 165-170 main. I'd call dynojet if that is their recomendation and ask &%$#@!?
Providing the carb checks out, including the acc pump and your getting gas metered in correctly and all seals and o-rings are 100% then I'd get the multimeter out and start checking ignition parts, could be something as simple as a bad sparkplug or corrosion on a connector somewhere.. Start cheap and work your way up.
Posted May 29, 2012 - 03:23 PM
Posted May 29, 2012 - 04:22 PM
Check the float level too it could be running out of fuel at sustained rpm. A long shot but again free. The previous owner of mine had the float way off.
And funny you mentioned cracked fuel line as mine was rotten plus the petcock was so dirty not much could get through it. And the tank was nasty inside again worth a look free and somewhat easy to fix.
It's always great if a friend has a 450 something with a FCR carb so you can swap to see if that fixes it too.
After that it's time to get a good multi meter and start checking electronics. Luckily the owners manual has pretty good info on checking all of your goodies.
Posted May 29, 2012 - 06:44 PM
First you said no air box mods, I hope you pulled the snorkel out to help it breathe easier esp with a aftermarket exuast letting more air out there has to be enough going in. I opened up the right side of my box to help a bit as it seems very restrictive compaired it's mx cousins.
Second you say it starts to run rough after it comes up to rpm. I assume you mean when the engine isn't under a load and freely revving. Have you checked your acc pump duration and squirt? It could be running well with the squirt but when it stops the small main jet can't supply enough fuel to satisfy a thirsty 450 and it goes lean. If you rode where the pump was working all the time it would be less noticeable but if you were somewhere more open it would stand out. Kinda like a bike set up for supercross doesn't work outdoors.
This is always my issue with jetting kits, they are expensive, don't come with all the jets and parts to make a bike run 100% and usually the jetting is a bit suspect as its done on a dyno or exuast monitor and not in the real world.
There is some great info on here under jetting 101 or something like that over in jetting and intake area and I even typed something similar to a post awhile back here in wr world.
Posted May 29, 2012 - 07:50 PM
Here is the AP 101 I was thinking about, this is what I used to set mine up plus some now missing posts. Some of the info is a bit old (the BK mod is a thing of the past with the MX version of the FCR). But the timing and explanation is dead on.
Does a good job of explaining the miss, pop, bog, funk that modern 4t's face.. My diaphram was rotten also BTW, so I replaced it with the shorter pin version through Yamaha. It was perfect.. I'll leave you alone now!
Posted May 30, 2012 - 04:20 AM
Posted May 30, 2012 - 05:45 AM
I even have all the part numbers saved on my computer because I'm a nerd..
Posted May 30, 2012 - 06:35 AM
Posted May 30, 2012 - 06:59 AM
Posted May 30, 2012 - 07:34 AM
The pinned thread "WR performance index" has all the jet part numbers from yamaha listed, yep its a bit more work but you will save a lot of cash and get OEM kehin parts, (thats huge to me). I used http://www.ronayers.com/ to order everything. Yamaha sells jets cheaper than KTM dealers can order them for..
If you do a 165, 168 and 170 main. 45,48 pilot and a 40, 50, 60 leak jet along with a NCVS and NCVQ needles (03-04 yz) you will have all you need to jet away to perfection plus you can pick and choose any random seals, diaphrams and o-rings out that you need. I recommend the 5JG-14940-17-00 acc pump diaphram (I have zero bind with this one) stock is the "18" longer pin diaphram.. Plus the advantage that I got new screws for my carb that the PO had rounded out with a cheapo screwdriver.
My jetting so far.. it's still evolving and always will be I suppose (If I had fuel injection I'd be so bored)
NCVS needle 4th clip
50 leak= just less than 1 sec squirt
fuel screw 1.5 turns, changes daily it seems with 20 deg temps range..
Posted May 30, 2012 - 08:42 AM
You have to buy needles through Yamaha (cheapest), Honda etc.. The rest of the jets are the same as long as they are OE Keihin. Jetsrus.com, sudco are good sources..
Posted May 30, 2012 - 09:48 AM
thanks again. that was all great info and much appreciates. i learned alot from it.
Posted May 30, 2012 - 10:11 AM
The air cut valve can affect this also, its suppose to help with decel popping but I disabled mine and really helped with erratic hanging, floating idle and again only takes a few min to change and can be put back if you don't like it.. Real dirt bikes should pop a bit I recon..
Far as valves go the manual is the bible.. Figure out what shims you need and a dealer should sell them by the piece.
Posted June 12, 2012 - 01:45 PM
Posted June 12, 2012 - 04:53 PM
Hope that didn't throw you too far off.
Try stock jetting, adjust from there.