'02 WR426 Starting Issues - Low Compression?
Posted May 06, 2008 - 01:44 PM
My bike is an ’02 WR426 with YZ cam timing, stock exhaust, not sure on jetting.
ISSUE: Very hard to start when bike is cold (not referring to cold weather). I am quite familiar with the WR starting procedure, but it’s not working for me. Here’s how it usually goes down:
1) Turn on fuel
2) Give throttle a couple of twists to get some gas into carb
3) Pull out choke
4) Kick slowly until I find what I (think?) is TDC
5) Pull in decompression lever, kick a couple inches past TDC
6) Release decompression lever, bring kick back up to top
7) Giver a full, hard kick
8) Seeing as the bike didn’t start, go back and do steps 4-7 about 10-20 times
9) Push in choke, pull out hot start, pull in decomp, and clear chamber with 15 kicks
10) Keeping hot start pulled out, do steps 4-7 about another 10 times
11) Lather, rinse, repeat…
The bike usually starts after about 5-10 minutes, and in the hot-start phase. Here’s what I have done in my attempt to improve things:
1) Pulled apart the carb and thoroughly cleaned with carb cleaner/compressed air
2) Checked my fuel screw while I had the carb apart. It was actually at 3 1/8 turns out, which is waaay too far (rich) from what I understand. I went with what I believe to be the stock setting, which is 1 5/8 turns. So far has made no discernable difference in starting…
3) Brand new plug with correct gapping
4) Fresh gas
IMPORTANT: Once I do get the bike started and warmed up, it starts like a champ with barely a half kick. Soo, here’s what I think might be the issue: I have difficulty finding TDC! Should I find TDC somewhere on every kick, or is it approximately every 2 or 4 kicks or something?
If I do have low compression, is it possible that I am kicking the bike too often (thinking I have TDC even when I don’t), which floods the bike, necessitating using the hot start button?
Am I on the right track troubleshooting this? I’m going to try and check compression tonight - any tips on doing this? If the compression is low, would this affect the bike noticeably when it’s running? I’m kinda a noob rider, so perhaps I’m not riding the bike hard enough to notice the issue?
I appreciate any insight on this – Thanks! If some of my conclusions or thought patterns are blatantly ignorant - I apologize - I'm just learning!
Posted May 06, 2008 - 04:18 PM
Posted May 06, 2008 - 08:01 PM
Easy to tell.
Put your foot on the kick starter, with a continuous movement push it slowly until till you feel resistance and you can't push it anymore. If you have good compression the kick starter will come to a stop and you will not be able to push it anymore with your leg. If you wait the air pressure will bleed off/pass by the piston rings and the kick starter will continue to move. This was your TDC -> top dead center. With good compression when you come to TDC the air is compressed enough that the kick level will support your body weight (well it does mine- 180Lb.) momentarily.
If you can make one continuous movement with a kick level than you have low (cold) compression.
As the engine warms up, metal expands, cylinder wall coated with oil, gives a better seal = better compression.
check the valve clearance, do a compression test.
Posted May 07, 2008 - 05:36 AM
How long have you had the bike? Has it always been like this or deteriorated to this state?
Once you have it running and warmed up (10 minute ride), how does it sound when you get off the throttle and decellerate in gear?
Does your bike drop to normal idle quickly when you give it throttle under no load or does it "hang" at higher rpm for a few seconds?
have you tried to adjust your air screw once warmed up, to see if your pilot jet is sized right?
To do so, set RPM at lowest smooth setting without stalling.
turn air screw in until rpm changes
Turn air screw out until rpm changes
Set it midway and record the number of turns out from lightly seated - this should be between 3/4 and 2 turns, if it's below 3/4 you need to go one smaller on the pilot, if it's beyond 2 out go one bigger on the pilot.
Set your rpm back up to a smooth 1300rpm idle.
Posted May 07, 2008 - 07:29 AM
Zsebi-2, the kick definitely can't support my weight, but I'm also 80 lbs (big guy) heavier than you. It is not hard for my to continually do slow, full kicks without the decomp lever pulled. So could tight valve clearances cause low compression?
Posted May 09, 2008 - 07:52 PM
1. choke on
2. DO NOT TOUCH THE THROTTLE. AT ALL!!! it's not a 2stroke
3. push the kick starter thru slowly until you can't push further (note compression issue earlier tho.) This is TDC.
4. NOTE THIS PART. With LIGHT pressure on the kicker at TDC pull in deco lever SLIGHTLY. ONLY enough to feel the slightest movement or release in compression with the kicker, and then let go of the deco lever and bring kicker back up (this is to give you the full travel on the kick). This step is critical!!! To much travel after TDC and you won't get it to fire, and it is likely to cycle thru and kick back and snap your leg or something hienous.
5. Give one solid, complete kick thru all the way down. DO NOT touch the throttle. let it idle on choke, do not touch the throttle, until it picks up revs, hold for a bit, then drop choke and you should be right. now play with throttle.
There is a knack to step 4, you will think i'm a nut until you learn it, i did off the guy i bought the bike off, but he was 100% correct. If i didn't get it right i was in the same position as you, i once spent 35 minutes kicking it over!! If you mess up step 4, you're in a world of pain. Never give it throttle, never travel to much with deco lever, millimetres, not inches. if you have the BK mod, don't touch the hot start unless it is really hot.
Get it right and the electric starter boys will be jealous, 1st go every go and quicker than electricity any day.
Posted May 11, 2008 - 10:57 PM
A good spark plug is also an important part for easy start.
And like they said before, do NOT touch the throttle.
If my bike have been standing several weeks I usually spray some starter gas inside the airfilter for easier starts.
Works every time
Posted May 12, 2008 - 03:12 AM
Posted May 13, 2008 - 06:11 AM
Posted May 13, 2008 - 06:46 AM
ever look to see just how much fuel the AP squirts in just one crank? It's quite a bit.
If my bike sat two weeks or a winter, I give it a single small blip on the throttle before doing the kick procedure without ANY throttle and it fires within 3 kicks.
If you crank the throttle twice you've dumped a lot of gas into the intake that it'll just flow in it's liquid state right into the bore when your intake valves open - likely too much gas.
If my bike sat less than two weeks, one kick is all it takes and NO gas or throttle blipping necessary.
Posted May 13, 2008 - 08:01 AM
Posted May 13, 2008 - 08:11 AM
Posted June 04, 2008 - 03:50 AM
Once you figure the compression/valves out you need to can this procedure and install an 03 ehaust cam. Auto-decomp is the ticket for that bike.
Can you fit auto-decomp to a 2001 WR 426 F?
Posted June 04, 2008 - 04:37 AM
Posted June 04, 2008 - 11:24 PM
yes you can, but if you don't have problems starting your bike, why bother?
Cause I was having problems starting it Until today, when I got the plug out, dried it, put it back and the baby fired up first kick. Anyway, good to know that i can fit the auto-decomp.