What Mod's to do to make this yz400f a one kick starter?


I've got a 99 yz400fl1 and i have done a ton of work to this bike. I have adjusted the valves, checked the timing, checked the stater and coil and rectifier and kill switch. All of these are checking out good. I adjusted the valves to within specs and i just rejeted the carb. I ordered a jet kit from JD Jetting and went compleatly throught the carb. I ran wire through all the jets and passages and it is compleatly clean. Nothing any where. Still having problems getting this bike started.

I can pull start it and as soon as i pop the clutch it fires rite up. I have tried everything that has been suggested to me and with no luck.

Ive tried kicking through the compression stroke, using the decompression lever to get it about 1" past TDC. Ive tried every thing from no pumps from the throttle to 5 pumps. No matter what i have tried this bike just doesnt want to start by kicking it. It normaly takes about 15-20min of kicking this bike to get it started. This isnt going to work trail riding.

I have herd some say that they can get thiers started on the first kick.

For those indaviduals what mods have you made to your bike?

because every thing i have done to this bike so far has not changed how this bike starts at all.

Im getting realy frustrated. I have a ride planed for next thursday and if i cant figure out somthing i am going to miss out on another ride.


Verry aggrivated yz400f owner

:smirk: :smirk: :prof:

get an iridium cr8eix spark plug check piston and crank bearings get the head worked (Clear casting flaws)

There are very few YZ400's left that will start on the first kick any more, and most of the problem relates directly to the carb and the amount of time on it. If the bike has low hours, but has been run often enough that the carb has never dried out for any length of time, and it is tuned impeccably, then yes, if you master "the drill", you can start them in one or two MOST of the time. Not many of them meet all those parameters any more, and to be frank, the early FCR carbs kind of stink when they get old.

The two best things you can do are to install an auto decompression cam, which won't fix the carb but it takes the starting drill down to two steps instead of three with no guesswork involved, and the big one; a late model FCR-MX carb from an '05 or later YZ450. It's basically a bolt-on, with a couple of minor details to work out, but it really is a major improvement. Be sure to buy one that includes as much of the hot start and cabling as possible.

One other thing is the strength of the ignition. A coil-over-plug conversion will help, and iridium plug will help, and making sure that the stator is in good shape will help.


Thanks guys. I just put a new plug in it. a NGK CR8E. The stater is testing good. Every thing on this bike is testing within specs. I will try to get the decompression cam and try that but it will have to be a winter project. I have about blown through my budget on this bike allready.

I will try to pick up one of those plugs and see if that helps. Im going to run up to Iron Poney tomorrow to look for a few things? I will see if they have any.

The carb seems to be in great working order. every thing is good and tight. Not much slop. The jet kit has helped the mid range and idoling issues i was having but it just the starting now...

Thanks for the tips guys. Im ready to hit the trail with this bike but where we ride if i get out and it wont restart its a 30+ mile hike back to the trail head... You can see why im hesitant.

Thanks again.

I don't know what my specs are, I believe my bike is bone stock. I ran a half-bottle of Seafoam in a full tank of gas and pulled the spark plug to clean it, and reassembled. As far as I know, bike's engine or carburator has never been rebuilt.

I kick it to TDC, then an inch past, crack the throttle once with the choke open, and kick it usually 6-8 times to get it to start cold, but it doesn't always idle until I get it warm.

When its warm though I never really have a problem starting it with the "TDC, inch past, kick" technique, but I find that when I can lean against a tree and kick while standing on the pegs its a lot easier, but I can kick it while standing.

i normaly lean it against somthing to kick ig over. thats the way ive been doing it. i have kicked this bike so much in the last week i have ruined 2 pairs of boots and my ankle is killing me. it would be nice if there was a inexpensive way to convert it to electric start!

i am planning on putting a kick stand on it for when im on the trail.

i just dont have any confidence in this bike rite now. when it runs OMG is it a power house. i love the power it has just not the problems im having starting it.

will the decompression cam hurt its performance any?

will the decompression cam hurt its performance any? no

ive herd some complaints that the new cam causes bogging issues? not sure.

I have yz450 cams In my 01 426f and it starts and runs great. The trick to my 426 and my kx250f is run 93 octane gas and octane booster. I use NOS octane booster and both bikes start on on or two kicks using this method; 2 twists of the throttle, at tdc kick it slow one time or two if required. And i do mean kick it slow!

ive been running 89 till yesterday. i did finaly get it started. i think ive got a bad pilot needle seal. i put a piece of tape over the hole where the pilot needle is. twisted ghe throttle 4 times and kicked it 3 times. then twisted it 3 times and on the 3rd kick it started.

hope this just isnt a fluke thing but it worked last night. thats the easiest it has started yet. oh and i didnt have the choke on or the hot start on either. it fired rite up. now im waiting on a new o ring and spring for my pilot needle then ill know what ive got a little better.

my 400 was always a one kick bike, I prefer the NON auto decomp cam because you can get the crank in exactly the right position before you kick

as long as it's jetted right and the valves are in spec it should start with one kick

mine had a 426 cylinder with 2mm overbore making it 444cc at 13:1 I ran it on pump 93 octane gas, the piston was special order, not sure if they are available anymore

The thing with the auto decompression cams is that simply by putting the crank against the compression stroke, you have already put it in "exactly the right position". In a manual setup, the crank is moved to the start of the compression stroke, the lever pulled, and the crank advanced a bit farther up the bore. In the auto setup, the exhaust valve is held off its seat until the crank gets to that same spot. Far too many people over think the whole thing and try to advance the crank to some other position after it hits compression with AD, when what they should be doing is just pushing it to "the hard spot", backing the lever up, and kicking it.

Octane has not one single little thing to do with how well the engine starts. It may well be that with two fuels of different octane ratings, one might start better than the other, or get better mileage, make more power, or any of a host of other things, but the octane rating will not give you any indication of this. Octane number is a measure of a fuel's resistance to detonation under heat and pressure; to ignition by sources other than spark or flame, and tells you no more than that.

That little o-ring around the pilot screw makes a big BIG impact. I cannot count how many FCR carbs I have worked on that have either a mangled or simply AWOL o-ring. Make sure you check the opening for any bits of the old o-ring before reassembly.

I have a 2002 426 and it is box stock, except for the exhaust. If the plug has less than 25 hours on it, it is a one kick affair.

That little o-ring around the pilot screw makes a big BIG impact. I cannot count how many FCR carbs I have worked on that have either a mangled or simply AWOL o-ring.
Good point, and often overlooked.

I also have a 99 yz400f and bought it last year. When I bought it, it would take 20 to 30 kicks to get it started but after a month or two of work it now starts after about three kicks cold and first kick every time when warm.

Things I did were; adjust valves, rebuilt carb, and replaced all seals where there could be any air leaks. I had many cracks in the seals from the airbox to the carb to the engine. I replaced all those and it made a difference. Also make sure your air filter is not over oiled and use the highest octane gas you can buy in your area. I think manual recommends 95 octane but the best in my area is 93. Recheck your valves as well. I adjusted mine but they were so bad when I bought it that I checked them again after two rides and had to adjust them a second time. A year later though and they are fine now. Hope this helps

...use the highest octane gas you can buy in your area. I think manual recommends 95 octane but the best in my area is 93.
The manual calls for gasoline with a Research Octane Number of at least 95. The roughly equates to ~86-87 Motor Octane, or, using the U.S. Anti-Knock index posted on gas pumps in the US and Canada, about 90-91. Any fuel sold in the US at 91 or more has a high enough octane rating.

Ok here is the latest on my bike. Im stoked rite now. Ive finally got the starting down finaly when its cold.

I just got my new pilot needle, spring, washer and o ring tonight and put it in.

I drained the gas and put some fresh 93 with ethanol which where i buy my gas makes it 97 octain. Now it runs like a dream. It idols and is very responsive when i crack the throttle.

I bought a new plug yesterday. Its a IRIDIUM CR8EIX and put it in tonight since i had it tore most of the way apart. It has seemed to help over the NGK CR8E.

The starting is sill alot different on this bike than what every one has told me to try.

Ive got to twist the throttle 4 times kick 3 with out the decompression lever!!!! twist it 3 more times and normaly on the second kick it fires rite up. (HELL YEA!!!) i can deal with that. This is a major relief for me rite now. I am going riding with 5 of my buddies thrusday at Wayne National Forest Thursday and i was worried i was going to miss out on another ride.

I have done a tone of work to this bike in the last week and now it is running and idoling great. Thanks everyone for all your help and ideas.

Ive finaly got it down and i couldnt be more happy about it.....

Its all about figuring what works best for your bike on these bikes. As long as it stays like this i wont have to mess with the cams. One thing i did do that has helped me kick it harder is bought a new pair of Thor boots with the reinforcment in the soles. Now i can kick it through the compression stroke and it doesnt kill my foot and ankle. I have ruined 2 pairs of boots in the past week trying to kick start this bike.

Thanks again.


I ran my 400 without the decomp conversion for about 2 years.

Once the carb was set up it started first or second kick and yes when stalled hot it was a 'b' to start sometimes.

The decomp cam just makes the kicking much easier, it just requires a smooth steady stroke of the kickstart without having to go through the motions of finding TDC etc.

Regardless, the key to starting is usually the carb set up.

I will probably try the decomp cam this winter. I am going to go completely through the top half of the motor. Im thinking new valves and ported and polished and new cams. I dont know how much this bike has been ridden? From the condition of the carb i dont think he rode this bike much but thats another story.

Im just glad it doesnt have the titanium valves in it. At $100 a pop its a large investment in a bike that is 12 years old.

Dee Cee

Does the decomp cam help with the hot start when you stall it?

I know its a bear when mine was hot. I havent really rode it enough with all the weather to start playing with the hot start.

Slyfox, my experience is similar to yours, in that you have to find what works to get yours going from cold, then don't screw it up! I have an 02 426 and if I flood it by incorrect start procedure, I can be there for the next half hour waiting or kicking....:smirk:

However.....I don't do that now, now that I know her well. She always starts within three kicks.

One comment I would have is that the auto decomp is not necessarily going to improve your starting. It makes it slightly less complicated, quicker and 'easier', which is great for racing, but, personally, I wouldn't waste the money on it unless you can't be bothered pulling the little lever....

If you've got money to throw at it, I'd get the carb set up properly then take your mates to the pub.:smirk:

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