426 Hard to start cold or hot

Ok guys, I have a 2000 426 and yes I have checked and double checked the valves. They are on the low side but within spec. It does have the 450 cam mod and let me tell you a little history. Before the mod it would start (cold) on about the 2 or 3 kicks and (hot) it would start on the first or second always. I did the 450 cam mod, reshimmed the exhaust valves (they are correct) and it was a little harder to start than before. I can kick it over but it is not as easy as some of you have proclaimed. I also swapped the 426 carb for an 03' 450 carb. Now it is really hard to start, about 10 kicks when cold, and hardly never when hot. I usually have to bump start it if I am in the woods so I have to watch out not to stall or turn it off. I am considering going back to the way it was but the 450 carb and cam made a big difference to me. Once the bike is started it runs aweswome but I need to figure out the starting problem. Any suggestions?

jets are all stock except for the main, it is 168.

check your carb settings and maybe consider going to different pilot jets. i dont know what the cam could of done. maybe your timing chain is off a little. also the 450 carb could be plugged some how. so clean it up try some different jets and see how it goes.

Did you do the cam and carb swap at the same time? If not, how did it start after only the cam swap? I'd work backwards one step at a time. Put the 426 carb back on first.

As with most others who have the 450 cam, it starts right up and runs fine with only a kick or two cold or hot (with the hot start lever).

That is exactly what I was thinking when I wrote the question. I believe that with only the cam mod it was still hard to start but I will swap back and see. I'll let you know and post my results. Thanks for the suggestions.

Also, I have had this bike about four years and have done nothing to the piston/rings, cam chain and have only adjusted the valves. It has been a great bike but I wanted to try a few things to it.

unhook the TPS and then try it. I am thinking I read where the 450 carb TPS sensor was not compatible with the 426 ignition? Or maybe I dreamed it.

Anyhow..try that first. Otherwise I would suggest your timing is off on the exhaust cam.

I'll give that a shot before changing things back. I did remember that I did the cam mod first and rode one or two times with it. And yes it was harder to start then my original setup. But with the 450 carb it seems to have gotten worst. With the cam only, it would start right up after about 8 - 10 kicks and when it was hot I would kick a few times, then try the hot start, then wait a second and kick it without the hot start and it would crank. It was a pain in the butt in the woods when it is hot and you are tired from riding. I'll try to figure this out. There seems to be alot of variables but I will get it. If I have too, I will go back to my original setup which worked just fine since I knew the routine.

Thanks for the help and I will be back.

I did check the timing and I do have 14 pins between the dots.

Should I try a 450 ignition?

Forgot to mention the jets; (165 m, 45 p, 4th position clip, 1 3/4 out fuel screw) and I am at sea level.

I did the 450 conversion at the same time as the carb and my Dr.D full pipe does not line up at the mounts so the slip joint is about 1/2" back which has allowed some exhaust leak at the joint. Would this cause a problem? Remember this was not the case with the cam mod only and still had starting problems.

I keep remembering little things as I go. When I installed the 450 carb on the bike it had a 42 pilot in it. The bike had a hanging idle that I couldn't get rid of regardless so I up the pilot to a 45 and that took care of it. Then I went riding and that is when I found out (the hard way) that it was a bear to start.

Sunday 08/27 - I tried a 48 pilot and shifted the exhaust forward to rid of the small leak. I kicked it a total of 30 times. I do not have a new plug so I will wait and try what I did until then. I'll be back.

Ok guys, here is what I did. I installed a new plug, started kicking and it took about 20 or so kicks until it finally started. I let it warm up and then I shut it off. I did a compression check but am not sure how reliable the results are due to the auto decompression. But anyway, the compression only got as high as between 85 and 90 psi. The question is, Is this enough to start the bike? I was able to get the bike started, after 10 or so kicks, and I rode it for about 5 minutes, turned it off and never got it started again. I kicked it about 20 - 30 times. I even disconnected the TPS and nothing.

So I have a conclusion of my own that I would like some feedback on.

Since the bike is a 2000 and I have owned it for about 4 or so years and I have never done anything to the piston or rings (I know I have put close to or over 100 hrs), could it be that I had low compression in the first place and due to the 450 cam addition, the cam is not allowing the compression to get high enough to allow the bike start easy? Before the 450 cam, I would go through the routine 426 starting procedure and the bike would start on about the 3rd kick cold and always 1st or 2nd time when hot. Even if I dumped it, hot start on and wham, it would start right up.

Any thoughts on that?

Thanks for anyone's input.

90 sounds a little low, but I would still try the 426 carb back on the bike first.

The auto decomp mechanism can be disabled for the purpose of a compression test by opening up the cam cover and wedging a piece of folded card, like a matchbook cover between the weight and the cam sprocket so that it will stay in the "out", or running position when put there. Hold the kill button or remove the plug wire and short it while cranking to be sure it doesn't start.

The other thing is the cam timing. Remember that the marks on the YZ450 OEM cam will not work in the 426. Time the intake correctly, then count 14 pins between the two "12:00 o'clock" marks on the two cams to time the exhaust. If the cam is retarded, cranking compression will be too low to run.

I do remember that the 426 carb did the same thing. I checked and double checked the timing; there are 14 pins between the marks and the lobes are in the correct position. When I get a chance I will post a picture or two.

I am thinking about rebuilding the top end anyway. I believe it is about time but I might just stick the 426 carb back on one more time just for kickers.

Alright, I put the 426 carb back on it and it took 11 kicks to get it started. I rode it for about 5 minutes, shut it off, waited a minuted and it started right up. I rode a little longer, shut it off, then waited about 5 minutes. It started right up. I again waited about 10 - 15 miutes and again it started right up. I am going to take it for a ride tomorrow to see how it will really work. Starting when cold I can deal with but starting it while hot is what I would rather be 1 or 2 kicks. I will be back again with more info.

I put the 426 carb back on. It started on the 11th kick. I rode for 5 minutes, shut it off ad nd it started right back up. I shut it off agani, waited 5 minutes and it started right back up. Waited 15 minutes and it started right back up. I will go for a ride soon and see how this works. Cold starting I can deal iwth but being in the woods and it not starting when hot is the problem. Maybe the 426 carb is what I need to go back to.

I put the 426 carb back on the bike. When it is cold, it takes 11 kicks. It starts everytime on the 11th kick. I believe I need a new top end. My thoughts are it is taking this long to build up the compression to fire.

I'll deal with it until winter.

Thanks for all that posted.


PS - 03 450 carb for sale.

Just an off the wall thought, is the carb plate hole on the down side? I had an issue of hard starting until I was pointed in that direction. Might be worth the few mins to pull the slide out and look. $0.02 worth

I finally went riding this weekend and I found out how the 426 carb worked. It was 41 degrees so it took some time to get it started. I kicked more than 11 times so I decided to replace the plug. First kick it started. In the woods it wasn't bad either, one or two kicks and it would fire back up.

mpl239 - If the carb plate was upsidwe down would the carb fit back together? Just a thought.

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