I heard my bike run for the first time today...

So, I purchased my 426 in mid-January knowing that it had a blown top end and would need a complete rebuild. The first thing I did, which has proven to be the most valuable step I could imagine, was to sign up for TT. :p

Well, after 3 months of buying parts, asking for help, rebuilding, tearing down, rebuilding, and so on, I finally heard the beast run today...Too bad it isn't running right.

I've used the search function and read hundreds of posts from people with similar problems to mine, I just want to make sure I'm on the right track.

The bike started today after 5 or 6 kicks. It would run when I was working the throttle, but wouldn't idle, was misfiring constantly, and wouldn't wind out like I think it should. It would die, I'd start it again. No trouble starting, just running and running smooth.

After it cooled off, I tore it back down, rechecked timing and valve clearance. Timing looked good and my center intake valve was .03mm on the tight side. On the way home, I purchased a new shim in order to fix that tomorrow. I also removed the carb, gave it a thorough cleaning and checked the jetting (its mostly stock, except for the needle clip and I'm at 5000'). When I pulled the plug, it was carbon fouled (black and dry) and it was a new plug this morning.

Tomorrow I'm planning to fix the valve clearance, put in another new plug (purchased the iridium this time), new air filter, check timing again, make sure the choke and hot start are functioning, put fresh gas in (that I purchased today), and give it another go.

Any other suggestions? Am I on the right track? Thanks again for all your help. You guys are the best!! :lol:

Well your chances that the one tight valve is the problem is next to none. If you haven't put in fresh gas from the start then I would start with that. I would start with your carb, do a test does it run better with the choke out or not? If so you have a fuel issue or if not I would spray brake clean around the intake to see if you have any air leaks. But to me it seems like a spark issue you might have, like coil or stator. I would be checking those with your manual to see if they are within spec.

If you had the carb apart, be certain that you put the throttle spring plate on the back of the slide the right way up.

Thanks for the advice guys! :p

I wish I had a PC at my shop so I could post updates, reference what I've read and ask more questions. If you think of anything else that I should look at tomorrow, please let me know. If not, I'll be back on here in the afternoon talking about my success :lol: or whining about my failure :cry: .

I share your excitement to hear her run. I also picked up my first 426 in Jan. It had a bad big end bearing, so I haven't even heard it run yet. Just put a new crank in yesterday, and hopefully the top end parts will be here this weekend.

Hope you get everything figured out!!!

Success!!!! :lol: :lol: :lol::banana: :banana: :banana:

Alright! It's not perfect, but its getting closer.

So, I got out to the shop early today and got strait to work. First thing, I double checked everything I did on the carb and even did the o-ring mod since I had the carb in my hand anyway. Then moved to the valve clearance issue and corrected that. Put the cams back in and set the timing. then double checked, triple checked all the timing. Satisfied with that, I buttoned the engine back up and checked the electrics. Everything was in spec except for the secondary coil resistance was a bit high. I think I'll be looking for a new coil, but it still produced good spark when I checked it, so I kept going. Installed the iridium plug, and new air filter, then put the rest of the bike back together. Added some fresh gas, pulled the choke, and kicked.

It started on the third kick and ran good (choke on) with no misfires like yesterday.:p It would rev with throttle (rather than die like yesterday) and just felt better. I let it warm up for a minute, then wanted to ride it. Pushed in the choke and...it died. Started again with the choke on. Turn the choke off, it dies. Crap. :cry: Clearly a carburation issue. I made a quick phone call (because carburators are still kind of a mystery to me) and put an action plan together. I backed out the mixture screw 1/2 turn and that seemed to solve the problem.

Women are less complicated that carburators.

Anyway, I took the bike for a short ride just because I could and HO-LEE-CRAP!!! :lol: That thing is a monster. :banana:

I still have a fair bit of tweaking to do. The carb still isn't right. It's way better, but not right. I get a little bog when I crack the throttle from idle, but I think a little research on here will give me some ideas about that.

I'm planning a "shake down" ride on Thursday and will tear into it again after that to double check my work. I'll have a little better idea about whats going on with the carb after running it for a few hours too.

I can't tell you how excited I am right now. :banana:

THANK YOU SOOOO MUCH for all your help getting this bike running!! TT is the best!!:lol:

The bog from idle when cracked is a common problem. I could be wrong but its an accelerator pump timing issue.

Big 4 strokes dont have alot of vaccum at or around idle, and when you crack the throttle, the fuel dosent get sucked in fast enough and it leans out temporarily. If the AP is timed right it will shoot fuel in there and solve your problems

Success!!!! :lol: :lol: :lol::banana: :banana: :banana:

Alright! It's not perfect, but its getting closer.

So, I got out to the shop early today and got strait to work. First thing, I double checked everything I did on the carb and even did the o-ring mod since I had the carb in my hand anyway. Then moved to the valve clearance issue and corrected that. Put the cams back in and set the timing. then double checked, triple checked all the timing. Satisfied with that, I buttoned the engine back up and checked the electrics. Everything was in spec except for the secondary coil resistance was a bit high. I think I'll be looking for a new coil, but it still produced good spark when I checked it, so I kept going. Installed the iridium plug, and new air filter, then put the rest of the bike back together. Added some fresh gas, pulled the choke, and kicked.

It started on the third kick and ran good (choke on) with no misfires like yesterday.:p It would rev with throttle (rather than die like yesterday) and just felt better. I let it warm up for a minute, then wanted to ride it. Pushed in the choke and...it died. Started again with the choke on. Turn the choke off, it dies. Crap. :cry: Clearly a carburation issue. I made a quick phone call (because carburators are still kind of a mystery to me) and put an action plan together. I backed out the mixture screw 1/2 turn and that seemed to solve the problem.

Women are less complicated that carburators.

Anyway, I took the bike for a short ride just because I could and HO-LEE-CRAP!!! :lol: That thing is a monster. :banana:

I still have a fair bit of tweaking to do. The carb still isn't right. It's way better, but not right. I get a little bog when I crack the throttle from idle, but I think a little research on here will give me some ideas about that.

I'm planning a "shake down" ride on Thursday and will tear into it again after that to double check my work. I'll have a little better idea about whats going on with the carb after running it for a few hours too.

I can't tell you how excited I am right now. :banana:

THANK YOU SOOOO MUCH for all your help getting this bike running!! TT is the best!!:lol:

I worked on a yz400f that had similar issues, it was all in the carb. The pilot jet was clogged, some passages on the carb were blocked, and the AP diaphragm was FILTHY and rusty. So I'd suggest that you give it another good carb cleaning, put a new pilot jet, and take apart the small cover next to the bowl, the one that contains the diaphragm and give it a good cleaning. The bike I worked on had such a dirty/clogged diaphragm that it just wasn't pumping any gas through the A/P. So, in the end it worked beautifully after a good cleaning. Since you're working on it at a shop, I'd recommend you give the carb passages a good blow with a high pressure air nozzle, find every tiny passage and give it a good amount of air. Good luck with your bike. It wouldn't hurt to read up the jetting database and make sure that your jetting is correct for your altitude.

Thanks for the responses.

I'm going to continue to play with it. I'm also going to ride it for a couple hours so that I can get more of a feel for what I'm working with and what the symptoms are. Remember, I'm brand new to this bike and just had it running for the first time yesterday. :p

I'm going to tear it all apart again next week after riding it, so I'll give the carb a deeper cleaning and check the jetting. Right now, I'm riding stock.

I did look at the jetting database, but there isn't much for Denveresque conditions. I'll be between 4000 and 10000 ft, almost no humidity, and riding between 30 and 100 degrees. Gotta love Colorado.

I, seriously, couldn't be more excited right now. I kinda want to call in sick tomorrow and go play with my bike some more. Is that a common feeling for a "hard seat" owner? :lol:

I'll be between 4000 and 10000 ft, almost no humidity, and riding between 30 and 100 degrees. Gotta love Colorado.

I, seriously, couldn't be more excited right now. I kinda want to call in sick tomorrow and go play with my bike some more. Is that a common feeling for a "hard seat" owner? :p

Sounds kinda like the Cali high desert...maybe not quite the extremes in altitude, but about the same extremes in tempertures...all onthe same day!

Congrats on getting it running and running better! Keep pluggin away and it'll be sweet!.

Yes, that is a common feeling...I may do it on Friday!

I'm (cough, cough) actually feeling a (cough) cold coming on for tomorrow...

:p

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