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[400exmodman]

I recently purchased a 2000 400ex needed rebuilt. It has a 11 to 1 wiseco, is bored to a 416, has a stage 2 hotcam, filter, and fmf slip on. Anyways I got it all put together and it backfires but wont start. I got it in time and have checked and adjusted the valves and its gettiing gas and fire. Any suggestions would be greatly appreciated.

Originally posted by 400exmodman
I recently purchased a 2000 400ex needed rebuilt. It has a 11 to 1 wiseco, is bored to a 416, has a stage 2 hotcam, filter, and fmf slip on. Anyways I got it all put together and it backfires but wont start. I got it in time and have checked and adjusted the valves and its gettiing gas and fire. Any suggestions would be greatly appreciated.

check your jetting.

[400exmodman]

Any suggestions on jet sizes with this setup i havent even messed with the carb so i dont even know whats in it

[hondaman146]

all i have is a slipon and i run a 155 main with an open airbox and k&n filter, stock is 148 so u might need somewhere around a 160 or up main jet, don't know about the slow jet i never mess with them

[3or4HONDA]

are you positive your cam isnt 180 degrees out?

[bbender85]

Originally posted by 3or4HONDA
are you positive your cam isnt 180 degrees out?

cam timing was the first thought that came to my mind too.

[JDMThoughts]

Like mentioned, your cam might be the culprit or your jetting could be the issue. You really should take your carb off the bike, and see what the deal is with it. Having the wrong jetting mixture would also cause this problem.

[400exmodman]

I havent had a chance to tear into the carb yet but will try in the next couple of days. When i put the cam back and first tried to start it it wouldnt do anything but through the process of moving the cam one tooth at a time,(it was real close when i put it in the first time), where its at now is the only place the engine would even try to hit. Plus the cam cant be 180 out because of the ghost spark on all strokes.

[400exmodman]

okay i got a chance to tear down the carb today. it has a 160 main jet and a 38 slow jet. would this jetting mixture cause my bike to back fire and not start?

[dariusld]

Do you have an aftermarket cdi or stock? Those will sometimes cause a no start.

[400exmodman]

its a stock cdi but if it was bad would the engine even try to hit?

[dariusld]

Originally posted by 400exmodman
I havent had a chance to tear into the carb yet but will try in the next couple of days. When i put the cam back and first tried to start it it wouldnt do anything but through the process of moving the cam one tooth at a time,(it was real close when i put it in the first time), where its at now is the only place the engine would even try to hit. Plus the cam cant be 180 out because of the ghost spark on all strokes.

I also think its your timing, especially after reading this^ Could you tell us how you set your timing? I love details, we get answers to the problem alot faster:)

[KEVIN300A]

try cleaning your carb and making sure your jets are not clogged!!

[400exmodman]

Originally posted by dariusld
I also think its your timing, especially after reading this^ Could you tell us how you set your timing? I love details, we get answers to the problem alot faster:)



I lined the t up on the flywheel with the notch in the inspection hole and set the cam in. I installed the cam with the lines level with the head and the lobes facing down. After installing the tensioner and putting the valve cover back on I tried to start it and it wouldnt even hit. So i pulled it all back apart and the cam was off like two notchs. After messing with it for who knows how long i finally got it to hit but all it does still is backfire. I took the carb off yesterday and have it soaking in some cleaner but it was fairly clean. It wasnt tarnished up and it didnt have alot of grime in it.

[drillteamleader]

when you install the cam gear, you should slide it in the chain and pull up on the front side to get the slack out. Then line up the cam bolts with the tension still holding the front side up. If it is still doing this, it is your jetting. One thing that you can try is, spraying some gas in the cylinder and try starting it. if it fires at all it is your jetting.

[400exmodman]

i decided to double check the timing today. I brung the t up in the inspection hole and the marks on the cam are lined up with the head. I had the carb off still so i just sprayed gas in through the valves. It just backfired out the exhaust and out through where the carb goes a couple of times. One thing i did notice is that the engine cranks over a good bit bofore it even does anything. I would think that spraying gas in to the cylinder would cause it to fire almost immediately.

[sc400ex_rider]

yes if your spraying starting fluid, carb cleaner, even wd40 into the carb while cranking, it will start and run a few seconds. its funny how you can keep spraying on and off and keep it going. your cam timing sounds good and your valve lash ain't to tight. the only thing i can think off is do a compression check. if its low check your valves to see if they are lapped in tight. do the water test or use a flash light down the ports (head off) if you see any light your losing major compression. the port should hold gas or water for a least a couple of minutes. after that it might be electrical with intermitten or weak spark. also try swapping out with a known good friends cdi. also it might be the run stop switch on the left handle bar. if it has a tether kill switch take it off. check all the elec connection for dirt or corrosion that can cause a voltage drop. also check the carb idle screw setting you should have about 1 MM of opening at idle it might be set to low. you bought it not running so you have to go through and check/set everthing cause you never know what some yahoo did. thats all i can think of right now good luck and keep us posted.

[JDMThoughts]

I totally agree with sc400ex_rider, the previous owner could've done more harm than good. I know when I bought my 400, it gave me problems every other weekend, finally after several thousand dollars in replacement parts, the bike runs great. Compression test would help rule out some possible problems. Also like mentioned if your idle screw is wrong you will have an issue. You mentioned you had a 38 pilot. That pilot might be too small. I had similiar issue with my bike a few weeks ago, it backfired consistently and wouldn't rev up, it turned out I needed to go higher on the main jet because of the winter conditions. I also had to play around with the pilot screw.

[exrider49]

maybe your fly wheel key could have got sheared from not having your cam in time possibly?? something i would look into because it would throw your spark off