416 popping no start?!?!?!

[Foxnake42]

just installed 416 with 12 - 1 comp from JE. Also did curtis sparks full exhaust. I jetted it with a 165 main, I have a 42 pilot for better idle. Went to start and it just pops even with the choke on. I sounds like it wants to start. ohh yeah a xr 400 can too.

[44oEX]

check all the small stupid stuff.
is the spark plug cap on? is the kill switch on?
is the gas on? do you have gas?
put in a new spark plug.
put in new gas if the one you have is old.
sometimes it's hard to start a new motor for the first time on the stock battery ( specialy since you have 12:1) . hook it up to a car with booster cables ( it happend to me before.) ones you get it started ones your battery will work nex time.

If all theat doesn't work im out of ideas
good luck let me know if it works

[Quadzilla]

I hope that you are not running straight pump gas with a 12:1 piston. If so, you will need race gas or a 50/50 mix of pump/race gas. That may solve your prob...

[44oEX]

yeah I forgot that.

[toby400ex]

Sounds like it is out of time or a fouled plug

[Hondaluva]

Once you eliminate all the easy no-brainer items and if it still doesn't start, take a look at the timing and make certain that the cam isn't 180 degrees out.

I just finished my 440 and cam project and it started instantly...no problems...good luck.

[44oEX]

if the cam was 180 degrees out the valve would hit the piston on the first turn of the starter.

[y2k400ex]

Did you put the spring and plunger back in the Head for the cam?

If your running a Stock or XR400 cam it will not start with out the little spring and plunger. If its not in there the decomperssor stays on all the time. A freind of mine did this when he rebuilt his 400. It would try to start then back fire out the exhuast like it was out of time. He thought it was out of time untill i looked at it.


Read this Thread:
http://www.exriders.com/vbb/showthread.php?s=&threadid=98999&perpage=15&pagenumber=2

[Foxnake42]

well, i am using 94 for gas, i left the plunger out because i have heard we don't need it. I would imagine the cam is in correctly because there is plenty of compression( almost starting) The whole bike shakes everey time it fires. i would imagine that is the high comp piston. new plug in it. white brothers rev box too. tried the stock one, still didn't go. anyone elses sound like a gun going off (not backfire) when it is cranking over? loud pipe and piston have to do with it huh? hmmm thanks guys

[Foxnake42]

oh yeah, do you needthe plunger?

[red400ryder]

Take my word for it..put your plunger and spring back in your motor if your running a xr400 cam like you said cause without it the decompression assembly will never allow it to start..mine was the same way..got it back together and never would start until i put mine back in and it fired right up..take my word and y2k400ex word for it...he helped me out..later mike

[y2k400ex]

that little plunger disengages the decompressor once the the motor starts. With out it in there the decompressor is holding the exhaust valves open just a little to help it start easier. So when it fires it goint right out of the exhuast

[quadkrazy400ex]

the post about mixing 50/50 with race fuel i have read before that the higher octane will now properly mix with the lower octane. so when you are driving, one squirt of gas will be the higher octane and the next might be the lower.

[y2k400ex]

i run straight 100 unleaded in mine and some time mix 114 and 93.

[Foxnake42]

another little thing...... you know how the sprocket lines are suppose to line up with the head top? mine did, but it was off by a miniscule amount, like maybe a mm. I then realized if it was off a tooth, it would be off more than that. so i don't think it is the timing. I am going to put the damn plunger back in..lol

[y2k400ex]

yea they will be off just a hair mine was the same way

[Foxnake42]

well, seems to have been the damn plunger after all. started right up and runs strong. just need to get it out in the dirt to tune. thanks for all the help. by the way the x 6 exhaust leaks from the back of the silencer, seems kind of cheesy for the pipe