wont start after rebuild

[hotrodbelair]

its 1:00 in the morning just got back in from trying to start my ex just put a new 11:1 440 bigbore in it new head thats ported polished biggervalves. i put my stock cam in it cause my hotcam aint gonna be in till january sometime. it acts like it wants to start it will pop like shes about to start then nothing. its getting gas, its getting spark and checked the timing twice. the only thing i can think of is the decompression valve. how do u take out the decompression valve do you take the lobe of the cam or do you take the plunger and spring out? cause i took the plunger and spring out but not the lobe.

[03pissedoff426]

all you need to do is remove what you did already. the lobe won't matter. it's not hitting anything now. Are you sure your timing is right? it could look right, but could be wrong. your spark plug actually sparks more than once. and on the right stroke? you know TDC comes around twice in one complete rotation. are you sure you put your cam in right? if not that could be trouble. at TDC all your lobes on the cam are to be facing down. clean up the plug or put in a new one. maybe it's getting to much fuel.

[Sjorge450R]

i am worring that i am going to have the same problem when i go to put my 300ex back together.

[hotrodbelair]

yea i had it at top dead center lobes facing down and the marks on the sprocket line up with the head. now when u set the timing on these like when your putting on the chain and sprocket u got to have the chain tensioner backed off right. now that u said the decompression releases isnt the issue im thinking it has to be the timing.

[jak1389]

if you really did take out the the spring and plunger, then thats your problem. you need that for the stock cam. for the hotcam, then you take it out. if its still inthere check your timing again and make sure its perfect.

[atvracer980]

I agree w/ JAK1389, you need the decompression system in there, triple check your timing, make sure your lobes are down and the marks on the gear are parallel w/ the deck of the head assumeing that your piston is at the TDC position, make sure your valves are set , .004 intake and .005 exhaust and make sure your rockers are in the right position. Also lift up on your rockers, if you have alot of play on either the intake or exhaust side- your 180 degrees out- the decompression has to be released- just rotate the crankshaft around another turn to the "T".

[hotrodbelair]

why does the plunger half to be in there with your stock cam and not a aftermarket? anyways ill try that then i just got done checking the timing again and tryed starting it again just dumped gas down the carb and tryed it, it was so close to starting.

[hotrodbelair]

found out one problem i had the piston in backwards. i got the head off pretty soon im gonna go out and take the cylinder off. would this be why it wont start. and i lost my plunger and spring from my stock head cause my dumb *** cousing was over and was looking at my stock head and turned it upside down and it must of fallen out so now what am i gonna do about that.

[jak1389]

you are going to need to buy that decompressor and plunger for your motor to run at all when you are running the stock cam. if i can find mine, i'll sell them to you for super cheap.

[hotrodbelair]

so i need the plunger and spring for the stock cam but not for the hotcam. right? i just got the piston turned around the right way got the cylinder on just waiting what i should with the cam issue. i feel stupid for asking but can i pluged the hole somehow?

[jak1389]

no! you can not plug the hole. those parts are there for reason. you dont need them for the hotcam, but you wont get the motor to run at all when you are missing those parts and using stock cam.

[hotrodbelair]

yea thats what i thought so im stuck till i get my new cam wich aint gonna be till january sometime. and me and a bunch of buddies of mine are goin riding next friday looks like i aint gonna make that. thanks for all the help guys.

[ZSK]

From what I've read/experienced the decompression mechanism will hold one exhaust valve slightly open allowing the built up compression to be released to allow easier starting. The decompression mechanism has a one way much like the starter and the plunger and spring actually hold it in one place to prevent any compression from being released. This is more important on the XR400 dirtbikes to prevent kickback. In the 400ex engines the starting system works to prevent the kickback. Even the stock battery has enough to start a built motor with no decompression release. Basically, you have three options that you can do.

1. Wait until the new cam comes in and don't ride the quad.

2. Buy the spring and plunger and install it in the head, if you can get them before you'd actually get your new cam.

3. Remove the decompression mechanism from the cam. It takes about five minutes and if you have a vice, soft rubber mallet, large socket, and a large punch, it's very simple.

[hotrodbelair]

are u saying i can take the decompression lobe off the cam and it will still run? or are u saying do that for when i have the plunger and spring in there. i was looking all over for the plunger and spring last night and only found the spring?

[03pissedoff426]

yea you can take off the decompression mechanism. you don't need that to run the stock cam. it's only on the cam to help with starting. which is why i said as long as it wasn't hitting anything, your quad should start. it's been awhile and i don't really remember what it even looks like anymore. but i have heard that you can press it off, or beat it off carefully. Good luck

[hotrodbelair]

so i do or dont i need the plunger and spring? i still got it sittin in the shop with the head off of it waiting to see on what i should do here. im getting all these different answers and im gettin confused lol. when i first toar the rocker box off i looked at the cam and i had it at top dead center and the marks on the cam werent lined up with the head. like one side was just a little higher than the other side but i couldnt adjust one tooth either way or would have been way off. what would have happened there?

[atvracer980]

That alright if the line is slightly higher, as long as the lobes of the cam are down. As far as running it w/out the decompression on it- Im unsure- some cams tell ya to have them removed, the cam I run on my 400ex still has the decompression on it- I guess it depends on how agressive the cam is, keep in mind that one of your rockers has a tab on it, that triggers the decompression system, you may or may not need to have that milled down- I had to on mine-it kept hanging up and makeing a horrible noise, my machine shop just took about 1/4-3/8 off the tab.

[hotrodbelair]

found the plunger today. got it together took a while for her to pop but she fired right up. but i think somethings wrong with the timing cause when she finaly started i tried getting it up to quarter throttle and it felt like it was kicking back a little bit. any ideas cause i set where i did before tdc marks lined up with the head except it would only get so close like one side is slightly higher than the other.

[hotrodbelair]

anybody? need to get this thing goin by friday and i cant think of anything here.

[jak1389]

recheck the timing, the lines should be perfect not off at all, once the lines are set, your timing is good.

[hotrodbelair]

i tried getting it to where its right on but as soon as i set the tensionar it throws it off. im getting a new timing chain but thats coming with the new cam and aint gonna be till january. i messed around with the timing for ever and cant get to where its right.

[AtvMxRider]

I am going to tell you whats going to happen. You are going keep screwing around and blow the motor up by trying to rig this thing together until the cam comes in. Either do it right or don't do it at all

[jak1389]

Originally posted by AtvMxRider
I am going to tell you whats going to happen. You are going keep screwing around and blow the motor up by trying to rig this thing together until the cam comes in. Either do it right or don't do it at all

i wish more people would understand this, you cannot halfass motor work it needs to be done right, or you will break stuff.

[AtvMxRider]

Originally posted by jak1389
i wish more people would understand this, you cannot halfass motor work it needs to be done right, or you will break stuff.


He will learn the hard(expensive) way

[jak1389]

Originally posted by AtvMxRider
He will learn the hard(expensive) way

that, unfortunatly is how many have to learn.

[AtvMxRider]

Originally posted by jak1389
that, unfortunatly is how many have to learn.


Yep but we have all been there:ermm:

[hotrodbelair]

what are u talking about riggin this thing together nothings rigged i put it together just like it was when i toar it apart. but i do think your right about waiting on the new cam to come in cause the only thing i can think of is the cam chain is streched. i cant think of anything to do with the timing to get it where it will be right on.

[jak1389]

re-check to make sure you have your flywheel lined up at the "t" mark and find someone who knows what they are doing to give you a hand;)

[JOEX]

Originally posted by hotrodbelair
i tried getting it to where its right on but as soon as i set the tensionar it throws it off. im getting a new timing chain but thats coming with the new cam and aint gonna be till january. i messed around with the timing for ever and cant get to where its right.
As long as the lines are even when the gear and chain are installed does it matter what happens when the tensioner is installed?

[hotrodbelair]

i think it does, if i remember right the marks were dead even when i first toar it apart. im gonna check it tommarrow im thinking also that i may have put the sprocket on upside down wich may throw it off a little bit but im pretty sure i put that on with the index mark facing up.

[03pissedoff426]

if you had yourself a manual on the quad you would know what your doing. my manual shows the motor at TDC and the cams lines arent exactly lined up with the head. the one side is down just a hair. my book is out in the shed. and i don't remoember to which side isn't inline. and now that you have it together sort of. are you using a new plug or still the old one that is all foulled out from trying to start it a 1000 times whithout the plunger?

[hotrodbelair]

ok friend of mine came over last night. we got it goin the only thing we did was just screw around with the timing alot. plan on taking it out riding sometime today after i adjust the valves one more time. now im wondering what jetting should i go with cause i had stock bore stock head and just a aftermarket exhaust and it ran a lil rich. i dont know what jetting is in it now but what do you guys think. and thanks for all your help so far.