done rebuilding...wont start!

[powderider87]

Ok so about a year ago my atv seized on me while riding with little to no gas in it trying to make it to the gas station. the rings were kinda molded into the piston, got to hot. So i got all the new parts and got it all put together. The cam timing was a ***** but got it pretty much damn on, with the Top dead center and all. I have compression of 100 to 110 but when i try to start it or get pull started it just wont start, kinda just pops and backfires but wont actually start running. i cleaned the carb out good so im confused as to what it could be. I just hope its not the cam timing becasue i got it as close as it could get with the 2 dots on the cam gear and the head of the cylinder being aligned.

[400exmodman]

I know how you feel mine is doing the same thing.

[2muchquad]

If the cam is timed properly and your getting fuel and good spark along with compression,it should light,UNless you are running the stock camshaft and you lost the plunger assemby for the decomp whille assembling or disassembling.Do you remember a pin and spring in the head near the cam sprocket?I went through this recently and i could even get it to backfire even with starting fluid.It drove me nuts and im usually fairly decent at troubleshooting,these motors arent exactly high tech;) So if your cam timing is on and you have spark and fuel along with seemingly good compression,look at the auto decomp,that was my problem

[powderider87]

heres a pic of the calve and cam assembly, i see the spring, its number 5. but does that go in a hole on the cam shaft itsself? would it be something that could easily pop out with taking out the cam?
http://babbitts.motorsportdealers.com/pages/parts/viewbybrand/7/Honda.aspx

[Bill Fuller]

You should not have any problems starting without the decompressor dowl. If you removed the cam and turned the cam bed over to look at the valves then you probably lost it. The motor doesn't have to have a decompressor, the stock cam doesn't really need it it will just tap a little. On the HotCams they completely remove the decompressor. Have you reset the valves??

[powderider87]

nope i have adjusted the valves yet, although it was ticking and blowing some smoke before it went on me. But i just wanted to get it starting first and it just wont start, just pops and backfires.

[Bill Fuller]

Valves are out of adjustment. Anytime you remove the cam bed you should re-adjust the valves.

[powderider87]

could they get that far out of adjustment were the atv wont even start?

[Bill Fuller]

Yes, if the valves don't seat prperly then You cannot have compression to start. A leak test only insures the valve aren't worn or the rings on the piston stuck.

[2muchquad]

You should not have any problems starting without the decompressor dowl. If you removed the cam and turned the cam bed over to look at the valves then you probably lost it.

I dunno bout'that one.Mine wouldnt start at all.It wouldnt pop backfire or do anything.I removed the mechanism so i could start it while i was waiting for my hotcam to arrive,it started right up once i put it back in,my cam was in time because i zip tied the chain to the cam sprockt while i removed the cam,put cam back in after loosing the decomp mech,it fired right up..go figure.

[2muchquad]

if it ran fine before,valves SHOULDNT be that far out of adjustment where it wont start,i have never seen it anyhow unless you replace valves or change your cam:ermm:

[Bill Fuller]

Oh just forget what I said in my earlier post, 2muchquad is obviously smarter then me. Hell I haven't owned a 400ex since I sold them in 04 to buy my YFZ I Only owned/raced and built four motors from the trannys up. :rolleyes: Stupid me ran 2 races without that dowl. But hey what do I know???????????????? I won't bother you with my .02

[2muchquad]

i guess we dont know what we are talking about,maybe Gp racer will chime in..

http://www.exriders.com/vbb/showthread.php?s=&threadid=348510&highlight=decomp

[trx250rider]

100-110 ponds of compression seems very low for a fresh rebuild

[powderider87]

so i did a valve job on it and now i have 120 lbs compression. But still no start. Do my timing marks have to be exactly alligned? i got it the best i could but one line is still very slightly higher off the head with the other line JUST under the head. i tried starting it and it would pop out the exhaust like it wanted to start, sounded so close to starting. pulled the plug and it stinks of gas too, so does the exhaust, maybe my valves are opening to soon? i can only think that it might be a stretched timing chain.

[lilyamaharacer4]

Adjust your valves.

[powderider87]

already have.

[powderider87]

heres a summary kind of.

I rebuilt it and it wont start now. i got 120 lbs compression. i have done a valve job on it as well. The only thing i can think of is my timing or the fact that i dont have the spring/plunger that goes into the cam bed. My timing is damn near perfect, all lobes are facing downwards and its at TDC. one timing line is slightly above the cylinder head and the other line is slightly lower, but if i advance a tooth its just visa versa with the lines. When i go to start it it will pop almost every revolution and it wants to start, just wont. the spark plug smells of gas and so does the exhaust. i can only think that the timing chain is stretched or the decompression dowl/spring isnt there. which ive heard isnt needed and heard that it is needed from different people.

[cam19aro86]

At TDC the lines on the cam chain sprocket should be right in line with the top of the head, my guess is your cam is outta wack. I would start fresh make sure the timing mark labeled with a T is in exactly the right spot with the line on the case and then readjust your cam shaft sprocket so the lines on the sprocket line up.

[2muchquad]

the cam is timed properly and your getting fuel and good spark along with compression,it should light,UNless you are running the stock camshaft and you lost the plunger assemby for the decomp whille assembling or disassembling.Do you remember a pin and spring in the head near the cam sprocket?I went through this recently and i could even get it to backfire even with starting fluid.It drove me nuts and im usually fairly decent at troubleshooting,these motors arent exactly high tech So if your cam timing is on and you have spark and fuel along with seemingly good compression,look at the auto decomp,that was my problem

I TOLD you what your problem was.Your taking advice from these kids on here that dont know what they are talking about.;)

[cam19aro86]

I'll bet you have the dealership do all your work! BTW kid mine ran perfect after my rebuild and yours you could only get to backfire with starting fluid!

[powderider87]

Originally posted by cam19aro86
I'll bet you have the dealership do all your work! BTW kid mine ran perfect after my rebuild and yours you could only get to backfire with starting fluid!

Hey little boy, i never used starting fluid but whatever! but i really look up to you and think very highly of you just like everyone who read your last post! way to go man! But anyways is there a good place i can go to to get the plunger and spring quick like overnighted? i know the dealership is like a week out. oh cam19aro86 what trailer park did you go to get your camaro?

[powderider87]

one more thing, i have read that you can take the decompression thing off of the cam? if i take it off the cam and do not have the spring plunger in the cam bed will it work?

[cam19aro86]

That was intended for 2muchquad but thanks for being a d**k Powderider! Did you even check to see if you were missing the decompressor? I don't believe that would cause it to not run, but I could be wrong.

[2muchquad]

but I could be wrong


you are.as for starting fluid...grow up:blah:

[cam19aro86]

All hail 2muchquad THE ENGINE GURU!

[2muchquad]

All hail 2muchquad THE ENGINE GURU!


no,not really,i just FORGOT more than you'll ever know.Have a nice day:D

[powderider87]

camaro1986 dude, my bad i just got done working on the machine again with no luck so you know my anger! and the decompression thing was not there, i found it in my tool chess tho! thank god. i have read that without the decomp plunger and spring and using a stock cam that the exhaust valve will open early which makes sence that my exhaust stinks of gas. going to put the plunger and spring in today and retime and put it all back and it better start!

[cam19aro86]

Alright 2muchquad I know you wanna hear it, you were right, I was wrong. Glad you figured it out though Powderider.

[2muchquad]

Alright 2muchquad I know you wanna hear it, you were right, I was wrong

Hehe..not really,this what this forum is all about,helping people figure things out and save some cash.Even i am still learning after all these years,im only 36:)

[Which 450?]

engine will start and run fine without the decompression thing. I had a tick in my old 400, thats one of the things I removed trying to find the noise, ended up being cam chain. It still ran fine without it, just cranked slower once it got to the compression stroke.

[powderider87]

i dont understand these posts where people say it runs fine without it. i just put mine in and it fired right up! it was a confusing prosess cause i never knew it was there. But man am i glad its running now, i still have ticking, going to adjust the valves again tonight. hopefully it isnt the chain but if it is i have one in the mail that i ordered last week. Thanks guys for your help!

[2muchquad]

If the cam is timed properly and your getting fuel and good spark along with compression,it should light,UNless you are running the stock camshaft and you lost the plunger assemby for the decomp whille assembling or disassembling.Do you remember a pin and spring in the head near the cam sprocket?



i dont understand these posts where people say it runs fine without it. i just put mine in and it fired right up! it was a confusing prosess cause i never knew it was there.

There is a lot of good info on here and a lot of b.s as well,try and seperate the two.It WONT run without the assembly as you have found out.Glad you got'er done:)

[Which 450?]

it will run without it, i bet he had the timing out.

[powderider87]

Originally posted by 2muchquad
There is a lot of good info on here and a lot of b.s as well,try and seperate the two.It WONT run without the assembly as you have found out.Glad you got'er done:)

I shouldve listened to you right away. but yea the ASSEMBLY is definatly needed! Thanks again 2muchquad for your help.!

[Which 450?]

it will run without it.

[powderider87]

this is how it worked for me.... no decomp. spring and plunger no worky. put spring and plunger in, worky. IT DOES NOT RUN WITHOUT THE SPRING/PLUNGER USING THE STOCK CAM. ONE OF THE EXHAUST VALVE WILL OPEN SLIGHTLY EARLY CAUSEING YOUR AIR FUEL MIXTURE TO SHOOT OUT YOUR EXHAUST.

[Which 450?]

Originally posted by powderider87
ONE OF THE EXHAUST VALVE WILL OPEN SLIGHTLY EARLY CAUSEING YOUR AIR FUEL MIXTURE TO SHOOT OUT YOUR EXHAUST.


This is what the decomp mechanism does...

[Which 450?]

What are you calling the "decompression mechanism"? explain what you are removing/replacing.

[powderider87]

whatever, all i know is that mine will not run without it. and seeing how pretty much all 400ex's are the same i would take a guess that others wont either. but it made mine work so thats all that matters. im just glad i didnt take your advice or the other guys advice on here who said that i dont need it. Thats for damn sure.

[Which 450?]

sorry, you dont know what you are doing. But it will run without it. Wanna place a bet?

[2muchquad]

im with you powerrider,mine wouldnt work without it either.I guess i didnt know what i was doing,i should have paid close attention to my manual,i feel like such an idiot..which450 was so right...sike:D after all,having a open exhaust valve shouldnt keep it from building compression and running:rolleyes:

[Which 450?]

Sry, Im right, wanna place a bet? Ill make a vid, taking it apart, taking the decompression mechanism out, puttin it back together, and running it. Lets start out at $200?

[powderider87]

Originally posted by 2muchquad
im with you powerrider,mine wouldnt work without it either.I guess i didnt know what i was doing,i should have paid close attention to my manual,i feel like such an idiot..which450 was so right...sike:D after all,having a open exhaust valve shouldnt keep it from building compression and running:rolleyes:

hahahahahaah exactly about the last sentence. you wouldnt think someone would have to be so smart to understand something so simple as that. but whatever. which450 why would you waste your time when we all know what will happen when its not in there?

[Which 450?]

Why would I be wasting my time if Im makin $200. now tell me this... How will an aftermarket cam work without it? Do a search, no one uses the decompression mechanism on an aftermarket cam because they have to be pressed off. The only thing different is the duration and lift. did you pull the pin and spring out of the head when you took the mechanism off? Im done. If you wanna bet me, pm me....

[the Z Man]

This happened to me too, if you remove the plunger and spring from the stock cam, you also have to press off the decompression ring from the stock cam, hot cams don't come with the ring so no plunger and spring necessary.. you guys are funny..lol