400ex no compression!

[zbojnik19]

Hi guys,

I bought this quad from a buddy that said it ran, but it didnt want to start. I checked the compression and each time it read under 20psi. So i replace the piston with new rings and cylinder to match, new head with valves, and still the same thing. I ran the test with the valve cover off so the valves were shut the whole time..

My friend said that maybe the crank bearing is badly worn and has alot of play in it.

Has this ever happened to anyone?

Thanks in advance!

mike

[samm3020]

I don't think that the crank bearings have anything to do with compression of the motor. That said always a good thing to check when you have the motor apart. If the entire top end is new, or at least doesn't have any holes in the piston/rings, jug, head, it should have compression. I'm not sure that you can do a compression check without the cam and rocker arms in place. Doesn't the motor need to inhale and compress multiple times in order to achieve a reading? Maybe try the test again with the cam box bolted on and the cam timed properly.

[CJM]

Timing or valve adjustment. Aint no way your doing a compression check without the rocker cover on either, put it back on and try it.

[zbojnik19]

put the valve cover back on and got 120psi.

thanks guy!
sometimes its just the most simplest thing.

[CJM]

Then you have plenty of compression. Something else isnt right. Did you check timing?

WHat does it do when you try and start it?

[zbojnik19]

yes, i lined up the timing with the "|T " on the flywheel and cam lobes facing down and line marking pointing up and across the head. I will attempt to start it tomorrow

[zbojnik19]

so i try and start it and it takes like 25 cranks before it finally starts, then once it dies and warms up a little same thing.
i sprayed starting fluid and didnt help.
this would indicated that the timing is off a little correct?

i set the timing with the tensioner off and once the thensioner goes back on the marks are off a little.
am i doing this right?

thanks for the support!

[CJM]

Timing should be set with the tensioner on. It will always be slightly off, but it sounds like your way off.

What jets are in the carb?

[zbojnik19]

from what i know its just a stock carb. I did put a big bore piston, now a 440 cc with a stage 1 hotcam.
i was going to get a bigger jet once i had it fired up and running.

[zbojnik19]

so timing looks like its ok
but when i spin the the crank around one time the cam is upside down with the lobes facing up this time.

[samm3020]

if you only spin the motor 1 rev past tdc the cam should be trying to open the valves the motor would be on the exhaust stroke. Not sure why you are having a problem getting it started...I would point to the carb but you said starting fluid didn't help so that kinda rules that out....if the timing is good and you have compression the next place to point would be ignition. not sure but could you be having weak or intermittent spark?

[zbojnik19]

i did have to buy a different coil because wire was cut. but i dont think that matters bc the ecu controls the spark i think.
spark is there because i tested it.
only thing i can think of is maybe i too small of a jet right now?
but it should still be able to start

[samm3020]

too small of a jet really wouldn't explain why it wouldnt start with starting fluid. If you hold the throttle just a tiny bit does it try to start, Don't hold it alot but just cracking it. I just got a 400 that the idle was set so low that it didn't like to start up either. Maybe check that, even if the jetting is alittle lean it should still start. But to rule out jetting you could always throw some jets at it while your in there.

[zbojnik19]

what controls the spark? would the spark timing be off? i did replace the coil.

and what should i look for when buying a jet kit?

thanks for all the support guys!

[jcs003]

did you do a leakdown test?

john

[zbojnik19]

did you do a leakdown test?

john

no, I have compression to 130+ on the 3rd bump.

[zbojnik19]

I adjusted the valves, got new jets, have compression and have spark

still doesnt start!!

Does anyone know what else can be the problem?

It seems like i have slow cranking. it might be the reason it wont start.

[CJM]

Try hooking up jumper cables to it?

[samm3020]

I agree i would try to jump start it or battery charger on a boost function. you said that you rebuilt the top end....just wondering did you replace the spark plug? If for some reason the plug is weak or cracked it would spark when you checked it outside the motor but when install it could be getting blown out or a cracked plug just shorts out to the head.

Sometimes if you get the motor pretty hot and the plug gets wet it can crack.

[zbojnik19]

I ordered a new timing chain for it, since it looks like its about a half-tooth off from the center-line marks.

i really hope thats the problem. it should start with starting fluid, but since it doesnt it has to be a timing issue. (at least i hope)

[ride red 14]

what are your valves set at? if they are too tight it will not start. if your getting spark and fuel, then that just leaves air. could be why it won't hit with starting fluid either.

[zbojnik19]

what are your valves set at? if they are too tight it will not start. if your getting spark and fuel, then that just leaves air. could be why it won't hit with starting fluid either.

I adjusted the valves to 0.010 intake and 0.012 exhaust.

Ive never had anything like this before.

[ride red 14]

should run on those. good luck

[Zakradu398]

I can't believe nobody asked...... WHATS YOUR JETTING??? You said you rebuilt it to a 440 and got new jets but what jets?

[zbojnik19]

I bought the jets from ebay seller 6 sigma. 180 main jet and 45 pilot jet. Even if it ran a little rich, I think it should ask be able to start. Bit nothing.

I just changed my timing chain today. Still nothing! !!

[ride red 14]

does it have an aftermarket cdi or aftermarket. some aftermarket ones can make it a pain to start.

[ride red 14]

also, did you leave the plunger and spring out that were used for the stock cam decompression? just a thought

[Zakradu398]

I bought the jets from ebay seller 6 sigma. 180 main jet and 45 pilot jet. Even if it ran a little rich, I think it should ask be able to start. Bit nothing.

I just changed my timing chain today. Still nothing! !!

Sounds lean on the main a bit and rich on the pilot.

[zbojnik19]

does it have an aftermarket cdi or aftermarket. some aftermarket ones can make it a pain to start.

Stock cdi that I know of.
And plunger is out.

[Mtndew99]

Sounds like the decompression spring on the cam is stuck happened to me after fresh rebuild I tore the whole quad apart trying to find out what was wrong

[zbojnik19]

Sounds like the decompression spring on the cam is stuck happened to me after fresh rebuild I tore the whole quad apart trying to find out what was wrong

I have a stage 1 hot cam installed, there is no decompression lobe. :(

[zbojnik19]

is it possible that the carb could not be delivering the fuel?

or spark timing is off?

[Zakradu398]

What is your jetting

[zbojnik19]

180 main and 45 pilot

[DragonGunner]

is it possible that the carb could not be delivering the fuel?

or spark timing is off?


Put a dry plug in....open throttle a bunch of times to try and flood the motor, try hitting the starter to crank it a few times while hitting the throttle. Take plug out, should be wet with gas....if its dry then fuel isn't getting to the cylinder to fire it.

[zbojnik19]

Put a dry plug in....open throttle a bunch of times to try and flood the motor, try hitting the starter to crank it a few times while hitting the throttle. Take plug out, should be wet with gas....if its dry then fuel isn't getting to the cylinder to fire it.

Took the plug out while cracking and doesn't seem to be getting fuel. I'll clean it the carb again but what else can block fuel from getting in?

[DragonGunner]

Took the plug out while cracking and doesn't seem to be getting fuel. I'll clean it the carb again but what else can block fuel from getting in?


Wrong timing, intake valves stuck closed.

Check if fuel is reaching carb from the tank. Clogged fuel line. Clogged strainer in tank. clogged fuel tank breather tube.

Carb float needle valve clogged or stuck closed.

[zbojnik19]

Cleaned the carb again and still nothing :( I put my hand over the carb when cranking as send like alot of fuel is sitting back out

I dint know what else to try

[DragonGunner]

Cleaned the carb again and still nothing :( I put my hand over the carb when cranking as send like alot of fuel is sitting back out

I dint know what else to try


so your getting fuel to carb, when you pump it fuel is coming out of carb.....so did you try and check your plug to see if its wet..? If its not getting fuel to the cylinder it will never start. I would double check how you timed it, doesn't sound like the intake valves are opening to allow gas in. We really can't go any farther until you find out the cause gas isn't getting to cylinder, check your T mark again making sure its TDC, check your valves.....or just take it to a bike shop. They will be able to see what I can't and can figure it out in probably 10 minutes and you'll be riding again.

[zbojnik19]

So I bought a new number 9 spark plug and now I'm getting back fires every 10th ish crank. Backfires from intake and exhaust.
Making progress but still no idea. ..

[CJM]

Still sounds like timings off.

[zbojnik19]

Is there anything else I can double check that is used with timing?

[zbojnik19]

So I put a screw driver down the spark plug hole and *** it came up I checked the timing hole and it was on T. One thing I havnt tired changing yet is the cdi box. Would that have anything to do with it? I'm getting spark. I changed out the spark plug coil bc the old one had a cut wire.

[CJM]

At this point anything is worth a shot.

[ride red 14]

when you put the screwdriver in the plug hole and the timing mark was on "t", where were your cam lobes and the marks on the cam sprocket?

[zbojnik19]

I didn't look at my cams. But I had them facing down and the 3 marks positioned with one facing up. And set that too the T mark when I installed my chain.

[slightlybent47]

Place both of your lips on the tail pipe and blow as hard as you can. If nothing happens, your not gay enough, But if it starts, then your hired! lol Just kidding!
I'm sorry, I couldn't let that one slip by. It was just too easy. lol

[ride red 14]

check your cam again when you have the piston up and the tdc mark lined up. lobes should be down and the marks at 9, 12 and 3 like you said. if all that is right on, then check your valve clearances at that point. intake should be .004in. and intake at .005in. if all that is right it should start if your gettting fuel and spark.