400ex will not start

[rhyno0089]

02 400ex will not start. I grounded the spark plug to the head and have spark. I metered out the stator and the voltage output was low so I replaced stator, coil, and voltage regulator. Still getting spark when grounded to head.

took off carb and cleaned it out. getting fuel to the bowl and when I hit the throttle it squirts gas. I can smell gas on the plug but it isn't really wet.

can feel compression coming out of the exhaust and intake sucks in just fine.

checked timing and valve springs and they are correct...at my wits end and need help!!! haha

[Racerjames]

Any chance it jumped timing? Super old gas?
Also, how would you feel about dumping some gas straight in the plug hole n firing it off? As I recall these bikes are a PITA to get to the plug, but it should provide enough initial bang to keep it going long enough to give you a sense of what might be starving. (could use ether thru the intake, but its hard on things, don't make a habit of it)

EDIT: sorry missed the timing part...

[Ian400ex]

I'm guessing it hasn't been pc'd?

Powdercoated.

[MtnEX]

Check your compression...

It's probably low...

[MidnightBlade]

Originally posted by Ian400ex
I'm guessing it hasn't been pc'd?

Powdercoated.
what would that have to do with anything

[hocman123]

Originally posted by MidnightBlade
what would that have to do with anything

if he just painted the frame the gounding for the engine will have a bad contection and would keep it from staring

[HondaRacing83]

try and pop start it

[rhyno0089]

Have not tried pop starting. Going to borrow a compression tester tomorrow and test comression so might try pop starting. If pop starting works what would be the cause of this??

[Racerjames]

I'm curious on the comp test results, you have all the conditions for operation, but low enough compression won't excite the molecules enough to fire it off. Granted it takes a pretty big loss to make it not even hiccup at all. Have you tried a different plug just on the offchance its not putting out healthy spark?

[honda400ex2003]

im also curious on the comp test results. make sure you do it right also. I would say that it eithe jumped a tooth on the timing but you said that it seems to be right so that is a no go. good voltage on the battery? i would check the switch connections on the bars along with the actual internals of the black box on the bars in case the switches are corroding. this would be tough too though since it is getting spark at the head. my vote goes for low compression at this point. probably time for a rebuild. steve

[rhyno0089]

yeah honda400ex2003 I think you could be right. We have metered it directly from the stator and right at the coil. It is pushing the same amount of volts as my buddies bike, which is an 03 and mine is an 02. We took apart the black switch just in case the on/off switch was dirty/faulty but we are getting spark when it is on so I don't think that is it (my understanding is that when it is in the off position it will crank but get no spark)

If it fails the compression test I will begin the rebuild.

My other question is this...this is currently bored over to a 426 with an after market cam (no decpmpressor on it) and a full big gun exhaust with header, I bought a stock cylinder on ebay tonight just in case this is what it is for like $40 bucks. My plan is to go to machine shop and have the stock sleeve bored to a 416 with a Wiseco 10:1 piston.

Anyone see any problems with this or have any advice since this is my first build on a 40ex ?

[dalejiw25]

If you're buying a new sleeve why not go go Big bore ? That will give you a nice 440 build. Either way you need a new piston. Why pay for a new cylinder only to go smaller ? If it were me I'd go 11:1 (10:1 IMO is pretty Lame) 440cc- (.160 over or 89mm) and a 4mm stroke = 460cc. Even without the Stroke I think you'd be much Happier. Just my thoughts.... Enjoy !!!!

[honda400ex2003]

I personally like the 10:1 416 since it is not real crazy and will run with 11:1 all day if done right. Mine does anyway... head to head with an 11:1 it was even a couple of lengths ahead with just about identical mods. some factors were there like grip and such since it was my razrs vs stockers but it was on grass so both spun anyway. I think that the 416 is a great option to run and then if you have any other issues you can go to the 426 again. teh only bad part about having the 426 already is that it is one of the fastest revving pistons for a 400ex and will probably be a bit faster than the 416 anyway no matter what comp it is. so that would be my only worry about going with the 416 instead. Back to the switches, get a voltmeter and check for resistance (0 or close )through them or at least check the continuity through all of them (beep on the testers i have used) to verify that they are working correctly in either position. one will beep, (closed) one will not(open) I think the switch on the bars is a normally closed switch but it has been quite some time. this would indicate that when in the run position it should beep. off it should not on either side. (this should be correct but if it beeps on off then it is normally open. ) I dont think that this is what it is though simply because when wiring a normally closed killswitch gets wired in line with the regular switch when done on the bars. the normally open just gets grounded and doesnt have anything to do with the other switch. the key switch will go on or not with the lights so that really isnt a worry to have to test. the lights should not have to be tested either lol. good luck and report back. Since it is getting spark that may not be the case either lol. steve

[rhyno0089]

honda400ex2003 I am with you on the 416. All I do is trail ride and a stock 400 has just about enough power for me so I don't need to go all out. I think a 416 with 10:1 should give me the power I need without putting too much strain on my bottom end seeing as I have a full exhaust and after market cam.

Still waiting to do a compression test. I did read on another forum someone mentioned his piston and sleeve were fine and his compression ring was messed up and by changing his rings it started and ran fine...does this sound common/normal?

[HondaRacing83]

did you try to pop start it yet?

[rhyno0089]

Have not tried pop starting yet it's been raining where I am. I did get the compression tester. Anyone know the correct compression for a 426? I am checking the forum now

Thanks

[rhyno0089]

Did compression test yesterday...30lbs is what I got.

Looks like I am taking a head off this week...ha ha

[honda400ex2003]

yeah that could be the case. imo that is too low to even run at all and would trigger something wrong with the test but since it doesnt start that is most likely the cause anyway. low comp would be around 110 in a cylinder that needs to be refreshed imo. although i should not talk too much about psi since i have never actually checked mine. lol usually 120+ is considered a good cylinder though. steve

[MtnEX]

Originally posted by rhyno0089
Did compression test yesterday...30lbs is what I got.

Looks like I am taking a head off this week...ha ha

Try again while holding the throttle WFO.

It will still be low though... probably like 80 PSI or so.

[Ian400ex]

Originally posted by hocman123
if he just painted the frame the gounding for the engine will have a bad contection and would keep it from staring
Haha, derp derp. Some people.

[rhyno0089]

Hey guys thanks for all the help...was indeed the compression. took the head off and the piston and back wall of the cylinder was scrapped up horribly..

I bought a new piston and cylinder and had it bored to 86mm. Put it all back together last night and started it up...

now for my next problem... It sounds like the timing chain is slapping pretty bad... when I had it apart I saw that the guy I bought it from has an aftermarket cam and timing chain and it was pretty much brand new...

Could the tensioner be bad and how can I tell?

[honda400ex2003]

just take it out and test it. it should be able to be turned in with a small screwdriver and should release and go all the way back out. replacement is only 40 bucks and would probably be pretty good reassurance for on the trail. just my .02, test out the tensioner first. steve

[MidnightBlade]

could just be the hotcams tick?

[honda400ex2003]

anything is possible. :D :p :blah: steve

[MtnEX]

Originally posted by rhyno0089
Hey guys thanks for all the help...was indeed the compression. took the head off and the piston and back wall of the cylinder was scrapped up horribly..

I bought a new piston and cylinder and had it bored to 86mm. Put it all back together last night and started it up...

now for my next problem... It sounds like the timing chain is slapping pretty bad... when I had it apart I saw that the guy I bought it from has an aftermarket cam and timing chain and it was pretty much brand new...

Could the tensioner be bad and how can I tell?

Glad you got it sorted out with a little advice.

Just take that tensioner out and test it.

[hiway6969]

loose valves sound like that too. if not the chain tensioner id re set the valves.....

[rhyno0089]

Was a combination of a loose timing chain and the valves needed to be readjusted...

took it for a ride last weekend and I love it...got plenty of low end for hill climbing and sounds great...

Nothing like a 400ex.

thanks for all the help.