[Jaka Klenovšek]

Hi, problems here with Honda trx 400ex, 1999 year. I bought new piston and cylinder 440 kit, now it wont start.
- got fuel
- got spark
- compression 120psi
- decompresor removed
- timing looks good

It just pops every second or two when starting, tried to push start - no luck. :sad

 

[shadetree]

not much for sport atvs ?, but if I had to guess ?, i'd would say something is not right with the timing.

 

[Jaka Klenovšek]

I have tried to move timing one tooth forward and one tooth backwards, and I heard just the same - poping out of exhaust. When I tried to push start, it started for few seconds but died then no matter that I was trying to keep it runing with throttle.

 

[shadetree]

I have tried to move timing one tooth forward and one tooth backwards, and I heard just the same - poping out of exhaust. When I tried to push start, it started for few seconds but died then no matter that I was trying to keep it runing with throttle.

moving the cam chain is not all that needs to be done. you need to check all your timing marks to make sure you have your cam chain set on the cam for piston to be on top dead center on the COMPRESSION stroke, and not the exhaust stroke !.

 

[Jaka Klenovšek]

I have tried to move timing one tooth forward and one tooth backwards, and I heard just the same - poping out of exhaust. When I tried to push start, it started for few seconds but died then no matter that I was trying to keep it runing with throttle.

moving the cam chain is not all that needs to be done. you need to check all your timing marks to make sure you have your cam chain set on the cam for piston to be on top dead center on the COMPRESSION stroke, and not the exhaust stroke !.

Yes all done properly, piston in tdc, timing marks aligned with upper surface of cylinder head, cam lobes facing down.

 

[shadetree]

I have tried to move timing one tooth forward and one tooth backwards, and I heard just the same - poping out of exhaust. When I tried to push start, it started for few seconds but died then no matter that I was trying to keep it runing with throttle.

moving the cam chain is not all that needs to be done. you need to check all your timing marks to make sure you have your cam chain set on the cam for piston to be on top dead center on the COMPRESSION stroke, and not the exhaust stroke !.

Yes all done properly, piston in tdc, timing marks aligned with upper surface of cylinder head, cam lobes facing down.

then this tells me either your not getting fuel ?, or not getting spark ?. to test this, take a can of starting fluid, spray a VERY SHORT burst of starting fluid into the air cleaner, kick it over or ele start ( which ever is easier ), if it '' hits'' when you do this ?, then you have a fuel issue, if it does not '' hit '' this way ?, then you have a spark issue.

 

[SamUK]

I’m with Shady on this one..

My first question is, have you jetted the carb to suit the new bore? Did you clean the carb before refitting?

I’m no sports quad expert by any means but the basics still apply..
@SlammedRanger may offer some all important advice..

 

[SlammedRanger]

Sounds like classic out of time to me. My brother had one he was building do this and he was on the wrong stroke. Did you just line the mark up or did you actually check that the pistons at at TDC? I remove the plug and use a 1/4 drive extension to tap the top of the piston to be sure its there. It is always possible the woodruff key on the flywheel is sheered and now your line used to time it is in the wrong spot. The above test will confirm this.

 

[Jaka Klenovšek]

@shadetree starting fluid does not help.. I tried to move carb, cdi, stator, rectifier to another trx which I have got and it started. Thats why I conclude that spark and carburettor is good.

@SamUK yes I have cleaned the carb and jetted to 175/42, dont know if its perfect but it should start :|

@SlammedRanger I have checked this today like you said, and the piston is in TDC when the mark is lined up. The marks on cam sprocket are slightly off (picture) but I think its not a big deal.

 

[shadetree]

@shadetree starting fluid does not help.. I tried to move carb, cdi, stator, rectifier to another trx which I have got and it started. Thats why I conclude that spark and carburettor is good.

@SamUK yes I have cleaned the carb and jetted to 175/42, dont know if its perfect but it should start :|

@SlammedRanger I have checked this today like you said, and the piston is in TDC when the mark is lined up. The marks on cam sprocket are slightly off (picture) but I think its not a big deal.

if it did not '' hit '' on starting fluid, then you have a timing issue, compression issue, or spark issue..one of these 3, i'll bank on this !.

 

[SlammedRanger]

Slightly stretched timing chain. It will run that way but a crf450 timing chain is in your future. What did you do to remove the auto decompression? This is a multi part process is why i ask.

Your jetting is gunna be way off. But it should still start.

 

[Jaka Klenovšek]

Slightly stretched timing chain. It will run that way but a crf450 timing chain is in your future. What did you do to remove the auto decompression? This is a multi part process is why i ask.

Your jetting is gunna be way off. But it should still start.

Yes I have crf timing chain, bought new one for trx and it was more streched than old crf chain.. crazy.. so I put old back in.
But forget about this I got it running!! decompressor is the problem. I have lossen right exhaust valve and it started. I have removed plunger and spring before which activates decompressor am I right? And looks like its not enough, can I remove the decompressor clutch on camshaft and put like this back in (picture)??

 

[SamUK]

Not sure on these sports motors but I’m assuming they have a woodruff key on the crank (flywheel) hasn’t sheered has it? Moved a fraction?
I had this on a trx420

 

[SlammedRanger]

Thats where i was headed. Figured the mechanism wasnt removed. Yes you can remove the mech but you need to cover the big oil passage that is drilled in the cam under where that mech was. I have done a few things to cover it with succes both ways. I have found a rod that fit up the center of the cam and filled the hole with sleeve compound and put the whole thing in a zip lock bag to remove as much oxygen as possible from it. Then removed the rod and was left with a perfectly shaped and covered hole. I have also threaded the hole and put a screw in it. Cut the end off so only the tip was left threaded in and red loctited it. I trimmed it as close to flush as i could so it would be the least amount of matrial to not throw off the balance of the cam. Aftermarket cams dont have that decomp mech at all. No real need for it. Its a by product of the fact the 400ex motor is a xr400 motor without a kickstart and a few power decreasing previsions.

 

[Jaka Klenovšek]

Thats where i was headed. Figured the mechanism wasnt removed. Yes you can remove the mech but you need to cover the big oil passage that is drilled in the cam under where that mech was. I have done a few things to cover it with succes both ways. I have found a rod that fit up the center of the cam and filled the hole with sleeve compound and put the whole thing in a zip lock bag to remove as much oxygen as possible from it. Then removed the rod and was left with a perfectly shaped and covered hole. I have also threaded the hole and put a screw in it. Cut the end off so only the tip was left threaded in and red loctited it. I trimmed it as close to flush as i could so it would be the least amount of matrial to not throw off the balance of the cam. Aftermarket cams dont have that decomp mech at all. No real need for it. Its a by product of the fact the 400ex motor is a xr400 motor without a kickstart and a few power decreasing previsions.

Thanks, done like you said, I have welded both holes. It has 170psi compression now :eek.. Now a question about jetting. Its 440 now, stock camshaft, fmf exhaust, K&N air filter.?

 

[SlammedRanger]

Airbox lid on or off? And holes or modifications? Full pipe or just a slip-on? Any port work?

 

[Jaka Klenovšek]

Airbox lid on or off? And holes or modifications? Full pipe or just a slip-on? Any port work?

Lid on with holes in it, full pipe, thats all.

 

[SlammedRanger]

180-190 main jet. 45 or 48 pilot. Should get you close enough to do plug chops and dial it in.