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I just bought an 04 crf250r, from a dude that has struggled with starting it. He is a bike guy, has many dirt bikes and got so frustrated with this one after spending a TON on it, he basically gave it away to me.

Its never started well according to him, so he went all out and bought/did every possible thing out there to improve it, with no luck.
List as follows.

APE cylinder head (new)
new piston/rings (13.5:1)
Hotcams stage 2
new CDI
new stator
new cam chain (oem Honda)
new kill switch
decomp mod to cam
new plug
new coil
new flywheel (stealthy weighted)
Carb rebuilt
valve clearance is: INT- .007
EX- .008
So maybe a bit tight on exhaust and a bit loose on intake, can this seriously affect starting that much?
I have read others like to set the ex a bit tight, but never seem to read much about intake being loose.

Cam timing has been checked by him, others, and myself probably 100 times. I have taken cam out, rolled motor over, reinstalled, lines up the same everytime.
It has spark, tried both cdi boxes, has tons of compression, gets fuel.
It will backfire/pop every now and then if I twist throttle enough times to prime it, but never comes close to starting.

It has a rekluse Z-start clutch, so can't bump start it.

Its getting frustrating, maybe the stealthy flywheel is causing issues? It looks fine, what can go wrong with it?

Thanks

Paul

Welcome to the site !!

Well it seems it has been gone thru extensively , when you say its getting gas , how is this being verified ?? , at the carb ?? , at the plug ?? (is the plug wet or damp with gas after trying to start and then quickly removing the plug ?? ) , and no the flywheel will not have a effect on starting by being heavier , if anything , it should start easier

What is the actual starting procedure ?? , and has it started at all since rebuild ??

What is your current elevation , and what jets are in the bike currently ?? (or have been in it) **Pilot jet/Main jet** , stock is 40/160

Thanks for the reply. I am at sea level, not sure what jets it had, but I put it back to stock for now.
It seems to make no difference to starting, as it won't start with either set.

I can see gas shoot in from the accel pump, and the plug smells like fuel.

I have tried every starting procedure out there that I have read about, choke on/off, 3 twists, no twists, hot start/no hot start, 5 slow kicks after 3 twist prime, then hard kick, 50 fast kicks in a row until exhaustion.

Apparently is has run twice at some point with the new head, but it was always a massive battle to start.

About the only thing that stands out is the valve lash , maybe tighten the 7 to 6 and loosen the Exhaust to 11 and see what it does , also , for kicks , take some gas and pour about a tablespoon down the plug hole then stick it back in quickly and snug it down , and try to start it and see if it does or coughs , also , try about 6 twists of the throttle cold then full choke no throttle and give it 1-4 hard kicks

When you twist the throttle prior to start, you are shooting a little raw fuel from the accelerator pump into the cylinder to help a cold engine start. Those slow kicks are pumping that gas out without giving you any benefit. Prime it, then kick it like you mean it. After 2-4 kicks, re-prime. That doesn't mean that your technique is at all responsible for the no-start.


I have seen plenty of times where a spark is visible, but not adequate for the bike to run.

You've spent a fortune on parts for an older bike. Now take it to a Honda dealer and have them diagnose it. Best money you will ever spend, and you will end your frustration.

I have tried pouring a bit of fuel down the plug hole, nice big pop, but thats it.
I don't want to, but I am going to try a spray of starting fluid, see if I can get it to do anything on that.
I will also get a new plug, although the one I have is new.

BTW, I didn't spend any money on it, previous owner did, I bought it for cheap non-running.

Hard to imagine .001 of valve clearance could have such an effect on starting?

Like Leardriver mentioned , you may still not be getting enough fuel to the plug , and you may not be giving it a hard enough kick , you have to put your weight into these things to start them , you can't just sit on the seat and give it a kick like a 2 stroke , these things need a firm hard fast kick , if you try to kick it like you would after you just ran a mile , then it wont start , you need to kick it like a Harley and put your weight and ferocity into it , or it could even have a loose connection somewhere that you did not catch , maybe go back and check every single connection from the Coil , to the wires going to the Stator , but i would still correct the valve lash as that does make a difference , it may not fix the issue , but it will be eliminated as a possible cause , which it could be

Also just for kicks , pull the Hot Start Lever while kicking it , and see if it makes any difference ......

How are you timing bike? I had 07 same issues check timing on flywheel and adjusted cam timing to match and she fires within 2 kicks now.

How are you timing bike? I had 07 same issues check timing on flywheel and adjusted cam timing to match and she fires within 2 kicks now.

I have read this in other places too, so disregard the timing mark on the right side?

Timing marks should be aligned in all 3 places (Cam Gear , Ignition small round hole and Clutch side large round hole) for timing to be correct

Did you try starting with the Hot Start to see if it made any difference ??

So it just won't line up all 3 timing mark locations perfectly, if the cam is lined up to the flywheel marks (ign), then the clutch side mark is off a bit, if the clutch side mark is lined with the cam, then the ign side if slightly off.
I took off the stealhy flywheel and installed the stock one that has clear marks on it, and no change.

So tonight I tried timing it in 3 locations, setup to the clutch side mark, then one tooth either way on the cam. It won't generally do anything with each of the +/- one tooth timing setups. in the "correct" timing, it just back fires, kicks back via the kickstarter, and on 2 occasions it sort ran for a second or so.

No variation of starting it made a difference, choke on/off, hotstart on/off, throttle closed, open partially, or wide open.

Everything seems within spec, and it just won't fire.

I am going to install the stock clutch so I can bump start it (it has a rekluse), and at least verify it *can* run, if it does with bump starting, then I will know its something small with valve lash or in the carb somehow, even though both seem completely fine, other than the ex valves being a bit tight at .008, instead of .011, although I have read some folks do this to improve starting!

I had a 2nd person who knows bikes very well with me all night tonight verifying everything I was doing, we are both stumped.

Question .... Did the gear on the cam come on it or was it installed ?? , I am wondering if the gear slipped , also , did you try the original cam ?? (you did not mention if you still had it) , I am concerned that the timing marks do not align , and the only thing i can think of causing that would be the gear slipping on the cam and throwing everything off , which is why I am suggesting trying the stock cam just to see if it makes any difference as the gear on the 250's are pressed on as opposed to bolted like a 450 ........ worth a shot ......

Also , have you verified the Auto Decompressor is functioning correctly ?? , if its sticking , it could be holding the exhaust valve open causing a loss of compression and not allowing the bike to start .......

Decomp does work, it moves freely and clicks before TDC.

Its a press on gear with the cam.
The bigger issue I have with timing isn't so much cam, its the fact the right and left side marks of the crank don't match, if the punch mark on the clutch side is lined up, the ign marks are not and vice versa.
I can get the cam to match one or the other but not both.

And your positive the Flywheel keyway has not sheared as well , correct ?? , something has to have caused the misalignment , not saying that is 100% the cause of the starting issue , but you need to rule things out so you can be sure it is not the cause of the issue

Also , try 1 more starting procedure , just to rule out a fuel issue (make sure it has FRESH Premium first , if the gas is older than 3 months it wont start , and could be a large part of the issue)

Once you have Fresh gas , and have drained ALL the old gas out (disregard if this has already been done) of the tank and carb , then give the throttle 6 full twists , and pull the choke , then slowly push the engine over with your foot , till you feel the compression , then bring the kickstart up till its all the way up , then with all your weight , give a good hard kick , do this up to 4 times kicking like that , it should start by the 4th kick or at least start and die , my 450X requires 6 full squirts and the choke to start cold (with a elect. start) , my R requires no pumps , and a full choke and 4 hard kicks to start cold ...... what i am getting at is sometimes , the starting procedure itself is specific to your bike , what works for 1 bike may not work for yours , and yourself and the prior owner may not have been doing what is needed to start that bike...... not saying this is the case , but its worth ruling out as a cause , since you have pretty much all the components to run , it is getting to the point of being a possible starting procedure , or something (a coil wire unplugged from removing the tank perhaps) that is causing all this , sometimes the simplest things can cause major issues

Try it and report back , running out of ideas , if that changes nothing then you may end up having to do as Leardriver said , and cut your losses and take it to the dealer to diagnose , it may end up costing a bit to find the issue , as they have the test equipment that you lack , so they most likely will find the cause , but its going to cost , unless you can get them to "diagnose" without replacing anything , for a set price that is agreeable to you , and unfortunately , none of us can physically be there to witness and go over things to be sure what is what , so we may be missing something , because you did not notice it , as we can only diagnose what you tell us is going on , if you missed something , then so do we .............. But try the starting procedure (including FRESH Premium) and report back , maybe your results will bring something to the surface for us to figure out ...........

Tank was drained, carb fully rebuilt with new everything last week.
It has fresh race gas.