Jump to content
Sign in to follow this  

03 CRF450R Hard to start when cold and backfires bad on decelleration

Recommended Posts

I just recently purchased a used 03 450r. I started it and rode it when I looked at the bike. It has plenty of power in all gears and rpms. It will idle but when decellerating either while riding or while rapping the throttle while on stand it will backfire like tossing a small pack of fire crackers on the ground. They are quick bang bang bang. Usually about 4-5 pops. I thought maybe the spark arrestor was clogged or something else. I removed the Spark arrestor and then it shot a flame out the pipe every time it backfired. So I put the spark arrestor back in so I didn't catch my garage on fire. I have cleaned the entire carb with no positive results. I checked the hot start and all is good. I checked the intake and exhaust valve clearance and it is off but not closed. The right intake valve is at .015 and the left is around .09. exhaust valves are spot on. I didn't check the decompression yet. I checked for airleaks form carb to intake good. I checked header pipe no cracks. Compression is great.

I changed main jets to see if it would help and didn't help any except with top end power. I pulled the pilot jet about 4 times and recleaned it incase somthing was in it. Put in fresh premium gas no improvement.

My jets are 45 pilot 178 main and needle at 5. I am out of ideas :banana:. it is pretty much stock except for a yoshimura pipe. Any input or ideas would be great. I just dont want to spend money on things that wont resolve it. I also changed the plug. the one I pulled out was dark in color at the base by the threads and the little arm that the electrode sparks to(I dont know the proper term) was frosty tan.

I played with the fuel screw went everywhere from 1 1/2 turns to 2 1/2 with no real noticable difference except for made it not idle as well.

PLEASE HELP!! :lol:

Thanks

Jason

Share this post


Link to post
Share on other sites

Main Jet seems large...also, check out the Intake Forum for correct procedures in setting the fuel screw, that can be a cause for popping on the decel. An exhaust leak can also cause popping on the decel.

Buying an after market fuel screw and adjusting while riding and testing with a load on the bike is much more accurate than stand testing.

Share this post


Link to post
Share on other sites

from what I see for 0-999 feet elev temp 19 degrees to 40 degrees

PS 1 3/4 turns out

SJ 42

JN clip 6th

MJ 172

and from 39 to 60 degrees

ps 1 1/2

JN clip on 5 th

the rest is the same as above

Share this post


Link to post
Share on other sites

I will pick up a 42 slow jet and give that a try along with putting the MJ lower. Yes the oring is on the pilot jet. I ofund it when I cleaned it the lat time.

Share this post


Link to post
Share on other sites

Well I picked up a 42SJ and 172 MJ and adjusted the PS to around 1 5/8 cause it was a little cooler out.

It started easier, ran better, kind of hung on the rpms when pulling in the clutch from a hard accel. It idled almost down to nothing. It still backfires not as much but some when letting off throttle without pulling in the clutch. It will still pop and bang some when blipping the throttle while sitting unloaded. All in all it did improve alot over previous run. I also changed the head pipe gasket just in case it was leaking.

I did notice it will heat up pretty quick though when just sitting idling. do you think my impeller may be bad or is it the nature of the beast. My CR250 will heat up to but no where near as fast.

I ordered a valve shim kit to get the valves closer to tolerance. I also adjusted the decompression arm out a little more the gap was at over 30 I set it to 28 and it made it alot easier to start. It will kick and sputter some when just idling but it may be cause of the cooler temps outside.

Any more input would be greatly appreciated. I want this machine to run like it is supposed to. Could I possible need a new top end. the compression feels great but haven't put a guage on it yet.

Thanks in advance

Jason

Share this post


Link to post
Share on other sites

My 03 was poping nicely( just got mine to) , had some leaky joints in the silencer and the connection to the header pipe. Runs way better now!

Share this post


Link to post
Share on other sites

Your impeller is probably fine....these bikes do heat up fast, they want to get moving. You could always re-furb the cooling system for peace of mind. New impeller, change the coolant and use an additive like water wetter or engine ice. Most likely end up with the same scenario though when in slow moving situations. I have the same problem when riding tight technical stuff on my 02' and really like the idea of fabing up an overflow under the skid plate using the system from a CRF450X. You can search "turkey baster mod" for more on this.

Symptoms don't sound like top end problems but if you recently bought the bike and are unsure of the maintenance history it would be wise.

Share this post


Link to post
Share on other sites

my silencer has the lead looking crush bushing in the silencer pipe to connect to the headr. Is there something I can do to tighten the joint? I know the joint isnt super tight and I broke the bolt on the flip lock clamp. I ma having troubles finding a new clamp. I rigged it for now with a heavy hose clamp but it is not holding tight at all. It did backfire before I broke the bolt but I didnt check the joint tightness before bolt broke. Could I put high temp rtv on the joint and seal it that way or should i buy a new lead crush bushing and find a alternative clamp?

thanks in advance

Jason

Share this post


Link to post
Share on other sites

My 05 was doing the same thing until I installed a 48sj. I am at 4500 feet and with temps in the 50's. Now it's a one kick start and no backfiring on decel.

Share this post


Link to post
Share on other sites

Well I shimmed the intake valves. Put in a remote fuel screw( no more screw driver and twisting carb for me :thumbsup: ), checked the stator for metal shavings ( None) . All of this and no change still hard as hell to start and idles rough with major backfiring. So after all this work with no positive results. I decided to try a couple more pilot jets. Picked up a 45 and a 48. I had a 42 in it and it worked better when it was in the 60s here but it is in the high 40s now so I am kicking my life away trying to start this thing plus when it was running better with the 42 in it I have a FS adjusted out to 3 turns. So since it is colder out and the fact I had the FS out 3 turns even when it was 60 outside. I decided to jump straight to the 48 PJ. Now it will start on second kick without choke on when warm. It still backfires a little but no where near as bad. It is a bit rich. Idle seems to fluctuate. If you rap it once it will idle up a little then slowly idle back down. I might need to raise the needle one notch since it is colder out and get the midrange a little richer. If this helps and it is groggy then I may put in the 45 PJ and see what happens. This is a long process but I am bound and determined to get it right. I would hate to pay a mechanic 80 bucks a hour to do something simple that I could have done myself.

Any other input would be great as I am just randomly trying things now. Also I know it is not an exhaust leak I have a new gasket on the head and have the pipe to header clamped as tight as I can get it without breaking the bolt again.

Jason

Share this post


Link to post
Share on other sites

FINALLY.

well with the 48 PJ and the FS out 2 1/4 turns. It is finally making me happy.

I took it out today and rapped on it a little bit. The idle was hanging when clutch depressed after a fast high rev run. So I kept lowering and lowering the idle to it quit. Now idle doen't hang high it drops instantly. It idles so low that I almost think it will die but it doesn't.Also the transition from idle to WOT is great. It still pops very suddle like when letting off gas from a run without disengaging the clutch but it is a very light pop or backfire.

I am new to four stroke race bikes but are these supposed to feel like a slight powerband like a 2 stroke when reves get up a bit? My 2 stroke has a nasty Power band but it doesn't feel like the four stroke one. I didn't know if maybe my midrange was rich and once it hits the higher revs it gets into the main jetting and pulls?

Jason

Share this post


Link to post
Share on other sites

its cured :thumbsup: I done a multiple of things but I believe it was the carb plate was installed upside down from the guy I bought it from. He said the carb was cleaned by a liscensed honda dealer but he must not have. Also I replced the head to header gasket. I was also having issues getting a good tight clamping on my stock head pipe to the Yoshimura muffler so I took the head pipe to a local service station and had the flare the pipe to fit the inner diameter of the yoshi pipe and it looks cleaner and seals alot better. After doing the multiple of fixes I was able to turn the throttle stop screw down about a turn and a half to get it to idle nice and it purred like a big kitty. I was able to start it on first kick to which I was never able to do before.

I am a happy happy camper.

Thanks to everyone who helped with the fixes.

Jason

Share this post


Link to post
Share on other sites

thanks for the follow up.. Good thread to find for folks having issues

Share this post


Link to post
Share on other sites

Well, you found it. It was the first thing I thought of. I dont care if your licensed or certified or what, getting the vacuum release plate in upside down is pretty easy if youre not familiar or distracted with what your doing. The crazy part is, it fits really good when wrong.

Now, fix your jetting. It's hellishly rich right now. Put the 42 PJ back and turn your fuel screw in to about 1.5 out and start dialing there. Otherwise it'll be lazy off the corner.

Share this post


Link to post
Share on other sites

yeah I am going to put the 42 back in and see what this animal has now that it is right. My only concern is how long the guy I got it from rode it like this? It may be why I got it so cheap from him cause he thought it was trashed. Well my gain I guess. I just hope that it being wrond for so long didn't hurt anything being ran like that.

Thanks again to everyone thta helped out

Jason

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×