Diagnostics on a CRF450 that won’t start, summary of fuel and Carburetor operation and diagnostics

It is common on older carbureted 4 strokes to have issues with starting and carburetor adjustment can be complicated. Although there are several issues causing your bike to not start, this video explains diagnosing your fuel delivery and carburetor operation. I explain jetting and the main components to setting you carburetor including jet needle placement, main jet, pilot jet and pilot screw setting along with idle and the fuel pump squirt to get your carburetor tuned right so it will run. If it still won’t start after adjusting the carb it is likely due to your valve conditions and adjustment in the head which will be covered in another video.
Video by Jay Clark
• 4 Stroke Fuel Mixture ...

[@d.l.horton2093]

I had a no start problem with a 03 CRF450R and rebuilding the carb and checking the valves revealed the problem. The valves were too tight and I went down the to smallest shim I had to get ,006 clearance and the carb was old and the gaskets were bad and jets were clogged. That and a quick oil change after a quick ride got a lot of black oil out of it. Runs pretty well now. 5 kicks maybe to start it up?

[@chadurbanski3468]

Man i need help bad. I have a 04 crf450r. Runs great when it starts. But ive been chasing this hard start issue all over. Did valve clearances plug carb clean and coil. Nothing has helped. When i kick it will pop with each kick like it wants to fire but just isnt happening at the right time. I checked timing so many times i lost count. I even went couple teeth forward and back and its always the same situation. I need some guidance please.

[@socal.hondabuild8349]

Have you rebuilt your head? Replaced your valves and recut your seats? I would take it to a mechanic that can rebuild your head and cut the seats, popping and not starting is not a carb issue, likely the head. Take it off and to a local dealership and have it inspected 👌

[@Megabiggie]

I would really appreciate your input, I have a 2004 Honda crf450r it only runs when you push start it or if you squirt fuel into the intake, it backfires when you kick it over. I cleaned the carb and everything so I’m not sure what to try next, thanks!

[@socal.hondabuild8349]

Have a look at the head, shim the valves, inspected the valves and seats. Go ahead and pull the head off and take it in to have it inspected. Have a look at this video

[@socal.hondabuild8349]

@@Megabiggie kzbin.info/www/bejne/rmGZgYqArciBg68si=DUEBYDd0ox-eDqW5

[@Megabiggie]

@@socal.hondabuild8349 appreciate it, I took of the head, put it at top dead center, and it turns out who ever put the cam in last put it backwards 🤦🏽‍♂️

[@Megabiggie]

@@socal.hondabuild8349 all I had to do was spin the can around, bikes than flawless now, starts first kick 👍

[@socal.hondabuild8349]

No comments or recommendations other than non-typical conditions would prompt me to pull the head and cylinder off and have a look, never hurts to have a look. If you can do this work it helps, check out some of my videos on top end disassembly

[@Playersclub415]

I have a question would really appreciate you input & help. I have a 2006 Honda 450R the carburetor in your video is identical. The Honda sat for about 2 years with the same fuel. I drained and refilled with fresh fuel. My quad would start only if adding some fuel in the intake run with mid to high throttle and shut down at an idle. I ordered a rebuild kit on amazon. Dis assembled cleaned all ports. Replaced true jets and seals supplied in the rebuild kit. After reinstalling the carb my Honda would not start. Not even with fuel sprayed in the intake. I ordered a replacement carb on line had the same results. I’m very surprised it will not even start for a moment. My next plan off attack is to check if the valves are too tight. Do you have any advise as too why i may have starting issues after rebuilding & replacing the carburetor?

[@socal.hondabuild8349]

Yes your valves would be a good place to start, when they wear they stay open from a tight or no gap with the cam. Take your head off and take it to a mechanic, have your valve seats replaced and recut and replace the valves with stainless steel they will last longer. If it won’t start this is certainly the issue, the bike absolutely will not start if the valves are wore and hanging open allowing air into the intake and preventing it from starting even if you added gas and fire from the plug. Hope this helps

[@Playersclub415]

@@socal.hondabuild8349 appreciate your reply. I did a compression test & have 40 psi max. That’s seems low, do you happen to know the compression specs?

[@socal.hondabuild8349]

@@Playersclub415 I do not, I would go ahead and pull the head and have a look at the valves, I’m pretty sure with the age that’s the likely case, if you flip the head over and clean the carbon with ether you’ll see the gaps between the valves and seats quickly

[@socal.hondabuild8349]

You are also going to want to disassemble the entire carb including the mid-body, that needs to be cleaned as well, it can get completely full of gunk

[@kurthaggarty2360]

Would this be the same carb as an 05 crf450x?

[@socal.hondabuild8349]

Yes very similar FCR carb, the book will outline any differences between years which are minor from 02-08….I would recommend getting the Clymers Manual for your year

[@gunterkison2700]

The bike at the end is a 2002?

[@socal.hondabuild8349]

Yes it is, I made brackets to mount 2017 plastics, check out my other videos on updating the plastics

[@socal.hondabuild8349]

kzbin.info/www/bejne/qpaQm42LmsiVebM

[@socal.hondabuild8349]

Video on modernizing this 2002 CRF450 kzbin.info/www/bejne/iIPYg2h_dsp-jrM

[@gunterkison2700]

Awesome thanks

[@azm1azm1azm1]

On a 03 KTM 450 after complete top end rebuild , cylinder re sleeve, new piston & new titanium valves and new adjustable accelerator pump with every thing tuned and running perfect. one day after a few months my muffler started melting my side plastic muffler cover, then a few days later the bike starts to lose power at higher RPM. Any ideas ? Thanks for any help on this. Carb is KEIHIN FCR-MX 39 Carb jets stock 170-40, in shop book 175-48 Jets In as of 03-22 - 178/50

[@mineer-pg5sv]

Did you ever figure out the problem?