2004 CRF450 carb issues, won't run!

[Kbritt14]

I just bought an 04 CRF450 that had been sitting for a long time. When I got it only ran with the choke on, and at idle only. If you turned the choke off, or give it gas, it immediately died. The gas was horrible, so I dumped it and even rinsed out the tank. I've replace the fuel hoses, petcock valve, bottom tank fuel fitting and filter, air cleaner, spark plug, and cleaned out the carb and put a new carb kit in it. I even checked the valves clearance and they were perfect! Put new gas in it and still get the same thing!! Ugh!!! I read on a previous post something about an air leak where the hot start cable connects to the carb. Could this be my issue??  

Any help would be greatly appreciated!!

Kevin

Edited August 1, 2017 by Kbritt14

[FORMA MOTO]

You need to rebuild the carb with KEIHIN parts only, no 'kit' parts. Besides, they skip the important stuff.

Read this link:  http://www.dirtrider.com/features/protips/141_0707_keihin_fcr_carb_rebuild/

You need to replace the apump diaphram, slide plate seal, Needle jet (emulsion tube), fuel screw oring (preferably just get an R&D fuel screw), service the hot start plunger and cavity for corrosion, and replace the hot start cap with a new alloy version (ebay).

You have to do all of this if you want it to work out!

 

You need to REAM the passage above pilot jet as it has a sharp bend. Use small copper wire and solvent.

 

 

 

[Kbritt14]

Ok, so I took another look at the carb and the schematic of all the parts. What I found, believe it our not, is the mixture screw was totally missing! I didn't even catch is because I never took it out. I put a new one in and got it to run, but it has issues. Couldn't get it to start with the choke on, but did with it off and a little throttle. It's popping bad when you let off the throttle and won't idle. I backed the mixture screw off 2 turns when I put it in. Too rich maybe???

I've worked on bikes for years and can rebuild anything, motors, transmissions, suspension, you name it. But when it comes to carbs, I need all the help I can get!!

 

Thanks!!!

[SlowDinoDog]

yep...won't start with enrichment circuit...but does with throttle...and you're running your fuel screw 2 turns out...quite possibly rich...

 

 

[Kbritt14]

Yep, went 1 1/2 turns, per stock setting. Waiting for the new floating valve set to arrive and putting it back together. May have had it in backwards, but when I pulled it out I noticed the rubber seal was toast!! 

[SlowDinoDog]

probably common on bikes as old as '04...unless you replaced it...then, yeah...maybe did something wrong

 

 

[Kbritt14]

Ok, got the new float valve installed and back together. It's starts right up with the choke on, but when I shut it off it won't idle. I can keep it running with the throttle, but she pops quite a bit. Mix screw is at 1 1/2 turns (stock). Also, when I pull the hot start she wants to die. I think, when the bike is running correctly, it should want to rev a little. 

So, too rich? issue with the hot start? Exhaust pipe gasket?

[FORMA MOTO]

Have you adjusted the idle screw ???

[Kbritt14]

Went from 2 turns out to 1 1/2 turns out, which is stock.

[FORMA MOTO]

1 hour ago, Kbritt14 said:

Went from 2 turns out to 1 1/2 turns out, which is stock.

Dude.....

Idle screw: turn it IN to raise idle. Turn as much as needed

Fuel screw: Turn to 1.5 turns out from full (soft) in,  to start

[Kbritt14]

Turned the idle screw in. Made it idle high with the choke on. Still wouldn't idle when I turned choke off. Mixture screw is at 1 1/2 turns.

[FORMA MOTO]

Yes, but did you adjust it / turn it in, with the choke off ?  With the choke, it is supposed to idle very high....

If it still won't idle...

...then your pilot circuit is still contaminated.  Ream the passage behind the pilot jet with soft copper wire and solvent. There is a very sharp bend.

[ossagp]

As old as that carburetor is I am counting on it needing ALL of the above suggestions.   For a carburetor novice it can look pretty intimidating.   The pilot circuit as mentioned would undoubtedly need attention by now.   

[Kbritt14]

Ok! So I pulled the carb apart....again, and pulled the slide out. The float valve seal was toast and broke in half. I replaced the float valve and seal, and pulled all the jets and made sure they where good. I even reamed the passage above the pilot jet. Put her all back together, adjusted the mixture screw to 1 1/2 turns and adjusted the idle screw.

SHE RUNS!!!!! Choke is working, she idles perfect! 

 

ONLY issues is she still pops a little when letting off the throttle. Not near as bad as it did, but I think just a little too much. Mixture screw setting????

 

[Kbritt14]

Well, I thought she was idling perfect. I backed the mixture screw out a 1/4 turn, but she still pops on deceleration. Also noticed that it wants to stay at a high idle when letting off the throttle for a few before dropping back down. 

[FORMA MOTO]

That is hanging idle

Can be caused by improper fuel screw adjustment ( you must start with a very low idle and one turn out, then raise the idle using the fuel screw) or an air leak ( most commonly at the hot start or the feul screw oring)

[Kbritt14]

Ok, Here's where we're at. Completely rebuilt carb (new jets, mixture screw, float valve, accelerator pump kit, everything!!). She seems to be running good now, with very little popping if any. I read that when you have the settings right, it should rev up when you use the hot start when it's idling (after it's warmed up of course). Mine still want to die. Could this be too rich or too lean???? I had the mixture screw at 1 1/2 turns (stock) and even tried 1 3/4 turns.

 

Any ideas???

[ScwhettyNuttz]

check your intake boot for cracks(between carb and head).  Also check your exhaust for cracks on the head pipe. 

Is the idle air jet still installed? Some people take them out.  On stock carbs thats a no no.  On aftermarket 41mm carbs its generally ok if you jump the pilot jet up. 

What pilot jet is in it? Should be a 42 from the factory, jump to a 45....Also what position is the slide needle in?

Edited September 11, 2017 by KeyKeeper

[William1]

Using the hot strt to 'check the fuel screw' is really terrible advice given by a guy who is clueless. The hot start is used for a over heated or dropped bike that is flooded. It dumps and unmeasured amount of air in to the inlet to dilute excess fuel. Not a method of checlking anything. some bikes will speed up a tiny bit. most might stall. Checking the adjustment of the fuel screw with the hot start is like seeing if you are too drunk to drive by having a shot of whiskey.

Fuel Screw/Pilot Jet
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the fuel screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle knob to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly).  Once warmed, slow the idle speed (knob) to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the fuel screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,850 rpm, but go by the spec in your manual.

[Kbritt14]

Totally stock carb. intake boot and exhaust look good, but I'll double check. I'm sure that pilot is a 42 and slide needle in center position, but I'll double check them as well. What will a 45 pilot jet do?

Thanks!