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Suspected Mixture Issues

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Hi All,

I`ve been working on a friend`s CRF450R 04 because it stopped starting for him. Upon removing the carburetor and inspecting it, it looks like the bike has sat for a while and got some sediment in the bowl, All the jets and pilot fitting was covered in corrosion so i purchased a carburetor rebuild kit from Pro-X here in Australia as it provides the aftermarket pilot screw i can adjust while the bike is running. I`ve installed the full rebuild kit and replaced all the jet`s and pilot screw as they come in the kit. Turned the mixture out 1 1/4 turns and the bike starts. So i took it out for a ride and noticed that when using the engine to brake on the downside of a hill the engine backfires alot. After some testing and mucking around with the mixture screw the only thing that will make it run smooth is having the choke pulled out all the time. If the choke isnt out the engine refuses to idle at all but with the choke out it runs perfect. Its got me boggled why this would be. I`ve had motorbikes and serviced my own since i was 16 and ive never had this issue before . Usually an adjustment of the mixture screw clears these idling/backfire issue right up.

My mate bought this bike second had and has maybe ridden if lucky 12 hours on it, so we are not too sure of any engine works that have been done. All i know is its got an aftermarket pipe. Everything else looks stock. i didnt see anything that looks like the carburetor has been modified either.

 

Anyone have any tips?

Regards

Danny

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If it runs good with the choke on, isn't that a sure sign that it's too lean?

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I would be really curious as to whether the jets that came in the kit were the same sizes as the ones which were removed,  and if the float level was checked and set upon finish. 

12 hours ago, Kornster said:

Hi All,

I`ve been working on a friend`s CRF450R 04 because it stopped starting for him. Upon removing the carburetor and inspecting it, it looks like the bike has sat for a while and got some sediment in the bowl, All the jets and pilot fitting was covered in corrosion so i purchased a carburetor rebuild kit from Pro-X here in Australia as it provides the aftermarket pilot screw i can adjust while the bike is running. I`ve installed the full rebuild kit and replaced all the jet`s and pilot screw as they come in the kit. Turned the mixture out 1 1/4 turns and the bike starts. So i took it out for a ride and noticed that when using the engine to brake on the downside of a hill the engine backfires alot. After some testing and mucking around with the mixture screw the only thing that will make it run smooth is having the choke pulled out all the time. If the choke isnt out the engine refuses to idle at all but with the choke out it runs perfect. Its got me boggled why this would be. I`ve had motorbikes and serviced my own since i was 16 and ive never had this issue before . Usually an adjustment of the mixture screw clears these idling/backfire issue right up.

My mate bought this bike second had and has maybe ridden if lucky 12 hours on it, so we are not too sure of any engine works that have been done. All i know is its got an aftermarket pipe. Everything else looks stock. i didnt see anything that looks like the carburetor has been modified either.

 

Anyone have any tips?

Regards

Danny

 

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You gotta love this; the thread started in Australia, went to Florida, now Alaska. Back when I started riding, you only found out about stuff from your ridding buddies in the neighborhood.

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18 hours ago, drumiv said:

If it runs good with the choke on, isn't that a sure sign that it's too lean?

Thats what i thought, but when i adjust the mixture screw out the bike immediately starts to run rough. So i started a 1/12 and worked up to 1 3/4

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11 hours ago, ossagp said:

I would be really curious as to whether the jets that came in the kit were the same sizes as the ones which were removed,  and if the float level was checked and set upon finish. 

 

The replacement float needle is exactly the same as the old one. The float itself is still the stock one. This is the kit i got http://www.bbimporters.com.au/search/myob_lookup.php?itemnumber=44.55.10462 

In the kit there was some additional brass fittings that i don't now where they are for. All i replaced was the mixture screw, Pilot,Throttle needle & Main jet. I was only really after the aftermarket mixture screw so i could adjust the mixture with the bike running as its impossible to do with the factory mixture screw with it being recessed into the front of the carby and bowl.

The only think i noticed was there was what i assumed to be Vacuum tubes that had been cut to about 10 cm`s and i was under the impression they are supposed to be longer to drain off excess fuel from the carby. They where connected to a t Junction pipe.

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1 hour ago, Kornster said:

Thats what i thought, but when i adjust the mixture screw out the bike immediately starts to run rough. So i started a 1/12 and worked up to 1 3/4

im 2 3/4 turns out, thats what it took to keep my bike from always wanting to stall and not wanna start. 

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1 hour ago, Kornster said:

The replacement float needle is exactly the same as the old one. The float itself is still the stock one. This is the kit i got http://www.bbimporters.com.au/search/myob_lookup.php?itemnumber=44.55.10462 

In the kit there was some additional brass fittings that i don't now where they are for. All i replaced was the mixture screw, Pilot,Throttle needle & Main jet. I was only really after the aftermarket mixture screw so i could adjust the mixture with the bike running as its impossible to do with the factory mixture screw with it being recessed into the front of the carby and bowl.

The only think i noticed was there was what i assumed to be Vacuum tubes that had been cut to about 10 cm`s and i was under the impression they are supposed to be longer to drain off excess fuel from the carby. They where connected to a t Junction pipe.

Since you didn't give me the sizes of the ones you took out,  I still wonder :ride::ride:

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You need to clean the carb as well as replace the jets. The fuel screw and pilot jet passages are really small and plug up almost always.

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On 24/03/2017 at 5:53 PM, ossagp said:

Since you didn't give me the sizes of the ones you took out,  I still wonder :ride::ride:

Hi ossagp, I just ordered a carby rebuild kit. I dont know the sizes sorry.

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On 25/03/2017 at 2:31 AM, galligar said:

You need to clean the carb as well as replace the jets. The fuel screw and pilot jet passages are really small and plug up almost always.

Hi galligar, This was the first thing i did with my compressor. Quite used to sediment getting run through carbys and blocking jets. The carby itself was stripped down and put in a container of kero for a few days to clean any crap out. I took it out and let it dry, gave it a clean and put the rebuild kit in.

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On 3/23/2017 at 10:53 PM, ossagp said:

Since you didn't give me the sizes of the ones you took out,  I still wonder :ride::ride:

I was afraid the question would be too difficult.  (Hint:  before you can undo something,  it is usually necessary to know what you did.) 

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20 hours ago, ossagp said:

I was afraid the question would be too difficult.  (Hint:  before you can undo something,  it is usually necessary to know what you did.) 

Hi ossagp,

 

I dont understand this response? 

Its an aftermarket Carburetor rebuild kit. All sizes are the same apart from the much better mixture screw which is really all i wanted it for. The jets looked exactly the same as well as the Throttle needle. The cir-clip on the throttle needle was placed exactly where the existing one was.

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I didn't understand your response either.   In a round about way you may be telling me that you checked all the replacement jets against the existing ones and found them all to be the same size.  But you never said that,  and that is what I wanted to know.  IE  if the previous owner jetted the bike for some condition,  and the replacement parts were different in size then you could produce the result you seem to have.

Best of luck.

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