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Yamaha Moto 4 YFM225 carb problems


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Hello all.  I have just stripped down the carb on my YFM225 as it is not running right.

I put it in the ultrasonic cleaner for half an hour and it has done a good job.

Nice clean jets but when I go full throttle it backfires, and there is a lack of power.

It also does not seem to take fuel in properly - it comes out the petcock ok so it is running freely enough, but it is not drawing into the carb.

If anyone has any ideas I would be very grateful.

 

Edited by Wolds Alpacas
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The ultrasound cleaner is great but will not get everything cleaned.  You may have to pull the carb off again and clean it out using a small piece of wire to get inside the jets. Use air to blow out all the orafaces. The float may be getting stuck and that may be your reason why fuel is not getting up into the carburetor.  Did you remember where the air/fuel screw was set at before you broke it down? If not set it at 2-1/4 turns out from a snug position. And adjust from there either in or out, which ever way the bike runs better while the bike is running and the air cleaner is installed. You may have to figure out a way to turn that air/fuel screw or make up a small angle screwdriver while the bike is running.   

 

Lastly what made you think it was the carburetor in the first place? What pointed you in that direction ? Had the bike been sitting ? 

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2 hours ago, 06kfx440 said:

That's to much fuel. Does your carb have an air fuel mixture screw? If so, turn it in 1/2 turn. If not then maybe something isn't set right in the carb. Or again. A vaccume leak. Check everything over.

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if its backfiring, doesnt that make it too lean?  And turning the air screw in would make it richer right?

57 minutes ago, Frank Angerano said:

The ultrasound cleaner is great but will not get everything cleaned.  You may have to pull the carb off again and clean it out using a small piece of wire to get inside the jets. Use air to blow out all the orafaces. The float may be getting stuck and that may be your reason why fuel is not getting up into the carburetor.  Did you remember where the air/fuel screw was set at before you broke it down? If not set it at 2-1/4 turns out from a snug position. And adjust from there either in or out, which ever way the bike runs better while the bike is running and the air cleaner is installed. You may have to figure out a way to turn that air/fuel screw or make up a small angle screwdriver while the bike is running.   

 

Lastly what made you think it was the carburetor in the first place? What pointed you in that direction ? Had the bike been sitting ? 

@Frank Angerano, is 2-1/4 turns out from snug generally the starting point for adjusting a carb?

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2-1/2 is where I start. But I’ve leared over the years that the smaller engines like my 220 bayou or my 250 bear tracker like to run at 1-3/4 turns out. My old bayou 400 was -2-1/2 turns out and and a hair further to be perfect.  

Have you checked for any rev limiters on the bike ? Does the throttle have any wiring going into it ?

Edited by Frank Angerano
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1 hour ago, Frank Angerano said:

The ultrasound cleaner is great but will not get everything cleaned.  You may have to pull the carb off again and clean it out using a small piece of wire to get inside the jets. Use air to blow out all the orafaces. The float may be getting stuck and that may be your reason why fuel is not getting up into the carburetor.  Did you remember where the air/fuel screw was set at before you broke it down? If not set it at 2-1/4 turns out from a snug position. And adjust from there either in or out, which ever way the bike runs better while the bike is running and the air cleaner is installed. You may have to figure out a way to turn that air/fuel screw or make up a small angle screwdriver while the bike is running.   

 

Lastly what made you think it was the carburetor in the first place? What pointed you in that direction ? Had the bike been sitting ? 

Thank you Frank, I did inspect the jets and could see through them properly which I could not before the ultrasonic bath.  This has a Mikuni carb and I am sure I read somewhere that they don't have a air/fuel mix screw - it is preset and been the cause of problems for other people..

3 hours ago, 06kfx440 said:

That's to much fuel. Does your carb have an air fuel mixture screw? If so, turn it in 1/2 turn. If not then maybe something isn't set right in the carb. Or again. A vaccume leak. Check everything over.

Sent from my SM-N920V using Tapatalk
 

Thanks for your feedback 06kfx440 - it is a Mikuni carb which I am led to understand does not have a mixture screw.  I need to look at the whole setup again in daylight.  I did see a video suggesting to check the inlet manfold which is rubber and always suspect on older machines. 

Edited by Wolds Alpacas
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4 minutes ago, Frank Angerano said:

2-1/2 is where I start. But I’ve leared over the years that the smaller engines like my 220 bayou or my 250 bear tracker like to run at 1-3/4 turns out. My old bayou 400 was -2-1/2 turns out and and a hair further to be perfect.  

Have you checked for any rev limiters on the bike ? Does the throttle have any wiring going into it ?

Thank you JacobSlabach for your input.  There are no rev limiters or wiring into the throttle Frank.

Tomorrow I shall spray some carb cleaner around the connections to see if there is a leak.

I have a Suzuki that is bogging down and backfiring as well which I recently bought which sounds like the same problem!

Thanks all.

Just now, Frank Angerano said:

It has to have the fuel air fuel screw. Some of them have a plug over them that has to be removed.  Weather drilled out or popped out. It should be on the bottom of the carburetor look for a round metal plug 

Thanks Frank - I will check tomorrow!  

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A quick update...

I sprayed carb cleaner around the hoses etc with no problems detected and so took the carb apart again and did a slight adjustment to the float and now fuel is running in much better.  I tried to make a tool to adjust the mix but it was pretty useless but I did set it about 1 3/4 turns out from the pinch point and it certainly runs a whole lot better so I have ordered up a small set of flat bladed screwdrivers that fit onto a 1/4" socket set - https://www.ebay.co.uk/itm/332842831621?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 which I think will allow me to get in there.  Once I get them I will fine tune that mix screw and let you know how I got on.

Thanks

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Well I got a small flat blade screwdriver now to adjust the mix but something is not right.  At a certain point I seem to get a lot of white smoke (odd as reading about that most answers refer to coolant mixing in - this is air cooled!)  Anyway, if I run it full throttle it bogs down or just runs rough - it seems to lack power, just seems to run out of steam and I can't get it to run smooth.....

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Well I got a small flat blade screwdriver now to adjust the mix but something is not right.  At a certain point I seem to get a lot of white smoke (odd as reading about that most answers refer to coolant mixing in - this is air cooled!)  Anyway, if I run it full throttle it bogs down or just runs rough - it seems to lack power, just seems to run out of steam and I can't get it to run smooth.....
Run a plug chop to confirm your on point with tuning you carb. Sometimes that's the only way to tell.

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It’s a carb adjustment most likely.  Unless the smoke is blueish? Then it would be burning oil. If not then it’s just a matter of dialing the carburetor in.  Try adjusting the needle on the main jet if needed but I would think it’s more of an air fuel adjustment.  Be sure the choke is opening and closing properly.   If it’s not opening all the way the carb will act up.    

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1 hour ago, 06kfx440 said:

Run a plug chop to confirm your on point with tuning you carb. Sometimes that's the only way to tell.

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Forgive my ignorance 06kfx440 - but what is a plug chop?

1 hour ago, Frank Angerano said:

It’s a carb adjustment most likely.  Unless the smoke is blueish? Then it would be burning oil. If not then it’s just a matter of dialing the carburetor in.  Try adjusting the needle on the main jet if needed but I would think it’s more of an air fuel adjustment.  Be sure the choke is opening and closing properly.   If it’s not opening all the way the carb will act up.    

Thanks for your continued support Frank - no, it is not blueish.  It is really in a bad place that adjuster so will have to spend some more time...

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A plug chop goes like this. Get a few spark plugs and put them in your pocket along with the socket or wrench. Start your quad and get it warm. Take it for a ride and when your almost to your house, run it full throttle for like 30 seconds to a minute. Then shut it off while your still full throttle. Coast to a stop. Take out the spark plug and look at it. If it's black and wet, then it's to rich. If it's dry and white. It's to lean. Do this a few times to get it really close.

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