Fuel pump?

Romanyak256

Romanyak256

PR Addict
So i have a question for the mechanical guru’s on here. I have a 2021 450 sxf and back in January i was at 62 racing. Practice the bike ran great. Come time for heat races, bike starts no issue, grab the holeshot and bike dies going into first turn. Get up off the ground and bike starts right up and i finish the heat and get 1st. Main event, same thing bike runs fine, go into first turn and it dies again… little harder to start this time. Finished 2nd, and as I’m pulling off the track bike dies. I put it on the stand, and try to start it and it runs for 2/3 seconds and dies, and it’s still like that today. I’m thinking it’s the fuel pump, but I’m no mechanic, so what do yall think it could be? Any advice helps. I just want the bike running before area qualifiers. I got the bike from a trade, and i highly doubt the pump or filters have ever been changed, and owners manual suggests fuel filters every 10 hours and pump yearly.
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Romanyak256 said:
So i have a question for the mechanical guru’s on here. I have a 2021 450 sxf and back in January i was at 62 racing. Practice the bike ran great. Come time for heat races, bike starts no issue, grab the holeshot and bike dies going into first turn. Get up off the ground and bike starts right up and i finish the heat and get 1st. Main event, same thing bike runs fine, go into first turn and it dies again… little harder to start this time. Finished 2nd, and as I’m pulling off the track bike dies. I put it on the stand, and try to start it and it runs for 2/3 seconds and dies, and it’s still like that today. I’m thinking it’s the fuel pump, but I’m no mechanic, so what do yall think it could be? Any advice helps. I just want the bike running before area qualifiers. I got the bike from a trade, and i highly doubt the pump or filters have ever been changed, and owners manual suggests fuel filters every 10 hours and pump yearly. View attachment 81143
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You running race fuel? I know there was some issues last year with bad race fuel taking out the seals in the fuel pumps.
 
MX955 said:
You running race fuel? I know there was some issues last year with bad race fuel taking out the seals in the fuel pumps.
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Nope just pump 93. The kid who had the bike said it sat in his garage for awhile. I’m thinking maybe the fuel went bad in it. I ran maybe a tank through the bike before this issue started. A few people who have had ktm’s said this is how the bike acts with a bad fuel pump, but i want to be sure before i dump out $300 for a new pump.
 
hershey said:
Do the 4 strokes have a crank case pressure sensor? Sounds identical to what happened to our injected 125
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"Crank case pressure sensor". . . . . that's crazy.
Might as well have a crank angle sensor, MAS sensor and O2 sensors while they're at it.
And then include an OBD-II port so you can pull down the bikes' diagnostic codes.
 
NQ1965 said:
"Crank case pressure sensor". . . . . that's crazy.
Might as well have a crank angle sensor, MAS sensor and O2 sensors while they're at it.
And then include an OBD-II port so you can pull down the bikes' diagnostic codes.
Click to expand...
NQ, have you even checked out a modern motocross bike? You do know that you can tune them with your smart phone? They are why my bikes are still premix 2 strokes with carburetors and kick starters.

Years ago my 520 KTM had a similar problem at a race. When I got home I drained some gas from the petcock into a clear cup. In time an iridescent sheen had formed on the surface. Then I remembered that I had found the cap off my gas can in the garage not far from a bottle of Mr. Bubbles bubble blowing solution. My very young at the time daughter had decided that my KTM needed premix just like my other bikes. I drained the tank and carb. With new fuel the 520 was back to normal. Would have been cool if it had blown a few bubbles along the way. Lol

e3963b46079d16fb5d443dd1295d43e4~2.jpg
 
hershey said:
Do the 4 strokes have a crank case pressure sensor? Sounds identical to what happened to our injected 125
Click to expand...
I just looked and it doesn’t have a crankcase pressure sensor. It’s jus weird if i hold the throttle open a little it stays running, but the moment you let off to idle it dies, that’s why im assuming its fuel pump… when the throttle is open its forcing fuel to be pulled, and when its at idle the pump isn’t pulling enough to keep the system fed.
 
k01 said:
NQ, have you even checked out a modern motocross bike? You do know that you can tune them with your smart phone? They are why my bikes are still premix 2 strokes with carburetors and kick starters.

Years ago my 520 KTM had a similar problem at a race. When I got home I drained some gas from the petcock into a clear cup. In time an iridescent sheen had formed on the surface. Then I remembered that I had found the cap off my gas can in the garage not far from a bottle of Mr. Bubbles bubble blowing solution. My very young at the time daughter had decided that my KTM needed premix just like my other bikes. I drained the tank and carb. With new fuel the 520 was back to normal. Would have been cool if it had blown a few bubbles along the way. Lol

View attachment 81149
Click to expand...
Yea,
I still receive my monthly MXA magazine and have seen the technologies working their way into the bikes over the years. When they began reporting on changing ignition mapping with your smart phone I began to glaze over and tune out. I fight through and troubleshoot technology issues every day at work and in my cars at home. I think about and ride dirt bikes to get my mind away from controls problems.

I wonder what the future for these bikes looks like when these technology parts phase out and become difficult to find, especially starting motors for those with only a button and no kicker? Even on the low and no-technology vintage bikes, many parts are becoming scarce.
 
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