Engine popping


8 replies to this topic
  • rhinoracin

Posted February 02, 2012 - 04:40 PM

#1

Have an 09 with 5 hours, it was sitting with gas in the carb for a while. When I'm riding it, the engine sputters if Im below 3/4 throttle. It cant keep a steady RPM without doing this, and the engine pops a lot when I let off the gas. I cleaned out the entire carb and all the jets yesterday, and replaced the spark plug, and it still has the same problem. I adjusted the fuel screw and I think that helped a little when I had it past 2 turns out. What could be causing this problem? the bike is basically brand new! I made sure the pilot jet was cleaned out, but should I just replace it?
Also the jet baffle in the carb was loose after I put all jets back in, is that how its supposed to be?

  • trevTFD

Posted February 02, 2012 - 05:53 PM

#2

i have the same issue with my 07 yz 450. i was told by some buddies it wont hurt the bike. When i rode in higher elevation, it went away....my guess would be its running too rich on oxygen....sorry not much help

oh and it came back when i rode in so cal low elevation

  • grayracer513

Posted February 02, 2012 - 09:43 PM

#3

That's called lean when they do that because the terms refer to the amount of fuel, not air.

If it isn't an air leak in the exhaust because of a loose joint, the idle's too lean (when you go to altitude, the bike gets richer because there's less air). See this thread:

http://www.thumperta...599#post3710599

  • rhinoracin

Posted February 05, 2012 - 09:59 PM

#4

Rode in the desert this weekend where it was much warmer, and it was still running lean. I know WR's and trails bikes come lean from the factory, but never knew MX bikes did. I will probably move up to a 48 pilot and 165 main, but what needle should i go with? Is it worth it to buy a JD jetting kit? or is the stock NFLR needle good?
I plan on installing a Twin Air powerflow kit to remove the backfire screen when rejetting. I ride all around so cal and desert, elevation 0-2000 ft, warm temps.

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  • yz450fcranker

Posted February 06, 2012 - 01:34 AM

#5

get a yamaha mechanic to do the carb work for you they are so good at it

  • grayracer513

Posted February 06, 2012 - 07:35 AM

#6

Rode in the desert this weekend where it was much warmer, and it was still running lean. I know WR's and trails bikes come lean from the factory, but never knew MX bikes did. I will probably move up to a 48 pilot and 165 main, but what needle should i go with? Is it worth it to buy a JD jetting kit? or is the stock NFLR needle good?
I plan on installing a Twin Air powerflow kit to remove the backfire screen when rejetting. I ride all around so cal and desert, elevation 0-2000 ft, warm temps.

A 45 should be big enough if the carb is clean internally. The PowerFlow kit will do nothing for you, BTW.

  • rhinoracin

Posted March 08, 2012 - 04:37 PM

#7

After some jetting changes, my bike still has the same problem. At constant RPM/throttle, it surges, sputters, and cuts out. It can also take forever to start and seems to use alot of gas. It's worse in colder conditions or when the engine isn't hot. Ive done everything I could with jetting and just ended up too rich, it covers up the problem a little but its still there. I've heard some people say the stock muffler causes the problem, but I find that hard to believe. I really want to find out what the problem is. Any more ideas?

What is the best way to check for intake leaks? Is it possible that dust could have been sucked into the motor if there is a leak?

Edited by rhinoracin, March 08, 2012 - 06:42 PM.


  • BBrown626

Posted March 08, 2012 - 06:46 PM

#8

Begin with a thorough cleaning and replace your jets. I soak them in simple green overnight and it works great. Just rinse with water and dry. if gas sat in there for more than a couple weeks, it may take a good cleaning to get the varnish out.
If you have a decent exhaust leak it should be indicated by a little soot. If you cant find a leak, take your exhaust completely off the bike. Reinstall with a new gasket. I use high temp RTv on the joints too.
While you have the carb off, go ahead and install an aftermarket fuel screw to make future adjustments easier. Two turns out is not too much. Follow the carb tuning threads.
Are you sure your carb is properly installed and sealed up tight?

  • rhinoracin

Posted March 08, 2012 - 07:33 PM

#9

Already cleaned the carb out good, put in new jets and a fuel screw





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