larger or smaller pilot jet??


8 replies to this topic
  • RD73

Posted January 02, 2006 - 11:13 AM

#1

My 426 is difficult to start. I adjusted the fuel screw and can get it running but it seems that the pilot jet is off. The bike stumbles when given small amount of throttle. Also, it pops out the exhaust when trying to start.

I've searched and read through other posts, and think I need a smaller pilot jet. Am I headed in the right direction?

  • falshh

Posted January 02, 2006 - 11:32 AM

#2

All that popping when trying to start it sounds like its flooded (wet plug) Why do you thing it all of a sudden need a new pilot jet.I would pull the plug dry it out and try starting it again.My bike had the same problem and I found the throttle had been turned a few times and wet the plug and flooded the engine.I could never get it to do anything right until I pulled the plug and cleaned it (dried it).Give it a try.If you are new to 4-strokes, make sure you arnt pumping that throttle before starting.

Otherwise find out where you are on the pilot screw the bikes normally run about 1 1/2 to 1/34 out if the pilot is sized correctly. Put it a 1 1/2 out and turn it in 1/4 -1/2 and try it and then put it back to where it was and turn it out the same and see what it does.If you turn it out mor than 2 to 2 1/2 think about getting a larger pilot or the screw will eventually fall out (not enough spring press on screw).

  • grayracer513

Posted January 02, 2006 - 11:43 AM

#3

I agree. Start with a new or cleaned spark plug. Then check your pilot screw setting. The screw should be set to provide a normal idle by running it in until the engine begins to falter, then back out. The rpm should rise as you back the screw out, but will stop rising at some point. It is right about there that you want it set.

If once you get it set you find that it is less than 1 to 1 1/4 turns out, the pilot jet is too large. If it's more than 2 1/4 turns out or so, it's too small.

In case you don't have a manual, here's the run down on the procedure. It's for a 250F, but it works the same way.

http://www.thumperfa.../jetting.htm#PJ

  • RD73

Posted January 02, 2006 - 11:43 AM

#4

Some more info. I put in the 450 cam and had problems starting. Some guys on here gave me good advice about turning the fuel screw in and turning up the idle to get it going. After getting the bike running, followed the posted procedures for adjusting the fuel screw. Adjusting it in helped, but I could adjust past one turn out and it would still idle. So, my guess is that the pilot is rich, but I'm not sure. It runs strong throughout the rev range, except idle (and is tough to start)

I do give it some gas (no more than a couple small twists) before kicking it. It has a new iridium plug.

Also, it will not start at all with the choke (which I think richens up the mixture). If the pilot was lean then choke would help. Right???

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  • grayracer513

Posted January 02, 2006 - 01:08 PM

#5

The fuel screw SHOULD set up between one and two turns out, so going past one is not a problem. It will in fact, idle at 3 turns out, but it won't be set right, and it won't start well. Go back and review the procedure another time.

Most 426's should start cold with 1-3 twists of throttle for a prime and the choke pulled out. Normally, you should leave the throttle at idle to start it, but your bike may prefer to have the throttle opened VERY SLIGHTLY when it starts. By that, I mean less than one eighth throttle.

When warm, avoid twisting the throttle, and never use the choke. Keep the throttle closed, as before. Try with and without the hot start to see what your bike likes in different situations. If you think it's flooded, try it with about 1/6-1/4 throttle and the hot start to get a bit more air in it, but don't crank on the twist grip any more than necessary, or you'll wash the spark plug downstream.

  • SureBlue

Posted January 02, 2006 - 01:38 PM

#6

Like RD73 said, turning up the idle helps in starting the bike, a fact that often is overlooked. Turn clockwise in the idle screw half a round and adjust the idle down when the engine warms up. Elevated idle is also a good trick to prevent the bike from stalling on tight trails.

  • RD73

Posted January 02, 2006 - 02:05 PM

#7

Most 426's should start cold with 1-3 twists of throttle for a prime and the choke pulled out.

Full twists or short?

Try with and without the hot start to see what your bike likes in different situations. If you think it's flooded, try it with about 1/6-1/4 throttle and the hot start to get a bit more air in it, but don't crank on the twist grip any more than necessary, or you'll wash the spark plug downstream.


Try hot start when cold? If that helps, what does it indicate?

I guess I'm asking, how do I know if I have a problem with the pilot jet?

  • RD73

Posted January 02, 2006 - 02:06 PM

#8

I screwed up the above quote and included one of my questions in it. Sorry.

  • grayracer513

Posted January 02, 2006 - 03:29 PM

#9

Try hot start when cold? If that helps, what does it indicate?

That paragraph starts with, "When warm..."

I guess I'm asking, how do I know if I have a problem with the pilot jet?

Answered:

If once you get it set you find that it is less than 1 to 1 1/4 turns out, the pilot jet is too large. If it's more than 2 1/4 turns out or so, it's too small.







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