Pilot jet problems

I bought the stock size main and pilot jets for my 99 YZ400F from rockymountainatvmc.com.

When I got the bike it was popping bad and dying when trying to get going,you had to rev high to keep it running.

I have had the carb off over 5 times and completely cleaned it and blown it out with compressed air.

I also changed the plug and gapped it properly.

I have taken care of the the bog with the mod I found on here and it doesn't bog while opening the throttle anymore.It had a 50 pilot and a 185 main in it,I bought a std 175 main and std 45 pilot.I installed the main but the pilot jet isn't even the same length or thread size as the old one but the site said it fits.

Anyway I went ahead and installed the main and with a little adjustment of the fuel screw the popping is completely gone but it still wont idle,I haven't put in the pilot because it is the wrong one,but it won't even Idle with the idle turned all the way up.***??? I'm hoping when I get the right pilot it will cure my ill.

I have spent hours reading past threads and I really hope the pilot fixes the problem,if not I'll have to move on the the valves.

Anyone have any more advice?

here is the jet I bought that sais it fits but it doesn't

The pilot should take care of it once you get it in. Pilot is what makes it idol cause it works from idol to 1/4 throttle. If you got it running thus far and thats all its doing then its the pilot IMO.

Forgot to tell ya.......once you get the pilot in and that solves it .....ride it for a few minutes (not real easy) kinda hard,to heat it up a bit and check the plug.

Just to make sure what the color of the plug is. Then you can determine which way to go.

Forgot to tell ya.......once you get the pilot in and that solves it .....ride it for a few minutes (not real easy) kinda hard,to heat it up a bit and check the plug.

Just to make sure what the color of the plug is. Then you can determine which way to go.

Huh? Which way to go with what?

It will be probably a little over a week before the pilot gets here.I hope that solves the issue,I do mostly trail riding with several big woods jumps here and there and stream crossings which require me to idle until I get to the crossing,it sucks having to rev to keep the rpm's up and sometimes when I hit a big jump the bike dies in the air which really sucks.

I had a '99 CR250 up until 2003,I had to sell that to finance a move and since then have been dying for another bike.A guy on C-list wanted some rifles in trade so I went for it.For a '99 it is in great shape,none of the usual stuff wrong you usually find on a bike this old,it was well taken care of but it just sat for a long time.I love the power delivery,after I did the AC pump mod this thing is a beast off the bottom.I'm 6'3 235 and it hauls me on one wheel no problem.I'm pulling my hair out trying to get this bike to idle.I'm sure I'll figure it out.I miss my 2 stroke because they are so simple to work on and keep in shape but the power of this thing is just awesome,I can't wait to get it running right. :)

Huh? Which way to go with what?

Meaning ......if he pulls the plug out and it is black and sooty then he needs to lean it out or if it white looking then he needs to richen it up some.

We'll just have to wait till he gets to that point and see how its doing then again maybe he will fix by just replacing the pilot.

If the pilot doesn't look exactly like the one you took out, one of them is wrong. The 400 used an earlier version of the FCR carb, and uses a different pilot jet style than the newer bikes.

Meaning ......if he pulls the plug out and it is black and sooty then he needs to lean it out or if it white looking then he needs to richen it up some.

We'll just have to wait till he gets to that point and see how its doing then again maybe he will fix by just replacing the pilot.

I've seen that work when trying to determine proper MAIN jetting on a two-stroke but never for anything on a four-stroke.

If the pilot doesn't look exactly like the one you took out, one of them is wrong. The 400 used an earlier version of the FCR carb, and uses a different pilot jet style than the newer bikes.

The one they sent me is the one thats wrong.The threads are bigger and the jet itself is a few 16ths longer.It said on their site that it fit my bike.I'm not even going to send it back because I would eat the return shipping,it's probably only a couple bucks but I paid 3 bucks for the jet so whats the point.I ordered the one I need from a different site and it should be here in a week or so.

.....

Edited by BallooTheBear
Double post

I have an extra size 45 and size 48 pilot jet brand new sitting in my box, PM me your Addy and ill throw it in an envelop and send it to you...

I must have fought for weeks trying to get my slant working correctly and in the end i bought an upgraded carb...

You can order those jets from this site, just have to know what to look for...

I disconnected the TPS and the bike is able to idle on it's own now,It still has a slight bog on the bottom but not as bad as before since doing the taffy mod.Just from the tps I now can pull the front end most of the time and there is no surging at steady throttle.

When I chop the throttle the idle hangs for a second before dropping back down,any ideas?

I'm really looking forward to getting the new pilot jet in the mail,I'm sure that will make a big difference. If all else fails tax time will bring me the edelbrock,hot cams and exaust.

I'll update the thread once I get the pilot in.

When I chop the throttle the idle hangs for a second before dropping back down,any ideas?

The idle is lean, there's an air leak, or the intake valves are tight.

The idle is lean, there's an air leak, or the intake valves are tight.

The previous owner welded the pipe to the silencer rather than buy a new clamp :smashpc: There is a bad leak at the weld,it looks as if he didn't take it off and just did it on the bike so he couldn't reach the backside to get it welded.I don't see anyway of getting the system off short of cutting it,I'll try removing the subframe and maybe it can be twisted enough to be removed.I can't afford a new exhaust right now.If I can get it off as a whole I can weld the leaks up,I have been welding since I was 16 and welded utility trailers together for 4 years,it looks like a 5 year old could weld better than this guy.

So that leak would cause the idle to hang like that.I'm pretty sure it's not running lean cause I get a little smoke out of the pipe,I'm running a little rich I think but that will be fine tuned once I get the new pilot.

An air leak in the exhaust won't affect the idle. It will cause excessive backfire on deceleration, but nothing regarding idle speed. The air leak would need to be in the intake tract or the carb itself.

An air leak in the exhaust won't affect the idle. It will cause excessive backfire on deceleration, but nothing regarding idle speed. The air leak would need to be in the intake tract or the carb itself.

Ok,I had the carb apart again a little while ago.The little rubber o-ring that goes between the intake bell and carb is missing,that's the first time I had that apart so I didn't notice before that it wasn't there.I don't see how he could have missed that. :smashpc:

I didn't see one in the oem parts here on TT,any Idea where to get one?

Well I opened up a can of worms tonight.I started out wanting to get the exhaust off to weld up the crap job the previous owner had done and get rid of all the leaks he left with his globs of flux.I figured on only having to take the carb off. :busted: No such luck.I had to remove the Seat,tank,sub-frame,rear shock and right radiator just to be able to twist and contort the pipe and silencer to get them off the bike.Genius idea he had welding the two together. :smashpc:

The original owner welded it while it was on the bike and he missed seams on the other side and underneath that he couldn't reach so I guess he never thought of taking it off,or changing the oil filter for that matter ever again.:lol:

Anyway I will be grinding down the welds and fixing all the holes sometime this weekend,while the pipe is off I will change the oil and filter as well.It will be a few weeks before I get her up and running again.I never understood what the hell people are thinking.Why not just do it right the first time so crap like this doesn't happen. :thumbsup:

I'll update with pics of the tear down this weekend.

Here are a few pics before the surgery.

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Update!

I got the exhaust welded up.Finished the oil change with the new oil filter.I flushed the coolant and refilled.I I also put new pads front and rear and replaced the clutch plates/fibers.

I have it running amazing.There is no more idle hang and no more popping,just slight sometimes when downshifting which is normal I have read,and heard at the track.

My only issue still is it won't idle.I have the idle screw all the way in but it wont stay running,it idles for a few seconds then dies.I'm thinking the valve clearances are off.I'll be tearing down the top end this winter anyway after seeing what the valves looked like.

Here are a few pics.

I'm guessing the PO didn't know how to change the oil filter,or he couldn't get it out because of his brilliant idea to weld the pipe and silencer together.

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The tears in the filter make me nervous.

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