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XR400 Jetting Woes

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Hi all,

Thumpertalk God's I need your infinate wisdom!!! I checked all of the past posts, but I do not see any problems like mine. I have not been here in a while, so I hope you all can help me with a jetting problem with my XR400.

I did all the Gordon Mods a few years back and bike was running fine. It ran fine for a long time. I got a FMF Q2 and a Power Bomb Header. I put a 160 main and a 160 pilot in it, like I was instructed. The bike seemed like it was running lean and would backfire on decel. Rode it for a little while and it would just die on me. Limped it home. Read some articles that said that I should be running a 162 main and a 162 pilot. Cleaned the carb, put in the new jets and the bike will not start. Seems like it is too rich. It backfired once while kicking thru to TDC. I tried all kinds of settings with the air screw 1/4 turn at a time from 1 turn all the way to 3 turns. Anyone have any ideas for me? I live at sealevel and ride up to about 5,000 feet. I need to get this thing running again!!!

Thanks In Advance!

Geoff.

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The pilot jet controls idel and starting. Was it starting alright before the change? If it was I would try putting the 60 pilot back in with the 162 main. If the popping was occouring at high speeds the main may have been too small, but I would think it would not be. 60 and 160 worked fine for me with the stock carb and I was using it at roughly the same altitudes you are. Sounds as if you might be flooding it at startup, will it start with the throttle slightly opened?

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First off, thanks for the reply, secondly that is the sickest XR4 I have ever seen. Where did you get the USD forks???

What kind of pipe are you running? Is that the stock header on a Q?

It would start with the old pilot, but would die on me if I took it for a ride down the street and it would backfire a little on decel .

I tried to start it with the throttle slightly open at full choke and with no choke and it would not start. How far out fo you have your airscrew?

Thanks

G.

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Thanks, the USD's came from a 2004 CRF250. White Bros.Header with a White Bros.E2 silencer. I use an Edelbrock Quicksilver carb now and do not remember air screw settings when I used the stocker (sorry).

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OK, I have tried everyting and this bike will not run. I drained all of the gas and put fresh gas in. I changed the spark plug as it looked too rich. Messed with the fuel screw too many times and it still will not run.

Since I have a steep driveway, I decided to give it a couple of push starts. I could get the engine to run, but it would just sputter with the throttle on. It was jerking back and forth like it was out of gas. If I let off the throttle it would die.

When I put the new pipe and header on I put high temp silicone on the header/pipe connection. If the silicone did not seal well, could this problem be caused by an air leak?

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When I put the new pipe and header on I put high temp silicone on the header/pipe connection. If the silicone did not seal well, could this problem be caused by an air leak?

I dont think so, an exhaust leak would make noise, if the plug is wet you are getting too much gas if it is dry your pilot might be clogged, have you changed your pilot jet back to the one that was working? (See Kevins XR 400 FAQ'S sticky post under jetting) He recommends 60 and 162 jets at sea level at 68 degrees.

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Just going to throw out a few things. Do you have one of those fuel tank vent valve things on your fuel cap? If so, take it off. Check the venting of the fuel cap itsself, make sure it passes air both ways.

Have you checked the valve clearances just for the heck of it?

Make sure the vent lines coming from the carb are not stopped up/kinked. I always split the ends on my vent lines to prevent them from becoming clogged. Those lines need access to atmospheric pressure.

Is the little spring loaded flap on the choke plate still there?

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I don't have one of the vent thingies, I checked my venting to make sure that I could blow thru the vent and it was fine. I think that with a 60 pilot it may be too rich. I had a 55 pilot in there before I did the pipe/header upgrade, but it was backfiring on decel. I may go back to the 55 to see if it will start again.

Thanks for all the help!!!!

Geoff.

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I don't have one of the vent thingies, I checked my venting to make sure that I could blow thru the vent and it was fine. I think that with a 60 pilot it may be too rich. I had a 55 pilot in there before I did the pipe/header upgrade, but it was backfiring on decel. I may go back to the 55 to see if it will start again.

Thanks for all the help!!!!

Geoff.

Sounds Like you are too rich. Did you mess with the needle position as well?

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60 to a 62 pilot shouldn't make that much difference. Screw the pilot all the way in and then back out 3/4 turn and go in half turn increments out from there.

Sounds like a spec of dirt some where to me or if it wasn't running well before, something else.

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Assuming you have all the old jets and exhaust parts and what not, go back to the last know set up that worked perfectly... if it still doesn't work you know there is somethign new wrong, if it works right, you screwed up someplace. Do one thing at a time till you get it to where you want it. That way, u know where you went wrong. Also, next time u get it to run right, warm up the engine and make sure to clean it out (rev it a bit, put some load on it), should make it easier to start next time. Also, don't even try a 160 pilot. Not sure if that was a typo, but that is gonna be WAY WAY WAY to rich.

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I did not move the clip on the needle, as it has been in the 3rd position since I did the Gordon Mods.

I cleaned the carb as well, so I dont think that there is some dirt in there, but I could have missed something.

I can get the motor to run when I push start it, but it will not idle and it misses at around half throttle.

I put in new gas and changed the plug, same problem.

Has anyone ever heard of the coil causing this problem. If so, how do you check the coil?

I am at wits end!!!

Thanks!

:thumbsup::ride::applause:

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Just a shot in the dark here... but any chance while messing with the fuel screw you seated it too firmly and broke the tip off in the carb? This would cause a blocked pilot circuit and exhibit symptoms like you describe.

... worth checking.

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Blind shooting in the dark, have you checked your air filter? A badly clogged filter can cause more vacum and a flooding condition. Be sure and take it off and check it, not just a cursory look see.

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So I put the old header and exhaust back on, jetted the carb back to the way it was when it was running good, 150main and 55 pilot, fuel screw at 1 1/2 turns out (not sure about that setting). Still will not start. I noticed that there was a little oil or fuel deposit on one of the exhaust ports. Not sure if that was from the problems that I am having or not.

Adjusted the fuel screw from 3/4 out to 2 1/2 turns out and still will not start.

I can push start it, but it is missing bad, up to about 1/2 throttle. Once I let off the gas it just dies. If I can push start it and it barely runs, that means I have spark right?? The bike is too hot at the moment to check the spark, I will check it later on.

I will check to make sure that I did not break the tip of the fuel screw off tomorrow.

The one thing that really threw me for a loop is when I checked the oil level on the dipstick. It was WAY over the full line. Last time I changed the oil I only used about 1 3/4 quarts. Could this be part of the problem?

I guess that tomorrow I will need to check the valve clearances. If it is an electrical problem, how do I check the coil and the regulator?

Sorry for the book, but this bike is really getting to me!!! I want to ride!!!

Thanks for everones help!!!!

Geoff

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To me it sounds like a plugged pilot jet or the passage in the carb. With the PJ in your hand can you see thru it?? If yes your OK if not use compressed air and blow out the plug. Then you will need to take the carb out and blow thru passage in the carb to clear out any blockage.

Let us know what you find.

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The pilot jet is clear and I have used a few other sizes with the same result.

What passage do I need to blow out in the carb? The same passage that has the pilot jet? Which way do I need to blow it out, from the inside out or from the inside into the carb?

Thanks for the idea.

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I Just rejetted today. I had the same problem. I got it all put back together and I could not get it to start at all. I couldn't figure it out. But, I remembered that the Pin holding the float had come lose. without thinking, i just slid it back in. It tuned out that when I did this, I failed to put the flange on the float under the spring on the valve. the carb was not getting fuel, because the spring held the float in the off position. Onece i Put the flange under the spring, It started right up. Turn the gas on, and loosen the drain srew on the right side of the bowl. If it does not drain fuel onto the ground, you probobly have a problem with the float valve. Hope this helps.

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There is an oring that goes on the rubber boot adapter from the carby to the head. Make sure it is not broken and that it is seated right. When i assembled mine after rejetting it did the same thing as you desribe, turns out the oring got pinched and was not sealing correctly. I did all the gorden mods and i run a 55/160 Runs amazing i might add.

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I am getting gas in the carb bowl. I will have to check the o-ring on the boot going to the head. Never saw an o-ring there.

No one mentioned anything about this:

The one thing that really threw me for a loop is when I checked the oil level on the dipstick. It was WAY over the full line. Last time I changed the oil I only used about 1 3/4 quarts. Could this be part of the problem?

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