Blindstuff

***This is from an old thread I did on thumpertalk, just to give you background on the issue:***

Hi everyone, here's the deal, I bought an 00 xr400 in the Florida through a friend and had it shipped to venezuela, cause the bike cost me a total of $2500 instead of the $5000 they go for here. Once I got the bike I assembled it and put something like 3/4 of a gallon gas in the tank just to start it and sputter around, bike starts just fine, half choked it takes 2 or 3 kicks to get it fired, once it's warm it fires up without choke with a single kick everytime.

I rode it just around the block and everything seemed fine, a couple of days later I rechecked all bolts for tightness added another half a gallon and went for a longer ride, just when I was getting back home the bike started backfiring except when I gave it very little to no throttle. I thought it was probably just out of gas, so I parked the bike, filled the whole tank and went for another ride, to my surprise the bike has kept with the bogging and backfiring after a certaint rpm or throtle opening (near WOT).

I have ever since changed the coil, and taken the carb apart to clean it. It has a 162 main that looked to be in pristine shape, everything in the carb looked to be perfect, no dirt, slime or worn parts.

Bike has an E series white brother exhaust, and foam filter(can't remember the brand) but it is in the stock airbox with no snorkel. The bike has no headlight just in case that matters lol. I live at about 3000ft over sea level and temperatures range from 20 to 33 degrees C. Do you guys think the jetting might be the issue? I tried running leaner by using the first groove on the needle instead of the 3rd and it seemed to ruin the part throttle area, which was fine and not help at all in the WOT area.

I doubt It has to do with jetting due to the fact the bike managed to ride fine but I'm open to all opinions.

***NEW INFO***

Since then I have, replaced the spark plug with a properly gapped one, I got a new coil and wire. I tore down the stock carb a billion times, I dropped 2 sizes in the main needle and 1 in the slow jet, and all combinations posible with those jets. That didnt solve anything. One day im going to try to see what the issue is, and it just starts and rides fine, going wot in 2nd would lift the front straight from low rpm. After about a month of fun on the bike the issue came back.

I searched on TT.com and I found that stock xr400 carbs suck, so I went ahead and got a mikuni pumper carb from XR's only. They ask for heigth and level of mods to the bike in order to ship you a carb with the correct jetting. I got the carb put it on and....no improvemnt. Now the bike fires up on the first kick instead of the 2nd or 3rd which is great, but it still bogs at high rpm or around 85% throttle.

So today, I take the stator down and check the whole wiring, everything seems normal, but I have yet to test the stator output. Assembled everything, went for a ride, and the bike just dies on me, I parked it somewhere safe, started it like half an hour later on the first kick and the bick was working just fine with a lot of power. I noticed I was running from the reserve "tank", so I thought maybe the petcock was clogged, I just cleaned the whole tank and petcock and now the bogging is back.

So, I would think fuel is not the issue here since the bike runs fine from time to time, apparently when it feels like it. Im guessing its some kind of electric mistery.

Basically, do you guys have any idea on what I should do or check, im really lost here, I have never had this much trouble pinpointing an issue.

Thanks,
Stefano

HatchbackFreak

not sure if you got it fixed but you may want to ck and see if your valves are tight and if your gas has the same octane we have in the usa the problem ur having can be a pain to troubleshoot for any motor on anything so dont get discouraged keep up with the process of elimination and you'll find it i'm sure of it i dont know bout there but the xr400 here is a monster of compresion and can be a beast to start if any internal mods are made like port and polish or a bigger piston. good luck and post me sumthin back!

Blindstuff

I was so looking into the "serious" stuff I forgot to look at the basic, a friend noticed it was the kill switch was getting pressed by the vibrations. Got a new kill switch and its running perfectly now.