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Posted by: swampyjunior
So it runs fine in neutral, and you can pin the throttle with no backfiring problems and plug is not discolored. Put it in gear, rev it up slowly to about half throttle and it begins to pop, make bad noises and foul the plug.You have changed the fuel, put fuel dryer in, blown out lines, cleaned carb, swapped out the CDI and still the problem occurs?
I have only three thoughts here:
1) There is a little rubber o-ring in the shutoff valve that can tear and partially obstruct the fuel line. It is worth checking.
2) I am wondering if your CDI may not be advancing your timing as you speed up. I know on older autos the distributors do this as the engine revs up, the timing is automatically advanced. I am wondering if the CDI operates the same way? Given the price of a CDI I think it would be something you would not want to buy a new one to see if it makes it better. There are test procedures for most the ignition electrical components including the CDI that could be checked cheaper. But you checked this by swapping with the other CDI.
3) Air leak in intake. If you have an air leak it may not be getting the air-fuel ratio correct at higher speeds. At a slower speed it can make it work, higher speed under a load it just won't. Check for air leaks by starking it when its cold and spraying WD-40 around the rubber boots on the intake side of the carb while reving the engine. You should notice a change in rpms if there is a leak.
Hope this helps
SJ
Posted by: DikTok
I had to rejet my 2003, 400i down to 145 main jet. I have a HMF muffler and it would not run well at wot. with stock 150 or larger 153. Put in the 145 and it runs ten times better. I think the stock 150 jet may be a bit too rich.
Posted by: Bear4570
Sounds too rich. Change the plug and check your gas for water.
Posted by: Bear4570
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Originally posted by: Luckycowdog
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Originally posted by: Luckycowdog
It was running fine one day, then the next morning it would not rev up past 20. I have drained the fuel, checked the carb for anything in any passages, jets, and bowl.
Drained the fuel how and did you install any fuel dry in the tank afterwards.
Posted by: Bear4570
Quote
Originally posted by: DikTok
I had to rejet my 2003, 400i down to 145 main jet. I have a HMF muffler and it would not run well at wot. with stock 150 or larger 153. Put in the 145 and it runs ten times better. I think the stock 150 jet may be a bit too rich.
No mention of an after market pipe. Was running good, the slowly went away. I would say jetting isn't an issue.
Posted by: deanz400
is the clutch hanging up ,or stuck
Posted by: oledad
Coil or spark plug wire could cause this also clogged Fuel tank vent.
Posted by: Bastosako
check the carb boot?
Posted by: Bastosako
belt driven? check belt slippage
Posted by: Bastosako
is the plug carbon fouled? (kind of black dirty/gritty looking) or the exhaust smoke a darker color?
Posted by: Bastosako
ya. plug says valve seats or gouged cylinder? maybe valve seal? but no smoke?
Posted by: Bastosako
how's the compression?
Posted by: Bastosako
right plug/ plug gap?
Posted by: truponycar
Mine does that when the choke sticks. You seemed to have ruled that out though. Can you swap the carbs from the '03 and '04? I don't know if they are the same. If you can do it, then that may give you an answer. Just something else to try. Keep us posted.
Posted by: truponycar
Glad you finally figured it out. What a PITA!!!
Posted by: stihl
The choke switch should be towards the front or the top. If you see the switch then the choke is on. Is the kill switch partually on? Do you have fuel in it?
Posted by: Crazyotto1
It could be the pick up that goes into the CDI. It sounds like it is running advanced. Maybe even timing off. Realign all the timing marks to make sure they are correct.
Posted by: Crazyotto1
I had a pick up (in a kawasaki) that went bad. It would run very good at idle. When it was sped up it would start missing pretty bad. Started firing every 2 or more turns which would make it sputter. Try swapping that out with your to see how it works.
Posted by: Luckycowdog
I'm working on an '03 400 for a friend of mine that will not rev up over 20 mph. It only has 980 miles on it. It was running fine one day, then the next morning it would not rev up past 20. It just pops, sputters, and back-fires once it gets there or anything past half throttle, but up to there it will run perfect. It also revs just fine up to the rev limiter when in neutral. I have drained the fuel, checked the carb for anything in any passages, jets, and bowl. Everything was clean and the jets are stock. The diaphram on the slide is fine with no tears or holes and the needle is fine. The choke is working properly and not hanging up. I have checked the valves and they are fine. The spark plug is black, which is a sign of over-fueling, or not enough air flow. The air filter is in great shape, and the exhaust seems to not be obstructed. I turned the headlights on while driving it incase it was overcharging and nothing changed. I also pressed the override button to see if it would make a difference and it didn't. I swapped the CDI out with the one on my '04 400 and still no change. The quad runs fine right up until about 20 mph or 1/2 throttle. I've checked and tried everything I know to do. I'm open to any and all suggestions.
Thanks in advance,
C.J.
Posted by: Luckycowdog
I forgot to list that I had blown through the fuel tank vent to make sure that it wasn't clogged. I also clipped about a 1/4 inch off the end of the plug wire to make sure it wasn't corroded or anything. I guess I'll try swapping the coil and then swapping the carbs. I'll keep you posted on what happens. Thanks guys.
Posted by: Luckycowdog
Carb boot is good. Thanks man.
Posted by: Luckycowdog
The belt seems fine. The motor is just poping, sputtering, and backfiring and wont rev up past 20 mph or half throttle.
Posted by: Luckycowdog
The plug is really carboned up, but i don't know how long he rode it trying to get it to clean out or something. If you screw in a new plug, it looks great after a short ride when you don't make it cough, but when you give it over half throttle or so it gets really black.
Posted by: Luckycowdog
But no smoke out the pipe. Kinda odd isn't it.
Posted by: Luckycowdog
I'm hoping the valvetrain should be ok since it's only got 980 miles on it. I checked compression the other day, 130psi.
Posted by: Luckycowdog
Yep.
Posted by: Luckycowdog
Timing marks are good, but i'm not sure about the pickup.
Posted by: Luckycowdog
I'll add that to the list of things to try. Thanks.
Posted by: Luckycowdog
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Originally posted by: Luckycowdog
It was running fine one day, then the next morning it would not rev up past 20. I have drained the fuel, checked the carb for anything in any passages, jets, and bowl.
Posted by: Luckycowdog
Just thought I'd let everyone know that the problem was the passageway, halfway up the carb, on the air filter side that leads to the main jet shaft was plugged off.
