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hi, new to forum, working on 400 foreman, runs ok w/ choke on. idles fine w/wo choke. no power w/ choke off, lots of exhast backfire, some in carb. poor gas?, coil voltage low?, has some blowby: oil in filter, acts like it is leaning out on accel...choke on 1/2 runs ok. been in carb, jets are clean, blew all passages out. would poor compression cause this, used bike, has run this way since purchased. no mods on it, question rejetting richer????
 

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I would think so... rejetting sounds like the fix.

Welcome to the site.
 

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its sounds like jetting, welcome to the forums.
 

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What they said^^^^ welcome to the forums also check and make sure your carb boots arent cracked dry rotted ect.
 

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thank you all for the welcome in.. i appreciate it. All of you say rejet, but no mods are on motor/exhaust, would rejetting be compensating for wear-related loss of volumetric effiency???other poss...coil is low voltage, runsw better rich. a richer fuel mix detonates at lower temp/heat of vaporization, or something like that, at the cost of cylinder wash. plan to use my fancy fiberoptic scope to look at cylinder walls, any feedback on that one
 

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Thanks again for feed back, except for the slinky comment.....I am new to the ATV arena, but have been building engines, trannys, setting up my gears for 25 years. Designing flowbench right now. there is money to be made in my geographic area. Lots of east Texas goodole'boys around here, no decent shops, other than hackjobs. My motto is "you gotta be smarter than what your workin'on", and this 400 es has got me beat, right now.....
 

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What comment?
Thanks again for feed back, except for the slinky comment.....I am new to the ATV arena, but have been building engines, trannys, setting up my gears for 25 years. Designing flowbench right now. there is money to be made in my geographic area. Lots of east Texas goodole'boys around here, no decent shops, other than hackjobs. My motto is "you gotta be smarter than what your workin'on", and this 400 es has got me beat, right now.....
 

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I know you stated that you have already cleaned the carb but my question is how long has it been running like this? also I would seriously remove the carb agian drop the bowl pull the main and slow jets run a welding tip cleaner in the jet passages it really sound like you have a clogged idle circuit or main jet passage, I had a 85 110 that was doing the same thing and I disassembled the carb and found the slow jet main orfice clogged and three of the main jet secondary orfices clogged I cleaned and sprayed and cleaned and sprayed until it was like new put it back together and it purrs like new there are alot of tiny and I mean tiny orfices throughout these carbs the tiniest spec of debris will cause uncertain headaches. you also want your pilot jet adjustment to be right or your going to run like an old JohnDeere 60 lol. I'm not sure how many turns out from seat it will be but I'd start around 2 1/2 to 2 3/4 . Oh and by the way make sure you airbox lid is on and box is clean.. and the frame air tubes are open to the front of the quad, Dirt Dobbers love those areas. Check the airfilter too new would be nice.

Refrence... the small holes on the side of the barrel need cleaning too, I know you know how to do all of this but I do this for other passer-bys
 

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Thanks again for feed back, except for the slinky comment.......
LOL, that wasn't a comment to you. That is a quote I heard and it is in my signature. That shows up at the bottom of all of my post. Again, that was/is in no way directed to you.
 

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hi, new to forum, working on 400 foreman, runs ok w/ choke on. idles fine w/wo choke. no power w/ choke off, lots of exhast backfire, some in carb. poor gas?, coil voltage low?, has some blowby: oil in filter, acts like it is leaning out on accel...choke on 1/2 runs ok. been in carb, jets are clean, blew all passages out. would poor compression cause this, used bike, has run this way since purchased. no mods on it, question rejetting richer????
I would say there is a blockage on the main jet.
 

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Discussion Starter #16
my bad, red racer

yea, I figured out the comments section, again, new to site, no foul, and thanks for all you guys advice. went thru slow jet thoroughly w/ torch cleaner, will take carb back off, and get magnifier to see in side all holes, i use various gages of stripped copper wires ot clean holes. regarding condition of slide barrel, it seemed a bit loose, w/ some linear wear on sides. this unit was purchaesd as-is for $1500. I gather previous owner couldn't fix it either...
I will figure this out, and post result-never give up or in
 

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yea, I figured out the comments section, again, new to site, no foul, and thanks for all you guys advice. went thru slow jet thoroughly w/ torch cleaner, will take carb back off, and get magnifier to see in side all holes, i use various gages of stripped copper wires ot clean holes. regarding condition of slide barrel, it seemed a bit loose, w/ some linear wear on sides. this unit was purchaesd as-is for $1500. I gather previous owner couldn't fix it either...
I will figure this out, and post result-never give up or in
I would do as TRX2five0 suggested and go back through the carb. I would also drop the carb into some kind of good cleaner over night. If there is a blockage of some sort this may help make it soft and easy to to dig out.

One other thing. If you know the person you purchased your 400 from? I would ask them if it has always done this since they owned it? A lot of times things are easier to troubleshoot and fix if you have an idea where to look?

Sure that is a given. But if they told you they had the carb off and cleaned it out, and then it started running like this? It would tell me there is a possibility someone messed something up inside of the carb. From what I've found it's usually the last thing done to an engine is the cause of a recent problem.

This kind of problem could be caused by several things. But it's the fact you put the choke half on is why the carb keeps coming back as the problem. You may find you have more than one problem? You just have to make sure if there is one within the carb, it needs to be taken out of the equation.

Also, if you can get one? I would definitely get a welding tip cleaner. If you don't have access to one near where you live. I'd order one over the internet. Wire to punch a small hole through something is one thing. But being able to actually clean all of the garbage out using a tip cleaner is the way to go. That stuff can be hard as a rock and can and will bend soft copper wire.

Good Luck
 

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Discussion Starter #18
Hey mechanics!
Everybody can slap me now, on 3...I figured out the problem. Simple, but elusive. The fuel tank was half full (or half empty depending on your outlook..) Filled tank<and it runs great! Must have cracked pickup line or valve switch problem. So it was running out of fuel, which would mimic a jet issue on acceleration.I always make things more complex than they are. Wlill be removing/replacing switch next week. Customer was so happy, he took it out and broke a front CV axle for me to fix! I guess it has enough torque for the vampires...Lots of mud here in East Texas (and people who use throttle at wrong time). Leads me to next question: When adding a snorkel, about 3 ft., one should increase diameter to compensate for flow resistance, is rejetting a trial and error process, or is there some rule-of-thumb formula? I snorkeled my son's Helix-fox 150cc go-cart, and the motor was unhappy/bogged down on acceleration..(the fuel delivery system was in order.. lol) used a tube that was 40% larger than carb throat, no angles. is that a jet issue or not.... thank you all again for you interest in my issue, I am starting a small shop here in conroe,TX, mostly brake/drivetrain/maintenance stuff, but pllan to venture towards engine/custom work if successful. I am a respiratory therapist by trade, and employed fulltime a a regional hospital. Been building my own engine/trannys for many years for hot rods, but see a market for ATV work. want to learn coveted porting secrets, and am building flow bench now. Due to my profession of 25+years, I know my physics of flow mechanics. Any of you guys do port work, or wish to do so???
Mike Jordan aka Badfinger22
 

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Unless you have a air/fuel ratio guage, jetting is trial and error. If you made your snorkel setup that big, you could possibly get away without jetting. You could always do a plug chop to see where your ratio stands after words.

If you are going to be jetting other people quads and charging for it, think about investing in an air/fuel ration guage. It will show you exactly where fuel needs to be added or removed.
 
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