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Low end bog problem

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I ride a 2000 WR400F and I have a low end bog when you twist the throttle at a dead stop or at low speeds. If I hold the throttle during this bog I can kill the engine. I don't know what it is and, being new to dirt bikes doesn't help. I had the top end redone a few months ago and that's when the bog started, but the guy who did the top end didn't touch the carb. A friend and myself took apart MOST of the carb and installed a R&D Power Pump 2 and a remote air/fuel screw. This didn't help at all. Can anyone give me any help here, I need that low end!:thumbsup:

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Try bogging out the engine, then pull the plug. That should tell you if it's rich or lean. I'd try messing around with the needle clip setting to fix it.

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First, has this aways been a problem or is it a new occurrence?

If it just started to happen, you may have either stuck/broken AP linkage, a bad diaphragm or a clogged AP squirter.

If it has always been like this you can try a smaller leak jet (#40 to $55) and check the AP timing. Old style FCR, you can do the Eddie mod and wire the linkage together to shorten and strengthen the squirt.

Do not screw with pilot, needle or main jetting to fix an acceleration issue

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No, this has only been an issue since I had the bike worked on (head gasket, new rings, adjusted valves). I later found out that the timing was off after I had ridden the bike a few times, that was $500 well spent. The bike has always had a low end surge but never this off-idle bog (thanks Clark, now I know what it's called!). I will try messing with it this weekend. I read some other threads (thanks Clark!) about this issue and will check on some other things like leak jet size (I think mine is a 45?) and AP linkage and diaphragm. I just think it's weird this would "pop up" all the sudden unless somebody went in and tweeked with the carb when the top end was done. Oh well, we'll find out soon enough.:thumbsup: Also, I have White Bros exhaust

Edited by 6BiG6HiT6

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By clogged squirter you are talking about jets, right? If so, which jets, specific ones or all of them? Unfortunately, it snowed this last weekend where I live and I did not get to ride. I will try to mess with this issue if I can this week. I am going to be "ON CALL" for work this weekend which means NO riding at all.:lol: So I will have to wait until a week from this Thursday to ride, but, I will have a 4 day weekend with no work to try and figure something out. I will post my results, thanks for the support. :banana:

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The squirter is the little brass tube (not a jet) you see when you look in the bell mouth of the carb. It is not removeable except by a carb expert. You can poke at it with some nylon (not steel) gutiar string (from the bottom). Some have use a syringe to 'pump' contact cleaner through at pressure. There was a thread about this in the last month or two.

FCR-Tuning Guide

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I was finally able to work a little on the bike. When I pulled the carb I tested the AP by twisting the throttle, nothing came out. I thought maybe the diaphragm or squirter was clogged like you said William1. I took it apart and cleaned out the squirter with carb cleaner and then compressed air (I didn't have any guitar string). Then I bought an AP kit with new diaphragm, o-rings, spring and rod. I put all these in and started it up and it's doing the same thing!:thumbsup: I don't know what else would be affecting this? I am getting ready to send the carb to Tokyo Mods to have it rebuilt but I would rather do this on my own. Help! Todd

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I worked on the bike more today. Pulled apart most of the carb except the slide and attatched springs and hardware. I checked/adjusted the TPS and it was a little high. Nothing. I used compressed air to blow out every hole and passage I could find. Nothing. The bog disappears when the choke is pulled which means that it is running lean?, I think? The AP squirter is still not squirting even though I blew compressed air thru it, which I still think is the issue, but I felt the compressed air going thru, so why won't fuel squirt thru??? I will try tomorrow to get that damn AP to squirt or it's off to the carb rebuild shop. Any comments would be killer.:thumbsup:

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