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Thread: 2007 honda foreman 500FM running lean Reply to Thread
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  Topic Review (Newest First)
04-25-2019 07:50 PM
dmtcm I just got done figuring out the lean condition on my 2008 500 Foreman. I had purchased a new carburetor on line that had good reviews but was only 65 bucks. I had problems from the get go with a lean condition. The problem with the original carb was the choke cable had cracked and rusted the choke plunger in the carb but other than that the engine ran fine. I had checked everything I could think of to find the problem with the new carb running lean. I pulled the tank and cleaned it out, cleaned the fuel valve and screen, checked the hose for obstruction, looked for vacuum leaks, exhaust leaks and all to no avail. I decided to bead blast the original carb and clean the ports and jets and try it to see what would happen. I transferred parts from the new carb to the old one to include the throttle tube ( vacuum piston ) on top and the spring. It ran lean just like the new carb did! Scratching my head, I thought of everything I had done and what could be causing the issue. The only part that could cause this problem and was in both carbs was the vacuum tube. I pulled the new one out of the carb and installed the old one. Walla !! It ran great! The new tube has a leak somewhere and the vacuum wasn't pulling the needle out of the main jet. A friend had made a comment about cutting the spring for the tube so it took less vacuum to open the jet. I cut 3 inches off and it made a huge difference in the off idle acceleration. Almost no lag at all now. I saw that there was no answer to the original post and I thought I would give my solution to this problem. It may not help everyone but anything is better than nothing.
05-25-2015 01:27 AM
jakep53
Quote:
Originally Posted by b52bombardier1 View Post
Take a look at #29 below. It will be what the main jet screws into. Also known as the "needle jet holder" though in smaller engines Honda refers to this as an emulsion tube . . . sorry for the misdescription. This brass tube will have tiny holes along the side that need to be cleaned with copper wire. Try to avoid using steel here to keep from rodding out the holes in the soft brass.

2007 Honda TRX500FM A CARBURETOR | Cheap Cycle Parts

Rick
Oh ok yes that is clean and I have also put a new one in from the carb kit and it made no difference any other ideas?
05-24-2015 04:34 PM
b52bombardier1 Take a look at #29 below. It will be what the main jet screws into. Also known as the "needle jet holder" though in smaller engines Honda refers to this as an emulsion tube . . . sorry for the misdescription. This brass tube will have tiny holes along the side that need to be cleaned with copper wire. Try to avoid using steel here to keep from rodding out the holes in the soft brass.

2007 Honda TRX500FM A CARBURETOR | Cheap Cycle Parts

Rick
05-24-2015 03:26 PM
jakep53
Quote:
Originally Posted by b52bombardier1 View Post
Is the carb, especially the main jet and emulsion tube scrupulously clean? You might try a fatter main jet. If you need choke, you are definitely lean and hot, possibly close to seizing a piston.

Rick
Main jet is brand new I have tried the old one back in and it ran the same, what is the emulsion tube?
05-24-2015 07:02 AM
b52bombardier1 Is the carb, especially the main jet and emulsion tube scrupulously clean? You might try a fatter main jet. If you need choke, you are definitely lean and hot, possibly close to seizing a piston.

Rick
05-24-2015 06:59 AM
jakep53 Ok I got my new cam in and out it all together it is now quiet and doesn't sound like a bunch of miners trying to escape but it's still running lean not as bad it pops on
de acceleration and sounds like it misses sometimes but when I put the choke on its fine and runs great I have adjusted the pilot screw gone through the carb 3 times and stuck a kit in it I shimmed the needle with thin washers since it has no adjustment and it's slightly better but still pops and farts and doesn't run well with no choke any ideas at all??
05-02-2015 02:00 AM
jakep53 Ok I think i have figured it out the depression mechanism on the cam is not working properly allowing the exhaust valve to stay open much longer than it should so I messaged partzilla to see if they have one in stock
05-01-2015 09:32 PM
jakep53
2007 honda foreman 500FM running lean

I tried different cam followers and it still sticks could it be a worn cam making it click??
05-01-2015 08:43 PM
jakep53 Ok i checked the timing and it is fine valves are fine, but I noticed a clicking sound in the push rod so I have pulled the head off and when I hold the exhaust push rod turning it over I can feel it click back down like its sticking for a little before coming back down, and its just not smooth like the intake side, could this be the problem? I have pulled the followers out swapped them cleaned them and its still sticking.
04-29-2015 08:07 AM
Jeepwm69
Quote:
Originally Posted by jakep53 View Post
Quote:
Originally Posted by Jeepwm69 View Post
Nope. You set the engine to TDC and make sure you do it on the compression stroke (lesson I just learned the hard way).

Engine to TDC, then flip the bike up on the rear rack and pull the front cover. You should see two index marks, one on the cam, one on the cam gear, and they should both line up with the index mark on the case.

https://www.hondaatvforums.net/forums...tml#post431939
Ok happy I dont have to take the engine back out I will check the timing on the weekend and see so if it was out it would only be out 1 tooth right?
Probably. Mine was out 180 degrees. Still fired right up, but sounded like little men with sledge hammers were trying to get out of the top of the engine.

Got it lined up properly, and it's as quiet as a new wheeler now.
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