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strange jetting issue...need help please

2K views 29 replies 3 participants last post by  shadetree 
#1 ·
Hi guys, first and foremost, i'm a newbie to the forums, this will be my first post! I recently purchased a 03 foreman 450 4x4 es. it didn't run but was said to have a fairly recent (a year ago) rebuild. i can see fresh gaskets all over the engine which sort of supports the rebuild. anyway, here's my issue:

I live closer to 600 ft above sea level and have cleaned and recleaned and cleaned again the carb and put brand new Keihin jets in every spot, placed clip on the 3rd slot, as well as a new choke needle....this is a factory set carb. I have a new, clean Uni filter inside the box, and it has an hmf muffler.

When attempting to start and idle, it would lean puff and spit and die without always using a little bit of choke. swapped pilot up to a 52 and now, with choke, it will start and after warmed up, idle without the choke. however, with a stock 130 main jet it boggs at what I perceive as mid rev range. if I pull the air box lid off the rev goes higher but still not the limiter. If I pull the air filter off, it will hit the limiter. this to me says i'm way rich, but it's odd that i'm using stock keihin jets with hmf pipe and running rich. i've installed a 128 main and it's a little better still, but still will not hit the limiter with the filter on and for sure spits and sputters with the lid on the box.

i've checked valve clearances and are dead on. i've done a compression check and turned up 170 psi without loosening the exhaust valve, so compression seems good, and doesn't seem to leak down through the valves.
what am i missing?
without the air filter or lid on, i did a wot run through 4th gear and killed the engine. pulled the plug and cut the threads down, the porcelain is a very soft peach/tan color which i would say is probably perfect.

so why does my engine require less than factory fuel considering mods?

sorry for the long post but I like to be thorough. i'm definitely not a newbie to carb tuning, i rather enjoy it. but I just want to know if there is something I am missing as I am new to this particular machine

thank you all in advance
 
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#2 ·
welcome to the forums. put all stock jets back in, and set the pilot jet/mixture screw to factory settings, then go from there, with what and where you live ?, I highly doubt this will make that much difference ?. get the pilot jet/ mixture screw needle set to factory, then go from there.
 
#3 ·
that is exactly what i did from the start. I completely disassembled the carb, soaked it in a bucket of chemtool, sprayed it clean. put it in the ultrasonic cleaner I have for 3 hours then sprayed clean. and repeated this process two more times. then i put in brand new, actual keihin brass and factory sized jets including factory needle and needle jet, and all new factory honda seals and orings. everything was dead factory. quad was lean at idle (but has an hmf exhaust and a brand new UNI filter) so i upped pilot to a 52 and adjusted the airfuel screw to a perfect idle. it idles smooth and starts easy. and spark plug is perfect color for idle.

a quick jab of the throttle and it responds perfect, does not bog or hesitate and returns to idle perfectly. the only issue i'm having is up top. it's feeding too much fuel to hit the limiter and it's a stock 130 main. if I use a 128 it's better but still will not hit the limiter without removing the air filter.
 
#8 ·
He said he clean it extensively...... You think an incorrect screw position would make that issue happen????
 
#10 ·
this is my only questionable thought. the guy said it was rebuilt within the year and the gaskets are definitely newer. he also gave me all the receipts and paperwork from the rebuild including parts and labor from a honda shop. so, i am pretty confident in it. however, i have not checked the timing chain and marks to verify timing but it runs TOO good to be out.
I also wondered about the cam lobes, if maybe they're worn out and not allowing the valves to fully open causing low air intake thus requiring less fuel?

food for thought
 
#15 ·
Correct me IF I'm wrong, but I thought if u adjust the screw and there is NO difference the pilot is too large. Which doesn't seem right if he has to choke it....
 
#16 ·
what your calling pilot, and screw is the same thing in my book. the pilot/needle jet/screw is what you adjust the air to fuel mixture. some folks call the idle jet the pilot jet ?, but I don't.
 
#19 ·
yes, the "t" mark is center of the sight window. I didn't really tear it down. I left the clutches in and only retracted the tensioner. I was able to pull the cam sprocket off of the cam and move the gear around inside the chain two teeth, without removing it from the crank sprocket. then reinstalled the gear to the cam and tightened the bolts and put it all in time.
The dots are really close to the notch in the case but not dead on, but again, there's no real way to make them dead on. They're either before or after the way I see it
 
#20 ·
if you can't get the punch mark dead on with the case ?, then this tells me the cam chain is stretched a little, but not enough to make a big difference in the way the motor runs, least never has for me ?. I know I would put a new cam chain in, if it were mine ?..but it's not, your call :).
 
#23 ·
1/2 to one tooth shouldn't hurt it ?, but two teeth ?, that's begging for trouble !..lol. from seeing your pic ?, you look to be ok for now ?, but I worry about it jumping time sooner or later ?, when you least expect it ?, like...miles from home ?!..lol.[/QUOTE]

yeah, i'm not super concerned with half tooth for now. and the tensioner had a firm push against the pivot guide so it should be ok for a short time at least. luckily where I live I can't really ride it miles from home and where I go to trail ride, I always ride with someone else anyway, so should be ok in the even something might happen lol! If all else fails, I have a winch bahahaha!
 
#24 ·
1/2 to one tooth shouldn't hurt it ?, but two teeth ?, that's begging for trouble !..lol. from seeing your pic ?, you look to be ok for now ?, but I worry about it jumping time sooner or later ?, when you least expect it ?, like...miles from home ?!..lol.
yeah, i'm not super concerned with half tooth for now. and the tensioner had a firm push against the pivot guide so it should be ok for a short time at least. luckily where I live I can't really ride it miles from home and where I go to trail ride, I always ride with someone else anyway, so should be ok in the even something might happen lol! If all else fails, I have a winch bahahaha![/QUOTE]

when the battery goes dead from not running ?, what good is that winch ?..lol.
 
#25 ·
Hey guys, so i just wanted to post back. I finally got my cover gasket and reinstalled everything. This thing is a whole new beast lol! it started immediately without the choke, idled smooth and strong after tweaking the fuel mixture screw, and hits the rev limiter without even trying! pulled the plug and checked it and it's now lean up top (with a stock 130 main using a uni filter and hmf exhaust) so, gonna start messing with the main tomorrow. but I just wanted to post back and let you know!
Thanks for all your help guys
 
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