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carb tuning?

This is a discussion on carb tuning? within the Yamaha YFM350 Raptor/Warrior ('87-Present) forums, part of the Performance /Technical category; i looked in the sticky thread about carb tuning... and i understand the concept... but i set the mix screw on the bottom of the ...


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Old 05-16-2010, 02:42 PM   #1
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Default carb tuning?

i looked in the sticky thread about carb tuning... and i understand the concept... but

i set the mix screw on the bottom of the carb on my 91 warrior 1.5 turns out... but it seems extremely rich.. it will smoke.. and purely smell like fuel...

after a few min it makes me smell horrible!

i have no idea how large the jets are in mine or even which ones im looking at really.

the carb is clean! i did that before i got it going.

i dont want to turn the mix screw in too far and risk a lean situation...

it seems hard to start from time to time.. and the idle will fluctuate.. it will idle low.. then 5 min after idling... it will idle itself up and then fall back down about a min later... and sometimes after that... it will just quit.. but it will start right back up

the choke wont stay open.. i have to hold it... which i dont think is a big deal... it only really needs the choke to start cold.. once i get it going its fine... but it smokes the entire time...

after roughly 10 min of idle time it will clear up untill i hit the throttle.. and it will smoke again. my plug doesnt seem fouled its black and sooty.. which to me says rich... it is a brand new plug only 2 days old.

so im not sure if i should look at my jets... or what? honestly i think i need a new carb... there were several parts that were extremely hard to get apart when i cleaned it. so i dont know..

help please?
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Old 05-17-2010, 12:43 AM   #2
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I'd check the cleanliness of that carb again #1

The choke on these carbs is supposed to stay locked open or closed, so something is not right there.

Also the screw is for very fine tuning, it will not make enough of a difference in how it runs for what you are explaining.
You'll need to pull the carb, and take the jets out. Check what sizes you are running, because its the jets and needle that do 95% of the work, with that screw only doing the remaining 5%

Learn which jet is which in the carb and remember as follows.
Pilot jet impacts throttle: closed - 1/4
Needle impacts: 1/4 - 3/4
Main Jet: 3/4 - Full

You need to play with the jetting and get the engine to run smooth. Start off with the pilot jet. Get it to idle and run smooth. Once it is idling smooth to the first 1/4 throttle you are in a good ballpark with the idle. Remember at this time to leave the adjustment screw at the standard start point (i believe at 1.5 turns out)
Next you want to focus on the main jet. Make sure that the engine at full throttle runs smooth.
Finally you Adjust the needle and its clip position. You want the engine to run smooth with no popping/backfiring/spuddering (lean condition) or bog (rich condition). Finally when thats all done you smooth out any small discrepancies with the screw (this is where that final 5% comes in). When this is all done you should be good to go. Dont forget to also check your plug and make sure the color reads good.
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Old 05-17-2010, 09:21 AM   #3
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well after i typed that i went out and pulled the carb and all the jets and had a look one more time.

im running the stock jets according to the manual

my pilot jet is a 42.5
my main is a 145
my starter is a 62.5

my carb is set back to the original settings...

i took the choke plunger out and played with it.. the clip is broken... so.. i have to get a new clip.. its no big deal as it doesnt need the choke to stay running


but... i think my problem is not in the carb anymore....

my compression reading was a 70psi... so im thinking my rings are shot... ill be doing further tests later this week to confirm it.. but with the carb at the correct settings... it still smokes a ton
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Old 08-11-2011, 06:55 PM   #4
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Sorry to dig up an old thread.

im having the same issue as many.

I just got this quad. When I got it it would start with half throttle applied. If you let off the throttle at all it would die.

I rebuilt the carb with all stock jetting but I DID NOT change the needle.

Now it starts easily and idles perfect but will not take any throttle. It imediately dies when throttle is applied. If I try to apply throttle gentle it will backfire.

Are the needles different with different jetting?
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