1989 Yamaha Exciter Carb help

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I searched the thread but could not find information that I am looking for so I apologize if this has been discussed, I have a 1989 Yamaha Exciter that I am having a slight loading up problem at wide open throttle, runs great up until, when the sled clears out it runs very well approx 7500 RPM's, I am wondering if my air screws may need to be turned oput slightly, they are at 5/8 turn out, Does anyone have any input? Thanks in advance Brian

PS, the carbs are nice and clean. :rulez:
 

Per tech pages 5/8 is where you should start with fuel screws, I would adjust per plugs. If you turn in or out to acheive what your looking for running wise I would at least pull the plugs a few times to check.
 
Here is an update, took the sled out today along with a screw driver, I started with the air screw @5/8" I slowly adjusted out with minimal results, I had to turn the air screw out to 2 1/5 turns out before the sled would clear up. I am certain that I should not run like this, it ran good, plugs looked fine, but I am going to pull the carbs tonight and see if there are any issues internally, am I correct in saying that I should not be out 2.5 turns on the air screw? Thanks Brian
 
Plugs

We need a plug read, take it out for a run up and down the field like i did here in the vid. I do this and then shut it down after a hot lap through the field and then i read the plugs and adjust per plug reading. I bet youll have a light smokey grey/brown to them if so drop the clip one and try it. ALso set floats and check for cracks in them. But take the needles out and roll them with the clips out on the table if they wabble you need new ones. My v-max 540 doing the same thing.

Might not wanna go this fast and pin it like i do i dont want you to blow it up. Just take it for a good run up through a field and back shut it down by the shop and look at the plugs take some pics of them and post them. BTW whens the last time you put new plugs in it?

http://www.youtube.com/watch?v=NK4h3oGYSPg
 
Here is my update, I pull the carbs, FLoat level good, nice and level, no leaks, I pulled the needles and rolled them, nice and flat, plug reading, brown, Air screw is @5/8 out, New plugs as of 1 month ago, I dropped the needle down, moved the clip to 2nd position, Today it is 37 degree's so I do not know if this is a fair test but the sled runs about the same. I took pictures and will try to post. Thanks
 
Something that I forgot to add, I turned my air screws out to 2.5 turns out, the sled ran better, again it is very warm, wondering if my current issues are weather related.
Brian
 
You need to go through everything , I couldnt make the SX run for anything until i thought id check the connections on the CDI . There lay 2 wires almost eaten through, i fixed them and screwed with the idle and it works great now.
 
make sure all up dates have been done to the carbs (disable powerjets air box mod and disable tors) but the way is sounds you have a needle and seat problem if you have the full metal needles way is happening at higher rpms they are vibrating allowing excess fuel into the carbs causing the rich problem at the top put a new set of viton tip needle and seats and call it good one another not the air screw is only evective from a half turn to 2 turns anything after that and the pilot needs to be changed you could also lower your needles a half or whole step to help the mid range

nutz
 
I want to thank everyone for the help, I have knew needles and seats coming, I also thought that because of the miles (4000) I would replace the jets. The bad, the snow is going fast but thanks to everyone for the advice, Brian
 
if the sled runs good up to 3/4 throttle and then bogs out my first guess would be the o rings in the bottom of the carb are missing or bad
 
I do not have any O ring's that I can see in the bottom of the Carbs, I don't have the power Jet carbs, standard 38 mm Carbs, I have had them apart probably 4 times, the sled runs great up until 3/4 throttle, at that pont it seems to load up, so I agree with the idea that it may need needles and seats, not saying that my carb does not have O rings I just do not have any idea where they are. Maybe that is why they are missing, I may have lost them during one of the cleanings. Thanks Brian
 
an 89 exciter comes with powerjet carbs with the main jet installed in the bowl rather than on the end of the nozzle like a standard vm carb

the o ring basically keeps the fuel from the bowl from going through the carb without being metered through the jets

a powerjet carb with bad, or without these o-rings will do exactly what you said run perfect up to 3/4 then bog badly

If you or someone did switch out these carbs to a nonpowerjet carb its possible the main jet is the wrong size what size do you have in

I honestly doubt that the needle valves are bad especially if both sdes of the engine show rich condition what are the odds both would go out --slim

also imo a needle/seat promblem would be more noticeable at low end and start flooding rather than high end when the needle would be open almost all of the time anyhow

another promlem I have seen often that sounds like a possiblity is that old gas dries out in the carb between the seat and the inlet and leaves you with a partial blockage not letting enough fuel in and at wot you drain the bowls and thats the bog
 
heres a powerjet
http://www.partforyamaha.com/pages/parts/viewbybrand/2/Yamaha.aspx
heres a standard vm
128-14.png
 
Very good information, My carb is identical to the one above, but I am still unsure of where the O rings goes, can you let me know which number it is? Also, my Jet is mounted to the bottom of #16, I am the original owner, I do not think it is a 90 but I can check, thanks for the help. Brian
 
Here is my update, I installed new needles and seats, 320 main jets and 42.5 Idle air jets, the carbs air screw were set @5/8 out. the sled runs very well, I could only ruin it on a stand because of the weather, maybe we will have 1 more dumping in March so I can try it out, I want to thank everyone for the help. Brian
 
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