Sx700 bogging/dropping cylinders

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BillyJoel

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Saskatchewan
Wonder if anybody has some suggestions. I have a 97 sx700. Has some clutching done and one layer out of headgasket. Race can. Recently new reeds. Carbs been cleaned. Jets are stock 143.5(I think). Idle screw set at 1.5. What’s happening is low/mid throttle cruising it doesn’t run smooth and if you pin it after cruising it takes a few cracks to get it to clean up. If I keep going full throttle and it goes amazing but if I’m down if a creek or something it stumbles and makes it hard to get out of a tough spot cause it doesn’t have full power. Sounds like it drops a cylinder. I think it’s running rich in that range and I’m wondering if I should lower my needles. It smells gassy sometimes while driving. Seems like it’s fuel related because it cleans up and rips at wot. Plugs are a nice light brown Color whenever I’ve checked them. Wondering if there’s anything else I should be checking?
 
BillyJoel said:
Wonder if anybody has some suggestions. I have a 97 sx700. Has some clutching done and one layer out of headgasket. Race can. Recently new reeds. Carbs been cleaned. Jets are stock 143.5(I think). Idle screw set at 1.5. What’s happening is low/mid throttle cruising it doesn’t run smooth and if you pin it after cruising it takes a few cracks to get it to clean up. If I keep going full throttle and it goes amazing but if I’m down if a creek or something it stumbles and makes it hard to get out of a tough spot cause it doesn’t have full power. Sounds like it drops a cylinder. I think it’s running rich in that range and I’m wondering if I should lower my needles. It smells gassy sometimes while driving. Seems like it’s fuel related because it cleans up and rips at wot. Plugs are a nice light brown Color whenever I’ve checked them. Wondering if there’s anything else I should be checking?
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You need new needle jets if they're available.

1999 vmax 500 - seems like its missing at lower rpm and getting 4 mpg

This sled has 4400 miles on it and it's super clean. I am at a loss as to why it runs so crappy. Any thoughts? It will still pull 8100 rpms and makes all the right noises at higher rpm - just not good at all down low. Plugs are black. Starts up and idles fine. Kinda sounds funny at idle...
totallyamaha.net totallyamaha.net
 
74Nitro said:
You need new needle jets if they're available.

1999 vmax 500 - seems like its missing at lower rpm and getting 4 mpg

This sled has 4400 miles on it and it's super clean. I am at a loss as to why it runs so crappy. Any thoughts? It will still pull 8100 rpms and makes all the right noises at higher rpm - just not good at all down low. Plugs are black. Starts up and idles fine. Kinda sounds funny at idle...
totallyamaha.net totallyamaha.net
Click to expand...

Yamaha Snowmobile 1997 OEM Parts Diagram for CARBURETOR FOR VX700 | Partzilla.com

Buy OEM Parts for Yamaha Snowmobile 1997 CARBURETOR FOR VX700 Diagram
www.partzilla.com

If this link works is it #23 you’re referring to? They call it Nozzle, main that the needle would go through.
 
I agree, nozzles may be worn, but may not be the cause of every problem.
4400 miles isnt that bad. And I am running several sets of carbs with more miles than that, and they are very crisp, and run great.
Each sled can be different, but you may want to start looking at other things as well.
Two things come to mind.
You said new reeds. Did you make sure they are seated at the tip of the reed? They can be installed on one side or the other.
I always install whichever side leaves no gap at the tip.
Other thing that comes to mind is needle and seat oring. If the have never been replaced, they can shrink up and let extra fuel through.
 
MURDER YAMAHA said:
I agree, nozzles may be worn, but may not be the cause of every problem.
4400 miles isnt that bad. And I am running several sets of carbs with more miles than that, and they are very crisp, and run great.
Each sled can be different, but you may want to start looking at other things as well.
Two things come to mind.
You said new reeds. Did you make sure they are seated at the tip of the reed? They can be installed on one side or the other.
I always install whichever side leaves no gap at the tip.
Other thing that comes to mind is needle and seat oring. If the have never been replaced, they can shrink up and let extra fuel through.
Click to expand...
Didn’t see this reply to today. I changed the needle nozzles and it runs crispy smooth on the bottom end. The old ones were noticeably worn out. I have an issue of it dropping a cylinder at WOT now just after installing nozzles. Not sure I’ll have time to look at it this season now might have to wait till next year. While it was apart I changed the pto main from 143.8 to 145 but I don’t think that would cause my issue. Maybe got something in the carb or bad plug maybe.
 
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