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Discussion Starter #1 (Edited)
2008 840; really down on power

I have an 08' Rex with an 840 kit on it (~30 miles since build) that seems to be really down on power. I just replaced the slides in the carbs with OEM ones.
A section I can normally hit 68mph on, I only hit 46 today. The thing is, it is running great! better than it has in a long time. Very smooth power, no hiccups, and only a little backfire on decel (Muzzys prob need repacking).
Ive sprayed carb cleaner all around the motor area looking for a vac leak.
New plugs, clean air filter. Everything seems great.
Could it be something to do with Syncing the carbs?
The motor was put together by an Ex-Kawi mechanic using JE pistons, OEM crank, OEM cams, and rods.
What should I check for? Its power seems like a stock 750 (maybe less :( )
thanks
A
 

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Belt is probably loose, therefore not shifting out the clutches all the way resulting in lower top end and sluggish performance. Maybe, if motor seems to be running good might be something else.
 

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Discussion Starter #4 (Edited)
The belt is new with the motor build, so that wouldnt be my first thought. thanks for the input.
Todd, if the slides arent opening all the way, what would cause this? I made a big effort to insure the diaphragms were seated correctly.

Its weird because its idling, starting and running like a dream.
 

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Hi I would say that one of the slid diaphragm is out of the groove. I had one out on my 08 and it ran fine until I got into it and it only went have the speed it could. Good luck!
 

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Discussion Starter #6
Also make sure the slides are opening all the way
I took your advice and popped the plenum off.
At WOT The front ne is about 7/8 in, the back is about 3/4 of the way in. How far should they be sliding in? given that the plenum is off and it isnt really under load.
thanks
 

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If it isn't the slide diaphragm out then it is a good time to polish the slides they work better polished anyway. I think your getting close to getting it fixed;)
 

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Discussion Starter #8
If it isn't the slide diaphragm out then it is a good time to polish the slides they work better polished anyway. I think your getting close to getting it fixed;)
I polished them ,redrilled the vac holes to 5/64
 

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I took your advice and popped the plenum off.
At WOT The front ne is about 7/8 in, the back is about 3/4 of the way in. How far should they be sliding in? given that the plenum is off and it isnt really under load.
thanks
They should be the same and expect some bouncing. I would say air leaking by diaphragm seal. hard to say.
 

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This is a long shot but I worked on a friends brute force and the carb slides were not working correctly and it was dirt getting through the air filter and restricting the slides. I removed and cleaned them and run fine.:confused: Your power loss is in that area and maybe the metering rods are not seated correctly:confused: good luck
 
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