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Discussion Starter · #1 ·
Hi everyone, purchased a non running basket case 2000 800xl. Complete rebuild, top to bottom. New crankshaft pistons, Nikasil and carb rebuilds with genuine Mikuni kits. Starts good, idles good but won't accelerate. Seems to bog out. If I give it a shot of primer it accelerates as it should. Above 4500 rpm it runs flawlessly. I just cant get it above 4500 without giving it a shot of gas with primer. Tried opening up low speed jets numerous times with no success. It seems like it's not getting fuel in the low speed circuit, yet idles fine. Looking for ideas. Thx
 

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Your pop-off may be a little high especially with aftermarket flame arrestors. Or low speed is a little lean. the only thing that gets fuel moving is the vacuum/pressure pulse in bottom end, to open pop off requires a certaian amount of fuel pressure to overcome the pop off spring pressure aided by barometric pressure on diaphragms. When you get to higher rpm from primer (sometimes barely moving throttle will create enough vacuum to increase fuel pump pressure to pop pop-off) you build enough fuel pressure to open pop off. I have seen ski's fresh out of storage not start from needle sticking at pop off lever, put fuel in spark hole, quickly finger tighten plugs, start and get rpm the highest you can with the least amount of throttle (high manifold vacuum/pressure pulse which creates more fuel pressure) and ZING, ski runs and no carb disassembly. Good luck.
 

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Discussion Starter · #5 ·
Your pop-off may be a little high especially with aftermarket flame arrestors. Or low speed is a little lean. the only thing that gets fuel moving is the vacuum/pressure pulse in bottom end, to open pop off requires a certaian amount of fuel pressure to overcome the pop off spring pressure aided by barometric pressure on diaphragms. When you get to higher rpm from primer (sometimes barely moving throttle will create enough vacuum to increase fuel pump pressure to pop pop-off) you build enough fuel pressure to open pop off. I have seen ski's fresh out of storage not start from needle sticking at pop off lever, put fuel in spark hole, quickly finger tighten plugs, start and get rpm the highest you can with the least amount of throttle (high manifold vacuum/pressure pulse which creates more fuel pressure) and ZING, ski runs and no carb disassembly. Good luck.
I'm thinking you are correct about high pop off pressure. That did cross my mind last summer. The Mikuni kits specific to those carbs only contained one spring so I thought it was an OEM replacement and so good to go? However, when I connected a 60psi pressure gauge and tested, I couldn't get the seat to pop at 60psi. I did a bunch of research on line and read that high pop off pressures were normal and had to do with emissions. Our local Yamaha dealer was useless with what the pop off pressure should be, hadno clue...but more than happy to book me an appointment for service...yeah sure!! So I rolled the dice installed the new pop off spring contained with kit and hoped for the best. Not so lucky! After attempting a few low speed jet adjustments, I gave up and put ski in storage. I have carbs off now and going to throw in the springs I removed and see if that does the trick? It's winter here so will have to wait till spring to see if I'm in business. Thx for the info
 
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