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I'm running a true keihin pc20 on my 88rh & it bogs just like the shengwey. I don't know what the answer is but it's not that. I think maybe mikuni? I've jetted up, down, left, & right & it still will fall flat on it's face if you snap the throttle. I imagine a keihin 22mm will be the same story. I've heard the 20mm responds better to the stroker crank but can't tell you from experince.
 
I'm running a true keihin pc20 on my 88rh & it bogs just like the shengwey. I don't know what the answer is but it's not that. I think maybe mikuni? I've jetted up, down, left, & right & it still will fall flat on it's face if you snap the throttle. I imagine a keihin 22mm will be the same story. I've heard the 20mm responds better to the stroker crank but can't tell you from experince.
My sheng wey doesn't bog. I got mine set up pretty good. I snap the throttle and the bike stands up. It took me a bit to get it tuned right.
 
Discussion starter · #26 ·
I think the carb has something to do with the bog, could be wrong but simply take a Japanese carb and look down it from one side to the other. Is one straight diameter all the way across for the most part. Look at the Shen way...first off its not round(idk if it matters but when I see all the Japanese carbs are nice n round it makes me question this design) and second look at the left and right wall of the inside of the carb. It has some weird notches..
 

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Well you're one of the lucky ones. I'm about 500ft 04 crf70(88rh/manual clutch) & fmf powercore. Running 90 main, 38 pilot, needle in the middle, air screw according. If I snap the trottle my bike will cut off. If I roll on it does ok. I've got the jets & have been up & down. The norm is you can make it better but never get rid of it.
 
Discussion starter · #28 ·
Well you're one of the lucky ones. I'm about 500ft 04 crf70(88rh/manual clutch) & fmf powercore. Running 90 main, 38 pilot, needle in the middle, air screw according. If I snap the trottle my bike will cut off. If I roll on it does ok. I've got the jets & have been up & down. The norm is you can make it better but never get rid of it.
I can snap the throttle on my bike with out dying/ cutting out. My problem is when I'm riding and I shift to second gear it's slow of the gear as it goes thru the rpms, it goes really good on the top end but my low end seems to not have the torque or power it should until it gets past 1/4throttle. I run 38 pilot, 92 main, needle clip one lean from center and a/f screw 1 turn out. Elevation is about sea level.
 
The bog is caused by the lack of accelerator pump (throttle valve opens quick, not enough vacuum to pull necessary fuel to prevent bog, engine falls on it's face). An accelerator pump would 'squirt' a bit of fuel into the mix when the throttles wacked open, temporarily rich mixture and no bog.

Seems to me a Mikuni VM22-133 would be about the biggest I would run on an 88. Reduced radius means an improvement on bog (more vacuum means more pull on fuel from main jet) and yet still large enough to feed that intake valve at WOT once it has it's legs under it. Flange style bolt on (49mm between centers) should work mint with most 22 mm intakes. Another thought is to run a longer intake manifold, which will help with low end power / bog.
 
Discussion starter · #32 ·
The bog is caused by the lack of accelerator pump (throttle valve opens quick, not enough vacuum to pull necessary fuel to prevent bog, engine falls on it's face). An accelerator pump would 'squirt' a bit of fuel into the mix when the throttles wacked open, temporarily rich mixture and no bog.

Seems to me a Mikuni VM22-133 would be about the biggest I would run on an 88. Reduced radius means an improvement on bog (more vacuum means more pull on fuel from main jet) and yet still large enough to feed that intake valve at WOT once it has it's legs under it. Flange style bolt on (49mm between centers) should work mint with most 22 mm intakes. Another thought is to run a longer intake manifold, which will help with low end power / bog.
What bike is that vm22-133 from?? And is that a bolt on to the tb intake?
 
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