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08 RMZ250 bog.... stumped

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I posted a topic in the intake section but I'm not getting far.

2008 RMZ250. Had it since new and never had bog issues. Last winter I decided to overhaul the bottom and top end just for piece of mind. I also went ahead and had the head ported/polished with all new stainless valves.

Bike has 14 hours on it since the rebuild but I have a horrible BOG when the throttle is cracked open (while riding of course).

First thing I did was install the JD Jet Kit. It helped alot with roll-on performance but the bog was still there when the throttle was cracked.

Next, I installed the Boyesen Quickshot 3 adjustable leak jet. Still a bog even with the screw turned all the way in (for longest duration spray). I also installed a new AP diaphragm and spring with no luck.

I never messed with the AP timing, and I won't since the timing seems fine, The fuel doesn't hit the slide. I will say the volume of the spray seems kinda weak. I tried spraying carb clean through the AP passage way but I'm not sure if it's normal or infact partially obstructed.

I'm thinking since the head is ported, maybe there just isn't enough fuel to compensate?

Anyone else have this issue after getting their head ported? What else can I do? I'm horrible stumped :smashpc:

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Go bigger on the leak jet. I had the same issue on my 07 rmz250. also do o-ring mod to accelerator pump

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Thanks, actually already had the adjustable leak jet and o-ring.... I safety-wired the AP so there was absolutely no delay since the o-ring stretches... that did the trick!

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I went to a bigger leak jet, not sure about Boyseen quick shot but I thought that changed the duration but not the volume, but I may be wrong. You could also have a small air leak at carb boot causing a lean condition and a bog. Just a thought.

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I dont think your problem is jet size, stock 08 jetting is pretty spot on for the most part, even with head porting exhaust etc. You havent mentioned fuel screw setting, check that first. Have you rechecked your timing? Also check your hot start plunger isnt hung up, take it out and lightly grease.

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I dont think your problem is jet size, stock 08 jetting is pretty spot on for the most part, even with head porting exhaust etc. You havent mentioned fuel screw setting, check that first. Have you rechecked your timing? Also check your hot start plunger isnt hung up, take it out and lightly grease.

Fuel screw has been set to 1.5 turns out from fully closed as recommended in the JD instructions. I have played with the fuel screw and when the bog was present, there was never really an affect on the bog when adjusting the fuel screw.

I have not re-checked my timing, engine has 15 hours on it since I did the full engine rebuild. I remember checking, double, and triple checking the timing when assembling. When I check the valves (which is soon), I will see if maybe the timing is actually off. Hot start plunger seems to be working fine. It releases fully and all.

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