Topic: air blowing out of #2 carb

[mAd mOrdigan]

so I haven't worked on the bike in a while but it's a cb750 k8 pd42 carbs. long story short It was running fairly decent  before I took the engine out of the frame to restore the entire bike. now I have it all back together, just finished checking the valve clearance, getting em back in spec. I'm about to adjust the timing but can't get the bike to idle too well. it seems to be spitting air back out of the #2 carb.

my question is where to go from here? will the timing fix this? because I can't get it to idle low enough to check the timing. I haven't done a carb sync yet at all but think that should be done after even the timing right? not sure what to go back and check.. vacuum leaks? floats? spark plugs? I'm just taking a step back at this point and letting this all sink into my mind then I'll tackle it again tomorrow or another day.

[madmtnmotors]

Set the timing at "full advance". Check the manual, but I believe full advance is achieved between 2500 and 3000 rpm. Set up a fan to blow air across the motor while you work since these are air cooled engines and crank the idle set screw to get the idle up to where needed for full advance timing setting. This should get your timing set properly, unless the advance mechanism is sticking.

[mAd mOrdigan]

oh dang I knew nothing about full advance. thanks. you think this is a timing issue? I'm dreading that it's a bent valve or something although idk how it could be

[HondaMan]

After setting the timing with a timing light at, say, 2500-3000 RPM to full advance, try to let it idle...if the air is still blowing back out #2 it may have a burned intake valve or heavily worn valve guide.

[mAd mOrdigan]

thank you gentleman! I'll give this a try

[madmtnmotors]

Have you "static" timed it yet? I can usually static time mine spot on. I only check the timing dynamically (with the strobe) to verify timing is correct.