Did you upgrade the stock fuel pump? or was the old one also a walbro 255?

 

It was a dw200 and I replaced it with a walbro 255 but I explained to my buddy who is mechanic he said he's 99% sure it's a timing issue I need to replace the timing belt which means I can re adjust the timing by the cam gears

 

What if you change the belt adjust timing and the problem persists? Can a scope be used to determine where spark happens in relation to tdc? Is the exhaust clear? Scan was ever done?