My FZR1000 top end

[Elimax]

Hi all: I hope everyone is doing okay.

To reintroduce myself, I am a 1986 FZX700 owner who transplanted an FZR1000 cylinder block, pistons, cams, and carbs to the FZX700 transmission. For air filtering, I’m using individual K&N air filters (one for each carb body.)

My problem is this, and I’m absolutely perplexed by it:

The bike starts fine, but the air filters on the carbs frequently “puff” back, as if pressure is coming up from the cylinders occasionally and pushing back through the carbs. I’ve checked NUMEROUS times that the camshafts are installed perfectly. I’ve even removed the FZR1000 camshafts and put in the FZX700 camshafts to see if that solved the problem…but the same problem occurs.

The only variable I can think of is that I do not have the crankshaft in the proper position, but I believe that I have followed the manual’s directions.

Do any of you have any input on something I could try to fix this problem?

Thanks very much!

Elimax

[Elimax]

Anybody out there have any ideas to help me?

Elimax