9.9hp 4stroke 2006 runs fine until the cowling goes on

[DarkStar]

Hello forum, new guy here.
I have a pair of 9.9 4strokes to power my sailing cat . I recently replaced float needle & mix screw, ran fine for a few hours,but now it runs fine until the cowling goes on, then it struggles & stalls after 30 secs or so. I assume a lack of air getting in, I’ve checked the cowling vents, even swapped cowlings, I’ve checked the intake mesh, I’ve checked that the cowling isn’t pinching a wire. In frustration in I drilled a 20mm hole in the top. It still isn’t happy unless the cowling is off. Any help appreciated

[robert graham]

Maybe an exhaust leak inside the cowling....

[99yam40]

maybe an exhaust leak cutting down the O2 under the cowling,
but I am not sure exactly where that would be a a 4 stroke

[DarkStar]

Thankyou, I went around the head bolts, one of them allowed a 1/4 turn, the rest a tiny bit, warmed the motor & put the cowling on, running fine now, taped up the hole I drilled, sweet as a nut, fingers crossed, thanks again. Robert graham & 99yam40. Gotta love a simple logical solution