VN running rough

[modcon]

I replaced my motor 2 weeks ago from the VN series 1 to the VN series 2. After changing the engine I took it for a 650km ride and it run sweet. I noticed it had a bit of trouble starting the other day, so I took of the crank pulley and replace the sensor,
It still doesn’t start straight away. The other night I took it for a drive and noticed it had a bit of a surge every now and then, so I replaced the coil and DFI with my old one, then it run like crap so I put the other one back on and it still run like crap. The car is now spitting and backfiring, and has loss compression when I accelerate, when I drive it it surges so I have to keep pumping the accelerator or it will vibrate hard core. The leads are in the right order, new leads and spark plugs, wondering if it has anything to do with the idle or throttle, a mechanic told me this morning it was the air flow meter. If I haven't put the harmonic balancer on straight would this cause this typr of problem?
I don’t know how to locate this or if the VN has an air flow meter. Any ideas or help would be appreciated

 

[modcon]

Well seems I have figured out the problem, there was air getting into the exhaust manifold

 

[1991_Vn2nV]

So there was a hole in the manifold or what?

 

[modcon]

The manifold had a crack in it. The other night I started the car and left it reving at 3000rpm for 30 sec, I stopped the car and looked under the bonnet
(at night time it was dark) and saw a bright red thing had a look and the manifold was glowing, so now a mechanic is fixing it!!!