vacuum lines and air noise tb 42s

[scubasteve]

gday guys
im having trouble with the maverick (tb42s carby) and backfiring/coughing spluttering. I know this is very common for this motor and theres a dozen threads outlining what to look for. Thing is im discovering more random stuff that I cant relate to other threads that is more unique to my car and I dont know enough to make any confident calls. Today i pulled the air box off the carby and had a look underneath at all the lines and found a line running to the vac tank (behind the left headlight) was disconnected so reconnected no dramas. Ive also found a few other lines that have been removed from underneath the air box too as per the photos. From what have seen vacuum lines are pretty important on a petrol and want to make sure they arent helping in the backfiring. Ive also attached another photo of another line with a bolt in it to block it off. I know im probably looking into things too much but its killing me having the engine backfire all the time. When i was running the car i also noticed a weird air noise that sounded like an air leak or something but couldnt pin point it. I thought it may have been coming from somewhere around the inlet manifold and i couldnt see an obvious gasket to seal it. is there some way of knowing without pulling it off? let me know what you guys think.
cheers

46101
46102
46103

[mudnut]

Have you tried spraying some WD40 or CRC around the inlet manifold while it is running? If there is a leak, the revs should pick up as the vacuum draws the spray in .

[mudnut]

Causes of backfire can be Faulty EGR valve, incorrect timing, Incorrect valve clearances, damaged or sticking valve, incorrect carby float level, and intake or vacuum leak or faulty thermostatic system.

[scubasteve]

Have you tried spraying some WD40 or CRC around the inlet manifold while it is running? If there is a leak, the revs should pick up as the vacuum draws the spray in .

Thats a neat trick ill give that a go when im under the bonnet next. Im slowlu working through the causes just trying to keep costs as low as possible. Ive got some new spark plugs too that ill install eventually and im in the process off getting a light to check the timing.

[madgq]

Check points, ignitions leads there normally the problem with carbys to backfire :)

[threedogs]

Gas running too lean will make it backfire, if running gas your electrics need to be spot on,
timing wise gas likes it a little advanced. Make sure all fitting are tight [snorkel] air box etc
how old are the plugs? check under the bonnet at night in the dark for any arcing from the leads or dizzy
you may even be able to hear it arcing.

[madgq]

Didnt think to check at night, nice thinking :)

[GQ TANK]

Could be an issue with the PCV valve (air sucking noise)

The PCV sits on the inlet manifold between the manifold and the carby. There is a pipe coming up from the PVC valve that goes to the rocker cover. Pull the pipe and temporary block it and see if you are still hearing the noise - (when the engine is running you should have a vacuum sucking n the pipe. As the PCV valve sucks internal emissions from the engine and feed them into to the inlet manifold to be burnt in the cylinders. (could be a blocked hose) - I picked up a replacement PVC valve from bursons for $21 (part number PCV100)

Also grab the top of the carby and give it a shake - any movement as there are 3 screws inside the carby that can come loose - I have had this happen on a tb42 and RB30 (carbys are very similar)

Photo 3 above shows the pipe going to the PCV

[scubasteve]

Could be an issue with the PCV valve (air sucking noise)

The PCV sits on the inlet manifold between the manifold and the carby. There is a pipe coming up from the PVC valve that goes to the rocker cover. Pull the pipe and temporary block it and see if you are still hearing the noise - (when the engine is running you should have a vacuum sucking n the pipe. As the PCV valve sucks internal emissions from the engine and feed them into to the inlet manifold to be burnt in the cylinders. (could be a blocked hose) - I picked up a replacement PVC valve from bursons for $21 (part number PCV100)

Also grab the top of the carby and give it a shake - any movement as there are 3 screws inside the carby that can come loose - I have had this happen on a tb42 and RB30 (carbys are very similar)

Photo 3 above shows the pipe going to the PCV

Thanks mate ill give it a check. Thanks for the technical info