engine Chuffing sound?

[Cheeky V]

Hi guys, Got a Chuffing sound coming from cylinder 3 when cranking the engine over on the starter

Any ideas?

Cu lump with solex carbs

Cheers

[jimpainter]

Loose or stripped spark plug, loose exhaust, loose manifold or pipes.
Does it keep doing it once running? Does it run ok?

Jim

[itchyfeet]

Small hole in the exhaust?

[Cheeky V]

Checked the plugs and inlet manifold, once its started it seems to turn into a squeak and Its generally only when under load or being rev'd hard, was setting the timing earlier and found that retarding the timing made it squeak less.

could this be caused by the valve not seating properly? not entirely sure the tappets are right (have re set them a few times, the last few of which the furthest adjuster screw towards the front has been wound out alot more than the others, double checked that the pushrod was seated properlly and the tappet isnt squishy, it will move with force but the tappet is def pumped up)

I'll check the exhaust tomorrow thanks guys

[CovKid]

Would agree with comments above - particularly gaps where exhaust meets heads as even a light leak, which might not be evident to the eye, can produce that chuffing sound. You can sometimes find it by placing your hand (BE CAREFUL) near exhaust outlets when its running (providing the engine isn't too hot) and feel for the exhaust blowing. Usually this will result in a slight popping or misfire when cruising downhill too. These engines HATE exhaust leaks. They impact on starting, running and performance. Back pressure gives the engine something to push against and is as important as suction for a steady idle.

Keep your hands (and anything else you value) away from moving parts when doing leak tests, but 'feel' is often the quickest way to find the source of them. Earlier engines with tinware make this more difficult although you can use a short length of hose against your ear and use the other end close to outlets to listen for leaks.

[ajsimmo]

Loose head.

[CovKid]

Yeah, had forgotten that one!

[Cheeky V]

Removed the twin ware yesterday and re-torqued the head, 2 nuts were at 25nm but the rest still at 30nm (I did wonder if it could be that the cylinders need lapping into the heads?)

Ah! now coming from a 2 stroke background I can understand the back pressure, this could also be making her hard to start when warm then?

thanks for the replies guys i'll let you know how i get on today

[Cheeky V]

Couldn't find/hear any hole in the exhaust but! there was oil on the cylinder fins at the head end so im thinking I need to get some paste on them and grind them in! will update once the paste has arrived