Bang!!

[SILICONEKID345HP]

I can see smoke coming out the manifold.

[blitzracing]

No points, electronic ignition.

[NZ fan]

Could it be the exhaust expanding/contracting with heat. Maybe not fully tightened somewhere.

[SLB]

Sounds like a leaky exhaust manifold gasket to me, or loose manifold bolt or hole in the manifold.

[guards red]

Sounds like a blown exhaust to me too. That or a loose spark plug allowing blow by.

[Discopotatoes]

Sounds like fuel igniting in the manifold, take out the plugs and check them to see if one is wet,

[jojackson4]

Duff plug

[Adrian@]

Maplins...buy a non-contact thermometer and quickly point it at each exhaust pipe and WATCH the cylinders warm up. You will SEE if a plug is failing swap leads around/swap shrouds around/swap plugs around.
Adrian@

[phazed]

That's the weirdest thing!

[roseytvr]

Sorry that doesn't sound like a backfire to me - as Peter says that's a weird noise. Have you done anything else that may have something mechanical loose?

[Chuffmeister]

That doesn't sound like a back fire. If it was, it would be far more frequent. More like something expanding with the heat or something colliding infrequently. Have you checked the seal and joins on the y-piece to manifold to make sure they're not moving and expanding with the heat? There's not a loose connection on the starter forcing it to click or engage during normal running is there.... Definitely a weird one!

[QBee]

Your profile says "Herts". Someone on here must live close enough to pop over and listen this weekend......

[s p a c e m a n]

That sounds like something big and hollow. Got any heat proof gloves so you can rest your hand on the plenum/y piece to see if you can feel it?

[spitfire4v8]

One word.
Cam.

• possibly

[s p a c e m a n]

Ah, if it's running lumpy I'm going for misfire. Step 1. Double check all of the leads are going to the correct cylinders, having 2 incorrect would probably do this.

[carsy]

I`d take the plugs out and see if any are wet indicating that possibly the plugs arent working. You say you have new plugs in. Did you buy them off ebay by any chance.

I made this mistake last year putting new ones in mine before a mapping session only to find 2 of them didnt fire. I have since been advised there are a lot of copy NGK circulating on ebay. I`d always buy from a good motor factors.

[phazed]

spitfire4v8 said:

One word.
Cam.

• possibly

That made me laugh,










Possibly!

[QBee]

Cad, you are correct - whip the plugs out, one at a time, and see if any aren't working.
It is a sudden change, so it has to be something simple like leads crossed over, or a duff plug.
Did you take care to swap the plugs one at a time, putting the leads back as you went?
Also, the ability of the number 8 plug lead (the one nearest the driver) to pop off is well known. I ran a 7 cylinder TVR until I met Alex.

[Adrian@]

IF you run the engine and get a PLASTIC TIE WRAP and touch that carefully against any exhaust pipe it SHOULD melt IF the cylinder is running correctly.
Adrian@
IMHO a thermometer is the cheapest engine tool you will ever buy!!

[Chuffmeister]

Adrian@ said:

IF you run the engine and get a PLASTIC TIE WRAP and touch that carefully against any exhaust pipe it SHOULD melt IF the cylinder is running correctly.
Adrian@
IMHO a thermometer is the cheapest engine tool you will ever buy!!

Virtually anything melts on those manifolds...