what causes backfire loud bangs ?

[sternal]

Van still still has speed issue but thats okay for now just going to enjoy for now.

With the van stationary and revving it up from the engine bay if I rev it up really high it makes loud bangs like a misfire/backfire from the carbs, is this normal ? (obviously I don't hold it for very long like this !)

is this an Aircooled thing ?

[kevtherev]

No it's a timing/weak mixture/holed exhaust/poor compression thing

[tobydog]

Probably the rev limiter cutting in.

This is not an Aircooled thing, it's a stupid thing to do for no reason. The engine's rattling around and trying to self destruct with any load on it!

Fell for it again.

[sternal]

no rev limiter on

i dont make a habit of it


fell for what again ?

[tobydog]

Brief synopsis,

Bought van.

Van runs `well'

Won't go fast

Lots of diagnosis from many people

Lots of answers, no outcome

Not mechanically experienced with engines

Relates a new symptom

Going off on another tangent?

[sternal]

i was only asking a question out of curiosity maybe the lack of speed is related to the backfire...

another tangent me

[tobydog]

no rev limiter on

i dont make a habit of it


fell for what again ?

Valves bouncing?

[sternal]

Valves bouncing? whats that then ?

[kevtherev]

I downloaded google

Works for me.

[sarran1955]

Hello,

Aircooleds....

Loads of poetry...

but alas no magic....

This is a rebuilt CU with the carbs as they were set:

http://www.youtube.com/watch?v=4qayyc9Z4E0" onclick="window.open(this.href);return false;

and then this is it set up properly, Valves then Timing then Carburettors

(with old type ignition ,a SVDA distributor bought for £10 off a well known auction site)

http://www.youtube.com/watch?v=dsfo5ATgBp0" onclick="window.open(this.href);return false;

You do need all the test kit to do this yourself...

Hope this helps..

Cordialement,

[lefty67]

have a read of this will give you some idea of what a weak mixture is
http://www.tech.plym.ac.uk/sme/ther305-web/Combust1.PDF" onclick="window.open(this.href);return false;

[jason k]

I thought you were getting the carbs rebuilt???????

[BOXY]

Code: Select all

loud bangs like a misfire/backfire from the carbs, 

If it's popping back through the carb surely that means the inlet valve is "open" during the combustion / power stroke? A weak mixture would only pop out of the exhaust wouldn't it? Unless the weak mixture had over-heated the engine enough to make the fuel ignite in the inlet without the need for a spark?

[mark]

it will sneeze at the/in the carb if the manifold is loose

mark

Code: Select all

loud bangs like a misfire/backfire from the carbs, 

If it's popping back through the carb surely that means the inlet valve is "open" during the combustion / power stroke? A weak mixture would only pop out of the exhaust wouldn't it? Unless the weak mixture had over-heated the engine enough to make the fuel ignite in the inlet without the need for a spark?