Help!!!

I have tried all the obvious things....

Anyone got any ideas, I rebuilt the top end and cant find the fault.

Its fine at idle but when I increase the revs, she backfires and doesnt run smoothly.

I adjusted the tappets - twice! checked the points.... could it be the carb? I put new vacuum hoses..

Any ideas

have you checked the exhaust for leaks cause that will cause backfiring when backing off.

I think you have a timing issue. Are the plugs on in the right order? Have you checked the timing? In addition, is the vacuum hose connected to the dizzy (standard dizzy, if it's a 009 don't worry)

BTW, is it off the throttle or on the throttle, under load or standing still?

is it running really lean? have u tried increasing the fuel mixture?

is it running to retarded? try advancing the timing a tiny bit.

could be a blocked jet in the carbie thats making the engine starve of fuel.

Yeah I checked the exhaust.... no leaks.

It backfires on acceleration whilst standing and under load, also when slowing in third gear .... so I guess it back fires pretty much under all conditions..... idles ok though!

I did the timing the old fashion method, static, and have tried adjusting it either way.... no difference...

Havent messed around with the carbie to much yet, I tried another carbie on it and it did the same so I thought it prob wasnt that...

Anyone got any steps to take from here???

I reckon static timing sucks,buy a strobe,the timing might be perfect at idle but max advance is well u never know till u find out.:P

Just to get it perfectly clear.
It "backfires" from where?
Out the top of the carby ?
or out through exhaust?

Are you running a standard carby and air filter? Is the air filter secured with no leaks?

How long has it been doing this for? Have you had a dodgy batch of fuel?

backfires out the exhaust....

Dodgy batch of fuel??? I hope not! :P

Stabdard carbie, does it with the air filter on and off! makes no difference

just put the motor back
together again.....

cam gear not in correct place... take of ya dissy cap get it ready to fire cylinder 1, go take off the rocker cover for cylinder one and see if the exhaust valve is open, spin it for how ever many degrees (some tell him when exhaust valve should open). If it seems outta wack then you are going to have to pull it all apart and realign the cam gear, hopefully it isnt that... bitch to fix

have you tryed the obivous... points in the dizzy????

several times i have bought new points that have NO tension in the spring

Even though it may be new - check the obvious several times

I had this trouble for two years and tried everything/ plugs /points / timing/ vac leaks.
I fixed it by putting in smaller diameter air correction jet.
If the air correction jet is to large it will lean out the mixture making it back fire. Air correction jets work opposite to the main jet. Mine was running 1.25 and I put in 1ml. A 127.5 or 130 main helps heaps also.
Trev//

What sort of heads have you got?

A cracked head can let gas in/out and let it backfire.

air leak in any vacuum lines

dropping spark

exhaust leak

If its no obvious, slowly go back over everything