carby explosion :(

dynabytes · rice boy Joined: 01 Nov 2001 Posts: 42

Hi all, just put a new head on, all is well with that. When start to crank the engine over white smoke comes from the carby and it back fires and pops and carry's on. I've got a feeling the idle and feul mixture screws have been turned a few times and may have thrown it our of calibration. Firstly, do you think this is the problem (i.e. with the idle and mixture screws) secondly is there a way to reset these to a default setting that will allow my car to start. there are also a bunch of wires that are hanging down from the carby, one looks like the choke not sure what the others are and whether there important for the car the start :/ joys of buying a broken down gemmy, prior to the head gasket blowing it used to purrrr like a kitten

Racegem · backyard mechanic Joined: 30 Jan 2002 Posts: 987

I'm willing to bet the camshaft is 180 deg. out.

dynabytes · rice boy Joined: 01 Nov 2001 Posts: 42

how do I set it? I have the bottom end on TDC i have the notch in the cam facing upwards.. i am concerned however that on the camshaft sprocket there is a circle and a triangle.. What is the story with that?

S N 3 A K Y · tinkerer Joined: 18 Jul 2003 Posts: 153

Agree with Yonnee, you also may find that you haven't lined up your cam sprocket properly and it's way out.
Did you use zippy ties or similar to hold the timing chain to the cam sprocket to ensure an exact refit ?
To readjust your carb, turn the fuel/air mixture screw in counting how many full rotations it was set at (For reference). Screw it all the way in gently till it seats, then turn it back out 3-4 full 360 deg rotations.
There should be 2 wires coming off the carb (Near the choke assembly), are they connected to the loom ? The engine wont want to idle without these connected - it will run at medium and higher revs but not idle.
Also, if you can get the engine to idle grab a timing light and have a look-see, timing should be on 6 deg BTDC. Symptoms you have described could also denote that timing is out.

S N 3 A K Y

Racegem · backyard mechanic Joined: 30 Jan 2002 Posts: 987

OK. You've set the crank and the camshaft correctly, but there are two Top Dead Centres for the crank. One when the dissy is firing No.1, and one when the dissy is firing No.4.
(If you know the internal combustion engine, the crank turns twice for the cam and dissys once.)
With the camshaft at the start of its cycle (Intake, Compression, Ignition, Exhaust), you can see that No.1 firing on the dissy happens the second time round for the crank (1/2 way through the camshaft revolution). If you've set it so that No.1 is firing at the start of the cycle, the resulting spark ignites the fuel coming down the open inlet valve, and back up through the carby.

Basically, the way you've set it, the dissy should point to No.4

The circle and triangle line up with two "bright" links on the chain. (There's another circle on the crank sprocket that you won't see unless you pull the timing cover off).

Clear as mud??

Yonnee.

dynabytes · rice boy Joined: 01 Nov 2001 Posts: 42

thankyou everyone. the camshaft was 180deg out lie you said Sad

Frederick Stienheld · petrol head Joined: 05 Sep 2002 Posts: 2719

that's a timing problem