I've Saved Moon Monkeys Cavalier !!!

[MANTAMAN]

Done more work on Custard and still not got anywhere, i managed to buy a new exhaust centre section,when i took the old section off there was alot of soot from the first joint spreading back over the first silencer box looking like it was being forced out of the joint because it had nowhere else to go. Fitted the new exhaust section with the usual struggle and it seemed to cure most but not all the backfiring.

This last weekend i took the Solex Carb off another 1.6L MK 1 Cavalier that runs nicely and put it on Custard in place of the Weber but this didn't stop the backfiring,so nearly everything has been changed on this engine and yet there is no cure for it spitting flames out of the carb.

So far the list of items that have changed and/or checked very carefully is-

Engine bottom end, only done 45k & shows no sign of ware.top dead centre checked & the mark on the front pulley found to be 2 degrees out so new mark added. Bottom timing chain sproket checked to make sure its being driven properly with no slack. top timing chain sproket aligned with mark on support plate.

Cylinder Head, strange one this,despite the low milage replacement valve guides have been inserted. I've had unleaded exhaust valve seats added but these should make no difference. The head has been skimmed alot & now the compression ratio is 10.5 to 1 which is high but shouldn't be problem in itself. The head has been checked for cracks & the seal of the valves vacuum tested. all valves checked for movement and none stick. Short pipe added to oil return to raise oil level in cylinder head as per latter CIH Engines. The checking has been done both by me and a local engine machine workshop.

Camshaft, this could be the root of the problem. The original cam had run hot and 'blued' one of the lobes so i purchased a replacement cam off e-bay but this cam might not be for a 1.6L as described but a 2.0L cam, maybe even an injection cam, its possible that the cam lobe profile might be wrong for a 1.6L Carb engine which is causing the backfires. i have fitted both solid and hydrolic tappets and adjusted both as per haynes manual instrucktions.

Inlet manifold, seperated from the exhaust manifold and checked for leaks/cracks particulary in the 'hot spot' heat transfer area.

Exhaust, probably had a blocked first silencer box but this has been replaced with a new section. exhaust now in good order.

Carb, originaly fitted with a Weber that it had been running with for some while before it came off the road, so i doubt that this Carb is the cause of the trouble. I've recently put the Solex Carb from another MK 1 Cavalier that is known to run properly but has made no difference to the backfiring problem.

Ignition System, THis has had two sets of spark plugs and ignition leads and then these replaced with a new sets of each. I have had four different Distributors fitted, two of the Dizzy's have been the GTE contact brakerless type, two the older points type,one of which is fitted now, the points type Dizzy's have been static timed with a test lamp & battery an both types have been timed with a strobe lamp and yes i did make sure i did the timing on the firing stroke not the exhaust.

the backfires only occurs now when the throatle is 'reved' this causes the RPM to drop to very slow for a moment then the backfire happens and the engine then revs up.

The only hope i have left is another 1.6L head that i'm having unleaded exhaust valve seats fitted and generally checked over, plus i've tracked down another genuine 'new old stock' 1.6L camshaft. so i'll completely change the top end of the engine for another one thats deffinately a !.6L type throughout. It better work because this car is driving me crackers!