[Corsa B 1993-2000] Carb Backfire... Help!

[Sam_Sri]

Hi guys

Cars been running fine up until starting it tonight, there's now a squeaking and backfire (throws the petrol out the carb) on cylinder 2. Never done this before and its even popping out the exhaust on idle (Sounds more clear with headphones)

Here's a video so hope someone can help:
VID_20131104_222317_zps19696f77.mp4 Video by liquidd_monkeyy | Photobucket

Left heavy carbon almost oil like deposits in the backbox after a few minutes of running very rough

[Taurus]

Start with checking the timing.

[Sam_Sri]

Start with checking the timing.

Will do thanks Taurus, Could the belt have slipped?

[P1nky]

Poorly valves?

[Taurus]

Will do thanks Taurus, Could the belt have slipped?

Possibly - anything to do with backfires, especially through the carbs, then it's always worth checking the timing is OK before progressing further.

Poorly valves?

That's a possibility of course - hopefully not. If the timing has slipped far enough then it can happen. Or they can just stick or burn out. If the timing is spot on then the next step is to check the compressions. As ever, take it one step at a time.

[Sam_Sri]

Thanks for the advice guys, I'll start with checking the timing tomorrow evening then go from there.

Hopefully its not head related as I've only just rebuilt it.

I find it odd that one day the cars fine and next time I start it, its like this, would have expected it to happen whilst driving or something.

[P1nky]

Iirc youre on bike carbs arent you? Ive seen them stick before

[Sam_Sri]

Iirc youre on bike carbs arent you? Ive seen them stick before

Sure am mate, yeah? Thanks for the info I'll add that to my list to check.

Found a total Vauxhall PDF which shows how to fully strip and clean bike carbs as I've only partially stripped and cleaned them before, so am going to try that after checking the above suggestions

[small9918]

id put money on it being the belt slipped a tooth or two. normaly happen on first crank. check the belt tentioner hasnt slackened off.

[Sam_Sri]

Timing will be checked tomorrow as i'm missing the socket i need to turn it over by hand and will be doing a compression test at the same time.

Last night i re-fitted the carbs, checked the plugs which looked awful, checked ht leads etc and when i started it, it run like normal! apart from a very unhealthy fuel/oil smell. Took it for a drive and it ran strong!

BUT.... Started up today and its doing the same as the first video but worse and gets better as the engine warms up (less carb backfire) but still runs lumpy.

Plugs...

/IMG_20131105_174407_zps3fc0c619.jpg.html]"]Photo Storage

I think the oil on this one is due to a rocker cover leak but will double check tomorrow.. Just to note this one looks the worst but is cylinder 4 plug but its cylinder 2 carb which is having the issue:

/IMG_20131105_174346_zps1ed7db0e.jpg.html]"]Photo Storage

Video after start up:

VID_20131105_190650_zpsa0ee7026.mp4 Video by liquidd_monkeyy | Photobucket

After 15mins running:

VID_20131105_192006_zpsa84ea064.mp4 Video by liquidd_monkeyy | Photobucket

After a drive round the block: (bangs are fireworks)

VID_20131105_193106_zpsc0b51ade.mp4 Video by liquidd_monkeyy | Photobucket

But obviously back to square 1 now. I've got HT Racing at brands hatch lined up to map the ECU on the dyno but i need this sorted first and the carbs balanced.

Any help is appreciated

[Hardcore]

When were the plugs last pulled to check them?
Is it just one cylinder that has oily deposits as bad as that?
Were the valve stem oil seals and guides done when the head was rebuilt, or was it pressure tested?

It looks like it's burning oil in at least one cylinder.

[Sam_Sri]

When were the plugs last pulled to check them?
Is it just one cylinder that has oily deposits as bad as that?
Were the valve stem oil seals and guides done when the head was rebuilt, or was it pressure tested?

It looks like it's burning oil in at least one cylinder.

Probably about 4 weeks ago and they just showed signs of slight over fuelling. And yes just the one cylinder but it's not the one that I'm getting backfire off.

Stem seals were replaced but not the guides, head was machined and tested and came back fine

[Hardcore]

When you done the sump gasket was there any smell of petrol from the oil?

[Taurus]

Hmm - to be honest I'd check the timing and compressions before doing anything else. You need to know those are good first of all.

[Sam_Sri]

I didn't notice a distinctive smell of petrol tbh seemed all normal when we did it.

Sure thing I'll report back tomorrow evening and go from there