Car dies - backfire through carb!

[hanvyj]

Ok, problem with my engine...

We drove a few hundred miles last time I used it, the car was working fine when we got back - though I thought it sounded a bit different.

Tried to use it this morning and had real trouble starting it. With full accelerator the revs eventually got up. However, releasing the accelerator instantly killed the car and the engine sounds "wrong".

I took off the air filter to check that it wasn't the airflow or anything (needing a new filter soon) and I noticed it was backfiring through the carb... Kind of dusty stuff came out.

Any ideas what the problem could be?? I made a video, I'm trying to get it onto youtube.

[bmcecosse]

Valve gaps all correct? Compressions good? Just 'feel' them with the starting handle (ign off) if you don't have a comp gauge. Do they all feel the same - or is one 'soft'? Backfire through carb suggests inlet valve stuck open. But also worth checking the carb piston is free to rise and fall - and some 3 in 1 in the dashpot. Just possible it could be shorting between HT leads - the spark then appearing at a cylinder where the inlet valve is open. Try cleaning them and making sure they don't touch each other.

[hanvyj]

Video uploaded: http://www.youtube.com/watch?v=yWEOi9Zr ... e=youtu.be

Valve gaps all correct? Compressions good? Just 'feel' them with the starting handle (ign off) if you don't have a comp gauge. Do they all feel the same - or is one 'soft'? Backfire through carb suggests inlet valve stuck open. But also worth checking the carb piston is free to rise and fall - and some 3 in 1 in the dashpot. Just possible it could be shorting between HT leads - the spark then appearing at a cylinder where the inlet valve is open. Try cleaning them and making sure they don't touch each other.

Ok, I knew this was going to come up - I have no idea how to check the valve gaps... I can't seem to find a guide on how to do it.

The engine seems to be running much better now - still a bit "uneven" though. I'll give it a go with the starting handle later, see if I can feel a "soft spot"

[bmcecosse]

Well - it's only running on 3, and there is a LOT of rattling going on - I have to say it could be a blown head gasket.......... Do you have a workshop manual? PM me if not!

[hanvyj]

Well - it's only running on 3, and there is a LOT of rattling going on - I have to say it could be a blown head gasket.......... Do you have a workshop manual? PM me if not!

Ok, I do have a workshop manual - "Haynes Morris Minor 1000 Owner's Workshop Manual" It has a section removing the head, there also seems to be a few threads on it on here. Being rather new and inexperienced I don't wan't to do any damage by doing something I'm not supposed to.

Going to have to go buy a torque wrench from B&Q. Its always rattled, it got worse recently but then quietened down.

Edit Obtained the pdf manual!

[mike.perry]

Take the rocker box off and look to see if any rockers have come loose. If nothing looks obviously wrong then check the gaps with a feeler gauge, they should be 0.012". Use rule of 9 ie with no 8 fully down, check no 1, 7 check 2 etc.

[hanvyj]

Taken rocker cover off, everything looks ok and they all go down (mostly in pairs, but I can't work out the logic of the order). Still struggling to work out where the gap I'm supposed to set is... I can see all 8 rockers, and springs etc. the right side (where I assume the valves are) each has a screw wick I guess artists the gap, but arnt the valves below that? Still a bit confused. Can't find any mention of the gaps in the manual yet...

[bmcecosse]

Counting from the front of the car ... when #1 valve is right down - go to (9 -1) = 8 valve and the feeler should slide in between the tip of the rocker and the valve stem top. Then when #2 valve is down - go to (9 - 2) = 7 valve and repeat. If they are all ok - then the head should come off to inspect the valves and the gasket.

[hanvyj]

Thanks, I got my head around the valve gaps now! Took me a while, so I haven't actually checked them yet - I'll do it tonight. Does it matter that when say, valve 1 is down valve 3 is also down when checking valve 8?

I think it was one of the first things you suggested - a problem with the HT leads/ignition. I replaced the points, and set the gap properly and checked all the leads were in properly. Running much better now, like it was before:

http://www.youtube.com/watch?v=l8iz1yOw ... 0buTXh0cOG

I'd appreciate someone having a listen to the sound of it though, its still a bit rattly but it has always been like that.

Thanks for all the help bmcecosse and everyone else! I really appreciate it.

[MarkyB]

It sounds much better, I assume the choke was out as that would be a very fast tick over.
Check the tappets now you have your head round it, that may reduce the noise.
Otherwise I'd suspect the timing chain as being a notorious source of A series engine rattles.

[bmcecosse]

When #1 valve is fully down, #3 valve may be part way down, but it won't be RIGHT down! If you keep track of which ones you have done - then yes you can go through the full set quite quickly just turning the engine the minimum amount to put each valve down in turn - and check the (9 -n) valve for correct gap. Yes - it's firing on all 4 now - so no gasket worries! But as marky says -it's very fast. You don't rev up and down in that vid - has the backfiring gone now?

[hanvyj]

When #1 valve is fully down, #3 valve may be part way down, but it won't be RIGHT down! If you keep track of which ones you have done - then yes you can go through the full set quite quickly just turning the engine the minimum amount to put each valve down in turn - and check the (9 -n) valve for correct gap. Yes - it's firing on all 4 now - so no gasket worries! But as marky says -it's very fast. You don't rev up and down in that vid - has the backfiring gone now?

It is fast, but lowing the idle screw doesn't seem to lower the revs past a certain point - and I was having a problem with the engine needing accelerator when its cold. I'll try slowing it a little more.

[BitMoreBlurred]

I would definitely recommend checking the value clearances even if it is sounding better. I had one that didn't have any clearance and it burnt out an inlet valve. Then it really did run on three cylinders and that required me to learn about removing the head and grinding valves which was new experience for me

[hanvyj]

Last lunchtime (only time I can get at the car without having to shove a torch in my mouth) valve clearances set to 12thou, only had to adgust 2 - I was wondering if I should have gotten it tightly pressing the feeler or more loosely?

Need to change exhaust to 15, yet to work out which exhausts are. I remember reading which in one of the manuals but can't find the page anymore.

Thanks for your help everyone.

[chrisryder]

from the front, valves 1, 4, 5, and 8 are exhaust valves.

[hanvyj]

Thanks!