TOPIC:

Kawboy wrote: Chances are if it's firing back through the carbs, you've got either tight intake valves or more likely a couple of high tension wires crossed. Check your spark plug leads first.
One coil (top coil)should be feeding cylinders 1 and 6,
second coil (right side coil) should be feeding 5 and 2 and
the third coil (left coil) should be feeding 3 and 4.

If the leads are all going to the right plugs, then I would check the firing order. Pull all the spark plugs and attach them to the high tension leads and place the plugs on top of the cylinder head to ground the plugs. Then ignition on and hit the starter button and hold it on. You should see the left side plugs firing 1-3-2, 1-3-2. your eyes and brain will prefer to see it as 3-2-1,3-2-1 same thing. Then look at the right side cylinders and you should see 5-6-4,5-6-4 or as your brain wants to see it 4-5-6,4-5-6, same thing. If they're not then the coils are plugged into the wrong ignitor feed wires. You could simply move the high tension leads around to get the firing order right or alternatively change the leads from the ignitors to the coils to achieve the same thing.

If the firing order is correct then you'll have to pull the cylinder head cover and check the valve lash. You may have tight valves holding the valves open and that will cause backfiring through the carbs, but if it's backfiring out the exhaust too, then you more than likely have wires crossed. Still, if you haven't checked the valve lash, I would most definitely confirm that as well. tight valves become burnt valves and that's not good.

If ALL that's good then check your ignition timing. If it's off a lot (like 30 to 40 degrees) then it will run and fart and back fire like stupid.

Hope this helps,
KB

Thanks Kawboy, I did follow the service manual as per page 49 regarding ignition coil install and I will triple check that tomorrow (can't be too sure!). One thing occurred to me is that it might be fuel has found it's way into the engine sump etc and there might be the effects of hydro-locking going on, I will check that tomorrow as well. So far I have failed the ignition timing course and I no doubt will have to get up to speed on that, although I hoped it would be ok seeing I have not removed the rotor at all.
Cheers

Yaegunp wrote:

Kawboy wrote: Chances are if it's firing back through the carbs, you've got either tight intake valves or more likely a couple of high tension wires crossed. Check your spark plug leads first.
One coil (top coil)should be feeding cylinders 1 and 6,
second coil (right side coil) should be feeding 5 and 2 and
the third coil (left coil) should be feeding 3 and 4.

If the leads are all going to the right plugs, then I would check the firing order. Pull all the spark plugs and attach them to the high tension leads and place the plugs on top of the cylinder head to ground the plugs. Then ignition on and hit the starter button and hold it on. You should see the left side plugs firing 1-3-2, 1-3-2. your eyes and brain will prefer to see it as 3-2-1,3-2-1 same thing. Then look at the right side cylinders and you should see 5-6-4,5-6-4 or as your brain wants to see it 4-5-6,4-5-6, same thing. If they're not then the coils are plugged into the wrong ignitor feed wires. You could simply move the high tension leads around to get the firing order right or alternatively change the leads from the ignitors to the coils to achieve the same thing.

If the firing order is correct then you'll have to pull the cylinder head cover and check the valve lash. You may have tight valves holding the valves open and that will cause backfiring through the carbs, but if it's backfiring out the exhaust too, then you more than likely have wires crossed. Still, if you haven't checked the valve lash, I would most definitely confirm that as well. tight valves become burnt valves and that's not good.

If ALL that's good then check your ignition timing. If it's off a lot (like 30 to 40 degrees) then it will run and fart and back fire like stupid.

Hope this helps,
KB

Thanks Kawboy, I did follow the service manual as per page 49 regarding ignition coil install and I will triple check that tomorrow (can't be too sure!). One thing occurred to me is that it might be fuel has found it's way into the engine sump etc and there might be the effects of hydro-locking going on, I will check that tomorrow as well. So far I have failed the ignition timing course and I no doubt will have to get up to speed on that, although I hoped it would be ok seeing I have not removed the rotor at all.
Cheers

OK! Triple checked the HT leads and all is good. Dumped the oil and put fresh stuff in just in case ( I can never tell if it smells like petrol or not). As far as the firing order goes, well my head just couldn't deal with it - way too fast for me.

I bought a colortune and here is what I discovered: -
1 and 6 are firing but sadly 2,3,4,5 are not although there is plenty of spark. Every now and then they light up and this is when it is backfiring in either the carbs or the exhaust. I'm about to do some more research on this problem but if any of you gents have info that can lead me in the right direction I would be very appreciative.

Oh, I am about to order a timing light, are they basically the same and will any old timing light do or should I look for a particular brand/model??

Sounds like 2,3,4,&5 could be suffering from idle-jet blockage. The fact that you indicate they occasionally "light-up" suggests this. Don't laugh (or cry) until you flush them (in reverse) and see what comes out. If this is the case it's a relatively simple albeit time consuming task. Just my thought.

Timing light? Anything that has a + and - battery lead and a "clamp-over" (inductive) pick-up". I think they're all made that way, now.

hope this helps.

scotch wrote: Sounds like 2,3,4,&5 could be suffering from idle-jet blockage.

Can you enlighten the novice in me - is the idle-jet the same as the pilot-jet??

You'll have to humor me here Paul. The only time you can have backfiring through the carbs is when the spark occurs when the intake valves are open so either the intake valves are tight (not likely) or your firing is way off and since you have 4 cylinders related to 2 of the 3 coils not firing properly, I suspect that your wiring is mixed up. Either the wires feeding the coils on the lower coils is backwards or your HT leads are backwards.

So humor me here please and take the coil wires from 2 and 3 and swap them and take the wires from 4 and 5 and swap them. Fire it up and see what happens. I suspect it will run fine. If so then you can figure out whether the primary fees to the coils is wrong or your HT leads are wrong.

Just a simple little test to see if in fact the wiring is off.

scotch wrote: Sounds like 2,3,4,&5 could be suffering from idle-jet blockage. The fact that you indicate they occasionally "light-up" suggests this. Don't laugh (or cry) until you flush them (in reverse) and see what comes out. If this is the case it's a relatively simple albeit time consuming task. Just my thought.

Timing light? Anything that has a + and - battery lead and a "clamp-over" (inductive) pick-up". I think they're all made that way, now.

hope this helps.

I pulled the carbies off tonight and performed the tasks you pointed out. I will re-install tomorrow and test for any changes