The V8 Owners Forum -

Hi folks.

Back again, got a new edelbrock/weber 500. engine still doing the same. checked and rechecked the timing, leads and firing order, still spitting back through carb, wont even turn over properly. Does no1 segment on dizzy cap have to be bang on with rotor arm when in tdc on cylinder 1? both valves are closed, so should be right?

The engine should be on the firing stroke but rather than use TDC you would be better off having the engine around 10-14 degrees BTDC. The rotor arm should then be more or less pointing at number 1 HT post. It will in fact be slightly further round past the post to allow for when the advance system kicks in.

I'd disconnect the vac system whilst messing about with the timing, you haven't fitted it to the non-timed port on the carb have you?

Personally I'd dump the vac system anyway as it does not work too well with this carb.

Finally the out of the box settings for the Eddy carb don't suit a 3.5 lump very well, it will be too rich. (But is will run, just don't do many miles with it set like this as it will wash the bores)

Finally, finally the pilots are usually set wrong as are the float heights! Go for around 1.5 - 2 turns out as a ball park for the screws.

cheers for reply, i havent connected up vac on carb, left them blanked off. it just seems very far off when turning over engine. it was running fine before i did the new loom, could the electronic ignition cause these problems? its the old lucas lopus system and i know they are prone for being faulty.

shawser wrote:wont even turn over properly

One wonders if that has anything to do the misfiring or maybe even backfiring????.

To eliminate that possibility, remove the king lead from the coil and try cranking the engine without the engine firing.

Does it still "not turn over properly"?

If so you have a battery or starter motor or starter solenoid or earth strap or heavy duty cable problem.

However, if the engine cranking is OK without the ignition connected, then I would say you have a serious ignition timing problem or possibly the firing sequence is wrong.

Hence the spitting back or backfiring!

As far as timing is concerned, with regular unleaded, try 4 degrees BTDC as a starting point, at 600 rpm, vacuum disconnected.

Regarding your older (ballasted?) OPUS ignition system, it is indeed notoriously unreliable but at least you have sparks so it must be doing something right. Normally they just croak and die.

You might however consider upgrading to the Lucas 35DLM8 non ballasted 12 volt electronic system because the reliability is much improved.

shawser wrote:cheers for reply, i havent connected up vac on carb, left them blanked off. it just seems very far off when turning over engine. it was running fine before i did the new loom, could the electronic ignition cause these problems? its the old lucas lopus system and i know they are prone for being faulty.

I've only worked on one car with the Opus system, it could be that the system I worked on was a bit knackered but I was not too impressed with it.
The main issue seemed to be the very small mount of mechanical advance that it offered. If you set it to round 14 degrees BTDC you still only get around 28 all in which is not enough on a 3.5.

I know the 'book 'states some really low figure for the static but believe me you will release a load of BHP if you run the static/idle around 14-16 and get the all in at 36 degrees. (You want it in at 2700-3000 RPM)
Leave the vac system off as it does not work well with the Eddy carb.

You must check that the damper pointer really does point at 0 at TDC,this can take an hour of more to do on its own!

Not running the figures above but running the standard setup won't be the cause of your mis-fire though!

The potential problem with the figures that I've given is that if you battery or starter motor is knackered you may find that you have problems cranking the engine over.

start it in the dark.

See if you are getting cross arcing on HT leads - they can set up a glorious light show!

Ian

cheers guys for all the advice, plenty to think about. Was wondering if iv rewired the electronic ignition back up properly, i saw a diagram on another site and it was slightly different to mine, maybe its sparking at the wrong time, is this possible? i dont have a tacho so that wire is doing nothing, could that cause problems? one diagram says a wire goes to the starter, the other diagram says to starter relay. how would you guys wire it?

Was wondering if i rewired the electronic ignition back up properly

Ooops! Sorta make any meaningful diagnosis a lottery - .

If you have a ballast resistor then something like this basic OPUS wiring diagram is needed to make a 9 volt coil system work without coil strain.



When the starter relay is energised and the contact closes, the 0.8 ohm resistor in the ballast pack is bypassed allowing the reduced battery cranking voltage of about 9 volts to reach the coil via the 1 ohm resistor.

When cranking ceases the resistor is back in circuit which effectively reduces the normal input voltage to the 1 ohm resistor to approx 9 volts, hence the need for a 9 volt coil. It never operates at 12 volts.

If someone has perversely fitted a 12 volt coil this makes the ballast resistor redundant and the voltage to the coil is usually direct from the ign switch. Involving a wiring change - of course.

Worse! On the other hand, if you still have a 9 volt coil and there is a wiring change, now the ballast resistor is not included, then the 30/40% extra LT voltage will cause excessive HT voltage, external sparking/tracking and eventually something will croak.

Might be worth you describing what you actually have, coil and dizzy part numbers, images, connections, etc. Something to eliminate the mystery.

I dont think this will help particularly as you do have sparks, but for what its worth, this is a diagnosis chart I redrew for basic OPUS

well today i took off the main ht lead to coil, engine cranked over fine and i heard a cracking noise, i noticed the negative on coil was arcing with where the ht lead goes in, it was like a lightning storm, very impressive. any ideas?

shawser wrote:well today i took off the main ht lead to coil, engine cranked over fine and i heard a cracking noise, i noticed the negative on coil was arcing with where the ht lead goes in, it was like a lightning storm, very impressive. any ideas?

To my way of thinking you have one of two possible problems

1 Simple HT tracking from coil king lead terminal to earth via the LT circuit due to damp, filth or carbon deposits thereabouts

You'll need to clean everything around the HT connections with degreaser first, then WD40 and wipe/dry it all off with a cloth.

or

2 Way toooooo much HT voltage due to incorrect LT wiring as already suggested, with 12 volts getting directly to a 9 volt coil when cranking ceases. That extra 5,000 to 8,000 volts will cause collateral damage eventually.

Check the LT wiring and components against the basic requirement and correct as necessary.

Worse case, you have BOTH problems!

think i will rewire the electronic ignition as per diagram you put up on forum, see if that will sort it.

I still think you've got the firing order wrong! The difficulty when cranking confirms this.

All this talk of ballast resistors etc is just confusing the issue, and while this may cause problems longer term, it wouldn't explain the spitting and misfiring.

Confusing? Why? He says:

checked and rechecked the timing, leads and firing order

Yet - because the PO definitely has the ballast resistor wiring wrong - he says - then its entirely possible that the HT voltage is far too high as a result.

He already observed spectacular high voltage sparks on the top of the coil with the king lead removed, therefor high probability of arcing (not cross firing) to other leads, probably due - in part - to dirt, etc, then the cylinders may fire randomly giving effect similar or worse to wrong firing order.

Confusing or not, if the ballast resistor wiring is incorrect (or an appropriate coil in not fitted) then that is what can happen IMO.

HT voltage is limited purely by the gap the spark has to jump. The HT voltage will not be higher if the ballast resistor is removed (providing the plug gap is unchanged), although it will have the capability to become higher if the plug gap is increased. You may get a higher spark current though, and of course you'd cook the coil.

I know the original poster has said he's already checked the firing order, but sometimes it's easy to miss such errors, especially if you already 'know' that it's correct. Sometimes you need a fresh pair of eyes to see some problems that keep getting overlooked.

Jeff

Well i cleaned coil, no arcing. Took ht lead off dizzy from coil and cranked engine, sparking no problem, so put it all together and guess what? spitting through carb. Getting p****d off now. I does seem like its the timing and its way out, but i just cant undersdstand why, when dizzy was never touched.