Help with problem

[Andyww]

Ah yes sorry, this was discussed on another thread, the later engines have some emission control gubbins.

 

Although it would not do any harm to at least check the advance with the vac disconnected, at idle and when 2000-3000 RPM to make sure the centrifugal advance is working.

[Sparky]

Mike, it doesn't matter how precise you think you've been with static markings; it's dynamic that counts.  Don't go off on any wild goose chases until you've got it right by the strobe.

[Mike6]

Thanks Sparky. Ran the engine up to operating temperature and connected up the strobe - timing is out by miles. So very carefully slackened the clamp and turned dissys left turn and engine stalled. Right turn and revs started to increase so going in right direction but then the advance/retard capsule hit the oil filter and no more movement. Strope just about shows the tdc mark in the viewing area so reckon I must be about 20 plus degrees out. The problem now is whether to take out the auxiliary set up rotate the wheel and try and slide under the cambelt or slacken the cambelt and adjust that way. Thinking about it slackening the cambelt seems simplest

But why would a rebuilt dissy put back in its previous location throw out the timing by such a large amount. 

[molemot]

Sod the clever strobes and measuring. Give it a twiddle until it sounds happy. See how it goes then...you can always go back to science!! Being slavish to numbers and measuring equipment can actually fool you.....if the empirical approach works, then you have to find out WHY!!

[Mike6]

Thinking about it further, if I simply alter the location of the plug leads in the distributor but sticking to the firing order might that give enough to adjust  

[Sparky]

Absolutely. Rotate the leads 90deg in the appropriate direction and hopefully you'll have enough leeway. Otherwise it's cambelt.

Molemot, I agree - but he's got to get it baselined first!

[Mike6]

Need putting out of my misery. Put distributor back to its pre rebuild position, removed spark plug 1 and rotated engine so that piston 1 was at top of its stroke. Then checked that cam dots lined up including checking inlet and exhaust markings. Then checked that tdc on flywheel and pointer lined up and moved car ingear a fraction so that pointer lined up with 10 degree btdc marker. Removed distributor cap and checked that rotor arm was pointing to plug lead 1 which it was and that  the reluctor lined up exactly with the pick up which it did. So static set up must be correct???.

If so why does engine sound like a dog and die when you try and rev it and strobe light doesnt even pick up on the 10 degree mark - suggesting that timing is way out which it sounds like.  

Even wondering if plug leads are on correctly but looking at dissy cap its 1,3,4,2 going anti clockwise.

[Mike6]

Just a thought but when the autoelectrician was here he remade a lot of the connections with new connectors etc and I am wondering if he reversed the two leads going from the dissy to the amplifier what effect that would have on taking a strobe reading. If I temporarily reverse these leads at the amplifier might it have any dire consequences

[Sparky]

I'll say it one more time, Mike, and then I won't bother again. Time it dynamically!

[Mike6]

That was it, the autoelectrician had reversed the wires from the dizzy to the amplifier - although the connectors are different sizes. Temporarily reversed the wires and car fired first time revved nicely and timing marks all line up. Therefore not my fault.

Will now tidy everything up and see whether it has resolved my original problem.

[Sparky]

I'm ready to be corrected, but I fail to see how wire reversal could alter the ignition timing.

[Mike6]

I would imagine its the signal from the dizzy pick up to the coil via the amplifier. Being reversed It must have confused everything which in turn affected the reading being given out via the strobe. Anyway it was the only thing I changed as the original set up was spot on statically. I have now got it back together and it runs fine with the timing all lining up and dizzy back to its original post rebuild position.

Thanks for your help Sparky.

[Andyww]

Yes that would be it.

 

The pulse from the reluctor coil would be inverted. The amp would trigger on the rising edge of the pulse so the timing would have been delayed by the width of the pulse. 

[molemot]

Nice analysis....! Having the "Prince of Darkness" optical system I hadn't thought of inverted pulses...something else to add to our communal store of obscure knowledge.....

Still, given that the engine did run, rotating the distributor until the engine sounded happy would probably have worked...but then there would still be the question of WHY??(!) This way, we all know......

[Chillidoggy]

Ever the curious one, I'd be inclined to swop the wires back over, and see if it reverts to causing the timing issues. It's the only way to be sure.

[molemot]

Spot on, Ian.....proof rather than assumption has to be the way to go; simple, too.....

[Chillidoggy]

It would bug me not knowing if I'd fixed the problem, or whether it was likely to reoccur.

[Mike6]

Swopped wires back over and yes it did revert back to problem. However that would not have been the cause of the original problem as autoelectrician did that just before he gave up on it and I stripped out the dissy for PNM to overhaul. Really nervous about putting the car on the tarmac as I only just made it home last time - will take it out in an hour or two when the traffic calms down. 

Wish me luck - first drive in several months.

[Mike6]

Thats me out of ideas. Car starts, ticks over and revs nicely but as soon as its on the road and it pulls away revs die and she backfires and refuses to accelerate but still ticks over. All that effort etc and shes doing exactly the same, must admit I had a lot of hope in the overhauled dissy as it must be a load issue which points to electrics.

Wife is now saying phone the scrap yard and cut my loses. BUT, just wondering if it could be carb related, although I have cleaned all the jets and set the float heights. Could it be accelerator pumps but dont these kick in above 3000rpm??????. or something else

[Barrykearley]

Wouldn't get much for it from the scrappy - it's mostly fibreglass.

I'd happily do you a favour and drag it out of your sight for you!!!!

Seriously - it has to be fuel supply related

[Mike6]

Hi Barry

Its got new filter, pump, all fuel lines and new regulator and i have re checked fuel pressure. Also if you disconnect a fuel line and turn engine a lovely strong gush of petrol shoots out. So blockage somewhere in the carb could be the answer. But why would it be possible to rev the nuts out of it on the drive but not even pull away on the road.

[Andyww]

What I would do is eliminate vacuum advance as a possibility as I have mentioned before. Even though its used in a "special" way with a valve on these cars something could be wrong with the system. On a standard installation vacuum will be lower under load than when revving stationary.

 

Try disconnecting/plugging the vac advance tube. Then check timing at idle and make sure it advances properly without the vac connected to around 25 deg or so. Then see if it drives without the vac advance. That way you can entirely test the timing is not the problem. Its not possible to test vac advance operation when stationary revving so you need to eliminate it by disconnection.

 

If the accelerator pumps were blocked it would still drive but hesitate under acceleration. It would still speed up gradually though but not backfire. Backfiring does not suggest a lack of fuel fuel issue, it suggests unburnt fuel, ie incorrectly timed or weak spark. Or possibly too much fuel somehow.

 

You might find the connections of the timing coil were correct. If the vac advance is advancing when it shouldnt be that would account for the timing being out.

[Barrykearley]

Vac advance could be an issue ......

When you rev stationary it is very different to driving under load. The whole air fuel load balance is completely different.

The backfire does suggest un burnt fuel in exhaust - but it could also be a valve or ignition issue. Spark at the wrong time - valve sticking open.......... Best of luck with sorting it

[Mike6]

Andy/Barry

Thanks for ideas I will try next week when I have time

 

Andy

I have both advance and retard on my dissy. Do I disconnect both and plug (to prevent loss of vacuum), then run engine up to normal temperature and check timing is still correct at 10 degrees btdc. The arrangement on my car is different to yours. Presumably with engine warmed up a run around the block will prove whether that is the problem with both pipes disconnected.

Barry

When I have tried above checking whether valve is sticking open sounds a good idea. I will take top off cam cover and see whether the bucket tappets move correctly

[Andyww]

Yes disconnect both and plug. The engine should run fine on centrifugal advance only. the rest is for emission control. As well as checking the timing for 10 deg at idle, check it advances properly at higher RPM.