Series 1.5 4.2L backfiring under load with new 123 distributor

[Freoway]

Hi all, in the process of rebuilding a Series 1.5 4.2L. RHD. Has a rebuilt engine, new electrics etc. Starts,runs and idles fine. Installed a 123 distributor with 16 curve (non-bluetooth). Timing set at 10BTDC manually and checked with strobe light at idle.

When I rev the engine it will backfire through the carbs and occasionally afterfire through the exhaust. I initially chose Curve '0' but only noticed a few degrees advance to 2000rpm. I then swapped to the other extreme - Curve ''F'. Much improved but still backfires when revving high.

I took the car onto my street and took it for a short drive (not registered).

I have also removed the inlet cam cover to make sure the cam/valve timing is set properly.

Yesterday I conducted a leakdown test on all cylinders. Results were excellent.

Given that I believe I have set the carbs correctly (according to the manual), static timing is ok, advance seems to function properly, I'm at a loss to work out where the issue is.

I'm running 98 octane fuel with valve lube.

Any ideas wise people?

[malcolm]

I have the same 123 as you, non bluetooth, and use curve 2. SNG use curve 5, but that advances a lot more than standard. Mine runs well on 2.
Potential problem though - when you install the 123, you set it up by rotating until the light goes out? or comes on? Anyway, that is quite critical and mine didn't seem to like it when we set it up - a bit of mild rotating with the engine running was needed to get it right.
Look at the initial installing procedure is my advice.

[mgcjag]

As above curve 2 should work ok....10btdc turn dizzy till light on. ....have you checked that your tdc is correct..ideally you need a dial guage through the spark plug hole to determine exactly when the piston is at the mid point of the top of its stroke.....this is tdc and cams should then also be at tdc...then set your timing pointer to tdc....Steve

[Freoway]

I have the same 123 as you, non bluetooth, and use curve 2. SNG use curve 5, but that advances a lot more than standard. Mine runs well on 2.
Potential problem though - when you install the 123, you set it up by rotating until the light goes out? or comes on? Anyway, that is quite critical and mine didn't seem to like it when we set it up - a bit of mild rotating with the engine running was needed to get it right.
Look at the initial installing procedure is my advice.

Hi Malcolm. I rotated my dizzy until the light just came on. I presumed if I was going to rotate it further I would get more advance.

[Freoway]

Update: I popped in the old distributor late yesterday to confirm that there wasn’t any issues with the 123 distributor. It ran much the same. I hooked up a vacuum gauge to the intake manifold and it read about 15 in-Hg. I advanced the timing until it read 18 in-Hg (which was wear it peaked at). That got rid of the backfiring on revving. I haven’t had a chance to see where the timing is now or to take it out on to the street. And whether it starts when cold with the timing advanced. I’ll give a progress update if I get a chance to look at it again today.

[Freoway]

Yesterday I advanced the static timing to something ridiculous (about 34 BTDC). Clearly something is out somewhere. I know #1 is at the back at #6 is at the front. Manual also says time with #6 which I am.

What should I look at?

[mgcjag]

Start at the basics and ensure that you timing pointer is set correctly...refer to my post above and set tdc...then at 10deg btdc on the compression stroke for 6 set your dizzy.....Steve

[malcolm]

And do read the set up instructions carefully. I think you can put the 123 in the wrong way round, then have to advance massively to get it running

[bitsobrits]

An E type distributor shaft can only go in one way due to the offset drive dog. The body of a distributor with vacuum advance only fits within a small range of positions. I don't see how it's possible, then, to install it "wrong way round".

[malcolm]

You're right, only goes in one way, I think what happened is that the whole thing was positioned about 180 out when it was put in? Just know there was massive rotating to get it firing!

[chrisfell]

My 123 allows adjustment to reorient the dizzie by 180 degrees. Can't remember how, but I did adjust mine.

[mgcjag]

Simple..its in the instructions..just reposition the drive dog on the 123.....or even easier just rearrange the ht leads on the cap....Steve

[Freoway]

Sorry for not responding to everyone's replies earlier (was out of town). Thanks for all your comments. I still seem to require significant static advance (roughly 20deg more than expected, ~34deg). Car starts at the turn of the key, so no issues there. Have double-checked timing on crank pulley against timing mark (and piston position). With distributor out, dog locator sits at around 11 o'clock. I took the car out for a couple of runs around the block today - literally the first time it's gone further than the driveway under it's own steam in a few decades. Goes ok, but will still backfire under heavier acceleration. Normal acceleration is fine. I'm also using the most aggressive advance curve on the distributor 'F". A mystery!!

Has the engine reconditioner not fitted the crank pulley properly (I'm saying that assuming it's a press fit on the shaft).

Lloyd

[abowie]

Has the engine reconditioner not fitted the crank pulley properly (I'm saying that assuming it's a press fit on the shaft).

Lloyd

There's a Woodroffe pin so no.

[mgcjag]

Hi Lloyd...you never know on an old car it may have an xj6 pully that's got different timing marks......ok we can help if you help us...turn your engine to your 10dbtdc on its fireing stroke and tell us where your rotor arm is pointing....a photo would be even better..
Steve

[Freoway]

Hi Steve, Thanks - I'll do that. Just going in for some cataract surgery today so might be a couple of days. I took a photo with the dizzy out that showed the dog locator at roughly 11 o'clock. I'll attach that one. From memory, the rotor direction is at 90 degrees to the dog locator slot, pointing across the wider side of the slot if that makes sense. So my guess is that it's pointing at roughly 8am. See 2nd pic. (R for rotor direction).

And yes - an actual pic would be simpler/easier!

[abowie]

With #1 at TDC compression stroke the slot in the dizzy drive should be at 10 minutes to 4, with the big D up.

Your drive is upside down (180 degrees out), and may possibly be one tooth out as well; parallax on your picture makes it tricky to be sure.

[Freoway]

Thanks. I’ll double check I set it up right before drawing any conclusions. With #1 piston raised fully and the crank pulley timing mark set at the pointer, it should be right. I didn’t use a gauge to accurately determine piston position as I saw the pulley timing mark was matching up nicely anyway.

Will confirm once I recover from cataract surgery.

Thanks again. Lloyd

[Gfhug]

Ironically my engine also had the dizzy drive upside down, but it was easily corrected by attaching the plug leads in the appropriate new positions. Remember no. 1 cylinder is at the back of the engine not the front and both 1 and 6 are at TDC at the same time but not both on compression stroke.

Good luck with the cataract surgery.

Geoff

[Freoway]

Thanks Geoff. 'I can see clearly now the blur has gone' (aka Johnny Nash).
Maybe I can blame some of my mistakes/missteps on bad vision!
Unfortunately I'm not allowed in the garage for a few days. If the 'D' is 180 degrees out, then I'll pop the pin out and turn it around.
That said, it still doesn't explain why I need so much extra advance. I'll use a run out gauge on the piston top to get an accurate TDC.

Cheers, Lloyd