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MG MGB Technical - Timing after rebuild

So it finally stopped raining here, but I still can't get my B to run right. It's a 1972 (currently set up with HS4's while the HIFs are rebuilt).

Both mixture nuts are set to about the middle of the travel, because for starters I'm just trying to get it to run. The distributor (25D) was rebuilt by a reputable establishment last summer. If I pull a plug and ground it to the chassis, I get good spark, so the coil (also new ~ 9mo ago) seem to be OK.

I've been working through Les Bengston's static timing instructions (one of the best explanantions I've seen so far for those of us who grew up with ECUs and fuel injection). The rotor is in the neighborhood of the #1 lead, with the engine at 10deg BTDC (based on the balancer mark) but my indicator lamp is not lighting regardless of rotating the distributor through about 60deg of travel. I can get it to run OK in the garage with the timing way retarded (crank the dist. over till the vac advance rubs the oil press. hose), but is very weak in motion. If I advance the dist (rotate clockwise off the hose) I start to get backfiring through carbs.

What am I missing here?


Thanks
Steve Aichele
Steve Aichele

I'm wondering if, as it just about works by moving the distributor through 60deg - you don't have the plug leads out by one on the cap do you?
Dave Smith

Steve
Barging in here from the midget board. You got your distributor installed 180 deg. out?
In other words, with the rotor pointing at no.1 lead (which is a good thing) and timing mark at about 10 BTDC (another good thing) - don't forget that the timing mark will also be at that position for the firing stroke of no. 4 cylinder.
To check for sure, pull off the rocker cover and check that both valves for no.1 are tight shut - then you know that no. 1 is on it's firing stroke. you should then get some sort of regular bang! If you find no.4 has valves closed and ready to fire - then the dissy is out 180.
HTH
Steve
Steve Clark

I did check the valves on number 1 - both closed, on the rotation following valve #2 opening. So it's the right stroke.

Can the engine run 90 degrees out? That is, with the plug wires off by one socket on the cap?

What bothers me is that it looks like I should have contact between the rotor and the appropriate plug on the cap but don't have anything on the light (did check that it had a good ground). If I crank the dizzy the other way (clockwise) I might be able to get to the next plug lead. Certainly easy enough to check this evening.

Thanks for the ideas
Steve
Steve Aichele

Read MGA Thread: Timing and tuning
Posted 26 May 2004 at 18:39:38 UK time
Henri Van Groningen
I am sending you my reply to Henri direct, may help.
I can't recall what was in your earlier thread, and it seems to be in limbo between current and archive.
FRM
http://www.usachoice.net/gofanu
FR Millmore

The dizzy turns ccw viewed from the top , make sure you are on the right side of the cam , ie not timing on closing .
S Best

Are you sure your leads are attached to the dist in the correct sequence. Real easy to do it in the wrong direction and end up with your symptoms. Plug wires should be intalled in the cap ccw. You'd effectively be running on two cylinders, with the other two firing off the compression stroke.
R. L Carleen

1 3 4 2 going CCW from no 1 when you have identified that , and set it to just open as cam comes round . I also tweak the rotor arm against the advance springs to ensure its in the static position , oh and you might want to check the vacumn diapragm by sucking on it , then letting go to ensure it's against the stop .
S Best

Steve. Make sure you are on the compression stroke. It sounds like you are since you watched the intake valve close. Then, check to see the position of the rotor. It should be pointing towards the 2 O'clock position. Pull the rotor off (you do not need it, nor the cap to static time). Hook up your test light. Rotate the dizzy counter clock wise about 35-45 degrees. Then, rotate it backwards (clockwise) until the test light comes on. That is the point at which the points have just opened and the spark impulse is sent out.

Since you have a 72, you should be able to see the timing marks from the upper side of the engine. If you have a dynamic timing light, you can simply hook up the light, have an assistant crank over the engine and turn the dizzy while watching where the timing marks are. By the time you get near 15 degrees BTDC, the car should start. If not, you have some other problem you need to work out.

Not sure what "mixture nuts" you are writing of. If they are SU carbs, you want to set the jets about .060" below the bridge of the carb. This is about two full turns (or 12 "flats") of the jet adjustment screw. Les
Les Bengtson

Thanks, all. Never take anything for granted - apparently when I switched from the HIFs to the HS4's, and switched dizzys to keep the vac advance right, I PUT THE PLUGS ON CLOCKWISE!!! Damn damn damn. But I also know far more about timing than I did before (in the grab the distributor and see what happens school).

Swapped the wires, now have compression, fuel, AND IGNITION, took a spin around the block and it runs pretty well. Next I may take a crack at the dynamic timing.

Thanks again.
Steve


Steve Aichele

Steve. Glad you got it up and running. Always something to learn about these cars, isn't there? Les
Les Bengtson

There is always something - what bothers me is re-learning. I've reconnected sparkplug wires dozens of times. But onnthat last dizzy swap I must have reversed them.

Thanks
Steve
Steve Aichele

Easily done , my B would not start (well , run) the other day , looked under the lid and had 3 and 2 swapped .
S Best

Congrats for persevering, Steve.

On my first engine change I "assumed" that the distributor rotated clockwise to match the crankshaft looking from the front - no logic! I actually drove the car round the block with 2 and 3 leads reversed but was a bit disappointed at the performance....

As a result, I often chip in to threads such as this with a reminder re anticlockwise rotation.

Regards,

Barry
73B
B.J. Quartermaine

This thread was discussed between 03/06/2004 and 04/06/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.