MGB MGB tuning conundrum

[drooartz]

So I'm working on getting the new MGB dialed in. It has a Pertronix installed inside the standard 25D distributor, and according to the records that came with the car it has 1 size richer needles (jets? can't ever keep these things straight).

When I first checked the timing (vacuum disconnected and plugged) it was set at about 30btdc at idle, and the car was running a set of Bosch WR8DC+ plugs.

I've replaced the plugs with the stock sized NGK (BP6ES 7333) and set the timing to 15btdc at idle (950 rpm or so). Piston lift on the carbs gives me just a slight raise in RPM. At one point I also tried setting it at 32btdc at 3500 rpm, which gave about 21btdc at idle. Not sure which is proper...

I'm no expert at plug reading, or any of this for that matter, but going by the pictures I can find the plugs look maybe a bit hot? Ceramic insulator is white and the strap on the top is grey.

Thoughts? I've no idea what is inside this engine, so I'm treating it as if it's in stock configuration. Car now seems a bit sluggish on the top end, and hesitates(?) sightly in the upper RPM ranges.

(the bit of dark coloring on the ceramic is left from cleaning the threads with a small brush)

 

[DrEntropy]

This is my personal opinion, so get out the salt shaker.

NGK plugs seem to be a "one size fits all", I would use a Champion (R)N9-Y(C) as a starting point. Gapped at 0.030"~ 0.032".

Time it at full advance, let idle fall where it will.

The needle moves inside the jet, FWIW.

That plug does look to be "hot" but again, I'd fit a set of Champs to see what/if the difference is noticeable first. If it stays the same, lower the jets by half a flat and look again. Your description of running out of huff at RPM sounds like a lean condition to me.

HTH

 

[drooartz]

Thanks, Doc. Car came with a still-packaged new set of Champions (that model). I'll pop them in and see if anything changes. Will recheck the carb settings as well.

Last summer I rebuilt the Bings on the BMW (very similar to SUs) and was throughly confuzzled by the jet needles and needle jets... clarity comes slowly sometimes.

 

[bob67bgt]

Just to throw a wrench in to the mix....The NGK has a broader range and will work over a wider heat range....???? The plugs are not going to be your problem unless they are in some way defective. Next topic may be your plug wires. On another site it was mentioned that solid core wires can sometimes give a bad reading on a timing light. I have a friend with a MGb that will not run at anywhere near a normal ignition timing. He is soooo far advanced its nutsy. We have not checked the theroy but he is running solid core wires. Its been set like that for years. If you have richer needles it sure does not appear to be a problem by looking at that plug. I say check the plug wires/timing first and maybe that will solve the issues with tuning. Good luck and report back! Bob

 

[DrEntropy]

I don't think the plugs are necessarily a problem, rather they (NGK's) are not a good indicator of where the mixture is set. The photo makes it appear the mix is a bit lean. N9-YChamps are what BMC recommended, I've never had an issue with 'em.

On another site it was mentioned that solid core wires can sometimes give a bad reading on a timing light. I have a friend with a MGb that will not run at anywhere near a normal ignition timing. He is soooo far advanced its nutsy. We have not checked the theroy but he is running solid core wires. Its been set like that for years.

That seems odd (and weird). Do you static time it then? Not sure about any oddity with solid wires and Pertronix/Crane/etc. boxes tho I would think the only issue would be radio static as a byproduct. I run solid wires in aout everything we own, no "smart iggy" boxes tho. Makes me wanna go throw a light on the Alfa to see if it acts strange. Points and resistor wires there. Only timed it static or vacuum method. mybad. :wink:

Drew: Put a TINY amount of anti-sieze on the plug threads, too, BTW.

 

[drooartz]

Not sure about any oddity with solid wires and Pertronix/Crane/etc. boxes tho I would think the only issue would be radio static as a byproduct.

On the Tunebug (points, solid core wires, non-resistor plugs) I've had trouble with a previous timing light -- RPM feature didn't work at all (crazy readings) and the timing seemed to be moving all over the place. An older/different light worked just fine.

The new light worked as advertised with the MGB. RPM feature was right on and the light was steady. No idea what sort of plug wires they are.

All this makes me wish I had more experience with these old cars. I really don't have *any* reference point as to how an MGB (or Sprite, for that matter) is *supposed* to run. Hard to dial it in when you can't see the target.

 

[Legal Bill]

Back in the day, we static timed all of them (after we made sure everything else was right) and then we drove it. If it did not run right, we would change the timing by a dagree at a time and repeat the process. The A and B series motors both should rev to red line without a problem. We would adjust until we found the maximium return based on seat of the pants, and sometimes a series of timed 0 to 60 runs. Engine pinging and run-on after switching off the ignition were the two fence posts we tried to tune between, followed by ease of restarting.

 

[drooartz]

I need to fly one of you out here...

 

[bob67bgt]

I do not run solid core wires. But with my good friends car there is a timing issue and he does have solid core. Just for a laugh I would static time it and see how it runs and throw the light on it for a reading. It may not be a issue but a very reputable source posted the info on the other board. If your mixture is set where it just rises and then falls back its pretty close UNLESS there is a real odd needle issue. Doc and I probably both have the time if you have the plane tickets! If it was running good before you messed with it then backtrack till you find what you did to change it. Sounds like the timing was a big change. I do not know how much you changed the mixture on the carbs and which direction you went. Keep your head down and you will get it! Bob

 

[Deleted member 8987]

I have never used anything BUT solid core wires, on Fords, Jags, all the Brit mobiles that came into the shop.
My Jag came from the factory with solid core wires. I have never, ever seen an issue with a timing light mis-reading using solid core wires.
But, if someone bought a brand new, state-of-the-art timing light set to trigger with the voltage at the end of the wire, who knows.
I still have, somewhere, one or two of those what, Xenon tube, non-powered lights you had to use with the bonnet pulled down over your cranium to see the light.....

And, I ONLY use Champions in Fords and LBC's. Never, ever had one fail me yet, and it's been, what, 46 years?

In fact, I clean the old ones, re-gap, and re-use next time. I've got plugs that they don't even make anymore!

Oh, and Drew....that black stuff from the wire brush on the porcelain.....that will eventually cause plug failure....flashover down the porcelain.
Sen it.
Just clean it off with spray carb cleaner, and maybe an old toothbrush.

My trick on cleaning is blast, blow with plug cleaner, wire wheel the threads, then hose it down (especially down inside) with carb cleaner, inspect and do again if needed, then gap and store or re-install.

 

[drooartz]

I need to gear up better for cleaning plugs...

Thanks all for the support, moral and otherwise. I do get frustrated at my own lack of both knowledge and experience.

As for my changes, carbs were leaned out a bit and timing backed off. Old timing was about 30* at idle, currently running 15* at idle.

New plan is to swap in Champions and readjust timing to 30* at 3500 rpm. Then either richen things up a bit or try and start fresh by resetting the jets.

 

[DNK]

Think Paul keeps a standard wire with his light when he tines his 6 with the Magnecore

 

[aeronca65t]

Just FYI-
I'm running solid core wires and a Pertonix set up just like your's (in the Spridget race car). I've been running that set up for 7 years with no problems. I just timed it yesterday (we're off the the races tomorrow).

Pertronix advices against solid core.....but they do not give a good reason for this advice. It has been no issue to me.

I have not seen problems with solid core via supressor plug wires with my timing light.

 

[bob67bgt]

I went back and did a search on the other site. B-racer (advanced distributors)posted that using the copper wires will change the reading on the light. I did get it backwards. He advised that the timing would be more advanced than shown. One of the posts mentioning this was on mar 18,2011. So your timing if anything is reading lower than it really is if I am processing his info correctly and if you are running copper wires. Hey, At least the Sprite is still running good -right? Be sure to keep us all informed when its running good again. Now I am wondering if this is a factor with points or electronic or both...Who knows....Happy tuning! Bob

 

[Deleted member 8987]

Then there is always the question, on the one you work on that's WAY off, is the pulley mark correct?

 

[drooartz]

All good questions, and I have no good answers! No idea if the marks on the MGB (that's the one that read really advanced initially) are correct. Don't know what sort of plug wires they are either. Lots of unknowns there.

Hey, At least the Sprite is still running good -right?

Sprite's got a probable exhaust leak, so it's not running much right now. And the BMW needs everything. At least the Honda runs!

 

[drooartz]

Okay, so I had an hour or two last night and did a but more tuning. Here's what I did:

* Swapped to Champion RN9YC gapped at .032
* Went 1 flat richer on each carb
* Verified that both carbs have a #6 needle
* Advanced the timing to what should be 30* -- closer to where it was when I got the car, but still not as advanced

Car ran smoother, but the plugs seem to still be telling me I'm either too hot a plug or too lean.

I then pulled the dashpots to verify the needles, and reset the jets all the way in so that I could figure out where they are and get a fresh start. The jets were at 17 flats front 13 flats rear. I did notice that when all the way screwed in the front jet sits noticeably higher than the rear one, and both were proud of the carb floor when all the way screwed in. So tonight I'm going to play with richening up the mixture and will verify the timing.

A question about installing the needles: how far into the piston should they be seated? Should the little shoulder be flush with the piston bottom?

 

[drooartz]

One other thought is that I did switch to the K&N RU4410 air filters on the stock MGB velocity stacks after I got the car. Car came with the factory cans, which I do still have.

 

[DrEntropy]

Needle 'shouler' should be flush with piston base.

The jet settings (13 and 17 flats) is odd. Start with 12/13 flats each, use the pin to raise the pistons and see what happens.

Have you a UniSyn or other manometer to be certain the carbs are balanced? That would be a good first step.

'smits commandeer'd the camera this AM or I'd be posting pix...

 

[drooartz]

Needle 'shoulder' should be flush with piston base.

Thanks.

Carbs were balanced (I have a sync tool and I'm not afraid to use it

Dangerous, I know ).

Oddest thing is that there is no question that the jets, when screwed all the way in, are at quite different heights (and both above the bridge, with the front one higher). I've got them currently both set down 12 flats, but that doesn't make them both the same height. I'm going to pull out my calipers when I get home tonight and set them to the same height regardless of the number of flats. According to some posts I was reading by Hap .070" down seems to be a good start point.