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1978 MGB Ignition Problems

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KRS Ken S
Sault Ste. Marie, Ontario, Canada   CAN
In my first post I was able to get my carburetor rebuilt and my automatic choke issues resolved, the car runs better but it's still off.

I checked my valve clearance and did a rough check on the cam lobes and they seem fine.

I checked the timing and it was set at roughly 30 degrees of advance at idle. I set it at the specified 13 degrees and the car wouldn't make it up a hill, so I put it back to where it was.

It has a recently installed (previous owner) Pertronix distributor, PN D176600. My first thought was that the outer ring had slipped on the harmonic balancer but now I'm not so sure of that. A few things that I've noticed are the distributor cap fits poorly (loose) and the rotor also has some play in it. There doesn't seem to be any mechanical advance when I rev it up to 3000rpm from idle. The distributor has mechanical advance but it's extremely loose, easily advanced. At this point I'm wondering if the mechanical advance is coming in at idle.

At this point the car runs rough at idle with all that advance. But a vacuum gauge is indicating late ignition timing.

Any thoughts or experience with an issue like this would be appreciated.



Edited 1 time(s). Last edit at 2017-07-15 09:39 PM by KRS.

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Steven 67GT Avatar
Steven 67GT Steven Rechter
Imperial Beach, California, USA   USA
Put cylinder number one at the top of its compression stroke and confirm if the timing mark on the harmonic balancer has slipped.

Second, dump the Pertronix distributor. If it is broken as you say it's not repairable since Pertronix doesn't stock replacement parts for it.

Replace the Pertronix with a Lucas 25D distributor.

Basil Adams Avatar
About 12 miles from Sears Point, CA, USA   USA
If your initial timing is 30°, there's an electrical problem. Buy a long 14mm bolt and take off the rocker cover and take the spark plugs out. Insert the bolt deep into the #1 spark plug hole and rotate the engine by hand until the #1 piston touches the bolt (don't force it or press hard.) Mark the crank pulley against one of the timing teeth. Then rotate the engine backwards until the #1 piston hits the bolt coming from the opposite direction. Mark the pulley against the same tooth. Top dead center is halfway between your two marks. Mark TDC on your pulley against the same tooth you've been using. Then, with the rocker cover off, rotate the engine until both valves on cylinder one are closed (both springs all the way up) that's TDC on the compression/ignition changeover. Put your plugs back in and attach the wires. Start the car and put the timing light in with the inductive pick up on the #1 plug wire. Fire up the car and shine your timing light at the pulley and the TDC mark on your pulley should be 10° before the tooth you marked. If it's there, it's not a timing problem. Could be coil, wires, cap, plugs or fuel. That's a good place to start only because an initial advance of 30° would be dangerous. Keep us posted and feel free to call or email if I can help. Thanks. Basil 707.762.0974 basiladams@yahoo.com



Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains

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Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, Ohio, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
Ken - Did you set/check idle timing with the vaccum hose on or off?

My "simplified" method to check timing is.

- rotate the crank until the timing mark is zeroed at TDC.
- rotate the crank forward to 10*
- Use a small file and make a second notch at TDC

Start the car and adjust the idle screws to 3,000 RPM.

Set the timing so that the new index mark points at 20* - this gives you 30* total timing at 3,000 rpm. My late model actually runs a bit better between 32 and 35.

The reason that I do this is because I don't know the dizzy curve for any of my dizzy's. But I do know I want 30-35 degrees total timing. I let idle timing fall where it may.



The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

KRS Ken S
Sault Ste. Marie, Ontario, Canada   CAN
I appreciate all the replies!

I checked/set the timing with the vacuum advance hose disconnected and plugged. Although the vacuum advance hose Is connected to a small solenoid that apparently only activates the advance in 4th gear, which seems really odd to me.

Am I reading correctly that the timing mark/notch on the harmonic balancer is 10 degrees before TDC?

If that's the case then, there's 10 degrees of advance built in so to speak, 13 degrees from setting the timing, and then whatever the mechanical advance adds.

I won't be able to do work on the car today but I will keep you posted.



Edited 1 time(s). Last edit at 2017-07-16 06:58 AM by KRS.

B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, Minnesota, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB
2014 Dodge Charger
The furthest mark CW is zero. The mark on the pulley is TDC. Each pointer CCW is 5 degrees.

Check your idle timing with the vac line disconnected from the distributor. Attach it to manifold vac, and you'll be around 25 degrees, which would be normal. More if you have the wrong vac unit installed.



jeff@advanceddistributors.com



Edited 1 time(s). Last edit at 2017-07-17 07:33 AM by B-racer.

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Jeff's the distributor wizard, so I know he was just sleepy when he posted this. Actually it's just the opposite. The large pointer, which is the one furthest clockwise, is zero; Each of the smaller pointers in the counterclockwise direction is 5 degrees advanced...

Jeff -- switch to decaf... grinning smiley

Dick



In reply to # 3552887 by B-racer The furthest mark CCW is zero. The mark on the pulley is TDC. Each pointer CW is 5 degrees.

Check your idle timing with the vac line disconnected from the distributor. Attach it to manifold vac, and you'll be around 25 degrees, which would be normal. More if you have the wrong vac unit installed.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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Attachments:
MGB Timing Marks.jpg    20.3 KB
MGB Timing Marks.jpg

KRS Ken S
Sault Ste. Marie, Ontario, Canada   CAN
Okay, everything is the way that I originally thought it was, notch on harmonic balancer is at TDC, and then starting on the driver's side the first point on the timing scale is zero, and it goes in 5 degree increments.

Does anyone know how many degrees the mechanical advance adds, I would guess it should be somewhere between 17-20 degrees?

To start I will probably try to confirm that the balancer ring hasn't slipped, set the timing to spec, retest the mechanical advance, and then verify the wiring of the distributor. The person who wired it did a bit of a butcher job.

It probably wouldn't hurt to check for vacuum leaks, what's the preferred method, a bit of oxygen from a torch? I will also see if I can pickup a distributor cap and rotor locally, I don't like the sloppy fit of the ones that are on it.

Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, Ohio, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
Ahh.. The "Transmission Controlled Spark Advance" - Yup it's an emissions thing.

I bypassed mine when I had the ZS and desmogged it.

I won't reiterate what I said in #4 above except to say it works. Remember now that you have the pertronix (You do have the original ZS carb?) you are already starting to go "off book" in terms of how the manual will tell you to tune the car.

Slipped harmonic balance, timing chain jumped a cog, aliens attacked are deep troubleshooting problems to turn to after the basics are squared away. Occam's Razor - Keep it simple.

In reply to # 3552852 by KRS I appreciate all the replies!

I checked/set the timing with the vacuum advance hose disconnected and plugged. Although the vacuum advance hose Is connected to a small solenoid that apparently only activates the advance in 4th gear, which seems really odd to me.




The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, Minnesota, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB
2014 Dodge Charger
In reply to # 3552923 by dickmoritz
Jeff -- switch to decaf... grinning smiley

Good catch Dick! I corrected my post. The problem is that the caffeine hadn't kicked in yet. smileys with beer



jeff@advanceddistributors.com

Peterz3 Peter Ray
Lodmore lane, Cheshire, UK   GBR
on the subject of timing marks on my 79 mgb gt the marks are on the under side of the crank pulley making it very difficult to see them with the engine running I have to use a mirror on a stick
peterz3

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Peter,

If the engine number tag is still affixed to your engine block you might check it, as I'd guess you have either an earlier engine, or an earlier timing cover and harmonic balancer, as the lower timing marks were long gone by 1979...

Dick

In reply to # 3553730 by Peterz3 on the subject of timing marks on my 79 mgb gt the marks are on the under side of the crank pulley making it very difficult to see them with the engine running I have to use a mirror on a stick
peterz3



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Team DNF Avatar
Team DNF David Dobbins
Kansas City, Missouri, USA   USA
Peter

If you do have an earlier engine, you might be able to change the timing cover and harmonic balancer with later model parts. You have to do them as a pair to the later style with marks on top. Did that with my 71 GT and it worked out slick. No more laying on the ground to check timing.

Dave

KRS Ken S
Sault Ste. Marie, Ontario, Canada   CAN
Dan D - yes it has the original single ZS carburetor.

So I finally had a chance to have a look at it tonight. On the way over to the garage where I have it parked I started thinking it must have a vacuum leak. Sure enough I found a missing vacuum nipple on the backside of the intake manifold. I temporarily plugged it and set the timing to spec, 13 degrees of advance. The engine is much smoother but has a backfire underload now.

There is still something off which I'm thinking is related to the distributor. It doesn't seem to give much mechanical advance. Is it possible that the Pertronix is designed to have the vacuum advance connected? (As previously mentioned mine goes through an emissions solenoid). After I check the harmonic balancer for slip and verify the distributor wiring I was thinking of connecting it to ported vacuum and see what happens.



Edited 1 time(s). Last edit at 2017-07-21 10:20 PM by KRS.

Vern Avatar
Vern Vern Smith
Athol, Idaho, USA   USA


In reply to # 3556375 by KRS So I finally had a chance to have a look at it tonight. On the way over to the garage where I have it parked I started thinking it must have a vacuum leak. Sure enough I found a missing vacuum nipple on the backside of the intake manifold. I temporarily plugged it and set the timing to spec, 13 degrees of advance. The engine is much smoother but has a backfire underload now.

There is still something off which I'm thinking is related to the distributor. It doesn't seem to give much mechanical advance. Is it possible that the Pertronix is designed to have the vacuum advance connected? (Mine goes through an emissions solenoid). After I check the harmonic balancer for slip and verify the distributor wiring I was thinking of connecting it to ported vacuum and see what happens.

Get rid of the TCSA solenoid valve. It does nothing until 4th gear anyway, and little to impact emissions. I have removed mine and my car still passed California emissions just fine. Never found a tester who even knew they existed, so removing it was not a fail. I think I'd quit worrying about the numbers and just set the timing for best performance. If it knocks a bit under heavy acceleration, back it off a bit. If it lacks power try advancing it some. These are not really high tech machines. If Canada doesn't have strict emissions testing, just de-smog it altogether. Remove the air pump and air rail and plug the holes. Since you still have the ZS carb, adjust the needle (you'll need the tool) for best performance, not best idle. Remove and plug the gulp valve, anti-run on valve, etc. Make sure the "water choke" on the carb is working correctly and is set to be completely off "choke" when the engine is warm. Lots of threads about de-smogging. My 79 still runs great, even with the ZS. Pertronix ignition has never given me any trouble. Of course you can improve things with different carb/manifold, but if all you want is a reliable, fun car, the stock equipment will suffice. Just my former Kalifornia opinion, though.



If you pretend it ain't broke, you don't have to fix it!

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