MGB 80 MGB ran great Friday - yesterday sounds like helicopter

[RickB]

I filled with gas at the place I always do, only one with pure gas near here.
Drove 15 miles, stopped to buy dinner and then drove 4 miles home.
Running perfectly - that was Friday afternoon.

Left it until today, got in, started it and it was sounding like a helicopter.
Like 2 cylinders and sometimes 3 were firing.
Ok, so I pull plugs and look and two were pretty ugly like soot.
Cleaned and checked gap and reinsterted.
Still not running on all 4.
Pulled the cap, put on a new one I had sitting around.
No change.
Sooty black plugs.
Clean and repeat.
Put in new plugs also.
No change.
Starting to think this electrical problem might be fuel related.
Look over carbs, seem good.
Pull fuel line and run in a jar, good flow and I couldn't see water.
Still no good.

It has electronic ignition with the Crane (IIRC) XR700?
Also has a pair of HIF4's and the '74 exhaust.
All that has been running great for 14 months (installed carbs and exhaust last March)

Also a new Bosch blue coil installed a few months ago.
Only other work I've done over the past few months is replaced the brake hydraulics and the exhaust from the downpipe back.

What can cause plugs to foul horribly withing a couple minutes of running badly?
Black sooty looking plugs, I can take a picture if it helps.
I checked my vacuum lines and all seem good, really don't have many to check since installing the HIF4's.
No smog equipment on this engine since before I bought the car.
Distributor is tight and hasn't moved, I can check timing with a light to make sure.
This thing where it fires on one or two cylinders is strange.
No overheating, in fact it's been running cool with the temp gauge only coming up to maybe 1/3.

 

[JPSmit]

I suspect it is running very very rich.

 

[RickB]

Thanks JP, it's a dry soot on the plugs btw.
Strange stuff.

 

[Mickey Richaud]

So many things to check! What I'd do is, at idle, pull each plug wire one at a time to determine which one's not firing. Then swap wires to see if that changes the plug firing to determine if it's a bad plug wire. Alternatively, you can put a timing light on each plug wire to see if they're all getting spark.

You said you changed caps; did you check the rotor?

Valves adjusted OK?

Fuel filter clogged?

All vacuum lines present and accounted for?

Checked the carbs with a Uni-Syn or something similar for proper flow?

I'm not familiar with the Crane system; do you have troubleshooting info?

Let us know how you get on.

 

[RickB]

Getting spark on each cylinder, verified with a timing light.
Once I did get it to idle long enough to look at the timing and it's right on.
Traded cap, rotor and plugs with new and back again due to no change.
Tried pulling a plug wire and then it wouldn't start at all any more.
Pulled one at a time with the other three connected, it still wouldn't start.
Sprayed in some starting fluid down each carb and then it started again very roughly.
Won't idle so I can't pull a plug while it's running.
Vacuum lines are good.
Fuel line to the carbs is providing good flow, don't know if it is flowing through them.
When it runs the best it can it does seem to be on three cylinders.
The 1,2and 4 plugs are black & sooty and #3 is clean like it's not firing at all.
Last time it ran on Friday it was running perfectly.
I use ethanol free gas.
I have compression of 155 - 145 - 150 - 150.

 

[Mickey Richaud]

One more question - Are you using needles and seats or Grose-Jets? The latter can be problematic.

Beginning to sound like you need to pull the carbs and see what's going on with them.

 

[JPSmit]

This is a long shot, but, a couple of years ago I pulled into the driveway and all of a sudden the car began to make the most incredible racket - and then I couldn't get it to run at all - after much invasive work (some of which still affects the car) I realized a bolt had fallen out of the intake manifold - totally throwing the mixture out of wack - the bolt was, I believe originally part of the emission system.

Before you go too far invasively remember these cars don't just fall out of tune - Step back and look for obvious things - is there a hole somewhere? a cable binding? some grit in something? has the distributor wiggled loose? this seems like it should be simple.

 

[RickB]

Mickey - needles & seats.
JP - yes I've been looking for anything like that - so far not finding.
You know from my years with Midgets & Sprites I'm used to things falling apart like that, it's been kind of quiet with the MGB.

So anyway, after messing with it some more now it will not start at all.
I still have spark to each plug.
Sprayed starting fluid down both carbs and still no fire.

 

[pdplot]

Remember the old saying - if it's got gas and got spark and they both arrive at about the same time, it's got to run. 98% of the time, it's spark not fuel. Since you checked for water in the gas and found none, it looks like your Crane ignition has gotten sick. Only way to tell. Disconnect it and reinstall points and see what happens. I had a similar problem with Crane years ago. I even sent the unit back to Crane and they said it checked out fine. I reinstalled it and almost got stuck on High Ridge Rd. when it started to run just like yours. I reinstalled the original system and have had no trouble since - and that was years ago.

 

[RickB]

I'm going to check my shed for a 25D distributor.
The one in my 80 MGB came from the factory as electronic so there's no switching it to points.

 

[RickB]

I've got a 73 Midget with a 1275 sitting right behind the B.
Tomorrow I'll see if it's a 25D in there and if it is I'll swap it in and see what changes.

 

[RickB]

As a last thing on my list of things to check before performing any major surgery I decided to call the place where I got the gas.
I asked if they have had any reports of problems after people filled up.
The girl who answered transferred me to the general manager.
He said yes, they have had reports and their premium non ethanol gas had to be "repaired".
He didn't say why or what was wrong but said if I had to have it towed to a shop and repaired due to something wrong with the gas they would pay for repairs.

Now - how do I find out if that's it?
I can get some good gas from a different place in a gas can and somehow pump that into the carburetors?
Any ideas?
If I can find a way to feed good gas in then I'll replace the spark plugs again and try to start it.
Of course I don't have a spare pump...
Oh yes I have an electric pump on one of the other Midgets I can steal for a little while.
Ok, I'll pump good fresh gas into the carbs and see how it runs.

Is there a chance that all this bad running has damaged something? Like a valve?

What's everyone's recommendation going forward?

 

[kennypinkerton]

If pull the carbs and drop the bowl to see if there was any crud in it. Could be their underground tank has corrosion problems... or who knows could be mixed with e85 or Lord knows what.

And/or check and change the fuel filter

 

[kennypinkerton]

With some fuel line and a small gas tank, you could gravity feed the carbs with some gas that you know is good.

 

[RickB]

Got my old fuel pump hooked up and pumped some fresh gas from a 2 gallon can into the carbs.
Put in new plugs.
It ran for a few seconds on all 4!!
Then it started missing and chugging and helicoptering again.
Wouldn't idle.
Pulled plugs, again 1, 2, and 4 fouled and #3 looking good.
Checked compression again, good still. (go figure)
Guess I'll go pull that 25D out of the Midget and try it.

 

[RickB]

It's running!

After my last post I went out and pulled the 25D out of the Midget.
Been a while since I looked at the old girl, had a Pertronix in there.
Ok I thought, I'll see if it works.
Hooked it up in the B like it was in the Midget.
No fire.
Dang.
Stomped around a bit, tried to see if it was something I did wrong, then pulled it and put the original distributor back in.
Played with timing a little and FIRE - the spark kind, not the bad kind.
Idling along I set the timing and then turned it off and tightened everything up.
Just in case it was a fluke I started it up again - running perfect.

This is all with a facet pump pumping gas into my carbs from a two gallon can.
Decided even though it would complete the experiment I would not run gas from the tank back into the engine.
Pumped all the gas out into several gas cans and asked the dear wife if she'd mind going and getting me a can of Seafoam and another 2 gallon gas can.
Headed out now to get two more gallons of good gas and then I'll see if I can get the car to drive to the station a block from home.
If so I'll put in the Seafoam and fill the tank with good old 76 station gas.
I'll let you know how it goes.

 

[RickB]

Ok, made it to the gas station, filled up.
Added seafoam first then filled up.
Running great!

 

[JPSmit]

Ok, made it to the gas station, filled up.
Added seafoam first then filled up.
Running great!

Hurray! and, amazing how often it is the simple things! get out and drive!

 

[RickB]

Drove it to work this morning, nice uneventful drive in.
Like it should be.
Might be a top down day here in western Washington!

 

[JPSmit]

Drove it to work this morning, nice uneventful drive in.
Like it should be.
Might be a top down day here in western Washington!

good news! still a bit cool here