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Mystery chugging

Moss Motors
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mgmidget76 Brian T
Chattanooga, TN, USA   USA
Need some help on this one. 1976 Mg Midget 1500 weber conversion 32/36 electric choke.

Issue:

Intermittent chugging. Sometimes runs perfectly no issues at all. Drives strong uphill, under load, idle. Sometimes it chugs on idle or acceleration at operating temp or cold doesn't matter. When it chugs it chugs. When it is not chugging it is perfect. When chugs engine is shaking. I have observed a bubbling in the fuel filter when it is chugging.

Replaced new:
Distributor system (new assembly) with new points (.015), condenser, cap, rotor
Electric Fuel Pump at 3.5 lbs max.
Fuel Filter
Carb Weber 32/36 jetted the same as old carb.
Plugs NGK platinum .026
Plug cables
Ignition coil (5 months old)

Timing is 10 degrees BTDC
Idle is 800 RPM
Mixture is set properly at 1.5 turns out from seated.

Any ideas?

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1974MGMidget Avatar
1974MGMidget Silver Member Jack Orkin
Grayson, GA, USA   USA
Brian, I can't speak specifically about the 1500 or Webers, but there is some discussion that platinum plugs with the fine electrodes are not appropriate for our cars. Supposedly, they are designed for modern ignitions with very high voltages, not our old systems. Try changing to NGK BP6ES, or equivalent, and see if that makes any difference.

littlecars Avatar
littlecars David Bassett
Nashville, TN, USA   USA
1965 Chevrolet Corvair "Ski Team Transport SOLD!"
1965 MG Midget MkII "Buffoon"
1966 MG Midget MkII "Swiss Cheese...SCRAPPED"
1970 Triumph Spitfire MkIII "Tamara's Turd... SOLD!!!"    & more
x2 what Jack says. I had something similar (Bosch platinum) that confounded me to no end until I switched back to what God intended for our 1970's cars. Is that a "new" Lucas coil or Chinese alternative? 5 months is 5 months longer than some of the new ignition stuff I've been dealing with in the last8-9 years.

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mgmidget76 Brian T
Chattanooga, TN, USA   USA
I was looking at a Lucas coil but my supplier is out, I did just order the one Moss has listed, should be here in a few days. I don't remember where I got this coil, probably O'reily's I was in a pinch at the time.

Replacing with Champion plugs now @ .025 gap.

Also going to switch out the electric fuel pump today with one Pierce recommends for Weber at max 3.5. After all this if still there I will send back the carb to bench test it. I feel like a carb though as there are not a lot of parts to these, would either work or not. The jets are not clogging so ..... unless the idle circuit is somehow freaking out in a gremlin way when I face the car east at midnight smiling smiley

I need to check the valve clearance but last I checked 6 months ago they were to spec.

I suppose too, I may be having a random short in electrical system .....

Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
Brian, if you can, try one thing at a time and test in between, so you know what the issue ended up being...

mgmidget76 Brian T
Chattanooga, TN, USA   USA
Update:

Replaced plugs with the Champion. Started it and it ran perfectly for about two minutes. Then chug and shake then perfect again, then chug and shake back to stable.

I checked the intake manifold at the rear of the engine again with the spray test and it chugged. I was expecting an increase in RPM but in fact it chugged. So I waited a bit for that to evaporate and sprayed again. Chug and stumble. It must be running rich. So thinking I have a manifold leak and it is running rich. I will seal this with gasket seal externally, adjust the mixture to test it. I don't want to rip off the manifolds right now as I plan to replace the header soon.

Mojan Mojan Norouzi
Fremont, CA, USA   USA
Perform leak down test. Or just do vacuume test. Watch this video.

You can rent it from autozone.




Edited 1 time(s). Last edit at 2018-04-19 10:09 PM by Mojan.

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mgmidget76 Brian T
Chattanooga, TN, USA   USA
OK. So I went after this like a hellfire tornado bomb and here is my synopsis. I feel like this was a combination of a manifold leak at the rear due to the roll pin missing and rising and the idler circuit in the weber carburetor 32/36 with electric choke.

I did replace the fuel pump and everything else in the process. Which needed to be done anyway. But I did approach this methodically and the problem persisted until I replaced the manifold gasket, put on the new header and reseated the intake manifold with a new roll pin. I did have a manifold leak at the rear of the engine which I found with the starting fluid spray test. I had used hi-temp gasket sealant to "fix" that, but then must have wanted to suffer more as I then took it all off and replaced everything. Now it looks proper (even though this is not stock).

I find all of this amusing in that, every time I talk with an old timer on the midgets I get the "you have run across one of the hardest things on the midget". smiling smiley That has been everything thus far beside the spark plugs and starting it.

The worst thing thus far has been the slave and master clutch cylinders. I had an awful time with getting the air out of it. I started to doubt my skills, but survived it.



Edited 1 time(s). Last edit at 2018-05-16 07:49 AM by mgmidget76.


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