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MG MIDGET.....Bad Gas Milage
- Thread starter DebH
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JodyFKerr
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Re: MG MIDGET.....Bad Gas Milage HELP!!
Do you mean bypassing the catalytic converter?
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I would check your engine electricals to make sure you're getting good spark at the plugs, and I'd see how rich your fuel mixture is. I've seen many cars bought over the years that got terrible gas mileage at first because they'd been made rich to overcome poor ignition.
Jody
Do you mean bypassing the catalytic converter?
--
I would check your engine electricals to make sure you're getting good spark at the plugs, and I'd see how rich your fuel mixture is. I've seen many cars bought over the years that got terrible gas mileage at first because they'd been made rich to overcome poor ignition.
Jody
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Re: MG MIDGET.....Bad Gas Milage HELP!!
How strong does the exhast feel? Does it make a hissing sound when you accelerate? Either Moss or VB sells a bypass pipe IIRC. IMO, that's not a bad idea either way. If you just bought it, I would do a complete tune up. New cap, rotor, plugs, wires, valve adjustment, air filter, the whole works. Chances are you don't know what you have (i.e, what's already been done to it or changed) and it's a really good idea to have a known starting point with a new-to-you old car, especially if it's giving you trouble early on like this one.
Got any fuel leaks, does the car feel down on power?
How strong does the exhast feel? Does it make a hissing sound when you accelerate? Either Moss or VB sells a bypass pipe IIRC. IMO, that's not a bad idea either way. If you just bought it, I would do a complete tune up. New cap, rotor, plugs, wires, valve adjustment, air filter, the whole works. Chances are you don't know what you have (i.e, what's already been done to it or changed) and it's a really good idea to have a known starting point with a new-to-you old car, especially if it's giving you trouble early on like this one.
Got any fuel leaks, does the car feel down on power?
D
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Re: MG MIDGET.....Bad Gas Milage HELP!!
Plugged cats generally exhibit HORRIBLE acceleration and speed before you get 1/3 the MPG's.
Point gap/dwell.
AIR FILTERS.
Fuel filter.
Timing.
Might as well check the valve lash.
Fuel filter for good measure (that way you will KNOW when it's been changed).
Then, carbs.
Plugged cats generally exhibit HORRIBLE acceleration and speed before you get 1/3 the MPG's.
Point gap/dwell.
AIR FILTERS.
Fuel filter.
Timing.
Might as well check the valve lash.
Fuel filter for good measure (that way you will KNOW when it's been changed).
Then, carbs.
Re: MG MIDGET.....Bad Gas Milage HELP!!
I have all the paperwork he replaced all hoses wires plugs filters. He gave me the bypass pipe for the converter. Car has plenty of power. When the engine runs it has the lag like a harly davidson bike. No gas leaks, (its in a garage with a carpet). Can smell faint smell of gas in garage sometimes.I have plans on the 28th of this month for a check up.
I have all the paperwork he replaced all hoses wires plugs filters. He gave me the bypass pipe for the converter. Car has plenty of power. When the engine runs it has the lag like a harly davidson bike. No gas leaks, (its in a garage with a carpet). Can smell faint smell of gas in garage sometimes.I have plans on the 28th of this month for a check up.
Trevor Jessie
Yoda
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Re: MG MIDGET.....Bad Gas Milage HELP!!
Is the carb original?
Is the carb original?
G
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Re: MG MIDGET.....Bad Gas Milage HELP!!
I once bought a car from the auction that would run for a few seconds and die. It wouldn't start right back up, but if you waited about 5 seconds it would fire, run for a few seconds and die. You could rev it a bit, say to about 2,500 and then it would die. If you immeadiatly tried to start it, it would try, but never would catch. After pulling my hair out for months. I changed EVERYTHING trying to figure out what it was. Went throuogh all of the injection and ignition. Changed from injection to carb. I could then see air/fuel mix cloud above the carb while it was running befor eit died. I checkev the lifter and clearance, everything fine. I check the cam, everythig fine. Pulled the head to check for bad seats or guides, everything fine. It still did the same thing.
I finally gave up and was writing the ad in my head. I listed everything I had done, and then started listing stuff that was done before I got it. Once I got to the fact it had new exhast on it, it hit me.
I blew air into the exhast pipe and it was clogged SOLID. I dropped the cat and it ran like a top. Once I got the cat off you could see it was plugged solid, just like you poured concrete in it. I've never seen one that bad before and never in my wildest dreams would have imagined....
I was ready to give this crap up entirly. If I hadn't figured it out, I wouldn't be here right now. It was that fustrating.
TOC said:
I once bought a car from the auction that would run for a few seconds and die. It wouldn't start right back up, but if you waited about 5 seconds it would fire, run for a few seconds and die. You could rev it a bit, say to about 2,500 and then it would die. If you immeadiatly tried to start it, it would try, but never would catch. After pulling my hair out for months. I changed EVERYTHING trying to figure out what it was. Went throuogh all of the injection and ignition. Changed from injection to carb. I could then see air/fuel mix cloud above the carb while it was running befor eit died. I checkev the lifter and clearance, everything fine. I check the cam, everythig fine. Pulled the head to check for bad seats or guides, everything fine. It still did the same thing.
I finally gave up and was writing the ad in my head. I listed everything I had done, and then started listing stuff that was done before I got it. Once I got to the fact it had new exhast on it, it hit me.
I blew air into the exhast pipe and it was clogged SOLID. I dropped the cat and it ran like a top. Once I got the cat off you could see it was plugged solid, just like you poured concrete in it. I've never seen one that bad before and never in my wildest dreams would have imagined....
I was ready to give this crap up entirly. If I hadn't figured it out, I wouldn't be here right now. It was that fustrating.
G
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Re: MG MIDGET.....Bad Gas Milage HELP!!
Changed the wire and plugs, what about the cap and rotor? What is your timing set at?
What do you mean by Harley lag? Does it run rough and miss?
Black smoke out the back?
Changed the wire and plugs, what about the cap and rotor? What is your timing set at?
What do you mean by Harley lag? Does it run rough and miss?
Black smoke out the back?
G
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Re: MG MIDGET.....Bad Gas Milage HELP!!
When converters strat to clog it increase the velocity of what little gasaes that can get through. The exhast sounds weird and "hissy". Kinda sounds like an air hose with the blower nozzle on it; same effect.
When converters strat to clog it increase the velocity of what little gasaes that can get through. The exhast sounds weird and "hissy". Kinda sounds like an air hose with the blower nozzle on it; same effect.
G
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Re: MG MIDGET.....Bad Gas Milage HELP!!
Smeel you dipstick and see if it smells like gas too if it's been flooding out.
Smeel you dipstick and see if it smells like gas too if it's been flooding out.
bthompson
Jedi Warrior
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Re: MG MIDGET.....Bad Gas Milage HELP!!
If you're running the original Zenith-Stromberg carb, the chances are great it's at least partly to blame. The ZS carb <span style="font-style: italic">wants </span>to run rich, and it's a battle of vigilance to drive it lean enough to work. Subsequent problems with plugs and timing are sometimes just the previous owners "work-arounds" to a ZS that's running richer with age.
ZS's need balanced vacuum on both sides of the venturi to work properly. It's very sensitive to vacuum leaks, there's a <span style="font-style: italic">lot </span>of places vacuum can leak, and <span style="font-style: italic">any </span>leak will drive it richer. Multiple leaks will add up. Think of it this way: its "choke" is really just a controlled vacuum leak that makes the piston sit lower in the bore, closing down the venturi, increasing the air speed, and sucking more gas thru the engine. <span style="font-style: italic">Any </span>vacuum leak, then, will "put the choke on." The challenge is to get the highest vacuum possible, popping the piston up <span style="font-style: italic">high</span>, thus keeping the airflow thru the venturi <span style="font-style: italic">slow</span>, pulling <span style="font-style: italic">less </span>gas.
In addition to the ususal vacuum leak areas, you can look for:
A torn piston diaphragm will keep the piston from rising.
A stuck or corroded piston damper will hold the piston down.
Too-heavy damper oil in a damper with corroded bleed holes will hold it down too.
Using an aftermarket air cleaner with "freer flow" will read like a vacuum leak and keep the piston too low. ZS's, unlike fixed-venturi carbs, need some airflow <span style="font-style: italic">restriction </span>to run economically. Paradoxical but true.
The mix needle is spring-loaded and runs along the side of the jet. Needle and jet wear over time will cause rich running. You can adjust it down a little from inside the damper hole, but if the piston isn't sitting where it's supposed to, no amount of adjustment will compensate for all that air being sucked thru a little-bitty venturi space.
When I got my '76, it was getting about 9 mpg too. I rebuilt my ZS as far as I could, but it was too worn to salvage without re-bushing things. I went the easy route and slapped a Weber DGV on there...but knowing what I know now, I'd'a put an SU from an MGB on it. It fits the 1500's intake manifold with just a little tweaking; and several folks here have done it.
If you're running the original Zenith-Stromberg carb, the chances are great it's at least partly to blame. The ZS carb <span style="font-style: italic">wants </span>to run rich, and it's a battle of vigilance to drive it lean enough to work. Subsequent problems with plugs and timing are sometimes just the previous owners "work-arounds" to a ZS that's running richer with age.
ZS's need balanced vacuum on both sides of the venturi to work properly. It's very sensitive to vacuum leaks, there's a <span style="font-style: italic">lot </span>of places vacuum can leak, and <span style="font-style: italic">any </span>leak will drive it richer. Multiple leaks will add up. Think of it this way: its "choke" is really just a controlled vacuum leak that makes the piston sit lower in the bore, closing down the venturi, increasing the air speed, and sucking more gas thru the engine. <span style="font-style: italic">Any </span>vacuum leak, then, will "put the choke on." The challenge is to get the highest vacuum possible, popping the piston up <span style="font-style: italic">high</span>, thus keeping the airflow thru the venturi <span style="font-style: italic">slow</span>, pulling <span style="font-style: italic">less </span>gas.
In addition to the ususal vacuum leak areas, you can look for:
A torn piston diaphragm will keep the piston from rising.
A stuck or corroded piston damper will hold the piston down.
Too-heavy damper oil in a damper with corroded bleed holes will hold it down too.
Using an aftermarket air cleaner with "freer flow" will read like a vacuum leak and keep the piston too low. ZS's, unlike fixed-venturi carbs, need some airflow <span style="font-style: italic">restriction </span>to run economically. Paradoxical but true.
The mix needle is spring-loaded and runs along the side of the jet. Needle and jet wear over time will cause rich running. You can adjust it down a little from inside the damper hole, but if the piston isn't sitting where it's supposed to, no amount of adjustment will compensate for all that air being sucked thru a little-bitty venturi space.
When I got my '76, it was getting about 9 mpg too. I rebuilt my ZS as far as I could, but it was too worn to salvage without re-bushing things. I went the easy route and slapped a Weber DGV on there...but knowing what I know now, I'd'a put an SU from an MGB on it. It fits the 1500's intake manifold with just a little tweaking; and several folks here have done it.
RickB
Yoda
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Re: MG MIDGET.....Bad Gas Milage HELP!!
I had a mid 70's Mustang a long time ago that acted the same.
Previous owner did a lot before giving up on it, I did a lot to it and gave up and donated it to a friend. It totally crapped out on him and he hauled it to a mechanic who found the CC clogged. After fixing that it ran great as it had all kinds of new stuff in the engine!!
I had a mid 70's Mustang a long time ago that acted the same.
Previous owner did a lot before giving up on it, I did a lot to it and gave up and donated it to a friend. It totally crapped out on him and he hauled it to a mechanic who found the CC clogged. After fixing that it ran great as it had all kinds of new stuff in the engine!!
G
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Re: MG MIDGET.....Bad Gas Milage HELP!!
I think that might be a good idea reguardless.
bthompson said:
I think that might be a good idea reguardless.