1966 MG Midget
Discussion
Please could someone help me diagnose an issue I've got with my Midget. I had the head converted to unleaded last year and in general the engine runs well and smoothly, but occasionally and randomly it will start to misfire, if I then pullover it will clear by either a gentle revving or stop and restart the engine. I've changed the coil and the petrol pump which seems to have made the problem occur less often, but never the less it still happens.
Many Thanks
Many Thanks
These random faults are always the worst to trace. You've changed the coil, but have you changed the condenser - which can intermittently go open circuit, or alternatively you could have a fuel supply problem. Assuming the car is running on twin SU carbs, check the float chambers for muck. Best of luck!
Hiccupping under load at low revs ie 30mph in top = plug lead
Coil break down usually causes it to die until the coil cools
Sounds a bit like muck in the fuel/ fuel line/ carbs
Prev poster suggested float(s) that could also be a problem
Also does it happen after roughly acertain/time/distance and does it clear whilst still running?
(Thinking fuel pick up in the tank sucking up rubbish until it blocks, stalls, rubbish drops off pick up, car starts).
Also check breather on tank, if you remove the filler cap is there a rush of air releaving the vacuum?
Modern condensers are notoriously faulty, cheap imported rubbish I think, the mini guys have regularly slagged them off.
Hope this helps, my first car was a 66 Midget, bought when I was 18 in 1972. FJR 494 C in red.
Coil break down usually causes it to die until the coil cools
Sounds a bit like muck in the fuel/ fuel line/ carbs
Prev poster suggested float(s) that could also be a problem
Also does it happen after roughly acertain/time/distance and does it clear whilst still running?
(Thinking fuel pick up in the tank sucking up rubbish until it blocks, stalls, rubbish drops off pick up, car starts).
Also check breather on tank, if you remove the filler cap is there a rush of air releaving the vacuum?
Modern condensers are notoriously faulty, cheap imported rubbish I think, the mini guys have regularly slagged them off.
Hope this helps, my first car was a 66 Midget, bought when I was 18 in 1972. FJR 494 C in red.
Electric or mechanical fuel pump?
My Frogeye (mech pump) suffered from fuel evaporation when 4 star wasn't available, but I think this is less likely with an electric pump, but check that it has the heat shield between carbs and exhaust manifold and fuel pipes aren't too close to the manifold.
My Frogeye (mech pump) suffered from fuel evaporation when 4 star wasn't available, but I think this is less likely with an electric pump, but check that it has the heat shield between carbs and exhaust manifold and fuel pipes aren't too close to the manifold.
hi, hello, welcome,
there's an MG section on PH, loads of info there in previous threads and on the MG BBS website
you need to do a proper diagnostic any any problem or you'll get loads of good suggestions as you have rather than the specific route to resolve your problem
do NOT change the condenser to a new one unless it's NOS or from the Distributor Doctor or other very reliable source
since having the head done have you:
had the head retorqued?
had the tappets reset, then CB points, then plugs, then timing then carb mixture in that order?
carried out routine servicing work?
driven the car frequently over reasonable distances?
added other new parts?
checked the CB points gap again?
checked the condition of all four plugs?
cleaned and checked the carbs, linkages and springs?
does the car overheat?
oil in coolant, coolant in oil?
any colour of smoke at, before or after misfire?
when the misfire happens does the rev counter twitch?
there's an MG section on PH, loads of info there in previous threads and on the MG BBS website
you need to do a proper diagnostic any any problem or you'll get loads of good suggestions as you have rather than the specific route to resolve your problem
do NOT change the condenser to a new one unless it's NOS or from the Distributor Doctor or other very reliable source
since having the head done have you:
had the head retorqued?
had the tappets reset, then CB points, then plugs, then timing then carb mixture in that order?
carried out routine servicing work?
driven the car frequently over reasonable distances?
added other new parts?
checked the CB points gap again?
checked the condition of all four plugs?
cleaned and checked the carbs, linkages and springs?
does the car overheat?
oil in coolant, coolant in oil?
any colour of smoke at, before or after misfire?
when the misfire happens does the rev counter twitch?
Edited by nta16 on Wednesday 29th May 15:45
Many thanks for all replies,
The previous owner renewed the fuel tank and fuel lines but I will check the float chambers and the breather. The carbs were balanced during the head rework along with the timing and servicing. The problem wasn't there before the work. The pump was replaced for an electric item which does feed SU carbs.
There is no pattern as to when the problem occurs, for instance at the weekend it first happened after roughly 7miles, travelling at 50-55mph. The rev counter did not twitch, it just misfired and the car slowed (engine didn't completely stop). I pulled over and revved it once, it clear and off I went. I then travelled another 40ish miles with 2 comfort breaks until it happened again travelling at around the same speed, but this time it wouldn't clear by revving so I stopped the engine for 5secs and restarted as if nothing had happened.
I've only completed 240miles since the work was carried out and was advised to have the clearances and head torqued after 500miles. It hasn't had much running as its a summer car only. There is no smoke when the problem occurs and no oil in coolant or coolant in oil, neither does it overheat.
I haven't renewed the condenser and it does have a heat shield.
Could the problem be fuel starvation and if so how do I check this and/or solve this?
The previous owner renewed the fuel tank and fuel lines but I will check the float chambers and the breather. The carbs were balanced during the head rework along with the timing and servicing. The problem wasn't there before the work. The pump was replaced for an electric item which does feed SU carbs.
There is no pattern as to when the problem occurs, for instance at the weekend it first happened after roughly 7miles, travelling at 50-55mph. The rev counter did not twitch, it just misfired and the car slowed (engine didn't completely stop). I pulled over and revved it once, it clear and off I went. I then travelled another 40ish miles with 2 comfort breaks until it happened again travelling at around the same speed, but this time it wouldn't clear by revving so I stopped the engine for 5secs and restarted as if nothing had happened.
I've only completed 240miles since the work was carried out and was advised to have the clearances and head torqued after 500miles. It hasn't had much running as its a summer car only. There is no smoke when the problem occurs and no oil in coolant or coolant in oil, neither does it overheat.
I haven't renewed the condenser and it does have a heat shield.
Could the problem be fuel starvation and if so how do I check this and/or solve this?
mg66 said:
The rev counter did not twitch
possibly HT side or fuel thenmg66 said:
I've only completed 240miles since the work was carried out
from last year - lack of mileage and use will not help find and iron out problemsmg66 said:
and was advised to have the clearances and head torqued after 500miles.
so get another 260 miles done ASAPmg66 said:
It hasn't had much running as its a summer car only.
there were many excellent driving days during late autumn, winter and early spring, I know I was out in them, most better than the recent spring weathermg66 said:
There is no smoke when the problem occurs and no oil in coolant or coolant in oil, neither does it overheat.
that's goodmg66 said:
I haven't renewed the condenser and it does have a heat shield.
goodmg66 said:
Could the problem be fuel starvation and if so how do I check this and/or solve this?
check to see if the fuel makes it to the front, very easy if you have a clear plastic fuel filter fitted before the carbs as it's a quick visual check, you could then check that the fuel makes it to the float bowls and that the float, needle and seats all operate correctly - careful with fuel it can damaged your paintwork and cause fireslast time we had a problem like this it turned out to be a faulty new fuel pump (which I'd already thought unlikely so I was wrong) your could also possibly wiring or electric connections to the pump (and other possible causes)
a wild, wild card - flapping obstruction in air filter
info here on carbs for you -
44 Secrets of the SU Carburettor Part 1 of 2 - http://www.youtube.com/watch?v=7GRAcqDySog&fea...
43 Secrets of the SU Part 2 of 2 - http://www.youtube.com/watch?v=60Bj_2cZQnc&fea...
29 SU H-Type Carburetters - http://www.youtube.com/watch?v=GHNlT5yHDxk&fea...
41 Matching SU Air Pistons - http://www.youtube.com/watch?v=IfU47Oqq9wA
123 MG Carburetors & Doors (first part needles and seats, springs and carb oil) –
http://www.youtube.com/watch?v=v9QI3NlvwiY&fea...
147 MG Carburetter Tuning - http://www.youtube.com/watch?v=4nvGLgO6pj0&fea...
35 Tuning HIF Carburetters - http://www.youtube.com/watch?v=ASeMfXfjNpw&fea...
Needle and seat - http://www.youtube.com/watch?v=pVX_JClyeDQ&lis...
Setting the Float Height - http://www.youtube.com/watch?v=82YNx-RkGNI&lis...
Edited by nta16 on Wednesday 29th May 22:54
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