Misfire

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RichardG

New member
Hi all. Matt and I have been out in the buggy a few times this week making the most of a few days away from the office etc. problem is that the buggy has been developing a mis fire that is getting progressively worse.

Starts with no problem, has got fuel in the tank, have checked the timing is OK, spark plugs look in good condition and battery is charged.

When stationary if I rev the engine up to 4000 rpm and hold it the mis fire will start after a few seconds and get progressively worse until the revs will just die off and the engine stall unless I ease of the gas. There is some poping and banging in the carb. When I take the air filter off I get the odd flame poping out of the carb.

When driving around the misfire comes and goes but is generally worse when under load. Again the misfire gets worse and the engine will stall unless I ease off the gas and let the engine settle.

Any ideas ?

The plugs and HT leads were new 6 months ago but I am going to get new ones ordered along with a new coil and try these.

The distribtor and points were brand new 6 months ago also.

If not electrical it must be fueling so could be fuel pump, filter or carb related?

Anything else I should be thinking about. Do the symptons ring any bells?

Thanks and Happy New Year

Richard
 
Phaeton

Phaeton

Moderator
Staff member
"RichardG"":6s4gkzbr said:
The distribtor and points were brand new 6 months ago also.
Click to expand...
That's your problem, throw the useless piece of poo away & get an electronic one off a Metro. I had no end of problems until I replaced mine & then all was fine thereafter.

Alan...
 
Asbo

Asbo

New member
Richard,mine was doing all that too on a 3hour run the other day,i thought it was bloomin marvellous like. Turns out the problem was a cracked spark plug,which only surfaced as i removed them for examination and number 4 plug cracked in half. Having replaced the offending item,mine is now running superbly on its forced diet of 75%unleaded/25%derv.(its free,hence it loves it)......its not just ordinary fuel,its M&S fuel.lol.

Have a great new year every-one....even Mister Smart,who is probably back in the West End devouring the Culture. :lol:
 
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RichardG

New member
Before throwing the dizzy away I am going to replace the coil as the one I used was second hand and of unknown origin so my money is on it being the problem.

Thanks

Richard
 
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hmalan

New member
Richard,

Alan (Pheaton) is right about getting rid of the points.

They will often close up, irrespective of what you do so it is better to go down the electronic route.

Also does away with condensor which can cause a similar problem.

Alan T.
 
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esdebe

New member
Is it a standard bore? is there any profamce changes done to the engine (cam) / carb (needle) / air filter? If so you may need to have a dizzy with a diffrent advance curve.

As dizzies get old the curve can change creating eratic behaviour. Making it harder to set the dwell angle on the points too. This is usualy set at lower revs, so by the time you reach 4000 it can be out completly....

I changed over to the electronic type, and bought one that matched my cam, and needle and airfilter better.

But before spending money do check the HT leeds and spark plugs, if the leeds are warn or if they run parrell they can cause sparing on other plugs... Its better to have them crossing than running parellel (althogh this is more for the old copper ones...)
 
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funbuggydave

New member
Also have a quick check of the oil in the damper in the carb, the fact it runs then dies often means there is no oil in the dashpot.
Unscrew the black plastic knob off the top of the carb and fill the dashpot with either 3-in-1 type oil or even engine oil. Be careful screwing it back in, it's very easy to cross thread.
Also check the air filter, we had problems with Danny's on the way back from Spain.
Dave
 
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hmalan

New member
Told that Automatic Transmission fluid is better than engine oil for the carb.

Have this in mine and it seems ok but has only been used on tickover and up and down the street
 
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RichardG

New member
:D :D :D think I found it. Changed the coil, HT leads and plugs but misfire continued. Started to take out the points and condenser to change them and found that the small wire that goes from the condenser to the base plate in the dizzy had broken.

Have fixed the wire and put it all back together. Will be off for a test drive in the morning.

Richard
 
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RichardG

New member
:( :( :( Oh well back to the garage then. Could it be a blown cylinder head gasket ? No water in the oil but I am still getting water pupmed out of the radiator into the overflow. Had always assumed this was due to over heating because of poor air flow. Could be due to exhaust gas pressure getting into the cooling system?

Oh well - order the electronic dizzy or whipp the cylinder head off ?

Richard
 
R

RichardG

New member
Had an idea this afternoon and drained out half the water then went for a drive - misfire gone ! So the head of coming off to inspect the gasket and valves.

Richard
 
S

Skirrow

New member
If you change your dizzy you will probably also need to change your coil and if you change your coil you might need to change one of the wires to it. Some coils have to be ballasted with a resistor wire. It's thicker than the standard wire, pink/white and might have the word resistive on it.

You need to be careful you get it all right or your coil might not last last long...
 
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Skirrow

New member
Easiest way is to get a second hand coil, dizzy and the ballast wire off a late mini or a metro.

And do a compression test before taking the head off, should give you an idea if there are any problems.
 
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esdebe

New member
Just get a balast resister (a small ceramic block with terminals on teh end and a wire coil behind it... I use it on my coil as I don't know if it was supposed to be ballast or not... With out it the coil gets very hot.. The resister costs only £6

Simon
 
R

RichardG

New member
:D Well making some progress. The head came off easy enough and there were definitely signs of the gasket leaking, probably due to not being torqued down properly as some of the cylinder head nuts came undone too easily :oops: .

So head refitted and off for another test drive but still the misfire continued :cry: :cry: Back to the drawing board this morning. My Dad noticed some air bubbles coming through the fuel filter!!! So flew down to Halfords and bought a new fuel filter and fuel pipe. We had got the filter fitted between the fuel pump and the carb. Have now fitted the new filter between the tank and the pump and hey presto I think we have cracked it. A short test drive in the pouring rain and no mis-fire.

Just need the weather to improve a little before taking it for a longer test drive.

Richard
 
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esdebe

New member
Yes, it is good practive to put the filter between teh tank and the pump as the pump won't appreciate durty fule, it can cause the seals to leak, letting air in / fuel out. Not sure it would cause the missfire though.

Does the missfire occur at the same RPM range? if you hold the throtal open at that range can you see fuel being sucked through the filter / is the filter filling up quick enougth?

One other thing to check is that the tank is asperated so that air can replace the fuel as it comes out if not the fuel flow will be less at high RPM.

Do you have a seperate breather on the tank or are using a filler cap that can breath? My original mini cap was the non breathing type and I had to buy a new one so that I didn't need a seperate breather on the tank.
 
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