Major Missfiring Problems

Post by **PaulJohnson** » Fri Aug 13, 2004 10:41 pm

Hello Everyone.

Ive got a big problem with "Olive" at the moment.
At the moment the engine sound very rough and everytime I take my foot of the gas pedel
there is a poping sound coming from the exhaust but when Iam doing over 35MPH & I take my foot of the gas pedel there is a big missfiring sound coming from the exhaust.
It has only been 3000 miles since "Olive`s" last service however I have recently changed the rotar arm + a new dizzy cap.

There has been no problem with power just this horrible noise.

Hope someone can help?

Post by **Cam** » Fri Aug 13, 2004 10:48 pm

Have you checked the timing and the operation of the vac advance unit??

when you take your foot off the gas there is a large vaccum generated which pulls the timing round advancing it (for economy purposes). Maybe it's already quite advanced? (timing slipped)?

Are you getting any pinking when you floor the throttle in high gears and low revs? or labouring the engine up hills?

Post by **Cam** » Fri Aug 13, 2004 10:52 pm

Maybe the popping is unburnt fuel? Have you topped the carb up with dashpot oil recently? or maybe you have a sticking carb piston.

Have you checked the mixture? is it way too lean? Have a look at the colour of the spark plugs and inside the exhaust, if it's whiteish then you are too lean and that would not help.

Post by **PaulJohnson** » Fri Aug 13, 2004 11:02 pm

Hello Cam.
Iam going to check the spark plugs this sunday, I have recently filled the dashpot with redex, however I have used redex for the last 2 years without any problems.
To my knowledge iam not suffering from pinking but there is small black oil deposits coming out of the exhaust when she is just ticking over both when the engine is cold & hot

Post by **rayofleamington** » Sat Aug 14, 2004 12:12 pm

filled the dashpot with redex

filled it with Redex what?

Post by **Willie** » Sat Aug 14, 2004 8:40 pm

THINK SIMPLE...if it was ok before you changed the rotor arm
and the dizzy cap then A. put the old rotor arm back and see
if it is then ok and B. if necessary, put the old dizzy cap back on.
It might not be the answer but it is well worth a try.

Post by **PaulJohnson** » Tue Aug 17, 2004 6:32 pm

I will answer all the question`s rasied here.

(1) Today me & my dad cleaned & adjusted the NGK spark plugs, the spark plugs were for some reason set at 0.065 ins ,the rotor arm was as good as new with no problems in the dizzy cap, the contact points are slightly pitterd but ok but these will be changed on sunday after only 3000 miles of use, we have also looked for air leaks which ment tighting all the mainifold bolts on the exhaust & also and the conection from the engine to the exhaust pipe.

This lead to the engine sounding a lot better, however "Olive" still was poping when I was going down a steep hill in 2nd gear doing about 15-20mph.

As for the redex in the Dashpot, if I remember rightly I started a post on the subject in Feb 2003 on what I should put in the Dashpot & it seems to me that a lot of moggy owners put redex into the Dashpot as it then cleans the Carburettor as it is used.

Post by **Gareth** » Tue Aug 17, 2004 7:33 pm

The dashpot holds oil... if you wanted to clean the carb, then surely a shot of redex in the float chamber would do that...? Or easier still, bung some in the tank and let it work its way through. Light oil (SU's own, 3-in-1, &c.) or engine oil all seem good for dashpots, according to some correspondents.

Popping can be valve seats, can't it? Phyllis never did it (despite one seat being a bit chewed...

) but she did backfire quite spectacularly on the day she went for her new head.

I've found the usual cause of snapping and popping being manifold air leaks - especially the manifold-exhaust joint.

Post by **Willie** » Tue Aug 17, 2004 7:51 pm

I would suspect that popping in the exhaust on overrun is due
to unburnt fuel in the system. Valves not seating properly or
excessively rich mixture??? You still haven't stated if the car
was ok before you changed the rotor arm and dizzy cap?

Post by **rayofleamington** » Tue Aug 17, 2004 7:53 pm

how different is the popping from normal over-run sound?

Post by **PaulJohnson** » Tue Aug 17, 2004 8:15 pm

The Car was OK before I canged the rotor arm, I forgot to say that we changed around then new rotor arm with the old one but there was no difference every time I took my foot of the gas pedel "Olive " there was a pop sound.

My dad was concerned about spark plug Number 4, 1,2 & 3 were normal but No 4 was black & all sooted up?
It seems that the valve seating problem could be the answer?

Post by **rayofleamington** » Tue Aug 17, 2004 9:47 pm

if it's black it could also be an oil leak (rings or valve guide)

Post by **Kevin** » Wed Aug 18, 2004 8:41 am

Today me & my dad cleaned & adjusted the NGK spark plugs, the spark plugs were for some reason set at 0.065 ins

I am amazed the car ran at all with a gap that size, had you just fitted the plugs without checking them straight from the box ? as they are not pre-set to suit all the cars that the plug is suitable for.

it seems to me that a lot of moggy owners put redex into the Dashpot as it then cleans the Carburettor as it is used.

Ist time I have heard that one.

Post by **rayofleamington** » Wed Aug 18, 2004 9:18 am

did you put redex in the carb dashpot (throttle damper) at the same time the problems started?

Post by **Cam** » Wed Aug 18, 2004 1:01 pm

Ist time I have heard that one.

Same here.

Post by **PaulJohnson** » Fri Aug 27, 2004 6:18 pm

Kevin wrote:
Today me & my dad cleaned & adjusted the NGK spark plugs, the spark plugs were for some reason set at 0.065 ins

I am amazed the car ran at all with a gap that size, had you just fitted the plugs without checking them straight from the box ? as they are not pre-set to suit all the cars that the plug is suitable for.

The Plugs were put in about 3000 mils ago by The Moggy Garage in Manchester.

Post by **PaulJohnson** » Fri Aug 27, 2004 6:31 pm

rayofleamington wrote:did you put redex in the carb dashpot (throttle damper) at the same time the problems started?

Hello Ray.
I have always put Redex in the dashpot, I was told by the Moggy place in Manchester that you could put anything in & Redex cleans as it passes thought.
The problems of misfiring started about 2 months ago.
If it is worn pistons ring is this caused by high revs?
I ask this as with Sheffield built on 7 hills, it is normal for my foot to be flat down on the gas pedel to get "Olive" up the hills could that be the problem?