Not the average misfire - SOLVED

[izzi]

Great news,
It is strange, my daughter's P reg Fiesta has a slight misfire under load, I have done the usual Plugs,leads tappets etc; clean air intakes and all that. never thought to change air filter.(I know)
I am now Thanks.
Roy.

[john hood]

I'm having similar problems with my traveller thatsmisfiring. My local mechanic (who restores minis) has fitted a refurbished SU carb, a new head gasket, refurbished the cylinder head, fitted a replacement s/h coil and checked out the distributor. He thinks the timing belt may be stretched and would benefit from a tensioner being fitted an the timing re-set. Due to other resto commitments he hasn't time to do this. I'm no mechanic and was wondering if this work could be carried out by a competent mechanic at my local garage. The engine appears fine when idling but misfires and loses power on acceleration between gears. Grateful for any top tips.

[simmitc]

First of all, find a mechanic who knows that Minors do not have timing belts They are chains, but he is correct that there is no tensioner as standard. I've never known a chain to be so worn that it causes these symptoms; and I'm sure that it would rattle an awful lot if it was really stretched. I think that the cause of your problems will have been highlighted in the thread, it's just a question of finding which one it is. Most things on a Minor are simple enough for you to learn, particularly with assistance from this site. As the current thread is already rather long, could you start a new one, and we'll run through the ideas and explain how to check them.

[bmcecosse]

I'm guessing the 'belt' is a slip of the fingers.... but he is wrong to think a tensioner would make any difference to the timing....it acts on the return leg of the chain and won't affect any 'timing' issues.. But on a standard engine a couple of degrees here and there won't make any significant difference.

[john hood]

Thanks for the advice guys next time I am home will start a new thread and work through some of the options from this thread.

[bmcecosse]

Good plan!

[TravellerTodd]

Howdy all - I'm new here, but this thread solved misfiring issues with my 1958 Traveller, so thought I would add my findings to the thread for anyone else searching for a solution.

My misfire turned out to be two distinct symptoms of from two distinct causes: a mid-range crackling sputtering jerky misfire and a nasty power-robbing miss at full throttle /high revs. It was pretty much running like a dog at anything above carpark speeds!

The mid-range miss was apparently caused by my Morry's dislike of NGK plugs. My Mechanic initially installed incorrect short neck NGK plugs which started missing immediately and the problem was temporarily resolved by fitting the correct long neck version. After about 500 miles the problem reappeared and I discounted the possibility of plugs as the cause for 2 frustrating weeks of changing distributors/condensors/points, checking fuel delivery etc (I had made numerous changes under the hood in the interim so I assumed one of those may be the problem). Finally, I chucked in the crusty old Champion plugs that were fitted to my parts engine and Voila! No more misfire from idle through the mid-range.

However, the full-throttle miss persisted. I suspected fuel starvation and was about to spring for a new fuel pump until I found this thread. Sure enough, it was the Air Cleaner. I have a cheap pancake foam filter and didn't like the look of the filtration so had doused it in the No Toil filter oil that I use on my dirt bike. Apparently this was strangling my poor Morry to death - cleaned it out and the misfire is all gone. Now I need to find a better quality air filter for the HS4 carb - any suggestions?

My biggest learning point from all this is to only change one thing at a time then test it before moving to the next - I still fail to heed this advice, but it really works (in theory).

[GavinL]

I'm sure others will give you further advice, but for my part i fitted one of these relatively low cost filters on a 1275 MG Midget fitted with an HIF44 carb https://www.ebay.co.uk/itm/CLASSIC-MINI ... 0677.m4598 which appears to do the job ( better than the ram pipe and no filter it had when i bought it) and HS4 versions also appear to be available. Doesn't appear to restrict performance.

[oliver90owner]

... was about to spring for a new fuel pump until I found this thread ...

It is even better to diagnose the fault, before changing anything, but well done to sort it out yourself. These engines are, relatively, low tech and only have low tech faults and remedies. First port of call used to be “change the condenser”, but the forum has, hopefully, moved on a bit from that... Most components are easy to check for serviceability, too.

Welcome to the forum, btw.

RAB

[TravellerTodd]

I'm sure others will give you further advice, but for my part i fitted one of these relatively low cost filters on a 1275 MG Midget fitted with an HIF44 carb https://www.ebay.co.uk/itm/CLASSIC-MINI ... 0677.m4598 which appears to do the job ( better than the ram pipe and no filter it had when i bought it) and HS4 versions also appear to be available. Doesn't appear to restrict performance.

Thanks GavinL - I appreciate the suggestion and will follow it up, the collapse of the Pound sure makes buying UK sourced parts easier on the pocket!

and thanks for the welcome RAB!

[Edward1949]

This excellent thread inspired me to check my air filter (newly-purchased 1098cc, vigorous acceleration from low to middle revs but very sluggish beyond that). Filthy! And the main culprit was clearly oil-laden fumes from the engine breather pipe. I've torn some holes in the filter until I can fit another. Performance and presumably fuel economy very much improved.

[TravellerTodd]

I just wanted to add another cause of high speed misfire to the knowledge bank - old fuel. After lockdown here in NZ I took my Traveller down to the local country garage and filled her up with Premium. About five minutes later she was spazzing out at anything above 50 MPH. It took me far too long to figure it out but it transpired that the fuel had been sitting in the garage’s tanks for over 10 weeks. A fresh tank from the busiest bowzer in town cured the misfire.