1098 not running right

[derekscoopers]

The engine is a new 1098 with 1 1/4 su basically the car does not feel right, I have had a series before including 1100's and this one feels wrong.

Here we go :-

does not pull well but gets there, I know they don't rev but this one has a vibration throughout, when coming of the throttle it feels hesitant and lurches almost if you had a binding brake, which I dont.

Another way to describe it is if it had a 649 cam that's how lumpy it would be but this one has a standard cam.

Idling is not great and it jumps between 600-850 ish revs on the tacho but jumps all the time.

Any ideas please ?

[bmcecosse]

Back to basics - what's the history of the engine? I suggest you set the valve gaps - then do a compression test and report back with results. Generally - gap the points, and check the vacuum advance unit is working (suck the tube..). Also check the air filter is clean, and the carb piston can rise easily and falls with a nice clunk. And put a few drops of oil in the carb damper.

[MarkyB]

As above, service the engine for starters.
While you have the dizzy cap off make sure the vacuum advance is working, it's the difference between a lively engine and one that just runs.

[derekscoopers]

Thanks for both your replies, yes you right I will start checking the obvious but everything is new, I know that does not mean it's right but Mini's were really my thing but am really happy with the MM and am sure it will get sorted.

will start the checks tomorrow bit by bit and see how we go.

[bmcecosse]

A Minor is a lot heavier than a Mini - so you can't expect the same performance.......unless you upgrade the engine of course!

[JOWETTJAVELIN]

Is there an air leak at the manifold gasket, carb or any other connections around here? Check the tightness of the manifold nuts.

What do you mean by a 'new 1098'? There are no new engines of this type anymore. Could it be the distributor has been put back in the wrong position, or the timing marks on the cam & crank sprockets mis-aligned?

[Jason87]

I agree with all of the above. One more thing to consider is the carb its self. A worn jet, wrong/worn needle or even a carb that needs adjusting could give you that kind of fault. If you have a good spark and everything is in time that would be my next shot. I personally use a gunson colourtune to set my carb, its simple to use and gives more than good enough results for road use, just be careful as they are very easy to cross-thread. If it’s a carb you have just bought, have you checked the needle is correct for the car? There are literally hundreds for different applications of the SU HS2. The standard for a 1098 minor is the “AN” needle, I personally use a “H6” it gives a little richer mixture on acceleration but is standard on cruse and idle. The type of the needle is stamped on the side at the top. Let us know if you need any info on stripping the carb, I found the best place to buy a needle (if you need it) is direct from SU from the uk website. I seem to remember it costing under a tenner including postage.

[bmcecosse]

No need for colour tune! The SU comes with a little lift pin that tests the idle mix for you. And running mix (which the colour tune can't check anyway) is tested by looking at the plug colours after a good run...... It's v unlikely to be a worn carb. That could possibly be guilty of high fuel consumption, but not poor running. I rather suspect that if Derek is used to Minis - he will know to advance the timing till it pinks, and then retard slightly - so it's 'not quite' pinking.

[Jason87]

As I said in my earlier post, “I agree with all of the above” and “If you have a good spark and everything is in time that would be my next shot.”

If the carb has been sourced from something else e.g. an 850 mini engine it will be fitted with an EB needle not AN. The mixture will appear correct at the carb because the carb is doing exactly what you are asking it to do. Similarly if a worn carb has been adjusted to give the correct mixture at idle it will be too lean on acceleration. Both of these issues will cause poor and lumpy acceleration.

I had noticed Derek’s reference to experience with minis which is why I did not want to recap the basics. But bear in mind that there are only 6 factors to consider; air intake, exhaust, spark, fuel, mechanical malfunction and timing. If the engine is running we can pretty much discount air intake and exhaust, and Derek has stated that this is a new (rebuilt) engine. So “If you have a good spark and everything is in time that would be my next shot.”

As for the colour tune, it is the only way to see exactly what is happening in the combustion chamber, and takes the guess work out of optimising the carb. I use one as part of my service routine. Each to there own, but the lift pins do not tell you what is happening inside the engine.

I must say I am not happy about having my comments so readily dismissed, especially as I am only trying to help. I will think twice about posting again.

Derek, I wish you all the best and hope you get it sorted soon.

[derekscoopers]

Jason and others

Thanks to you all for suggestions, A series are not difficult engines to get running correctly and that's why this one is a bit of a mystery, yes I have checked most of the basics and still it does not sing along, I am aware that it's the long stroke and will not rev as eagerly as the 948 but when you are so used to a series you get the feel that something ' aint right' the £1000 !! recon engine and brand new SU and dizzy came already installed and has only done 1000 miles since fitted.

I had changed the leads myself but have now refitted the old ones in case they were causing any tracking, no difference though, adjusted the dizzy and carb until it sounds right, slight improvement but still something isn't correct.

So I think its time to get a second opinion, I have used Adrian Dodd before to tune my cooper S etc and I am sure with his knowledge he will resolve it.

Shame really as I had hoped I could have diagnosed and sorted it myself, that's the fun of a Moggy surely.

[bmcecosse]

Indeed - ACD will sort it out. If all else is good - you need to consider the engine itself - it's possible the camshaft has been incorrectly timed - and also possible that a small valve cylinder head (as a cheap way of going 'unleaded') has been fitted - look under the rocker cover to find the 12G202 on the casting. Otherwise - if both these are correct - it can only be down to fine tuning. Try advancing the ignition till it pinks - WILL it pink? - and then retard slightly. As for colour tune - seriously..... although it 'may' have a use on cars fitted with inferior non SU carbs - where there is no built in 'lift pin' to check the mixture. And yes - it is worth checking in case a completely wrong needle is in the carb. An easy check though is to pull out the 'choke' (it's really a 'mixture increase device') and if the car runs obviously better - then indeed the needle may be too weak at that point. The lift pin tells us precisely what's going on inside the engine AT IDLE. Otherwise - spark plug colour is the guide - unless (like ACD) we are lucky enough to be able to use an exhaust gas analyser as we drive the car under different conditions - cruise/flat out/hill climbing at mid range revs and so on. ACD will profile you a needle using that tool - and will do an excellent job too! Unfortunately we don't all live within travelling distance of him.

[derekscoopers]

bmcecosse

wise words, you speak the same language as Adrian, I had never come across a man that could file a needle like him and know what it needed to make that much difference, he tuned my Speedwell 1275 S and it went better than I had ever known, anyway back to the MM, I will check the casting etc I di intend to go down the 12g295 or 12g940 route + bits but it's nagging me to get a bog standard engine running right so for a while I will persevere.

Really appreciate your efforts to help

Derek

[bmcecosse]

Who did the engine rebuild Derek? Do you know the 'easy' method for checking cam timing?? An engine with even one tooth out on the cam will never run properly...if all else checks out ok, that could be the problem. A standrd 1098 can never be described as 'nippy' - but it should pull well enough!