616 replies to this topic

[johnR]

Not sure about what it would do if 4k held in a lower gear, but there as you can see there is a filter between the (vented)tanks and the pump and I pumped a litre through it in 40 seconds so I no longer think the problem can be supply to the carbs. It could be the carbs themselves (float needles checked and tops flowed Ok on jamjars) or electrics?(new coil)

Edited by johnR, 04 June 2020 - 05:20 PM.

[imack]

Have you tried it with any different carburettor needles?
I had a problem with my new engine build a few years ago with misfiring between 4000 and 5000 rpm, ok at lower and higher revs. Turned out to be over fueling in that part of the rev range, could get rid of misfire with another set of much leaner needles I had. Got set up on rolling road and perfect ever since.

[Tones61]

Looks like the rubber hose is kinked on outlet from pump?

[johnR]

Have you tried it with any different carburettor needles?
I had a problem with my new engine build a few years ago with misfiring between 4000 and 5000 rpm, ok at lower and higher revs. Turned out to be over fueling in that part of the rev range, could get rid of misfire with another set of much leaner needles I had. Got set up on rolling road and perfect ever since.

I'm using M needles which are the recommended ones, but I guess the rolling road session will show up the need for leaner ones if necessary

[theclassicminishop]

Hi John

 

Had a very similar problem last year on my GTS, where car is fine to drive and revs good until you get In 4th gear when you rev also near to 5500 to 5800 then seems to loose power, then I would take my foot off the gas and within a few seconds the car is back and running good, till a certain revs then bogs down again.  Only did it in 4th gear no other gear and at no other revs.  Also running twin SU carbs and also fitted a uprated Facet fuel pump. This issue also drove me insane, after a million checks and adjustments I just drove the car like that and kept the revs down.

 

Long story short, engine is fitted with high compression pistons, massive valves and kent 286 cam with kent double valve springs.  Car finally broke down on my way to Johannesburg one morning.  After removing the head, had a very very slightly bent valve on no 3 cylinder and two other valves just just contacted the top of the piston on cylinder 4 and 1.  So in my particular case then after fitting new valves and determining that the valve fitted height differs, I had to shim the rocker shaft pedastals to compensate.  Also unlike the first time when I just bolted the engine together, I used clay to check valve to piston clearance to ensure no contact like I should have done on the first engine assembly before the car broke down.

 

I also read earlier in your thread that you had the engine built by a 3rd party, just ask them IF they had done the above test.  Further you did have problems on initial startup with incorrectly adjusted valve clearances.  Maybe something went wrong then already, just a thought.

 

Since you are planning on fitting another head gasket this should all just be double checked then.

[johnR]

Interesting to hear your experiences with a similar engine spec. There was no sign of valve/piston connection when I replaced the head gasket the other day and the pedestals were shimmed to compensate for head skimming at the time of the build 130 miles ago. I replaced the original standard rockers recently merely because there was some concave wear on them (which would have led to a greater valve gap so less chance of connection with pistons?) and I ran out of money at the end of the initial build-up!

So whilst I think this scenario unlikely in my engine I will certainly bear it in mind as we move forwards because of the strikingly similar symptoms.

[Cheeser]

A few thoughts some of which you may have done or eliminated?
As I understand it your engine is modified in several ways and will need a different needle from the standard M needles, modified head, different lift,duration and overlap of cam excentuated by the use of 1.5 rockers, also LCB and K&N cone filters
Did you carefully adjust the needle valves in the float lids?
When you get to the point of the engine not pulling have you tried carefully pulling out the choke to see if richening the mixture mskes any difference
I haven't a clue whin it comes to the 123 system, but is it possible for it to be set up with a rev limiter such that it is not allowing maximum speed?
Are the butterflies opening fully when you push the throttle pedal down?(also carpet/floor mat not in the way!)
It's often the simple things that get missed, we've all done it!
Good luck and hope you can get it running better before fine tuning on thr RR

[johnR]

I've tried a richer needle (AH2) - too rich. The M needles seem fine by plug deposit colour. Rockers are only 1.3. We did check the needles and adjusted them to corrct spec - more difficult with the newer ones as they dont have the bendable flap and need to be shimmed. There is a rev limiter on the 123 - it was set to 6k - I did wonder if that was an issue (although my problem seems to be coming in at only 4k) I changed the rev limit to 8k. I haven't specifically checked the butterflys but I think restricted opening would lead to a restricted top speed whereas what is happening is a collapse of revs/power at 4k revs. Pulling the choke out during collapse makes no difference. I checked my HT leads today - they seem to be the carbon cored type which is correct.I hope it is one of the simple things - god knows what though!

[tankertanker]

Hi John did I catch a glimpse of you today in Westbay ?
Car looked good and sounded nice ....

[johnR]

Yes, I did pop down - it's not running properly but it's still nice (but frustrating) to potter out in it. Looking forward to Thursday when I hand it over to the garage! What were you in/on?  

Edited by johnR, 09 June 2020 - 10:16 PM.

[tankertanker]

Been following with interest am sure it's going to turn out to be something not to difficult to sort,
I was grabbing a 99 when my other half prodded and said quick a proper mini .... well educated I think :)

We were in the van not brave enough for the mini

Good luck for Thursday

[johnR]

I set off for Tipton St John but not long into the journey ominous noises started coming from the engine accompanied by a lowering of oil pressure. I persevered for a few more miles but eventually had to admit defeat and got towed home rather than risk more damage. Turns out it must be something more fundamental than set-up!

Engine apart I think - may look at re-instating the 998, only using the HS2s etc as a temporary measure so we can still use the car.

[imack]

I set off for Tipton St John but not long into the journey ominous noises started coming from the engine accompanied by a lowering of oil pressure. I persevered for a few more miles but eventually had to admit defeat and got towed home rather than risk more damage. Turns out it must be something more fundamental than set-up!

Engine apart I think - may look at re-instating the 998, only using the HS2s etc as a temporary measure so we can still use the car.

I feel your pain.
A few people on here seem to be suffering numerous engine and gearbox problems on here at the moment after extensive rebuilds. I don't know how you manage to maintain enthusiasm let alone the expense.
Let's hope it's not too expensive to put right.

[johnR]

When you see it's little sad face you can't give up on it!

[johnR]

So rather than getting depressed I've decided to crack on with a light resto of the original 998 so i can use the car while I investigate the cursed engine.

Stripped it down a bit, looked out the stored parts that came from it and started splitting the inlet and exhaust manifolds so I can still use the RC40.

A good start - now to order a new timing chain, gaskets etc. - retail therapy!