5 replies to this topic

[Smithys999]

In the last 5 months, I finally have my mini out of storage after 8 years and have ploughed through a significant list of technical issues and repairs. However, I have one final symptom, which is proving very difficult to resolve. The spec. is as follows

 

A+ Block 1293 compression ratio 10:1……

Kent Cam 296 with Vernier duplex chain

1.7:1 roller rockers

HIFF44 with ITG filter and stub stack Manifold ported and polished

Head 38mm inlet 31mm exhaust fully ported

LCB manifold

123+ Distributor with competition coil and leads spark plugs standard

1000miles on engine since full rebuild

More but probably not relevant to the issue but ask if you want to know.

 

Prior to going into storage the car ran very well with stable idle at 900 to 1000 rpm (Little lumpy as expected but free return to idle). I have had numerous problems and symptoms to sort out and am now to a single symptom, which is causing a slow return to idle. When coming to a stop the revs take approx.. 20s to drop from 2000 rpm back to a stable idle at 900-1000 rpm. This appears to happen only when warmed through and the drop gradually slows and stabilises at the set idle. I have checked the following:

 

Throttle cable (free return to idle stop...)

Butterfly valve moves freely (No visible signs of damage or wear)

Vacuum leak at all points to the head (Excluding vacuum advance hose and crankcase breather pipes, which I will check today)

Inspected the dash pot damper / spring and oil level (I use 3 in 1 have used the SU damper oil but found very little difference in the past) Moves as expected.

Timing Static and at set intervals against two curves both setup on rolling road

Checked mixture

HIFF44 refurb kit (to resolve leaking choke seal)

Exhaust removed and resealed due to knocking on rear sub frame and running to close to CV joint boot.

 

Any suggestions or questions are welcome.

Edited by Smithys999, 11 May 2022 - 02:45 PM.

[slidehammer]

Could it be an air leak on the inlet manifold anywhere? I think that is where I would look once all the breathers are checked and leak free

[cal844]

Air leak somewhere or something sticky in the carb.

[sonscar]

I would start with mechanical fault on carb or cable,air leak or worn spindle bushes or advance mechanism sticking.Steve..

[andyapanel]

It might be the throttle return spring needs replacing
It has happened twice to me, once the engine staying at 2000 rpm, which was rather exciting till I could pull over

[Smithys999]

So after a hour of investigation and finding nothing. I took the hiff44 off the head to look at the gasket. In doing so noticed the center pipe on lcb exhaust was really lose. So under car seems the joints have all worked lose on the y branch again and it's been blowing again. I have a new manifold gasket coming and going to refit exhaust and inlet with hiff44.... does anyone know if a flexible joints a good solution ? I have top and gearbox stabilisers on this engine so I am at a loss as to how it keeps doing this as full body weight against it I can not get it to rock. Also not sure the exhausts the cause of the idle issue but I did find a lump of metal in the gasket that might have stopped the inlet manifold seating as well as it should.

Edited by Smithys999, 16 May 2022 - 07:11 PM.