31 replies to this topic

[motlymo]

Bought a 1991 1275 re-shelled Cooper last year with a Hif44 carb, K&N, MG Metro needle, lcb and centre exhaust.  Engine ran ok but a bit lumpy and too rich as well as being jerky/hesitant on trailing throttle or low revs. causing engine to rock/ kangaroo when slow speed or town driving.  Car also a bit too loud for my liking. To try to improve matters fitted additional bottom engine stabilisers, swapped needle and filter to standard Cooper spec. along with standard side exit exhaust. Car set up on rolling road, now much quieter and smoother, producing a nice power curve and a top end of around 76 bhp.  Unfortunately whilst much better to drive than it was it is still jerky/hesitant at low speeds/trailing throttle, particularly at around  the 2000 revs. mark making it difficult to drive smoothly around town.  Anyone got any ideas for a cure apart from driving everywhere flat-out?

 

 

 

[sonscar]

Too much advance in this area,too lean or combination of both would be my guess.Steve..

[coopertaz]

do you know what cam is fitted? could be a lairy or mistimed cam, if not then sounds like drawing air, disconnect and blank off advance and check around inlet manifold with brake cleaner for air leaks. also check for split or missing breather hoses.

[D 'n A]

Maybe vacuum advance leak? Make sure there are no cracks in the elbows.

76hp is a decent number, can you post the dynosheet to show the curve?

[D 'n A]

The Cooper BFY needle is a bit lean in the bottom end of the rev range. You could put the Metro needle back in just to see if it improves, it's an easy job to swab them out. The Metro BDL needle is near identical but richer on the top of the needle, so in the low revs.

[motlymo]

The Cooper BFY needle is a bit lean in the bottom end of the rev range. You could put the Metro needle back in just to see if it improves, it's an easy job to swab them out. The Metro BDL needle is near identical but richer on the top of the needle, so in the low revs.

[motlymo]

Hope I've managed to attach the dyno print out  Adobe Scan 06 May 2022.pdf   370.15K   28 downloads Put the metro needle back in and a bit better on drivability but engine still a bit jerky/rocking when driving around town, despite additional lower stabilisers and new bushes. Is it maybe just the way it is with later rod change boxes?

[ACDodd]

The needle needs profiling at part throttle to clean this up.

Ac

[Spider]

,,,,,,,, Is it maybe just the way it is with later rod change boxes?

 

Definitely not.

The Dyno Printout (and likely the Rolling Road Session) only shows Wide Open Throttle Conditions, and even then, they are usually just a run up to maximum RPMs, I'm sure few would hold the figures on the printouts for 20 - 30 seconds or more, but that aside, the Part Throttle Conditions also should to be set up when a Rolling Road Session is done.
 

[motlymo]

Still got the problem Ive tried a few different needles in the hif 44 carb including BFY (Cooper), BBW (mildly tuned 1275) and BDL (MG Metro) . All still produce the same jerky/ engine rocking problems on part/trailing throttle between around 1500 and 2500 revs. Also tried fitting a new throttle butterfly with poppet valve fitted thinking this might help but it didn't. The MG Metro needle seems to suit it best up through the rev range and it pulls really well. Everyone I've spoken to with more knowledge than me cant put their finger on it  but say it cant be a mixture problem given the different needles I've tried. It is fitted with 65DM4 42664A distributor and the vacuum advance seems to be working as the tick over revs drop and it runs lumpy when its blanked off.  Might it be the distributor itself or timing fault? As I say I'm not an expert and just seem to be going round in circles at the moment. Any help would be greatly appreciated.

[stuart bowes]

do you really lose 50% of engine hp through the mini drivetrain?  I always figured it was more like 20% or so for most cars (not that I'm any sort of expert of course)

Edited by stuart bowes, 07 September 2022 - 03:32 PM.

[ACDodd]

What coil is fitted?

Ac

[motlymo]

honestly dont know its plain black and i can see any I.D. on it

[motlymo]

Could post a photo tomorrow if that any use as its pissing down up here at the moment

[ACDodd]

Measure the coil primary resistance and post back the result.

Ac