11 replies to this topic

[Callump]

Hey guys, I recently completed a carb conversion on my 1275 1995 mini Mayfair, the spi was driving me crazy and was riddled with problems I had to get rid of it. I have installed a facet fuel pump and a Nikki downdraught twin choke carb. Also my car has a hi lift cam. The ecu is still connected running the timing although i have a A+ dizzy to go on hopefully this weekend. At first it was pretty much undrivable, spluttering abs hesitating like crazy. I read a few forums online on how to tune the Nikki carbs and now it’s running a bit better but still not what I want, so hopefully someone on here can help me with my problem. After trying to tune the carb the best I can I find that above about 1500~2000 rpm it’s perfect, but as soon as is drops below that it runs horribly and cuts out quite often (I’ve noticed this only tends to happen when the car is warm) could this be an issue with the timing, carb tune or something else? Also the car overruns everytime I turn it off, putting in gear and dropping clutch fixes this but annoying to do everytime and looking for a more permanent fix. Any help would be much appreciated. Callum

[cal844]

More information needed on the specification of your engine. Depending on the spec of cam fitted the idle may well need to be at the 12-1500 mark to idle nicely, the higher lift the lumpier the idle.

Being honest the SPI system is very basic and with a multimeter and the correct diagnostic plug (£40 all in, for the plug and application for your phone) can be repaired.

YouTube DB mini DIY for all there is to know about the SPI and diagnosis

Running on is an issue, you are doing the correct thing by stalling the motor, however you can minimise the frequency of it by leaning out the mixture (set accordingly for year of car) and tweaking the timing.

You say you still have the ecu fitted. If you have carb converted the engine you don't need the ecu.

Edited by cal844, 10 November 2020 - 11:23 PM.

[Callump]

The cam is a “264 fast road evo” camshaft, car also has a 2” decat straight theough exhaust and lcb manifold.I think I would rather stick with a carb for now just for the tuning capability, sending my head off for bigger valves and to be flowed soon would rather have a carb to better fit these modifications. Yeah the ecu is still in only running the timing, only reason it’s still in is that I was waiting for a A+ dizzy to arrive and decided to run that for a week.

Edited by Callump, 10 November 2020 - 11:54 PM.

[Cooperman]

It does sound like the mixture is out at low revs.

Your exhaust pipe is a little too large for that engine, especially at low revs and a 1.75" is generally accepted as best for a 1275 engine unless it is in full-race tune and using over 5000 rpm most of the time, although I doubt it is the cause of your bottom end running issue.

[sonscar]

It is possible you may encounter problems at the MOT as your car is on the Efi/cat test list,unless you can prove you "have fitted" an earlier engine.Good luck,Steve..

[nicklouse]

I would bin the carb. And as mentioned you will need to pass the injection emissions level at the MOT.

 

not to mention it will need the cat fitted for the MOT.

Edited by nicklouse, 11 November 2020 - 09:19 AM.

[Callump]

Thanks for the replies guys, I’m going to keep the carb, I will take care of it come MOT time ;). All I’m looking for is any tips on how to try and get it running better. I will raise the idle today to 1200~1500 and make the mixture a little leaner and see how it goes

[Callump]

So I set the idle to roughly 1200 rpm and made the mixture slightly more lean, when idling it hunts from 1100~1500, it drives much better although has a flat spot when accelerating. Also when coming to a stop or going over a speed bump it will idle crazy high maybe 2000 rpm sometimes higher. The car is still running with the ecu controlling the timing could this be the problem? Hopefully I can get the A+ dizzy on this weekend

[cal844]

You can get a 65D with the vacuum can, that way the timing and advance should be about right

But id also suggest sending the new dizzy to be recurved and rebuilt.

Check for air leaks on the manifold gaskets including the carb abutment plate gaskets

Edited by cal844, 11 November 2020 - 10:34 PM.

[Callump]

That’s great cheers mate I’ll have a look into possibly purchasing a 65D dizzy then. Sure I’ll have a look around for any air leaks tomorrow cheers, seems to be loads of little pieces on the Nikki carbs where air could get in

[cal844]

That’s great cheers mate I’ll have a look into possibly purchasing a 65D dizzy then. Sure I’ll have a look around for any air leaks tomorrow cheers, seems to be loads of little pieces on the Nikki carbs where air could get in

65D is the electronic dizzy that came on the 1990 onwards cars that didn't have injection. I have them on 2 earlier minis, a 1980 estate and a 1989 Mayfair. I also have a 1275 sprite with the same set up. All run perfectly well with no issues.

My opinion is to get rid of the Nikki carb and use an SU, either an HIF 38 which will best suit your spec for more torque

Edited by cal844, 11 November 2020 - 11:14 PM.

[Callump]

That’s great cheers man I’ll have a look into it.

That’s what I’m thinking to be honest, Nikki carbs look wicked and the idea of the twin choke opening at higher rpm sounded cool but think their more effort than their worth especially with the lack of spare parts. Will have to run the Nikki carb for a while as I’m only 17 and out of a job due to COVID ? I’ll see how well I can get it running and probably eventually switch out the carb