Morris Minor Owners Club

Hi all, I am having some power issues when i put my foot down at the lower rev range. I have done 800 miles so far on a recon 1275 A+. I have hiff 44 carb, inlet manifold etc...

What seems to happen is if I put my foot down(ish) when the revs are low then the engine seems to want to pull briefly but then it seems to lack something - I can hear what I assume is the air filter kicking in (noisy K&N) but not a great deal happens in terms of power until my revs increase to a certain point. Then the power seems to come on. So if i slip down a gear it seems to be ok but I don't feel that this is what should be happening - its a very unsmooth power curve! It's not misfiring at all.

Is this because the engine isn't yet run in 100% or should I be looking at something else as a symptom? Or is this normal?

Cheers

Sounds like it could be an air leak at the inlet manifold, I've had to file the head/manifold before to get them to mate properly. The car was a complete dog at low revs before that. I seem to remember that spraying WD40 around the inlet manifold gasket area while it's running and looking for exhaust smoke suggested as a check, but I've never tried this myself. Anyone know if this works? I'd guess you should avoid the exhaust manifold unless you want smoke under the bonnet too!

I assume you've got the timing set correctly and it advances with revs as it should. Oh yes, and the carb dashpot has got oil it it hasn't it?

Hi there, thanks for the reply. The carb dashpot seems ok + the timing is fine as well (I think).

I'll give that WD40 idea a go, like I said, there is a noise when I put my foot down, a kind of squeeky air noise but I assumed that was the K&N air filter coz I've heard that they are noisy. Then, the power comes in (kind of lumpily) and eventually better when revs are higher.

Sorry if my descriptions are not brilliant

Seems pretty clear to me

bigginger wrote:Seems pretty clear to me

Excellent! Now please solve my problem!

Anyone out there know what a 1275, HIF 44 with K&N air filter should sound like?

I wish I could - but when it comes to engines, I'm still wearing 'L' plates . I've got the 1275 and the HIF 44, but I only got it in and running the day before yesterday

Well, you've got a lot to look forward to then

Anyone else fancy a stab at why my car is running badly at low revs?

I'll give that WD40 idea a go, like I said, there is a noise when I put my foot down, a kind of squeeky air noise but I assumed that was the K&N air filter coz I've heard that they are noisy. Then, the power comes in (kind of lumpily) and eventually better when revs are higher.

With my pipercross filter I get kind of a whistley high pitched noise at certain revs, particularly if I utilise a lead-footed approach.

My insulator has no gasket on it though, and I suspect that that is the cause of my problems, and possibly also my entertaining whistle.

If you're running with a "free flow" filter have you got the right needle? It'll need to be richer, otherwise you'll get major leaning out at points in the rev range!

Could be you're simply getting too much air for the needle (and maybe springin the dashpot?) to cope with.

i'm not sure if the needle is correct, i bought all the gubbins at the same time (carb et al) from birmingham MM parts and I assume that they gave me all the correct bits to go together!

What needle should I have?

That goes for me too - yes please! I know it's a black art, but g'is an idea!

Kirsty,
Try pulling the choke out when you get your flat spot. If it goes better you'll know its weak at that point. One advantage of the SU is its "choke" is an enrichment device rather than the old fashioned true choke.
Regards, MikeN.

Unfortunately I have no idea what the right needle would be, but I very much doubt it's the one that's currently fitted! Best bet is a rolling road, but that's expensive - Maybe see what's included in the stage 1 kits and have a go with that?

Checking for air leaks is still a must if you have any doubts it's all sealed up, and gaskets tend to be handy ;)

Agreed using a bit of choke to smooth it out is a good idea

Thanks for all the replies. I'll try the WD40 method to check for air and will give the choke cable a pull when it happens to check the mixture.

Pyoor_Kate: that noise description seems familiar, esp when I have a lead foot too.

First - advance the ignition as far as possible without any obvious pinking just to make sure it's not that. I suspect it is a weak mixture - but leaks are rare - so check all the pipes are on where they should be! Put normal engine oil in the damper to stop it 'gasping' - and adjust the mixture when the car is right up to working temperature - these carbs have thermostat inside the float chamber. If it's still no good - it could be the fuel level which might be worth checking - and for a needle try BDL - the MG Metro one. Do you know what needle is in there at the moment ?
And you originally asked what it should sound like - well my Mini has this carb - with a 'bell mouth' hand worked into the air entry and the carb has in fact been 'Vizardised' - and it runs with NO air filter - and the noise is fantastic !! Loud roaring sucking noise - can't hear a thing inside the car - and it goes well too.

Unfortunately I have no idea what the right needle would be

I would eliminate all the easily investigated possibilities first. Unfortunately there is no single 'right needle' for a 1275/HIF44/K&N combo. There are loads of different needles available to compensate for individual charateristics of an engine. Picking the right needle and eliminating flatspots is the job of an experienced engineer with a rolling road and is money well spent.

bmcecosse wrote:First - advance the ignition as far as possible without any obvious pinking just to make sure it's not that.

sorry to be a thicky, can you explain what pinking is?

Don't worry about the pinking for now as it's just complicating matters. It's like a metallic sort of tinkling sound heard usually when slogging up banks at low revs with your foot too hard on the throttle!

You probably need a 'stage one' needle as you say, so get one from a Mini specialist and you'll probably be fine. If it's an air leak (which DO happen) then an easy way to check is to remove the manifolds and look at the gasket. All the five holes (ports) should have marks around them where the gasket has been tightened and compressed. You can see if there is an area that has not compressed the gasket and remedy that area by checking the manifold thickness etc.

At full throttle a K&N 'suck' sounds like the sort of noise you get if you partially cover up the end of a vacuum cleaner hose. It's quite loud.

Oh and whatever you do DON'T run without an air filter. My mate did that with his car and ended up with a scored bore (and subsequent knackered engine) thanks to a bit of grit that got ingested and stuck down the side of one of his pistons. It's not much fun for the bloke following behind (me) either when you can't see as the front of your car gets covered in oil mist!

Well it looks like my mixture is weak. Only just had a chance to drive the old bugger and it seems that with a warm engine the flat spot is allieviated by driving around with the choke 2/3 out. I'll sort this at the weekend.

I dont know, you ask a garage to stop the running on that their service caused and TELL them that it is likely to be a weak mixture and they hand back a car that revs lower at turnover but is still weak as hell! I'm doing everything myself from now on

QUESTION!!: When I increase the strength of the mixture, do I do so until I have reached the max rev point and knock it back 1/4 of a turn. Then adjust the idle speed down if necessary?

KirstMin wrote:doing everything myself from now on

QUESTION!!: When I increase the strength of the mixture, do I do so until I have reached the max rev point and knock it back 1/4 of a turn. Then adjust the idle speed down if necessary?

Sounds about right to me. Depending if you want slightly better pickup, or slightly better mpg go a fraction of a turn lean or rich in my experience