Ok Deb, here's another thing now that you mentioned hills.


check your oil level. 

Has it been overfilled?  If so it can wet the clutch disc and slip.


To test for a slipping clutch, warm up the engine,  put the emergency brake on tightly.  Put car in 4th gear and release the 
clutch.  It should stall immediately. 


As you release the clutch, give it enough gas to keep the engine running and it should stall. If your emergency brake does not work,

you can do this test with your heel on the brake and toe on the gas.  Make sure there is nothing in front of you in case

the car breaks loose from your brake.



don't over fill the oil. (crankcase)

If I understood your previous posts, you had to downshift to bring the revs up and try to maintain speed.

For tasks like going uphill, a certain amount of power is required.  When your carb is unable to provide enough fuel to go the desired speed, you downshift.  The engine RPM go up but the road speed is probably still dropping... until you reach the new steady-state condition.  The engine RPM are only being limited by the inability of the carb to provide enough fuel for the power required. 

On level ground you probably are not approaching the power limit for the available fuel delivery.

There's an internal fuel filter in the bottom of an HIF carb. 

Dirty fuel can clog them quite easily if there isn't an inline filter between the tank and the pump or pump and carb and take the edge of the performance.

I could certainly believe fuel filter.  Reminds me of the time we had a brand new--but faulty--fuel filter on the 356.  We were 80 miles from home when it started to malfunction, in a fairly similar way to this, and managed to limp 75 miles when we gave up because it was getting dark and there were no more shoulders on the road, with a long uphill grade.  Towed the rest of the way.  

It certainly would fit with the theory that fuel is at least part of the problem.  If I got bad gas, or stirred up crud at the bottom of the tank, the fuel filter might have clogged up.  Then again, why would 3000 rpm be okay?

Will put it on the list of stuff to check when I get home next week.

Typical mechanical fuel pump location - back side of engine near radiator.

As Ian said, the K&N filters like the one you posted the link to are washable and then have to be re-oiled once washed.  Reconditioning kits are available at local parts stores like Advance Auto and the kits come with directions.  And don't throw out or replace K&N filters.  They are too expensive to dispose of.

You said the coming and going of the problem with RPM also involved changing gears (frequent downshifting).  That suggests that the car is running out of fuel or air... probably fuel.  I only mentioned the air filter as a possible contributing factor since a plugged air filter can surprise you with its effect.  However, your last post said the problem came on suddenly and that the engine used to run OK.  That suggests it is not the air filter.  

Mechanical fuel pumps are located on the back of the engine block.  Follow the fuel lines back from the carb and down.  If a mechanical pump is present you'll see it.  If you don't see it, keep following the fuel line under the car looking for owner installed fuel filters.  If an electric pump has been fitted (or factory installed) it will not be under the car.  Keep following the fuel line to the back of the car.  Factory pumps are located under the boot floor and were mounted on the rear subframe.  Factory electric pumps are often replaced by less expensive Facet brand pumps (or similar brands).  These pumps may be in the factory location on the subframe or in the boot.  Google "Facet" fuel pump for images showing what to look for.  There are several styles.  Also Google for SU electric fuel pump so you know what the factory pump looks like.

Just remove the air filter and go for a run.... If a blocked filter is the problem it will be obvious.  K&N filters (if you do have one) are washable..... and need to be oiled afterwards.  There should be instructions on line...

However, I don't believe this is the issue ...why would the filter affect performance at 2500 revs and disappear at 3???

Cheers, Ian

Hmmm, Doug.  I've been wondering about the air filter, but haven't pulled it.  Another thing to do, I guess.  I don't know about the fuel pump.  I suspect it would not be anything very exotic.  Maybe malsal knows, because he knows the previous owner, and probably the car as well.  

How do you clean an air filter?  I thought you just replaced them.  In looking at the pictures on the MiniMania site, it looks like this one;

//www.minimania.com/part/56-9320/Austin-Mini-Kn-Air-Filter-For-Hs4-Hif4-And-Hif38

I don't know if that is the exact type because I'm not where the car is, but that's the shape.

Sorry to be pretty ignorant, but I guess that's why I named the thread "How should I troubleshoot this?"  I don't want to go 6 directions at once, or throw all kinds of money at it.  I know it CAN run well, because it did for the first 4 months.  This last month hasn't been real fun, though. 

I'm out of town for a few days, but when I get back early next week I'll check out the things everyone has mentioned.

That's interesting. I tend to suggest looking at cheap and easy things to check first.  In this case I suggest what was mentioned earlier, check the fuel flow.  Were you able to look for filters installed by previous owners?  Also check the condition of your air filter.  I was very surprised several years ago when a friend's Mini could not go over 45 MPH.  It turned out he had purchased a used Stage 1 kit and the K&N air filter was totally choked with dirt.  After cleaning the filter he was able to drive at highway speeds again.

Sorry if you have already answered this, but is your car fitted with a mechanical or electric fuel pump?  If it is electrical, is it a factory SU pump or an aftermarket replacement like Facet or similar?

EDIT:  Sorry, I also meant to add a comment about pumping the gas pedal during engine starting.  Unlike a lot of carburetors, the SU carb (as used on the Mini) has no accelerator pump to shoot a jet of fuel down the carb throat when the throttle pedal is pushed.  Pushing and holding the pedal does change how the air flows through the carb but pumping the gas pedal does not deliver "a shot of gas".

"The smoothing out above 3k RPM is a bit surprising..."

Has anyone already suggested/ have you checked for an intake manifold air leak??

Cheers, Ian

For some reason I don't seem to get notices of responses (even though the box is checked), so pardon me if it seems like I'm ignoring comments or questions.

First, to malsal:  Yes, oil has been added to the dash pot.  It was actually the first thing I did.

dklawson:  By "One shot of gas, and I'm good,"  I mean that I press on the gas pedal once while the starter is cranking, and she lights right up.  Probably not the best terminology.  I tend to forget you're not in the right seat, LOL. I'm not using starter fluid or adding anything to the carb.  I've been driving her once or twice a week.

I agree that the idle is too slow, but that's obviously not why it's running badly at higher rpms.  I mention it because someone asked about whether or not the engine was happy at idle.  If I boost the rpms to 1000, no problems at all.

You have me scratching my head a little on the first few lines of your comment, trying to remember the sequence.  Maybe it's best to say it this way--I have to downshift to bring the rpms above 3000, unless it's totally flat or a slightly downward slope.  Where I live it's very hilly, so right now I'm having to constantly downshift.  This is NOT the way it was before this problem started.  I'm downshifting a lot more now, and while there's a lot more noise in third, there's really not much power.  I'm even having to drop down to second at times, and that's absurd for the grade where I'm doing it.  It's the 3000 rpm that is keeping it happy.  Again, not the way it was just a few weeks ago.  

I'm heading out of town early tomorrow for a few days, so I can't drive it tonight to pin things down better than that.  On the good side, I'm going to where a good friend of mine lives.  He was a Mini mechanic back in the day in Finland.  He might have some ideas.

The smoothing out above 3k RPM is a bit surprising.  When you experience that transition is it perhaps because you are backing off on the throttle and intentionally slowing your acceleration?  If the smoothing out of the engine above 3k RPM occurs because you are easing up on the acceleration and it reoccurs when you get back on the gas, that suggests fuel starvation. 

As others suggested above, you should check the fuel delivery and look for crud in the gas tank, inline filters installed by previous owners, and if necessary check for a plugged float valve filter/screen inside the HIF carb.   I use the inline disposable fuel filters often used on air cooled VW Beetles.  They are inexpensive (off eBay) and you can see crud collecting so you know when you need to change the filter.

Your 600 RPM idle speed is lower than I would ever try with my car.  I would love to idle as low as 800 RPM but typically set my British cars to idle somewhere close to 1000 RPM.  

When you say "One shot of gas, and I'm good" what do you mean?  Are you spraying starter fluid in the carb or pouring gasoline down the carb throat to help it sart?

Yes you can siphon fuel out of the tank with no obstructions. As i suggested an easier way would be to pull the fuel inlet line off the carb and crank it over with the coil wire disconnected (non start) with a manual pump or turn on the ignition with an electric pump and collect the fuel in a water bottle then let it settle and see what it looks like.
Have you checked the oil level in the dash pot (the black plunger on top of the carb). It needs to be full up to the inner circle inside the dashpot, any more than this will just leak down the inside of the carb and be burnt off during the combustion process.

Wrong Again. Adjusting valve lash will have absolutely no effect of ignition timing. Especially with an electronic ignition system.
A tune-up may require valve lash adjustment (due to wear of the valve train); ignition points adjustment (due to wear of the points where they contact the cam) which would result in timing needing to be verified; and the idle speed and possibly idle  mixture because of the adjustments to timing and points gap.

cheek,  the thing of the matter is, if you adjust the valve, automatically you need to adjust the ignition timing and the carb tuning as well, it's kinda like a domino effect, you can't just adjust one department and ignore the others...this is what i learn from DM, once upon a time he told me this.

"Check everything else before doing any carb adjustments."

Words to live by! I get tired of working on peoples' cars and finding the problem being one of Compression or Ignition, fixing it, and then having to go back and reset the carb which was way off because it was tackled first.

Almost all of the suggestion are very good ones. Go at it and be up and running soon.

Thanks, everyone, for your input!  A lot to think about.  I'll see if I can answer everyone's points.

First, it starts right up, every time.  One shot of gas, and I'm good.  On cold days (this is Arkansas), I use the choke, but still, starting is absolutely not a problem.  It idles a bit rough, as if it needs a little more rpm.  Idle speed is about 600 rpm.  It doesn't die, though.

The rpm range where it isn't happy, for whatever reason, is 2100 to 2900.  At 3000, everything smooths out.  Trouble is getting to that point.  Here in the Village, we have a lot of hills, both gentle and fairly steep.  A typical scenario, but only since this problem started, is that I'll be in 4th on level ground, running about 45 to 50 mph.  Then the road will have a mild incline, and I have to drop down a gear just to maintain smooth running.  Lots of engine noise, but no real power, and before this all started, I wouldn't have had to shift at all.  Sometimes I have to drop down to 2nd, and that's ridiculous for the grade, but that's what it's taking to keep from chugging.

I think the suggestion to pull the fuel line and check is a good idea.  Again, I feel strongly that this started after the last tank of gas, whether from bad gas from the station or running too low before filling up.  That was why I put the Seafoam in, but I can't say there was any improvement.  In fact, after cleaning and gapping the plugs the other day, I thought there was a little improvement, but driving it over to the doctor today (9 miles round trip), I'd say no.  It ran like doo-doo, frankly, unless I was at 3000 rpm.  Then all was well...until the road sloped upwards.

Back in the old days, when I flew, part of my preflight was to drain the sumps and look at a sample for water.  Is there a way I can check the bottom of the tank without draining it?  Or would I run into an obstruction if I tried to stick a tube down in the tank?  (I don't see anything using a flashlight, BTW.)  I've got some clear plastic tubing.

Compression check before purchase last fall was 160 on 2 cylinders and 170 on the other 2.

All 4 plugs were equally sooty, so no evidence of anything running lean at all. 

You can look inside the gas tank through the filler neck with a small flashlight and see if there is any rusting. As Bob used that car frequently i imagine there should be none or minimal amounts.
Compression figures should be within 10% of each other. Look at the fuel issues first though before diving in. If you need to adjust the HIF carb turning the adjustment screw in (clockwise) richens the mixture and out (counter clockwise) weakens the mixture which is the opposite of the usual way.
Check everything else before doing any carb adjustments.

MiniMike's advice to do small things and drive (without messing with timing or fueling settings) is good. 

I'm not convinced you must drain and clean the tank, but it's never a terrible idea to ensure your tank doesn't have little bits of rust granule in it. A 30 year old fuel tank that's been half full or less for a LONG period of time can get condensation inside the "air" part and eventually cause a flash of rust on the inside tank surface that can be rinsed away after the next fill up and repeat itself and put fine sand-like silt in your tank.

The other think to consider as a possibility-- not the first thing you should check for, but a possibility-- is if you've had a vacuum leak in the system you could have been experiencing a lean running condition which will start to burn away a valve. When it gets a significant enough breech, you will get a sudden change in engine performance. A compression check will show a significant drop in compression on one cylinder (along the lines of 120-116-79-119 for example). The other thing it could burn is a head gasket. On a 1275, that's most common between cyls 2&3. If you have access to a compression tester, you may want to rule that out. It's an easy thing to check for. Don't worry about slight variations in compression numbers or what the absolute number is. Just use it to compare one cyl to the next.

That is Bob O's old Mini and i am pretty sure it has a HIF with a 1275. As this happened after a fill up i am thinking too that fuel is the issue. Maybe pull the fuel line off the carb and pump some into a bottle to determine whether it is contaminated.