13 replies to this topic

[MotorBoatMyGoat]

Hey

I've had a search on previous threads but couldn't find my problem.

I've had my mini for a few months with no trouble. I first noticed the issue a few weeks back. The mini starts easily enough, timing is right and doesn't misfire.

So, I started the mini (998 mayfair 85) with no problems, got a few hundred metres down the road and while accelerating and at about 3000rpm there was power loss/hesitation for a few seconds then power kicked back in. Then a short while later the same problem. I didn't take much notice to begin with as the problem seemed to dissappear.

Today I went for a long drive down the motorway, down the country lanes which was fine until there was the same power loss again. But this time I gradually lost speed and tried to accelerate down the gears with no luck until I came to a a complete stand still and the engine cut out. I then started it and it was as if nothing had happened....accelerated up to 70 again and was fine for a few miles. Exactly the same thing happened again. This happened 3 time. I then nursed it along the motorway at 50 and I didn't have a problem.

I'm a bit confused as it'll lose power but be totally fine once restarted.

any ideas/help/advice would be greatly appreciated.

Thanks

[KernowCooper]

Have you checked the supply from the pump is working ok into a jampot while cranking

[crackfoo]

Hey

I've had a search on previous threads but couldn't find my problem.

I've had my mini for a few months with no trouble. I first noticed the issue a few weeks back. The mini starts easily enough, timing is right and doesn't misfire.

So, I started the mini (998 mayfair 85) with no problems, got a few hundred metres down the road and while accelerating and at about 3000rpm there was power loss/hesitation for a few seconds then power kicked back in. Then a short while later the same problem. I didn't take much notice to begin with as the problem seemed to dissappear.

Today I went for a long drive down the motorway, down the country lanes which was fine until there was the same power loss again. But this time I gradually lost speed and tried to accelerate down the gears with no luck until I came to a a complete stand still and the engine cut out. I then started it and it was as if nothing had happened....accelerated up to 70 again and was fine for a few miles. Exactly the same thing happened again. This happened 3 time. I then nursed it along the motorway at 50 and I didn't have a problem.

I'm a bit confused as it'll lose power but be totally fine once restarted.

any ideas/help/advice would be greatly appreciated.

Thanks

 

carbs running/tuned fine?

 

Mine had a bout of that yesterday. Was running fine, pulled up to a roundabout and was next to go, when the engine cut out. I pumped the pedal a couple times as it was fading out thinking it was fuel, but it had no effect. Started back up and went on my way... curious to see what people think about your issue. I'm thinking it is one of my carbs as mine was off the road for 10+ years and one of the carbs was blocked up with old gas. I suspect something isn't running quite right in it even after it was serviced.

[carbon]

+1 for KernowCooper's suggestion of checking fuel flow into jar or similar.

 

If you were running estate or van I would have also suggested taking close look at petrol tank filler cap, as these tanks do not have a vent and must be fitted with ventilated filler cap - if not the air won't get in and the fuel can't get out. Gives similar symtoms to the ones you have described, but typical indications are substantial loss of power on long hills.

 

With saloon petrol tank there is a vent pipe from top of tank, worth checking this is not kinked or blocked.

[Spider]

Good suggestions there guys, I'd also suggest checking the fuel pressure at the carb, should be around 2.5 - 3.0 PSI.

 

I had a failing electric pump a few years back and it wasn't easy to track down as it only played up every now and agian, but I did manage to catch it one day with a gauge.

 

<edit: Another one I recall was after doing an overhaul, the damn thing drove OK, but when you put the boot in, it had every since of fuel stavation, yet all that checked out. It did have me stumped for a few days and eventually I found an insect had made a nice home in the carb fuel bowl vent........>

Edited by Moke Spider, 29 November 2014 - 09:44 PM.

[dklawson]

All the above are good suggestions.  As a footnote I will add that if you have a tachometer fitted, glance at it the next time the problem surfaces.  If the tach slowly drops as you loose power and come to a stop, that says the low tension side of the ignition system is working OK.  If the tach drops like a stone or bounces wildly while this is happening, you have an ignition related problem.

 

Crackfoo, if your car's problem reoccurs, pumping the gas pedal really has no effect when SU carbs are fitted.  Some cars have other carburetor designs which include an accelerator pumps that will shoot more fuel into the intake manifold when the the pedal is pumped.  SU carbs have no such pump so tapping the gas pedal a few times does nothing but open up the throttle butterfly.

[Spider]

Crackfoo, if your car's problem reoccurs, pumping the gas pedal really has no effect when SU carbs are fitted.  Some cars have other carburetor designs which include an accelerator pumps that will shoot more fuel into the intake manifold when the the pedal is pumped.  SU carbs have no such pump so tapping the gas pedal a few times does nothing but open up the throttle butterfly.

 

Yes, but it does make you feel better

[crackfoo]

All the above are good suggestions.  As a footnote I will add that if you have a tachometer fitted, glance at it the next time the problem surfaces.  If the tach slowly drops as you loose power and come to a stop, that says the low tension side of the ignition system is working OK.  If the tach drops like a stone or bounces wildly while this is happening, you have an ignition related problem.

 

Crackfoo, if your car's problem reoccurs, pumping the gas pedal really has no effect when SU carbs are fitted.  Some cars have other carburetor designs which include an accelerator pumps that will shoot more fuel into the intake manifold when the the pedal is pumped.  SU carbs have no such pump so tapping the gas pedal a few times does nothing but open up the throttle butterfly.

 

OK, thanks for the bit of info. Good to know, I just remember my dad in his old cars given'er a shot with the pedal. Wasn't a mini though hah. My tacho unfortunately doesn't work ATM. Will see how the next ride out in it is. It's getting cold over here in Halifax now, perhaps that is a factor as well.

 

I'll follow along here now, I don't mean to thread jack.

Edited by crackfoo, 30 November 2014 - 08:07 PM.

[Poppet2]

I had this problem last year year. There was a blockage in the rear of the exhaust due to all the rust, corrosion and crap coming from the tank.
It had to get blown out with great pressure, then a filter was added so the rust from the tank didn't do it again. But my mini fuel tank is 30 years old.
Perfect after that.

[dklawson]

There was a blockage in the rear of the exhaust due to all the rust, corrosion and crap coming from the tank.

then a filter was added so the rust from the tank didn't do it again. 

 

 

While there may have been exhaust blockage it would not be from anything coming from the tank.  Any debris coming from the tank would first have to pass through the tiny jet openings in the carb before reaching the relatively large diameter openings in the exhaust.   However, it is not unusual for exhaust pipes to corrode from the inside out and large bits of scale from those pipes could plug the tubes inside the muffler.

 

Regardless, operating an old car without inline fuel filters can lead to dirt, rust, and scale plugging the carburetor.  Adding the fuel filter is a good idea.

[MotorBoatMyGoat]

I have an inline fuel filter fitted. I can't imagine it could be corrosion in the exhaust as it was relatively new.

What's confusing is that its a smooth gradual power loss. If The carbs were dirty or had a blockage of some sort it would make a jerking spluttering motion as the air/fuel mixture would continually change. Please correct me of I'm wrong in saying this.

The power loss was as if I had just come off the accelerater and the engine gradually lost revs then cut out. Once restarted it was fine for a few miles.

If it helps, while I was revving the balls of it through the country lanes (while sticking to the speed limits) it was ok, but on the motorway at a constant speed, it was then it had the issues. But only every few miles

[MotorBoatMyGoat]

Thanks for the advice guys. Keep it coming. I will get to the bottom of this!!!

[dklawson]

Which carb(s) are on your engine?  If they are the HS series carbs, the easiest screening test is to drive the car hard until the problem reoccurs and immediately switch off the engine, press in the clutch, and coast to a stop on the side of the road.  (Doing all those steps at once will prevent the fuel pump from delivering any more fuel to the engine once the problem starts).  At the side of the road do two things.  First go to your fuel tank and remove the filler cap.  If there is a sudden inrush of air as you remove the cap, the tank vent is not operating and your car is developing vacuum in the tank and use fuel.  You must have a working vent or the pump will eventually be unable to move fuel.

 

Assuming there is no inrush of air as the tank's cap is removed, the second test (for HS series carbs) is to remove the three screws securing the lid to the carb's float bowl.  (DON'T DROP THEM!)  With the lid removed you should find the float bowl 1/2 to 2/3 full of fuel.  If you find less, that says you either have a float valve set way too low or you have a fuel delivery problem.  I don't think there is an easy way to check this on HIF carbs... others will have to comment on that.

 

Sources for problem/low fuel delivery can start in the tank and move forward.  As stated in test 1 above, the tank is supposed to be vented (at least on early cars) using a plastic vent tube that is connected to the top of the tank and exits the boot floor.  If that vent line is plugged for any reason (bees and wasps can block these), a vacuum can develop in the tank while driving and fuel delivery will eventually stop.  There is also a coarse screen on the fuel pickup tube inside the tank.  If the pickup is blocked by large amounts of debris fuel delivery can be stopped.  Previous owners may have installed inline fuel filters that you are unaware of and those can block fuel flow when plugged.  If there is no filter between the tank and fuel pump, debris passing from the fuel tank may have disabled the check valves in the pump.  Any old fuel hoses that have been disturbed may have shed crumbs of rubber that are partially blocking the float valve in the carb.  There are other possible sources of blockage but these are the ones I would look at first once you know for sure that you have a fuel delivery issue.

[carbon]

Doug makes a really good point about the coarse filter inside the petrol tank getting blocked.

 

I had this happen on my '69 automatic a couple of years back, it was getting serious fuel starvation problems. Turned out the filter inside the tank was well blocked up, and even putting 100psi workshop air pressure on the fuel outlet would not clear it out... Ended up putting in a replacement tank.

Edited by carbon, 01 December 2014 - 06:05 PM.