9 replies to this topic

[BenCoul]

Hello there,
I have a 998, with...

Rebuilt standard carb (SU HS4), standard air filter with K&N element, new plugs, leads, dizzy cap, rotor arm, points condenser and starter coil, new radiator, thermolstat, throttle and choke cable, engine temp sender, new exhaust manifold gasket. And a silly exhaust (whith no holes). Recent oil change, not changed oil filter.

The problem:
I can run her around town all day, and she'll be fine and won't miss a bit. The problem is on motorways.
She'll really struggle to get up hills, 55 tops, and struggles at times when I put my foot down to over take.
When I pull off the motor way, I have no power. When i put my foot down, the rev needle just blips up for a microsecond, and the I get no power, and it takes forever to build the revs up. After a while again of normal road driving, she'll return to normal. But as soon as I come off the motorway she's barley drivable.
Once when I piulled off the motorway and dipped the clutch, the revs dropped to 500rmp!

From left to right, the spark plugs are colourd white, black, white, black.

Down hill she'll do well over 90mph!!

I'm really at a loose end now, any help would be gratley appriciated.

Ben

Edited by BenCoul, 16 February 2013 - 02:08 PM.

[MRA]

This sounds like you either have far too much retard on your ignition or that your valves are "cracked" open......

NOTE ! I have noticed a few Minis lately that the rockers are too tight, apparently this is done to close the gap that the wear creates on the rocker pad, this is very bad practice, new rockers from the likes of Mini Spares are about £9 each which is considerably cheaper than repairing a burnt cylinder head

[sledgehammer]

A wild guess - wonder if the air flow on the motorway is keeping the engine bay cool

when you pull off , the heat rises around the hot manifold area , and boils the petrol in the float chamber

messing up fueling

- but wouldn't make the plugs them colour's - check for air leaks at manifold area

[BenCoul]

This sounds like you either have far too much retard on your ignition or that your valves are "cracked" open......

NOTE ! I have noticed a few Minis lately that the rockers are too tight, apparently this is done to close the gap that the wear creates on the rocker pad, this is very bad practice, new rockers from the likes of Mini Spares are about £9 each which is considerably cheaper than repairing a burnt cylinder head

Thanks for the advice, sorry, I'm not too clever, what do you mean by too much retard on my ignition?

Ben

[BenCoul]

A wild guess - wonder if the air flow on the motorway is keeping the engine bay cool

when you pull off , the heat rises around the hot manifold area , and boils the petrol in the float chamber

messing up fueling

- but wouldn't make the plugs them colour's - check for air leaks at manifold area

I have a fibre glass front end with no inner wings, and an air scoop, so she's weel ventilated, maybe too ventilated :/

[MRA]

More likely retarded ingnition... where are you ? have you got any manuals ?

Retarded ignition, means that the cylinder is expanding (piston is on its way down) as the fuel/air mix is ignited, this causes the gas to expand faster than it should, other effects, are overheating and your oil light may come on at low revs

[sledgehammer]

More likely retarded ingnition... where are you ? have you got any manuals ?

Retarded ignition, means that the cylinder is expanding (piston is on its way down) as the fuel/air mix is ignited, this causes the gas to expand faster than it should, other effects, are overheating and your oil light may come on at low revs

& hot exhaust ?

Had an allegro with the same problem , fine while motoring at speed , when slowed down after very wooly

lots of space in the engine bay , the heat came up from the hot exhaust & boiled the fuel

fine around town - exhaust never got hot enough

Edited by sledgehammer, 16 February 2013 - 03:15 PM.

[Cater_Racer]

Air scoop.................. Carburettor icing?

[MRA]

Air scoop.................. Carburettor icing?

Yes, but not with the possibility of 90mph down hill, I assume you mean 70mph though as its illegal to do over 70mph in the UK ;)

[BenCoul]

Hhmm, thanks for all the advice people