5 replies to this topic

[Majikthyse]

Hi folks - new here but not at all new to Minis and A-Series engines. I have been running a 998 with the following spec for over 15 years:

 

Metro 998 cc gas-flowed cylinder head:

      1¼ inch inlet valves

      1 1/16 inch exhaust valves, with seat inserts for unleaded fuel

      CR 10.5:1

Maniflow medium bore LCB

SU HIF44, modified as per Vizard, and with ported vacuum advance

MG Metro inlet manifold

Ram pipe

K&N cone filter

A-Plus distributor with Powerspark electronic ignition pack - Lucas 59D4 41907A (998 Mini)

Lucas coil DLB105

 

Most of the time this has been fine, but over the last 3 years or so the idling has gone to pot. Often when hot the idle sticks at 2500 or so. It will sometimes drop back very slowly. At other times it will idle at 1000-1100, but after a minute will suddenly slow down or even stop. I am unable to get a stable idle at 900. It is very tiring to drive the car on a long run when the idle is frequently going up. It's much worse on long runs as it gets hotter. I am at my wits' end to solve this. Here is what I have tried:

 

New throttle shaft

New carb seals - repeatedly

New piston spring, correct type

New damper rod LZX2085

Manifold gaskets checked and sound

Throttle cable has a little slack.

Changed to contact breaker - no difference, so back to electronic

Fiddled with ignition timing - no difference

Float chamber bottom cover was warped - none in stock anywhere so as a temp measure I have lapped it flat, which has improved the starting.

Removed ram pipe - no difference

 

Last year I spent £200 on a session on Janspeed's rolling road, and the technician could not identify the problem. Last week I thought the old damper was sticking, so shelled out for the new one. I can't imagine what else there is to try. I hope one of you guys is an HIF44 expert! I buy all my carb bits from Burlen here in Salisbury so I'm reasonably confident that the problem is not quality of parts.

 

 

 

[sonscar]

Either the throttle is physically sticking or the blade not centred,is it the correct way round?
Air is leaking in somewhere,vacuum can punctured?breather system correctly functioning?Steve..

[PoolGuy]

Have you tried spraying brake cleaner around the inlet gaskets and the carb? That can identify air leaks. What needle does it have? It probably doesn't affect or cause your problem but I'm interested to know what needle a 998 requires with a 44.

[fatcatvera]

The bimetallic strip that changes float height with temperature can cause this sort of problem. Make a solid metal equivalent.

[croc7]

It is my understanding that in the HIF44, the bi-metallic temp compensator adjusts the jet height to richen/lean fuel mixture. In an attempt to have a more stabilized AFR during carb adjustment, I disabled mine by removing the strips from either side using a Dremel tool. Seems to work fairly well.

As mentioned, this sounds like a carb problem. I’d start by checking throttle pedal linkage, cable, where the cable passes through the firewall, etc. Maybe even check the throttle shaft bushes for wear.

Edited by croc7, 29 May 2022 - 05:22 AM.

[PoolGuy]

I think we may be talking to ourselves.