8 replies to this topic

[minimikej]

Hi,

Almost embarrassed to ask here, I'm sure I would have sorted this out in 5 minutes 30 years ago.

 

My blue Mk1 (rebuild here: https://www.theminif...1-mini-rebuild/) is currently fitted with a used but apparently rebuilt ADO16 MG1098 unit.

I cannot get the engine running properly. The engine bogs down on full throttle, sometimes pops back when cold. At full throttle uphill will be fine for about 10 seconds and then start to misfire.

 

Initially I was on a twin 1.25" HS2 setup, but ditched these because I didn't have the correct manifold, or air filters, or heat shields, to sit well with the LCB manifold.

 

Replaced with a brand new old stock HIF38, from one of the economy metros.
 

I blanked off the lean running pipe as described elsewhere.

 

Breather inlet capped off as described elsewhere.

 

New K&N conical filter with brand new AAU needle

 

New minispares BAU1962 distributor: https://minispares.c...cs/BAU1962.aspx

 

New Lucas Gold 12v coil, non-ballasted.

 

Vacuum hose is connected.

 

New leads

 

New N5YC plugs

 

Can't hear any vacuum leaks on inlet using small hose to ear technique.

Set timing using adjustable strobe to 12 degrees BTDC, but have experimented with timings all the way from about 20 degrees advance to zero.

Setup idle emissions using old Gunsons Gastester, 3.5%CO at idle.

 

Compression across all cylinders is good and similar across all pots, can't remember the exact figure.

After a hard run up the local test hill, the plugs are a light brown and oil-free.

Sounds okay when it's idle or part throttle, no misfire. Plant your foot down though and it bogs, may pop back through carb.

 

I've tried disconnecting and plugging the vacuum advance to see if it's over advanced at idle, doesn't seem to help.

What's left to check? Cam timing??

 

Thanks
Mike

Edited by minimikej, 02 November 2022 - 02:45 PM.

[Retro_10s]

Backfiring through the carb is usually something that indicates a lean mixture, and although i don't know the exact profile of the AAU needle you have fitted, It is incredibly rare for a needle to fuel correctly across the entire drivable RPM range straight out of the box,.. They all need optimising by hand, to the exact set-up of the car.

 

Have you tried using the choke when driving uphill to see if it affects the bogging down you're experiencing?

[cal844]

Get the needle and parts optimised by someone who is AC Dodd trained, worth the money

[minimikej]

Backfiring through the carb is usually something that indicates a lean mixture, and although i don't know the exact profile of the AAU needle you have fitted, It is incredibly rare for a needle to fuel correctly across the entire drivable RPM range straight out of the box,.. They all need optimising by hand, to the exact set-up of the car.

 

Have you tried using the choke when driving uphill to see if it affects the bogging down you're experiencing?

I have, no obvious difference.

[minimikej]

Forgot to add,

The dashpot oil is full, 15/40.

Fuel pump is new, it's s solid-state version of the SU electric pump.

[minimikej]

Get the needle and parts optimised by someone who is AC Dodd trained, worth the money

I will definitely consider getting it professionally tuned, it's just that it feels like there is a problem to be fixed before that can happen, like I'm not even in the right ball-park and the tuner would be spending their time diagnosing a fault rather than actually tuning.

[cal844]

Get the needle and parts optimised by someone who is AC Dodd trained, worth the money

I will definitely consider getting it professionally tuned, it's just that it feels like there is a problem to be fixed before that can happen, like I'm not even in the right ball-park and the tuner would be spending their time diagnosing a fault rather than actually tuning.

Try a heavier grade oil, 20w50 engine oil as a test

[sonscar]

Ditch the cone filter and put a standard airbox back.If the cone filter is important to you then fit a stub stack.Is the gasket for the filter the correct way round?Just a few thoughts,Steve..

[Lplus]

Not sure why the breather inlet is blocked off. SU fitted a breather for a reason.  I'd try with the breather open. Blocking the breather means the pressure above the fuel in the float bowl is either the reduced pressure inside the air filter or even lower.  This lack of pressure will affect the fuel flow through the jet, and the higher the air flow the lower the pressure.

 

If that doesn't help I'd try an ABD needle and if that didn't help enough try an AAM needle.  I realise that's yet another £15 or so for each needle but if it helps it points you in the right direction.  Having tried an 12G 295( skimmed to give standard compression) on an 1100 engine , the AAM needle in an HS4 with K&N filter solved the misfire/bogging down problem I had.