13 replies to this topic

[Straker Junior]

I have a 1293cc with a decent head (Stage 2 MED from memory), MED road sport cam and HiF44.

If I am driving along on a steady throttle and then apply a bit more throttle then it feels like the car loses power and sounds very ‘fluffy’ until I break through past that throttle position.

Happens at all throttle positions and same thing when I move from a trailing throttle on a dual carriageway for example, to a bit more throttle.

If I give it full beans everywhere it seems fine, but that’s just not suitable on the roads.

I thought maybe the dash pot oil was too thick and taking too long to pick up. I am using Penrite SU dash pot oil.

The car is running MED supplied ignition only ECU. Fully set up on a rolling road.

For reference, car is running a red spring and the rolling road fitted a BDL needle I believe. I know the rolling road very well and have used them for many years. Just too far to travel to take it back up to have them look at this issue.

Any suggestions?

Edited by Straker Junior, 21 October 2023 - 12:12 PM.

[PoolGuy]

Thicken the oil, that’ll answer your question? The standard su oil doesn’t work in mine, but it’s fine in others, there isn’t a one size fits all solution.

[ACDodd]

What you’re describing is carburettor that has not been setup properly when it was last tuned. Nowadays this is extremely common and is indicative of the decline in skills in those individuals who say they can tune su carbs properly. What would help you here is to install a wideband gauge so you can monitor what’s going on in all conditions then you can decide what needs to be done to correct it. I suspect the Mai issue here is part throttle fueling is too lean. Carb oil can only be selected once the needle profile is finalised.

Ac

Edited by ACDodd, 21 October 2023 - 02:00 PM.

[Straker Junior]

What you’re describing is carburettor that has not been setup properly when it was last tuned. Nowadays this is extremely common and is indicative of the decline in skills in those individuals who say they can tune su carbs properly. What would help you here is to install a wideband gauge so you can monitor what’s going on in all conditions then you can decide what needs to be done to correct it. I suspect the Mai issue here is part throttle fueling is too lean. Carb oil can only be selected once the needle profile is finalised.

Ac

I took it to the same guy I have been using for SU carbs for decades knowing that it’s a skill that is hard to find many rolling roads nowadays. That said, I am not sure how much part throttle work he did.

[Lplus]

 

What you’re describing is carburettor that has not been setup properly when it was last tuned. Nowadays this is extremely common and is indicative of the decline in skills in those individuals who say they can tune su carbs properly. What would help you here is to install a wideband gauge so you can monitor what’s going on in all conditions then you can decide what needs to be done to correct it. I suspect the Mai issue here is part throttle fueling is too lean. Carb oil can only be selected once the needle profile is finalised.

Ac

I took it to the same guy I have been using for SU carbs for decades knowing that it’s a skill that is hard to find many rolling roads nowadays. That said, I am not sure how much part throttle work he did.

 

it isn't clear to me whether this problem has been present since the set up on the rolling road or if it has started after a long period of working properly.

[mbolt998]

I've always just put a bit of 20/50 engine oil in mine. Seems to work absolutely fine. But am tempted to try the proper oil now that I know it's a thing (we didn't have the internet back in the day when I put most of the miles on the car).

[cal844]

I've always just put a bit of 20/50 engine oil in mine. Seems to work absolutely fine. But am tempted to try the proper oil now that I know it's a thing (we didn't have the internet back in the day when I put most of the miles on the car).

SU oil to 20/50 is a huge change, best to start thin and go thicker

[mbolt998]

 

I've always just put a bit of 20/50 engine oil in mine. Seems to work absolutely fine. But am tempted to try the proper oil now that I know it's a thing (we didn't have the internet back in the day when I put most of the miles on the car).

SU oil to 20/50 is a huge change, best to start thin and go thicker

 

 

Thanks! Have ordered a bottle of what Minispares says is the right stuff. Checked the owner's manual and it does just vaguely say "engine oil". There's a list of lubricants in the back but that doesn't mention the carb (mainly focussed on the engine and the grease points).

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[Lplus]

The correct SU oil is SAE 20.

 

Older engine oils were generally 30 SAE or 40 SAE

 

The later engine oils for minis were 20W-50 SAE and then a 10W-40

 

Note that The dual ratings are at -17.8C and 100C so a 20W-50 is around about 25 to 30 grade at the sort of temperatures carbs usually run at most of the time.

[imack]

There is no single grade of damper oil that is right for every engine spec, especially a modified one. You won't go far wrong taking AC Dodd's advice.

[ACDodd]

Watch this for more info ref setting up SU carbs;

https://youtu.be/nv0...1-h4lNpDg9cXlss

This is part 1, watch all 4 parts.

Every carb is different, there is no one grade of oil for every carb.

Ac

[Straker Junior]

Thanks all. In answer to your question above AC, the engine build was brand new and was set up and run in on the rollers. I noticed the bahaviour the first time I then drive it on the road. The power curve was great on the dyno but just doesn’t drive well.

If I started with the Penrite stuff, should I try going thicker on thinner next please? Depending on which direction you advise, what oil should I pick?

Thanks again.

Watching videos today.

[ACDodd]

The point is power curve bears no relation to how it drives, a common misconception. The rolling road operator failed to set the fueling correctly for part throttle running.

Ac

Edited by ACDodd, 23 October 2023 - 06:48 AM.

[coopertaz]

sounds like too lean a mix and / or su rising too fast i run a yellow spring and 20/50 engine oil since i flowed carb. as per mr vizards book! maybe try these?