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| SU Carb Question https://www.ausmini.com/forums/viewtopic.php?f=2&t=101707 |
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| Author: | cooperess [ Wed Feb 08, 2023 3:48 pm ] |
| Post subject: | SU Carb Question |
I have twin 1.5" on my Mini but they are from a MGB. How can I block the advance and air holes as am using non vacuum advance dizzie. |
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| Author: | timmy201 [ Wed Feb 08, 2023 3:54 pm ] |
| Post subject: | Re: SU Carb Question |
A vacuum cap would work, just get some the right size https://outlawspeed.com.au/shop/mg3704 |
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| Author: | cooperess [ Wed Feb 08, 2023 4:31 pm ] |
| Post subject: | Re: SU Carb Question |
Once again 'timmy' your insight is very helpful. |
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| Author: | simon k [ Thu Feb 09, 2023 8:59 pm ] |
| Post subject: | Re: SU Carb Question |
I run a HIF44 that had the engine breather air hole. I got a piece of aluminium rod the right size and araldited it into the tube, then neatly shaped the inside to match the carb bore so there wasn't any interruption to the airflow.... because, you know, it might gain me 0.0002 bhp |
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| Author: | slacko [ Thu Feb 09, 2023 9:04 pm ] |
| Post subject: | Re: SU Carb Question |
Check the float bowl angle is right . 30 deg not 20 deg |
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| Author: | 68+86auto [ Thu Feb 09, 2023 10:36 pm ] |
| Post subject: | Re: SU Carb Question |
Repco usually have vacuum caps the right size. |
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| Author: | 1071 S [ Fri Feb 10, 2023 8:16 am ] |
| Post subject: | Re: SU Carb Question |
Better off getting a vacuum unit for your dizzy. Cheers, Ian |
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| Author: | cooperess [ Fri Feb 10, 2023 9:12 am ] |
| Post subject: | Re: SU Carb Question |
slacko wrote: Check the float bowl angle is right . 30 deg not 20 deg This has been addressed. |
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| Author: | cooperess [ Fri Feb 10, 2023 9:13 am ] |
| Post subject: | Re: SU Carb Question |
1071 S wrote: Better off getting a vacuum unit for your dizzy. What is the argument for vacuum dizzy?
Cheers, Ian |
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| Author: | timmy201 [ Fri Feb 10, 2023 10:28 am ] |
| Post subject: | Re: SU Carb Question |
If you want to keep it a genuine cooper S then they had a non vacuum distributor The vacuum adds timing at low load to increase economy and part throttle response You’ll get just as many mini people to tell you to take if off as will tell you to leave it on. Another mini topic for endless debate! |
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| Author: | 1071 S [ Fri Feb 10, 2023 11:22 am ] |
| Post subject: | Re: SU Carb Question |
Vacuum advance is fuel economy device. For race only forget it. However, at a steady cruise (I live in the bush) you can expect up to a 30% reduction in fuel use (measured tank to tank). If you're not running exclusively on a track then I don't see the downside. 1.5 SUs are not genuine Cooper S anyway so having gone that far why not use other improvements. Maybe those who argue against them haven't had access to the expertise to set it up properly ...or are just repeating "received" wisdom. Cheers, Ian |
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| Author: | Steam [ Fri Feb 10, 2023 12:24 pm ] |
| Post subject: | Re: SU Carb Question |
I was under the impression tht the economy savings was more like 10 to 15 % thn 30%. Having had both on a more sporty engine I am happier with non vac advance. The performance and response throughout the rev range is better than with a vac advance. However I respect other peoples opinions and experiences, life would be boring if we all thought the eame. |
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| Author: | timmy201 [ Fri Feb 10, 2023 12:37 pm ] |
| Post subject: | Re: SU Carb Question |
Once you have wide open throttle the performance should be identical as there will be very little if any vacuum. As far as I can tell, adding timing with the vacuum advance only brings advantages to a road engine (provided the mechanical and vacuum advance is correct for the engine). It does bring a slight complexity for race engines, and seeing as they are pretty much only run at full throttle & have wild cams with low vacuum, you won’t see any advantage with vac advance I got an OBD2 scanner for my Mazda as I was curious how the advance is mapped against load in a modern engine. At 3000rpm in 4th gear the timing varies from 17 degrees at full load, all the way up to 55 degrees at low throttle cruising. Obviously most modern cars are mapped for reliability and economy over performance, but it does go to show how much you could be missing if you remove the vac advance on a distributor car (and mine is disconnected at the moment!) |
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| Author: | 1071 S [ Fri Feb 10, 2023 1:02 pm ] |
| Post subject: | Re: SU Carb Question |
I could not disagree with Steam's comment re varied opinions and experience. The 30% I quoted was based on well over a year's worth of log book entries so is my personal real world experience and not an opinion. I can't comment on performance before and after but I don't remember any significant seat-of-the pants concerns.. Mind you, we also tampered with things like needles etc so some of the benefit may have to be allocated there. Cheers, Ian |
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| Author: | drmini in aust [ Fri Feb 10, 2023 3:07 pm ] |
| Post subject: | Re: SU Carb Question |
My experience with many old Lucas dizzies is the vacuum advance plate gets loose with wear, rocks about, giving spark scatter and varying dwell. I've fixed a few (pun intended) by tack welding the two plates together and tossing the vacuum can. In the case of my brother's Hillman Imp (25D dizzy), fuel economy improved along with performance. |
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