Setting the mixture on Carbs by ear?
Moderators: hot66, impmad2000, Nige
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mycar
- Nurse, I think I need some assistance
- Posts: 7490
- Joined: Sat Aug 04, 2007 3:05 pm
- Location: Harrow Gate.
- Contact:
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911hillclimber
- Nurse, I think I need some assistance
- Posts: 20729
- Joined: Mon Mar 10, 2008 6:26 pm
- Location: West Midlands
Re: Setting the mixture on Carbs by ear?
You shouldn't be having all this grief imho.
I agree with mycar, all these basics must be right or you will be road-side tinkering until you retire!
I really would book it into HiTech and let him go through the whole thing, top to bottom, sparks to fuel. (Old Mick is the boss, the one you need for old skool stuff)
The carbs are new, I presume correctly and equally jetted left and right Are the manifold to carbs and to heads sound?
To check, get the car running and selectively spray carb cleaner on the joint faces, ie base of one choke of one carb, if engine note unchanged, go to next choke. If all 4 are clear, do the same with the manifold to head areas.
If all ok then no leaks on the 'cold' side of the engine.
Next are the jets, all clear?
Set the screws right (I used the PMO set-up guide, see no reason not to follow them) (etc)
Seems to me something basic is awry and you need to fix before you go to HiTech or just deliver the car to be fettled and sorted.
This would drive me nuts!
When I had such running issues on my big 3.2 with PMO all my troubles were down to an air leak on one choke between carb and manifold.
Once I'd found that and sorted it (found by carb cleaner, fixed by new gaskets) the carbs balanced with a meter like yours, the mixture set by Colour tune and the engine is great since (2 years ago)

I agree with mycar, all these basics must be right or you will be road-side tinkering until you retire!
I really would book it into HiTech and let him go through the whole thing, top to bottom, sparks to fuel. (Old Mick is the boss, the one you need for old skool stuff)
The carbs are new, I presume correctly and equally jetted left and right Are the manifold to carbs and to heads sound?
To check, get the car running and selectively spray carb cleaner on the joint faces, ie base of one choke of one carb, if engine note unchanged, go to next choke. If all 4 are clear, do the same with the manifold to head areas.
If all ok then no leaks on the 'cold' side of the engine.
Next are the jets, all clear?
Set the screws right (I used the PMO set-up guide, see no reason not to follow them) (etc)
Seems to me something basic is awry and you need to fix before you go to HiTech or just deliver the car to be fettled and sorted.
This would drive me nuts!
When I had such running issues on my big 3.2 with PMO all my troubles were down to an air leak on one choke between carb and manifold.
Once I'd found that and sorted it (found by carb cleaner, fixed by new gaskets) the carbs balanced with a meter like yours, the mixture set by Colour tune and the engine is great since (2 years ago)

73T 911 Coupe, road/hillclimber 3.2L
Lola t 492 / 3.2 hillclimb racer
Boxster 987 Gen II 2.9
Lola t 492 / 3.2 hillclimb racer
Boxster 987 Gen II 2.9
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neilbardsley
- Nurse, I think I need some assistance
- Posts: 8637
- Joined: Mon Apr 16, 2012 4:31 pm
Re: Setting the mixture on Carbs by ear?
It is sounding better after my last fiddle but in thinking there is a leak somewhere but before I take it to someone else I think I need to give the place that replaced the carbs the chance to get right?
“A REMINDER. I would be grateful if those members who have borrowed bits from me in emergencies (e.g starter motor, oil cooler, etc) would return them and/or contact me”. – Chris Turner RIP
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911hillclimber
- Nurse, I think I need some assistance
- Posts: 20729
- Joined: Mon Mar 10, 2008 6:26 pm
- Location: West Midlands
Re: Setting the mixture on Carbs by ear?
Certainly you should, you have a lot of patience, and it could pay off.
Let us know what is found please.
Let us know what is found please.
73T 911 Coupe, road/hillclimber 3.2L
Lola t 492 / 3.2 hillclimb racer
Boxster 987 Gen II 2.9
Lola t 492 / 3.2 hillclimb racer
Boxster 987 Gen II 2.9
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Bruce M
- Me and DDK sitting in a tree! KISSING
- Posts: 2910
- Joined: Fri Aug 27, 2004 1:07 pm
Re: Setting the mixture on Carbs by ear?
Did you check the exhaust for leaks?
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neilbardsley
- Nurse, I think I need some assistance
- Posts: 8637
- Joined: Mon Apr 16, 2012 4:31 pm
Re: Setting the mixture on Carbs by ear?
Ok I'm taking it back on Thursday to the place that did the work. Perhaps that is where I should of starter. Couple more points I thought I would check the value gaps on Sunday but found the cover was sealed on! Well it felt glued on and the place confirmed this morning that they also put sealant on, so I decided not to proceed. In my limited experience I've always found the good quality cork seals good enough. Does anybody else use sealant as well?
The chap that did the work was leaning toward my distributor being at fault (one of the only components they didn't replace). Well to be fair he said it has to be the dizzy or carbs. I'm open minded but the 123 Ignition ran well on the old carbs and has lots of happy clients in the 356/912 world.
The chap that did the work was leaning toward my distributor being at fault (one of the only components they didn't replace). Well to be fair he said it has to be the dizzy or carbs. I'm open minded but the 123 Ignition ran well on the old carbs and has lots of happy clients in the 356/912 world.
“A REMINDER. I would be grateful if those members who have borrowed bits from me in emergencies (e.g starter motor, oil cooler, etc) would return them and/or contact me”. – Chris Turner RIP

