ausmini :: View topic - how to test if your car is running lean?

Relying on black smoke out of the exhaust as a way of telling you it's rich isn't any good - it's waaay too rich at that point, not just a little bit rich.

There's a little button under the dashpot at the side of the carb, you push it up which raises the piston - if the revs increase, then it's rich, if it the revs decrease & the engine starts to stall, it's lean. Ideal is when the revs increase slightly, and then drop back to idle. However, that's only setting the idle mixture, you've got no idea what it's doing elsewhere in the rev range

You really really need to get it tuned properly - take it to Greig and get them set up, balanced and spot on, doing it yourself without the right equipment will take months of trial and error, likely as not will wreck your engine in the process

i sat down with the boss to work out possibilites today and the thing we came up with is:

the carby is sucking air somewhere else therefore causing the idle revs to lift and running lean.

Tiny

Be a mechanic - grab a can of carby cleaner and spray all around the junction between the manifold and the head and do this with the engine running. If the engine revs rise then its because the manifold is sucking air.

Why - because they have just fitted new carbies and maybe a nut hasn't been tightened properly. Then again being a mechanic you can hand check and tighten each of the again. Maybe a manifold gasket gasket compressed a but much somewhere.

If the revs don't rise - do the same thing where the carbies are bolted ontot he the manifold - same reason - maybe its sucking air there. Again retighten.

If still no rev rise - spray carby cleaner at each of the butterfly spindles and see that causes a rev rise - maybe one of the spindles bushes isn't sitting properly. If revs rise - then its sucking to much air there - get in contact with your carby reco guy.

Do all of this before you play with linkages or swap carbies - look for the easy things first.

Mike

read the only useful thing I have posted on this forum

http://www.ausmini.com/forums/viewtopic ... light=tune

Author:	tinymorris1969 [ Tue May 20, 2008 10:18 pm ]
Post subject:	how to test if your car is running lean?
anyone? oviously if its running rich you get black smoke and can smell it but what about running to lean. i was talking to the doc about my carbies last nite and struck me with something i never really thought about. the needles that are in the carbies are GY which are standard for a 998 cooper so technically it should run a 1098 fine. however these specs were conducted with standard air filters so what happens when you put ranflows on which have a great air flow? will the car run leaner?

Author:	simon k [ Tue May 20, 2008 10:51 pm ]
Post subject:
Relying on black smoke out of the exhaust as a way of telling you it's rich isn't any good - it's waaay too rich at that point, not just a little bit rich. There's a little button under the dashpot at the side of the carb, you push it up which raises the piston - if the revs increase, then it's rich, if it the revs decrease & the engine starts to stall, it's lean. Ideal is when the revs increase slightly, and then drop back to idle. However, that's only setting the idle mixture, you've got no idea what it's doing elsewhere in the rev range You really really need to get it tuned properly - take it to Greig and get them set up, balanced and spot on, doing it yourself without the right equipment will take months of trial and error, likely as not will wreck your engine in the process

Author:	Hanra [ Wed May 21, 2008 10:03 am ]
Post subject:
I thought you said you had M needles in em?

Author:	drmini in aust [ Wed May 21, 2008 11:54 am ]
Post subject:
He had Ms in but it ran rich as hell apparently, I didn't do the job so I'm not sure why. I've always found twin HS2s and Ramflos on a modded 1098 run fine with either M or AH2 in. Maybe his jets are worn....

Author:	Hanra [ Wed May 21, 2008 12:53 pm ]
Post subject:
Surely the jets would have been replaced as part of the overhaul? Maybe its running 100 thou jets.......... AH2 and M's are listed for a stock 1275, so yeah on a modded 1098 it should be close.

ausmini https://www.ausmini.com/forums/

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Author:	cush [ Wed May 21, 2008 4:24 pm ]
Post subject:
simon k wrote: Relying on black smoke out of the exhaust as a way of telling you it's rich isn't any good - it's waaay too rich at that point, not just a little bit rich. There's a little button under the dashpot at the side of the carb, you push it up which raises the piston - if the revs increase, then it's rich, if it the revs decrease & the engine starts to stall, it's lean. Ideal is when the revs increase slightly, and then drop back to idle. However, that's only setting the idle mixture, you've got no idea what it's doing elsewhere in the rev range You really really need to get it tuned properly - take it to Greig and get them set up, balanced and spot on, doing it yourself without the right equipment will take months of trial and error, likely as not will wreck your engine in the process you just need someone riding on the bonnet while checking the mixture..

Author:	tinymorris1969 [ Wed May 21, 2008 7:47 pm ]
Post subject:
lol cush. yeah im apparently Ms were no good which im abit disappointed about so now i got some GYs but its only in one carbie these problems are coming from. i sat down with the boss to work out possibilites today and the thing we came up with is: the carby is sucking air somewhere else therefore causing the idle revs to lift and running lean. so cylinder 1 and 2 will be running lean while 3 and 4 will be normal. right?

Author:	Hanra [ Wed May 21, 2008 7:57 pm ]
Post subject:
tinymorris1969 wrote: i sat down with the boss to work out possibilites today and the thing we came up with is: the carby is sucking air somewhere else therefore causing the idle revs to lift and running lean. Joe, why do you not take anyones advice on here? This is from one of your many threads about your carbs... Mike_Byron wrote: Tiny Be a mechanic - grab a can of carby cleaner and spray all around the junction between the manifold and the head and do this with the engine running. If the engine revs rise then its because the manifold is sucking air. Why - because they have just fitted new carbies and maybe a nut hasn't been tightened properly. Then again being a mechanic you can hand check and tighten each of the again. Maybe a manifold gasket gasket compressed a but much somewhere. If the revs don't rise - do the same thing where the carbies are bolted ontot he the manifold - same reason - maybe its sucking air there. Again retighten. If still no rev rise - spray carby cleaner at each of the butterfly spindles and see that causes a rev rise - maybe one of the spindles bushes isn't sitting properly. If revs rise - then its sucking to much air there - get in contact with your carby reco guy. Do all of this before you play with linkages or swap carbies - look for the easy things first. Mike

Author:	tinymorris1969 [ Wed May 21, 2008 8:01 pm ]
Post subject:
i have taken that advice onboard hanra just havent been able to put it in affect. i get home around 6.30 from work and i have a baby that sleeps next door so i dont get to work on the car when i get home. but because me and my boss were talking about it today he just threw in what he thought and we discussed it. i havent forgotten wat everyone has told me and ill go through it on saturday

Author:	Hanra [ Wed May 21, 2008 8:03 pm ]
Post subject:
Well Mike's approach is a tried and tested way to determine if you have a vacum leak. Quick, easy and it works! Perhaps give it a try during your lunch break?

Author:	Blokeinamoke [ Wed May 21, 2008 8:49 pm ]
Post subject:
read the only useful thing I have posted on this forum http://www.ausmini.com/forums/viewtopic ... light=tune

Author:	sports850 [ Wed May 21, 2008 9:07 pm ]
Post subject:
Are you unsure of how well it was tuned , if so take it back to the place that did the work and explain to them what you think and see what they can do . Quickest way to see if it's been running lean is to go for a quick run at about 80 k's or so then stop straight away and look at all 4 plugs , if 1 and 2 are dry and grey and 3 and 4 are black then there's a mixture/synchronising problem .

Author:	tinymorris1969 [ Wed May 21, 2008 9:09 pm ]
Post subject:
nah its not if they tuned them. i know they tuned them up cause the car ran fine. but something is now wrong with the passenger side carby cause it doesnt sound like its sucking in air thus losing vacum

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