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 Posted: 07-17-2019 01:39 am
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CDA951
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For posterity's sake, here are the carb specs on my 2.0L 907 with 9.5:1 pistons, stock cams, intake ports at or near "Spec 5":

Carb model: DHLA45C

Idle air: 7850-7
Idle jet: 58
Main air: 220
Main jet: 160
Main emulsion: 7772-8
Pump jet: 60
Starter emulsion: 7482-1
Starter jet: 70
Venturis: 36
Float: 7298-3 gr. 7 (float level set to just under 14.0MM)

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 Posted: 07-18-2019 02:47 am
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DonBurns
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Thanks for input. I think my first step needs to be verifying that those A/F readings are real. I have read that even a very small leak in the exhaust can skew readings to lean. Seems strange that I went from basically OK to seriously lean with a pretty small change in jets. I'll make sure no leaks then take somewhere to get A/F verified. The Innovate meter required a calibration in air - the new A/F gauge has the "feature" that no calibration is required. Maybe I am being paranoid, but if 17.5:1 is a real reading, isn't that enough to burn valves and melt pistons?

Any input from anybody about how steady an A/F meter should read?

Thanks

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 Posted: 07-18-2019 03:33 am
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CDA951
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In my experience they are fairly steady, with the most fluctuations happening in the idle range.

Exhaust leaks absolutely can be an issue with sensitive AFR meters---small leaks can be hard to find, however. Sometimes they can be heard from under the car (on a lift) while it is running, or a telltale black streak can be seen. Sometimes you need to use a smoke machine (the type used to find intake/vacuum leaks) and pump smoke into the tailpipe to find a leak. You probably don't have one of those, so a shop would need to get involved. You could also compare your AFR gauge's readings to that of a shop's 5-gas analyzer to see if they are in the ballpark.

Regardless of AFR readings, my comment about the idle jets being lean in the transition period between idle and main jets was based on your assertion that the carbs are popping in that range, which does indicate an actual lean condition. The lean AFR readings that you posted in that RPM range bear this out. Make sure the idle jets aren't plugging up like mine were, which is quick and easy to do (can get compressed air in a can if you don't have an actual source of compressed air).
EDIT: 17.5:1 is quite lean, but won't do damage unless you are stupid enough to hammer on the engine and give it sustained periods of full load in that condition. It sounds like you are doing short test drives while monitoring AFRs, so you probably haven't hurt anything.

Last edited on 07-18-2019 03:38 am by CDA951

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 Posted: 07-18-2019 01:42 pm
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Bfitz241
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RE: the LM-2, I found mine to be very sensitive to grounding. I run it directly off the battery and it has always worked well.
Otherwise, it looks like you've got this in hand and should have it set the way you want pretty quickly.

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