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wkilleffer
05-19-2006, 09:28 AM
Hello,

Is it normal for a 1974 MGB's idle speed to change with the engine temp when the choke is off?

I've done alot to try and get my carbs properly adjusted with the correct idle speed. The books all say to warm the car up to NOT before making any changes. Trouble is, NOT seems to be a bit subjective. I run with a 195 deg. thermostat, and on the warm days we've had recently, the temp gauge gets just to the right of the N. I've never seen this as a problem. So, I adjust the carbs at that point, and the idle is probably around 850 RPM's, at a point between one and two gauge needles below the 1000 mark.

Trouble is the cool mornings we've had the last couple of days. The temp gauge didn't go beyond the N, and the idle speed wouldn't drop below 1000. Is this sort of thing normal, or do I need to make some sort of adjustment. If the engine gets hotter than typical, the speed drops lower than my adjusted speed. I'm afraid all this is playing havoc with my fuel/air mixture, gas mileage, and engine lifespan. It's frustrating because I've put alot of effort into this, and get irritated when things don't work the way they're supposed to.

Any advice or suggestions would be appreciated.

Thank you,

jgbowman1
05-19-2006, 10:09 AM
My car reacts the same way. Don't know if there is a fix or not.

wkilleffer
05-19-2006, 10:13 AM
[ QUOTE ]
My car reacts the same way. Don't know if there is a fix or not.

[/ QUOTE ]

Well, I guess it's ok that I'm not the only one. This may not be unusual, but it's a bit frustrating. It would be nice to know if there's a fix.

Rob_Edwards
05-20-2006, 05:44 AM
It's normal. HIFs should be less susceptible to it than HS4s, but in my limited experience they all do it, so don't be too concerned. The mixture changes with ambient temperature so the idle will change. HIFs can self-compensate somewhat, HS4s can't.

I also run a 195F tstat, and my gauge usually shows between just right of 'N' and just left of 'H' depending on ambient temperature. Since yours read so much lower, you might want to verify that your engine is really warming up fully. If you've got one of those infrared thermometers you can take a reading at the gauge sender. If not, you can stick a cooking thermometer in the radiator neck -- not quite as accurate, but good enough. The low reading might just be the gauge, in which case no worries. It wouldn't surprise me that it's the gauge, as these are not exactly precision instruments! And since the reading seems to center around 'N', I'd leave it as is if it was mine. ;-) If it's not the gauge though, you might have a faulty thermostat.

HTH!

tony barnhill
05-20-2006, 08:17 AM
How's the oil level in your damper?

wkilleffer
05-23-2006, 04:58 PM
[ QUOTE ]
How's the oil level in your damper?

[/ QUOTE ]

The car seemed to sputter some when going into sharp turns with the pedal down, so I checked that. The oil levels were too low. Now, I've got them to where it's just under an inch from the top of the dashpots, like the diagram in one of the books like Haynes or Bentley. This helps some with the sputtering, but hasn't eliminated the problem.

wkilleffer
05-23-2006, 04:59 PM
[ QUOTE ]
It's normal. HIFs should be less susceptible to it than HS4s, but in my limited experience they all do it, so don't be too concerned. The mixture changes with ambient temperature so the idle will change. HIFs can self-compensate somewhat, HS4s can't.

I also run a 195F tstat, and my gauge usually shows between just right of 'N' and just left of 'H' depending on ambient temperature. Since yours read so much lower, you might want to verify that your engine is really warming up fully. If you've got one of those infrared thermometers you can take a reading at the gauge sender. If not, you can stick a cooking thermometer in the radiator neck -- not quite as accurate, but good enough. The low reading might just be the gauge, in which case no worries. It wouldn't surprise me that it's the gauge, as these are not exactly precision instruments! And since the reading seems to center around 'N', I'd leave it as is if it was mine. ;-) If it's not the gauge though, you might have a faulty thermostat.

HTH!

[/ QUOTE ]

I forgot to mention that my car's engine is a 1972 with HS4's.