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Proper idling RPM

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L

LLAngus

Jedi Knight
Offline
What is the correct RPM for a 73 MGB GT? Dual SU, the 1200 seems too fast and I noticed JB said hers idles at 750 to 850 RPM. What is the scoop?

/ubbthreads/images/graemlins/troll.gif /ubbthreads/images/graemlins/driving.gif
 
Mine's at about 950-1000 in nuetral, and around 850-900 with the clutch in... electricals on or off don't make any difference on my car.
 
850 was perfect with the ZS, but 950 seems about right with the SUs in her.
 
My GT idled at 1000, which I thought was too high. Last time I changed the oil and used synthtetic, the idle dropped to 750, which I always thought was about right. I have no idea why this happenned, but I like it a little better personally.
 
Depending on how warm she is, my 74 with HIF's idles at between 600 and 750...the 600 is a little low when she is cold, as the ignition light comes on. When I engage the choke, it brings the idle up to around 1000...but I never leave it there for long. In fact, she doesn't get to idle too long, ever /ubbthreads/images/graemlins/driving.gif

Bruce /ubbthreads/images/graemlins/cheers.gif
 
I'd always shoot for 650~800 as idle RPM. Lower is better IMHO, so 600~650 on my own cars.
 
How come the repair book says 1200RPM? If I knew you guys when I set the carbs up I would have put the RPM at 800. See this forum does work.

Bruce L
/ubbthreads/images/graemlins/cheers.gif
 
[ QUOTE ]
... See this forum does work.

Bruce L
/ubbthreads/images/graemlins/cheers.gif

[/ QUOTE ]

I don't think there was ever much doubt of it.
 
Found it!! The manual says to have the fast idle speed at 1300 RPM. Next sentence (didn't read) set the regular idle to 850 after getting the fast idle to 1300. Just a case of a new toy and only reading enough directions to get it started. Now I have something to do while waiting for the game.

/ubbthreads/images/graemlins/crazy.gif /ubbthreads/images/graemlins/hammer.gif
 
Mine goes pup-pup-pup...pup-pup-pup...pup-pup-pup...choke..pup-pup-pup...pup-pup-pup...pup-pup...cough

Shakes & idles like crap but.....It goes BurrrrrraaaaAP when ya step on it. /ubbthreads/images/graemlins/grin.gif


With a stock cam, go as low as possible while still maintaining a smooth tick-over.
 
Ok, I've readjusted the idle. When I start the car everything is peachy keen. But as soon as I get going down the road and the RPM gets up there, the motor goes back to idling at 1400 RPM. What adjustment am I missing?

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Which carbs are you fighting? If they have the throttle plates with those poxy "pop-off" valves, R&R 'em and solder those things SHUT!

EDIT: All cautionary warnings re: GASOLINE and heat apply here, BTW! /ubbthreads/images/graemlins/yesnod.gif
 
SU HIFs. They seem to work great except the idle.

Edit: Do you mean the overrun valve?

/ubbthreads/images/graemlins/savewave.gif
 
The spring governed ones on the throttle blades. Gotta heat 'em to disassemble (as they're soldered at the threads) for cleaning, prep to solder 'em shut. If you've already stripped the rest of the em*ss*ons stuff then DO this. You will be rewarded with a rock-steady idle.
 
OK Doc. You have convinced me to remove the e "missions". This car runs too good to hamper it with excess baggage.

/ubbthreads/images/graemlins/hammer.gif /ubbthreads/images/graemlins/hammer.gif /ubbthreads/images/graemlins/driving.gif
 
It sounds like a little carb cleaner would clean up the linkage to allow the throttle to return to the lower idle position, rather than to the old setting that has been worn into the gunk. /ubbthreads/images/graemlins/confused.gif

Bruce /ubbthreads/images/graemlins/cheers.gif
 
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