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Do your RMP's drop when at idle with clutch in?
- Thread starter AUSMHLY
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tahoe healey
Yoda
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Yes, Roger. That's one of the reasons you do not start the car with the clutch pushed in. I've never paid attention to how much, but not much. I think Dave Russell discussed this a couple of years ago. I had always put the clutch in before I hit the starter just in case I was in gear. He cured me of that. It should go back up when released but I've never paid attention.
Hey, have you been away? No posts for a while.
Hey, have you been away? No posts for a while.
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It is because of slight movement forward of the crankshaft and friction at the thrust bearings when the clutch is depressed. The drop will be slight, perhaps 100 rpm's but nevertheless something not to do.
OP
AUSMHLY
Yoda
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Re: Do your RMP's drop when at idle with clutch in
Hi Guys,
Thanks for your help. My question is not directed towards having the clutch in when starting the car, but having to push the clutch in a lot when I'm in stop and go traffic on the road.
I'm trying to sort though some carb adjustment issues.
The other day there was an accident on the freeway. Well, traffic was at a walk pace, stop and go. I found I was having to push the clutch in a lot when in first. My tach would not settle in one place. Sometimes the car would even want to stall.
I sent my carbs to Joe Curto and installed them back in the car. My mechanic says there's something wrong with the rear carb. Last night I took them both out and their now on his bench. Later today he will tell me what he's found.
Hi Guys,
Thanks for your help. My question is not directed towards having the clutch in when starting the car, but having to push the clutch in a lot when I'm in stop and go traffic on the road.
I'm trying to sort though some carb adjustment issues.
The other day there was an accident on the freeway. Well, traffic was at a walk pace, stop and go. I found I was having to push the clutch in a lot when in first. My tach would not settle in one place. Sometimes the car would even want to stall.
I sent my carbs to Joe Curto and installed them back in the car. My mechanic says there's something wrong with the rear carb. Last night I took them both out and their now on his bench. Later today he will tell me what he's found.
Bob_Spidell
Yoda
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Re: Do your RMP's drop when at idle with clutch in
The RPMs--in my experience--will drop 50-100 from normal idle when you push the clutch pedal in; e.g. if your engine is idling at 700rpm, when you push the clutch pedal in the rpms could drop to between 600 and 650rpm, but the tach shouldn't bounce around (RPMs should be steady at one speed with the clutch in, and another with the clutch out--the pressure plate springs and throwout bearing are a steady load).
Don't understand why you pulled the carbs off the car--unless you have a very sophisticated test bench you can do more diagnosis with them on the car and the engine running. The first thing to do is pull the vacuum pistons--aka 'dashpots'--and turn the ignition on. The tops of the jets should be 1/16" to 1/8" or so below the brass jet 'bridge.' The fuel level should be about the same amount below the top of the jet. If that's true and needles are located correctly in the vacuum piston the car will run decently unless there are major issues with the throttle plate, bypass circuit if you have one or with the vacuum pistons or cylinders (or you have a serious vacuum leak). I wouldn't expect any of that after an overhaul by a respected SU rebuilder.
Why is your mechanic convinced there is a problem with the back carb? Remember the old adage '99% of carburettor problems are in the ignition.'
The RPMs--in my experience--will drop 50-100 from normal idle when you push the clutch pedal in; e.g. if your engine is idling at 700rpm, when you push the clutch pedal in the rpms could drop to between 600 and 650rpm, but the tach shouldn't bounce around (RPMs should be steady at one speed with the clutch in, and another with the clutch out--the pressure plate springs and throwout bearing are a steady load).
Don't understand why you pulled the carbs off the car--unless you have a very sophisticated test bench you can do more diagnosis with them on the car and the engine running. The first thing to do is pull the vacuum pistons--aka 'dashpots'--and turn the ignition on. The tops of the jets should be 1/16" to 1/8" or so below the brass jet 'bridge.' The fuel level should be about the same amount below the top of the jet. If that's true and needles are located correctly in the vacuum piston the car will run decently unless there are major issues with the throttle plate, bypass circuit if you have one or with the vacuum pistons or cylinders (or you have a serious vacuum leak). I wouldn't expect any of that after an overhaul by a respected SU rebuilder.
Why is your mechanic convinced there is a problem with the back carb? Remember the old adage '99% of carburettor problems are in the ignition.'
tahoe healey
Yoda
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Re: Do your RMP's drop when at idle with clutch in
Also, when the car is getting hot as in traffic, you will drop some RPM and get funky, inconsistent running. I think this is because the rear carb gets hotter than the front but I'm just guessing. I would not fuss with anything Joe does. You did not ever switch the dash pot domes did you?
As always, good luck.
Also, when the car is getting hot as in traffic, you will drop some RPM and get funky, inconsistent running. I think this is because the rear carb gets hotter than the front but I'm just guessing. I would not fuss with anything Joe does. You did not ever switch the dash pot domes did you?
As always, good luck.
dondel
Freshman Member
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Re: Do your RMP's drop when at idle with clutch in
I do have the same behaviour on mine. It's getting really nasty during summertime in a stop and go. In general, you should not keep the clutch pushed for too long; that's what is always recommend you on the new cars. So my guessing is that this also applies for the "older" ones. Anyway on the new cars, the gears are all synchronised, so there shouldn't be a reason why keeping the clutch pushed...
I was also used to this having the clutch pushed when starting the car (I still do this on my every-day-car) as I was thought at driving school, but for the Healey, I don't do this any more.
I do have the same behaviour on mine. It's getting really nasty during summertime in a stop and go. In general, you should not keep the clutch pushed for too long; that's what is always recommend you on the new cars. So my guessing is that this also applies for the "older" ones. Anyway on the new cars, the gears are all synchronised, so there shouldn't be a reason why keeping the clutch pushed...
I was also used to this having the clutch pushed when starting the car (I still do this on my every-day-car) as I was thought at driving school, but for the Healey, I don't do this any more.
AH100M
Jedi Trainee
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Re: Do your RMP's drop when at idle with clutch in
When I drove a jeep a couple of times in the (US) Army back in 1969 the starter button was on the floor near the clutch pedal. The only way to press it was to depress the clutch pedal all the way with your foot and hit the button with the toe of your boot. Took some getting used to!
When I drove a jeep a couple of times in the (US) Army back in 1969 the starter button was on the floor near the clutch pedal. The only way to press it was to depress the clutch pedal all the way with your foot and hit the button with the toe of your boot. Took some getting used to!
Rob Glasgow
Jedi Knight
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Re: Do your RMP's drop when at idle with clutch in
My first car was a 1940 Nash given to me as a hand-me down by my father when I was 13. Among the other advanced features of the car was the starter switch was on the floorboard under the clutch pedal. To start the car, you simply pressed the clutch pedal all the way to the floor and the engine started. You used the clutch to change gears as normal, just didn't push the pedal all the way to the floor. It also had a switch on the floor that changed the radio stations and an air-actuated radio antenna. Nash was way ahead of their time, but the styling in the early 50's may have been a little too futuristic. Unfortunately,my Dad got tried of having the non-running car arround and sold it for $15 to the junk man. Boy, what I wouldn't give to have that car today. Maybe that experience taught me to hold on to important cars.....I still have and drive my 1960 BT7 I bought in 1963.
My first car was a 1940 Nash given to me as a hand-me down by my father when I was 13. Among the other advanced features of the car was the starter switch was on the floorboard under the clutch pedal. To start the car, you simply pressed the clutch pedal all the way to the floor and the engine started. You used the clutch to change gears as normal, just didn't push the pedal all the way to the floor. It also had a switch on the floor that changed the radio stations and an air-actuated radio antenna. Nash was way ahead of their time, but the styling in the early 50's may have been a little too futuristic. Unfortunately,my Dad got tried of having the non-running car arround and sold it for $15 to the junk man. Boy, what I wouldn't give to have that car today. Maybe that experience taught me to hold on to important cars.....I still have and drive my 1960 BT7 I bought in 1963.
B
BobHorvath
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A couple of thoughts: I once built a 327 S.O. and shaved a little too much of the flywheel for faster shifting. The added angular momentum of the engaged clutch plate was just enough to improve the idle characteristics. The stock flywheel mass in the Healey is actually more (in my opinion) than is needed and some folks talk about removing metal. Have you looked at and then compared your flywheel to the stock heavy weight? If the car once idled good and now does not throw away the previous info and go on to the next idea. Idea #2 I spent two years trying to improve or just at least keep constant my engines idle performance. Distributor re-build off-stock timing, curve adjustments, Pertronix, sync meter & everybody's trick ideas. Not until I noticed an oil residue on my coil bracket did i begin to make any progress on getting the idle where it should be. The coil, The coil, The coil is where my problem was.