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 Posted: Jun 28, 2017 02:40AM
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There is a list of stupid somewhere here on the forum. I'm a frequent offender. When I got my mini running the first time I had the choke and throttle cables swapped. I pulled the choke to start it and nearly blew up the engine.

Welcome to the shade tree mechanic site. Enjoy your car. Laugh with friends about how it came to be.

Mark Looman, Ada Michigan 1967 Austin Cooper S
 Posted: Jun 21, 2017 03:52AM
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CA
Tom: nothing to be embarrassed about. We've all been through trying issues only to find the "DUH" solution. I've seen threads here in the past with people sharing such experiences.

Thanks for reporting back - every solution to strange happenings builds the Mini Knowledge. Without the final answers, nothing gets learned. (I learned something about right hand drive throttle cables!)

Glad you've got it sorted.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jun 20, 2017 04:55PM
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I am extremely late on replying to this but I was able to figure out the issue.  Dan was correct- some embarrassment is involved.  The cultprit-  Engine movement under stress.

When I put my foot on/off the clutch while the car was in motion, the engine rocked back and forth due to the relief of stress being pulled off.  I could not see the rocking due to the seating position in the car, however it was enough to cause the throttle to pull, and subsequently add power.  Hence the sudden power when I pushed in the clutch- the engine was rocking forward and pulling the throttle.  I bought an engine steady kit from mini mania to settle the rocking.   I also relocated the throttle cable to reduce the potential to recreate the issue.

The steady kit does a great job- upper and lower.  I need to relocate the upper now due to the supercharger, but the issue has been resolved.  Thanks for everyone's input!

 Posted: Jan 16, 2017 05:08AM
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CA
I'm starting to think it was something obvious or simple (like the throttle cable hung up on the clutch lever) and he's too embarrassed to admit it. 

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 12, 2017 09:34PM
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US
Did you figure this out yet Thommy?

Wondering where your right foot is and what it's doing when you put your foot on the clutch.

 Posted: Jan 8, 2017 06:00AM
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CA
Thanks for the clarification on the righy throttle cable locatíon. I've never been close enough to a righty Mini to see the throttle cable. 
And you're right about the cable passing horizontally through the firewall..... in my defense, it has been over a year since I've even looked under my own Mini's bonnet. 

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 6, 2017 05:21PM
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Quote:
Originally Posted by Dan Moffet
Quote:
Originally Posted by 1963SV2
"....then when manifold vacuum drops, the engine "sees" timing and mixture for much higher rpm/power and responds accordingly..."

I don't believe this is true...  There is no physical (logical??) reason for manifold vacuum to increase as the clutch is released.   Indeed, the extra load will cause  the revs to drop and vacuum to decrease....

I would be looking for a manifold leak, the throttle plate not entered properly, inadequate return spring(s) or the wrong (or missing) piston spring....  

The throttle cable passes close to the clutch release lever as it passes through the engine bay firewall and its entirely possible that the clutch lever is pulling on the throttle as the clutch pedal is depressed......

Cheers, Ian
We're clutching at straws for ideas "why" in this case. But here's my thinking on the mixture/vacuum idea:
However the engine may be tuned, it could be it is idling on spark way off, too rich(or maybe lean) and the throttle plate actually being open wider than typical idle, say part-throttle. When the engine gets loaded by the release of the clutch, manifold vacuum changes (probably drops, which is what I wrote), affecting the timing.
Suddenly the engine sees better timing for the throttle position, the dashpot responds to increased air velocity through the throat (as it would) producing improved fuel mixture and (as Jackie Gleason used to say) " awaaaaay we go!"

(Sorry about the "clutching" pun!)

I think a manifold leak might contribute to my strange tuning scenario.

I suppose your idea about the clutch lever pulling the throttle cable might be possible... on a right-hand car with an A-series lever. No chance on a lefty. But it would have to be a really long throttle cable to hang low enough to catch on the clutch lever. On a righty, doesn't the throttle cable pass through the firewall on a vertical angle as on a leftie, then arch over to the carb throttle?
Don't you mean it passes through the firewall horizontally.
Thommy. When the car is idling normally are you referring to it with the clutch disengaged (foot pressure on the pedal) if so you may have worn thrust washers producing crank end float.
FWIW the throttle cable rests on the clutch arm on most RHD non verto Mini's.

If in doubt, flat out. Colin Mc Rae MBE 1968-2007.

Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.

 Posted: Jan 5, 2017 02:26PM
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Quote:
Originally Posted by Dan Moffet
Quote:
Originally Posted by 1963SV2

I would be looking for a manifold leak, the throttle plate not entered properly, inadequate return spring(s) or the wrong (or missing) piston spring....  

Cheers, Ian
I think you meant "centred"

I saw this somewhere....
"Every time you make a typo, the errorists win!"
At least I know someone is reading my posts .  I blame most such terrors (ooops on unsupervised spell checkers... 

Cheers, Ian

 Posted: Jan 5, 2017 09:25AM
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Quote:
Originally Posted by Dan Moffet
We're clutching at straws for ideas "
 
while we are clutching

was carb oil topped off?

does the car have power brakes? By letting out the clutch, one takes their foot off the brake pedal, so could this somehow cause an rpm increase due to  a vacuum leak coming through the vacuum powered brake booster? I do not know when these things leak "normally" when they go bad ,whether it is while foot is on or off the brake. Both?

 Posted: Jan 5, 2017 07:20AM
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CA
Quote:
Originally Posted by 1963SV2

I would be looking for a manifold leak, the throttle plate not entered properly, inadequate return spring(s) or the wrong (or missing) piston spring....  

Cheers, Ian
I think you meant "centred"

I saw this somewhere....
"Every time you make a typo, the errorists win!"

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 5, 2017 07:11AM
 Edited:  Jan 5, 2017 07:16AM
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CA
Quote:
Originally Posted by 1963SV2
"....then when manifold vacuum drops, the engine "sees" timing and mixture for much higher rpm/power and responds accordingly..."

I don't believe this is true...  There is no physical (logical??) reason for manifold vacuum to increase as the clutch is released.   Indeed, the extra load will cause  the revs to drop and vacuum to decrease....

I would be looking for a manifold leak, the throttle plate not entered properly, inadequate return spring(s) or the wrong (or missing) piston spring....  

The throttle cable passes close to the clutch release lever as it passes through the engine bay firewall and its entirely possible that the clutch lever is pulling on the throttle as the clutch pedal is depressed......

Cheers, Ian
We're clutching at straws for ideas "why" in this case. But here's my thinking on the mixture/vacuum idea:
However the engine may be tuned, it could be it is idling on spark way off, too rich(or maybe lean) and the throttle plate actually being open wider than typical idle, say part-throttle. When the engine gets loaded by the release of the clutch, manifold vacuum changes (probably drops, which is what I wrote), affecting the timing.
Suddenly the engine sees better timing for the throttle position, the dashpot responds to increased air velocity through the throat (as it would) producing improved fuel mixture and (as Jackie Gleason used to say) " awaaaaay we go!"

(Sorry about the "clutching" pun!)

I think a manifold leak might contribute to my strange tuning scenario.

I suppose your idea about the clutch lever pulling the throttle cable might be possible... on a right-hand car with an A-series lever. No chance on a lefty. But it would have to be a really long throttle cable to hang low enough to catch on the clutch lever. On a righty, doesn't the throttle cable pass through the firewall on a vertical angle as on a leftie, then arch over to the carb throttle?

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 4, 2017 10:36PM
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"....then when manifold vacuum drops, the engine "sees" timing and mixture for much higher rpm/power and responds accordingly..."

I don't believe this is true...  There is no physical (logical??) reason for manifold vacuum to increase as the clutch is released.   Indeed, the extra load will cause  the revs to drop and vacuum to decrease....

I would be looking for a manifold leak, the throttle plate not entered properly, inadequate return spring(s) or the wrong (or missing) piston spring....  

The throttle cable passes close to the clutch release lever as it passes through the engine bay firewall and its entirely possible that the clutch lever is pulling on the throttle as the clutch pedal is depressed......

Cheers, Ian

 Posted: Jan 3, 2017 02:58PM
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I started by doing a standard shift.  When I noticed the problem I changed to not pressing the accelerator when shifting into gear when I experience this issue.  I was letting it slip to diagnose the problem and rule out the throttle cable as a possibility.  

We are checking the oil today. I have some SU oil in the shop and some extra springs from same model SU's that may come in handy in the carb.

Dan makes a good point as well regarding the vacuum advance, timing, and some other disconnected bits.  I am not really testing the system as if it were being driven under normal conditions.  I will start diagnosing these as possibilities and get back.

 Posted: Jan 3, 2017 07:08AM
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CA
Check that the timing is set properly, with the vacuum advance disconnected and plugged while you do. Check also that the vacuum advance is functioning properly. There may be a chance that tuning is way off but producing a good idle - then when manifold vacuum drops, the engine "sees" timing and mixture for much higher rpm/power and responds accordingly.
Tuning should of course be done with the air cleaner system and a complete exhaust in place to replicate the "normal" conditions under which it will be operating.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 3, 2017 02:25AM
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GB
Put an exhaust pipe on it and try again.

 Posted: Jan 2, 2017 05:29PM
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need more clarification

when you say put it in gear and engage clutch are you also pressing on the accelerator?
and
when you disengage  the clutch are you letting off the accelerator like most of us do automatically?

if so, then with insufficient oil in the carb dashpot, and giving it gas pedal,
the variable venturi flies open too fast and the engine could race (even though now the mixture is too lean) .

Mine 'bucks" when it needs carb oil, not runaway like you describe.

Is the problem really caused by using the  clutch or gear selection?  I doubt it. 
If so, then it should do what you describe if you keep your foot off the accelerator.
If it is accelerator-related, then my bet is on the simple carb oil fix


 Posted: Jan 2, 2017 04:04PM
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Hi Dan,
Yes- by "drive" I mean in gear.  It is not limited to any specific gear, 1-4 and R all demonstrate the same issue.

It is an SU carb.  Great thought regarding the dashpot, I have some oil and a few springs around.  I will check this.
I added a stronger spring for the throttle return.  I will double check that this isn't getting hung up somewhere.

It is odd to me that it only takes on this extra RPM when the car is under stress.  I would expect it to do the opposite and lower RPM under these conditions.

 Posted: Jan 2, 2017 11:11AM
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CA
Tom: a bit of clarification is needed - you talk about a clutch but putting it in 'drive'.  You do mean 'gear' don't you... you have a manual transmission? If you had an automatic, I'd suspect something in the shift control system (which I know nothing about!) but it wouldn't have a  foot-operated clutch.

On your carb (a SU type?), check that you have a smoothly operating dashpot,  that it has the big spring in it, and that it has damper oil. Check also that your throttle return spring is working properly.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jan 2, 2017 09:48AM
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I completed installation of my engine yesterday and started test driving when I noticed an odd issue.  The car idles normally.  I dont have a Tach set up, but I would equate to somewhere in the 1000rpm range, nothing odd.  However, when I place the car into gear and release the clutch, it suddenly wants to race!  The RPMs shoot up very high and it really wants to pull until I put on the clutch and the problem subsides.  (most people wouldnt complain about extra power, but if definitely affects driveability).

I checked the accelerator cable, thinking it was getting stuck.  This appears to be just fine.  I am wondering if the carburetor is (for some reason) acting to the added stress of being in drive, and compensating with the added power? 

Any idea what could be contributing to this and how to resolve?

Engine:  A-series 998cc with stock carburetor. 
No air cleaner attached (no resistance currently)
No exhaust (straight pipe)

Thanks,
Tom