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bmwsog
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After a 15 mile ride, my 1951 R-51/3 developed a high non responsive idle: goes to
about 3000 RPMs and stays there-checked cables for kink or mis-routing. Almost acting like stuck floats.......

Thought about valve adjustment....but this is not symptomatic ...open for suggestions....

It COULD really be stuck float.....

At any rate it is not responsive to throttle control to lessen RPMs...only to increase...

Wonder if some junk is jamming my needle or crud in the carbs..............next step is to
examine and clean carbs..........left plug a bit rich............

This R-51 has less than 2K miles on a complete engine-transmission-final drive re-build by Vech at Benchmark.
Has run well to date...............

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LTC R Marriott--1951 R-51/3
1962 R 69 S 1975 SS R-90 S
1974 SS R 90 S

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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Can you get the idle to come

Can you get the idle to come back down by loading the engine? Put the bike in gear, brakes on, and slowly let out the clutch...that will drag the RPMs down. Will it idle fine? If so, then the advance unit is not coming back down...the weights are sticking out.

Usually a high idle like that is due to an advance unit that is sticking. If the RPMs go back up after dragging the clutch, then the carbs need to be looked at. Typically, if someone makes a carb tweak on a cold engine/carb, then go out and warm up the bike, the carbs will react differently and could cause a high idle. Carb work needs to be done on a warm engine.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

bmwsog
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Duane Auscherman...............

Auscherman has a similar test for the advance unit., involving the ignition key-slowly lifting 1/8 inch-watching the recovery and advance
unit weights with a strobe light. They appear to be returning but-I am not absolutely certain-as the fast idle returns after the test-not supposed to happen. I will try your test again..

The other concern on this early advance unit are the two types of springs: the limiter flat spring appears OK-that one is prone to breakage.

The other two are small coil springs which may weaken. Given that this is a newer restoration-the springs should be OK..
But you never know-and they don't make a lot of N-OS like they used to as to quality long term.

Now can those coil springs be adjusted by the plate screws to safely give more return spring tension, with just the right return tension...???
I finger tested the springs & weights-and it seemed not to put as much return spring pressure as might be required.

Kurt-what do you think...............

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LTC R Marriott--1951 R-51/3
1962 R 69 S 1975 SS R-90 S
1974 SS R 90 S

schrader7032
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San Antonio, TX
Joined: 10/27/2006
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In my R69S, I had the later

In my R69S, I had the later spring. I have since completely removed it and replaced it with what is known as the "Brian Caro" stop screw. It's a fixed screw which physically limits the full travel of the advance so that it's not possible to over advance the engine...bad thing for high compression R69S engines. So in my case, the small coil springs that hold the weights is what's controlling my advance curve. I never really understood the reason for the question-mark or the newer curved springs.

I don't think these springs could cause the your high idle. High idle could be an advanced timing situation...these springs tend to do the opposite...they restrict advance.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

bmwsog
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Advance unit springs

I am still suspicious of the two " fly weight" springs, as they are called.
A couple of reasons: The high idle could well be caused by weak spring action-which will not pull
the advance weights back when spun on the cam nose. Thus: high idle continues.

1. The test done did not really return the idle to normal.

2. When manipulating the fly weights by finger light pressure, when extended out-they would NOT return by spring tension.
This is also after lubing slightly the spring base posts with dielectric grease -recommended by Auscherman. I suspect the springs
need replacing.

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LTC R Marriott--1951 R-51/3
1962 R 69 S 1975 SS R-90 S
1974 SS R 90 S

schrader7032
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San Antonio, TX
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There you go...if those coil

There you go...if those coil springs aren't doing their job, need replacing. As I recall, but worth checking, the two springs are different, so be sure and get the new once back in the right order.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

wa1nca
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Ashfield Ma.
Joined: 09/27/2012
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spring tension

bmwsog wrote:

I am still suspicious of the two " fly weight" springs, as they are called.
A couple of reasons: The high idle could well be caused by weak spring action-which will not pull
the advance weights back when spun on the cam nose. Thus: high idle continues.

1. The test done did not really return the idle to normal.

2. When manipulating the fly weights by finger light pressure, when extended out-they would NOT return by spring tension.
This is also after lubing slightly the spring base posts with dielectric grease -recommended by Auscherman. I suspect the springs
need replacing.

My 2 cents
Their should be no free play on the springs when engine is off
If so you can loosing the small nut on the fly weight and take up any slack so weight and spring work at the same time

Tommy

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Tommy Byrnes
54 R51/3 55 R50 64 R27 68 R69US 68 Sears Allstate 250 (Puch)

bmwsog
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Vech input

Craig Vechorik is 85 miles from this R-51, so managed to get his input.

Vech Test on advance unit. The early advance unit on this bike has
9 and 11 weight coil return springs. His suggestion was to place a
thumbnail between the points-THEN see if the fly weights snap back
when they are extended. They should snap back with spring action
smartly. They did.

Further investigation with the control/carb cables revealed that
the right carb did not respond properly when both cables
were pulled a tad to check each slide action. The culprit appears to be in the
carburetion/spark on right side. Will advise.

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LTC R Marriott--1951 R-51/3
1962 R 69 S 1975 SS R-90 S
1974 SS R 90 S

Beemer100
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Germany
Joined: 05/15/2018
Posts: 7
I would also recommend to

I would also recommend to check more on the carb side. On my old Harleys with manual advance mechanism, the difference in idle revs is not as high as described above. I would assume there is something stuck in the throttle mechanism

my 2 cents
Klaus

Daves79x
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You Have

It sure sounds like you have a carb slide sticking. Identify which one it is , remove and take off the high spot you will find.

Dave

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Dave

The Plunger
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Yup, a little rub with 600

Yup, a little rub with 600 grit in the barrel did the trick on my sticky slide. Look for any obvious gouging from any debris that may have gotten in. A thin film of grease wouldn’t hurt either.

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Brian
'52 R67/2, '53 R51/3

Captonzap
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Wrong

The Plunger wrote:

A thin film of grease wouldn’t hurt either.

Yes it would. Grease collect crud and turns to sludge.
If you want a lubricant, try graphite, (Lock Lube), or dry Moly (Dri Slide).
Mostly, keep them clean and you don't need a lubricant.

CZ

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