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R51/3-carbs leakage and tuning issues

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Micha
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Pictures enclosed - a stuck plunger?

Post by Micha »

Another update: I took both left & right carbs cover's off. The problematic leaking carb has the lower plunger (arrow) stuck alternately, and when I try to blow air with my mouth into the bronze fuel hose stud (arrow) - I can't go through.
The lower stuck plunger can be pulled out when I gently use some long nose plyers.
On the right carb everything is free and ok. Air flow through the fuel stud is free.
These covers where soaked in carb. clean solution for 24 hr.
Should I soak it again?

P.S.
The tank is primed/painted inside, the fuel lines are new, the petrol tap is new.
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carb cover.jpg
Michael Steinmann
R51/3 1952
Engine Nr. 529466

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schrader7032
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Re: R51/3-carbs leakage and tuning issues

Post by schrader7032 »

Ah...nice work. That plunger is stuck in its position and lets gas through. Definitely soak it some more...maybe even use a penetrant like AeroKroil, PB Blaster...heck even WD40 to help dissolve and loosen things up. Then back to the regular soaking/cleaning bath and blow things out.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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Micha
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Re: R51/3-carbs leakage and tuning issues

Post by Micha »

Thanks. They went both back into the solution. Will see them on monday and update.
Michael Steinmann
R51/3 1952
Engine Nr. 529466

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Micha
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Re: R51/3-carbs leakage and tuning issues

Post by Micha »

Came back to update:
Took the carb out from the tank and installed it back on the bike.
Opened fuel tap and still leaking.
Swapped the head assembly with the other side with no change.
Took the complete carb off and put it into a vinegar bath for 48 hr, will come back for update.
Michael Steinmann
R51/3 1952
Engine Nr. 529466

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Re: R51/3-carbs leakage and tuning issues

Post by wa1nca »

Try swapping the floats
Check the 2 floats and see that they both have a small washer on top of the float #40 in salis pic
If one is missing the float has to
rise too high which will flood that side

https://www.bmwclassicmotorcycles.com/p ... arburetor/
Tommy
Last edited by wa1nca on Mon Apr 12, 2021 7:25 pm, edited 1 time in total.
Tommy Byrnes
54 R51/3, 55 R50/Velorex 560 sidecar, 64 R27, 68 R69US, 75 R75/6
Ashfield, Ma
USA

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TaosTwinCam
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Re: R51/3-carbs leakage and tuning issues

Post by TaosTwinCam »

Micha: Carbs do not come pre-calibrated. They are set close enough to start but have to be dialed in once the bike is running. Cable length needs to be equalized, air mixture dialed in and idle speed adjusted. This needs to be done by someone experienced, that knows what he (or she) is doing. If you have one side turning the exhaust pipe red hot, something is way wrong and almost certainly not cracked floats in new carburetors. Floats last 20 years or more before showing cracks. Perhaps you put something together wrong. Where do you live? And what was wrong with your original carburetors? Todd

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Micha
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Re: R51/3-carbs leakage and tuning issues

Post by Micha »

Morning Todd,
First, many thanks to you and all the rest here, willing to help with lots of good will.

I'm located in Israel.
The first original carbs where unrepairable. I tryed it with them but gave up finaly. I re-bored them and tried all kind of other stuff until I realized that they should go.
As I mentioned before, I then bought new carbs from Mark Huggett and they where installed as is. Maybe (can't remember after all these years) I had to regulate the idling.
The bike was a first kick starter and all was ok.
Then I "abandoned" the R51 for 5 years (covered and under a roof) witout draining the fuel system (Big mistake).
Now I want my 2 wheels back.
Overhauled the engine and gearbox.
Only the covers, slides and floats of those carbs where took appart and soaked in a bath of aceton and clean fuel.
I never touched those idle and fuel bolts. The cables are both new and match ok.
It is hard to start her, but when running, she's ok. However, I can't start her with only one cylinder and as mentioned - the leaking carb cylinder is running hot. I am not a carburettor expert, I only assume that this cylinder is getting a mixture with low fuel, hence the overheating. Another thing I suspect is that there are limescale residues at the bottom of that float chamber, where the needle should enter so they are sitting now in vinegar for 2 days. The floats are in a very good condition.
Michael Steinmann
R51/3 1952
Engine Nr. 529466

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Micha
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Re: R51/3-carbs leakage and tuning issues

Post by Micha »

Short update: I now had the opportunity to access the carb lying in vinegar.
Lucky I did so, I planned to let it lie there another day. It turns out that the vinegar attacks the alloy of the carb's body.
I immediately took it out, rinsed well and scrubbed with a toothbrush.
Tomorrow I'll take it to work where I have air pressure.
Will install after that in the evening and update.
Hope I was not late.
Michael Steinmann
R51/3 1952
Engine Nr. 529466

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Micha
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Re: R51/3-carbs leakage and tuning issues

Post by Micha »

I installed the carburetor back, after making sure that this plunger is not stuck any more.
Blew air pressure in all the openings and ports.
I can now know for sure, that there is no more dirt in the carburetor...
Still - I have the same strong leak from the exact same place (Idle mix screw).

So, I'm really at a dead end now.
Maybe lower the slide's needle will help?

What's going on here anyway?
What could be the reason for this leak?
Michael Steinmann
R51/3 1952
Engine Nr. 529466

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Re: R51/3-carbs leakage and tuning issues

Post by jwonder »

Michael, Lets do a bit of debugging.

What I wold suggest first to ensure that the needle valve is indeed working. What I would do is to take the flotbowl top off, wash it in water, and then blow ever so slightly through the brass inlet port. Then lightly move the arm (that the float presses on) up and ensure that the needle valve is stopping air. Do NOT press too hard as you can make it seal with enough pressure, the float does not exert that much pressure on the arm. It should seal completely and with little pressure.

If the needle valve IS functioning and seems to be doing what it should do, then I would look at where the float is riding on the shaft and ensure that it is at the right height. If I remember correctly (it has been awhile since I have been in the lever-tops) that there is a groove cut in the shaft. Is it possible you installed the shaft upside down?

Do those two test and get back to the forum.
James Wonder
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