R27 Mystery

Begonnen von Jom, 20 Juni 2021, 13:36:04

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Jom

Hello everybody
I read this forum regularly with interest but have a mystery problem with my R27 (1964).
I have this bike for over 25 years and restored it completely. The only problem I had was the carb 1/26/79 but at that time I was able to buy a new 1/26/93.
The bike has now 8000 km and never had any problems with it, until now.
On my first ride of the season I lost the aluminium screw on the carb that covers the idle jet. I mounted the one from the old carb and have the following problem:
Cold start +- OK, cold Idle OK but after a few minutes or 500m of driving the engine dies slowly on idle.

I checked the following:
Gastank / fuel/ fuel tap / fuel filter/ gas OK
Parkplug OK
Contact breaker OK
Spark plug cap  OK
Condenser checked and OK (also no sparks at breaker contact)
Battery and voltage OK
Charging system OK
The engine drives and pulls well.

I replaced a lot of things but NO SUCCES.
All that is left is the aluminium screw in the carb, but what could be wrong with that??

Any idea?

Kind Regards,
Jom

Jom


Taz

Hello Jom.

Yoiu are mentioning a number of done checks re. the fuel system....did you consider the fueltank cap as such? those have a rather delicate system of gaskets and other stuff that is supposed to keep the fuel inside and still let in enough air to compensate for the fuel leaving on the other end. If those pathways are clogged up then your machine would show exactly the symptoms you have described.

Just do another test and leave off the tank cap (or loosen and retighten every 200m)...easy to check and possibly a quick win...

All the best, Taz
Ich hab noch nie einen Sarkasmus vorgetäuscht


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rolf.soler

So you ONLY changed the cover of the idle jet ? gasket still there ?
could be that now to little or too much air gets through in idle position
in theory it's possible that the "uncovered" jet got stuck by dust or particles... but seems unlikely. The jet itself ist still there ? I would unscrew the idle jet, put in another one (ideally a new one) and see what happens. I would also regulate the idle adjustment screw on the side (tip still OK ? turn all the way in, 1 1/2 - 2 1/2 turns out and then fine-tune as described

Jom

Hi
The fueltank cap is the same an checked, but even without the cap the problem remains.
Carburetor cleaned an new fiber ring installed, also no leaks.

Thanks for your ideas.
Jom

rolf.soler

change the idle jet

strichzwojan

Perhaps you lost the screw at the end of the last driving-season, and everything was open for dirt, dust and humidity during the wintertime?

Jom

Hi
No, carburettor dismanteled cleaned and checked and all OK, so I am in the dark.

Eppo

Zitat von: Jom am 20 Juni 2021, 13:36:04
...
I mounted the one from the old carb and have the following problem:
Cold start +- OK, cold Idle OK but after a few minutes or 500m of driving the engine dies slowly on idle.
...

Hy Jom,
what you describe sounds like the engine got a good mix for cold start, but maybe when the engine became warm the mix in the intake is too rich on gas.
After the engine dies, did you check the spark plug? Was it dry or nearly wet?
Maybe there is a little leak in the carburetor and too much gas went its way to the combustion.

Cheers  :saufen:
Geht nicht, gibt's nicht. Einfach kann ja jeder 😁.

4Taktix

... and that can happen if the brass-float leaks (heavier) and/or the float-bowl-valve doesn't seal 100%.
Or else, if the small recess in the bowl-lid is clogged. That would prevent the float-needle from going up all the way and thus the fuel-valve in the bottom can't
fully shut off.

Regards,
Sascha
Think outside the box !

Jom

Hi again,

Problem solved!

Yesterday the new alu srew arrived and.... was 1,5 mm shorter than the one I took from the old carburettor.
Everything back to normal.
Thanks for all suggestions,
Jom

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