Forum bmwbike.com

Idle not stable and more problem?
I'm restoring a r75/5, the carb has been let with fuel on for many year, so the carb are very clogged, rusty and everything you can imagine. I send those carb to overhaul but it still not working properly.
Starting is good but idle is rough and going up 1400 rpm for 1 minute and drop down to the idle again. If idle is set low 600 rpm the problem is is less is the idle is set at 700 the ploblem remain more often.
thank for any anwser .

What kind of place overhauled the carbs?
What exactly did they do to the carbs and what parts did they replace?
Do you know how to install the carbs, adjust the mixtures, and synchronize the action of the cables?

What kind of place overhauled the carbs? Motorcycle shop specialist on Bmw restauration
What exactly did they do to the carbs and what parts did they replace?Diaphram ,needle jet ,idle jet , float pin, float needle, gasket seal has been replaced and all hole has been cleaned and blowed
Do you know how to install the carbs, adjust the mixtures, and synchronize the action of the cables? Carburator has been installed and adjust as per Clymer book.
The needle jet is adjust at de second nocth leaner.the float level is parallele to the housing. No vaccum leak beetween the engine and carb, checked with soap.

You are in Canada - what was the name of the shop that did the carbs?
I have that Clymer manual and owned a /7 with vacuum carbs for 12 years. Does the engine idle at the same RPM when each plug lead is removed?
It is not clear what you mean by the idle going up to 1400 RPM when set for 600-700 RPM. Perhaps that is happening when the cold engine is first started on the choke - if so, that is normal. Start on full choke, immediately reduce to 1/2 choke, and when the idle rises, turn off the choke.

Montecristo
After the warm-up has been done, whitout any mouvement it going up to 1400 rpm, sometime when i stop at the light it still to 1400rpm to 1600 rpm and sudden drop to 600 again. i open the carb myself and know i didn't anything wrong except when the float is parralelle to the case the ajusting tab have a big angle down like if the needle is too short
the rpm is about 620rpm hot and if i try to fix upper the problem is more bad.
Somebodyelse answer a problem like mine and tell , it is on advance init sring is bad, what do you think about that?
Thanks

A sticking advance unit can cause the RPMs to remain high when the throttle is closed.
Such an advance unit may be dirty and need cleaning and lubrication, or it may be worn and need replacement.

Hello!

I have a BMW R75 in May 1972. it has only 10,000 mil. but I have a problem rpm. when it is hot the rpm goes up for no apparent reason at 1600 rpm or 1900, my carbs are in excellent condition. I heard that it is possible to install a spring on the valve slid. who can say this will solve the problem ...thank you .........Daniel

Have you synched the carbs lately? It's important to do this after you've warmed the engine and carb up after a 15-20 mile ride. Be ready with a box fan or something to blow air over the engine while you idle it and set the mixture, idle speed, and cable tension. A creeping idle when hot is an indication of making adjustments when the carb is cold.

It could also be a sticking advance. If the idle goes high, hold the front brake while in gear and let the clutch out, enough to put some drag on the engine. If the idle comes down and stays down, then it is your advance which needs to be taken off and cleaned. Be careful of the 10mm nut at the tip of the camshaft that holds the advance unit on. It doesn't need much torque to keep it in place.

Kurt in S.A.