R90S misfiring

[Larry Langford]

,,also the air breather could be clogged up .... might be a big rats nest in there .....

 

[tiktok]

Fuck me,
It’s not fucking brain surgery.
Suck squeeze bang blow.
The other side seems to be working.
Has it got compression?
Has it got a spark.?
If it has compression and spark on the bad side,there’s only fuel that’s not happening.
If this is the case with Dellorto carbs they need cleaning properly.

Probably best if you read my previous posts, before you post advice.

 

[mikeyboy]

Probably best if you read my previous posts, before you post advice.

Probably best if you learn how to fix your own motorcycles if you need to ask advice on an internet forum,then post sarky comments to folk that might actually know what they’re doing.
Just saying,,,,like

 

[tiktok]

Probably best if you learn how to fix your own motorcycles if you need to ask advice on an internet forum,then post sarky comments to folk that might actually know what they’re doing.
Just saying,,,,like

As you said it’s not brain surgery.
These things take time, and right now I am still going through the bike.

If you don’t like me asking for advice or trying to build a thread, detailing my experience as I learn about a new bike, you could always say nothing.

 

[tiktok]

The R90S is starting easily, running, idling and no longer misfiring!

I ended up ultrasonically cleaning and rebuilding both carburettors and resetting the points gap (it was way less than 0.4mm). I then spent a bit of time finding idle - it's now idling at just under 950rpm and with the idle mix set to 1 turn out. If I wind the throttle stop screws out any further, it cuts out.

Additionally I checked and adjusted the valve clearances, dropped the sump, replaced the oil and air filters, fresh oil, lubed up the shaft on the on the starter Bendix, cleaned up a load of grubby bits and then put it back together.

Next on the list is to borrow a carb balancer device, test ride the bike and fit new tyres (current ones are 10 years old).

Question: Is it normal to hear a little bit of valve chatter when the bike is idling?
Other question: There is a little intermittent popping under gentle throttle when stood, the rpm blips slightly at the same time. Is this likely to be the carb setup?

 

[Kenny]

Valves are noisy.
Check intake rubbers for cracking ( look inside them as well ).

 

[mikeyboy]

The R90S is starting easily, running, idling and no longer misfiring!

I ended up ultrasonically cleaning and rebuilding both carburettors and resetting the points gap (it was way less than 0.4mm). I then spent a bit of time finding idle - it's now idling at just under 950rpm and with the idle mix set to 1 turn out. If I wind the throttle stop screws out any further, it cuts out.

Additionally I checked and adjusted the valve clearances, dropped the sump, replaced the oil and air filters, fresh oil, lubed up the shaft on the on the starter Bendix, cleaned up a load of grubby bits and then put it back together.

Next on the list is to borrow a carb balancer device, test ride the bike and fit new tyres (current ones are 10 years old).

Question: Is it normal to hear a little bit of valve chatter when the bike is idling?
Other question: There is a little intermittent popping under gentle throttle when stood, the rpm blips slightly at the same time. Is this likely to be the carb setup?

The popping noise is probably the early type breather valve on the RH top of the engine casing next to the starter motor,
It can be updated to the later reed valve type if it annoys you.

 

[tiktok]

Valves are noisy.
Check intake rubbers for cracking ( look inside them as well ).

Thank you. Forgot to mention, I ordered new intake rubbers and checked for air leaks.

 

[Posh Pete]

Valves are noisy.
Check intake rubbers for cracking ( look inside them as well ).

Better looser than tighter. Aside from that general advice, airheads do tend to favour slightly wider gaps.

 

[Stirlingmoz]

The R90S is starting easily, running, idling and no longer misfiring!

I ended up ultrasonically cleaning and rebuilding both carburettors and resetting the points gap (it was way less than 0.4mm). I then spent a bit of time finding idle - it's now idling at just under 950rpm and with the idle mix set to 1 turn out. If I wind the throttle stop screws out any further, it cuts out.

Additionally I checked and adjusted the valve clearances, dropped the sump, replaced the oil and air filters, fresh oil, lubed up the shaft on the on the starter Bendix, cleaned up a load of grubby bits and then put it back together.

Next on the list is to borrow a carb balancer device, test ride the bike and fit new tyres (current ones are 10 years old).

Question: Is it normal to hear a little bit of valve chatter when the bike is idling?
Other question: There is a little intermittent popping under gentle throttle when stood, the rpm blips slightly at the same time. Is this likely to be the carb setup?

Glad you have got it running well - good work.

Valve gear can be noisy compared to newer airhead models. Some quietening can be achieved by adjustment of the rockers vertical play (as well as the actual clearance) but it’s all part of its character

BMW did have a special tool for /5’s to align the rocker pillows and ensure correct vertical clearance but you don’t really need it.

 

[tiktok]

Still dialling in the bike. Fitted an electronic ignition, which seems to have cured the misfiring.

I’m having minor issues on the right carb idle circuit so have run it through the ultrasonic cleaner again and used my compressor to blow out the channels. All seems clear.

Float needles both look worn, so have ordered replacements.

Once it’s idling properly, will check the timing properly.