Is your Paralever running rough at tick over and low revs?

[Rob Farmer]

I had a look at one of the local guys Paralevers last night, it has always run rough at tick over and has stuttered as he opens the throttle to pull off. I've come across this problem on three bikes now so it may be an issue on more of them.

There's an O ring on the Paralever bikes that sits round the slide in the carb providing a cushion for the slide. Part 22 on the drawing. It actually pushes up the slide and sits against the shoulder at the top.

The bikes mentioned above all had a 4mm thick O ring fitted holding the slide open slightly, if you have the needle on the factory setting the taper on the needle is just starting to let fuel through making the bike run too rich and stutter just off tick over. I don't know if this O ring is standard or is supplied as part of a rebuild kit. But fitting a thinner O ring (3mm) make's a world of difference, cleaning the throttle response up and making the bike's tickover smoother.

You don't need to strip the carb to check, just pull the inlet tube and look at the slide, it should just be touching the flats on the side of the carb, if there's a gap you need to fit a thinner O ring. I have one of those cheapo O ring kits with loads of O rings in, it just happens that it has a 3mm thick one of the right diameter in there.

 

[slowkitty]

Thanks for the tip. Finny but MAX does not seem to carry the part. It is listed on Motobins as part No. 60323 but can anyone provide the diameter of the ring itself?

 

[Rob Farmer]

I couldn't find the diameter either. I wouldn't imagine that they came from the factory like this so am assuming they have been changed.

It's very obvious when you see the gap at the bottom of the slide.

 

[Timpo]

Nice call Rob..... mine runs rough at the points you describe, and it smells rich with a tad too much blackness to the exhaust fumes, so I will be inspecting tonight.
I wonder if this will help the cold starting problem......?

Timpo.

 

[SeanW]

worn needle/main jet could create similar problem

ie, is the issue that because of the "too big" O-ring the needle is sitting 1mm too high wrt to the jet, and letting thru extra fuel as a result?

...or is it that the needle is at the correct height, but it is worn and letting thru extra fuel as a result?

Is the postion of the carb slide you refer to the approved factory setting?

 

[Rob Farmer]

Sean,

The O ring was holding the slide up enough to let fuel past the taper on the needle. The needles and jets had been replaced by the owner in an attempt to cure the problem.

Obviously I'm not saying that this is going to cure all the bikes with rough running issues but it's something worth checking if there's no obvious reason why the bikes running rough.

 

[Padmei]

Great bit of info Rob cheers.

 

[Bill-H]

My Bing book (admittedly American) doesn't show this O-ring in the schematic, how odd.
I've a similar problem with my '89 R100GS, and will check it out later, cheers Rob.

 

[Rob Farmer]

The US bikes have 32mm carbs Bill. I think the o ring is unique to the 100 gs and 100R Paralever bikes with 40mm carbs.

 

[(RIP) Kaister]

black nitrile o rings will swell after a while

viton brown ones won't

worth a think

 

[Rob Farmer]

Tis indeed

 

[Bill-H]

The US bikes have 32mm carbs Bill. I think the o ring is unique to the 100 gs and 100R Paralever bikes with 40mm carbs.

There are 40mm carbs in my book (type 94/40), but of course the 100R isn't in the American book either, guess they didn't export those to the US.

I got the book because it covers the carbs on my old R67 engine, and if anyone wants copy of the specifications, jetting etc covering Slide 1/22 through to CV 94/40 pm me an email address.

 

[slowkitty]

The US bikes have 32mm carbs Bill. I think the o ring is unique to the 100 gs and 100R Paralever bikes with 40mm carbs.

Hiya, Rob.

Opened my Mystic's carbs and there is no o-ring. I guess that this is for 40mm carbs only.

My bike runs rough at idle up to 2,700 rpms. You reckon the idle jets needs attention?

Cheers