Carb Mixture Screw Question

[Rick]

Making progress on the 1979 R65 refurbishment.  I was able to get it out on the road for the first time last weekend and it ran well for just rough set carb settings.  After a ride to ensure it was warmed up I attempted adjustments on the carbs.  The right side mixture screw did not seem to cause a change in idle if turned in or out.  The screws were rough set at 1 1/4 turns out initially. The left one acted as expected, i.e., turned in until idle slowed and then back out until rpms came back up and I set it at a spot somewhere in between.  (A least I think that is correct).  When I tried to do the same on the right side I found that the screw didn't have an affect.  I was able to screw it all the way in without a reduction in rpm. Could it be that the floats are set incorrectly on that side causing too much gas in the bowl thus affecting the screw setting?  Both carbs were disassembled, cleaned and floats and O-rings replaced prior to riding.  Any ideas on what else I might check?  Thanks!!

[Bob_Roller]

The first place i would go, is the idle jet .
The metered orifice is so small, even when it's clear it's hard to tell .
 The jet has two holes drilled at ninety degree angles, close these off with you finger and spray carb cleaner into the end of the jet that has the slot for the screwdriver and see if any cleaner comes out the very end .

[Barry]

When the idle mixture screw has no effect on the idle speed it can only mean that the carb is flowing air/fuel from someplace else. Perversely there is no one easy cause to point to because the idle mixture screw even when screwed all the way in doesn't shut off all of the mixture passing through the idle jet. It can mean some passage or jet is blocked or there is an air leak or the enricher mechanism is flowing air/fuel when it shouldn't. The best solution is to thoroughly clean the carb, check all passages and jets are clear, O rings are good and everything is as it should be.

If you want to try something easy before going the whole hog then your question about float levels is valid in that when the fuel level in the float chamber is too high it can get to the point where fuel overflows into the venturi. A tell tale way of checking if that might be happening is to remove the idle mixture screw. If fuel drips out after the screw is removed then that is a sure sign the fuel level is too high.  To be honest though it has to grossly to high for this to happen and would usually not be the case with new floats.
 

[Rick]

Thanks for the input Bob and Barry.  That gives me a starting point to look at anyways.  I won't get back to it for a couple of days but I will update when I get a chance to check things out.  

[Semper Gumby]

Agave.  A Colourtune plug will allow you to "see" if the mixture is correct.  Blue is the correct colour for 14.7 to 1 air to fuel.  Too rich will be yellow. and too lean will be white or nothing.  BTW you will also be able to see the spark.

When the bike is set up right the idle will be blue.  When you crack open the throttle it should go yellow for a bit and then as the engine comes up to speed it should go back to blue.

Also the is a "range" that the flame will be blue.  I set my idle on the rich side of blue.  When you set  it to the lean side you can get some popping with the throttle closed running down to a stop.

Regards,

[MichaelSydney]

Could it be a problem with the butterfly? On the carb which continues to deliver air/fuel mixture with the mixture screw fully in, perhaps the throttle butterfly is cracked open and it is running on the main jet. This could be either due to the throttle screw being adjusted wrong or the butterfly incorrectly rebuilt (I understand they can be fitted back to front and not close properly)

Perhaps remove the carb and check that the butterfly seals 100%.

[thrang]

If the worst comes to the worst just rebuild the carbs! Its not a hard job, and a rebuild kit is not that expensive, which is just as well given that high alcohol content fuels can really mess up old o-rings. Think I did both mine before Easter for under £60.

[Rick]

Did the simple checks with carb still on bike when I found a little bit of time recently.  Checked the idle jet, all passages clean and clear.  Checked float adjustment and everything looks good.  Idle mixture screw still not having an effect.  When turned all the way in, the idle didn't change much and actually increased a little bit.  I will pull the carb, diassemble, and inspect when I find more time to work on it. Will check butterfly but am fairly certain it is good.  Carbs were disassembled cleaned and O-rings had all been replaced when I first got the bike so all should be good there, unless there is still a bit of dirt somewhere in there or there is an issue with the enricher.      

[Red_Hen]

what helped me was purchasing a small ultrasonic cleaner from Harbor Freight - sound to me like a jet or passageway is clogged - suggest having a high air pressure nozzle to dry and hopefully clear debris - also you can take a strand of electrical wire and use that to run it through the small holes - just make sure the strand is small enough so it doesn't damage the holes!  Sounds like you're almost there!

[Mike V]

O-rings had all been replaced when I first got the bike so all should be good there, unless there is still a bit of dirt somewhere in there or there is an issue with the enricher.

Agave,

Make sure the new O-rings are still in good condition and they did not tear or roll during reassembly. I like to put the slightest tiny bit of smear of Silicone Grease on them. No big globs.  When removing and re-installing, turn the jets slowly.

I echo Bob and Ken's advice also, be sure the very small venturi orifices in front of the butterfly are clear. Compressed air is a great way of checking all channels are clear of debris and obstructions if you don't have an Ultrasonic Cleaner. Use a rubber tipped air nozzle for one channel end and observe the exiting of air with your other hand/fingers.  I keep many small single soft copper strands of electrical wire stripped from insulated electrical wire for carefully poking and prodding carbs. Use caution when doing this not to break the wire strand or force things.