R69s Bings

[Dover Rider]

Hello
I realize this has been talked about alot but I have not heard of THE FIX for this other than Mikuni...
Due to the extreme $$ it takes to get the carbs done or new, I am taking the shotgun approach. The bike is well sorted and runs great.
My problem is after it gets warm I get serious throttle sticking midrange. I installed new jets and slide needles, polished the slides.
Do the bodies get warped at temperature? Is there a remedy for this? A machine or engineering Co that does this work.
Cables are new and not binding.
Thoughts and solutions much appreciated.
Regards
Paul

[malmac]

Paul

This is just how I would approach such a problem.
You seem to have tried the simple, intuitive things.

STEP 1
I would use my digital temperature device, and measure the temp of the carbs, when they are causing the problem.
That way you have a point to work from.

STEP 2
I would remove the carbs from the bike and warm them in the oven to that same temp.

STEP 3
I would, with the use of some good welding gloves, manipulate the slides and determine if one or both carbs are causing the problem.

Some thoughts.
Is it the slide/s sticking or is it the cables or something else?
Are the carbs correctly mounted with the mounting blocks etc?
Are they running really hot?
Is there an air leak causing them to run lean?


I am sure others here will have some really good advice.
I have found it is helpful to test assumptions.... as too often they are only partly right or maybe even just plain wrong.

I hope you get it sorted out.

Regards

mal

[Daves79x]

Sticking slides are common enough. Likely only one of them, determine which one and message the slide where you find shiny spots.

Dave

[vechorik1373]

Yes, carb bodies can and do warp and get distorted. Check the flange to see if it is warped from being over-tightened, and left that way for a long long time. If the flange is warped, it may/will have a vacuum leak. Check for a vacuum leak. Which will make that cylinder run HOT. which will make the carb warp and distort, and can cause the slide to stick in the distorted bore.
Use sandpaper on a piece of glass, and hold the body with your fingertips only, in the bolt holes of the flange, and sand the flange surface until it is flat. Replace the isolation spacers with new ones. put a little sealant on the surfaces and don't overtighten the mounting nuts. See if that helps. It may not, if the carb is that bad, but it is worth a try.

[Dover Rider]

Thanks all for the replies. I guess I was just being a little lazy/ impatient about further diagnosis. Before posting I did polish the slides on the buffer to take out the wear marks I also lapped the flanges when I cleaned/ rebuilt carbs. New insulator blocks with Hylomar applied and not over tight( carb cleaner test). I do feel like it is just one carb but I'm not sure. I also swapped sides on the slides to see if the miscreant would behave but no change. I don't have a bore micrometer to measure variances. Something to consider...

Mal, your scientific approach was my next move with a thermal scanner to get a base temp when the problem occurs. Then an isolation technique as you suggest, then all I hope will be revealed, : ) This is a static variable: hot sticking/ cold free,easily repeatable. It eliminates the cables or other mechanical variables? My next thought was how would this be fixed if the bore is becoming oval or distorted from heat. As with any cylinder a re-hone or sleeve would be the repair but is this even possible with a carb slide(jiffy sleeve) . There is no indication that the motor itself is getting too hot( timing ,leanness etc.) I do have another set of carbs that I will swap and see if the result changes. I'll let you know. A little bit of high stakes poker, these old bikes... : )
Thanks to all on the forum for your advice. The journey continues...
Best regards
Paul.

[sherman980]

Paul,
Take a black Sharpie or some machinist's blue (or something similar) and "paint" the slides with it. Run the bike up to temperature and work the throttle at the point where the slides stick. If you unscrew the throttle tops and manually work the sticky slide up and down a few times, even better. It should be obvious from the marks left on slides where things are sticking. Proceed with your fix from there. Hope that helps.

Chuck S.

[Dover Rider]

Chuck,
That sounds like an easy thing to try without taking off the carbs. Thanks for the tip, I'll give it a shot and see what develops.
Thanks,
Regards
Paul

[jwonder]

One last pint of advice. Don’t overtighten the flanges. Not only will the flanges warp, but it does not let the metal walk or grow as it heats up. They warp because they don’t have room to move.

Use a NEW wavy washer to stop the nut from backing off, tighten until the wavy washer is compressed and just add a slight bit more torque. This will let it move when it gets hot.

[Dover Rider]

Thanks James. Will do after I recheck flanges.
Paul

[Dover Rider]

Thought I would report back with results on sticking slides. Success !

I went back through and checked the flange with parallel bars and did some sanding to completely flatten the flange. Then with a magnifier I was able to see a slight, very slight edge on one bore and lightly sanded with 1000 grit until smooth. It didn't take much but with new nuts and wave washers, there is now no sticking problem.

Yay! But the caveat is that it is only 40degrees today so maybe not hot enough....
But wait, Gotta love Bings. The idle jet screw cap fell out on the test run pouring gas on the exhaust! Yikes. It turns out that the 57 year old carbs lost the 7mil threads. Not from over tightening just fatigue.
Does anyone know of a good fix besides JB weld? Heli coil? longer cap screw to virgin thread material.
As Always
Thanks to all
Paul