Clutch slippage in 4th gear, RPM gauge dropping

[gggGary]

But you DO have vacuum ports my friend!

BS 38 vacuum ports and adaptors

 

[retiredgentleman]

Thanks for all the help guys!
Now that I have those little issues solved I have 2 more that have risen doh!!

I know these two issues are related

First issue is when ever I stop at light or anything and I am waiting to go my bike will stall if I don't blip the throttle every so often. Is this a too rich or too lean issue ? The bike idles at about 1400rpm

Second issue is while cruising around at 30-60km/hr the bike will stutter and faulter a bit. Again a carb issue. But where do I start? When I bought the bike I cleaned the carbs and checked it all out the butterflies are synced or damn close to it. I haven't done the dead cylinder method yet as I have a pamco and I'm not 100% clear on how to ground my caps safely. Ie. Can I clamp a wire to the plug threads and the. To a fin?

The bike is a 75 with BS38s so no barbs for vacuum syncing

Thanks again guys

Yes, you should adjust the mixture screws, using the dead cylinder method. My picture shows a simple tool I use. I use a short length of wire that is clamped to the spark plug body with a hose clamp. The other end of the wire is just an alligator clip to clip it to an engine fin.

Warm up the engine (use a fan for cooling), then shut it off and remove one spark plug which is set aside. Connect your test spark plug to the spark plug wire. Start the engine running on just the one cylinder and adjust the mixture screw on that side. It works best if you use the carbs throttle speed screw to run the rpm on the low side, perhaps down around 800 to 1000 rpm.

Edit: Its important that the carb butterflys are perfectly sychronized, before doing the dead cylinder setting of mixture screws. If the carbs are on the bench, then a "piece of paper" feeler gauge is quite accurate. If carbs are on the bike, then I use a manometer.

 

[3andit]

Thanks RG that's exactly what I needed to see! Don't want to fry something haha I'll report back when I get a chance to try it out.

 

[3andit]

Hey guys,

So I tried my hand at the dead cylinder method after recreating retiredgentlemans plug ground and I followed the directions laid out in the guide , but when I would turn the fuel screw In or out from its .75 set point there was no change in idle weather it was screwed all the way in our out a few turns... I did turn the fuel off to the dead cylinder when doing this, should I have left it on ? Or am I not doing something right ? I even pulled my carbs off and cleaned them again, this time I took note of the Jets and the pilot is 45 main 127.5

Thanks again for all your help

 

[retiredgentleman]

Hey guys,

So I tried my hand at the dead cylinder method after recreating retiredgentlemans plug ground and I followed the directions laid out in the guide , but when I would turn the fuel screw In or out from its .75 set point there was no change in idle weather it was screwed all the way in our out a few turns... I did turn the fuel off to the dead cylinder when doing this, should I have left it on ? Or am I not doing something right ? I even pulled my carbs off and cleaned them again, this time I took note of the Jets and the pilot is 45 main 127.5

Thanks again for all your help

It does not matter what you do with the fuel to the dead cylinder.

You said the engine only idles down to 1400 rpm. That tells me that you have extra fuel/air going to the engine via the pilot jet and the butterflys. That is why you see no change when you adjust the mixture screws. You have to eliminate this extra fuel/air mixture before the dead cylinder method will work.

First thing is that the butterfly on each carb must be able to close fully. If the butterfly screws have been removed in the past, then the butterfly plate may not be centred in the carb bore.If not centred then the butterfly will not be able to close fully, i.e. the plate binds on one edge and stays slightly open. You will have to remove the carbs to check that.

Caution: In the next step, you must use a screw driver that fits the butterfly screws perfectly. If you don't, you will strip the screw heads. They are JIS screws, so a regular phillips does not fit properly. Its best to buy JIS screw drivers. I have had success by blunting the point of the correct size phillips, so it fits exactly into the head of the JIS screws, but that might not work for you.

Once the carbs are on the bench, back out the throttle speed screw, so that the throttle spring is forcing the butterfly closed. You should not be able to see light under the butterfly. If you can see light, then you will have to loosen the butterfly screws, and allow the plate to snap closed so that the plate is self alined in the carb bore. Once alined correctly, the screws can be re-tightened. Its wise to use blue lock-tite on those small screws.

With 1975 carbs, which I believe are not linked, you will have to follow the correct steps to be sure they are correctly sync'd.

Also while the carbs are on the bench, you need to try to wiggle the needle jet. It should not wiggle. If it does, you must replace the rubber O-ring. A bad O-ring allows extra fue/air, and a high idle results. The needle jet is just a push fit, so they can be tapped out for inspection.

Also, if you have any air leakage around the carb manifolds or the carbs themselves, the dead cylinder method will not work.

 

[3andit]

Thanks for the info RG I did have a look at the butterflies but I didn't not even notice any O-rings in the pilot or anything, maybe they are missing. I know there is no leaks around the carbs already I checked that first thing. I will report back this evening when I get home and confirm everything

 

[retiredgentleman]

Thanks for the info RG I did have a look at the butterflies but I didn't not even notice any O-rings in the pilot or anything, maybe they are missing. I know there is no leaks around the carbs already I checked that first thing. I will report back this evening when I get home and confirm everything

Not in the pilot jets, the O-ring I'm taliking about is on the needle jet.

 

[3andit]

Ok gotcha ! I'll have a look

 

[XSLeo]

You can't shut off the fuel to just one carb. There is a crossover tube between the fuel inlets of the carbs.
When you "kill" one cylinder you should back off the idle speed screw on the running cylinder till it runs as slow as it can without stalling. Then try the mix screw adjustment.
Leo