Reed Valve Breather

I have a '74 R90s that I installed the new type reed breather valve. I oriented it to face the right carb (but now I'm finding this might be wrong.

Most info. I find says to face the opening towards the 11 o'clock position, as when sitting on the bike. This would be about 180 degrees opposite of how it's oriented now. Also, I just replaced the original disc system with the new reed system and used the stock cover, which of course directs oil mist into the right Dellorto carb.

Does it matter?

I'm chasing down a weird rough idling issue and trying to eliminate anything I haven't thought of.

Thanks much,

RPGR90s

Tom Cutter had indicated that the orientation should be with the mounting screw facing the right foot peg, so that the opening would be 11:00 as you suggest. I think this helps to minimize how the air has to turn to get into the outlet to go to the carb. On my R100/7, the air goes forward through a engine cavity before emerging into a rubber hose run to the right carb. Not exactly sure how it's oriented for the /6. But I think it would work best if the opening had the most direct route to the outlet from the cover.

Can't say it would have that kind of effect on idling...but you never know. I'd probably track other things down before diving under the starter cover. Check the usual suspects, valve clearances being the easiest to check. Is it idling rough on one side only? Do the usual swapping of things to see if the problem moves. Could be plugs, plug wires, corrosion in the coil tower...

20774 said:

Tom Cutter had indicated that the orientation should be with the mounting screw facing the right foot peg, so that the opening would be 11:00 as you suggest. I think this helps to minimize how the air has to turn to get into the outlet to go to the carb. On my R100/7, the air goes forward through a engine cavity before emerging into a rubber hose run to the right carb. Not exactly sure how it's oriented for the /6. But I think it would work best if the opening had the most direct route to the outlet from the cover.

Can't say it would have that kind of effect on idling...but you never know. I'd probably track other things down before diving under the starter cover. Check the usual suspects, valve clearances being the easiest to check. Is it idling rough on one side only? Do the usual swapping of things to see if the problem moves. Could be plugs, plug wires, corrosion in the coil tower...

Click to expand...

Yes sir. Usual suspects tracked down. Valve clearances are .006" intake and .008" exhaust.

the problem stays with the right cylinder. I installed my older Dellorto carb on the right side and started the bike. Idle smoothed right out so figured something in the newer right side carb. Let the bike warm up in my garage for about 15 min., with cooling fans on the cylinders and set the idle and mixture and it was idling perfect at 900 rpm, smooth as silk.

Went for a five mile ride and at the first stop sign, idle was rough again. Anything above about 1500 rpm seems fine. Plenty of power, silky smooth, but returning to my house, idle was still rough and more importantly, NOW the right carb mixture screw had no effect. Even closing it completely would not stall the motor. That's when I pulled the valve covers and checked the valve clearances. And checked the spark on both sides. Appears blue and crisp, plugs gapped at .028".

Bike has the Alpha V.3 Ignition, with the correct plug wires from Rick Jones as well as an older Dyna Green dual output coil. Measured the primary and secondary windings just to check. 3 ohms on the primary, 13,700 ohms on the secondary, which appears to be in spec. This problem was happening with the stock points and condenser so don't think that's the issue. Just trying to think what it might be and that led me to maybe the breather, which of course vents to the right side carb only.

Something's amiss on the right side for sure.

The plug gap of 0.028" is on the wide end of the scale. I typically run mine at 0.026" which is in the middle. Not sure it would make much difference running, but it could help a bike to start easier with a smaller gap.

With the stock ignition, the resistance from cap to cap is supposed to be around 20-22K ohms. What would the measurement be with the Alpha? What does Rick suggest? So maybe your 13.7K reading includes both coils? If you have the 5K ohm spark plug caps, the total reading cap to cap seems like it would be in the 23-24K ohms range...doesn't seem out of whack.

Breather

Thinking about this some more and going back to what I've done, I had the heads rebuilt a few years ago and that's when I first started seeing the problem.

New valves, springs, guides and seats were re-faced.

I've never had an engine with a sticky valve but could that be what's going on?

Maybe a compression or leak down test is in order once I've warmed it up?

Thanks,

RPGR90s

I can't see the breather causing your issue.

When you think that the old style was just a round disk that vented around the disk and into the vent tube, the orientation of the new style reed valve should have little affect. It's purpose is the same as the old one in that it is there to relieve crank case pressure. The air stream going by the tube opening before the carb, would help draw this pressure and oil mist into the right carb on the old style round air filter. What is basically going on is that you have an air of high pressure flowing to an area of low pressure. The real problem with the old round vents is that they would break, or quit working and they made an annoying noise.

Even with the newer style rectangular air filter set up and the fact that the tube coming from the vent is split to both air intakes, the bulk of the air & oil mist still goes to the right carb.

I installed a catch can between the crank case breather and air filter. I have no vent oil collecting on the floor of the head before it goes into the intake valve. Most of what is collected in the catch can is water with a small amount of oil and I dump it out every couple of thousand miles or when I change the oil. The amount of oil/water collected would be in teaspoon amounts, very little actually at least on a good motor.

Breather and Poor Idle

I think I got it figured out. The right side Dellorto had two air leaks as revealed by spraying carb cleaner around the intake manifold area (as it seals on the carb) and the choke cover with the engine running. I sealed both areas, and went for a long ride and idle is silky smooth and consistent again.

Oh, and my float level was way off on the right carb.

In troubleshooting, I checked for sticking valves, compression (175 right side, 185 left side).
I also changed the breather orientation to point towards 11 o'clock, although I can't believe this has any effect.

When running right, this old girl still pulls like a locomotive.

Thanks everyone for your help.

RPGR90s

It took a few turns to get there, but you found one of the simple solutions! Nice that you kept at it to figure out what the problem was. And to top it off, you likely have your reed valve oriented correctly...or not depending on your point of view!

Eilenberger's Law states that your problem will be on the last thing you touched.