Rocker Clearance Adjustment

Right cylinder of my '73 850 is still intermitently misfiring at idle. Left side is steady, and strong, but right will sort of cough. I cleaned out the air circuit of the Amal 932 carbs with wire and carb cleaner, then blew out the circuit with air. I switch from NGK BP8ES to BP7ES plugs.Right carb gets excellent fuel flow. I am thinking this is probably an ignition issue. Boyer stator wires were replaced a few weeks ago. Today I decided to check the rocker clearances. Following the shop manual I found that when checking clearances for inlet and exhaust, the clearances were less than .006, and .008 . I found that when adjusting them that there was some slight play in the rocker arm if I lifted up on the arm, so that I didn't know if the feeler guage should nip with the rocker lifted up, or if the guage should nip with the rocker pushed to the down position. I elected to set the clearance in reference to the arm in the pushed down position, thinking that at least the clearance would be more than adequate. After starting up the engine, the left side was again strong and steady, but the right side is much the same, and seems like there is less compression. If you put your ear near the right muffler, you can hear the exhaust tone is hollow sounding, which was not apparent before I did the adjustment. I will have to go back and check those clearances again, but I would like to know if I did it the right way. I don't believe I did.

I believe it should be done with the arm "up" if there's play. At least that's how it's done on airhead BMWs. Really shouldn't make much difference if you're adjusting to "moderate drag." You won't get that much drag without the feeler gauge exerting enough pressure on the arm to use up its play.

Not an expert - could be wrong.

This doesn't sound to me as a valve adjustment issue.
Adjusting with arm up sounds right to me.
Unless one valve was obviously over tight enough to cause leakage or loose enough to not open enough for adequate intake or exhaust function.
Since you've verified they are reasonably well adjusted I'd discount that possibility.
You've tried fresh plugs so that's not it.
Throttle cables and idle screws adjusted so both carbs open equal at idle. Chokes equal setting.
Did you trade plug wires over to see if one is bad?
Swapping coils to see if problem moves to other side.
Compression check to see if bad rings/valve?
Do the carbs have enough miles on them (15-20K) that possible slide wear, pretty common in Amals?


Bob

Right cylinder of my '73 850 is still intermitently misfiring at idle.

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Perhaps the carbs are a little out of sync. Try turning the right hand carb slide stop in a little to lift its tickover, it costs you nothing to try.

Cash

Yes, I didn't think that the valve clearances would be the erratic idle issue source, but I had the tank off, so thought I'd check them. My spark plug wires are too short to cross over, so will try to find a longer set. I will reset the rocker clearances properly, with the rocker pulled up for each valve. I noticed that the coil on the left side is pinched from the clamp, but that is the good side. I will try wrapping some electrical tape around each coil, where they clamp, and see if there may be a bit of shorting relieved. Thank you for the input.

Well I'm no expert but I can tell you I had this exact same problem with a Moto Guzzi V-50 Monza I had for years. It would get better as the bike warmed up but drove me nuts. Tried all the usuale stuff. Carbs, adjustments etc. Two pro Guzzi shops didn't find the cure. Finaly I put a used set of Dyna Coils on & it ran like a little pissed off banshee after that. Check ALL your coil connections. Take them off & switch the whole asembly (coil, plug wire, plug ) from the left to right side. See if the trouble follows the coil. Good luck.

In order to have a set of carbs run as a pair the floats must be set as a pair before anything else. This is the first thing you have to be sure of before you touch a screw on the carb.

old adage: 90% of "carburation" problems are resolved in an "electrical" solution

Well, I re-did the rocker clearances, and the engine runs great...very strong. I was able to move coils enough so the spark plug wires would crossover and reach the plugs on the opposite cylinder...seems I have a carburation issue, as the intermittent cough at idle remains on the right cylinder. I noticed that the right carb float bowl gasket sticks out somewhat. I removed the float bowl, and I see that the gasket is not a perfect fit...could be the previous owner replaced the original gasket with a generic, rather than an Amal OEM gasket. The air/fuel mixture holes were a bit obstructed by that gasket, so I used drill bits to gradually increase the opening, then gave the float bowl a good cleaning even tho it looked fine. I replaced the float bowl, then switched the spark plugs wire back. Bike runs a touch better, but I now wonder if either the right float needs adjusting, or the throttle adjust screw on that carb needs proper settting as I find the rightso cylinder fire real fine with some throttle. How can the float be adjusted, and what is the proper procedure to setting the throttle screws. Since the left side runs well, would I find it's throttle screw number of turns from zero, then reset it and the right side accordingly?
thanks

A simple method is outlined in the Norton manual. 1st make sure the slides move up and down in the bores equally. Check by feel with your fingers to see they disappear at the top in sync and visually at the bottom to make sure they are the same distance before you touch the throttle grip. Adjust with the cable adjusters on top the carbs to make them equal. Take one plug wire off and find the sweet spot to have the bike idle at 2000 rpm's. Do the other cylinder and then hook both plugs back up and back off on the adjustment screws equally on both sides to get 1200 rpm idle.

This one thing about removing the plug wire on a running bike is very bad advice and yes it is in the manual. When the secondary winding of the coil cannot find ground Via the spark plug it finds ground somewhere else normally in side the coil body not good. There are many posts on setting up carbs step by step on this site.

You remove the plug wire on a running bike (unless you're wearing very thick rubber gloves) and I can tell you where that current will find a ground - and it will start with your hand and end up at your heels.... NOT a good idea. Not so great for electronic ignition either....

I'm not following the original question about valve adjustment... up or down? You set the left intake clearance when the right intake valve is fully open (down), and vice versa. Same with exhausts.

I too have a misfire on one cylinder at idle that drives me nuts. I've replaced everything except the engine...

maylar, I found that there is a bit of play where you can physically move the rockers up and down, creating a tap sound, against the top of the valve stem. I first adjusted the rocker tappet with the rocker in the "down" position, which was a mistake. I took advice from others who suggested adjusting the rocker tappet with the rocker in the "up" position, and I found that the engine performs much better.

To set my carb throttle screws, I will remove the plug from the cylinder, attach the plug wire, and ground the plug against the cylinder head. This would avoid the ignition searching for ground.