Good News/Bad News

[Downeaster]

The Good News is that the charging problem is definitely fixed. 14+ volts @2500 RPM.

The Bad News is that that didn't improve my left cylinder problem one damn bit.

Starting over at the beginning. Checked point gap (a little tight but in spec) noticed the left cylinder points were pitted a little so cleaned them up.

Checked the valve lash, it's good. Checked the compression on the left side, 140psi on a warm engine.

I was a bit over-confident this morning and put all the airboxes and suchlike back on the bike before I took it for a test drive. Still runs great at mid-range and above, still runs on right cylinder only at idle.

Crap.

Back to square one, pull the airboxes off, pull the carbs off and tear that left one down again.

Unless someone has a better idea or a Magic Wand...

 

[TeeCat]

Hey, DE... I may have missed it in the other thread, but have you ruled out an air leak on the offending side (throttle shaft seals, carb boot)? I suggest this because I'm wondering if you might be getting enough of a rich mixture off-idle and above to compensate for leanness (due to air) in the pilot circuit (at idle). I may be off the planet there, but just a thought.

TC

 

[1974jh5]

'90% of carb problems are actually ignition'. I'd put another plug on that left wire, ground it solidly to the engine and be REAL sure I had spark before digging into the carbs again.

Assuming you verify that you have spark, before snatching the carbs back off check the balance. If the throttle valve on the left cylinder is closing all the way at idle but the right is not, [Jamie] 'there's your problem'.[/Jamie]. A manometer is easy to make.

That's a 4 cylinder version, a 2 cylinder is even easier. You just make a single loop in some 3/16" clear vinyl tubing then put ~2 oz of ATF (or even motor oil) in the tube, then connect one side to each carb adapter's vacuum tap and fire it up. Watch the level of fluid in the tubes. The side with the lower level of fluid is the one that needs to be opened more with the balance screw.

If they are both balanced according to the fluid level but the left side is still dead at idle then I'd be tempted to pull the slow speed jet out of that one and check it very carefully.

 

[jayel]

now that it's charging proper try the jumper from battery to coils trick again, have you tried switching the coils themselves? switch points condenser wires and cross plug leads to opposite cylinder no need to actually unbolt stuff... but cleaning the carbs never hurts...... much

 

[picker]

It shouldnt be too hard to find the source. Start the bike and use some fuel in a spray bottle and squirt a little into the intake of the offending carb, if it jumps and responds then it is fuel related, if not then electrical.
Also check that pilot jet. That little opening gets clogged real easy.

 

[mouser]

I'm thinking throttle flaps. I had chronic problems with one cylinder. When you have the carbs off keep them bolted together with the top mount and the bottom angle support and check them by holding them up to a light with the slides open. Adjust the flaps then sync them. This cured the issue for me. Good luck!

 

[Downeaster]

All more better now!

Hauled the carbs off (again...) and tore the left one down. Checked all the orifices with particular attention paid to the pilot jet and the mixture screw passages.

Didn't really find anything definite.

While reassembling the carb, I got to looking at the bowl gasket. It appears to be ambidextrous, but I flopped it 180º from where it was just as an experiment.

Runs perfectly. 2-1/2 turns out on the mixture screw as a starting point, idles well, no stumbling on acceleration, pulls like a freight train.

Now I'll do the dead cylinder adjustment and sync them and I think I'm done frigging with carbs.

48º and sunny, so I rode for a couple of miles just to be sure . Don't want to push things both because there's a lot of sand (and quite possibly the hidden patch of ice) on the roads and because I don't have an inspection sticker for it and the local constable is a prick.

Doin' the Happy Dance here in East Overshoe!

 

[jayel]

ah good now you are a certified (able) XS mavin you get to walk the next guy thru his problem

 

[1974jh5]

Glad it's straightened out! Something I learned the hard way a long time ago: if the pilot jet is not fully seated or if there's a tiny piece of grit etc on that 'cone' there will be a leak at the tip and that will really screw up the mixture. It will make the thing impossible to tune also.