One side good, one sick. Arrgh!

So, after putting it aside for months, I've returned to working on my '69 350. It's driving me nuts! Left side runs well, right side starts and idles ok, but revving it and putting any load on it - right side starts breaking up and missing. I've done all the normal tune up stuff a couple times. New points, condensors, coils, set point gaps and static timing, lube auto advance, cleaned carbs, set floats, replaced diaphragms, set valves, compression check (very good and same on both sides). The bike sat for 40 years, and although the odometer only reads 3,xxx miles, the cosmetics of the bike (it has patina in spades) might suggest otherwise - I know virtually nothing of it's history. The plug is getting wet so I don't think it's a fuel delivery problem, certainly feels like ignition. But spark looks great, not seeing any significant arcing at the points. Watching a timing light blink while the engine is running doesn't look like the sparking is getting erratic.

Anyway, I'm throwing this out partly to vent my frustration, but also hoping for a pearl of wisdom or 2, if anybody has some to share.

Steve

Have you tried lifting the throttle arm on the right side carburetor independently to see how the motor responds with no load?

If you remove the air box on the right side, what happens if you cover the carburetor intake with your hand? (Simulating the choke, but only on that cylinder.)

Have you tried swapping the coils or swapping the condenser leads to make sure both are good and grounded properly?

How many turns out are the mixture screws? Does the one on the right have any effect on the idle speed?

What point gap did you use?

Any chance your choke flap linkage isn't hooked up?

Moved to 350 Electrical and Ignition section.

+1 on checking the right side choke linkage connection based on the mention of wetness of the right plug.

Thanks for the comments/suggestions - much appreciated. Haven't had much time to follow up so far but did pop the airboxes. Confirmed the choke linkage is working fine, in fact that was even the carb I'd removed the little flap from as the spring had broken. If I cover the carb mouth with my hand, there's good vacuum, it will want to completely die and my hand gets soaked with gas. I currently have the mixture screws at 1 turn out on both sides. If I just actuate the right side throttle it'll rev up but break up just like when both are being actuated - also get white smoke. Both carb slides look to have about the same movement when you rev it up.

Will move on to re-rechecking ignition next...

Steve

And you're sure the right diaphragm is solid? I'm not familiar with the replacement options out there but it's been mentioned here that some are better than others and can be replaced without causing issues with the original slide attachment design.

Could be weak spark due to a failing condenser.

ancientdad said:

And you're sure the right diaphragm is solid? I'm not familiar with the replacement options out there but it's been mentioned here that some are better than others and can be replaced without causing issues with the original slide attachment design.

Click to expand...

Yeah, I replaced both with new ones from 4into1, which seemed to be the "more original design" ones. They were thin and allowed use of the original mounting rings. Install was a little tricky but I'm pretty sure they came out well.

Well, it's fixed. The short answer is - I'm an idiot. The longer story... After going back through everything - changing condensor, coil, re-setting valves, floats, ignition gaps and timing and having no joy, I decided I'd install the carb rebuild kits that came with the bike when I bought it. Thought possibly needle was worn, needle jet was oval, who knows. The carbs originally cleaned up well enough that I figured no point in not using the original parts. So as I'm doing the right carb with all the bits out, blasting solvent through every orifice is clear - I do the 2 ports on the top of throat that provide the air flow to the bottom of the diaphragm - and find one of them is completely plugged with some schmutz.

How I missed this the first couple times around, I have no idea. Probably was doing it late at night after a few beers, that's the only excuse I can come up with. Anyway finished putting in the new parts in both carbs, put the bike all back together and rode for ~10 miles, and I'm THRILLED to report it runs like a top! Just had to adjust the idle but it's running like I'm sure it hasn't in 40 years!

Kind of embarrassing, but I'm so tickled right now, I'm not ashamed to admit my faux pas!

"95% of ignition problems are carburetion" :lol: :lol: :lol: