Hello everyone, Jared here, I am relatively new to the motorcycle world, and 2 stroke world. For my last birthday my Grandpa gave me his rd350, and it was sitting for a few years. Now what i've done is tear down the carbs a few times, got carb rebuild kits, new gaskets etc. and changed the oil. upon trying to kick it over, it will only fire up if i place my hand over one of the carbs. Now when it is idling, will only hardly idle on choke and as soon as I turn the choke off, it dies. You might be thinking the jets are clogged and I thought that too, But every time i take the carbs off the jets are nice and clean. Another weird thing is white smoke is only coming out of the kick side exhaust, none or hardly any smoke is coming out of the clutch side. Im thinking maybe the left cylinder isnt running consistently? Ive checked both sides for spark, and have replaced plugs. Im running out of ideas. Anyone have any suggestions? They would be greatly appreciated!

Thanks so much

-Jared

Possibly if its sat for a very long time the smoke could be just oil that's gravity fed through the pump with a faulty miniature ball & spring on the feed from the pump union to 'that' cylinder only. Then the oil gets fire out into the exhaust & smokes for a very long road ride. BUT--a favourite trick on those to cause bad running is people have both slides out & put them back in the wrong cab so the cutaway ends up facing the motor & goes super rich. Doesn't actualy sound that way from what you say but check it amyway. Another trick is people don't connect the choke linking hose between carbs & tat would go super lean on the right carm & weird on the left without thinking too hard. So go check that first [those two things first]. Welcome too.
But wait--there's more haha. On reflection by meory only one bowl has the choke jet so 'that' bowl must go to the left carb. Choke jet is a little one down in a cavity & the choke tube goes down there IMPORTANT.

+1 to RT325's comments.

If you got the jets from a non Mikuni kit, junk them and buy original Mikunis (they are still available).

White smoke is usually linked to gearbox oil - are you sure it isn't a light blue smoke?

Photos of your bike would be great (if not already posted elsewhere!).

I didn't read your post properly so what i said may not fully apply to your problem but all things to keep in mind as have dealt with them all when these bikes were popular back in the day. What i used to do if one cylinder was running bad compared to other--is pull one carb cable up at a time to note how each cylinder speeds up from idle compared to the other. Wont hurt doing that but don't get the cable so you cant get it back in the adjuster so you can't slow it right down. Not that difficult really. But if you have the later carbs with tall slides & tops then you'll have angled cable pieces C-clipped into the top & i can't remember if the cable pulls out of the adjuster at the top of the angled bit or if the cable is retained in adjuster. Link below to show carb top differences.

www.partzilla.com/catalog/yamaha/motorcy...75/rd350b/carburetor

Pic in post #4 is slightly confusing as don't show both carbs & differences. Shows some parts unavailable "76 RD400 shows the old style tops so i don't know. & also shows both bowls separate with different part numbers due to the choke operating only in one carb.
www.partzilla.com/catalog/yamaha/motorcy...76/rd400c/carburetor

I definitely echo all the above suggestions.
Especially the hose between the two carbs, mix-matched floats & slides, and the off brand jets. Do not use the jets from those kits. Buy genuine mikuni from Sudco, hvccycle, yambits (UK), etc. Do you have the old jets that were in there before you tore into the carbs? Try to match those numbers to start with. 

Here is a little write up that might help you: rdlccrazy.proboards.com/thread/7089/help-setting-carbs

Did you set the float height? Did you sync the carbs (or set them close enough)? Does it matter which carb you place your hand over to get it to fire? And speaking of that, does this bike have the original airbox or a aftermarket pod/paper filter. Test starting the bike without an air filter element could be letting more air in than its jetted for. have you tested started it with your air box or filter element installed properly? 

Its hard to say without more info.  But the process would be to go down the list and rule out things till you figure out the cause of the problem.  

One thing I didn't see you mention is the battery. Is it new and fully charged? Unlike the DT series, the RD350 requires a fully charged battery for it to run correctly on both cylinders. Usually spark will fail on one cylinder before the other when the battery dies. It could be possible that you have spark when the plug is out, but the spark fails under compression.

I usually think of the twins as two separate engines strapped together when troubleshooting. You can check which one is running my measuring the temps of the headers after running it. Make sure you have a nice healthy spark (replace battery, clean and adjust points), check the compression and, then move onto fuel.

I've had 9 RDs of various flavors over the years and dead batteries/poor charging systems have plagued pretty much all of them. Issues usually manifest themselves with only running poorly on one cylinder or not running at all.

Does side that is not smoking have compression?

Also make sure carb slides are in correct carbs.  Cutaway on slide faces rear of bike.  Easy to accidentally swap them.