Stumped... CB350 Won't Start

So stumped that I had to join Do The Ton. First post so don't tear me to shreds! Appreciate the read.

Got a '72 CB350 I've had for a few years now. Buddy of mine got in a small accident on it a while back (he's fine) but it's since been fixed by my regular show. Damage was mostly the front end. Bent the front forks and took out the headlight and front assembly. Since I've got it back it's been problem after problem.

First few rides after getting it back it seemed like it wouldn't hold a charge. Was able to diagnose it with my shop and figure out it needed a new charging system so I bought the Rick's Stator Kit.

http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-electronic-parts-ricks-electric-hot-shot-honda-cb350-cl350-cb360-cl360-charging-kit-99-101.html

Had the shop charge the bike to ride it home so I could put the new kit in myself. When I left, I barely made it to the end of the street... Turns out gas was barely dripping out the petcock. Towed it home and waited for the new petcock to come in the mail.

Installed the new petcock, saw I was getting plenty of gas in both carbs and thought great, all fixed.

Nope. Won't start and haven't been able to start it. Can't even get to putting the charging system yet! So frustrating since it was running even when I picked it up from the shop!

Worth noting that the carbs we're replaced with the Mikuni kit about a year ago and I've already replaced the spark plugs, checked the ignition coils, points and timing in trying to troubleshoot it.

Any suggestions are greatly appreciated. I'm really trying to solve this one myself and avoid going back to the shop.

Thanks!

A fully charged battery is essential for these bikes.
Try jumping the battery from a non-running car.

+1 on checking for a full battery. Also check to make sure the main fuse hasn't blown. When I rebuilt my 350's wiring, I accidentally caused a short, which blew the fuse. Took me embarrassingly long to realize it. With the fuse blown you can have full battery but nothing will be able to get through to the coils to fire the ignition.

If the battery and fuse are fine then I would check to make sure you are getting spark at the plugs. Pull one sparkplug from head and with the high tension lead attached and the tip of the pulled plug touching bare metal on the head or case, kick the bike over. You should be able to clearly see it spark. No clue about your experience so I feel obliged to mention that you should not hold the sparkplug with your bare hands while doing this (holding it by the plug boot is okay though).

If there's no spark then I would go back over the points and timing system. You mentioned that you did something with it so it's possible it could be out of spec. Refer to the shop manual or the numerous threads on here for full procedures.

Thanks for the suggestions guys! Much appreciated. Trying these out this week and will keep you updated.

Still stumped guys...

Charged the battery with a trickle charger for 6 hours and event tested the spark plugs like BarnBurner suggested but still nothing. I was seeing a clean blue-ish / purple spark too which is good.

Any other suggestions? Starting to wonder if my carbs have something stuck or need to be cleaned or re-tuned but you'd think it'd at least start and run rough right?

Is the timing okay?
how about compression?
Does how were the plugs? Were they damp by any chance? Maybe try throwing some new plugs in.

tsivero said:

Still stumped guys...

Charged the battery with a trickle charger for 6 hours and event tested the spark plugs like BarnBurner suggested but still nothing. I was seeing a clean blue-ish / purple spark too which is good.

Any other suggestions? Starting to wonder if my carbs have something stuck or need to be cleaned or re-tuned but you'd think it'd at least start and run rough right?

Click to expand...

I really recommend trying a different battery. If the battery is bad, charging it wont help much. Hook it up to a car and cross that off the list. Then I would make sure you have spark, then check timing.

Your motorcycle's engine only needs 4 things to run: fuel, air, spark and a compressed cylinder for those to be combined. Air is a given unless you've completely restricted the intake side of the carb. You said you were getting a fat blue spark so we can cross spark off the list (for the moment). I'd cross compression off also since this was running very recently. That leaves fuel.

To diagnose the fuel system I'd start by pulling off the hoses coming from the petcock to the carburetors and see if fuel is flowing when the petcock is turned to the on position. If fuel is making it through then I would pull the carbs off, clean the jet passages well with compressed air, check the float needle for proper operation, and check the float height. Then reinstall and try to fire it up. If it still does not fire pull the plugs and smell them for fuel. If you can detect it, or the plugs appear damp at least, chances are that fuel is getting to the cylinder.

If you have all 4 things then you get into higher order problems, like timing. If your timing is off you may be getting air spark and fuel but it is not at the proper time to produce combustion. In that case I would double check your timing with a test light (search here for instructions).

It lives! Got to say you guys were a ton of help.

Once I took the carbs off to check them, I knew something was immediately wrong when I took noticed a white powder substance in the drain plug (before even taking them apart). Once I did remove the bottom of the float, a dust storm appeared. The white powder had glombed up in a spider web fashion and was in a large clump, in both carbs! Definitely not good. Went to my local shop and they said it looked like carbs that had been sitting for years. They ran them through their dishwasher type thing to clean them. I also cleaned them even further with carb cleaner after and re-adjusted the float level to spec. After a few kicks she started right up. ;D ;D ;D

Good news is she's running. Bad news is she won't do much more than a healthy idle. Once I give a little gas, it stumbles and dies. Won't go anywhere in gear either.

Thinking it's a float level adjustment but curious to other suggestions.

What kind of a Mikuni kit did you install? If you mean new carbs then are they set up for your bike, were they new carbs? Did you touch the timing or valve setting if not then I would check the carb setup more closely. Test that battery too, some of these older bike do not charge well at the lower revs and you need a good battery to get a good spark.