Author Topic: 74 honda cb350f wont start  (Read 4781 times)

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Offline rice rat74

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74 honda cb350f wont start
« on: August 09, 2012, 02:33:16 AM »
Could use help getting non-running bike 18 years past back to life. So far I replaced coils w/dyna+solid core wires. put in a K&L carb kit. minus the new needles. Put on open air filter pods. Cleaned pertinent connections, set & double checked points gap & static timing. I have spark at both points and at spark plugs. It will light pop(spit) once only while it's cranking over w/ 1-1.25 turns out on carb. air screws. The exhaust baffles are not installed. I've tested the basic starting/charging electrical components minus the stator. Is this a lean carb. issue ?  open to any suggestions, thanks.

Offline Dimitri13

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Re: 74 honda cb350f wont start
« Reply #1 on: August 09, 2012, 02:38:41 AM »
The carbs are very lean, considering you're using pods and a baffle-less exhaust with the stock jets.

Did you do the 3000 mile tune-up?

Offline rice rat74

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Re: 74 honda cb350f wont start
« Reply #2 on: August 09, 2012, 03:57:34 AM »
I've change oil+filter. Cleaned lt. surface rust out of inside of gas tank w/ a three minute bath of "the works" cleaner, rinsed 4x's then denatured alcohol 2x's to absorb any residual water.  universal paper inline fuel filter added. The plugs are new, but I have on good used Accell copper core wire and stock end caps. No resistance on solid core plug wires, and no unusual high Ohm numbers reading w/ cap ends tested.  New points were put on the bike before long storage and it was never run. I ran a points file on contacts before setting gap just to be safe. No doubt.... probably missing some important steps somewhere right ?  3k mi.

Offline flybox1

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Re: 74 honda cb350f wont start
« Reply #3 on: August 09, 2012, 07:40:39 AM »
What exhaust do you have?  you didnt say.  what jets do you have in there? needle clip position?  did you just swap parts, or did you clean and bench sync?

you're lean. its probably choking out as you probably have not cleaned or bench sync'd your carbs.  you'll ultimately need to go to 90's or 100 mains.  and drop the needle clip position.

for what you have in there now, you'll need to turn your air mixture screw in to 1/2 or 3/4 turns out to richen you up to run, and if it runs it will run poorly.  choke lever up, and then when warmed, press it down.  check your idle set screw on the right end of the right end of your carbs.

Did you pull out the emulsifier tube from under your main jet to clean?   
set your valves.  see if it starts.  if it does, do a vacuum sync of your carbs. 
then its on to plug chops to dial in your A/F mixture...

« Last Edit: August 09, 2012, 08:10:11 AM by flybox1 »
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline rice rat74

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Re: 74 honda cb350f wont start
« Reply #4 on: August 09, 2012, 05:35:15 PM »

Thanks for the reply. 4into2 exhaust, stock aftermarket jets, default needle clip position. Before, took apart soaked w/solvent & cleaned the carbs with brushes n wires., must confess didn't use compressed air,  found out later that is a part of the process. So maybe adj. the needle one position and bump the main up to richen it, but if it wont start, it's hard to gauge right ?  I've read several  bench sych posts with 1/8in. drill bit, and another says 1/16in. and the other w/ paper clip n last one w/ tight clearances but accurately wrong micrometer.  I didn't pull out any internal metal tube in the carbs. Based on your response I should open carbs, remove emulsifier tube?  how is that safely done? , use compressed air in all orifices (#&^*in forgot to do), jet 2 sizes up to start, move one needle position up, then set valves. Which bench sych.  is most popular and/or more accurate of the bunch here ?   

Offline harisuluv

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Re: 74 honda cb350f wont start
« Reply #5 on: August 10, 2012, 06:05:52 AM »
That is a very long laundry list of stuff to do.  I would try and not try and do all them at once, cause you won't know what it was that you did that had a specific effect on the bike.  Basically, you probably aren't going to get EVERYTHING exactly right the first time.  It is possible but not likely.  With pods and no baffles however I think it is safe to say that you are running lean.  However, what is the history of the bike, did you mod the airbox and exhaust or was it the previous owner.  It might be jetted properly but you missed something during the cleaning.  As you can see there are many variables, unfortunately that is probably going to mean you might have to take them on and off more than once.  What are your jet sizes, are they stock?  If not what size are they?  Seems like from what you have said you have done somewhat thorough job on the electrics, but not as extensive with the carbs. 

Commonly a 1/8" drill bit is used for bench syncing.  All this will do is sync each slide so they are all at the same level to start with.  The other part of bench syncing comes from setting them at that level where you still have a range of motion both ways to allow adjustment with the idle screw when it is running.  For example, I can adjust all them with the 1/8" bit and get them all synced at that level WITH the idle screw maxed or close to max in one direction.  They would all be "synced" but would not be able to be adjusted with the idle screw properly, if that makes any sense.

The emulsifier tubes are just pressed in, so they have to be pressed out.  It should not take a lot of force to do this and if it does there is something wrong.  The little flange opening where the needle goes into the emulsifer tube is thin, so you want to avoid pounding it out with something metal, or maybe you could get it out with a proper sized punch.  Basically don't be silly and use a screwdriver or something cause you are going to mangle it.  I use wooden dowels, gently. 

The emulsifier tube is a separate circuit from the idle circuit though, so your symptoms are not necessarily indicative of that being the problem, but that could still require cleaning.  From what I read you can't start the bike at all?  Basically it sounds like you need to go through those carbs properly, it can be a pain to do but people here will help you or answer any questions you might have.

I just finished this set of carbs and here is just what kind of visible effects can come from a bike sitting for a long time.  This is just what you can see, now imagine all the little passageways with similar problems. 


« Last Edit: August 10, 2012, 06:26:07 AM by harisuluv »

Offline flybox1

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Re: 74 honda cb350f wont start
« Reply #6 on: August 10, 2012, 06:51:07 AM »
 :o the dreaded black goo of death  :o

...but i bet they came out nice.
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline rice rat74

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Re: 74 honda cb350f wont start
« Reply #7 on: August 15, 2012, 07:21:09 PM »
Harisuluv,those are nasty looking decades of goop. Ok, I took the carbs off again and pulled the emulsifier tube out wired w/ .13 A guitar string and then soaked it along w/ carb. rack Instead of solvent or laquer thinner. I used Pine-sol from walmart in a cleaned cooler. The results were excellent. Fired up the air compressor and blew out all holes. Once primarily together, the float bowls were adj. to 27/32in. Readied the drain screw hole w/ heat tapered/ stretched 1/4in. clear tubing that will be watched  tomorrow when turning gas on and attempting to start once again. I don't get the bench synch. steps at all. Where do I start the Idle screw at ? It's now three turns in from the screw thread end being flush on the inside starting point. The jets are K&L brand stock sizes 75main, 35 slow. Moved air screw out to 3/4 turn out to hopefully start it Thur. Thanks for any ideas.

Offline rboe

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Re: 74 honda cb350f wont start
« Reply #8 on: August 15, 2012, 08:12:23 PM »
If it's not firing at all then you gotta ask yourself; is it getting any gas? You need spark, air and fuel. If the filter ain't plugged, sounds like you have the electrical covered (unless it's firing about 180 degrees off) but no mention of fuel getting into the cylinders. EVen if it is way lean it should at least fire a bit.

I skimmed the posts; are you getting a nice spark?

And check the dang kill switch. I've been burned a couple times by that bastard!
1974 CB350F
2008 XR650L
2012 Griso SE

Past iron
1971 Suzuki TS125
1977 Honda CJ360T
1981 Kawasaki 550Ltd
2000 Moto Guzzi Quota

Offline Spanner 1

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Re: 74 honda cb350f wont start
« Reply #9 on: August 15, 2012, 08:41:30 PM »
The bike should at least start despite pods and drag/open exhaust ( no effect on start/no start )...
If your happy with all 4 plugs sparking external to their plugholes, then are the plugs wet after a starting attempt ?
If your sure it's a carb problem; it's ignition,
If your sure it's an ignition problem; it's carbs....

Offline 72_350_FOUR

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Re: 74 honda cb350f wont start
« Reply #10 on: August 16, 2012, 10:26:16 AM »
I'd check the coil wires coming from the points plate, (end of the grey wire running up over your engine case, plug in with bullet connectors) ..make sure they are plugged in tight and correct. the PO of my bike had them switched.  They are close to the rear brake light wires under the left side panel.  Coil wires should be yellow to yellow, blue to blue.

Also my bike wouldn't start till I pulled the emulsifier tubes, (under the slides in your carbs) and made sure i could see light coming through those tiny little holes.. I used a toothbrush and stuck the bristles through the holes.

Just keep trying what these guys tell you and you'll figure it out.
1972 Honda CB350F

Offline rice rat74

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Re: 74 honda cb350f wont start
« Reply #11 on: August 19, 2012, 03:54:57 PM »
Ok, got carbs back on and give it some fuel down the line, and was about to see if it fires up and next thing I know all four carbs are puking gas out the mouths(pods off), and #1 over flow also all over the engine and floor(new problem).  A few days before I did adjust the floats to factory spec.21MM=27/32 following my two manuals and factory honda carb. manual photos/instructions. Rechecked all measurments *&*# times till blind. All but one carb. float height was waaaay MORE than than factory numbers. lt.smack w/ end of screwdriver for stuck valve, no change. Everything is clean enough to eat off of inside. Now I feel like a govt. worker. Fix it till it's broke........I mean seriously ?!  :o

Offline harisuluv

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Re: 74 honda cb350f wont start
« Reply #12 on: August 19, 2012, 04:07:35 PM »
Hmmm did you replace your float valves or did you use the old ones?  It seems like they are not functioning properly.

Offline robvangulik

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Re: 74 honda cb350f wont start
« Reply #13 on: August 19, 2012, 04:17:10 PM »
Solution is in the opening post: the points are sparking, the condensers are shot.
Replace them and try again.....

Offline rboe

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Re: 74 honda cb350f wont start
« Reply #14 on: August 19, 2012, 04:20:15 PM »
I replaced my float valves and when I placed the test fuel bottle on the bike it had so much head (a good three feet above the bike the float valves puked gas like crazy. Still does.

Found out, if you replace the male part of the float valves, and they are metal, you have to dress the seats (basically you lap them in like valves) so they will seal properly. Talking with a local fellow that builds race cars for a living says he laps them by attaching a bit of hose to the new needle then slowly twisting/spinning them by hand on the seat. I intend to use semi-chrome polish (it's handy) for my lapping compound.

With the heat in Phoenix I have begged off pulling the carbs again until it cools off.
1974 CB350F
2008 XR650L
2012 Griso SE

Past iron
1971 Suzuki TS125
1977 Honda CJ360T
1981 Kawasaki 550Ltd
2000 Moto Guzzi Quota

Offline Spanner 1

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Re: 74 honda cb350f wont start
« Reply #15 on: August 19, 2012, 09:02:18 PM »
rboe +1.... Toothpaste works great as a lapping compound too  :o... that's what I used on my K8 carbs ( the whole bike sat outside for years  and the carbs never leaked once when I put them back on... honest !! ).
If your sure it's a carb problem; it's ignition,
If your sure it's an ignition problem; it's carbs....

Offline rice rat74

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Re: 74 honda cb350f wont start
« Reply #16 on: August 20, 2012, 12:57:24 PM »
Hey guys, the coil wire connections are color matched and snug. I replaced both the float valve and valve seat, using a new kit. The originals on bottom is float and its pin. Fine emery cloth was used on pin before soaking of parts for cheap insurance. The condensers were replaced a month ago, forgot to mention that earlier. This puking of gas is a completely new problem. The carbs never leaked before (until) I adjusted them according to the manual so that no important steps were missed. Should I open them up and adj. them back to some unknown crazy high number(IOW guess game) for float level where they were days earlier without leaking? The lapping procedure would only be required and apply for someone replacing the float valve only but keeping the original seats intact then right?