CB350F poor starter runs irratically

[Budgie955]

Hi
I picked up a 350 four cheap but I'm struggling to get it to run right. It fires up eventually without choke won't rev cleanly ,just runs generally rubbish . Pots 1 and 2 down pipes are hot , 3 and 4 Luke warm.
It's running on electronic ignition, timing is spot on , valve clearances are spot on . I've had the carbs off cleaned the jets out  cleaned the bodies out with carb cleaner . Blown through with compressed air, I put the bodies in ultrasonic cleaner at 80 degrees for an hour .Float height checked ,  I put it all together, no different. Still struggles to start . Runs terrible
I've not checked compression yet as I'm waiting for the correct adapter to come . As this is my 1st four cylinder (I'm used to honda twins) just wondering if there's something I have missed ? I was convinced it was carburetion because putting the choke on killed the engine even from cold . It's also had new plugs new battery. The spark is good on all pots ,
Any advice welcomed
Thanks
Dave Sheffield UK

[K2-K6]

What's the air filter element like ? Old, new, suspect origin  ?

They are very sensitive to flow of anything to do with intake volume/ vacuum etc.

From your description,  it sounds rich, too rich.

Try without filter in place to see what you get.

[Mikep328]

Some thoughts...

 Of course if the compression check reveals a problem, that has to be sorted first.  ASSUMING there is no issue there...

Are the ignition advance weights free and moving properly/weight springs present and in good condition?

I know you said you are getting a good spark but it's still worth checking...are the ignition coil spark plug wires connected to the correct cylinders - left coil (as you sit on the bike) goes to 1 and 4, right coil goes to 2 and 3).  IOW, if correctly connected, your cool cylinders are each fired by a different coil which would tend to eliminate a coil as a problem.  I know you said there was good spark but coils can do strange things...

It sound like it's running rich.  Are you SURE the idle/slow speed passages/emulsion tubes are clear AND undamaged?  I pulled the carbs on my poor running 400F twice before discovering two distorted emulsion tubes (damaged by some previous owner's disassembly/reassembly) and one clogged idle air passage that I was sure I had cleaned thoroughly.  The bike went from being somewhat recalcitrant to totally smooth acceleration - no hesitation/flat spots.  As others more knowledgeable than I have pointed out, the idle/low speed system on these bikes has greater effect on higher RPM ranges than is usually considered "normal."  The bad emulsion tubes had holes that were compressed and egg-shaped.  As others have noted - aftermarket carb "brass" (jets emulsion tubes/float valves needle/seat) seem to be randomly unreliable compared to the OEM Honda parts.

E-ignitions can cause problems in odd ways - components/connections become intermittent/fail.   One of my old bikes with an aftermarket E-ignition ran horribly when I bought it. I removed the E-ignition and installed the OEM points system and the bike ran perfectly...  

GOOD LUCK!!!! 

[Budgie955]

Thanks for the pointers , the air filter is good . I'm trying to get it sorted without it in place , just easier to get carbs off. Advance weights are fine too. Pots 1 and 4 run off the same coil, pot 1 is hot 2 is luke  warm. So it's not the coil . I have the carbs off again . I'm going to clean again just in case .
I'll keep you all posted
Cheers

[K2-K6]

Also have a read of this thread https://www.sohc.co.uk/index.php/topic,32423.60.html should be page 5 as it details recently made inspection of needle and jet interface for wear etc.

If there's substantial wear in the main jet/emulsion tube/needle etc, then uncontrolled fuel from that source will overwhelm the concise metering needing and delivery via the idle circuit at this lower rpm operating range.

[Otis]

When I first got mine it ran but didn't feel right. Re did the tappets and carbs to no avail. Checked the electronic ignition and it was spot on.

By chance, a neighbour who knows a helluva lot more than me was assisting and felt something wasn't quite right with the ignition. We advanced the ignition a tad and the bike suddenly came alive.

Might be worth playing a bit?

[Budgie955]

Timing is spot on
I've fitted new inlet rubbers and it's the same 1 and 2 running . 3 and 4 warm not hot
I pulled out no4 plug today and it runs on all 3   so no 4 is pulling it down . Carbs off again cleaned again , so I'm a bit baffled as to what is going on . Big fat spark and good compression on all 4 . Has to be carb issue surely??
Regards

[Mikep328]

Did you perform the compression check?  Seems unlikely to be the problem but be good to rule it out.

[Budgie955]

I did
All good at 135 psi ..pot 3  a little lower but the issue is no4 cylinder

[K2-K6]

Timing is spot on
I've fitted new inlet rubbers and it's the same 1 and 2 running . 3 and 4 warm not hot
I pulled out no4 plug today and it runs on all 3   so no 4 is pulling it down . Carbs off again cleaned again , so I'm a bit baffled as to what is going on . Big fat spark and good compression on all 4 . Has to be carb issue surely??
Regards

As a course reality check, you can introduce e-z-start via the sync port, you can use one of the screw in tubes from carb sync to squirt it in there.

All this does is introduce alternative fuel to that cylinder to see IF it fires competently with that. This is just to prove its fuel not ignition or other. Just a binary test.

Another test (if the above picks that cylinder up) is start from cold, run 20 seconds, switch off and then check the headers for temp to see if those stay cold.

The combination of, pick up with additional fuel & cold cylinder at start, almost confirms its back to looking at idle circuits again.

[Budgie955]

Great idea I tried it , killed it stone dead . I'm convinced it's over fuelling, because it won't have it on full choke. I've played around with float height and had it running on all 4 , but rough.
Carb kits ordered so let's see when they're installed
Cheers guys

[Mikep328]

Don't know what type of floats were used on the 350 carbs (foam, hollow plastic, hollow brass, etc) but I can say that non-floating floats are not unusual.  Plastic/brass floats are pretty easy to tell - is there fuel inside or cracks/pinholes?  Foam floats, OTOH, look the same whether they float properly or not.  Some particular foam floats were known to lose buoyancy over time as they slowly absorbed fuel and it was considered "normal" to replace the factory floats after not all that much time.

The normal float level procedure does not account for floats that do not have their original buoyancy.  Consequently, they can be set perfectly but fail to shut off the fuel at the proper point.

[Skoti]

Great idea I tried it , killed it stone dead . I'm convinced it's over fuelling, because it won't have it on full choke. I've played around with float height and had it running on all 4 , but rough.
Carb kits ordered so let's see when they're installed
Cheers guys

Make sure the kit includes new slide needles and needle jets, because those are the bits that most often wear resulting in over rich mixture.
Plus another symptom of the wear is cold starting without needing choke.

[Athame57]

I had a problem like this on a Suzuki GT380, in the end all I had to do was get new plug caps.

[Otis]

Timing is spot on
I've fitted new inlet rubbers and it's the same 1 and 2 running . 3 and 4 warm not hot
I pulled out no4 plug today and it runs on all 3   so no 4 is pulling it down . Carbs off again cleaned again , so I'm a bit baffled as to what is going on . Big fat spark and good compression on all 4 . Has to be carb issue surely??
Regards

Yes, your timing is spot on as was mine but it was clearly not correct. I cannot explain why it was incorrect but we advanced it a tad and the bike suddenly sprang to life. It's just worth giving it a try as you seem to have pretty much exhausted other options.
Cheers