CB350 - Topping out at 45mph??

AlaskaCL350

AlaskaCL350

New Member
Hey guys / gals,

Picked up a '73 CB350 a few months ago and have been tinkering with it trying to get it running right. I'm currently battling with the fact that I can't get over 45mph. I've seen a few posts around about this issue with various solutions but haven't found one that nailed down my issue yet.

ms2nm5q


Things I've noticed:
- Left cylinder doesn't always start firing right away and usually needs some help
- Left spark plug get's kinda black at times (might be just being flooded... hopefully not bad rings / piston)
- Float in left carb was punctured... ordered new one, hasn't been replaced yet
- Battery is new but will not stay charged, possibly rectifier... (please advise on this one)

Things I've tried:
- Compression test (left cylinder was a little lower than the right, but over minimum expected based on manual)
- New plugs
- Checked coils / wires
- Set timing / points gap
- New battery
- Cleaned carbs
- Confirmed both cylinders are firing
- Popped open fuel door while riding to confirm that it wasn't sealing / starving motor

Things still on my list:
- Check / confirm float heights
- Swap out rectifier (attempting to fix battery charging issue)
- Replace float gasket on both carbs (both are looking less than amazing)


Please advise as to anything I should be doing also or things I should look into as well.


Thanks
 
New points to start with, had the same issue when getting mine running right. I tried cleaning them 100 times, didn't help until I replaced them.

New float will help also.
 
Check the timing advance mechanism behind the points. It gets rusted tight and will not advance as it should................ :o
 
Have you checked the carb diaphragms for any tears? Its fairly common and will make a cylinder run rich.
 
I've got new points, floats, and float bowl gaskets on order right now. Probably a week to get up here to AK.

Diaphragms looked really good; didn't see any tears on them.

I'll let y'all know when they get in and installed.
Hopefully it's one of those two issues.

Thanks for the responses

-T
 
Hey Alaska, I repeat, check the timing advance mechanism behind the points. Make sure it moves slightly when turning it back and forth and that the springs snap it back into place. I'm willing to bet you a beer that is your problem.........
 
GLENNWOOD55CAMEO said:
Hey Alaska, I repeat, check the timing advance mechanism behind the points. Make sure it moves slightly when turning it back and forth and that the springs snap it back into place. I'm willing to bet you a beer that is your problem.........
Click to expand...

Hey there, took off the points plate and gave that timing advance mechanism a twist. It looks like it's springing back and forth just fine. I'll enjoy that beer from you once I figure out what the issue really is. ;)


UPDATES:
- Installed new spark plugs.
- Received new points, but can't install until new screws arrive... old ones were stripped to $hit. Not okay...
- Installed new float to replace punctured one. Question: My Clymer manual says to set the float height to just over an inch (1.02in), which it is now set to. However, I've read in various places online that the float height for pretty much all CB350's up until 1976 was right at about .75in.

Can anyone shed some light on this topic? I tried setting the floats to the .75in just to see if it was possible, and I can't even get it that far down bending the adjustment all the way flat. Thoughts??


Still haven't nailed down the issue. New floats, setting timing, spark plugs, cleaned out carbs, diaphragms look excellent, timing advance is still springy, have new points and will try them soon, and I'm still concerned that I'm going to have to put a set of piston rings in her...


Thanks guys/gals for the help

-T
 
If you have the circular brass floats use 26mm, the 'plastic' ones (CB360) use 19mm but 21mm works better without stock air filters
I think the lower number was a screw up in re-prints of 350 manual, I have a 360 one that gives 350 specs (and pictures of CB350 motor ::) )
When you checked diaphragms did you stretch them (very gently) to check for pinholes?
 
What model carbs do you have? It should be stamped on the body. You can then compare them with the specs in these grids, the model is the 'setting mark'.

carbspecs.jpg


722a_carbSpecs.jpg
 
Also, if you have the carbs off again, be sure to check the jets to ensure they are all the correct size, never know what the PO may have put in there. Are you using the stock air filters? Worth checking them as well.
 
That's a good point, even if the numbers are right the jets could have been reamed or drilled oversize
I'm doing a set of 360 carbs at present, (I 'blueprint them before any modifications)
When I checked secondary main jets they are marked as stock 100 but have been opened up to just over 115 (also one of the worst made Kei-Hin jets I've ever seen)
Isn't there a problem with baffles collapsing in CL exhausts as well though?
 
Wait a second. I'm still hung up on that you cant get your battery to hold a charge. Is it cause you cant get your RPM's up high enough to charge or is this a symptom?
 
The way I read it, battery is a primary problem as is flooding carb, should fix the known issues before doing anything else
 
He wrote that it's a new battery and it's draining. I was just wondering if he has an electrical issue that's causing the battery to drain or not be charged. If so it would narrow it down.
He also said that the spark plug is firing intermittently and needs help to get going. Also sources to an electrical issue.
Or you're right and it's an unrelated separate issue. I'm not much of a mechanic and you definitely know WAY more than I do on this stuff. Just my 2 cents.
 
Oh wait...he says cylinder doesn't fire but has spark and its running too rich as indicated by the black plug. Never mind.

Could it be that he's not getting strong enough spark due to the battery issue? Maybe that's causing the cylinder not to fire properly.
 
He said he had a float on order to cure flooding, that's a major problem that needs fixing. low battery voltage will also cause missfire
I was just looking through my Photobucket pictures, forgot 350 has two different types of float, the round ones are 26mm but they also have 'square brass ones, they are 19~22mm
When the jet holder clip breaks you have to use 'C' clips and springs to hold them in ;)


BTW, here's the pics of the 'bad jet' I've never seen a genuine Kei-Hin so far off center



It's also reamed way oversize, 115+
PJ
 
Hey guys,

On the topic of the battery: I've put in on a trickle charger several, several times and I usually only get a few starts out of it before it's too dead to start it up again. Engine RPM rarely gets above 4.5 - 5k (due to lack of fully functional left cylinder). I don't know if this isn't enough for it to charge the battery... but it would seem like it should be fine under normal conditions. Bad battery may be possible, but I'm thinking the rectifier / regulator may be crapping out.

Anyone seen this fail and cause the battery not to charge?

Back on the carbs / left piston issue: The carb is a type KEI HIN 722A. Stock air filters.
Based on the chart posted by HerrDeacon (thank you btw), I should be at a 26mm (1.02in) height which I'm currently set to. Took her for a spin without any noticeable improvement in the overall cylinder performance.
~sad trombone plays in background~

I'm going to pull the carbs back off soon and check the jets out once I get some time. I think I picked up from one of your posts that the Jet size is etched onto the side of them, is this correct?
#68, #105, and #35 are my goal numbers based on the same spec chart for the carb type I've got.

Thanks for your help everyone.

-T
 
Hey guys,

I've ordered new pistons / rings that are .25 over and will be working on that project once they arrive.
Installed new points and re-set timing. No improvement yet.
Left cylinder still isn't providing very much power. ~sad trombone~

On a more interesting note, I checked my compression again today and the left cylinder had a very respectable 150psi. No idea why the other compression checker I was using showed it around 100psi... it's just strange.

Furthermore, While I was running out of fuel, the left cylinder started firing like a bat outta hell. Hit speeds not previously available just prior to it putting out due to empty bowls (swapped to RES and the newly found power was gone). :'(

Is is possible that the left cylinder is just flooding out with regular mixture?? How do I experiment with this??
I assume there is a fuel mixture screw or something on the left carb... or maybe adjusting the float height / jet diameter.

Please advise. Thanks.


-T
 
AlaskaCL350 said:
Hey guys,

Furthermore, While I was running out of fuel, the left cylinder started firing like a bat outta hell. Hit speeds not previously available just prior to it putting out due to empty bowls (swapped to RES and the newly found power was gone). :'(

Is is possible that the left cylinder is just flooding out with regular mixture?? How do I experiment with this??
I assume there is a fuel mixture screw or something on the left carb... or maybe adjusting the float height / jet diameter.

Please advise. Thanks.


-T
Click to expand...
You could try it again by turning off the fuel supply while running it and see if it duplicates the good running condition again, then when it starts running out of gas, slightly open the fuel a little at a time and see if you can find the sweet spot. If you can then it will be the float height that needs adjusting...........
 
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