[dslenz]

It was a beautiful spring evening in Wisconsin, so I took my CB350 out for a ride through America's dairyland. Once I got out onto county roads, I noticed some weird activity at higher speeds/RPMs. In 4th and 5th gear, I could not get above 5,000 RPMS, nor could I get much above 42 mph. If I continued to throttle up, the engine sounded bogged down - like it wasn't getting enough air. I would also start to lose speed/RPMs. I haven't tested exactly, but I'd say it happened at the final 1/3 of throttle travel.

By way of background: I've owned this CB350 for about a year. Last year, I definitely did not have this issue. After a long winter, I drained and refilled the tank, changed the oil, checked tensions, etc. but otherwise the bike is stock. The only other issue it has is electrical (which I'll post in the proper forum).

Any ideas?

 

[dslenz]

Two other notes:

First, I note that this is in the incorrect forum. If a moderator could move it, I'd appreciate it.

Second, I've been riding around town without significant issue. I can rev to higher RPMs in lower gears without issue and felt like I had normal power getting up to 40 MPH.

Thanks!

 

[66Sprint]

Ok....At 40 MPH, you should just be getting ready to shift from second to third gear (possibly just completed that shift)...Third is good to about 55 MPH, and forth to about 65.....
IF you are in fourth or fifth gear at 40MPH, OF COURSE you are "lugging" the engine...... Throttle response will be dismal, and revs will build so slowly you will think you hit a wall.....
You HAVE to use and run-out the gearing if you want good acceleration.....Your bike is likely simply responding to being in way too high a gear.........

I use the approximate shift points I just mentioned on my 175 (which is basically a "high-powered-Hoover" compared to a 350) and neither redline or experience your "bogging" symptoms.....

 

[dslenz]

Ok....At 40 MPH, you should just be getting ready to shift from second to third gear (possibly just completed that shift)...Third is good to about 55 MPH, and forth to about 65.....
IF you are in fourth or fifth gear at 40MPH, OF COURSE you are "lugging" the engine...... Throttle response will be dismal, and revs will build so slowly you will think you hit a wall.....
You HAVE to use and run-out the gearing if you want good acceleration.....Your bike is likely simply responding to being in way too high a gear.........

I use the approximate shift points I just mentioned on my 175 (which is basically a "high-powered-Hoover" compared to a 350) and neither redline or experience your "bogging" symptoms.....

Thanks 66Sprint. Even if I'm slightly embarrassed, I'd be mostly relieved to find out this is operator error. I'll give this a shot, hopefully tonight.

 

[66Sprint]

Don't be embarrassed, we know that you were just trying NOT to abuse an old engine......

I Shift out of first @ 20 to 25 MPH....Second @ 35 to 40....Third @ 50 to 55, and fourth @ 60 to 65....and that's probably STILL short-shifting slightly on a bigger bike....

These engines LOVE to rev......

 

[dslenz]

Update: I tried this out this evening, again on back roads. Wound out the gears as described. I still didn't have enough power. I got back up to 42 mph in third gear at around 7200 RPM and couldn't push it to go any faster (except downhill), even with the throttle totally open. I tried upshifting, but it went back to sounding like it was underwater. Some other factors: One, I noticed that when I would back off the throttle (i.e. to take a turn), the bike sounded like it was missing. Two, I think my battery is going - despite an overnight battery tender, I had to kickstart.

Any other thoughts? Could the whole thing be associated with a dying battery (it was left on the bike all winter in Wisconsin).

Thanks again for your sage guidance. I will say that after about an hour riding in lower gear the engine was... hot. Like I could barely grab the key to pull it out of the switch hot.

 

[Yendor]

A fully charged Battery is a MUST for these bikes.
Anything less and the performance will suffer.

That said I would check your timing with a Strobe light and make sure that both sides are even with the proper marks at idle and full advance 4000 rpm or better.
Also pull your plugs and show us pic's of them - both sides, so we can see how it's burning - Rich/Lean or just right.

 

[66Sprint]

Update: I tried this out this evening, again on back roads. Wound out the gears as described. I still didn't have enough power. I got back up to 42 mph in third gear at around 7200 RPM and couldn't push it to go any faster (except downhill), even with the throttle totally open. I tried upshifting, but it went back to sounding like it was underwater. Some other factors: One, I noticed that when I would back off the throttle (i.e. to take a turn), the bike sounded like it was missing. Two, I think my battery is going - despite an overnight battery tender, I had to kickstart.

Any other thoughts? Could the whole thing be associated with a dying battery (it was left on the bike all winter in Wisconsin).

Thanks again for your sage guidance. I will say that after about an hour riding in lower gear the engine was... hot. Like I could barely grab the key to pull it out of the switch hot.

​IIRC, 45MPH in third on my 175 is only about 6K/6.5K RPM (hard to be more exact as it's immediately after shifting into third and still accelerating)...You MUST be running on JUST one cylinder at least part of if not most of the time....OR your compression is very low.....

Yes, let's see the spark-plugs.......

The "Burbling" (underwater sound) is/could be the non running cylinder pumping air.... The excess heat is due to the extra work the one running cylinder has to do to both move the bike and pump the non firing cylinder's piston up and down.....Therein lies the loss of power......This theory explains a lot...

 

[crazypj]

After I 'played' with it my 1968 CD175 would lift front suspension at 60mph in third going to 4th.
OK, Back to normal program, What oil are you using and have you fitted heavy duty clutch springs? Do you have cheap pods or stock air-box

 

[dslenz]

Thanks again team. I'll pull the plugs this weekend and send pics as a start. If that doesn't answer the question, I can get it in to a shop with a strobe (sounds like I might be headed to one anyway). After yesterday, I'm more confident that the bike is actually underpowered.

To answer the other questions posed: The battery was fully "charged" when I started out on both trips - tender indicated full charge, had been on overnight. I haven't tested the battery to see if it's no longer holding charge. I changed the oil with motorcycle oil - I don't remember the label, but I used the viscosity recommended in the original manual, and an oil specified for motorcycles. Oil change within the last 100 miles. I have not fitted heavy duty clutch springs, and I'm 95% confident the previous owner did not either. I have the stock air box. The bike is completely stock as far as I know.

 

[Yendor]

Strobe Tiiming Lights tell you a LOT about what is going on with your Spark.

The INDUCTIVE Type (Sensor Wire Clips over the Plug wire) Will ONLY trigger the Strobe when a Charge actually travels thru the wire to the PLUG and successfully finds a ground path.

Good information to have as it can indicate coil issues and Points/Condensor issues.

But just because it found a path to ground does NOT mean it actually did so by jumping the gap inside the cylinder.
The Plug could be cracked or shorted.

It is NEVER a bad idea to replace your plugs with NEW ones when going down these trouble shooting paths.
I have had even NEW Plugs that Fail to fire under compression.
Plugs are cheap - even if yours are already new it can't hurt and they are a low cost elimination of potential problems

 

[crazypj]

It would be cheaper to buy an inductive timing light from Harbor Freight tools than even a half hour service charge at a shop. It doesn't matter they are under $30.00, they work. With ANY inductive light, make sure the clampis on properly, there is usually an arrow fro the direction current is flowing which may need to be reversed on dual lead coils (one side fires + theother side - to complete a circuit) Also, the inductors are pretty fragile so don't drop them onto hard surfaces. As long as the oil you used during oil change is JASO spec it shouldn't cause clutch slip but if springs are originals I would recommend changing them for heavy duty. OEM springs were marginal pressureand have probably taken a 'set' after 45 yrs. I rarely replace clutch plates OEM clutch is good for over 100,000 miles in my experience

 

[jjdugen]

I'll throw this one in as I was experiencing almost the same symptoms. Around town no problems, rev right through in the lower gears, nice and perky. But, on the open raod it would run fine for a short while, then gradually slow and then cut onto one cyclinder. Long story short. I found one of the fuel galleries in the R/H carb from inlet pipe to needle valve blocked with a hard residue, just allowing enough fuel to trickle through at low revs, but starving at higher revs/fuel demand.
Thought I had it cracked, but another run threw the same fault. Turned out that the fuel tap itself was full of this old, powdery residue,INCLUDING the tap handle, this has a half moon shaped channel to guide fuel between main and reserve outlets. This was full of the powder. Once that was all cleaned up she will now sustain high revs for as long as I can hang on.

 

[crazypj]

Good point. 'we' assumed that had already been checked and sometimes forget the obvious

 

[dslenz]

Assume nothing, I'm very much new to all of this. I ordered a new set of plugs to be delivered tomorrow. Sounds like the better bet, before I start toying with the ignition timing, is to open up the fuel tap/carbs?

 

[crazypj]

If you try and drain tank through fuel tap it will give an indication of how good or bad flow is.Use the original lines , disconnect from carbs into a can. Leave filler cap closed for first 5 minutes then open it and see if flow improves.

 

[shukae]

I also have a 1971 CB350 and live in Wisconsin and I am experiencing the same issue. The bike had sat for ~8 years before I started working on it this winter.
Work done so far:
rebuilt the carbs
one of the diaphragms was bad so I replaced that
new air filters with the original air boxes
new spark plugs
new clutch, throttle and brake cables
new rear brake shoes
changed oil, used standard 10w-40 non-synth oil
new tires
new chain
new battery [have not tested to see if rectifier is working/recharging]

As the others stated, plenty of low end power, in any gear aroudn 5k RPM, starts to miss or bog down. Shift helps meaning that the lower RPMs have better power than 5k+

Thanks!

 

[chaindrivecharlie]

I also have a 1971 CB350 and live in Wisconsin and I am experiencing the same issue. The bike had sat for ~8 years before I started working on it this winter.
Work done so far:
rebuilt the carbs
one of the diaphragms was bad so I replaced that
new air filters with the original air boxes
new spark plugs
new clutch, throttle and brake cables
new rear brake shoes
changed oil, used standard 10w-40 non-synth oil
new tires
new chain
new battery [have not tested to see if rectifier is working/recharging]

As the others stated, plenty of low end power, in any gear aroudn 5k RPM, starts to miss or bog down. Shift helps meaning that the lower RPMs have better power than 5k+

Thanks!

Are you using aytomotive oil?, you need a jaso ma type oil. Shell rotella diesel oil 15W40 is easy to find , walmart. The regular automotive oils have friction modifiers in it and will mess up your clutch.

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[shukae]

Yes I am using automotive oil. I will pick up some diesel oil and change that out this weekend, thanks!

 

[chaindrivecharlie]

Your welcome!, dont want to see you have clutch problems. I live in sheboygan, where you located?

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