Topic: CB350F camshaft difference by year?

[northbilt]

Hi everyone,

  Long time lurker, finally bit the bullet and registered. To introduce myself, I have a shop in Indianapolis on the famous "Gasoline Alley" and we do quite a bit of sohc Honda work. We have built several 750's and shipped them all over the country and a few internationally. About 9 months ago we had a customer task us with building him the first "CL" 350F. It's turned out great and everyone is very happy with it. It's gotten featured in several online magazines and the response has been overwhelmingly positive. It has given me significant trouble tuning it. We built custom scrambler exhaust for it and it is running velocity stacks. Just to cover all of the bases the carburetors are perfectly clean, they were disassembled and ultrasonically cleaned then thoroughly inspected before reassembly. We also do quite a bit of carburetor work so I'm well versed on the details to pay attention to for a successful carb rebuild (learned from the school of hard knocks) I also personally rebuilt the engine. New bearings, primary chain, timing chain, yada, yada. A complete properly done rebuild. The camshaft that came out of it had a couple of damaged lobes and a few rockers as well. They were replaced but in particular the camshaft we sourced does have different markings than the one that came out of it. I honestly didn't think much of it being that it was a low production bike, only around for a few years so I assumed (I know, I know) any 350F cam would be the same, I was more concerned with the condition. Currently running 35 pilots, 80 mains with the needle raised one. 1 1/2 turns out. On the main jet it runs great. It does not want to idle below 1500 rpm. It will idle at 1500 for as long as 90 seconds. Not real solid as the tach needle is bouncy but it stays right around there. After 90 seconds or so it starts to drop and will die, unless you give it a little blip. The plugs come out super fouled, solid black. Running a dyna ignition and it is spot on. I've checked it 10 times. Valve lash was good, checked it 10 times. Mechanical timing is good, also checked it several times before putting the rocker cover on. Here's the kicker. When I go to sync the carbs it barely registers on the gauge. 1 to 2 psi. They are the same gauges I use to sync every other bike that comes through so I know they're good. 160 compression on all 4 cylinders. That's where the cam question comes in. Are there differences between the 72/73 cam and the 74? Is there a way to tell via markings? The cam that came out of it was marked with a W or M and no other markings. The replacement has a B on one side, a G and R1 on the other. I'm at my wits end here. I've always been able to figure anything out eventually but nothing is adding up here. Any help would be greatly appreciated. I will include a picture in the thread, I'm on the wrong machine for that at the moment.

[bryanj]

It has been found that the dyna ignition draws a bit too much power for the small Honda four generators to cope with, i know you say you have done a lot of Hondas but have to ask if its possible the bench sync may be out.
On all other fours the cast marks on the cam mean nothing at all and in fact the only way to differentiate is measure the lobe and degrees of valve.
Getting any of the fours to run right with no airbox and open exhaust has always been a hit or miss afair taking lots of time, retesting and patience

[northbilt]

I had not heard of the dyna drawing too much power but that is a plausible scenario. Especially with it being such a little bike. I did get the correct ohm rating dyna coils for it keeping the charging system in mind. I use the dyna almost exclusively for the bigger bikes and have never had a problem. I will look into that. Thanks.

[bryanj]

Its not really that the charging system is deficient just that it dont break even normaly till about 3,000 rpm so you are riding like an old style hooligan just to keep up, the later ones where Nader stuck his oar in and insisted lights had to be on all the time made it worse.

I would suggest doing a charging system check as the Hondas do have a nasty habit of loosing voltage between battery and black wire at volt regulator due to corroded connectors.

Didnt mention all this previous as i am in UK with the time difference and tiredness involved!!!

[northbilt]

I’ve done a charging system check and it’s good. I maybe should have mentioned that this is a complete custom build. It has a brand new custom built wiring harness with all brand new connectors. There isn’t anything used from the original on it so no chance of any corrosion. Thanks for the heads up.

[bryanj]

Cant help much more then sorry, only time i have that particular problem was on the last 550K with the abysmal PD type carbs that block pilot jets for a passtime, could just be you are going to have to mess about with jet and needle settings

[northbilt]

I certainly appreciate it Brian, being across the pond and all. Thanks again, cheers.

[Robbo]

I remember seeing the bike featured on the Old Bike Barn website.  Nice looking build .

Did you swap out the original brass when you did the carb rebuild?

The air mixture screw doesn’t look stock to me.  There’s a noticeable gap around the head (see pics).  Not sure if the taper is the same as stock but if you still have the original brass, I would clean that up and put that back in.

Regarding the lack of vacuum during your carb sync, did you not get an increase when you screwed in the vacuum adjustment screws?






Sent from my iPhone using Tapatalk

[seanbarney41]

all the symptoms indicate a vacuum leak.  I would be looking for that first. 

[HondaMan]

The Dyna: it is impossible for the 350F to support it for very long. Below 4000 RPM, the battery is losing charge from the extra 1.5 amps that ignition is drawing from the bike, so it will only 'break even' on power budget above about 4500 RPM. When idling, the battery voltage will steadily fall, making for weaker and weaker spark until it just stalls. The problem is in the dwell time of the Dyna: instead of 180 degrees of "ON" time for charging the coil, it is ON for 350+ degrees, and both coils at once. This adds up to a lot of lost power. Even the larger bikes are challenged to try to feed those units at idle for any length of time.

Did you also change the O-rings where the carb hose castings meet the head? They are now hard as a rock and don't seal for beans (if at all). This is a constant trouble in e-mails I field about black plugs on the 500/550 bikes.

The velocity stacks are also NOT helping you. The complex airbox of the CB350F/400F was an expensive part, and Honda never did anything for these bikes that cost a Yen unless it meant something important: the airbox of the 750 proved marginal for the smaller-bored Fours and was replaced with a great design that creates the 3 distinct pressures needed for these tiny carbs. At the very least, make sure the air pressure entering the venturi is lower than that in the carb float bowls, otherwise it will always foul plugs, and very quickly.

[scottly]

The plugs come out super fouled, solid black.

Too much fuel, or too little air carbon fouls spark plugs. If there is a fault with ignition, there will be no spark and no fire so no carbon.
Once fouled, plugs won't un-foul by themselves, even if the original cause is corrected. Trying to adjust idle with fouled plugs is an exercise in futility. What are the stock jet sizes? 

[Trevor from Warragul]

The Dyna: it is impossible for the 350F to support it for very long.

I have a CB350F with a Dyna S ignition & Dyna 5 ohm coils.  I have run this setup for many years with no issues.  It's fine, as long as you don't run with the headlight on for extended periods (which suits me, as I don't like riding at night).  It idles happily at 1000 rpm, pulls away cleanly, and revs freely.

As I said in another thread:

I've owned my 350 Four for about 30 years.  On leaded petrol (gas) it ran perfectly, then, when modern unleaded was all you could get, it began to foul the plugs & display all the symptoms of rich running.  I reduced the main jet size (to 75's from memory), and the bike ran like its old self.

 

[HondaMan]

The Dyna: it is impossible for the 350F to support it for very long.

I have a CB350F with a Dyna S ignition & Dyna 5 ohm coils.  I have run this setup for many years with no issues.  It's fine, as long as you don't run with the headlight on for extended periods (which suits me, as I don't like riding at night).  It idles happily at 1000 rpm, pulls away cleanly, and revs freely.

As I said in another thread:

I've owned my 350 Four for about 30 years.  On leaded petrol (gas) it ran perfectly, then, when modern unleaded was all you could get, it began to foul the plugs & display all the symptoms of rich running.  I reduced the main jet size (to 75's from memory), and the bike ran like its old self.

 

Here in the USA, there are only a few States where you can run without the headlight ON, even in daytime. That's why it is a bigger problem here,

[Trevor from Warragul]

That will make a difference...

[HondaMan]

That will make a difference...

What I try to recommend in this situation is things like LED headlights and taillights, but they must also use less power than the 45w headlight and 24w taillight did: lately the LEDs are just as power-hungry!

[Trevor from Warragul]

The 350F has a 35w headlight. I installed a Candlepower unit in mine, so I could run a halogen bulb. It used to cast a dull yellowish square at night, now it's a dull white square. 

[RFogelsong]

All 350/400 cams are the same.  The Dyna might not be ideal for the smallest fours, but should be relegated as secondary problem at this point.

Get your hot rodder brain on...this is a gasoline alley problem to solve if I've ever seen one...

You're not getting strong enough "signal" across the carbs at low engine speeds.  This is where all of the talk of airboxes comes from.  This jives with what Hondaman says, essentially, the bigger the CB, the less the airbox matters....huh, you know what else increases as piston size and stroke increase?...vacuum/signal strength...

Call up your library of what happens to vacuum and timing when you put stroker rods in an engine, or how cam timing can affect jetting...it all fits together.

These carbs really need much longer intake tracts than you're providing, and ideally a balance/reference to each other to even everything out.  Look at the intake length on a CB/XL 100/125.  I think the easiest way out of the woods is to find the "plenum" section of an original airbox and slap a K&N on the end of it.  The exhausts were originally double walled and restrictive as well, adding to a change in pressure differential across the engine...you're into an engineering problem now...this is why I ended up searching out and buting the entire stock airbox tract for mine after much research and calculation. 

Btw, here's all of Honda's science...in my opinion, after reading this, you'll never want to alter a Honda intake system again: https://www.bevelheaven.com/Articles/combustion/combustion.htm

Awesome build btw!