Topic: 1974 CB350F - Fixin' Her Up for Daily Riding - Plugs fouled

[Robbo]

Centre to centre of the holes is 15mm.

The hole where the signal arm goes into the bracket sleeve is 10mm.

Here’s what it all looks like…








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[themrbruceguy]

Thank you so much for the detailed reply, Robbo! This is super helpful for me to see up close how everything is designed.

Perhaps I'll just buy some old turn signals off of eBay and then replace the posts with studs from 4into1 (link here: https://4into1.com/honda-14mm-front-turn-signal-stem-stud-type-65mm-length/)

Robbo, would you be willing to measure the stock stud length of the rear tail lights? There are a few lengths to choose from on 4into1 and I'd like to get as close to stock as possible.

Thank you!
~ Jake

[Robbo]

Happy to help you Jake.  If I measure the stud from where it meets the mounting bracket to the tip of the stud, it is 65mm.  Those 55mm ones should be fine.

I actually have a set of the studs and turn signals from 4into1 mounted/relocated further back on my bike because I use a rear rack and with saddle bags, they would be impossible for other vehicles to see in the stock location.  They are good quality.

The originals I am keeping in case I return it to stock.






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[themrbruceguy]

Thanks for sharing that you have the 4into1 parts on your bike and that you've been happy with them. The main complaint I've seen is that the turn signals aren't gasketed and folks have had water enter in during rain. Have you had that issue? That was my main hesitancy to buying the 4into1 turn signals. Maybe there's a way to make a DIY gasket in order to seal the assembly and prevent rain from entering.

I like your luggage rack! I plan on using my CB350F as a commuter bike to and from work once she's road worthy, so a luggage rack wouldn't be a bad idea. Yours looks to be fairly unique. Care to share where you bought that from? I'd be curious to see a photo of what your setup looks like from a bit further back with the whole bike in view (if that's not too much trouble).

I could try and look around for a stock luggage rack online (I think I see one on eBay for not a bad price - $75 + freight), but maybe there are aftermarket racks that fit the bike too? If you have a recommendation, please don't hesitate to toss a link in your reply

Thank you for the help!
~ Jake

[Robbo]

I haven’t been caught in the rain since I added the rack and moved the signals to be honest Jake, so can’t speak about that issue.

The rack was gifted to me from a member here on the forum and I am forever grateful.  I only had to cover the shipping cost.  It has a sticker on it from Accurate Accessories Inc., Lynwood CA.

I’m currently working on changing some o-rings on a leaking oil pump but will post a pic later when she’s all buttoned up.


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[HondaMan]

That rack is well-designed: not many come with the brackets to connect to the taillight. Without those, the rack causes nasty handling problems (on all bikes) by wiggling with loads on it, trying to turn the steering head on the other end of the bike. I used to have to "fix" a lot of those sorts of troubles back in the day, making straps between the racks and the license plate brackets.

[themrbruceguy]

I received the CB750F petcock in the mail yesterday and did as nor_al_67 recommended: cut off one of the two brass tubes and install it into the stock CB350F petcock. I cut the tube off on my bandsaw, and when I went to install it into the CB350F petcock, I noticed that the tube's OD was 1mm larger than the petcock's ID. So I tossed the tube into my cordless drill and used a piece of 150 grit sandpaper to sneak up on a good fit. I intentionally created a slight taper when sanding the brass tube so that I could ensure a decent fit once the OD was sanded down to a better size. After a few checks, I got the tube to fit inside the petcock and gave it a few light taps with a hammer to seat it into place.

I mounted my freshly cleaned tank onto the frame, ran a new length of 1/4" fuel line to the carbs, and started cranking on the starter. She took a little while to start, but eventually kicked on. I felt that the #3 cylinder's exhaust was still cold and saw that I forgot to reattach the boot to the spark plug. After connecting the boot she was running much better 

I was able to ride the bike about 12 miles last night and had an absolute blast. I did perform a bench sync with an 1/8" drill bit, but I think it's probably in need of a vacuum sync job. The bike ran pretty sputter-y between 2k and 4k rpms. But above 4k it smoothed out greatly and sounded very nice. So I'll be looking around for a decent 4-carb synchronization kit. Any recommendations?

I also am still acquiring the parts (slowly) that I need to get the front end back to stock. I have received the upper and lower fork guards as well as the reflectors w/ the reflector bases. However, I just realized today that I am still missing several parts according to this parts diagram:



Here are links to each of those parts:
 - Item 13: Upper rubber fork cushion (https://www.cmsnl.com/honda-cb350f-four-1972-usa_model435/cushion-cover_51601317700/)
 - Item 19: Lower rubber fork cushion (https://www.cmsnl.com/honda-cb350f-four-1972-usa_model435/cushion-forkcover_51622286010/)
 - Item 16: Chrome rib that sits on top of lower fork cushion (https://www.cmsnl.com/honda-cb350f-four-1972-usa_model435/rib-front-fork_51608286010/)

Would anybody happen to have some (or all) of these parts laying around that I could purchase? I found them all in separate listings on eBay, but the total price after purchasing them all is pretty expensive, so I thought I would check here first.

Thanks for all of the help and tips so far! It's been a fun project.

[carnivorous chicken]

Glad to hear the petcock worked and she's up and running.

For a sync tool I go with Morgan Carbtune. Seems like a lot of folks here like 'em too. I have had issues with the Motion Pro tool that uses the blue liquid (mine formed bubbles). I used to have a mercury tool and I liked that a lot, but the Morgan uses stainless steel rods and is much easier to deal with. Here's the site: https://www.carbtune.com/ Super easy to use, and you can pay a little extra for a nice bag. They ship from the UK, but it looks like they use dealers in the US and elsewhere now so shipping might be cheaper.

I don't think I have any of the spare rubber or chrome parts for the forks but can check when I get back to the States (and my stash) in June. I'll be going to Bob's Salvage in Phoenix and they have a few 350Fs in the yard, I can check if they have the chrome rings (any rubber would be toast sitting in the PHX sun for years). That is if you haven't found them by then.

[Robbo]

Jake, I use a Morgan Carbtune for carb synchro.

Btw, David Silver Spares (USA) sells an aftermarket rear luggage rack for the 350four.

Haven’t forgotten about posting a pic of the bike.  Stay tuned.


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[themrbruceguy]

I don't think I have any of the spare rubber or chrome parts for the forks but can check when I get back to the States (and my stash) in June. I'll be going to Bob's Salvage in Phoenix and they have a few 350Fs in the yard, I can check if they have the chrome rings (any rubber would be toast sitting in the PHX sun for years). That is if you haven't found them by then.

Thanks for being willing to check on my behalf! But no worries, I ended up submitting some Best Offers on eBay that the sellers ended up accepting. I should have all of the parts on order now to return the front end of my CB350F back to stock condition, which I am excited about

I will probably end up purchasing a Morgan Carbtune for myself in a couple weeks (I'll be out of town until then anyways). Thanks for the recommendation there. It's a little pricey, but hopefully is more accurate and dependable than the Chinese blue gauges. It seems like some people have fine results with those, but others can't stand them. So I'm thinking maybe it's best to just cough up the dough for the more expensive Carbtune and call it a day.

For anyone who knows, is it likely a carb sync issue with the sputter-y sound between 2k and 4k rpm's? Or is it likely some other issue? If you would help, I could try borrowing a GoPro and strapping it to my chest while riding. Maybe the audio would come through and help diagnose what may be going on.

Thanks!
~ Jake

[Robbo]

As promised…




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[HondaMan]

Beautiful!

[themrbruceguy]

Wow, Robbo! I am thoroughly jealous. That is a beautiful cb350f you have there! Thank you for sharing the photo. I looked up the "British Pride Bakery" and it seems like they're all in Southern Ontario. I happen to be visiting family in Toronto right now and will be here for the next couple weeks I love a good bakery, but the closest location to me is a little ways away. But perhaps I'll get some time to adventure out of town to check it out.

Continuing on the topic of odd running issues with my cb350f, does anybody think that I should try re-jetting the bike? I have the stock air filter and air intake, and non-baffled (open) 4-into-2 exhaust. I verified that my carbs have the stock jet sizes (75 mains, 35 slows) and are still the stock Keihin jets, not a 3rd party replacement. I'm at 1,000ft elevation in Kansas City, MO if that helps at all.

I haven't checked for air leaks in quite some time, so perhaps that would be worth doing. Is the most-recommended method to basically spray carb cleaner at the junctions and rubber parts? I've never loved the idea of doing this for fear of degrading the rubber parts with the intense carb cleaner. But if I'm just paranoid for no reason then I'll be happy to do it

One thing that I noticed when cleaning/rebuilding my carbs a couple weeks ago was that the part of carb #4's casting that houses the main jet was slightly damaged. It wasn't totally destroyed, but it was missing a bit of material right where the main jet's o-ring would seal in the casting. It looked like it was still possible for the o-ring to properly seal, but it was close... Here is a picture of what I am trying to communicate. The red/pink color is showing the part of the casting that is damaged, which may be hindering the main jet's ability to properly seal. This is just a random Google photo that I edited since I forgot to take a picture while I had the carbs opened.



Hypothetically, if carb #4 wasn't sealing well in this area, would there be any noticeable symptoms? Could this perhaps explain some of the issues of my bike running oddly?

There is currently a Facebook Marketplace listing in KCMO (where I live) that has a functioning cafe'd cb350f (albeit, disassembled) and a parts bike as well. The listing has two sets of carbs included. I have been slightly tempted to go give an offer for these two bikes, take the #4 carb off one of them, and finish assembling the cb350f and selling for a potential profit. Oh the possibilities...

Feel free to share any thoughts or suggestions on how I can start making progress on getting my cb350f running a bit better. Like I said, once I'm bike in town, I will try and get some video + audio of the bike running in order to help capture the issues I'm trying to address.

Thanks guys,
~ Jake

[HondaMan]

Try posting in the "Wanted" section: I've had good luck there.
I'll look, but I don't think I have any left. I think I used my last ones like that on a 750 some years ago. They were all similar on the 750/500/550/350 bikes. Even the CB/CL350 Twin used them on the grab rail.

[themrbruceguy]

Hey all. It's been a little while since my last post. I have since put on about 100 miles on the bike! However, she definitely could be running better. I have followed the advice of several folks on this forum and have purchased a Morgan Carbtune 4 that should arrive next week. I imagine that will help.

However, it looks like the bike may be running very rich. A couple days ago I started the bike (she starts 1st kick every time now, which is amazing) and noticed that cylinder #1 wasn't warming up. I pulled the plug and saw that it was very fouled and wet with gas. I replaced it with a new spark plug and that did the trick. So I rode to work and back home later that afternoon (total of 50 miles). When I went to start the bike again this morning, I had the same problem: all cylinders were warming up except cylinder #1. So I pulled all of the plugs and saw that they were all pretty fouled. It would be great to receive some tips about how I can go about addressing this issue.





Some details about the bike:

• Freshly cleaned carbs as of 1-2 months ago
• All original Keihin jets in the stock sizes (75 mains, 35 slows)
• Mixture screws were set to the factory-recommended 1-1/2 turns out
• Float heights were set to the factory-recommended 21mm
• Freshly cleaned gas tank as of 1 month ago
• Have only used non-ethanol gas since then
• Stock air intake setup
• 4-into-2 exhaust, open (no baffles)
• The open exhaust, combined with the stock jet sizes, would lead me to believe that the bike would tend to run lean instead of rich, but the plugs definitely don't agree with that.

Some things I can think that may need to be checked (feel free to agree/disagree/add to the list):

• Perhaps performing a carb sync will help the issue? I'm not sure if this is true or not, but something worth mentioning I think.
• Didn't look at where the clip was on the needle within the carbs, not sure if this makes a huge difference regarding air/fuel mixture ratio?
• Reduce fuel height within the bowls (have found several posts recommending changing float height from 21mm to 24mm)
• http://forums.sohc4.net/index.php/topic,172263.msg2005505.html#msg2005505
• http://forums.sohc4.net/index.php/topic,70791.msg786677.html#msg786677
• Adjust mixture screws to a different setting?
• Replace air filter? (it is the same air filter that came with the bike when I bought it 10 years ago, although it looks fairly clean and hasn't been ridden much at all since then)

Any tips would be appreciated!
~ Jake

[carnivorous chicken]

A couple of ideas...
I'd change the other three plugs for new, and get a new air filter.
Is your battery charged and strong?
Did you replace points and condensors?
Check wiring from points?
Check contact from plug wires to plug caps?


I'm thinking the needle clip is kind of unlikely, I doubt it's been fussed with. But maybe weak spark is your culprit, maybe t the points or condensors. There are three "zones" of throttle in which different parts of the carb play a role, idle jet, main jet, and needle clip, depending on how much gas you're giving it. But I'd look for other causes first.

**I should add: I can't remember if anyone has mentioned it, but these things need to be ridden above 5 or 6K rpm to get anywhere, you gotta wind em up.

[Robbo]

Jake, is that a mix of spark plugs you are using?  I use NGK D8EA which is a standard non-resistor type plug.  I suggest you try using the same or equivalent.

I assume the plug photos are taken after the bike has been idling.  You could adjust the idle mixture on each carb in small increments from 1 1/2 up to 2 turns and see how that affects performance.

New air filter would definitely give you a more optimal air flow which would allow a better read on the spark plugs.

And once the carb sync is done, you can look at plug condition at various throttle positions.


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[Robbo]

Advice on the Morgan Carbtune…

The nipples that thread into each carb are plastic.  I usually put the rubber hose on each one and slowly screw them in and snug them as tight as possible.

Once you are finished with the carb sync procedure, resist the urge to remove the nipples when hot or they will deform, especially if you try and use a slotted screwdriver.  Again, all I do is let the motor cool and try to grab the hose as close to the nipple as possible and back them out by hand.


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[HondaMan]

If you are running hi-octane gas now, switch to Regular grade. This engine originally ran on Regular in the 1970s, and even today's Regular grade burns slower than 1970s premium did: this alone can foul the plugs! Also, try setting the idle air screws inward toward 1.25 turns instead of 1.5. This will lean out the idle a bit (yes, leans it out...).

Also: the intake manifold O-rings, if you haven't already changed them, are 27x2.4mm size (27x2.5 also fits, and is more common). They probably leak: they turned hard somewhere around 1995...

[Robbo]

Thanks for clarifying the idle screw setting (I was simply quoting the manual).  I went in the garage and quickly checked my two outside carbs and they are set at approx. 1.2 turns out from lightly seated.  You probably gave me the same advice Hondaman .


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[themrbruceguy]

A couple of ideas...
I'd change the other three plugs for new, and get a new air filter.
Is your battery charged and strong?
Did you replace points and condensors?
Check wiring from points?
Check contact from plug wires to plug caps?

Interesting. Would you mind elaborating on why it may help to replace the other 3 plugs?

Battery is charged (purchased this April) and strong. I recently installed a combo reg/rec unit which has been performing well.

I have not replaced the points or condensers, they are stock. Is this something that most folks prefer to do as their bikes age? How would old/worn out condensers effect the operation of the bike? (I am unaware of their purpose)

How does one check the wiring from the points?

All plug caps are making contact with the plug wires. I pulled off the #4 cap and swapped it with the #1 cap this morning and the problem persisted (ruled out a faulty cap).

**I should add: I can't remember if anyone has mentioned it, but these things need to be ridden above 5 or 6K rpm to get anywhere, you gotta wind em up.

This is a good point. I'd say that I spend most of my time in the 4k-5k rpm range on my CB350F. Perhaps I need to rev it a bit higher. Could this riding condition be contributing to the fouled plugs? I wouldn't think so, but perhaps...

Jake, is that a mix of spark plugs you are using?  I use NGK D8EA which is a standard non-resistor type plug.  I suggest you try using the same or equivalent.

I assume the plug photos are taken after the bike has been idling.  You could adjust the idle mixture on each carb in small increments from 1 1/2 up to 2 turns and see how that affects performance.

New air filter would definitely give you a more optimal air flow which would allow a better read on the spark plugs.

And once the carb sync is done, you can look at plug condition at various throttle positions.

All of these plugs are NGK D8EA. The one on the left is brand new, the other 3 are probably 5 years old or so.

Yes, the photo of the plugs was taken after the bike had idled for a couple minutes. I was waiting to see if cylinder #1 would start firing and become warm, but no dice. So I shut off the power and removed the plugs.

It seems like it would be safe to order a new air filter and rule that out. I'll get on that soon.

Advice on the Morgan Carbtune…

The nipples that thread into each carb are plastic.  I usually put the rubber hose on each one and slowly screw them in and snug them as tight as possible.

Once you are finished with the carb sync procedure, resist the urge to remove the nipples when hot or they will deform, especially if you try and use a slotted screwdriver.  Again, all I do is let the motor cool and try to grab the hose as close to the nipple as possible and back them out by hand.

Thank you very much for the Carbtune tip! I would be pretty bummed to ruin the tool upon its first use haha.

If you are running hi-octane gas now, switch to Regular grade. This engine originally ran on Regular in the 1970s, and even today's Regular grade burns slower than 1970s premium did: this alone can foul the plugs! Also, try setting the idle air screws inward toward 1.25 turns instead of 1.5. This will lean out the idle a bit (yes, leans it out...).

Also: the intake manifold O-rings, if you haven't already changed them, are 27x2.4mm size (27x2.5 also fits, and is more common). They probably leak: they turned hard somewhere around 1995...

I believe the first tank of gas that I put into the freshly-cleaned tank was 91 octane w/o ethanol. That was all the gas station had and I didn't feel like driving around looking for other options. The day that I rode to work (~50 mile day) I filled up next to my office with 87 octane w/o ethanol, so that is much better. Then I rode home ~25 miles and the next time I started the bike is when I noticed that cylinder #1 wasn't firing again and I removed all of the plugs.

I will give the 1.25 turns a shot and see how things go, thank you for the tip.

Thank you for the recommendation on replacing the intake manifold o-rings. I'll add those to the list!

~ Jake

[carnivorous chicken]

Interesting. Would you mind elaborating on why it may help to replace the other 3 plugs?

Battery is charged (purchased this April) and strong. I recently installed a combo reg/rec unit which has been performing well.

I have not replaced the points or condensers, they are stock. Is this something that most folks prefer to do as their bikes age? How would old/worn out condensers effect the operation of the bike? (I am unaware of their purpose)

How does one check the wiring from the points?

All plug caps are making contact with the plug wires. I pulled off the #4 cap and swapped it with the #1 cap this morning and the problem persisted (ruled out a faulty cap).

**I should add: I can't remember if anyone has mentioned it, but these things need to be ridden above 5 or 6K rpm to get anywhere, you gotta wind em up.

This is a good point. I'd say that I spend most of my time in the 4k-5k rpm range on my CB350F. Perhaps I need to rev it a bit higher. Could this riding condition be contributing to the fouled plugs? I wouldn't think so, but perhaps...

So I am thinking that weak spark might be causing the fouling. You've already discovered one plug was bad. Plugs are a couple bucks and I usually as a matter of course just replace all four when I get a bike that hasn't been running for a while. Maybe it's overkill, and you can always get a bad new plug, but there you go.

The condensor stops arcing between the points and allows the current to change more quickly, getting you more voltage to coils and a stronger spark. There are electrical gurus here who can explain it in more detail, but that's the basic point.

The stock points and condensors are good, it's usually aftermarket ones that are crap. But they can go bad, and points can wear. For the wiring, I'd just check to make sure nothing is exposed or getting pinched. And the tips of the spark plug leads can get corroded. IF they are, you can trim them back a couple cm and screw the plug cap back in for a better connection. But if you're swapping caps and the problem stays with #1, that's likely not it.

If the bike is spending a lot of time idling, then leaning out the idle misture screw makes sense. I dunno if continuous riding and 4k or below would foul plugs, but you're definitely not getting into the power band.

*Modified this because the quotes were wonky, but this popped up today as well:

http://forums.sohc4.net/index.php/topic,190196.0/topicseen.html

[Robbo]

Aren’t those three other plugs resistor plugs or are my eyes tricking me?


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[themrbruceguy]

I pulled the boot off of the lead to cylinder #1 and took a photo. Is this what you would expect to see? Or should there be more exposed wires? I'd hate to trim off 1 or 2 centimeters only to find out that my leads are now too short haha. For whatever it's worth, the spark on cylinder #1 (when using a brand new plug) looks strong.

Aren’t those three other plugs resistor plugs or are my eyes tricking me?

Ah yes, upon closer examination you are correct. I pulled the remaining 3 plugs and replaced them with NGK D8EA plugs. All plugs are now brand new NGK D8EA, with the exception of cylinder #1 which has 50 miles on it and is already pretty fouled. I cleaned it up and got it to spark again no problem. My guess is that the next time I start the bike it will fire on all 4 without issue. But after some riding I am speculating that it will foul up again and present the same issue. I'll update the thread after tonight! I'll be riding ~25 miles this evening.

I also set the mixture screws at 1.25 turns out. Hopefully this helps?

The Carbtune should come in the mail tomorrow, so hopefully I can find some free time to get the carbs synced. I am hopeful that this will improve how the bike runs. If done correctly I don't know how it would hurt it haha 

[Robbo]

Best of luck on the ride tonight and tuning on the weekend.

One more thing I just wanted to point out.  When you take out each screw where the carbtune attaches, there’s a tiny washer that needs to come with it (sometimes it sticks in place and you’ll need to pry it off with a fingernail).  Try not to lose them .


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