Topic: 1974 CB350F Problems

[sean350f]

Hi all,

First time poster here, thought I'd ask some advice from you experts.

Here's the scenario:
I bought a 1974 Honda CB350F last year. After a few minor tune-ups I got it running, but it still had a few problems. There are 3 holes in the exhaust, each left muffler has a hole, and there's a hole where the header connects to the lower right side muffler. The carbs leaked from time to time, and it would top out around 80mph. Because I wasn't getting the spec top speed and the fuel efficiency was inconsistent I decided to rebuild the carbs last fall. I bought a kit for the 74' CB350F from Bike Bandit or JCWhitney or someplace like that, did a thorough cleaning and put it all back together but left it off the bike because we'd started getting some snow.

Here's the problem:
Now that the summer is upon us again, I had the bike running.. but not running well. I'd noticed the carbs were a bit out of alignment before re-installing on the bike, so a local bike mechanic tore them all apart and rebuilt them (again) for me. I guess that was good since there was some corrosion from sitting all winter. Now the carbs are back on the bike but there's a flat spot around 4000rpm. The bike refused to go over 5000rpm and had a top speed around 40mph.

So I've tried doing a couple things while waiting on a few tools to be delivered. I changed out the spark plugs and it ran a little bit better. I synchronized the carbs and it ran a little better. It still wouldn't go above 6000rpm with a top speed of around 50mph.

I'd read somewhere on here that the adjustment screws on the carbs were only supposed to be a few threads out after synchronization, and mine were much farther out than that so I re-synced it with them farther in. Now it seemed to run a little bit worse! ... of course that may have been because I forgot to turn the fuel on!!!

So here lies my second problem.. after stalling because the bike had no gas, I let it sit and tried to re-start it. After quite a few attempts and cleaning the spark plugs a bit, it did start up but the starter refused to disengage! It seemed to spin up with the engine. It also seems to be engaged if I use the kick start. It DOES turn off when I flip the kill switch to off however. What's going on?

So thanks to anyone who hung in there and read this long post. Does anyone have an idea what my problems may be? I'm going to try it again after work today to see if I can get it going without the starter.

Any help, greatly appreciated.

[mattcb350f]

Welcome aboard fellow 74' 350F owner 

First off, the spec top speed of the 350F of 98 mph is a tough one to reach. 80 mph is nothing to snicker at on one of these.

Second, you have to be carefull with the aftermarket carb kits. Usually the gaskets and jets are ok but many on here have had problems with the needles (the ones that go in the carb slides, not the fuel metering jet needle). The aftermarket carb kits seem to have needles with various tapers when compared to the stock Honda ones. That being said, It sounds like your issues go beyond what putting the bad needles in would cause.

Now, for the carb syncing....when you talk about the adjustment screws on the carbs, are you talking about the idle mixture adjustments screws on the side of the carb bodies or the slide adjustment screws on the top under the covers. The ones on the top under the covers are for syncing only while the ones on the sides of the carb bodies adjust the idle mixture.

There is a base line factory setting (1 1/2 turns out I think) for these, and adjusting them out further leans the mixture and in makes them richer. You may have to change the setting for your bike, I know I have on mine.

As for the starter issue, I bet the starter solonoid is stuck. The solonoid is located on the side of the airbox (left I think). The positive wire runs from the battery to it, and from there, another runs to the starter. There will also be a trigger wire attached to it to activate it.

Hope some of this helps.

 Matt.

[sean350f]

Hi Matt, thanks for the welcome and reply!

As for the aftermarket parts, the one thing that I did not replace with the new part is the needle. I wasn't able to remove it from the throttle valve because the screws were in too tight and my screwdriver was junk. Needless to say the screw heads on a couple didn't fair so well, and the needle stayed in there. I was worried about that not playing nice with the new jet, but the jets were the same size and the needles looked like they were in great shape so I hoped for the best.

I'm talking about the slide adjustment screws. They're all set to have only a few threads showing (more or less to get the sync right.) The bike idled rreal nice after those were synced, but still had the problem at the higher rpm. It would go up to red line at idle though.

The idle mixture screws are all set at 1.5 turns out. Do those affect the engine at a higher rpm?

As for the starting, does the solenoid come apart on the cb350f or should I start shopping around for parts there? I was thinking of trying to get it going after work today.. tap it to get it unstuck or something? I'm a bit of a noob.. anything that Clymers doesn't tell me, I'm in the dark about.

[tomkimberly]

The correct air screw setting is 7/8 +/- 1/8 tuns out from lightly seated. 1-1/2 turns out is too much.


Tom

[flybox1]

80 mph is poor if you're a 140lb japanese test rider.  
I weigh 230, and get giddy when i hit 70 on my 350F!

I would guess that the "kit" you used for your carb rebuild was not Honda, and probably keyster?
if it is, you'll find keyster jet sizes are a little off, and this may be causing your flat spot. if you can, clean the originals, and put them back in.
Keyster fuel valves will not close completely when your floats are set to 24mm's, and they may drip out your overflow tubes. clean the originals and put them back in.  set your floats to 24mm's

The air screws on your carbs (airbox side)are to be adjusted separately, and between 1 and 2 turns out, but only after your carb sync is done. will lean or richen the mixture based on your plug readings.  these are 2 separate adjustments.
I would suggest removing your plugs and cleaning them.  do your carb sync again.
once done, set your air screws.

Do a search for "plug chop" here on the board.
you'll need to do this to better determine airscrew setting and main jet sizes.  #75 is stock, i think.

+1 on starter solenoid having issues.

[sean350f]

Thanks tom & flybox!

The kit I used was from bikebandit.com it was a K&L. The only thing that was noticeably different was the float needle.. the button was a little longer and the taper wasn't quite the same..

I'll see if the mechanic that did the last rebuild has all the parts still. I'd brought them there as a comparison because originally the overflows were pouring out gas and we couldn't figure it out. Turns out the float needles were dropping down too low with no gas in the bowls. Then they'd get all jammed up and the floats couldn't rise.

What are my options if I can't get a hold of the originals?

I thought about a plug chop, but I'm not going to be able to do it with the throttle wide open.. it just won't get there. I could do a mid-range plug chop though.

24mm on the floats? everything I've seen (repair manual, online etc.) has them at 21mm.. which is what they're set at now.

[flybox1]

i have heard both 22 and 24mm.  Shop manual and wise sources on this board say 22-24(clymer says 21) Mine works best at 24.  if the float valve does not seat well, fuel will keep overflowing, and yes, the original float valves can be had.  check Z1 Enterprises.

http://www.z1enterprises.com/detail.aspx?ID=1913

if the fuel level is off, then the mains might be sucking gas at a rate off the charts.  get the fuel valves correct, and you might see better performance at WOT.  
(then you can do your plug chop for main jet selection.)
try your chop (new plugs) in 4th gear and at the hightest rpm you can get before that flat spot. show us the results.

[sean350f]

Ok, so I finally did get it started. I checked the solenoid and everything seemed just fine. I disconnected the wire out to the starter, pushed the starter button and the solenoid clicked just like it's supposed to. So I tried starting it up again.. the same problem with the starter at first but then it snapped out of it!! Of course.. that was followed directly by some sort of clang in the engine.. I can't imagine that's good. After a little bit of checking, it seems my cam chain tensioner adjuster bolt is completely gone. That really can't be good.

So, if that bolt has been missing and the cam chain is not tensioned correctly.. could that cause the valves to be so far out of alignment that it hasn't been running well? Is that going to damage the engine if I run it?

Also.. anyone know what size that bolt is so I can replace it?

[nealcuda1]

I have a 1973 cb350f and had the same problem of not going over 5000rpm. I resolved the problem by changing the main jets from 75's to 85's. Now it will rev on up like it should.

[Lars]

Hello and welcome, Sean.

As pointed out, when rebuilding the carbs, use all the brass parts possible that still looks OK, buy the o-ring and gasket set and make a proper cleaning. The slide needle goes into a brass pipe which has to be taken out and cleaned well, too.
When reassembling, the float hight has to be correct at 21 mm and check out that both floats are aligned in each carb.
The idle airmix screw is to be set at 0.75 out from lightly tight position. I have been working on engines that needed a bit more to run well, but start with what the book says. After installing the carbs on the stayplate, hook up the fuel tank and check the float height. If they leak - adjust. This is not very fun to discover after the carbs are back on the engine.

Fix the cam chain tensioner, get a used one from a salvage yard.

Get a clean airfilter

Get the correct sparkplugs - D8ESL or D8EA

Adjust the valves - 0.5 mm on both intake and exhaust.

Adjust the timing.

Now - and only now - synch the carbs. Give the idle screw a few turns first, so it engage and gives you an opportunity to adjust the idle to a lower level later. The carbs should be synhed at close to 22-24, but you don't always get there. Most important is to get all 4 of them pretty close, altough you will never get them completely aligned. Use your ears, you can hear when the engine goes smooth.

Maybe some tips here: http://www.hondahobby.no/website.aspx?displayid=1736

Lars

[sean350f]

Well, let's hear it for the weekend! Finally got some sun today. I went to a salvage yard around and found a replacement for my cam chain tensioner bolt, but of course as another stroke of bad luck, upon closer inspection the bolt wasn't missing, it's actually broken off in the engine. I bought a "Spin-It-Out" bolt remover from Ace to hopefully do the job of removing it after reading about the same sort of troubles here http://forums.sohc4.net/index.php?topic=35331.0

Since I didn't want oil spilling out all over the place when I removed it, and I intended on changing the oil anyway, my first task was to drain the oil.. but of course the bolt for the oil filter case is completely rusted on and the PO had completely rounded out the bolt head. I figured that bolt would be a good "trial run" for the bolt remover so I gave it a go... no luck. After that I tried using a dremel type tool and cutting a slice down the middle for use with my impact driver.. no luck there either. I just ended up tearing up the bolt even more. Fantastic!!

So, that's where I'm at now. I've sprayed both areas with some penetrating oil and I'll try again tomorrow. Any suggestions on how I could get either one of those bolts free?

[fmctm1sw]

Get a clean airfilter

+1.  Mine did exactly this today.  Removed the filter and it was fine.  Rode to the Honda shop and ordered another filter.

[sean350f]

Ok, good news and bad news.

The good news is I was able to get the oil filter bolt off the bike. Four days of spraying liquid wrench on it seemed to do nothing, but I purchased a replacement bolt, drilled in pretty far and used a bolt extractor to get that one out. Now I've got a new oil filter and new oil filter bolt in there. The bolt is OEM 15420-333-000 for anyone who has the same problem. http://www.z1enterprises.com/detail.aspx?ID=1858

The bad news is that I tried the same with the cam chain tensioner bolt and it didn't go so well. In fact, despite carefully trying to avoid the situation, the extractor snapped off inside the bolt.

So how screwed am I? I'd really like to avoid taking the top end of the engine off, because I'm pretty sure that's out of my league. I might be able to try and re-drill the extractor and hope that the bit catches it and spins it out.. leaving me to try again on the bolt with a new extractor.

Any thoughts? I'm going to have to assume that bringing it in to a "professional" is going to be quite expensive. I'd like to avoid that as well.

[sean350f]

Has anybody used Loctite Freeze & Release for things like this?

[fmctm1sw]

Now I've got a new oil filter and new oil filter bolt in there. The bolt is OEM 15420-333-000 for anyone who has the same problem. http://www.z1enterprises.com/detail.aspx?ID=1858

They made an aftermarket one with a huge nut on the end of it.  Can't tell if that one is like that.  One of my 350Fs have one.  

The bad news is that I tried the same with the cam chain tensioner bolt and it didn't go so well. In fact, despite carefully trying to avoid the situation, the extractor snapped off inside the bolt.

So how screwed am I? I'd really like to avoid taking the top end of the engine off, because I'm pretty sure that's out of my league. I might be able to try and re-drill the extractor and hope that the bit catches it and spins it out.. leaving me to try again on the bolt with a new extractor.

Any thoughts? I'm going to have to assume that bringing it in to a "professional" is going to be quite expensive. I'd like to avoid that as well.

If I can visualize, the tensioner bolt is in the lower end.  Somewhere there is a post discussing removing that bolt and flaring out the threads somehow.  I'll see if I can find it.  How far broken off inside is it?  I wonder if someone could weld onto it?


*edit*  Here:  http://forums.sohc4.net/index.php?topic=38484.0

[sean350f]

Here's a picture of the broken off extractor. It's kind of a b*tch to get to because it's recessed inside an 11mm or so hole, so I can't really get a file or a dremel or something like that on it. The part that's actually lodged in the engine is a 6mm bolt.

*edit*  Here:  http://forums.sohc4.net/index.php?topic=38484.0

I've seen similar posts to this floating around the forum, fortunately I was able to find the exact replacement at a salvage yard.

[hoodellyhoo]

Ouch! I think I remember reading a thread about this and the only recommendation they had was to take the case to a machinist for removal

[sean350f]

Ouch! I think I remember reading a thread about this and the only recommendation they had was to take the case to a machinist for removal

Well that definitely stinks. I've called some bike shops around and they pretty much laugh at me and tell me they won't touch something like that.. so great.

Get a clean airfilter

I ran it without the air filter and it had the same issues.

[sean350f]

Well, it's been a while since I've gotten around to tinkering with my CB but I was finally able to track down the old carb parts. I figured that the new K&L main jets were junk since a careful inspection showed that the holes were not all the same size. After putting the original jets back in with new o-rings she finally runs up to the correct RPMs again!! I was only able to do a quick test-ride yesterday since I had company coming over.. but it was very promising!

I rode it in to work this morning and there seem to be two small issues. The first is that it idles very poorly. I was afraid I'd stall out at more than a couple stop lights and I couldn't get the idle adjustment screw to help much.. I'd either idle up around 3k rpm and be fine, or setting it lower to the correct 1200ish rpm and it would want to stall out. Am I correct in assuming that this is a carburetor sync issue or possibly the idle screws are set incorrectly? I haven't had time to really tune it yet, but that's the next step.

The other issue I had was that putting it down into a turn a little bit it seemed like it wanted to stall. I thought that might be because the engine wasn't getting enough fuel when it's tilted to the side? Maybe the floats are set too high? I've got them at 24mm now based on the feedback in this thread. Any thoughts on this? On a side note, I've got a GS850 that's doing the exact opposite. When that one is leaned over a bit it revs way up.

Any help on these issues would be GREATLY appreciated.

Thanks in advance,

Sean

[flybox1]

Sean~
did you do a bench sync to get the slides set the same?  if not, do a search for it here, there are tons of how-to's listed. set your air screws at 1 turn out(start from 1 turn and adjust later per your plug readings, later)
if your carbs are off, verify all your main/pilot jet and emulsifier holes are clean and clear.

timing and valve adjust? gotta get those crossed off your list.

only after that, throw in some new (ngk D8EA) plugs and get a carbtune attached to her and get it sync'd.
once warm, she should idle smoothly at 1100-1200 rpm.

remember, seafoam is your friend.

[sean350f]

Hi Flybox,

I didn't bench sync with any instruments but I did eyeball it to see if it was all the same. From what I understand the bench sync is pretty much just to get it started right? The real synchronization comes after other tune-up items?

Next on the list is definitely valve clearance and timing. Hopefully I don't screw anything up 

I'll post results after I get it tuned a little better.

Unfortunately the plan is to tear the whole sucker apart at some point to get the cam chain tensioner bolt out.. so this all might change after it's had it's guts pulled out.. but that's for another time. For now I'm just glad it has a smooth throttle up to the higher rpms.

[faux fiddy]

Hi Flybox,

I didn't bench sync with any instruments but I did eyeball it to see if it was all the same. From what I understand the bench sync is pretty much just to get it started right? The real synchronization comes after other tune-up items?

Bump.


Brushing up on the old search results.

I think I was told they used an 1/8" dril bit shank to adjust the slides bench syncing so that's what I used.