Topic: 350f issues

[flankspeed]

Sorry in advance about the long windedness...

Back history:
350f, near 20k on the clock, stock aside from a hondaman ignition.  Bike has run great in the 7 months I've owned it, but it does have a leaky head gasket (I was hoping to not have to address this until my triumph build is done) and on startup I usually need to adjust the idle mixture waaaaay up until it starts, will rev instantly to 2500 or so and then I instantly back it down.  I've tried using just the choke but it won't start choked alone.

I only get to ride at most for one week every other week (joint custody of my son and he's still too small to commute with safely) so the bike was sitting for a week prior to last night. 

The new issues:
1. Heading to a show last night I noticed that my #1 exhaust was puffing out white smoke.  Not a ton of it and it doesn't have any blue to it.  This morning I noticed that I forgot to tighten my dipstick after checking my oil last night.  Even though I live in a really dry place (Denver), could moisture have infiltrated that way?  This morning there is still some white smoke but not as much, and not until bike was fully warmed. 

2. Bike likes to stall now when ridden hard (it's a 350, I tend to flog it).  It happens when I'm slowing for lights only, I've adjusted by slowing with the engine more and/or popping it into 2nd and bump starting it before I'm totally stopped. 

3. When bike is fully warmed I get a very subtle flat spot around 5k.

So far all that I've done is check timing (spot on).

My next plan of attack is to adjust valves, clean plugs and change oil (has been about 800 miles since last change).

Bike has never left me stranded so I'm not really complaining, I can just be really anal about getting things spot on.  I guess my question is should I do anything else besides what I've listed above?  Are there too many flags to wait until winter for a rebuild or new engine (new engine if I can find a 400f mill to dump into it). Keeping in mind that I'm not planning any long trips this summer, just around town stuff and maybe a 3-4 hour jaunt through the mountains here and there.

Cheers

[bistromath]

Adjust valves, check timing, balance carbs, and tune idle mixture screws, in that order. Then and only then start looking for other problems.

[333]

When you say "idle mixture" do you mean "idle adjustment", the screw that adjusts the level of RPMs on the right side of the carb bank?  If your choke linkage is adjusted correctly, it should kick up the idle when even slightly applied.  You can't adjust the mixture.  It is changed only by switching out the jets(main and slow), which requires disassembly.  Some carbs have an air adjustment screw, but the 350F isn't one of them.  But that brings me to my next question.  What color are the plugs?  Has it been re-jetted for the high altitude?  These beasts run a little rich at low RPMs anyway.  I'm sure the high altitude makes that worse.  That would surely make it stall out at stoplights.

[flankspeed]

When you say "idle mixture" do you mean "idle adjustment", the screw that adjusts the level of RPMs on the right side of the carb bank? 

Sorry, should have proof-read, yes idle adjustment.  Just the choke alone is not enough to get her to fire, I usually have to turn it up double if not triple of what the choke alone kicks it up.

And, according to the PO it has been jetted for altitude, it has lived it's whole life in metro denver (I have the original sale papers and registration history).  Haven't done a formal plug chop since my kill switch is broken and key sits on the motor, it'll be tricky.  But after parking they are all nice and tan, very normal looking.

That would surely make it stall out at stoplights.

To clarify it doesn't stall at stoplights when idling, just on descelleration if I throw it into neutral and coast to a stop.

Thanks and keep it coming

[Gordon]

Adjust valves, check timing, balance carbs, and tune idle mixture screws, in that order. Then and only then start looking for other problems.

+1

There's no reason to look for other possible causes to a problem when these things haven't been done yet. 


The 350F does have idle mixture (air) adjustment screws, and I'm pretty sure it doesn't have a fast idle cam on the choke linkage so you will have to either turn up the idle stop screw or hold the throttle open slightly when starting the engine cold, so there's nothing abnormal about that. 

[flankspeed]

Sweet, I'll start there and see what shakes.

Cheers

[Jugghead]

I'm pretty sure it doesn't have a fast idle cam on the choke linkage so you will have to either turn up the idle stop screw or hold the throttle open slightly when starting the engine cold, so there's nothing abnormal about that. 

actually it does have a fast idle circuit! see page 7 of the honda shop manual for instructions on how to properly set it.
in fact, if you don't have a shop manual yet, i highly suggest you get one and follow the tune up instructions and ORDER of doing them, to get your 350F in top form.
good luck!

[strangedaze39]

Sounds a lot like my bike which is also a CB350F, except for the idle and warm up issue. It's floggy (or boggy) when riding low rpms, it has a slight weak spot (almost like a very quick stall) around 5k. I haven't timed my bike appropriately yet, so that might be the reason (you timed yours with a good timing light while running right?)  Another thing you might want to take a look at is the spark plug reference table. Which will tell you a lot about it's running condition. I'll be checking back, I'll let you know if I find a solution 2.

Here's that spark plug reference link:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Hope that helps,
SD

ADDED:
Also just for a reference, when I start my CB350F I only keep the choke on for about 2 seconds, then middle for about 5-10 then just set it to full open. It will idle at about 900rpms till it warms up and then speed up to 1,100-1,200 where I like it. Normally I don't let the bike sit and warm up and just take out  on 900rmps and after a few minutes it will be idleing 1,100. 

A quick idle fix if the basics don't help is to take the air screws out (see attachment pic) When you take these out make sure to count how many turns they take to come out so you can put them back the same way. It's a lot easier if you mark one side with a sharpie so you can remember which side was which.

Once you take them out there will be a little spring in there, you can just leave that in and take compressed air (you can go pretty strong) and blow down the hole, alot of times this will clean the idle jets out enough to make it run smoother.

Hope that helps, sorry i had type fast (in a rush :p)

[Gordon]

I'm pretty sure it doesn't have a fast idle cam on the choke linkage so you will have to either turn up the idle stop screw or hold the throttle open slightly when starting the engine cold, so there's nothing abnormal about that. 

actually it does have a fast idle circuit!

That's not fair...   Why does the 350 get a fast idle cam on the choke but my '76 550 doesn't?

[TwoTired]

How old is the air filter?

Paper filters need replacement once per year, the fibers collapse, and trapped dirt can't get cleaned out, so they get more restrictive over time.

Cheers,

[flankspeed]

Thanks for all of the help everyone...

The filter is something I didn't consider, I'll try to pick up a K&N on the way home from work.

Here's that spark plug reference link:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Mine look to be a 17 or 18 on the chart, but again that's from parked.  Really I'm thinking I just need to do some basic maintenence and it'll be tops again.

I am pretty relieved that no one seems too worried about the head gasket seep for the time being.

Cheers

[TwoTired]

I am pretty relieved that no one seems too worried about the head gasket seep for the time being.

Head gasket weep is pretty common on the SOHC4.  It's actually not the head gasket, BTW.  Bit, rather the o rings in the oil galley going to the cam/lifters.  They get hard from the heat/ age and weep.  They can run for years this way without detriment.  Most decide to fix it when it start splashing onto clothes.

Cheers,

[Jugghead]

ADDED:
Also just for a reference, when I start my CB350F I only keep the choke on for about 2 seconds, then middle for about 5-10 then just set it to full open. It will idle at about 900rpms till it warms up and then speed up to 1,100-1,200 where I like it. Normally I don't let the bike sit and warm up and just take out  on 900rmps and after a few minutes it will be idleing 1,100. 

sound exactly like my 350F.  put the choke all the way on, and it starts immediately on 1st kick,
then quickly put it in the middle so it idles at 1200-1500 while I put on my helmet,
by that time the idle has crept up enough that when I open the choke all the way it sits at 900 RPMs until it is fully warmed up at about 1100-1300, depending on ambient temp.

A quick idle fix if the basics don't help is to take the air screws out (see attachment pic) When you take these out make sure to count how many turns they take to come out so you can put them back the same way. It's a lot easier if you mark one side with a sharpie so you can remember which side was which.

to reset the airscrews, simply screw them in until they seat lightly, then turn them out counter-clockwise 7/8s of a full rotation. this is the factory setting, +/- 3/8s of a rotation.

 
PS: Can anyone point to a source for a UNI foam filter that fits the 350F?  I found one for my bro's 1977 550F, but they didn't have a fit for my bike.  Any one have a link with a supplier?  Thanks!

[333]

I haven't checked in many years, but the 400F is the same filter.

[strangedaze39]

Hey Jugg, you just need 35-36mm foam filters. I think these are what you want. Better check that over with someone else first though.

http://cgi.ebay.com/ebaymotors/35mm-Air-Filter-Pod-20-24-carb-Pitster-Big-Bore-Mikuni_W0QQcmdZViewItemQQcategoryZ35597QQihZ021QQitemZ310031230059QQrefidZstoreQQtcZphoto

[Jugghead]

thanks, strange days, but everything is pretty much stock on this bike, so it has the original air box w/ filter element.
old bike barn doesn't have 'em , out west is out of stock, eBay has none,
if i can't find a source i think i will buy bulk foam and make my own.  shouldn't be too hard.