Topic: Finally Admitting I Need Professional Help

[saha6818]

My girlfriend bought a 1974 CB350F from a friend for $200 a few months ago, and we've been plugging away at it since then. It had sat for 14+ years. Everything is okay now except for the carbs, apparently. (New plugs, checked points, new air filter, lots of other new stuff.) I've had them apart about 5 times, and they're nice and clean and moving well now. All the valves and jets seem okay. However, I didn't buy full carb rebuild kits, so the float bowl seals, for example, are still old.

At the moment, I can get the bike running with lots of cranking and 50% throttle with the choke off. No luck if any of those variables change. When it slowly starts, it idles very high for a few minutes and then dies completely. All cylinders are firing (all exhaust outlets get hot). Is it possible that the float bowl seals are so worn that they're not maintaining the right pressure? Is that even a thing, carb pressure? And I haven't got it running well enough to start gathering the equipment to sync the carbs. Maybe that's the problem? Any other ideas? I'm about to take it to a professional shop, probably ruining their day, and emptying my wallet.

Thanks in advance!

[madmtnmotors]

I'm about to take it to a professional shop, probably ruining their day, and emptying my wallet.

All they will do is empty your wallet and probably cause even more damage. You need to ship them to someone that specializes in these old machines. Most shops won't even mess with them, and those that do don't always know what they are doing. 

Member harisuluv here on the forum specializes in the carbs for these old bikes, so reach out to him for a quote. You might be able to get it done cheaper somewhere else, but harisuluv will stand behind his work and you can rest assured that he will do it right. 

[rocs]

Have you chcked all of your jets to make sure they are all the same #?

Also, let us know where you live. May be a local member able to help you out.

I disagree with sending to a professional shop. these are simple bikes and anyone who knows how to read should eventually be able to fix their bike. However, for a full carb clean and rebuild, I do agree with sending them to harisluv.,

[evanphi]

the float bowl seals, for example, are still old.

buy new ones. Look for Viton material.

I can get the bike running with lots of cranking and 50% throttle with the choke off.

wut? choke off? You need to use the choke to start these bikes. you also need to keep the revs up a bit to keep them from dying until the engine is nicely warmed up. Not like EFI where you just hit the start button and it works.

Is that even a thing, carb pressure?

nope. those seals just keep the gas in the bowls.


Talk to member harisuluv. He'll sort your carbs out.

[madmtnmotors]

I disagree with sending to a professional shop.

 I do agree with sending them to harisluv

+2

[70CB750]

Forget synchronizing carburetors for now, carbs out of sync will not cause problems you describe.

When the K0 came to me, I fought the longest with the idle air in, on the picture I circled it in red.  It is a tiny hole going to the bottom of the threaded hole for the idle jet.   Finally I used a thin string to clean it up and it went well from that point.

[millla03]

Could be any number of things causing your problems. I don't know if the float bowl gaskets are to blame. The only problem those would cause would be gas leaking from the carbs if they weren't sealing properly. Carbs aren't a pressurized system like you describe it. They are gravity fed and engine vacuum pulls gas through the jets. Bench synching the carbs will get them close enough to get the bike running before a vacuum synch. It's good practice to replace all rubber parts when rebuilding carbs, jets and needles are usually reusable if they haven't been damaged.

Have you set the float heights correctly and made sure all jets and passages are completely clean? Any rust from the fuel tank that might be clogging things? If it will only start with the choke off that would suggest a rich condition. The spark plugs would give some insight as to whether you're running rich or lean. Checked the intake rubbers for leaks? Intake and exhaust changes from stock can require jetting changes too. I'm throwing out general possibilities here, someone with experience specific to the 350f might have more insight.

I've attributed problems to one part before that turned out to be fine, so the problem could be something other than the carbs. A full tune up should be done, if you haven't already.  There's a link on the forum to a good Mikuni carb manual that gives a good overview of how carbs function that might be of some help. I have a copy on my home computer I could link to this evening if you'd like.

Be methodical and you can figure out what's up. Time is cheaper than shop labor rates.

[70CB750]

Just an afterthought.  You have spark, but did you checked and verified timing?

[rockthehellout]

Check for airleaks? Start with the stupid and work your way up.

[flybox1]

No, its not the bowl (seals) gaskets.  They only prevent leaks from an overflow. 
There are atmospheric vents in other places to equalize pressure.
you can fix these yourself.
you should have 38 pilot jets and 75 main jets. please verify this.
Did you pull the main jets out and the emulsion tubes underneath them to check for corrosion?
Cleanliness here is imperative.
did you verify your float height?  21mm?  Air screws....1 turn out?
did you bench sync these carbs? 
using the choke lever properly?

[RevDoc]

No, its not the bowl (seals) gaskets.  They only prevent leaks from an overflow. 
There are atmospheric vents in other places to equalize pressure.
you can fix these yourself.
you should have 38 pilot jets and 75 main jets. please verify this.
Did you pull the main jets out and the emulsion tubes underneath them to check for corrosion?
Cleanliness here is imperative.
did you verify your float height?  21mm?  Air screws....1 turn out?
did you bench sync these carbs? 
using the choke lever properly?

+1 to all of the above from Flybox and, if you have not already done so, use this link to the download page for the manuals.

http://manuals.sohc4.net/cb350/

And as Rocs pointed out in reply #2, if you let us know where you live there may be a member close by who could lend a helping hand. For example, I have every diagnostic tool and instrument that would be needed. 

[saha6818]

Holy crap. You guys are all awesome. I have lots of things to check now. I think my first step will be to check the air idle inlets as 70cb750 suggests. I've got my optimism back. If I still can't get it sorted out after trying all of these things, I'll try harisluv. Whatever the case, I'll post the resolution (or my final resignation) here.

FWIW, I live in Seattle.

Thanks again!

[mrbreeze]

There are a few members in the Seattle area and also Portland. It was mentioned earlier not to waste money at dealerships. There are plenty of parts available through this forum and internet. Ebay and Craigslist are good also. This forum has parts for sale, parts wanted and even a good seller/bad seller section which is very handy. Dealerships mark up prices on parts and most of their employees don't know a whole lot about older bikes and can quickly break your bank with their outrageous labor rates. Your best tools are a good shop manual and this site.

[RAFster122s]

You can do it if you are willing to put the effort in to learn and can post pics when needed, etc.
Doesn't sound like a spark problem so it is likely and air or fuel issue causing the shutdown.
So, getting the carbs  clean and bench sync'd and verify that the brass is good and you have replaced the float needles and their seats.
old float needles & seats are just asking for trouble and they are inexpensive.

[SOHC4 Cafe Racer Fan]

If you run into serious difficulties, talk to Tower or Isaac at Twinline Motorcycles. 
OPEN: Tue. - Sat. // 9AM - 6PM
TELEPHONE: 206.768.8686
Twinline Motorcycles
2106 South Holgate St.
Seattle, WA 98144

[Kingmambo]

Saha - the best advice I would give someone new to these bikes (or someone who thinks they know more than they really do (looking in the mirror here) is get comfortable on these boards. 

The volume and breadth of information already here is voluminous to put it mildly.  The experience of the people on this board continuously blows me away.  Some on here has seen everything that could possibly go wrong with these bikes.  Every time I see a problem posted - no matter how out there - someone has the answer.

The willingness of these experts to help us non-experts is amazing as well.

Search first then ask away and you'll get all the help you could ever need.

[xntrik]

A lot of "carb" problems have been solved with a palm to the head after adjusting valves. It's happened to me more times than I'd like to admit with these old machines. Verify that everything outside of carbs is good to go.... Timing (not just spark), valves, boots, etc..  Pick up a set of guitar strings to aid in cleaning carb passages. They work like a charm. Some music shops will just give you old take-offs out of the trash. I also LOVE my cheap-o harbor freight ultrasonic cleaner.


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[przjohn]

How come I can't find a bike for $200 that starts?  Here on the right coast you get a bent frame and maybe, just maybe, a couple of wheels, with a, "Now get the hell outta here"

[saha6818]

This was definitely the friend deal, and my girlfriend had to talk him up from $0. The bike had a long history with the family, so it was not about the money. It had sat without any winterizing for all those years, so it was far from running. I think the friend was just excited about stopping watching it slowly rot and dragging it from residence to residence. But I agree - excellent deal for such a cool bike. We're going to keep it as original as possible (a long shot from my own chopped-up, fun-time bike).

[przjohn]

This was definitely the friend deal, and my girlfriend had to talk him up from $0. The bike had a long history with the family, so it was not about the money. It had sat without any winterizing for all those years, so it was far from running. I think the friend was just excited about stopping watching it slowly rot and dragging it from residence to residence. But I agree - excellent deal for such a cool bike. We're going to keep it as original as possible (a long shot from my own chopped-up, fun-time bike).

Good for you, have fun!

[saha6818]

Good and bad news on my progress with my girlfriend's bike. I did another round of carb cleaning to no avail. I also did some minor electrical work (turn signal flasher, loose connections). Right before loading the bike onto the trailer to take to a mechanic, I decided to give it one last try, and it started right up. It seemed to run well for a minute, but then was lacking power, so I pulled the carbs for the 7th time. 7th! I'm wearing the bastards out. Anyway, I found a little gunk in the float bowl of carb #1, but the jets were all clear. It seemed like the bowls on carbs 2 and 3 were not full. The float in one seemed almost dry.

The tank was resealed by the previous owner, and there's a little rust, so I got a big clear fuel filter just to ensure that there's no gunk getting in. I reinstalled the carbs. Now the bike will start and idle just fine. As soon as I get on the gas to pull out of the driveway, it runs on fewer than four cylinders. If I drive down the street and goose it onto the main street, I top out at maybe 15mph, and it dies as soon as I'm off the throttle. If I let it sit a minute, it catches back up.

My first suspicion was fuel starvation. But I checked the flow into a gas can, and it seems to work fine. I tried riding the bike with the fuel cap open (what a mess) - same result. I removed the fuel filter and ran the gas straight into the carbs. Same result. I removed the petcock and took it apart - everything looked fine. The petcock seems to function fine too. When I had the carbs apart, I blew into the fuel supply ports, and they all seemed fine. I tested the float valves while blowing, and they worked fine. Also, I checked and adjusted the floats, so assuming I did that correctly, those are fine too.

So maybe it's not a fuel issue? If I can rule it an electrical issue, maybe I can stop smelling like gasoline all the time. On that front, I have gapped and changed all four spark plugs, confirmed spark in all four cylinders (while turning the engine over without fuel), and confirmed that the wires are in the correct order. The points look fine to my uneducated eyes, and the gaps are good. I have not changed any spark plug wires, coil wires, coils, or points. For what it's worth, the guy I bought the bike from said the bike would probably need new points because it had been sitting for so long. And there were spider webs everywhere on this bike, which hadn't run in at least 14 years. They were inside the tach and speedo, inside the points cover, the handlebar switches, etc. I cleaned as best I could. Maybe there is filth in some electrical connection somewhere?

Or maybe I have an air problem? The air adjustment screws are out 7/8 turn. The air box and a new air filter are connected correctly. Everything on this bike, I should mention, is stock. There are no apparent vacuum leaks on the engine side of the carbs. I haven't been inside the engine at all.

I'm in the sad situation where my (licensed) girlfriend is finally excited about practicing riding, but I can't get her little bike working! She refuses to ride either of my other bikes too. So any advice you can provide will be fantastic!

[Gene]

Points.  It's always points.  They don't look like much, and you may not think about them all the time, but they are persnickety.
You may have to play with the points as many times as you've played with the carbs but it's a lot less messy.

[chewbacca5000]

How come I can't find a bike for $200 that starts?  Here on the right coast you get a bent frame and maybe, just maybe, a couple of wheels, with a, "Now get the hell outta here"

O I'm sorry didn't mean anything by it.  Now release the hounds!

[saha6818]

Thanks to Gene's input, I just ordered a set of points and condensers. Can I troubleshoot coils? Just see if they get hot quickly?

[mrbreeze]

Check the connectors going into the coils. Should be under the front of the gas tank....black/white wires. Make sure the connections are clean and tight. Check float bowl levels with the clear tube method. Float height adjustment isn't always precise. Do a search on the clear tube method if you're not sure what I'm talking about. Stick with it!! You'll get there.