Topic: Hesitation and Stalling Issue

[WWrides]

Having some symptoms and would like some help to diagnose the problem with my '73 CB350F:

Run 1: drove the bike up and down the hill a couple of times after service and power seemed fine. Came to a stop and everything seemed normal and I hit the kill switch.

Run2: drove off to my destination, after initial 20 meters or so, I felt a loss of power. Switched to reserve thinking my gas was low, but there was really no change, there was hesitation again, and the bike engine shut off.

Run3: start bike and let it idle. Idled fine for about 3 minutes, I tried to drive off, experienced hesitation again and engine shut off.

Run4: started bike, let it idle longer, and got about 50 meters down the road before the engine shut off.

Run5: drove for about 2-3 miles, accelerating normally, revving to about 9,000 RPMs through gears and back down several times. Then experienced some hesitation after first stop (in first gear). Another 1/2 mile down the road in 2nd gear, experienced slight hesitation during that time until the engine shut off again.

Run6: after starting, in the last 1/2 mile, no hesitation, and engine seemed fine.

Peculiarities about this bike:

• Left turn signal does not blink
• To start, choke has to be fully closed, and immediately upon ignition, it has to be moved to some level of open to idle properly

Service done:

• Wiring was just redone due to old ground wire being burned out and a dead regulator/rectifier
• Petcock fuel line nipple not secured. Fuel resistant epoxy applied to secure into place
• Brake master cylinder replaced

[WWrides]

Also, is this a reasonable fuel level in the fuel line?

[denward17]

With the fuel line routed in that fashion, I think that is your problem.  It is gravity fed, that loop is causing it to starve for gas.

[HondaMan]

Well, that fuel filter is likely to be the very cause of this run-sometimes issue(!).
In order for the carbs to fill normally with fuel, the fuel line must be a downward slope between the petcock and the carbs.
If you suspect that grit and particles are getting into the fuel, open the small bowl on the bottom of the petcock. Above it is a screen: if the screen is damaged, replace it with a new Honda part. You can get them from CMSNL.com.

Very often, these fuel filters cause just the symptoms you describe. In the larger bikes there is room to install them at least horizontally, which, while it does delay filling of the carbs somewhat, does not slow it down so much as to have the troubles you are seeing. The miniscule 350F carbs are sensitive to grit, so it appears someone thought it a good idea to add that filter: it is not, at least not in that style. The resulting fuel line is going down (from the petcock), then up (to the filter), then down again (to the carbs), which prevents gravity from feeding it to the carbs.

About the choke: that operation is completely normal: it is a manual choke. Modern vehicles, especially those with fuel injection, manage the rich-choke to -normal-run mixing automagically: you are instead the choke controller on this system.

[WWrides]

This is what the fuel line looked like previous to being taken apart and attached in the manner you saw earlier (see attached picture). It looks fairly similar to me, so I'm not positive it is the fuel line causing the issue. However, I will fiddle with it tomorrow to see if this is the case.

A friend of mine thinks it could be an issue with the ignition coils. Is there a way to test this theory?

[scottly]

A friend of mine thinks it could be an issue with the ignition coils.

It's not likely, especially considering the empty filter. Like others, I've had problems with the pleated paper filters. It seems any trapped air can't get through the media, and the air needs to be "burped" out before fuel can flow. Try the bike without the filter first.

[Nurse Julie]

Fuel starvation.

[Don R]

 There are a few decades of experience commenting above, your friend could be right but try the fuel line first. I also run an inline filter but it goes down and back up not, down/up/down. Mine isn't ideal and my gas tank will be serviced soon to eliminate any rust so I may remove it.
  I've had several episodes of the inline filter acting up and even posted a video of it not flowing even with the hose off. A full tank helps provide a bit of pressure to overcome the resistance some filters and gas line get, we don't have a fuel pump like most vehicles these filters are made for.

[newday777]

Also, is this a reasonable fuel level in the fuel line?

No. Your in line filter is empty.
The filter is empty because the fuel line with the added inline filter is running uphill.

There can Not be any uphill flow in the line between the petcock and the carb inlet!!

Any uphill in the line at any point impedes the minimum gravity flow these have. (Get rid of the filter as has been said already.) Replace the fuel line with new 5.5mm line cut to correct length so there is no uphill flow between the petcock outlet and the carb inlet at any point in when hooked up. You have to use needle nose pliers to hook up the lines and clamps when correct length of line is installed.

If the filter was installed because you have any rust in the tank??(most are put on because the tank is not rust free) then you need to de-rust the tank and get rid of the in line filter so the line is all downhill from the petcock to the carb inlet. Period. As Hondaman said, be sure that the brass screen in the petcock is clear and good.

I have found that electrolysis cleaning method(3-4 days) followed up with a full tank of Evaporust (2 days) gives great results. I rinse the tank with water after the electrolysis cleaning and drain fully, then immediately fill the tank with Evaporust to the cap and close the cap for 2-3 days. Then empty the Evaporust, strain as you empty through a large fuel funnel that has a brass screen, back into a 5 gallon bucket to be able to reuse the Evaporust again when needed. Then immediately rinse 4 times with fresh diesel fuel (2-3 quarts per rinse), well shaken in the tank before draining out the fuel cap. After final rinse I use an old clean white sock on a 2' flex grabber tool to wipe out any excess diesel fuel/water mix, then pour in 6 oz of 2 stroke oil and turn the tank all around in multiple directions so to coat all surfaces of the tank with the oil to prevent flash rusting. Then dump out the excess oil, then fill with fresh gas. The little oil left coating the tank will mix with the gas and will burn fine in the carbs and helps lube the carbs and valve guides. I suggest that you continue to add 1-2 oz of 2 stroke oil to every other tank of gas to help prevent rust from happening again.

I've included pictures of 2 tanks before and after that I have cleaned as above, one was very rusty but didn't leak so it was usable still(green 500/4 tank) and my blue 750 tank had just surface rust that left particles in the carb bowls that effects running quality.

Hopefully someone hasn't lined your tank previously.....

When the brass outlet of the petcock was epoxied back in, was a drill bit(carefully turned by hand with a pin vise !) used after the epoxy hardened to ensure there was no excess epoxy blocking the flow?

What is a pin vise you ask? It is a holder for micro drill bits, to hand turn the small bits, up to 3.1mm bit. Find the bit that fits the brass inner diameter.
Carefully turn the bits by hand to ensure a clear path for the fuel to flow.

Hopefully you have read through this dissertation and understand the problems and fixes.

Report back with your findings and results. Don't leave your thread hanging.....

[WWrides]

Thank you, all! I will work on it today, starting with the fuel line, and report back with the results.

[Johnie]

Besides the fuel filter placement issue does this bike have a gas tank vent? On the CB750's it's under the gas cap. Not sure what you have on that 350.

[newday777]

Besides the fuel filter placement issue does this bike have a gas tank vent? On the CB750's it's under the gas cap. Not sure what you have on that 350.

The 350F uses the same gas cap and has a vent, but it could be rusted or gummed up.

[WWrides]

Okay, a good step forward, but have run into another issue. I removed the filter and connected the existing tube to the petcock after cleaning it out. I was easily able to start it up, and it ran with no issues for a good 10 minutes. Yay!

Unfortunately, it looks like I may not have the original petcock on it because the the fuel nipple is facing down and causes the fuel tube to get pinched if I try to put the tank back on all the way in this configuration (see pictures). Any suggestions?

I also really need to replace the fuel line, but I cannot figure out how to connect the new one to the carb inlet (it seems very difficult to reach and get a clamp around.

[newday777]

Again you still have uphill. You have to reroute the line from the carb through the rack so it runs downhill from the petcock to the carb inlet. No uphill... Unless someone posts you a map, you will have to be creative in your mind to see how to route it.
I don't have a 350 to show you how.

[newday777]

Going over the top of the carbs is wrong. Find a path lower than where you have it so it is all downhill to the carbs.

[newday777]

Find a clear path through the carbs lower where the line doesn't get pinched

[WWrides]

So, I have two specific questions:

1. Is the petcock I have on my bike the correct one for a 350F?

2. I want to route a new fuel line. How do I access the carb side of the fuel line?

[newday777]

So, I have two specific questions:

1. Is the petcock I have on my bike the correct one for a 350F?

2. I want to route a new fuel line. How do I access the carb side of the fuel line?

1. Probably is correct.

2. Long needle nose pliers

[newday777]

Harbor freight has some decent pliers

[HondaMan]

So, I have two specific questions:

1. Is the petcock I have on my bike the correct one for a 350F?

Simple answer is: no. The 350F fuel petcock has 1 outlet, angled backward off the valve toward the single inlet on the carbs. It is about 4" of hose length.

2. I want to route a new fuel line. How do I access the carb side of the fuel line?

The only way is with the tank lifted up (or off) and using long tongs or needle-nose pliers, in my experience. My fingers are too thick to get in there. If you use the correct hose size (5.5mm) you won't need a clamp, although Honda adds some small wire clips at each end to meet certain import requirements of a "clamp" on fuel lines.

[WWrides]

The reason I asked about the petcock is because in the manual, the fuel line is attached to a nipple that comes out perpendicular to the petcock assembly (Pic1 from the manual) rather than straight down (Pic2 from my bike), which would make more sense for the configuration of the fuel line so that it it won't get pinched on top of the carbs.

If I stay with the existing petcock, I will need to find a way to run the fuel line down around the carbs while keeping it from looping up.

[HondaMan]

With what your tank has on it, I'd recommend routing a new (rubber, flexible w/o kinking) fuel line back out of the front spigot and around the top of the #1 carb. then down to the fuel inlet tee. This will give you a little more turning room to prevent the kinks. The clear hose, in my experience, never works well, nor long, on these bikes as is it 1/4" ID - that's just a tad too big, so it weeps fuel. Then someone adds clamps to stop that, then the hose kinks. Using the right hose is the trick for the CB350F/400F setups. It would also help if you can contact CMSNL for a proper petcock, as shown at this page:
https://www.cmsnl.com/honda-cb350f-four-general-export_model14632/partslist/F11.html

[RAFster122s]

Worst case scenario is to pull the carb rack out then fit your new fuel line on the bench, then reinstall and fit the line to the petcock...
The clear lines tend to not be long lived, the price you pay for visually being able to check your fuel flow

[jonda500]

I can't be the only one who believes that with the inline paper filter removed fuel will happily flow through the fuel line as long as it doesn't run above the fuel level in the tank - even if it goes up down, up down, around the barrels, under the engine and back up to the carbs.
John

[grcamna2]

Find a clear path through the carbs lower where the line doesn't get pinched

+1  very important.

How is the condition of the inside of your fuel tank ?  A clean tank will keep your 4) carbs. Clean 
I recommend removing the wrong petcock/fuel valve and installing the correct OEM Honda stock new one;also open-up(and fully drain each carb.)the large brass drain screws(one per carb.)on the bottom of each carburetor fuel bowl which will help you see what type of sediment has gotten into the carburetors. I imagine your small pilot jets(they control 0-1/8 throttle i.e. 'around town driving')in each carb. are somewhat clogged.
I use a small,white aerosol can cap underneath each one to catch the drained-out gasoline from each carb.;the white color of the cap lets me see every bit of 'rusty dust' which drains-out.