Topic: My CB550 always dies after a 10-15 min ride? Huh?

[CarbasaurusRex]

So I’ve got this strange issue with my 1975 Cb550 F SS.

It runs well. It’s almost a one kick start bike thanks to a handful of helpful folks on here. Now I’ve checked almost everything, in turns of making the bike run well.

My issue is I CANT TRUST THIS BIKE TO NOT DIE ON ME.

Occasionally I hear the bike wanted to die out coming to a complete stop/idle, so I blip the throttle to keep it from dying and thus keeping me from getting stranded. It only does this every so often. Only issues i have involving idle are slow returning idles(will hold idle at around 1500 rpm then fall back to 900-1100k)

After getting home, I usually let it idle to see if it’ll die on me. It’ll hold idle for about 5 min after it being parked and then...it’ll die. One thing that was also unusual is I have to run the bike on reserve because in the “ON” position, no fuel comes out. (I’ve ordered a new petcock anyway, as the one I’m running is the incorrect nipple direction)

Can anyone take a guess what it could be? I’ve been researching that it may have something to do with fuel starvation from a vent hole being blocked in/around the fuel tank. But I’m not certain of that.

I only have about a quarter tank of fuel but everyday it’s been able to ride for about 10-15 min before this issue arrives. If it was low on fuel, I wouldn’t be able to start it so easily everyday. So it can’t have to do with how much fuel I have in the tank...does it?


Any help would be appreciated!


Things that are unusual to be noted:

- Clutch is slipping
- Choke seems like it’s does nothing for the bike. Bike starts better with choke off and just adjusting idle screw up than back down when it’s hot
- slight low sound sputters in exhaust(sounds like a very quiet miss-fire almost)
- occasionally a float will get stuck (fuel pouring out of bowl nipple)


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[rocket johnny]

fuel tank vent plugged ??

[CarbasaurusRex]

fuel tank vent plugged ??

Is it the hole on the bottom/upper portion of the tank, or the small hole in around the gas cap?


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[nanahan]

Ok, things you can do to start eliminating causes is while idling open the gas cap and leave it open and open the petcock to ON, if you see fuel coming down than it could be a clogged/ bad gas cap.
I was having a similar issue with no fuel coming down, my gas cap was good, I had a aftermarket petcock. So i bought a HONDA petcock and my fuel starvation issue when away.
As for the carburetor floater leaking fuel, I would take the carbs apart and rebuild them and give them a good cleaning. This should also help with your idling issue.


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[CarbasaurusRex]

Ok, things you can do to start eliminating causes is while idling open the gas cap and leave it open and open the petcock to ON, if you see fuel coming down than it could be a clogged/ bad gas cap.
I was having a similar issue with no fuel coming down, my gas cap was good, I had a aftermarket petcock. So i bought a HONDA petcock and my fuel starvation issue when away.
As for the carburetor floater leaking fuel, I would take the carbs apart and rebuild them and give them a good cleaning. This should also help with your idling issue.


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I see! But how would a gas cap be clogged?? Isn’t it supped to seal the tank from fumes venting out/gas leaking?


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[nanahan]

There’s a small hole that its purpose is to not only prevent from the fuel inside the tank to over pressure on a hot day or when riding for a long time but also for the fuel to flow out of the tank.


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[CarbasaurusRex]

There’s a small hole that its purpose is to not only prevent from the fuel inside the tank to over pressure on a hot day or when riding for a long time but also for the fuel to flow out of the tank.


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Are you talking about the upper left hole or the tiny hole on the cap itself?


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[nanahan]

Hmmmm ... mine does not have that hole in the tank, just the small one on the actual gas cap.


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[CarbasaurusRex]

Hmmmm ... mine does not have that hole in the tank, just the small one on the actual gas cap.


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It seems to lead to the bottom of the fuel tank. I’m guess if any gas was to leak out it would just seep into that hole and expel you the outside. But could I just clean the tiny hole on the cap itself you think?


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[CarbasaurusRex]

Pulled plugs, none of them smell like fuel which means that they aren’t flooding? Last time I researched though, slight fuel smell on sparkplugs is a good thing? But I smell just burnt plugs(no smell of straight up fuel)


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[CarbasaurusRex]

Could it be coils are getting hot? Maybe they aren’t wired correctly?


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[Bankerdanny]

The hole in the cap is the vent, the one in the tank is the drain in case you over fill. The cap vents do get clogged, that is why it was suggested you loosen the cap to see if it makes a difference.

Why haven't you filled the tank up? It is very difficult to see how much fuel you actually have by looking in the tank.

What kind if ignition do you have, points or electronic?

I am not thrilled with the way that fuel line is run, the big loop back up rather than straight over to the splitter.

[CarbasaurusRex]

The hole in the cap is the vent, the one in the tank is the drain in case you over fill. The cap vents do get clogged, that is why it was suggested you loosen the cap to see if it makes a difference.

Why haven't you filled the tank up? It is very difficult to see how much fuel you actually have by looking in the tank.

What kind if ignition do you have, points or electronic?

I am not thrilled with the way that fuel line is run, the big loop back up rather than straight over to the splitter.

So I have only replaced the points condenser plugs and coils. Adjusted everything. I have a Dyna S ignition but I don’t think I need it. Most likely returning it. I called a shop down here and a very nice gentleman(very experienced vintage bike mechanic) told me some very specific causes to this issue. The lot of you were correct. A common issue is a blockage in the tiny cap vent that allows air to come in. He recommend to clear the passage with compressed air or simply replace the cap(which is hard to find honestly) When the bike started to die, I opened the cap and it still died. However, I believe this is because there was a big enough “air bubble” that it couldn’t recover enough gas to continue to run. He also mentioned that the fuel lines and petcock MUST be genuine Honda parts to insure proper set up. And an insanely clean tank, free of all rust, as these bikes are really sensitive with the fuel delivery system, as he stated. I have a petcock already on the way, but now I must purchase the correct fuel lines as well as clean the surface rust in my tank. Hopefully that will correct the issue. The loop could also be a factor in contributing to air bubbling/not enough fuel getting to the bowls.


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[Bankerdanny]

The lines don't need to be genuine, but it is worth getting the correct size (5.5mm) so you don't need to use clamps.

Have you removed the petcock and checked the screen that is inside the tank to make sure it's clean?

[CarbasaurusRex]

The lines don't need to be genuine, but it is worth getting the correct size (5.5mm) so you don't need to use clamps.

Have you removed the petcock and checked the screen that is inside the tank to make sure it's clean?

Alright, I ordered the 5.5 and I will have to check the petcock either way when the new petcock comes in.


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[CarbasaurusRex]

Do you guys run 87,89 or 91 octane fuel in 550? Does it really matter?


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[2wheels]

Not sure if those carbs have the O'rings and little tiny washers on the slow jet adjustment screws.  Like the PD42 on a 1978 F750.  But your problem sounds a little like the o rings or washer are missing or damaged.

And I would never expect my bike to idle for more that a minute or two, like at a stop light.  No cooling if your not moving.

[CarbasaurusRex]

Not sure if those carbs have the O'rings and little tiny washers on the slow jet adjustment screws.  Like the PD42 on a 1978 F750.  But your problem sounds a little like the o rings or washer are missing or damaged.

Do you mean the idle mixture screw with the spring on the sides of each carb?


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[Bankerdanny]

Do you guys run 87,89 or 91 octane fuel in 550? Does it really matter?


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standard 87 regular. There is no benefit to premium in a stock bike

[CarbasaurusRex]

Do you guys run 87,89 or 91 octane fuel in 550? Does it really matter?


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standard 87 regular. There is no benefit to premium in a stock bike

Whoops I got 89


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[2wheels]

Not sure if those carbs have the O'rings and little tiny washers on the slow jet adjustment screws.  Like the PD42 on a 1978 F750.  But your problem sounds a little like the o rings or washer are missing or damaged.

Do you mean the idle mixture screw with the spring on the sides of each carb?


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Yes

[CarbasaurusRex]

Not sure if those carbs have the O'rings and little tiny washers on the slow jet adjustment screws.  Like the PD42 on a 1978 F750.  But your problem sounds a little like the o rings or washer are missing or damaged.

Do you mean the idle mixture screw with the spring on the sides of each carb?


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Yes

I checked the diagram and there’s seems to have no o ring between the two parts. (Spring and screw)


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[2wheels]

Ok.
On the fuel lid, the part that swings open.  Is there a piece of foam.  like air filter foam?  My 1978 750F had that.  The foam was causing that little vent hole to plug.  I removed the foam and problem fixed.
As above , you may want to try a different routing for the fuel line.  Get some tygon yellow stuff if you cannot find the original 5.5 mm that honda used.

[CarbasaurusRex]

Ok.
On the fuel lid, the part that swings open.  Is there a piece of foam.  like air filter foam?  My 1978 750F had that.  The foam was causing that little vent hole to plug.  I removed the foam and problem fixed.
As above , you may want to try a different routing for the fuel line.  Get some tygon yellow stuff if you cannot find the original 5.5 mm that honda used.

There appears to be no foam.


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[2wheels]

I didn't mean the gas cap, shown in picture.
But on the lid, hinged and opens up.  but when closes hides the gas cap.