Topic: Runs good for first minute.

[Coredozer19]

I start it up. And then rip down the road. Stop at a few stop signs and then it starts running like #$%*. Can someone please help me. 1973 Honda cb350f

[jonda500]

Sounds to me like it's running rich.
Does it readily start cold without choke?
Are you possibly forgetting to turn the choke off? (that's probably not it I know!)
Probably you're going to have to delve into the carbs to fix it (float levels/jets/needle clip position)
John

[Scott S]

 You're not working the choke backwards, are you?
 It wouldn't be the first time!

[flybox1]

How about a little backstory on what you have done to the bike 

Its like going to the doctor and saying "i'm sick, fix me"....andnot offering up any other information 

[TwoTired]

How about a little backstory on what you have done to the bike 

Its like going to the doctor and saying "i'm sick, fix me"....andnot offering up any other information 

Get ready for that prostate exam, AND a colonoscopy!

[flybox1]

*cough* 

[Athame57]

I had just this sort of trouble recently, needing to close the choke to get me home. I cleaned the carbs out and that solved it.

[2wheels]

Gas tank vent plugged?

[Coredozer19]

1973 Honda cb350f
New pistons rings gaskets.
All new timing components. All new ignition parts.
All recommended tune up services done.
Stock airbox stock jets sizes.
I completely restored. So almost everything is new.

I set float hight level. But I think I did it wrong because I pushed the float down to measure it. But I don’t get how running rich would cause my condition. It runs good at first then runs like crap. It would be the other way around if it was rich.

I’ve been trying to solve this problem for months on this forum. And I’m just ready to scrap the bike. I have over 2500$ into it and months of time and energy. I just want to fix it to enjoy it.

Please help me.

[cjespersen]

I don't know exactly what running like crap means but maybe it's not getting enough fuel? The carburetor bowls could be full  when you take off but the motor could be starving as the bowls get depleted. How long are you running it before it turns to crap?

[TwoTired]

If you are running rich at a certain throttle position (or with choke), the excess fuel will deposit on the spark plug center electrode insulator.  This conductive coating will provide an alternate path for the spark energy away from the spark gap and make igniting the mixture problematic.  I.E. it will run like crap until the conductive coating is removed from the center electrode insulator, either by cleaning, or by selecting a throttle position that operates lean, thereby allowing the spark plugs to "self-clean".

[Robbo]

1973 Honda cb350f
New pistons rings gaskets.
All new timing components. All new ignition parts.
All recommended tune up services done.
Stock airbox stock jets sizes.
I completely restored. So almost everything is new.

I set float hight level. But I think I did it wrong because I pushed the float down to measure it. But I don’t get how running rich would cause my condition. It runs good at first then runs like crap. It would be the other way around if it was rich.

I’ve been trying to solve this problem for months on this forum. And I’m just ready to scrap the bike. I have over 2500$ into it and months of time and energy. I just want to fix it to enjoy it.

Please help me.

If you think that you set the float height incorrectly, that is the first thing you need to check.  Float height is critical for these small fours to run well.



So while you pull the carbs, might as well check fuel flow through the petcock in both the ‘on’ position and ‘reserve’.  Just open the fuel tap/petcock off the bike into a jerry can or any other container.  If the fuel does not flow well for one setting or both, disassemble and clean the petcock.  Also, as mentioned above, check that your gas cap vent is not blocked/corroded.

Btw, are you running an inline fuel filter at all?  And did you replace any of the main fuel line recently?


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[jonda500]

I don’t get how running rich would cause my condition. It runs good at first then runs like crap. It would be the other way around if it was rich.

A cold engine needs a richer mixture, this is why the bike is fitted with a choke to help start the bike when it's cold. As the bike warms up the engine needs a leaner mixture (less fuel or more air) - this is why you turn the choke off after a few minutes or else the bike starts to run like crap.

Your symptoms sound exactly like how my 500 ran after I sent the carbs to harisuluv to be completely restored. Despite having stock air cleaner, exhausts, jets and carb settings the bike would only run well for a few minutes and then would start to run like crap. It took a lot of trial & error and time & money(for genuine keihin jets) to get it to run well. I tried lots of different combinations of jets/settings before I finally got it very close - close enough that 99% of the time it runs smooth and well.
   I currently have the float levels 2mm lower than stock (4mm below seam), the pilot jets 2 sizes smaller than stock (#35's), the needle clips in the stock position (#4 from the top), the main jets 1 size larger than stock (#105's) and the air screws turned in 3/8 more than stock (screwed all the way in, then 5/8 of a turn out)
   Possibly I could get her running even better as I haven't tried every single different combination but I got sick to death of wrestling the carbs in and out, and trying in vain to find a grip glue that will prevent the grip from gradually rotating on the throttle tube so that my throttle position marks wont keep changing position. I am just happy that my sparkplugs look normal now rather than black!
  Good luck - don't give up on it, you'll get there if you persist. Just take a long break from it if yur really frustrated, The more information you give and the more questions you ask, the more help you'll get from the forum,
John