[proto2zoa]

Hey everyone! Just bought my first bike 2 weeks ago - 1982 CB 450T Hawk. The bike starts fine and runs well during my first 10 minutes of riding and then it will start to bog down when I come to stops along with popping and general loss of power until it won't even idle. I'll start it back up a couple minutes later and it will idle for maybe 5 seconds before it stalls again. If I keep on the throttle it will stay running. I was told new CB carbs were put on it at the start of this summer. Should I take the carbs apart and clean them or do you think it's something else since it runs fine for the first 10 minutes?

 

[longdistancerider]

Take your gas cap off and go for a ride. There's a vent in the cap to equalize pressure and it may be plugged which causes the tank to go into a vacuum condition and stop fuel flow

BTW, I deleted the other post

 

[proto2zoa]

Thanks, I'll give this a shot tonight and let you know!

 

[proto2zoa]

Hey Everyone, I've been away but was able to test out having the gas cap off and it didn't work. I ended up stranded in a parking lot. After it shut off on me I could start it again with the choke on and it would idle at low RPMs like if the choke was off and then it would all of a sudden jump up to high RPM for a bit and then go to super low. There was no in between like when I start the bike cold with the choke on. The bike would not start/stay running with the choke off. Again, this happens after riding for about 7 minutes or so. The first 7 minutes it runs absolutely fine. Any other ideas?

 

[J-T]

Still sounds like fuel starvation. Could be crud in the fuel tank/petcock, restriction in the fuel line, do you have an in line fuel filter? I believe your bike has a vacuum actuated petcock which may not be functioning properly.

 

[longdistancerider]

It's either fuel or ignition. Do you have spark when this happens? You can test on the side of the road if you carry an extra sparkplug in your pocket, simply plug that into one of the wires and hold the threads against the head while cranking, you should see a faint blue spark.
If that's good pull the fuel line off the carbs and see if it's flowing.

 

[proto2zoa]

So, I pulled off the fuel hose from the petcock and tested going to on and reserve. Found out that when I went to On gas wasn't coming out. If I went to half way between off and on then gas would start coming out. Then if I went all the way to reserve gas would pour out quite fast. When my bike would start sputtering and stalling I never thought to put it on reserve. Is this my issue? Should gas be pouring out quite quickly with the valve at the On position? Not sure how vacuum actuated petcocks work. Would gas not flow out if it was vacuum actuated like it's doing now?

 

[dtsmjr8dan]

I don't know how those taps work because I've never seen one, but, if you were to get a regular petcock instead of that vacuum one, you would be singing.

 

[workdogz2]

I have a 1982 cb450 Hawk not a vacuum petcock. I would drain the gas tank remove the petcock and pull the screen that extends up into the gas tank,flush your tank and clean the screen,more than a few people don't even know about this screen.

 

[longdistancerider]

Vacuum petcocks work when the engine is running, theory is if the bike stalls or crashes fuel is shut off. Also for the lazy rider who can't figure out to turn the petcock off when parked.
However if the vacuum hose is kinked, torn, worn or loose then there's no vacuum to open the petcock. IMO they're more trouble than their worth.
So, start the engine and check the fuel flow in the ON and RES positions, they should flow the exactly same.

 

[proto2zoa]

First, just want to say thank you so much for all the help. I am a very happy boy right now because I just went on my first ever motorcycle ride longer than 10 minutes!! One and half hours to be exact I road it on reserve and it ran perfectly fine the entire time. Not a single stall or even sputter. I've been all smiles for the last 2 hours.

I'm going to drain it and take the petcock out to see if I can at least clean it or see what might be wrong with it but it's good knowing I can ride it now.

Thanks again for all the advice!

 

[longdistancerider]

The filter screen will be stuck to the tank, use a screw extractor to turn it and pull it out.