Topic: Runs great for 15 minutes, then dies...Please Help

[siedsma6]

So here's the story.  I got a 71 CB500-4, spent the summer rebuilding the carbs, replacing brake lines, cables, electrical, etc.  I finally got it to start and run and it runs great.  After about 5-15 minutes it starts to sputter out so I choke it and I get sudden jolts of power back until is finally dies completely and then refuses to start again for a while.  We are almost positive that it is something with fuel delivery but can't decide what it could be. PLEASE HELP. 


The carbs are clean, there are filters on the fuel lines, the air filter is clean, and the fuel lines are brand new. 

If you have any ideas as to what this could be I would greatly appreciate it.  Thank you for your time and help. 

Mike

[kghost]

Did you turn the gas on?

Check the fuel petcock strainer?

Take a flashlight and have a look that theres not a piece of trash floating round in the tank.

Saw one once with a piece of cellophane....would get in just the right spot and suck! fuel was cut off.

the fact that the choke helps tells me your running out of gas.

If theres nothing in the tank try removing the fuel filters or rerouting lines with no bends below the carb bowls.

[siedsma6]

Thanks for the reply.

We did rerout the lines as directly as possible and fuel flows rapidly from the petcock.  I will check that tomorrow just to be sure.  We only put the filters after we cleaned the carbs again to be sure that there is nothing flowing from the tank to the carbs. 

I agree that it seems I am running out of gas, but after it dies and sits for a few minutes it wont start back up.  I will try using a different tank tomorrow to be sure it is nothing from that end. 

Any other possible reasons? or has anybody had this problem before?

[kghost]

Bad coils sometimes act like that too......

Get warm then poof they lay down on ya even tho they work cold

[scunny]

kghost said it all so far,but I'll add another, is your petrol cap breather clear. try running the bike with the lid not fully closed

[750goes]

How much fuel is in it when the problem starts  - do you need to switch to reserve ?

Other than what's already been mentioned - are the fuel hoses being "pinched" when running the bike???

Sounds like it is possibly running out of fuel or needle valve is/are blocked...

When it stops, turn off the fuel straight away, undo the drain screws of the carbs and check each one for a similar volume of fuel...if there isn't any... work backwards from there to check the fuel lines again...... if there is plenty..........look at the electrics.......

[Peterbylt]

My 550f was running exactly the same way. It was the vent in the fuel cap. I ended up taking the smallest drill bit I have and drilling a hole in the cap. No more problems.

[hymodyne]

could your choke be stuck, or the control lever not fully opening when in the open position?

[SohcCBs]

My 550f was running exactly the same way. It was the vent in the fuel cap. I ended up taking the smallest drill bit I have and drilling a hole in the cap. No more problems.

Yes, tank vent.....tank vent.....tank vent

[jdamman]

I had similar symptoms on my 750K1, turned out the two 1/4" filters couldn't supply enough fuel to keep the float bowls full more than a few miles, (mass flow rate in<mass flow rate out) and I would have to stop and wait for them to refill.  Removed the filters, and didn't have any more problems.  The filters were conical shaped clear plastic ones used on lawnmowers and small engines.  Now I just depend on gravity at the float bowls and sediment bowl to filter my system and has worked well for 2,500 miles (clean tank)

[Gordon]

I had similar symptoms on my 750K1, turned out the two 1/4" filters couldn't supply enough fuel to keep the float bowls full more than a few miles, (mass flow rate in<mass flow rate out) and I would have to stop and wait for them to refill.  Removed the filters, and didn't have any more problems.  The filters were conical shaped clear plastic ones used on lawnmowers and small engines.  Now I just depend on gravity at the float bowls and sediment bowl to filter my system and has worked well for 2,500 miles (clean tank)

You may want to try a different brand of inline filter.  I have two small filters on my 750K1 that I got from cycle-re-cycle that flow plenty fast enough for the old beast. 

[gregimotis]

I had rust in my tank when I bought the bike. 

Bike would start great, then slowly the junk would plug the petcock intake and starve the bike.  Let it sit long enough and the bowls would refill and the junk would slosh away from the petcock.



A very through tank cleaning and an inline filter solved it.

[siedsma6]

You guys are awesome, thanks for all the advice.  I will run through everything again this evening and let you know what the outcome is.  Thanks again for the help.

Mike

[dusterdude]

i skimmed this,so if i repeat something,just tell me to shut up.take off the gas cap and see how it runs,if it still stalls,put your mouth over the gas tank opening and blow real hard into the tank.that may loosen any stuff in the lines or petcock.good luck

[heffay]

duster... you'll blow anything won't you? 

this wink's for you     

jk

[Peterbylt]

Don't blow to hard or you may inflate the motorcycle. Then it will make a farting noise as it flies about the garage when you let it go.