Bike running bad and cutting out 5 mins into ride!?

MRFINCH

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So the last few times I have been out it runs fine then about 5 minutes into the ride the bike will start to run really badly, no throttle response, sounds like its only firing on one cylinder then cuts out completely. thats with the petcock on the "on" setting. If i then put it to the "prime" setting it fires straight up and runs fine, but absolutely drinks the gas! Anyone had similar problems? :confused::confused::shrug:

Cheers, Sam
 
Check the vacuum line that goes from the left-hand carb boot to the petcock. If it has any cracks in it, the engine will run lean on the left cylinder, and it might not have a good enough seal to pull the diaphragm inside the petcock when it's on the "on" setting.

The "prime" setting allows gas to flow freely even when it's not getting suction from the engine.

Also make sure your plugs are clean. If it's still running rough, time to do the typical checks on the carbs - check for air leaks, clean the carbs, check the carb diaphragms, sync the carbs, etc.
 
The vacuum hose is on and looks ok, when i suck on it petrol comes pouring out of the main hose. Probably should have mentioned that i had it at a shop last month to have the carbs checked as it wasn't running right, he said he cleaned the carbs and didnt see any problems. Also, i synced the carbs when it came back from the shop. :/
 
MRFINCH, did you ever get a solution to this. I am currently dealing with this exact issue right now. Cleaned the carbs, I know they are tuned right, but it seems I am running out of gas in the carb. I prime the carbs for 10 – 20seconds, then I kick it and bam sounds great, runs great. About 3 – 5 minutes later it will putter and die on me. Prime it again, and bam runs great and over and over I go. Can't go more than a few blocks without seeming to suck all the gas from my carb.

I plan to pull the petcock and clean it, change the vacuum line and fuel lines just to be safe, and I am going to toss in an inline filter, but I was curious if you found a quick solution to this problem? Hope I am not too late seeing this was in 2015. :laugh:
 
MRFINCH, did you ever get a solution to this.

Well, last time Mr. Finch was around was in 2017, so I wouldn't expect much here..

a solution to this.

If it runs on PRI and cuts out when ON, there is something wonky with the vacuum part of your petcock. Spring, diaphragm, vacuum hose.

You can rebuild your petcock, or you can replace it with a manual one and just try to remember to turn it on and off.
 
Be sure it's the fuel and not the CDI unit. On my 81 after 5 min of running it would run on one cylinder, Wait a few min and it runs for another 5.
Bought a replacement unit on Ebay. Now have 53,000 miles on it...
 
So, as embarrassing as it may be, I feel I need to post the truth of my experience for any new comers who stumble across this thread as I did seeking guidance. Before I do, it is important to note this is my first bike, and I am very unversed in mechanics and I am self teaching / researching this whole process — this is an excuse, a sad excuse, but one I had to note! HAHA

After reading another thread, where the participants inquired about fuel levels, and posted some great videos on how a petcock functions (i.e. the straw) I realized that the bike was likely to low for "on" and that I should check how it ran on "reserve" since prime and reserve drink from the same point on the straw. The second I switched it there, boom, no issues on running. I was simply starving the bike — luckily, there were no long rides or damage accrued while doing this. SO, my solution... fill it up with gas. :lmao: My bike has been running flawlessly since then, so, lesson learned, when you have no gas the bike doesn't run... who would have thought??? ;)

Thanks for your time and posts everyone! Hope this helps others in the future.
 
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