Most motorcycle problems are caused by the nut that connects the handlebars to the saddle.

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billybozo
billybozo
Squiddy
Squiddy

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Post by billybozo on Sat 30 Mar 2019, 12:43 pm

Hi Folks , 
As my intro said in the watercooler , got a very low mileage cb500 a few weeks ago , rode it home all good , rode and ran very well.
Got it home decided to change all fluids ect ,new plugs, genuine air filer , just a good general going over .
Put all back together ,
Now here's the problem  -
been out to start it the past couple of days for work and its only firing on one cylinder !!!!!!!!!!!!, pulled out the plug of offending cylinder (left hand side) nice fat spark ,put back in ,start straight away but again only on Right hand cylinder .
I am thinking a fuelling problem as the bike has such low mileage and was obviously standing for a long time , but the guy I bought it off said the carbs were cleaned out and it ran well on both all the way home (260 miles).

So why now is it only firing up on one ????, could a bit of crud been dislodged and now blocking a jet ????, before I take the carbs off , anyone had the same problem ????
possible carb rubber due to age ????
all idea's . suggestions greatly received 

Billy
liverpool_f_
liverpool_f_
the 900
the 900

Posts : 458

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Post by liverpool_f_ on Sun 31 Mar 2019, 10:25 am

Not too likely but an easy fix if it is. Did you remember to put the rubber hose back on the vacuum connector on the left carb? Your tap shouldn't work without it, but if the tap is not original, it may still run on 1 cylinder because of the vacuum leak.
wrighty
wrighty
Four's a...something...
Four's a...something...

Posts : 151
Location : Market Deeping Lincs

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Post by wrighty on Sun 31 Mar 2019, 11:52 am

Having paid someone to ultrasonicly clean my carbs I still found a blocked main jet!!! Unfortunately taking carbs off to access float bowls is a real faff!
billybozo
billybozo
Squiddy
Squiddy

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Post by billybozo on Sun 31 Mar 2019, 4:17 pm

Thanks for the replies guys ,
yeah all was re-connected correctly , bike fires up first push of the button on no 2 cylinder ,so i'm now thinking about the coil , once I can find my multi metre i'll check that out .
teamster1975
teamster1975
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Location : Woking, Surrey

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Post by teamster1975 on Mon 01 Apr 2019, 6:33 pm

Why don't you swap the coils and see if the fault moves to the other cylinder?
billybozo
billybozo
Squiddy
Squiddy

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Post by billybozo on Wed 03 Apr 2019, 3:39 pm

Ok -

rest day of work today - swapped the coils over - same problem , instantly fired up on right hand cylinder, running lovely on one  Smile - left hand one completely dead  - 
So guys am I right in thinking a possible fueling issue ?????
Anyone ????
Jameshambleton
Jameshambleton
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Post by Jameshambleton on Wed 03 Apr 2019, 9:10 pm

Check the spade connectors on the loom
wrighty
wrighty
Four's a...something...
Four's a...something...

Posts : 151
Location : Market Deeping Lincs

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Post by wrighty on Thu 04 Apr 2019, 3:12 pm

Well, I guess you need a spark, fuel, and for them to come together at the right time. You have a spark, the timing is not adjustable on these and the other cylinder is firing ok, so I'm thinking fuel. I would be looking in the carbs. Open the float bowl drain and check there is fuel in the bowl, if there is then something is stopping it from getting to the combustion chamber.
billybozo
billybozo
Squiddy
Squiddy

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Post by billybozo on Thu 04 Apr 2019, 6:08 pm

OK -So when I got home from work earlier I decided to whip out the spark plug and drop a couple of teaspoons of petrol into the chamber - and guess what !!!!!!! fired up straight away on both - so as wrighty says got to be fueling issue ,opened the float bowl drain screw  and nothing !!!!!!!!, not a drop of petrol !!!!!!
So now in the middle of removing the carbs -will be looking at the jets - although had to stop as Mrs Bozo called me in for dinner  Very Happy 
Thanks for the input guys .
hh_12345
hh_12345
Running out of unique names
Running out of unique names

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Post by hh_12345 on Thu 04 Apr 2019, 7:53 pm

Is it possible that a float is stuck, could a light tap on the carb body help?
RossObey01
RossObey01
Scratcher!
Scratcher!

Posts : 25

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Post by RossObey01 on Sat 06 Apr 2019, 5:12 pm

How does it run with more throttle?

I had a very similar issue last year, despite replacing coils, plugs, rebuilding carbs etc it just wouldn't run on both.

Turned out to be a partially blocked pilot jet, which I didn't pick up even after having the carbs apart more times than I remember.

Reason being, each time I stripped them I did each carb individually. This meant I couldn't tell one pilot jet was caked up compared to the other, because there was still light shining through I assumed it was good.
billybozo
billybozo
Squiddy
Squiddy

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Post by billybozo on Sun 07 Apr 2019, 9:44 pm

Guys ,

 I am in the process of a carb strip down , I strongly suspect as mentioned fuel starvation so currently have the left hand carb appart  and will do one at a time to avoid confusion ,although due to my weekend on at work have not began to clean yet ,
I greatly appreciate the input guys and will keep you posted .
billybozo
billybozo
Squiddy
Squiddy

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Post by billybozo on Tue 16 Apr 2019, 5:36 pm

Epilogue - 
Bike now up and running on both again , but what a faff !!!!!!!!!!, taking the carbs off was easy enough , my problems started when I tried to undo one of the tiny allen screws holding the heater unions under the float bowls which both were rusted ,and have to be removed prior to float bowl removal.
I stripped cleaned and reassembled each carb in turn,giving each jet a blow with compressed air although to be perfectly honest could see nothing untoward. The only thing I found was a bit of crap in one of the fuel pipes leading into the carb of the cylinder that would not fire so I can only assume that was source of the problem.
Second major faff was trying to refit the carbs , its a tight fit and involved mucho bad language and general fiddling but finally got them refitted .
Anyway now back up and running , hope I do not have to remove those carbs again anytime soon !!!!!!!!!!!!!.
Thanks for all advice offered guys 

Billy
teamster1975
teamster1975
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Post by teamster1975 on Tue 16 Apr 2019, 6:41 pm

Nice one Billy! Yes not my favourite job refitting the carbs, especially if it's cold and the rubbers are hard.

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