Honda xbr500 fueling problem

[Paul F]

Hi all. Having a problem with my 1985 xbr500, when riding on constant throttle it is like a misfire hesitation, normally around 2000 to 3000rpm. So if doing speed limits 20, 30, 40mph it is noticeable, but open the throttle and it will pull strong right to redline and through the box. Have sonic cleaned the carb and fitted new jets. Valve clearance is ok and new plug and cap. Have set the mixture screw to 2 turns to 2 1/2 with no joy.

Going to try it without aircleaner filter tomorrow, if that don't work will try with choke on a bit to see if rich or weak. 

Any other ideas.

Thanks Paul 

[Simon Davey]

27 minutes ago, Paul F said:

Hi all. Having a problem with my 1985 xbr500, when riding on constant throttle it is like a misfire hesitation, normally around 2000 to 3000rpm. So if doing speed limits 20, 30, 40mph it is noticeable, but open the throttle and it will pull strong right to redline and through the box. Have sonic cleaned the carb and fitted new jets. Valve clearance is ok and new plug and cap. Have set the mixture screw to 2 turns to 2 1/2 with no joy.

Going to try it without aircleaner filter tomorrow, if that don't work will try with choke on a bit to see if rich or weak. 

Any other ideas.

Thanks Paul 

 

Did you change the idle jets, main jets, or all them them?

[Paul F]

All jets #58 main and a #52 air. Left the needle jet the same. 

[Simon Davey]

I asked as I had trouble with mine at the same rev range. It was constantly coughing and spluttering 2000-3000 RPM. 

Two mechanics put the carb's through an ultrasonic cleaner, which made no difference. It wasn't until all four idle jets were actually replaced along with carb seals that I got a smooth running bike. 

[RideWithStyles]

LEAVE THE AIR FILTER ON as its doing its job unless its really dirty, just replace.

 

Some people get lazy and assume Ultra sonics will be the god cleaner but usually don’t do jets well even if separated, let alone down the deep ports /pathways of a carb.

Does it seems better with the choke on as its running at that rev?  But as soon as you take it off it’s rough? 
chances are it’s still got a blockage in the pathway, to the idle.

or less likely might be something up with slide or diaphragm/rubbers.

[AstronautNinja]

Ultra sonic cleaners really don't do half the job they promise to do. The lack of water flow will often leave crap sat in place, just looser than it was initially. Carb cleaner and air jets will do a better job. 

 

Having owned an ultra sonic cleaner for many years it really only loosens the dirt rater than moving / expelling said grime 

[RideWithStyles]

I know a place that has an industrial custom SC (sadly not used for bike parts or owt) that doesn’t soak and hope bubbles do the work, no it is with actual heating, very high pressure jets (pointing to small indents on a chromed surface) and a special solutions (ranging from a very strong fairy liquid cleaner to xenomorph level of blood acid attack to plastics etc if it comes into contact with ).  

Anyway even in its usual design and above average spec solutions it still has direct access too, let alone anything hidden in a passageway of or has to bubble away at, can require repeat goes (if at all manageable) just to lift a bit of dirt,contamination from, but still weakens/wears out chrome at the same time.

so a small glorified deep fat fryer and diluted rats piss solution that most places sell (avoiding acid attacks and exposure risks etc) isn’t going to be great at the finer/hidden or stubborn stuff.

 

another thing which might be it rather than the carb (if your absolutely sure its not carb based problem) to check is air leaks from or something silly like pin hole somewhere, gasket gone, packing broken down, baffle removed etc in the exhaust can affect in a similar way.

[AstronautNinja]

For any baths to be remotely efficient the part would need to be rotated. You can't "jiggle" dirt away with gravity involved most of the time. Loosen it yes, remove it no. 

[Simon Davey]

With carburettors, the jets need to be removed before cleaning. The holes are so small that cleaning just isn't effective if left in the carb recess.

[RideWithStyles]

3 hours ago, AstronautNinja said:

For any baths to be remotely efficient the part would need to be rotated. You can't "jiggle" dirt away with gravity involved most of the time. Loosen it yes, remove it no. 

Correct.
That’s what this machine does, rotates the piece/item placed in it while jetting the crap out of it, can do well but still…

[Paul F]

Hi all and thanks for the information. I did a plug chop on the bike today and found it rich. Put new plug and took ot out again but kept the revs down to 3-4 where stutter is. Took plug out and its black soot. Took out aircleaner and tried again, it is running great and no stutter. Done a chop again and plug came put perfect. So it must be jets. Will have a play in the week maybe come down to 50 on airjet and 56 main.

[Tinkicker]

Unless I am missing something, the elephant in the room is the air filter.  Toss it in the bin and fit a new, genuine filter.  

[Paul F]

Yes air filter is in the bin. Been out on it and it is running that well I may just  leave it and enjoy. Thanks all for your advice. Much appreciated and very knowledgeable. Cheers Paul