Hanging idle please help

[the-chauffeur]

If it's only at idle that you're struggling to hit the sweet spot, it might be that you need to look at a set of different size pilot jets.  As I'm finding with a different bike and non-standard carbs/filters, the wrong size jets for any given application will cause some odd things to happen.

In my case, I was told the jetting was spot on, but it clearly wasn't - after a short time running at idle, the bike would die.  I was adjusting the air screws and it was making no significant difference.  And pulling the plugs showed they were black with carbon.  So what that told me was the slow/pilot/idle jets were too big.  I've gone down one size and the bike doesn't die at idle, but the plugs get blacker than I'd like (but nowhere near as bad as they were) so I'll try going down one more.

As the others have said, pod filters/different exhaust are likely to change the airflow characteristics to the point where they move away from the book settings and you won't be able to iron out the idle/fueling without changing something.  Fortunately, that something is likely to be pretty small in the grand scheme of things, but it might take some messing around to get to where you want to be.

[Wenman]

Thanks for those responses I have some 38’s that I can try so that will be my next move. I feel like it’s not a jetting problem tho!

The issue is I can be going 20-30 mph and when I change gear with the clutch the revs maintain whatever I’m revving say around 5-6000rpm, I also feel like I’m braking against a reving engine.. like having one foot on the brake and the other foot on the accelerator (car reference before someone asks why I’m using pedals lol)

Occasionally when coming to a stop the rpm also remains high when clutch is disengaged??

Alan

[Johnwebley]

Two things. Make sure the slides always slam shut.if necessary shut them by closing the throttle hard using shut cable.

Also check again for air leaks

Sent from my SM-A750FN using Tapatalk

[the-chauffeur]

Sorry - my earlier post was predicated on the fact that you'd mentioned idle being a problem.  Based on your last post, it sounds as though you've got issues with your throttle cables.  If the revs don't drop, chances are the slides aren't closing after being held open so there's either something odd about the cables themselves, or the routing's not right.

What sort of handlebars are on the bike - are they standard or aftermarket?  And if they're standard, are they UK or US spec?  The UK spec were the flatter type; the US have a higher rise on them.  If they're the US spec and you're using UK spec cables, it's possible one (or both) of the cables is fractionally too short.  And that being the case the throttle slides will be prevented from shutting freely/completely under certain conditions.  Silvers sell both types - look down this page.

If it's not that, have a look at how you've routed the cables.  Any sort of sharp bends in the way they're routed can cause  the inners to get hung up on the outers.  Another test - if the revs rise/fall when the handlebars are turned lock-to-lock, something about the cables is not right.

I'd also add that pictures (of both the front end and the cable routing/carbs from above) will help more knowledgeable folk here help you narrow down what needs attention.

[Wenman]

Okay thanks for all the replies!

The bike has aftermarket clip ons with venhill Cables. I have a domino aftermarket throttle too.
The venhill cables were cut to length by myself. I have slight play at both the carb end and about 5 degrees at the throttle grip.

Routing is somewhat questionable however there are no sharp bends.

On opening and closing the throttle when looking into the open carb bodies the sliders slam shut as the return spring pulls them down.

If the sliders weren’t closing properly surely I would feel that in throttle grip as if one holds open they all must be open due to all being on the same lifter?

Thanks again I’ll try and get some pics!

[K2-K6]

Adding some additional checks to the list;-

Check that the ignition advance retard mechanism is working and drops back to baseline as revs drop ( probably worth removing and checking for operation if not sure of condition) as advance timing will certainly promote higher idle speed.

Same as you Alan,  in that it doesn't appear like jetting as that is usually consistent. Either right or wrong. But uncontrolled revs are nearly always a scource of air that you aren't able to control.  With that in mind,  the intake head to carb rubbers are one of the prime suspects here, even if they look ok.  Plus the clamping bands have to have good integrity to both fit in their groove and clamp to eliminate 100% of any potential leaks.  If they are either very hard or you've any doubt about them,  then a spray around them with carb cleaner (sparingly with tank removed and outside as it's a flammable risk) will ordinarily show you.

Specifically an air leak must be between the carb slide and the combustion chamber to achieve uncontrolled throttle effects,  just to add a clear problem statement. 

Another "potential" scource, if all of the above posts don't effect a cure. If you can get it to "hang" while stationary,  place the engine breather pipe into a clear bottle (small plastic water bottle) with some engine oil to submerge the pipe,  and closely monitor the level while revving and closing the throttle,  it shouldn't suck the oil level to a lower position. 

[Wenman]

https://youtu.be/wTdmuhMUE1Y

Okay so I think I’ve found the culprit.. you were correct in that the sliders aren’t seating properly.
If I blip the throttle the Return spring and Weight pulls them closed.

If however I slowly open the throttle to say 2500 revs and let go they struggle to fully seat and remain open about 2-3mm. They do slowly go down which can be seen in the last 3 throttle pulls in the video.

What could remedy this? I believe the cables are adequately routed with no sharp bends. Could it be a fault internally inside the carbs bent needle or faulty slider.

Any recommendations would be helpful thanks guys!

Alan

[JezzaPeach]

Could it be slides gumming up? Mine did when I left it for a long time. I sprayed GT85 or similar via the air box which seemed to help and use Sta-Bil in the fuel.

[Wenman]

Could it be slides gumming up? Mine did when I left it for a long time. I sprayed GT85 or similar via the air box which seemed to help and use Sta-Bil in the fuel.

Worth a try.. I just sprayed them with gt85 and it didn’t revolve interestingly it does NOT do it when the engines off!!!
So whatever is causing it is a result of what’s happening when the engine is running!!

Please help 😂

[JezzaPeach]

Can you hear the slides metallic click as they hit bottom?

[JezzaPeach]

Just another obscure random thought! Is the choke lever catching on the breather pipe. (my 500 did yours my not apply)

[K2-K6]

At least you've now got a postive identification on the cause.

The little rods from outside to inside of the slides can get a bit "gummy" so worth a spray of lubricant there to see if it improves and helps you diagnose.
They should  be clean and run dry though ultimately,  along with the rubber boots to keep them clean and avoid impairment.  You see many without the boot but they are important and effective.

Another is to clean the polished slides with something like turpentine substitute to degrease,  and just dry them with a clean cloth,  the carb venturi too along with the slide bore ( you really need slides out to properly inspect and clean this way thoroughly).

[Wenman]

I’m pretty confident the internals are clean and gum free, I stripped them down prior to rebuild and there was nothing untoward.. plus I’m a sucker for carb clean so they would have had a fair share of it.

Is there anything that may cause this effect when the engines running like vacuum?
Only it dosent repeat the fault when the engines off.. they seat well and quick. Only does it when the engines running?

Thanks for all your replies.. together we will sort it!!

Alan

[K2-K6]

Ok,  in that direction of "oddness" what have you ended up at when setting the idle mixture screws?

Projection to try and see if if makes a difference,  turn the mixture screws IN a quarter turn from where they are,  this should slow the tickover down ( makes it richer) forcing you to wind up the main tickover rpm control for the carb rack to bring it back up to normal level.

Let us know if that changes it.

[JezzaPeach]

Is it possible for the return spring to bind in its shroud (if it has one )?