Initial Startup really bad idle - Help Needed

[paulbaker1954]

All back together and ready for MOT now BUT..............really poor idling problem 

Symptoms --- starts OK even from cold but sounds like a tractor    moving choke doesnt seem to make a whole lot of change. Also I noticed that adjusting the pilot air screws doesnt seem to induce any change in engine note but to be fair this is the first time I have worked on a four and I was only moving the screw about 1/4 turn either way. SO I am not sure really what I should be listening for here.

Once warm she sounds better but still a bit lumpy, blipping throttle off idle to say 3k RPM sounds really good

What I have done ........


A) Carbs all cleaned out including all jets removed and cleaned and all appear clear. All jets are original Keihin and fitted with new O rings.

B) Carbs have been balanced

C) New points and condensors fitted and timing strobe checked

D) New intake boots and no air leaks detected

E) All pilot air screws set unitially at 1 turn out


Overall it sounds to me like overfuelling at idle the only thing I have NOT done is removed the pilot air screws and cleand all their orifices


My plan as I really dont want to take the carbs off agaiin

1) Recheck timing with strobe

2) Recheck float heights and fuel levels using "manometer" tubes

3) Remove all pilot jets reclean and squirt a ton of carb cleaner in the pilot air  screw holes


Anything else anyone can suggest ?

[Bryanj]

May sound like a daft question but you haven't left anything under the seat then shut it have you? Also check that the advancer is working Plus Idle is normally at about 1100 RPM

[Sgt.Pinback]

Did you check the valves? Spark on all pots?

[paulbaker1954]

nothing under seat and yes firing on all pots

As I said runs great at higher revs

[Johnwebley]

try checking plug caps,

 as they get older the resistance increases,

 

[Noelia]

I have more or less the same problem with my cb550... Checked valves, cam chain... All is good carbs are balanced but the idling is still shit! Getting very frustrated... The rattling noise goes away if the revs are higher... I got it in a garage right now for second time...


Noelia

[Aly-b]

I think item three on your to do list is a good starting point as you may have some blockages.

[Aly-b]

May sound like a daft question but you haven't left anything under the seat then shut it have you? Also check that the advancer is working Plus Idle is normally at about 1100 RPM

Not a such a daft question,I owned a Bonneville back in '73 and left an item under the seat (where the coils are located).
Caused a short on one coil thus giving an intermittent misfire while riding.

[paulbaker1954]

Noelia be keen to hear what the garage pro finds on yours

I agree with Aly that most likely is a blockage in the primary idle circuit as once the main jet takes over all is good

[deltarider]

Did you adjust the camchain?

[paulbaker1954]

Fixed
Pulled carbs and found 1 blocked and 1 partially blocked pilot jets. Cleared with a wire from wire brush (don't play guitar!!!). Also liberally sprayed through all mixture screw holes with carb cleaner

Purring like a kitten now 😀😀😀

[Aly-b]

Great when a plan comes together,well done.

[matthewmosse]

Thanks for sharing the result, may help the next of us to encounter similar issues to get to the culprit quickly.

[Ashdowner]

I have exactly the same problem - idle shocking to non-existent yet over 3000rpm as sweet sounding as any engine could be. Looks like a carb clean for the new season.

[totty]

If you're not planning to use it any time soon just poor some redex down the fuel pipe to fill the bowls and leave it. You know the carbs aren't filthy as you've already stripped them so I can't see it doing any harm. I've cleared pilot jet passages this way before.