SF2 erratic idle issue.

zorba75482

zorba75482

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Location
Sulphur Springs, TX, USA
My SF2 started acting up a couple of hundred miles ago. Runs fine, but when hot wil not return to idle quickly.
I had planned to swap carbs anyway and assumed carb or air leak, so changed carbs, checked cables, air leaks and still have same issue. I cleaned and lubed the advance mechanism. Points clean. Enricheners seated. Slides returning properly. Any suggestions.
 

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Has there been a change in weather conditions - much colder could result in a lean idle mixture?

regardless of this try turning the idle mixture screws out a further 1/8-1/4 turn. I always found that my Dells on the SF would need this little bit of extra richness to get a clean return to idle, even though highest idle was a tad leaner. Some SF2s also came with a too-small pilot jet (#45 from memory - too small!).

If this doesn't have any effect, it sounds like air getting past the o-rings in the intake manifold isolators. Have never tried it, but you can spray starting aerosol around the intakes and see if it has any effect. One of the popular starting cans here in Oz is called Start Ya Bastard!
 

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Thanks for reply. I will check airs
piranha-bro2 said:
Has there been a change in weather conditions - much colder could result in a lean idle mixture?

regardless of this try turning the idle mixture screws out a further 1/8-1/4 turn. I always found that my Dells on the SF would need this little bit of extra richness to get a clean return to idle, even though highest idle was a tad leaner. Some SF2s also came with a too-small pilot jet (#45 from memory - too small!).

If this doesn't have any effect, it sounds like air getting past the o-rings in the intake manifold isolators. Have never tried it, but you can spray starting aerosol around the intakes and see if it has any effect. One of the popular starting cans here in Oz is called
Click to expand...
 
Checked the fuel filters? Jets clear?

P.S. it looks like you have a comfortable folding chair in your workshop. Not good. Workshops are for WORKING, not sitting about.
If I see that again I'll dock your pay.

;)
 
zorba75482 said:
I did spray WD40 around inlet manifolds and saw no change to idle. Cheers
Click to expand...

I am not sure (or better: doubt) that WD40 is highly inflamable. Brakecleaner works though.

I would check the following:
is it improving when you slightly pull choke? If so, it's running lean. If not or getting worse, it's running rich. typically, if it only happens when the bike is hot, it should be rich mixture, but who knows...

Tank:
-Check for water or rust/dirt in the tank. If there is water, you'll see kind of bubbles around the pet cocks
-ventilation: does it improve when you open the tank filler cap?

Carbs:
-balancer tube in place and air-tight?
-sliders are moving freely and are closing completely? (cable routing was already mentioned, but could also be dirt or wear causing a resistance)
-same for choke sliders (that would make it rich though). This is very often overseen... they need to be balanced, too, and - much more important - really sealing when closed!
-open float bowls and look for dirt or water.
-check float hights and -movement. low float hights can cause lean mixture in idle (and beyond), too
-O-rings between head and inlet-stubs/manifolds; also check that the sealing surface is flat! had some that were bent to almost 2 mm... the best O-Ring can't seal then...
-next to check is the jets of the carb - all tightly fastened and free?

Ignition: seems you are running points? If so - does the centrifugal adjustment work properly and the ignition timing is OK?

Exhaust: Are the tubes air-tight at the head?

Valves: correctly adjusted?

Let us know what you find ;-) and we go from there

cheers
 
I sprayed some arcing plug leads with WD40 once with the bike running and I can assure you that it burns very well. Surprised me anyway.
 
Andy said:
Checked the fuel filters? Jets clear?

P.S. it looks like you have a comfortable folding chair in your workshop. Not good. Workshops are for WORKING, not sitting about.
If I see that again I'll dock your pay.

;)
Click to expand...
Using a remote tank at moment, carbs just rebuilt. The chair is an important tool. it's where I sit and sip whisky to aid diagnosis of issues. Maybe the whisky content is insufficient in this case.;)
 
zorba75482 said:
Cheers. I just rebuilt and ultrasonic cleaned the new carbs. Was having same issue with another set of carbs, so digging through cables, inlet manifolds etc.
Click to expand...
With all these suggestions we're waiting with baited breath to see what the solver was, Zorba! If something changes suddenly it's a different species of search than if something goes out over a longer time frame. How long since it's run off idle to your liking? I'm thiunking it's a simple prob, easy fix. But as per suggestions above a full tune is always appreciated by your beast.
 
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