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Fine tuning an 850, part 2

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Guest
A couple of good mates hijacked the other thread a bit :p so I'm bringing it here...

So, here's the baseline:
  • individual foam filters and V&H 4-1
  • rebuilt top end with new o/size pistons/rings and lapped valves, valve clearances in spec
  • carbs ultrasonically cleaned with all new o-rings and synced; fitted with DJ Stage 3 kit,
  • carb boots intact with new orings
  • Dyna coils and ignition, coil-relay-mod, new sparkplug leads
  • exhaust tested for leaks at the headers - no leaks
The problem:
  • pops on decelaration quite a lot, through the exhaust
  • occassionally pops through the carbs: At a steady speed only, at small throttle opening like 1/8 to 1/4 turn.
Bike idles well and pulls with no coffing / sputtering in any gear at any rpm and from any throttle position (i.e. no noticeable issues while riding other than the two mentioned above).
 
I have tried adjusting the mixture screws as per the highest rpm method. This requires about 3 turns out. However, at that setting the popping increases dramatically.
When I turn the screws out to 5 turns the popping reduces substantially (but it's still there even on mild deceleration in the same gear). The pilot circut is so rich now that I can start the bike with no choke on a very cold day after sitting overnight. It also fumes white smoke like crazy when cold.

So, where to next ??
 
Do you think the foam filters are choking the motor? I have the exact same set up on my 850 and jetting was a PITA until I took off the EMGO pods and bit the bullet and bought the K&N's. It's ran like a bear since.
 
stain, that thought HAS crossed my mind... and I was planning on eventually getting K&Ns anyway. But MORE air would only mean LEANER condition and this should lead to increased popping... as far as I understand things :o

But you're right I think in that the DJ kit was made for when using K&N filters and my foam filters may be incompatible in some way
 
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Popping from the carbs is lean--popping from the exhaust is rich. Remove the filters and see if the problem gets better/worse. Also while the popping is occuring if you can pull the choke to see if its better or worse will tell you which way to go.
Not sure of the mileage on your carbs but I did have a set of emulsion tubes wear out and that made evrything rich.
 
Hey Psy ........... after riding your bike today, I couldn't put a finger on what was the likely cause of that stutter off idle. It is a type that I haven't experienced before, but I feel sure it's somehow related to your pilot circuit.

On my ride home, I remembered that I had been supplied the incorrect type of pilot jet from Z1 a while back when I was still tuning my VM's. There are 2 types, and both will screw into the pilot jet circuit, but do perform differently because of differing emulsion hole positions and seating configurations. Is it possible that you have the wrong type pilot jets fitted to your CV's? Just a thought!;)

Also, did you enlarge the vacuum holes on your slides?
 
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psyguy said:
I did enlarge the vacuum holes.

Good point on the pilot jets. I have those jets that have side holes in them while there are others found on 850s (same size jets) that have NO side holes in them... may well be the problem if DJ kit is made for USA market...

Could anyone confirm if the USA 850s come with pilot jets that have no side holes ??

http://www.motorcyclecarbs.com/Mikuni_Pilot_Jet_BS30_96_C23.cfm

OR

http://www.motorcyclecarbs.com/Mikuni_Pilot_Jet_N151_067_C26.cfm[/QUOTE


Psy, another possibility is that with the extra vacuum pull on your diaphragms, they may be oscillating just above idle position, before the needle would normally transition. Did you fit lighter springs above the diaphragms?
Click to expand...
 
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Stock springs.
Morgan carbtune didn't register any great oscilation in vacuum even as low as 1000 or 1500 rpm, and closing the throttle off from 3-4k rpm the vacuum settles quickly.
 
I think I'll lift the needles a couple of notches next and see what that does.
 
I also removed the foam filters altogether but that didn't make any difference to popping, it only made the throttle a bit less responsive just off idle.
 
psyguy said:
I think I'll lift the needles a couple of notches next and see what that does.
Click to expand...

One notch should be a significant enough change.

Do your pilots have the emulsion holes? If not, they should have according to those links.
 
I melted some plastic and am waiting on a set of new K&N filters :) so will hold off with further tuning until the filters arrive.
 
The K&Ns arrived today and I had my toolbox opened before the mailman even left :D
The filters are on and I raised the needles a notch. Lost one needle E clip in the process :eek: but had a spare :)

Now need to find a bit of time and the rain to stop for some road testing.

Will keep you posted.
 
psyguy said:
The K&Ns arrived today and I had my toolbox opened before the mailman even left :D
The filters are on and I raised the needles a notch. Lost one needle E clip in the process :eek: but had a spare :)

Now need to find a bit of time and the rain to stop for some road testing.

Will keep you posted.
Click to expand...

Good luck Ivor, hope it works out for you this time. We all desire smooth, rapid power delivery.
 
update well overdue

update well overdue

bike's been off the road for a while for (ahem ahem :rolleyes: ) more cosmetic enhancements... but is now back together so i was able to test ride it after i played with the carbs:

lifting the needles by a notch took almost all the popping out! :)

though, something's not quite right now just off the idle... but i guess that at 4 turns out the pilot screws are too rich so i'll play again with the "highest rpm method" to set them correctly

(previously, i turned the pilot screws down but the popping increased so i turned them out again to decrease the popping. obviously, i was working with the wrong carb circuit - pilot instead of needle.)

this excercise made me aware of how much noticeable performance can be gained with proper tuning so although going back and forth with carbs re-adjustments can be a pain it's all worth it in the end ;)
 
Hey PSY, glad you got the bike back on the road and are more happy with it now. No more popping. Often when you adjust one circuit, it does affect another circuit. I had a stumble just off idle and thought it was too lean, the screws were 2.5 turns out. when I pulled the plugs they were showing a bit rich. So I turned them all in to 2 turns out and the motor runs great now, no more stumble. So what I thought was too lean was actually too rich and screwing the mixture screws in 1/2 a turn leaned the idle enough to take the stumble away. I found the beauty of checking the mixture strength at idle was to just let the bike idle for 5 mins or so with a fan on it and then check the colour of the plugs. Well that worked for me anyway.

The other thing to be mindful of is that there are three small pilot holes in the throat of the carbs adjacent to the throttle butterfly. Only one of these is controlled by the mixture screw, the other two are controlled by the size of the fuel pilot jet. So if adjusting the mixture screws does not give you the required results then you can go up or down one size on the pilots depending whether you think you are too rich or too lean where the stumbling is happening.

Hope you get it sorted soon.
 
If you have to go more than 3 turns out on the pilot screws I suggest you go up one size on the pilot jets themselves.
 
psyguy said:
lifting the needles by a notch took almost all the popping out! :)

though, something's not quite right now just off the idle... but i guess that at 4 turns out the pilot screws are too rich so i'll play again with the "highest rpm method" to set them correctly
Click to expand...

I have set the mixture screws as per the highest rpm (at aprox 2 turns out). This has made the transition just off idle smoother :) but resulted (again) in some poping on deceleration - and overall on decel it felt like there's not enough gas getting through :mad: .

So I lifted the needles by one more notch. This took care of the popping and lean mixture on decel :) but the stumble just off the idle is even more pronaunced :mad: .


What shall I try next? I was thinking either
  1. lower the needle but try larger main jets (currently I'm using the mid size of the three sizes suplied by dynajet), or
  2. lower the needle and set the mixture screws out by an additional half or one turn (i.e. from aprox 2 turns to aprox 3)
What do you think?
 
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