Fine tuning an 850, part 2

[psyguy]

A couple of good mates hijacked the other thread a bit 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).

[psyguy]

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 ??

[stain]

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.

[psyguy]

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

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

[stain]

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.

[49er]

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?

[psyguy]

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

[49er]

[QUOTE=psyguy;1450631]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/Mikun...51_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?

[psyguy]

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.

[psyguy]

I think I'll lift the needles a couple of notches next and see what that does.

[psyguy]

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.

[49er]

I think I'll lift the needles a couple of notches next and see what that does.

One notch should be a significant enough change.

Do your pilots have the emulsion holes? If not, they should have according to those links.

[psyguy]

My pilots DO have emulsion holes.

[psyguy]

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.

[psyguy]

The K&Ns arrived today and I had my toolbox opened before the mailman even left
The filters are on and I raised the needles a notch. Lost one needle E clip in the process 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.