Jetting and choke issues '74 850T

[James K]

Hi all,

My 74 850 T has 36PHF carbs, Gilardoni cylinders, pod filters and Staintune aftermarket mufflers (Australian). Standard 850T compression.

Question 1 - JETTING - What jetting should be ideal for this setup on my 850T?

It's mainly ridden at ground level to 600 metres elevation.

Its currently running 50/3 slide, 265 needle jet, K16 needle, 52 pilot jets (have changed them from 57's) and 130 main jet. Float height 18mm.

Question 2 - Over rich - Why would one plug be turning black and heavy soot but have also had the problem on the other side (at different times) Choke issue or something else?

The problem - The plug on one side turns very black and sooty after even a 10—20-minute ride. Then, it starts misfiring and hesitating. The other plug is also black but nowhere near as much. As mentioned this problem with one plug turning very black has switched cylinders so maybe it's choke-related but all seems to check out ok).

We changed plugs to a new set, then a 10-minute local ride, and the same problem.

Have cleaned out the carbs, the fuel tank, balanced the carbs, done timing, checked valve clearances. All set correctly.

New electronic ignition fitted, just replace the Dyna 3 with the Aussie TriSpark, The problem occurred with both fitted so have ruled out the ignition as an issue.

Much appreciate your thoughts!

Cheers, Terry

 

[john zibell]

Check the bottom of the plungers for the enriching jet (choke). The rubber there may be worn/damaged. If worn/damaged it will need to be replaced.

 

[V700Steve]

To me it sounds over fueled. The euro PHF for the G5 or Cal2 were a bit less both small valve heads. Here it is--------------------------

Slide- 60/3
Atomizer- 264
Needle- K23
Idle mix screw - shorter tip
Around 50-55 pilot
Around 145-150 main
Pump jet 33-35
The choke is better w/a #60 jet or less you don't need a 70 or 80 on choke, it comes strait out of float bowl
Seen as slides cost now days you could use the 50/3

To check set up a piece of tape on throttle and mark it 1/8, 1/4, 1/2, 3/4, wide open run 2mi on steady setting, cut ignition & check plug w/o moving throttle down.
It is all in tuning guide from DelOrto available in download section.

 

[James K]

Much appreciated! Will give it a go.

To compare, before posting we had been thinking about using this jetting, what are your thoughts on this setup of using a Mk3 Lemans jetting?
50 idle
115 Main
K18 needle
268 needle jet
60/3 slide
Keeping in mind mine is the first model 850T with pods, aftermarket pipes and Gilardoni cylinders.

 

[V700Steve]

One thing I always remember, on loops idle jet was 45 & main 145, my new 850T in 76 was 52 & 142 mains. No airbox & open pipes I had 60 pilots & 150 mains. Same worked on my new 1000SP w/K&N's & Bub exhaust system. On my LM3 I burnt the valves by making it too lean. That was in 85. Good luck & read your plugs, they tell you what you need in different throttle settings.

 

[James K]

Much appreciate all the great advice, now to sort out those carbs! Cheers