Lean - White Spark Plugs - Aftermarket Exhaust

[Lithil]

Hello fellow riders,

 

new to the forum, thanks for validating. 

 

I bought a time ago TDM 850 4TX (2001 year) - latest model on Europe market. I drove bike first few tousands kilometers and realized my bike smells of fuel. I swapped aftermarket exhaust (more open cans) and bike started to be more alive and started heavily popping on decceleration only - thought when bike runs better, no issue. After time i have checked spark plugs - one white, one totaly black - i thought there is an issue in carb (bike was poorly maintained by prevoius owner). I have rebuild carbs (MK2a carbs - Mikuni BDSR38), including new needle jets pressed out and new needles. Cleaned spark plugs and after 50km checked - both white (one maybe slightly, veeery slight starting tan color). Decceleration popping is same, performance same except thorttle is smoother. 

 

And now question - what would you do to improve mixture and how to spot good mixture at best ? 

 

I hope i explained story of my bike well. My english is learned only from hearing and reading, sorry for that.

 

PS: valves clearance not done, tried to measure, but stripped water flange screw head .... peep

 

Thank you in advance

[fixitsan]

Are the carb rubbers leaking air through cracks ?

[Lithil]

Carb rubbers completely new - gaskets, mambranes and joints carb/intake. Same before as after

This post was last modified: 18-07-2024, 12:38 PM by Lithil.

[fixitsan]

Carb rubbers completely new - gaskets, mambranes and joints carb/intake. Same before as after

 

All good ?

 

You have to consider the carbs then. Have you ever modified a needle ? If you can figure out where it's at it's most lean it might be a case of marking the needle and rubbing it down in that area. But a new needle/jet would be better

[Lithil]

As i wrote above. There is completely new needle and needle jet. 5 days ago exchanged. Carbs serviced. The lean condition is same before and after carbs service.

[Catteeclan]

Is the bike riding ok or are you chasing the popping on overrun?

[Lithil]

riding is good - its my first bike, so i do not recognise some slight power loss. But i think reponse from throttle could be better. Popping is smaller issue than white spark plugs 

[dapleb]

What brand emulsion tubes and needles did you use?

[fixitsan]

As i wrote above. There is completely new needle and needle jet. 5 days ago exchanged. Carbs serviced. The lean condition is same before and after carbs service.

OK thanks, I'm assuming you've checked the plug types are the exact type recommended ?

And also keeping in mind the known existence of fakes of every manufacturer's spark plugs.

 

NGK's website recommends the DPR8EA-9 (as does owner's manual).

This post was last modified: 18-07-2024, 07:23 PM by fixitsan.

[Lithil]

What brand emulsion tubes and needles did you use?

 

Mikuni original, replaced at Topham-Mikuni workshop in Germany. 

 

to fixitsan: Spark plugs are replaced 2k km ago by me for DPR8EA-9 from reputable dealer (i do not know if they can fake it), but i have pair of new ones on table prepared in need . 

[Lithil]

Today added on mixture screws +0.5 turns. No effect.

 

Thinking two options:

1. valves are out of tolerances or chain is sadly worn

 

2. aftermarket exhaust allows more air to be sucked back in to process, so i need to:

                                           a) give more turns on mixture screw

                                           b) put needles on higher position to allow more fuel flow 

 

 

 

Your thoughts ? 

[Catteeclan]

Mixture screw will only richen tick over and a little above. Think I'd restrict the air coming in to see if it improves the engine response.



Could always check the valve clearances and timing to rule them out.

[fixitsan]

Today added on mixture screws +0.5 turns. No effect.

 

Thinking two options:

1. valves are out of tolerances or chain is sadly worn

 

2. aftermarket exhaust allows more air to be sucked back in to process, so i need to:

                                           a) give more turns on mixture screw

                                           b) put needles on higher position to allow more fuel flow 

 

 

 

Your thoughts ? 

Option B worth trying

[leehenty]

I agree raise the needles a notch, if still too weak at max needle height you might have to go up a size on the main jet

This post was last modified: 20-07-2024, 04:25 PM by leehenty.