One white plug

Thank you for your post. Last year I was running my crappy CV with pods because I don’t have original air box and my dyno guys say wouldn’t touch it at all!! Not with my VM28 Im very happy with the result!! Just my 3000-4000rpm make me have some questions!! I appreciate your help guys

Injected wrote:

At 3000-4000 RPM a bunch of different things are happening in the carbs and engine. Your going from pilot (idle) circuit to the needle circuit plus the ignition timing is going to full advance. At that same time the butterflys (CV carbs) are wide open but the slide may only be partially up depending on vacuum.

Transitions like this are hard to tune in general, going slightly lean for a very short duration at low RPM is not going to hurt the engine especially if the main jet is correct. I have seen dips like that in AFR graphs before, not uncommon at all. I would concentrate more on getting the plugs to burn tan than black instead of a small AFR blip.

There is a limited tune up for gasoline carbs and its very narrow, not too many changes can be made unlike electronic fuel injection.

I think the issue is more about a "hesitation" that can be felt on the road around 3000rpm than it is trying to smooth the graph but I absolutely agree regards getting the "over rich" situation sorted first (if it burns cleaner at low revs it may help the hesitation issue)

Yess it feels like hesitation!! A little more gas, just a little and bang hes ready to go through 10 000rpm

Maxbou92 wrote:

Thank you for your post. Last year I was running my crappy CV with pods because I don’t have original air box and my dyno guys say wouldn’t touch it at all!! Not with my VM28 Im very happy with the result!! Just my 3000-4000rpm make me have some questions!! I appreciate your help guys
 

Oh, I took it you were using CV carbs because I saw "Dyno Jet" mentioned in one reply. Very seldom would you need a different needle on VM's.
You have fully adjustable needles on VM's. After you get the choke plungers renewed run it like that. Then you can go up or down one notch on the needle clips to see what the results are.
Like I mentioned one change at a time, its possible you might not have to touch the needle height.

I will check the plunger this winter!! But Im not sure that I want to play with needles !! It cost me 600 buck on the dyno!!  Does Valve lash can cause the symptoms I have?!

Maxbou92 wrote:

I will check the plunger this winter!! But Im not sure that I want to play with needles !! It cost me 600 buck on the dyno!!  Does Valve lash can cause the symptoms I have?!


 

If you had tight valves there would be less compression, not a bad idea to check a few times after a rebuild but the HP chart looks good for your mods. The black plugs just look like a rich condition that could be cause by fuel leakage (choke plungers) at idle.

Yes the dyno is not the cheapest place to go to do tuning. I do all my tuning on farm country roads with next to zero traffic. I have been on the dyno several times to check HP, here is my 831cc 650 engine 10 years ago before guy had AFR/RPM showing, just shy of 90 HP.



I plan to check my 1200cc engine on a dyno this summer once its broken in. I also have a portable AFR gauge setup now that I can also use to get closer on jetting.

 

Nice numbers you have!! I dont know the clip needle position.. I call him today for black plugs.. and he says the bike runs so good that he doubts the choke could be problematic!! I will check it out.. he says there’s nothing to do with it. Carbs are carbs like you say before!!  

Maxbou92 wrote:

Nice numbers you have!! I dont know the clip needle position.. I call him today for black plugs.. and he says the bike runs so good that he doubts the choke could be problematic!! I will check it out.. he says there’s nothing to do with it. Carbs are carbs like you say before!!  

I'm sure you will figure it out, be well

Maxbou92 wrote:

I call him today for black plugs.. and he says the bike runs so good that he doubts the choke could be problematic!! I will check it out.. he says there’s nothing to do with it. 

I suspect he doesn't fully know what he's talking about..
The "choke" is actually an enrichener and worn seals will cause rich running.
It is a common issue experienced by many members which is why they highlighted it.
It mostly affects 0 to 1/4 throttle initially showing up as sooty plugs and then progressing to hesitation but depending on the extent of the wear and leakage can cause severe bogging and loss of power higher up especially when the engine is up to temperature. 
 

The sooting on the three plugs may be due to the plungers but you should maybe investigate the leaner one to see if an air leak or very tight valve clearance is happening to either feed just enough air to correct the mix or cause the cylinder to run hotter and burn off the soot on that plug.
Plunger seals do wear at different rates but usually there is evidence of leakage on all cylinders to varying degrees with some sootier than others.
The one that's showing a good colour may be subject to more than one issue which is masking either fault.
 

I have spray some brake cleaner everywhere and I haven’t find any leak!! I remember that the machinist who has rebuilt my head, he has to make this cylinder (4) a bit more loose than the others due to available shims thickness., does it can cause that color ?!

A little loose is ok and better than tight.
A valve with very little to no clearance which didn't seat when hot would be a likely cause and not one that has a slightly wider clearance.