jetting for unleaded gas

[theo305]

Hello
I have some cold starting issues with my DOHC.
 If the bike seats for 2-3 days its very difficult to start in the morning especially in colder days.
Also some times when i am trying to start it burns the sparks no difference
 If i use ngk or denso plugs.
A mechanic told me that the main problem is the gas and that these bikes
Where made to burn only super petrol.
In my country the gas stations have only uleaded 95 and 98.
He told me the only solution its to change the jets to 105 ,(I have 102 and 68)
also the needle height and  the air mixture.
 Is there a meaning to all this?
Thank you

[TOOLS1]

Your mechanic is both right, and wrong here. He is right about ethanol gas creating a lean condition, and needing larger jets. However he is wrong on the octane. The higher the octane, the slower the fuel burns. Higher octane does NOT make more power. What it does is make the fuel burn slower, so that you can run higher compression (this is what makes power) without pinging, or knocking, otherwise known as pre-ignition. Now this will destroy an engine. These engines were not really designed to use "super" gas. They actually run better on regular. However if you hear pinging, or knocking, then go to a higher octane. However the better solution is to re-jet, because pinging, knocking is also caused by a lean condition.
Now to your running problem. You could have several things going on here. The cold starting could be a lean condition. It could also be dirty pilot jets, a vacuum leak, or an ignition problem. Your bike should not be burning plugs. This could also be a lean condition, or improper heat range on the plugs. It would be helpful to see a picture of the plugs. They should be a light brown color on the insulators.
TOOLS

[theo305]

The colour of the plugs looks ok.Usually are burned when
the bike sits more days and the battery voltage is down.
As for the leaks i have changed the boots last year and upgrade the
Ignition with cbr600 coils also direct feed from battery with relay mod.
I am not sure if i have to change the plug cups , i am using the stock with
resistance.
 We dont have regular petrol here,only unleaded 95-98!
What about the air cutoff valves?

[TOOLS1]

I do not know where you are at, but here in the states, we just refer to the 95-98 octane unleaded as regular. The aircut valves can leak causing a vacuum problem, but that usually causes backfiring/popping. I am not familiar with the CBR coil swap, but that might have something to do with your burned plugs. However the hard starting after sitting would be caused by the fuel settling into the float bowels out of the jet passages, and the engine needing to suck it back up. Do your choke butterfly's close properly? Also the sitting should not be causing the spark plugs to burn.
Maybe someone will be along that knows more about the ignition mods then I do.
TOOLS  

[theo305]

The problem was there before i make the coil mods so
It must be something else.

[shinyribs]

Is your accelerator pump working and is it pumping fuel out of all four carbs?

Nearly impossible to start a bike with these CV's and no accel. pump.

I know one guy that runs CBR coils on his '79F. Rest of the wiring is all stock. No problems and no burnt plugs.

[motogrady]

id look at the choke butterflys, are they closing all the way when you pull the choke knob out?
maybe pull a plug when it doesn't start, after cranking, is it wet with fuel?
if not, something is clogged in the carbs.  try squirting some raw gas or starter fluid
into the carbs with the filter box off.  if it starts then, it's obvious not enough petrol is making it to the airstream.  something is clogged.  accelerator pump maybe, twisting the throttle a few times should squirt fuel into the rack, helping with start up.

if the plugs show wet after a failed start attempt, id then go to battery, weak spark, hard to start.

octane, a non issue in my book.

[theo305]

My carbs are vb52A European model without accelerator pump.
I think in US you have the vb42A i dont know difference.
About the hard starting issue I also believe its not electric
but a gas problem so i have to do it
by the hard way,pull out the carbs clean and inspect everything.
Maybe i will bypass the air cuttoff valves.
I did this on my1100f and never had a problem.
How often do we have to clean these carbs?
Last time was about 2 years ago and i have replaced
everything except the small rubber plugs.


 

[shinyribs]

They don't require constant cleaning with normal use. Bit if the bike had been sitting for an extended period of time then you'll likely need to clean them.

If you dont have an accel. pump circuit and the choke is operating then I'd suspect dirty pilot jets.

If it's been parked for two years then the previous cleaning is out the window.

[shinyribs]

And what do you mean by the plugs are burned? Are the electrodes melted?

[theo305]

They just dont work and need replacement.The colour of the sparks looks ok,
no carbon no oil.Some times one plug failing sometimes 2 or 3 together.
 Its easy to understand which plugs are failed, just touching the exhaust pipes
and find the cold ones.
As i said the plugs are failing usually after many attempts to start the bike and battery
 level goes lower.

[shinyribs]

So the plugs are firing intermittently? Are your plug caps making good connection to your wires?

[TOOLS1]

After studying all the information you have supplied, I can just about guarantee you are having a carb problem, and not an ignition problem. I would be giving the carbs, and especially the pilot jets a through cleaning.
TOOLS

[theo305]

Just find time today and pull my carbs out for cleaning and guess what?
Tools was right the jets where clocked also find some rust from the gas tank.
After cleaning everything I changed the main jets from 102 to 100 because spark readings
looked like rich condition. I put back the carbs but they were leaking  gas from that T pipe
where the gas hose connected. So pull out again  and replaced the o rings.Also reset the choke
butterflies that were not closing properly
Give it a start  and the engine started immediately!
It's like i am driving a new bike good throttle response and lots of power!
Now I have to sync the carbs for perfect tuning.
I want to thanks tools for all support giving us every time always replying first to help us with
the deep knowledge he has for cbs