[gashousegorilla]

Hi guys,

with a long period of in-activity at the bike (too much other things to do at home, at work and the rest of the cars and bikes...apart from some health trouble); I re-assembled the engine in the last days.

As Wahl-pistons are extremely busy during summer, I decided to keep the original piston for the moment and raised CR a little by using a 0,1mm paper for the cylinder-base gasket.

Well, put everything together (with the Hitchcock cam kit - heaven, these double springs are hard stuff ! Map is "as it comes from Hitchcock with the cam-kit") yesterday and started.....

1. started immediately with a little bit of throttle
2. no mechanical noise, valve train just fine
3. NO idle...without a bit of throttle but biting immediate on the throttle
4. feels powerpul and crisp on the throttle, spinning up very quick (for a thumper)

Point 3 is the problem, I don't find an acceptable idle....lifted the tank to get access to the idle-adjusting-screw and turned counter-clockwise in 1/4 increments - first it was too low (under 800 rpm) or it's too high (around 2000 rpm) but even with slight adjsutmenst of the screw, the reaction might be a) none or b) extreme.....

Moved the injector/throttle-unit with engine running to see changes (false air), no change....but the PC5's red (status) LED was flickering for perhaps 1-2 seconds when the idle was very low...

Any ideas about this ?
Help is VERY appreciate...thanks a lot in advance !

    Yes, I think I understand Hardy .     Your too rich at start up and idle. The bike needed throttle to start initially.. which gave it some air.  Turning the idle air screw out , will put the idle into a surge.   Turning it IN and the idle is too low . Correct ?   Your effecting what the Map sensor is "seeing" as far as manifold pressure.  And you have to adjust for this lower vacuum in the intake. You probably need to adjust your fueling at zero throttle from 500 rpms up to around 1500 -2000 rpm.... Taking fuel out in that area.   This should get you into a nice stable idle in the 1000 to 1200 area.

   Here is a video demonstration... with a more radical cam profile installed on the bike.     This is from a DEAD COLD start, all the way up to operating temp. It shows fuel corrections , manifold pressure and cylinder head temps.   You CAN tune it to a nice idle.

 https://www.youtube.com/watch?v=sYuuSHFSu7U

[Otto_Ing]

My experience just tells me that with the stock combustion chamber you will get a very temperature dependant idle. In my stock bike the idle would increase to 1600rpm at higher temperatures while it would idle just fine when cold around 1000 rpm. Nothing one can't live with but just saying. With the Fireball combustion chamber i've go a death stable idle at all temperatures. Maybe there is a tiny deviation from 1000rpm as cold to 1100 rpm when wery hot. That's about it.

In my view your bike should idle just fine with the sock settings even though the cams changed. It could be a bit too rich as GHG said due to lower dynamic compression ratio caused by the long duration cams.

[Jako]

I also have  rich weak idle after installing Hitchcock cams and valves in my B5, I use the EJK fuel controller that only adds fuel  so I have no way of leaning out the idle mixture . Mine runs nice other then the weak idle.

[gashousegorilla]

  Speaking of the Bullet... The GT's mapping I'm sure must be a little different.... but the concept is the same if not the actual amounts. 

   The Bullet dumps in a BUCKET load of fuel at start up and at idle .  When you turn the key on and hit the kill switch it fires a shot of fuel into the chamber... this helps when one has a kick starter.    It kind of simulates one ticking an Amal carb  .    If you notice , whenever you kick the bike over, the pump comes on firing a shot of fuel.    Once i'st running at idle , it idles very rich.  I have seen numbers around 10-1 AFR at idle before the o2 sensor kicks in to start switching between  too rich and too lean. If one does not have and o2 sensor.... like that shunt one puts in  when using the PC-V, to eliminate that o2 sensor so one CAN tune... the  Air fuel ratio stays at that rich mix at idle.

  A stock bike and it's associated ECU and sensors , are just that .... STOCK .   And the ECU is programmed as such.  And EXPECTS to "see" certain voltage and resistance values , because it is stock.   Once you change things, and depending on how far you go ? 

  For example... Cams.  Cams affect the air flow though the motor, when and how right ?    So. lets say you put in longer winded  Cam, with more duration  and more lift.  This LOWERS manifold vacuum at idle... less suction at low rpm's.  Less suction means less air flowing into the chamber.  So you need less fuel to go along with it.. Right ?    You would normally in stock form at idle see HIGH suction in that intake manifold .. especially with that throttle plate closed.  And that is where the MAP sensor lives, right in that intake manifold.   At idle, with some Hot rod cams in there, with the less vacuum going on , the MAP sensor MAY interpret this as the throttle plate being WIDE open !       You have less vacuum on a wide open or partially open throttle plate  generally, and this is exactly what the MAP sensor measures.... MANIFOLD ABSOLUTE PRESSURE.   Sooo.... ones bike MAY be dumping in more fuel " mistakenly" then it needs !

  Increasing ones compression ratio will generally increase efficiency... higher pressures squeeze the air and fuel molecules tighter together for a quicker and more efficient burn.... you generally need less fuel to do the same thing.

  Now, one has Cams in there effecting the air fuel requirements.... depending, but generally for long duration Cams,  less fuel at idle and MUCH more as the RPMS come up.  Then throw on top of that HIGHER compression ratio !       And you fuel requirements, depending on what you want to gain and at what RPM... Are going to be WAY off from stock.    And if one is using a "Canned "  map , that some one has created for a certain bike with exactly the same modifications... it will be "OK"  Air and fuel wise.     But if one deviates from having those "exactly the same  modifications" .... one might not be so " OK"  air and fuel wise when and where in the RPM range.

[gizzo]

   When you turn the key on and hit the kill switch it fires a shot of fuel into the chamber... this helps when one has a kick starter.    It kind of simulates one ticking an Amal carb  .    If you notice , whenever you kick the bike over, the pump comes on firing a shot of fuel.   

I didn't know that. I just assumed it was the fuel pump making fuel pressure for when it's ready for it but not running continuously when it's not needed. Not that it makes any difference to me but it's good to know. Thanks.

[gashousegorilla]

  Yeah, it would be interesting to test and see if it does on the GT... I'm thinking it does.   Just hook a volt meter to the injector and see if you are getting Voltage at the injector when you flip the kill switch to run..when you are in neutral.   Or... as you kick it over.  It's gotta get fuel in there when you try to kick start it .  And it's really just "mimicking" what one would have to do if it was an  Old style motor.. which it is... if it had a Carb on there.

[Chilliman]

It may be worth noting that engines with high lift, and long duration cams also don't scavenge well at low revs, hence the lopey idle associated with "big" cams.
The cylinders don't fill well with fuel/air because of low intake gas speeds at low revs, because of the phenomenon called "reversion".
Some engines that don't scavenge well at low revs have considerable exhaust gas dilution causing a leaning off of the idle mixtures.
A common modification in carburetors asked to work with "big" cams, is to modify the pilot jet or idle feed restriction by making it a little larger ie. richer, to compensate for the exhaust gas diluted low speed mixture.
Depending on what efi control system you have you will have to play with that low speed area for sure.