carb setting for wiseco 615cc big bore kit

Hi All, 
So seems I successfully installed a Wiseco 615 kit in my 550.  Nothing blew up and bike is running super strong (I feel like I can teleport now from stoplight to stoplight ).  I already had a Factory Pro stage 1 kit installed, and just bumped the main jets to 112/115 (stock is 108/110).  No problem on mid to open throttle, nice smooth power. But I'm having problems with idle.  By the time I can get a good idle speed the rpms will hang a bit when I blip the throttle. I've checked for air leaks, pretty sure it's just a fuel metering issue.  I followed Marc Salvisberg's excellent advice pasted below and bumped the pilot jet from a 38 to 40 (35 is stock).  Issue is a bit better but the rpms are still hanging slightly.  I'm thinking about installing 42 pilot jets but that seems really high for my set up (615 kit with a Kerker exhaust).  Maybe not, I don't know. Ironically, I'm thinking of moving to pod filters because I know people on this forum have dialed those in with the 615 kit and I know exactly what jetting should work. 


Marc's troubleshooting suggestions: 

Idle Diagnosis
How to determine  whether you are too rich or too lean on your pilot jets and fuel screw settings.
When the pilot jet is the right size and each of the fuel screws is set right, the bike will  accept the throttle nicely and drop back down to your set idle without hanging up
If the idle mixture is significantly too rich or too lean, the engine rpm will tend to hang up at around 3000 rpm after lightly blipping the throttle.
 
Procedure:
1  Set all Fuel Screws to your favorite number of turns out. Suggest starting, at 2.5 turns out from lightly bottomed out on each fuel screw.
2   Start the engine.
3   With the single Idle Speed screw, set the idle speed to the manufacturer's suggested  idle rpm. Play around with the throttle a bit in neutral until you get  a feel for how the engine responds.
 
4    Now, with the engine still running, reach in  and adjust the  idle rpm to as low an rpm that the engine will idle at.
5    One at a time, adjust a fuel screw to  it's  Happy Place - the idle will rise. After optimizing the one fuel screw, now, lower the rpm back down to as low as it will possibly idle (again) then go to the next fuel screw and optimize it, then lower the rpm.  Repeat series twice. Expect that each fuel screw will be different
 
6    If you end up at with the fuel screws at 1.5x, then you need a smaller pilot jet.
7    If you end up at with the fuel screws at 3.5x, then you need a larger pilot jet.
8    And when you have optimized all 4 fuel screws, raise the idle rpm to the desired idle rpm.

 

I have run into this with my cvk carbs multiple times. 
Here are three things have fixed the issue..
1.  My throttle cable needed lubed. It was sticking and if I physically forced the throttle all the way back the idle would drop. Some times if the throttle tube is incorrectly run through the frame, it puts tension on the cable that will not physically let the carbs fully return to idle. 
2. What has happened more often is that I would rejet or mess with the carbs for some reason and I would have to raise the idle to get it to start/run. What happens is that there are 3(I think) microscopic idle ports in the cabs. Only ONE should be uncovered by the throttle butterfly at idle. If you start messing with the idle knob, it will uncover another port (letting in more fuel and keeping it running) but when the engine warms up, it gets too much fuel and the rpm’s won’t drop.(it keeps getting too much fuel) 
I have had to remove the carbs, adjust the idle knob so the first port is just visible. Put the carbs back on and focus on adjusting the fuel metering screws (or jets) until it idled properly. And of course, everytime you start messing with fuel mixture screws, you HAVE to re-sync the carbs. 
3.  Take the carbs off and do the ghetto carb sync first. Put a small/tiny drill bit in the throat of the carb and adjust the butterfly until it juuuuuust touches the drill bit. Do this on all four carbs using the exact same drill bit. This makes sure when the carb throttle is released, all four butterfly’s are at the EXACT same spot. 
Only then can you put the carbs on the motor and then actually synchronize them  while the engine is running. When the engine is running, you are micro adjusting the carbs to the vacuum demands of each specific cylinder. (Differences in compression due to valve lash, blow by, valve seats…etc, is what you are then adjusting the carbs too) 

If have chased this issue more than I care to admit, so I hope this helps. 

Awesome advice, will give it a shot.  Thank you!

Hey Zaddict, can you tell me what kind of piston ring compressor tool you used (if any) when you did your big bore kit installation? 

I bought some ring compressors off Amazon and found out at the last minute they were the wrong size, so stuck with using stainless steel adjustable clamps.  I will say fitting the rings into the cylinders was much harder than on standard pistons because the overbore gets completely rid of the chamfer at the bottom of the cylinders. What should have taken 20 min took four miserable hours. That job would have probably been much easier with a helper.  
Also, I still haven't been able to get the bike to idle properly without hanging, despite a whole lot of troubleshooting and time.  I just moved to pod filters just because at least I know some carb settings that have worked with the 615 kit and pods, but I'm still fighting the same issue. One interesting thing I've found in my research is that often times an overbore and increased compression requires smaller jet sizes, since relatively more fuel is pulled from a given jet size given the increased velocity of air flow. In any case, I'll post when I find a solution with jetting that works.

I always wet check the fuel level in all 4 float bowls before making any jets changes. If the fuel level is off then the jetting will not be in the correct range.

I also swear by checking the pilot circuit jetting using a ColorTune kit after running the engine on the road for about 15 minutes to make sure it is up to operating temp. The ColorTune is a good tool for checking low speed jetting and fuel burn. When I am doing these checks I run a large fan on the front of my engine.

Once its hot enough you can then set the idle RPM after the pilot jet settings are confirmed.

You mentioned having a Stage 1 jet kit and a Kerker exhaust on yours as well though correct? I know I may have to re-jet, but I’m starting with completely stock sizes. 

Stereordinary wrote:

You mentioned having a Stage 1 jet kit and a Kerker exhaust on yours as well though correct? I know I may have to re-jet, but I’m starting with completely stock sizes. 

 

Yes, I have a Kerker and I started with a Factory Pro stage 1 kit after the overbore but had issues with idle. I tried probably a half a dozen different pilot and main jet sizes and finally switched over to pods because at least I new some jet settings that would work the 615 kit and pods (variations on Factory Pro stage 3 kit).  Still having some issues dialing things in but bike is running OK. I really want to put it on a dyno but want to break in the rings a bit more beforehand, only 200 miles since the head rebuild.