scotch wrote: Again, I have no experience with setting up carbs for a big-bore kit, but I'll put my spin on this.
First thing to consider is with respect to the "Idle-Mixture Screws" (6). In my opinion the term "Mixture" is misleading. The actual mixture of fuel/air is basically pre-determined by two factors. 1) The AIR metering orifices that supply air to the idle circuit. They can be seen in the air supply ports on the Filter side of the carb. The upper ports provide mixing-air for the idle circuit - the lower ports supply mixing air to the high-speed circuit. For each idle circuit there is another ("blind" - not accessible) air metering orifice, buried in the carb.. For the purpose of keeping this simple - The mixing-air available to the idle circuit is Fixed, as determined by the size of these metering orifices. 2) The fuel for the idle circuit is metered by the idle jet, however; Given that the Mixing-Air is "fixed", the latitude for changing the Fuel/Air ratio by changing Idle-Jets, is narrow. This is where I have an issue with the term "Mixture-screws" (6). These do NOT adjust the fuel/air ratio. The fuel/air ratio and actual mixing of the fuel AND air has already been predetermined by jet and air orifice sizing. The Mixing of the two takes place immediately above the idle jet, where the air is injected into the drawn-up fuel. What the six idle-screws do is supply more OR less mixed fuel/air to the idle ports in the venturi.
The puzzle to your dilemma is - Why are you reading a leaner A/F ratio with larger Idle jets? This makes no sense so I can only surmise that it's due to some quirky dynamics of how the fuel/air is supplied and mixed within the carb galleries which are unique to the carb design in itself - exacerbated by the increase in jet size. In other words - some weird law of physics that makes things work in the opposite/inverse to what's expected and considered normal. This might be the case, specific to the big-bore kit and how the increase in displacement is affecting the draw of the idle fuel mixture at the point of entry into the venturi and what(?) dynamics it could be inducing in the intake runners; the physics of which is above my pay scale.
I need another coffee so will leave this for the moment with the hope that something written here, turns a "Light-bulb" and sparks some additional dialogue.
To those who have done a big-bore kit ...........Don't ya'll jump in at once ! ( cuz there's no Imoji for "Sarcasm")
Problems that appear to have arisen since the installation of the big bore kit.
After reading Franks issues with a lean condition/ stumble during transition from idle. This condition did not exist before I did the big bore kit. What is the problem ?
Bike starts and idles good, even after sitting for weeks. The problem arises as I ride down my back driveway in first gear and make a 90 degree turn onto the paved road and ride up 4% grade to get to the main road. Opening the throttle from a slow idle to ride up the steepening grade , the engine faulters badly, so much so sometimes, that I have to roll back down the " hill " and start again- often repeatedly.
Attempted solutions. Applying partial choke to get the bike moving didn't help . Carbs have been cleaned repeatedly. Visually checked all carbs, one at a time flowing a good volume of thinner out the transition ports. Another cleaned set installed but made no difference. Both sets of carbs have stock jetting ie. 42.5 pilot jets, 110 mains. Jet needle set in the middle notch.
Engine has plenty of power once underway. The stumble reappears once again, on the idle circuit I assume, when increasing speed only slightly, from say 80km/hr to 83. A typical situation when cruising as speed somewhat fluctuates.
Valve settings were rechecked yesterday and all within spec.
I did a leak down test several years ago -even with 100psi in each cylinder, only #6 cylinder had a 2lb leak into the crankcase.
What to do now ?
PS. Installing big bore kits on these engines is not new. Even tho' they are more readily available thru Cruisin Image, on the old forum, there were a few European owners that had done the rebore. But they may have been done on fuel injected engines
Modified 1980 B2
2016 MV AGUSTA TURISMO VELOCE LUSSO
South West Saskatchewan ,Canada
I don't see the "big bore kit" as being a problem. If anything, pulling more air through the carbs should help not exacerbate the problem.
Since you've gone over the carbs and have good flow through the idle circuit ( and I assume you saw thinners flowing out of all 3 idle ports orifices) then the only thing that comes to mind that I would check next is the valve timing.
I really don't like the engineering Kawasaki put in to the valve drive chain. The crank drives the secondary shaft through the primary drive chain which can stretch and the secondary shaft drives the camshaft chain which also can stretch. Compound the 2 possible chains stretching and I can see the possibility of the valve timing being late. The later the intake closes, the more likely the intake pulse reverses and upsets the airflow at lower rpm's. Assuming you kept the timing between the 2 camshafts at 17 links, depending on how much stretch there is in the camshaft chain, the intake timing will be more late than the exhaust timing. Late intake timing will decrease the effect of the valve overlap so the intake charge will be delayed and more than likely that issue will be compounded by the reverse flow in the intake tract.
Bottom line - late valve timing can really mess things up.
Another problem late valve timing causes is a lower compression because the intake charge has pushed back out the intake tract so less volume to be compressed.
270 degree cams are fairly fat but that effect would not be as noticeable on long stroke engines because of the relationship of the bore size to conrod length.
I would be putting a dial indicator on the intake bucket on #6 cylinder (#6 or #1 doesn't matter but #6 is on the side of the crank timing mark) and checking for opening at .010". Do the same for the exhaust on #6 at .010" and see where the intake and exhaust timing is. In discussion with Web Cams, the stock timing of the camshafts is spec'd at .010" ie 270 duration at .010" lift.
I suspect that if you haven't done the primary chain and there's some miles on the engine, the cam timing may be as late as 15 degrees from spec.
Just as a piece of info sort of relevant to this problem- the Honda CBX uses a camshaft drive chain directly off of the crankshaft thus reducing the possible valve timing lateness to just the stretch of the camshaft chain. A much better design in my opinion.
Looking forward to seeing you work through this problem and I hope my thoughts here are of some worth.
As this problem has existed during the use of two different carb sets, it certainly seems worthwhile to try something outside of being fuel related.
This thread from a while back, although incomplete, would you suggest setting the cams as Daro had done here ?
Daro has obviously thought this through and concluded that the cams were too retarded and causing spit back or reverse flow in the intake tract, so he advanced the cams 1 tooth which equates to 20 degrees and found things improved.
For me, I need to understand the problem before "trying something"Changing cam opening and closing by as little as 3-4 degrees can make a huge difference and there's a lot of science to it. I would be trying to set the cam timing as per the manual and the only way to determine where they are at and where they could be is with a dial indicator.
If I was doing this job "my way" , I would set up a dial indicator on intake lifter #6 and have a degree wheel set up on the crank with 0 degrees set at top dead center. Then rotate the crank and figure out what lift translates to 270 degrees duration. It could be .010" to maybe .015". Once you've determined the duration starting point and closing point, rotate the crank till you have the opening point lift set and then read the degree wheel and see where the cam opening point is. Do the same thing with the exhaust and record the opening point of that cam. That info will help you figure out the cam timing problem.
Moving the cams by 1 tooth will alter the timing 20 degrees and that's a lot of "adjustment " but if the chain stretch is big, then advancing the cams 20 degrees may put the timing closer to spec.I'd rather see cams advanced 5 degrees from spec rather than 15 degres retarded from spec.
When I finally get around to it, I have plans to install Honda CRF 450 adjustable cam sprockets from either APE or Falicon on to my cams so that I can accommodate anything I want. I'm stalled out now with the sale of our house and the purchase of a 20 year old house requiring a complete reno and it will cost me a year of my time. Happy wife ........maybe happy life. I'm losing my 4-1/2 car garage and going to a 2 car garage with a shop in the basement. Really going to have to put my thinking cap on to get set up to get me happy.
Anyway, I digress. If you don't have a dial indicator, I'd be buying 1. $50-$60 would do it. There are jeweled indicators out there at $200 a piece but you don't need to spend that kind of money. Also you'll need a degree wheel. $20 should do it. and you can make a indicator needle from a piece of wire and bolt it to the stator cover mount hole in the engine case.
Ok, thanks for working the process thru' for me. I'm going to a vintage bike show this weekend- maybe someone has a degree wheel etc that I can borrow.
Moving and taking on a project of that size at our age is a huge undertaking. However, a happy home life has to come first, that's for sure - not always perfect, but the alternative is what ?
Stan Scotch. If you want a day out and a bit a ride , the vintage/classic bike show is in Peachland BC this Saturday along the lakefront. Actual address , I don't know , but the main street is only about a mile long.
Modified 1980 B2
2016 MV AGUSTA TURISMO VELOCE LUSSO
South West Saskatchewan ,Canada
The following user(s) said Thank You: scotch, StanG
I'm going to beat the same drum again. From once frustrating personal experience:
Carbs have to be clean - we all know that!
Pilot-needles must be PERFECT! Take them out and look at the tips under some good magnification. The slightest bend and/or deformity to the tip
(mushroomed from being dropped) replace them ! Any scratches or other marks anywhere on the tip - replace them !
Pilot (idle) jets: Again, look at them CLOSELY under some good magnification. If there is any galling, scratches, crystallization of the brass......anything other then good clean, smooth surfaces - on both ends! - replace them.
The problems these three concerns can create individually relative to getting idle and transition satisfactory.....will drive you crazy.
Combine any two...or all three and you can do the all emissions/O2 etc monitoring in the world......the engine will still run like crap .....and drive you crazy !
And don't forget the float levels ! It only takes one incorrect level to screw things up. OEM Nitrophyl floats? If they're absorbing fuel as many have - the float levels will be all over the map as they are run (wet) and sit (dry out) during the course of riding and being parked !!!!
I'll leave the topic of metal things, gears and chains to those who have that knowledge.
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !