[shinyribs]

I tried to find some tuning charts online but didn't come up with anything useful.

It's a 823 cc engine now (stock stroke) with stock CB900F cams and mildly ported heads. Aftermarket 4-1 exhaust (free flowing,full size header w/"performance" muffler) and K&N pods.

Anybody got anything similar I can baseline against?

Here's the catch. My carbs are "Euro" carbs,but i don't know what that means. It's just what the PO called them and I'm clueless there. My carbs have three jets in them and the pdf at Dynojet only say they have 2(US models only). So...yeah...

Right now my jets are

Main jet 145
Primary jet 74
Pilot jet 35
Idle mixture 2 turns

*note:I have no clue if any of my terminology is correct on these jet names.


Right now the bike revs hard up to about 7k then just stops. No pops or sputters,just stops revving. Pulling the choke has no affect,so I don't think it's lean. The chrome exhaust is brand new and it's not yellowing as if lean. The pipe for the #2 cylinder is starting to color just a tad,but i found that the vacuum plug screw (synch port) was missing it's crush washer. I'm kinda hoping that was creating a vacuum leak which caused this,but it doesn't seem likely that such a small leak would do that. But it's possible,I guess.

I did check the synch and the are spot on.

Any suggestions? Thanks

 

[jmartin1110]

I have no clue what jet sizes are in my carbs since it was tuned spot on when I bought it, but it almost sounds like you aren't getting enough air. Mine did the same thing...would pull hard and then just stop but I just swapped out the cheap crappy pods for some decent ones and it solved it...plus the cbr coils and straight pipe!!

I hear a lot of horror stories about pods on the cv carbs. You should just upgrade to some CRs!!

Edit: I do know that the mixture screw needs to be 1 1/2 turns out if that helps

 

[gsf1200R]

 

[gsf1200R]

i always set my pilots at 2 to 2 1/2 to start and go from there

 

[gsf1200R]

http://www.duncanracing.com/TechCenter/KeihinCarbJetting.pdf

 

[gsf1200R]

http://www.4strokes.com/tech/4sjetting.asp

 

[gsf1200R]

http://www.iwt.com.au/mikunicarb.htm

 

[gsf1200R]

Pilot circuit; 0 to 1/4 throttle



Start by bringing the engine up to operating temperature. Open the throttle slightly. Does the engine pick up speed smoothly? If it doesn't, the fuel-mixture screw may be out of adjustment or the pilot jet may be either too small or too large. To determine the pilot screw setting, adjust the idle-speed screw so that the engine is idling slightly fast, somewhere between 10 and 20 percent above the recommended idle speed. Using either the manufacturer's or the jet kit's recommended pilot screw setting as a starting point, turn the fuel screw left or right between 1/4 and 1/2 of a turn. Select the screw position where the engine speed increase is the greatest. Readjust the idle speed to the correct level.



Next, take the bike for a ride, preferably on a relatively quiet, straight section of road. Using your throttle index, run the bike at 1/4 throttle. If the pilot jetting is correct, the engine should run smoothly, and it should be easy to maintain a constant speed without varying the throttle position. If the bike surges or hunts, the pilot jet is probably too small (lean). Other indications that the pilot circuit is lean are popping or spitting through the carburetor when the throttle is opened and popping or backfiring through the exhaust when the throttle is shut. If the pilot circuit is rich, the engine will have a rough idle or may not return to idle without "blipping" the throttle. You may also notice a distinct smell of raw fuel and some eye irritation from the exhaust.


Low- to high-speed transition; 1/4 to 3/8 throttle



Although the throttle cutaway plays a significant role between 1/4 and 3/8 throttle, it is seldom changed when rejetting a streetbike, particularly a cruiser. For that reason I'll gloss over it. Basically the only time the cutaway needs changing is when the transition from the low-speed fuel circuit (pilot jet) to the high-speed circuit (needle, needle jet and main jet) gets seriously out of whack.


Medium throttle opening; 1/4 to 3/4 throttle



The fuel delivery at this stage is controlled by the jet needle and the needle jet. At one time all carburetors came with adjustable jet needles. Once the smog Nazis got involved, fixed-position needles became the standard. Jet kits will usually include new needles that can be raised (to richen mixture) or lowered (to make it leaner) to suit or, less often, shims to change the height of your stock needles.



To evaluate the needle/needle-jet performance, run the motorcycle in second or third gear. Roll the throttle on from 1/4 to 1/2 throttle only. The engine should accelerate cleanly without sputtering or bogging. If so, you're all done with the midrange; if it doesn't, you'll need to do some experimenting to determine if the needle position is too rich or too lean. Assuming you've installed adjustable needles from the kit, begin your experiments by trying some alternative needle-clip positions, perhaps a step richer to begin with. If that makes the situation worse, try a step leaner. If the jetting is stock and problems crop up, it's time to order the appropriate jet kit.


Top end; 3/4 to wide-open



At this stage of the game, the majority of the fuel flow is controlled by the main jet (remember some fuel is still flowing through the pilot jet). The time-honored method of determining main-jet size is via a plug chop. If you've never done one, a plug chop is pretty simple. Start with new spark plugs. Run the bike flat out (full throttle), in as high a gear as possible, for eight to 10 seconds (don't hold the bike at the rev limiter, as it'll give you a false reading). Without cutting the throttle or slowing down, simultaneously pull in the clutch and hit the kill switch. Coast the bike, with the clutch still in, onto the shoulder and remove the plug(s). The plug insulator should be tan to grayish-white. A white plug indicates a lean mixture; a dark gray or black one means it's rich. You then select the main-jet size accordingly.



Unfortunately, plug chops present a few problems. Some bikes require an inordinate amount of work to remove the plugs�at least more than you want to do on the side of the road with a smoking-hot bike. And in most parts of the country, the law takes a very dim view of banzai runs down the main drag followed by an impromptu tuning session on the side of the road.



The alternative, and the method I personally prefer, is to use a dyno. It's certainly a lot easier and arguably more accurate, but it may not be convenient.

 

[gsf1200R]

Troubleshooting



A lean condition is the end result of too little fuel and too much air. Slightly lean conditions create drivability problems. Worst-case scenario: Lean conditions can and do destroy engines. Holes in the pistons, burnt valves and trashed main bearings are the direct result of lean mixtures.



Rich mixtures are the end result of too much fuel and too little air. Rich mixtures waste fuel, contribute to carbon buildup and pollute the air.



Typical Lean Conditions:



- Poor acceleration; the engine feels flat.



- The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.)



- The engine runs hot, knocks, pings and overheats.



- The engine surges or hunts when cruising at part-throttle.



- Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle.



- The engine runs better in warm weather, worse in cool.



- Performance gets worse when the air filter is removed.


Typical Rich Conditions



- Engine acceleration is flat and uneven and loses that "crisp" feel.



- The engine "eight-strokes" as it loads up and skips combustion cycles.



- The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle.



- The throttle needs to be open continuously to maintain acceleration.



- Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel.



- Poor fuel economy.



- The engine works better when cold. Performance falls off as it warms

 

[shinyribs]

Thanks guys! I understand the basics of a carburetor,I just am not familiar with these particular units.

I did some research in the FSM and found this.





Stock primary is 68 vs. my 74.
Stock main is 102 vs. my 145. <- excessively over-jetted possibly?

There is no mention of pilot jet sizing in the FSM (my current is 35) but it says that it is a pressed in jet. Mine are screw-in type.



As far as idle mixture adjustment:



^^^But neither of these carb numbers match mine. I don't remember my carb numbers,but I'm gonna check that soon.

*EDIT* Mine are VB43D



I also saw a device on there called the air cut-off valve. I have no clue what that is/does so I need to research that. The FSM gives no information there.


One thing I have noticed when accelerating hard from 1/4 throttle is a fluttering sound at times. Typically when climbing a steep incline and really loading the engine. It almost sounds like the slides are rattling/jumping if that makes any sense. They are tight in their bores and move free.

Also,and I just remembered this,sometimes the bike sorta stalls when cornering hard(peg dragging) under heavy throttle. At higher rpm's it's fine(6000-8000)but while in the midrange(4000-6000) it feels like its running out of fuel(maybe flooding?) and recovers as soon as you upright the bike. It's not a rough break-up of engine rpm,just gets sluggish. Not subtle though,it's very noticeable.



Also, I ran a compression test after noticing that the #2 header pipe was looking a little lean/hot.

#1- 160 psi
#2- 160 psi
#3- 135 psi *added a few drops of oil then 160 psi not happy about this
#4- 160 psi

All the spark plugs look exactly the same. The bike has Dyna coils on it now and I'm not sure if that dictates the use of non-stock spark plugs or not. I thing I did see is that the spark plug gaps were pretty far off from the FSM settings.

My bike has DR8EA plugs right now. I'm not sure why it's running resistor plugs vs. the stock non-resistor plugs(D8EA),like I said,that may be for the Dyna coils. *EDIT* I was wrong. I have D8EA plugs. Coils are 3 ohm units. All should be well there.

I cruise at about 6000-6200 rpm at 65mph and wonder if I should be stepping up the the next heat range of plugs to the D9EA's. My gaps measured .030" and the tips of the electrodes do not look perfectly flat across the ends. Possibly eroded from excessive heat?







Sorry for rambling or making a mountain out of a mole hill,just trying to put as much info out there as possible. I keep hearing horror stories about pods on CV's and I'm determined to do my best to make these work.

Thanks again for any help.

 

[shinyribs]

I have no clue what jet sizes are in my carbs since it was tuned spot on when I bought it...

Aaaargh! :fu: We're pretty much set up the same and when i saw you posted I thought I was saved.

Thanks for the help bud.

 

[shinyribs]

I found this concerning the air cut-off's:




Hmm...thoughts?

 

[jmartin1110]

Aaaargh! :fu: We're pretty much set up the same and when i saw you posted I thought I was saved.

Thanks for the help bud.

If you don't figure it out soon, I plan on taking them off to have them cleaned...I can look when I do bud

 

[shinyribs]

Dude, I would hate to see you split the carbs open if your bike is running fine. I do appreciate that, though.

Im working on them right now and found a set of 125 mains in the bikes tool pouch. Interesting. Dynojet call for a 126 main for a stage 3 for a 750. I'm gonna clean these things and pop in those 125's and see what's up.

 

[jmartin1110]

I'm fairly positive that's what I'm running...the PO said he went up one or two steps from factory IIRC. Like I said...it sounds like you are getting way too much fuel and 145 sounds huge!! The bore of the 823 isn't THAT much bigger than the 750

 

[shinyribs]

I agree. That's nearly a 50% increase, which is nuts. But I guess the needle was saving my ass on that? Besides, the way I understand it, a larger bore will require additional air/fuel mixture, but that not to say it requires a richer mixture.

Anyway, its all cleaned up and back together now. Id test if it wasn't threatening to spit ice out here. Gonna do some more research instead. I'd really like to know what these carbs are I have. I might just be screwing the pooch messing with these things.