Tuning problems

[phate]

Hey guys i've been trying to nail down my carb tuning after installing mikesxs pods with stock exhaust. I must have taken off the carbs at least 30 times changing jets, adding washers, ect. and still cant get it done. I'm currently at 145 mains (but started at 140-147.5), 2 washers on the needle (i believe equal to one clip position raised) 42.5 pilot with about 3.5 turns on the mixture screw. I seem to have good (than again I dont really know what good is) pull at the low to mid RPM's (1/4-3/4 throttle) but when I go to about 6k RPM then jamb the throttle open it pulls then stops and then surges (signs of leanness). Here's the catch my plugs are carbon BLACK as can be and when I take off the carbs there is even a little pool of gas in the intake boots. My float level is dead on at 26mm. I want to know what you guys think as well as your current setups and jetting. I know it changes with many variables (weather, height, etc.) but I still would like to have some clue. Thanks in advance. 1980 special II (BS34 with brass floats)

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[16VGTIDave]

Rather than measuring float height, check the fuel level in the bowls. A piece of clear tubing inserted into the float bowl drain and routed upwards will show the level when the drain screw is opened. Make sure the bike is on the center stand and level front to back and side to side. Make sure the petcock is set to reserve or prime!

It sounds to me like your main jets are still too small, or your diaphragm(s) may be leaking. And that you are too rich with the needle.

Remember, these carbs have to be tuned for the main jet first, at full throttle and high RPM. Then the needle at full throttle and mid RPM. The pilot jets and screws are for part throttle cruising and idle. Float level is also used for cruising mixture adjustment.

Have you read the info from the sites I posted a few weeks ago? http://www.xs400.com/forum/showthread.php?t=9939

 

[phate]

Thanks for the reply. I would like to check the fuel level that way but as soon as I would unscrew the drain port gas will come out and by the time I'm able to jam a tube in there too much gas would have escaped to get an accurate result. I think that's only an option for the Dohc models. My diaphragms are brand new from JBM and was checked by putting my over the front and lifting the slide. I am aware that I have to tune the main jets first and I have been following that xs650 guide that been going around but I will defiantly check out you link. I thought the mains were too small but then I thought how much bigger do they have to be from stock with just pods added (I'm at +3 on the mains)?? And if that's true how can be one position on the needle be too rich?? Ahh I guess its just gonna take more fiddling, will keep you guys posted.

 

[Scorpio1963]

Seems to me your mains are too big for just pods.I would no more than 2 sizes up.Too much fuel going through the carbs.I would try 1 and half sizes up and see what happens.Also are you running direct carb fit pods?Make sure the rubber lip inside them isnt obstructing anything.Also 1 other thing have you changed the slide needle heigth?

 

[phate]

I'm using mikesxs pods that have no inner lip and they are direct on the carbs. I have already tried using sizes 140-145 (1-3 sizes up) and still weirdly lean (surging) with WOT at 7-8k rpm. I have the needle raised with 2 washers (=1 clip position). Like I said I'm just as confused as you with the +3 sizes with just pods guess the only way to tell is to see what 147.5s do

 

[Scorpio1963]

Are you running NGK plugs?If they have been fuel soaked they are trash

 

[16VGTIDave]

Why don't you shut off your petcock, drain the float bowls, insert a tube into each one, and then open the petcock? The fuel level will only increase until the floats are raised.

 

[phate]

They are Ngk but they are not fuel soaked just carbon fowld. Dave that's a good idea but its gonna be hard to put a tube in that hole that wont leak. better yet I have a few fuel nipples it would be great if they would thread in so it would be leakproof

 

[phate]

I have once again tried all jets from 140-147.5 and no matter what when I go up to about 6.5k RPM then jamb open the throttle it looses power then surges (not smooth acceleration). I cant figure out if its rich or lean (they both seem to feel the same) except that when I put in the bigger jets (145-147.5) it seemed to bog as it was loosing power rather when it was lean it just sort of dies (then surges). I dont understand why I cant find a compromise between all those jets.

 

[Scorpio1963]

Have gapped the plugs at the correct measurement?

 

[phate]

U bet 3 times actually

 

[16VGTIDave]

At 6500 you will still be on the needles and not the main jets. Have you ridden the bike for about 15 minutes to make sure it is fully warmed up? Have you tried using part throttle to get up to 8000 RPM before going to full throttle?

If it is surging (lean) or sluggish (rich) at high RPM with full throttle, close the throttle a little bit and see if it smooths out or pulls harder.

 

[phate]

thanks for the reply and yes I make sure to run the bike atleast 15min when testing jet sizes. I didnt know that 6500 was still in the midrange I will try starting at 8000 and going WOT. Going part throttle it will reach redline but it feels boggy so i will probably lower the needle.

 

[16VGTIDave]

Good plan, I think that was one of my first suggestions...

 

[phate]

some new information to report. I actually raised the needle 1 more notch (equivalent) just for the heck of it and while it actually produced a much better pull from about 4-7 RPM it still does the same thing with the surging with WOT (from 7k). I then as per suggestion went from 8 then WOT and it didn't surge but was kind of hard to tell because I hit the redline to quick. I then also as you suggested before I went slowly through the rpm with half throttle and it bogged at about 7k. I thought it might be my electrical system so I pulled out the plug of 1 cylinder, grounded it, and fired up the bike. I then brought it to 7k and it kept a nice crisp blue/white spark all the way. I repeated it with the other cylinder and same results. What do you think?
PS: Tomorrow I will try lowering the needle as per original suggestion and see what happens

 

[16VGTIDave]

Stop confusing the issue! Get the main jets sorted out before making any other changes. If you are redlining too quickly, find a road where you can make runs in a higher gear without risking your life or others. If that means running on a highway in 3rd or 4th for a couple WOT pulls, so be it. If you can find an uphill stretch even better.