Stuck..please help. carb issue?

gk45011

gk45011

Coast to Coast
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Back up and running. Seems to want to max out between 7-8K on the tach. Obviously running in the red line is bad, but should it be dieing flat just blipping the throttle? If not do I need to turn the mixture screws out more? I thought I had it synched and running pretty well :( First time messing with the BS34 CV carbs. stock pilot. 122.5 main. What am I missing here?
 
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Thanks again,
GK

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Sounds way out of sync as well
Is stock main jet 115?
You probably need a larger pilot jet as well, info I have says 17.5 or 42.5, depending on model?
BTW, running at redline is OK, even 1,000rpm above is ok when overtaking or 'panic' passing
 
Thanks guys. Stock main jet was 115 on the 450L per the manual. as pods but they are cheapies for now (out of box specials at the local chop shop). Neighbor "synched" them today. I used to have no problem blipping into the red but the idle was slower to return.

Do you think turning out the mixture screws may help to richen this up a little? I have a post up on the Cincinnati Cafe racers FB page in hopes someone who knows what they are doing will help (or be bribed into) helping me sych the carbs correctly or help me work through this issue.

Alpha. The 122.5 should in theory be the right main jet with stock exhaust. If i need to jump up to a 125 or 130 I can do so. I thought I would be able to get the carbs fairly close by going two up? Carbs are obviously not my strong point and I am having a hard time finding a local who is willing to drop by and impart their knowledge.

GK
 
When you jet for top end the mid range transition WILL be rich.
You can compensate slightly by re-setting float height 1mm higher than stock
 
I know 115 is the stock jet. I HAVE a GS450L. <G>
Pod filters, (even the undersized cheapies you have on there,) have WAAAY more effect on the jetting than does the exhaust. The stock airbox is highly restrictive and stock jetting is way lean. 122.5 is only 3 jet sizes larger than stock, and could almost be spot on with the stock airbox and exhaust, because the stock jetting is so lean to begin with.

When going with pods, (and exhaust,) on a GS450, I start at 140 then lean it down a tad if it breaks up on top end. Changing your air screw will not correct what you are seeing. Going up one jet size on the pilot usually works well with pods, too, but is not mandatory.
 
Alpha,
I know you have one thats why I inquired further. The description of the super lean jetting to start makes much more sense to me. My Yamaha xs11 didn't seem to have been jetted so lean to start. Two up on her and a good synch and she ran like a scalded dog. Obviously the 450 will be much more tame on the top end side but I would like to have her as quick and responsive as possible around town and for the occasional hwy jaunt.

I will look to order a set of 130 and 132.5 mains and try it again If I was that far out its no wonder I am having some issues. Makes sense now I think.

Was the 140 jet comment a typo? seems like that would be rediculously high. I want to order what I need so hopefully i can get moving on to finishing up some other issues.

What Is a good recomendation for the pilot jet bump? I know I may go to some sporty mufflers or some more free flowing exhaust. I would need to bump the pilot at that point regardless (correct me if I'm on the wrong track)

GK
 
No, 140 was not a typo. I have 150 main jets in mine. I am running large K&N oval pod filters, and a Mac 2-into-1 pipe with modified strait through fiberglass packed baffle. It's a little too rich, and I plan to put 147.5 jets in it next.

One size larger pilot is all you need to go. Pod filters don't have that much effect at idle.
 
Your 450 should be a screaming machine. I would love to see it in person sometime. You had stated 130 and 132.5 in a previous post I had thought. Without a two into 1 high flow exhaust should I still start at the 130 and work up as you previsouly meantioned? :-\ :-\

With the pilot jets how do the sizes run. I think i should have a 17.5 stock on my L. Do I just jump one size to a 20? ???

Thanks for your time, I know many find all this second nature but it seems like every time I try something new it is an adventure. Good news is I shouldn't have to ask the same question twice once I get the answers. ;D
 
When I said 130 or 132.5, I was allowing for the exhaust you have and the undersized pods. Mine is much freer flowing on both exhaust and intake, so I have a bigger jet than would work for you.

Whatever the increment is for the pilot jet, just go one size. I don't recall what the stock pilot jet is. I haven't changed mine yet.
 
AHHH Gotcha Alpha. So I will look at the 130 and 132.5 for ths go around. I am pretty sure the pilot is a 17.5 stock on the L. I know the main jet sizes go up by 2.5 then by increments of 5 at a certain point. I just don't know what the increments are for pilots. If it is the 17.5 as the book decribes (can't read it on the jet) what is the next increment or size up? I've never actually had to change a pilot jet yet.

Figure if I am in there for the main again I might as well go ahead and change the pilot too. Any recomendations or changes on the needle? Should I change the shim? have you had to do this yet, or will i need too?

PS. Is this why people run from the old style CV carbs whenever possible?

GK
 
You have to be resourceful to change the shim on the needle. To move the needle, you have to add or remove shims from the right place. I had poor results raising the needle. It gave me a really bad rich-flat spot in mid throttle. Seems to work better to go a little richer on the main jet, then lower the needle to lean it back down and not be too rich in mid-throttle.
 
Awsome advice. I will work the main and pilot and then see what needs to be done with the needle. A guy could get luck (I doubt it), but worth a try.. :)

GK
 
Spent one of the two nice days tinkering with the bike. One picture is a plug chop i did today. Running 122.5 and previously was under the impression i would need to jet richer. I pulled the plugs today and found a dark soot covered plug. Unless i am way off base that means I am running rich. I have some 120 mains that i could change to. the origional jets were 115. I do however get a little stumble pulling from a stop sign right off idle. I am getting to my wits end with this. If anyone has ideas I would love to hear them. I am new to the cv carb game and am learning as I go.

Picture of plug chop:
305625_334846683281032_436272431_n.jpg
 
Yep, that looks rich, is that at red-line?
Problem with CV carbs, you never really know where the slide is so you will have to do plug chop in lower than normal gear for max opening/airflow then you will find rich at mid-range.
ADC tells you to drop needle, there are usually nylon washers on Mikuni CV carbs, a thick one and a thin one, may be able to swap them top to bottom?
 
Yes that was as close to a redline chop as the little 450 would go. I was thinking of trying the 120's out. I am at a loss why I am getting a bog want to stall takeoff though. perhaps I need to richen at the pilot fuel.air screw and the lean it out a little at mid to wot? Does that sound right?

GK
 
The air filters provide zero restriction at low to medium rpm so it should operate exactly as if you still had filters on.
Most likely you have a problem with pilot circuit
 
gk45011 - Let me know if you find a set of mains that work for your setup, I've been decifering your convos here and grabbed some great info. Thankyou for sparking this thread ;D I just know you were having mixed results.

I'm thinking with the small pod filters i ordered, shorty mufflers on right now; the mains should be 132.5 and 130 pilot? But, did you even need to up-size your pilot?
 
I currently have my carbs ready to be pulled and ultrasonicly cleaned. I have not changed the pilot as of yet. But I haven't gotten my issue fixed off idle yet either.

As I start playing over the next few weeks i'll let you know where I end up exactly on jets.

Problem is evey engine and setup is still slightly different.


GK
 
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