WTF? I'm so tired of this game....

[Smokinapankake]

So many moons ago I delved into the carbs and all the joy THAT brings.
After going to pods, jetting, and many many plug chops, with somewhat successful results, I decided it wasn't performing as well as it could/should. So I reverted back to stock settings, airbox, etc...
And now it runs like the crap. What is going on?
Replaced boot o-rings
Thoroughly cleaned carbs.
Soft rubber everywhere.
Good compression on all 4 (130-145)
Strong spark, 12.4 v at the coils.
Fuel delivery confirmed (all 4 pipes get hot, all 4 bowls drain gas)
Plugs sort of a rusty brown.

So this is what the new iteration is doing: Approx 5k rpm, 55-60mph, throttle just cracked enough to maintain speed, it kind of surges as though it's running out of gas. Whack the throttle and it responds appropriately, i.e., accelerates about like it should, but upon closing the throttle will sometimes pop and backfire.
If I gotta pull those damm carbs out again I think I'm going to sell the stupid thing.

 

[hampshirehog]

CV carbs - makes me think damaged diaphragms if you're sure you've set everything to stock (did you put the needle height back right?).

 

[TheCafeKid]

So many moons ago I delved into the carbs and all the joy THAT brings.
After going to pods, jetting, and many many plug chops, with somewhat successful results, I decided it wasn't performing as well as it could/should. So I reverted back to stock settings, airbox, etc...
And now it runs like the crap. What is going on?
Replaced boot o-rings
Thoroughly cleaned carbs.
Soft rubber everywhere.
Good compression on all 4 (130-145)
Strong spark, 12.4 v at the coils.
Fuel delivery confirmed (all 4 pipes get hot, all 4 bowls drain gas)
Plugs sort of a rusty brown.

So this is what the new iteration is doing: Approx 5k rpm, 55-60mph, throttle just cracked enough to maintain speed, it kind of surges as though it's running out of gas. Whack the throttle and it responds appropriately, i.e., accelerates about like it should, but upon closing the throttle will sometimes pop and backfire.
If I gotta pull those damm carbs out again I think I'm going to sell the stupid thing.

you need to pull the carbs again. REMEMBER: These bikes came from the FACTORY LEAN. This means if you reverted back to STOCK, you're a touch lean. Pull the main, bump it up one size. Shim the needles. A question for you tho. When you had it modded with the pods and pipe, did you drill the slides? If so, this is going to make you lean out also.

 

[IluvmyGS]

check the petcock to see if it feeding enough fuel to carb when you hit 5K rpm. It might be clogged and therefore can't deliver enough fuel when the bike needs it at 5k rpm.

 

[Guest]

Did you adjust the valves?? If they haven't been checked yet, this is your culprit until proven otherwise.

 

[Smokinapankake]

TCK,

Did not drill slides as I'm very leery of mods that are permanent.
It's such a Gawd damm pain to pull the carbs! It's a pain to do a simple plug chop because you gotta pull bodywork. On the side of the road in 98 degree weather. Ugh.

I don't get why factory stock exhaust, carb settings, etc... would be so sensitive. I mean, they sent these things all over the world (except the good ole US of A), so what gives? I shouldn't have to jet for elevation, right? I'm at approx. 4500'.

I can move the needles around, it has multiple slots as its a JDM motorcycle. So do I move them up or down? Up would lean it out more, down would richen.....Probably move them down. And I shouldn't need to do anything with the pilot jet.

Diaphrams are solid, no rips tears or even pinholes.
Thanks for your patience, I could really use some right now.

Does anybody know if these have the reusable rubber valve gasket, like the 550's did?

 

[dtkid]

Hey in Utah:

I'm not sure what you did to the carb/jets when you decided to go with PODS...but I would bet my collection of pubic hairs that you simply didn't get the jetting correct. I am also riding at 4000k elevation.

What sort of pods did you replace the airbox with and what sort of changes did you make on the main jets??

This situation my have a relatively easy fix. (Then again it may not; but I'm willing to hear you out).

 

[fallous]

TCK,

Did not drill slides as I'm very leery of mods that are permanent.
It's such a Gawd damm pain to pull the carbs! It's a pain to do a simple plug chop because you gotta pull bodywork. On the side of the road in 98 degree weather. Ugh.

I don't get why factory stock exhaust, carb settings, etc... would be so sensitive. I mean, they sent these things all over the world (except the good ole US of A), so what gives? I shouldn't have to jet for elevation, right? I'm at approx. 4500'.

I can move the needles around, it has multiple slots as its a JDM motorcycle. So do I move them up or down? Up would lean it out more, down would richen.....Probably move them down. And I shouldn't need to do anything with the pilot jet.

Diaphrams are solid, no rips tears or even pinholes.
Thanks for your patience, I could really use some right now.

Does anybody know if these have the reusable rubber valve gasket, like the 550's did?

hmm, I may be high but I do believe raising the needles richens the mixture, lowering leans it. If your needles are raised, more fuel is allowing to come through the emulsion tubes and into the motor.

 

[Smokinapankake]

I should have clarified - moving the CLIPS down will raise the needle, richening, while raising the CLIPS will lower the needle, leaning out.
Correct?

 

[Clone]

TCK,

Did not drill slides as I'm very leery of mods that are permanent.
It's such a Gawd damm pain to pull the carbs! It's a pain to do a simple plug chop because you gotta pull bodywork. On the side of the road in 98 degree weather. Ugh.

I don't get why factory stock exhaust, carb settings, etc... would be so sensitive. I mean, they sent these things all over the world (except the good ole US of A), so what gives? I shouldn't have to jet for elevation, right? I'm at approx. 4500'.

I can move the needles around, it has multiple slots as its a JDM motorcycle. So do I move them up or down? Up would lean it out more, down would richen.....Probably move them down. And I shouldn't need to do anything with the pilot jet.
Diaphrams are solid, no rips tears or even pinholes.
Thanks for your patience, I could really use some right now.

Does anybody know if these have the reusable rubber valve gasket, like the 550's did?

Ok, you got that backwards, if you move the needle up a notch or shim it up you will be richer when the slide goes up.
If you move the needle down a notch or remove a shim, you will lean it up more when the slides go up.

 

[Clone]

I should have clarified - moving the CLIPS down will raise the needle, richening, while raising the CLIPS will lower the needle, leaning out.
Correct?

If you move the clips towards the pointy end, you will get richer, if you move the clip towards the blunt end, you will be leaner

 

[TheCafeKid]

TCK,

Did not drill slides as I'm very leery of mods that are permanent.
It's such a Gawd damm pain to pull the carbs! It's a pain to do a simple plug chop because you gotta pull bodywork. On the side of the road in 98 degree weather. Ugh.

I don't get why factory stock exhaust, carb settings, etc... would be so sensitive. I mean, they sent these things all over the world (except the good ole US of A), so what gives? I shouldn't have to jet for elevation, right? I'm at approx. 4500'.

I can move the needles around, it has multiple slots as its a JDM motorcycle. So do I move them up or down? Up would lean it out more, down would richen.....Probably move them down. And I shouldn't need to do anything with the pilot jet.

Diaphrams are solid, no rips tears or even pinholes.
Thanks for your patience, I could really use some right now.

Does anybody know if these have the reusable rubber valve gasket, like the 550's did?

Yes, you DO have to adjust for elevation. When a bike came into a dealership, they prepped it for sale in their shop. Meaning, they tuned it to get it running for the area of the world it was in. They dont just roll em off a truck and put gas in em and fire em up. This elevation would actually RICHEN your mixture, as compared to sea level or lower elevation, as the higher you go, the thinner the air becomes. Move the clip DOWN one notch, which RAISES the needle, fattening the mix. Set your screws to 2.5 turns out on the outer cylinders, and 2.75 out on the inner. See how that works for you Also, ASSURE your float levels are set as well. This played a big part in how my bike was running. They were close, but the more exact you can make them, the more balanced everything is. Did you sync them when you put them back together as well? And YES, Valve clearance could definately be playing a role in this as well. Dont thank me, glad to pass on what knowlege i have gained

 

[dtkid]

Well said.......I don't think it gets any simpler than that!

 

[Joe Guilbeau]

TCK,

I don't get why factory stock exhaust, carb settings, etc... would be so sensitive. I mean, they sent these things all over the world (except the good ole US of A), so what gives? I shouldn't have to jet for elevation, right? I'm at approx. 4500'.

Wrong answer clyde...

As a matter of fact, the closer to a perfect tune on the carbs, the more you have to adj for elevation.

From sea level to 4,500-feet is a significant change in rich vs lean settings.

From what I have been able to determine you get the float bowls set perfectly first thing.

Then wide open blasts down the road by whacking open the throttle after a good cleaning of the plugs and hitting the kill switch at wide open throttle (stay off the freeways for this) so that you can inspect each plug.

Get them all to be light tan.

After this step it is mid range roll on, by marking the hand throttle from 1/4 to 3/4 and staying in that range, wind it through this range to compare the mid range settings, lowering/raising the clip (start with manufactures recommended setting for the e-clip).

Once all plugs are tan again, then go the idle adj by turning set screws until they slightly bottom out, and then backing out the "air" screws until you meet the manufactures guidelines. (around 2 turns out... various models will be 1.5-2.5 turns out).

That ought to do it....

[Edit] Ooppssss Just read Cafekid posts...doh! What he said!

 

[TheCafeKid]

Wrong answer clyde...

As a matter of fact, the closer to a perfect tune on the carbs, the more you have to adj for elevation.

From sea level to 4,500-feet is a significant change in rich vs lean settings.

From what I have been able to determine you get the float bowls set perfectly first thing.

Then wide open blasts down the road by whacking open the throttle after a good cleaning of the plugs and hitting the kill switch at wide open throttle (stay off the freeways for this) so that you can inspect each plug.

Get them all to be light tan.

After this step it is mid range roll on, by marking the hand throttle from 1/4 to 3/4 and staying in that range, wind it through this range to compare the mid range settings, lowering/raising the clip (start with manufactures recommended setting for the e-clip).

Once all plugs are tan again, then go the idle adj by turning set screws until they slightly bottom out, and then backing out the "air" screws until you meet the manufactures guidelines. (around 2 turns out... various models will be 1.5-2.5 turns out).

That ought to do it....

Not always. As he's said, his plugs looked good. MY plugs looked good in my 1100G. But it still wasnt quite running right at high speed roll ons. Smokin, give the adjustments i suggested a shot. See if it works for you. At your elevation, you MAY want to try the outer cylinders screws at 2.25 turns out and the inner at 2.5 out, since you'll naturally be just a tad richer than me.

 

[dtkid]

Agreed............let me just add this:

No one that has not worked on these machines can trully appreciate just how ultra-sensitive the air/fuel mixture is.

My buddies that race Chevys thought that I was stupid or just over-stating the facts...until I proved it to them. These machines simply won't run without the correct mixture. They ain't like a truck; where you can take off the air-breather or filter or make large adjustments on the mixture screw (to pass a Vehicle Emissions Test).

These babies are super senistive to air-fuel ratios.

 

[Joe Guilbeau]

Not always. As he's said, his plugs looked good. MY plugs looked good in my 1100G. But it still wasnt quite running right at high speed roll ons. Smokin, give the adjustments i suggested a shot. See if it works for you. At your elevation, you MAY want to try the outer cylinders screws at 2.25 turns out and the inner at 2.5 out, since you'll naturally be just a tad richer than me.

I got my experience and info from Sudsco/Mikuni 4th Edition tuning manuals.

http://www.lambretta.net/shop/shopexd.asp?id=3996

Here is a Mikuni tuning guide for the VM Series
http://www.mikuni.com/pdf/vmmanual.pdf

A quick how to guide for the Mikuni CV Series
http://vmaxoutlaw.com/tech/cv_carb_tuning.htm

Here is a write up on the ST series of Mikuni carbs, go to the thread with all the pictures...
http://www.gixxer.com/forums/showthread.php?t=159718

In any case, there seem to be a lot of opinions on how to get something done.

Hope some of this helps in getting ya'lls jetting straight...




http://www.sudco.com/mikuni.html

 

[TheCafeKid]

I got my experience and info from Sudsco/Mikuni 4th Edition tuning manuals.

http://www.lambretta.net/shop/shopexd.asp?id=3996

Here is a Mikuni tuning guide for the VM Series
http://www.mikuni.com/pdf/vmmanual.pdf

A quick how to guide for the Mikuni CV Series
http://vmaxoutlaw.com/tech/cv_carb_tuning.htm

Here is a write up on the ST series of Mikuni carbs, go to the thread with all the pictures...
http://www.gixxer.com/forums/showthread.php?t=159718

In any case, there seem to be a lot of opinions on how to get something done.

Hope some of this helps in getting ya'lls jetting straight...

While I do appreciate your experience, there is one thing that *I* have learned about thes guides. They are just that. Guides. We could put the same model bike next to eachother. Same miles, same valve clearance, same modifications such as pods and pipes and the EXACT jetting settings would be different, and sometimes VASTLY. What may work for me, may not work for his bike, even if it were the same. Also some peoples perspective of what a perfect running bike is, is subjective. These guides are great for getting you in the ballpark, but the fine tuning can only be done by the person who has to turn the miles on it. Mind you, i dont have nearly the experience on tuning and jetting that alot of these guys have, but i have listened intently, and studdied, and tinkered untill my eyes were red. There are a few basic rules of thumb that i follow that i have been taught by a few people here, and i pass that knowlege along. There ARE varrying opinions on how to do this, but the bottom line is ultimately its up to him to decide, based on however many suggestions he can gather, and tinker with, what feels BEST to him. Get it in the ball park. Tweek it to suit from there. As long as you're not overly rich, and not lean, what feels good to you is best. What opened the flood gate for me was actually gathering an understanding of HOW and WHY the carbs work the way they do. What affects what, what circuits are in use at any given point in the throttle. I still have a lot to learn, but i simply passed on some settings that i found worked for me for him to try.

 

[Joe Guilbeau]

I wholeheartedly agree with you, my original comment was addressed at the altitude thing.

I just added the links to help others decide, not to bolster any position I have, as a matter of fact a perusal of the various links will expouse differing tuning stratagies.

Rodger Baldridge a Ford service manager out in Oracle AZ schooled me on the carb thing for the bikes. Guy is amazing in overall breadth of knowledge.

In any case, I am sure that with some patience and skill and perservance the jetting will be fine.

Heck, it MIGHT even be a intermittent spark issue... who really knows?

Hugs and kisses all around, eh?

 

[Smokinapankake]

Thanks guys for all the help, I've clearly got a lot of learning to do. My patience right now is at about its lowest point and so I'll step away for a few days to regain some composure.
I will look at the valves as I've never done that, but the floats are all set. I'll check them again.
Maybe go up one on the main jet size?
Raise the needles and set air screws to 2.5/2.75.
But not today.