I'd add another shim or two, one is probably not enough and that's where you're popping anyway...

IMO, the main jet is a little big but not *too* big.
There was no need to change the pilot jet but again, it's not *too* big.
2.5 turns on the a/f screws seems to be right for all SV's.

 

I reassembled my carbs using 3 shims (i had 2 previously) and I still have backfireing. Sound like a .22 cal hand gun when its cold. After it gets very warmed up, the poping sound becomes much quieter. Bike feels much stronger in the middle now.

Anybody heard of using 4 shims on a similar setupas mine?

 

how do your spark plugs look? Have you checked for vacuum leaks?

 

I honestlly wouldn't know where there could be a vaccum leak. I have checked every hose connecting the carbs to the tank and to eachother. Synced the carbs, I made sure the ballance is good from idle to 5500. Double checked, triple checked. rode it, came back, ballanced the carbs again and adjusted idle.

Maybe 3 turns or 2 3/4 turn on the idle screws? or upgrade my gas to 89 oct? I remember when I ran the UNI pods with 2 shims and straight pipe. backfireing was never as bad as it is now. I will check out the plugs when I get home tonight.

I find myself downshifting often so I can have the throttle closed at above 5000 rpms. Hopefully I'm not doing too much damage. Acceleration is fantastic. I barely feel any dip in power. The front end is definatly feeling alot lighter at WOT.

 

backfiring is a lean condition. The question is why are you lean when you should already have plenty of fuel?

The first thing you should do is take some srtating fluid or carb cleaner and spray around the carbs while idling. If the idle goes up while doing this then you're leaking air.

Then check the plugs. Do they look dark? Covered in any soot?

After that I'd put a piece of duct tape over the air box. Cover ~25% of the inlet hole and go for a ride. Does it run any better or worse? Is the backfiring any better? Now check the plugs again. If they're not dark or sooted up then shim your needles a little more.

I wouldn't mess with the A/F screws much, maybe an extra 1/4 turn but no more. I've never seen a bike, regardless of mods, need more than 2.5 turns.

 

Check that the carbs are seated completely on the intakes, and that the airbox is seated completely on the carbs. This was an issue for me one time.

 

Backfiring can be either a too-lean or a too-rich condition. Quickest and easiest way to figure it out is to get an EGA run on it.

Most SVs are a bit lean. Mine, however, was rich. It won't tolerate idle mixture screws (that's what they are, folks, not air/fuel mixture screws) more than 1.5 turns out.

 

Pulled the plugs this morning and took some pictures. As you can see the coloring of the plugs is quite good. Dare i say close to stoichiometric. perhaps only little bit rich.

 

Your plugs do look decent, maybe a little rich like you said but not bad... I kind of suspected this with the 152.5 main jet, I usually suggest 150 for stock exhaust and de-snorkel.

Andy is right that too rich can cause popping but it's usually a dull pop as opposed to a sharp crack like a gun shot that is usually associated with lean conditions.

Most bikes, at sea level with the snorkel removed will work best with the A/F screws 2.5 turns out. Like Andy said these mostly effect low RPM's.

Though it's unusual that you should have to add another shim, on occasion there are bikes that need it. For example when fitting a carb off a newer Harley onto my 1964 Sportster I needed to go to some very large jets for no good reason. Even the largest main jet in the kit was just too lean. I finally ended up going a size or too bigger than a HD big twin!
That said, I'd still encourage you to chack for vacuum leaks but if there are none then try adding some shims and see what happens

 

DonnieJ and I are about to disagree. The pictures are not good enough to see what we need to see, but with porcelains that white I'd say you were lean. The sooty appearance of the base is less important.

 

Sorry, I have a cheap assed camera that will not focus in on things that small.
But I assure you the plug looks close to optimum. The tip of the plug has a nice tan color as do the electrodes. No pitting, just looks like a light coating on a nearly brand new set of plugs. the whites might look whiter because of the flash, but it is on the pale side. I suspect it is rich during low rpm~ idle, causing the slightly rich looking plugs. The loud bang has shifted ever so slightly up the rev band to 5000~5800rpms. Still kinda loud. I may have to invest in different taper profile needles. I will throw on another shim and see what happens first.

 

Sounds sketchy but try the tape over the intake trick...you'll force the bike to rich'n up. If it gets better or worse you know were to go.
Besure you put the carbs back together correctly.

 

I remember Cat man poop (John) saying that the Snorkel Ectomy is only to be done if you have a full exhaust:

http://www.geocities.com/catpoopman/sv650_snorkel.html
This should only be done after a full performance exhaust is installed -rejetting will be needed. Slip on systems do not qualify.

Hope this helps
Rob

 

I may have to invest in different taper profile needles.

I doubt that. Many many people have done this without replacing the needles.

 

I remember Cat man poop (John) saying that the Snorkel Ectomy is only to be done if you have a full exhaust:

A full exhaust helps but is not required. I ran desnorkled and rejetted with the stock exhaust on my 2002 for quite a while. I got a great power increase out of it too.

Many many people have done this without replacing the needles.

Yes, many have. As I mentioned before though, some bikes require unusually 'generous' jetting. I'll agree that this should be able ot be accomplished with enough shims though.

 

I'll disagree with DonnieJ again. All the dyno runs I've seen show just a couple of HP doing any of the modifications. At mid range that increase looks to be (realistically) about 5% to 7%. No human being could feel that as a nice increase in HP. Butt dyno can be very deceiving, especially if you're looking for wonders.

 

I'll disagree with DonnieJ again. All the dyno runs I've seen show just a couple of HP doing any of the modifications. At mid range that increase looks to be (realistically) about 5% to 7%. No human being could feel that as a nice increase in HP. Butt dyno can be very deceiving, especially if you're looking for wonders.

I'm not sure what you mean.

What I was saying is that if you desnorkel and rejet then you will get a noticable increase in power, even with the stock exhaust. If you later upgrade the exhaust and rejet again then you will have even more power.
I know this for fact.

 

I got bored last night and decided to install my UNI's just to see how the current jetting would react.

I rode it this morning and results are just as expected.

start up: had much difficulty with the cold starup, wasn't even realy that cold.
I had to bust out the jumper cables again. Started right away after I
hooked it up to my car. Choke down and turned the idle adjuster an
extra 1/2 turn before I started it up.

idle: Definatly lean. It will not hold the idle at 1300. had to adjust to +1500
Idle also fluctuates.

cool accel: feels dead between 4500 ~ 6000 rpms REALY lean. Backfireing sounds
like a 9mm vs. a .22 previously. also the bakfireing has broadened to
4200 ~ 6500 rpms. Much more pronounced and frequent. What is
wierd about all this is that the plugs are reading rich wth slightly pale
porclain. I havent added shims yet. I will probably also increase the
idle mix screw another 1/4 turn. I'll let you guys know my results
tomorrow. :thumbsup:

hot accel: Same as above, but not as pronounced.

 

if you were a little lean with the air box, then you're *way* lean with those pods.

 

Um, so you couldn't figure out your carbs, so you put those on? Good luck with that.

 

if you were a little lean with the air box, then you're *way* lean with those pods.

I know... I was just fcuking around with it. I'm currently working on some 2-2 dual exhaust I will eventually install along with them there UNI pods.

I will revert back to the desnorked box after I add the 4th shim and 1/4 turn out richer on the screw.

 

Just got back from test riding my bike after installing the 4th shim and turning the idle mix screw 2 3/4 rurns out, airbox.

Acceleration has improved noticably. The loud bang is now a mild pop. Pulls realy hard past 5000 rpms. Only problem is now it will not idle. Not that it was idling well in the first place.

I had to change out the springs that goes on top of the needle jet and under the needle jet holder. I was only able to find springs that were slightly more springy and larger at ace hardware. It fits nicely after I trim the springs to size. I'm not sure if this is causing the idle problem or from the 2 3/4 turn on the mixture screw. Idle also fluctuates alot. When I put the vaccume guage on it appears that the vaccume in the front cylinder is inconsistant campaired to the rear cylinder. When the vaccum in the front cylinder goes up the idle moves up and smooths out. And when it the vaccum pressure drop lower during the fluctuations the idle becomes extreamly unstable and low. I would turn the idle adjuster, t would then jump from 1400 rpm to 2500 rpm then back down to an unstable 1300 rpms.
What can cause this?

 

Here Check this post of mine from a while back
(Click the pic if ya want the post but the pic is the IMPORTANT thing):


mainly: NOTE the graph is in % of throttle, 0 to W.O.T.
This, I think, shows where you're having problems.

You are trying to fix a WOT problem by adjusting a 0 - 1/4th throttle control.
It doesn't matter if you add 5 shims or use a 3 turn Air/Fuel screw setting.

If you are still lean you need bigger mains.

When syncing the carbs the gauges will fluctuate by a lot at low rpm, mine did. You can resolve this by squeezing the line to reduce the amount of air can go in and out or using a shut-off valve. This reduces the release of pressure causing the needles to stay centered longer.

Hooya,
Rob

 

When syncing the carbs the gauges will fluctuate by a lot at low rpm, mine did. You can resolve this by squeezing the line to reduce the amount of air can go in and out or using a shut-off valve. This reduces the release of pressure causing the needles to stay centered longer.

Why not just adjust the amount of bounce allowed in the carb sync tool?

 

The reason I didnt go to larger mains in the first place is because I'm already running 152.5's front and back. Along with the desnork and stock can, "usually" the 152.5 mains would be much more than enough. I'm sure many SVRider's with experience tuning carbs will agree with this assumption. Anything over a 152.5 with a stock pipe is unheard of in SVRiderdom. But my particular SV is an unusual one, apparently.

With my current settings and the additional 4th shim, the acceleration @ WOT is very good. Much, much better than 3 shims. the power dip at mid-revs is all but gone. So, I think that took care of the lean spot at 4500~6000rpms. But mild exhaust popings sounds are still present. I still need to pull the plugs to see whether if the current popping is caused by a lean or rich condition.

Right now my main concern is my idle. Since adjusting the idle mixture to 2 3/4 from 2 1/2 turns, the idle has become much worse. Before, with the old settings, it will have a slightly poor idle at 1500. Now, the rpms wont even get that low without cutting out. It might stay at 1300 shortly, struggling to stay alive. Cruizing at 1/8 ~ 1/4 throttle has similar but less pronouced results. Engine "bucks" at low rpm cruising.

What do I do next? I realy dont want to upsize the mains untill I finish my exhaust. So I think I will stick with the 152.5 and 4 shims for now, turn the idle screw back to 2.5 turns or 2.25 turns and slap some tape over the air filter opening.

Hopefull the spring that I replaced has nothing to do with my current idling condition. The spring that I used are one size larger in wire diameter, therefore stiffer than the stock springs. I lost one of the spings when I was taking the jet needles out for re-shim. So I replace retainer springs in both carbs.

----------New spring on the left-----------------stock spring right

The fluctuation I was talking about isnt the normal kind. I know how to use a carb sync vaccum guage. What I was talking about is the inconsistancy of the fluctuations causing the idle to also be inconsistant. The front carb vacum reading will be high(normal) in one second then it would drop to barely any vacum. When this happens the idle will either drop to an unstable 1300 rpms from a adjusted +2000 rpm idle, or the engine will simply cut off if idle was below 1500 rpms to begin with. Most likely an issue with the idle screw adjustment.