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Discussion Starter · #1 ·
Hi all

2000 Marauder VZ800 all stock, the front and rear air filter are K&N reusables

front carb mj 90 pj 40
rear carb mj 100 pj 100

Im not looking to go nuts (just yet) but where should I start keeping things the way they are and just upjetting with stock pipes, how much should I go up?

If I decide to get some exhausts like cobra or vance and hines what should I jet to in that instance?

Whats other things would you look at to add performance to this bike?

TY for you help
 

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Im not looking to go nuts (just yet) but where should I start keeping things the way they are and just upjetting with stock pipes, how much should I go up?
None.
Seriously. The air restrictions are in the air box inlets. K&N filters don't make much difference.
Now if you opened up the air box air inlets a bunch, then you would have some jetting to do. Even with the stock exhaust system.

S F
 

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K&N can actually make CV type carbs open LESS as the slides slow down in response to them. When the slide slows down then the bike runs richer during a slide move as the effective air passage becomes smaller because slide slowed down. Smaller passage then bumped up airspeed to pull harder on jet.

I find myself wondering about the one 'rear carb pj 100' thing. OP seems to be saying one is 40 and one is 100, that is a pretty impossible difference unless I'm missing something.

And, nobody competent can even think about offering a jetting spec on different mufflers, there is often a wild difference on some based on the baffling inside, some may have to DECREASE jet size. CVs though commonly need no change as they self jet and why the slides change opening speeds to compensate.

Why the Dynojet filter kits put drill bits in to enlarge the slide holes to pick the slide action back up. And also why many jets they supplied may have numbers stamped on them but are not right, on Honda DOHC we found the bigger numbered jets were actually smaller if you carefully measured the holes in them. Owners would be downjetting when they thought they were going bigger, quite a stunt. Yet bike seemed to run better...........????
 

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We disagree on the effect K&N filters have on tuning CV carburetors as well as what makes the slide open and how.

The OP probably had a miss-type on the 100 pilot jet.

I've never seen a performance exhaust system (that was any good) that needed smaller main jets when tuning for the pipe.

Dynojet does change for the sake of change and they don't even get that right. The logic, or approach, Dynojet uses is to make the slides open sooner, richen the heck out of midrange running and use smaller main jets to compensate for what they did to midrange tuning. It works okay for anybody that goes by the instructions and tunes using the "seat of the pants" method instead of reading the spark plugs. The problem is they end up with an engine that runs LEAN at top speed. Dangerous for the life of an engine. Like I said, all wrong. That's why I will not use Dynojet and only use Factory Pro.
The only thing I need a "jet kit" for is to get jet needles that have been engineered for the particular application. I've yet to see a time when Factory Pro didn't supply the correct needle taper.

S F
 

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They likely stagger jetting to keep rear cylinder a little cooler since it is blocked by front. When jetting keep the stagger in place.
That bike uses two totally different carburetors arranged in two totally different ways. EVERYTHING is different about them.

S F
 

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So? They still had to hit close to the same metering overall unless the cylinders are different sizes, which they aren't. It's common to jet a bit richer for center and back cylinders to help even out cooling. Who cares what the carbs look like? The fact that both pilot and main increase on the rear scream what I said is likely true. I did the same on Kaw triple middle cylinders and Honda the same on early DOHC four RSC racebikes, the center cylinders ran hotter so they bumped the jets up on them.

'...is to make the slides open sooner, richen the heck out of midrange running...'

Uh, somebody is welcome to explain how every other carb on earth including direct lift run LEANER the faster the carb slide is opened up. That quote cannot be true, it is in defiance of physics. Unless it is implied the new needles did that. I use no new needles in anything, always been able to get a good fuel ramp using the ones that got millions spent on them, the OEM ones. If I modded on needles I would do airbleeds first as they are much easier and easy to revert back to old setup too.

The slide drilling is actually an attempt to get the slide just back to where it was before somebody yanked the common airbox, which then let the slides plummet because the individual K&N filters got put on bike.
 

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So? They still had to hit close to the same metering overall unless the cylinders are different sizes, which they aren't. It's common to jet a bit richer for center and back cylinders to help even out cooling.
The differences below are some of what I was referring to.
The air filter housings. Both very different. The carburetors. Front downdraft. Rear side draft. The intake manifolds. Front takes a 90 degree turn going down into the port. The rear, a straight shot in. The exhaust head pipes. Really different. How much depends on model. And then there are differences in the ports to consider.
I have had all of these induction / carb parts in hand when doing make run jobs on both Intruders and Marauders. (The reason I don't care for this design, it's screwy). If I've ever done a performance tune on one I've forgotten, probably intentionally. Doesn't matter. Tuning is tuning.
I'm guessing the OP might have this exhaust system. Very different head pipe / mid pipes...
Or even worse. This system. Check out the U in the rear head pipe...

Low pressure created along the wall of the carburetor venturi pulls fuel up thru the jets and operates the vacuum slides. Years of experience re-tuning a bunch of different designs tells me the venturi doesn't care what air filter is up the line or how open the air inlet is, but you do have to tune for it. (As a matter of fact more open, more flow but a runner of some sort is ideal to avoid turbulence at the back of the carburetor and there is a way to tune the total intake tract length for a given RPM). The venturi does what it does independent of air filter type or a smaller or larger air inlet opening. That is where a less emissions friendly, adjustable, correctly designed performance tapered jet needle is useful. A partially closed slide (at rest) could be seen as a super, or boost venturi creating lower pressure under the slide (as air flow increases) creating a vacuum inside the vacuum diaphragm (by way of lift hole/s) raising the slide but it also depends on spring pressure. Both of which can be adjusted but rarely needed.

S F
 

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'A partially closed slide (at rest) could be seen as a super, or boost venturi'

Uh no. a boost venturi is a second stage air acceleration point with accelerated air flowing outside it but not as fast as the booster makes. Why the second air speed is 'boosted'. Ever seen triple boosters? But before you say it, I know, a difference meaning nothing. LOL.

Ever tune using the lowest vacuum you can get in top gear at wide open throttle before? One of the most direct ways to discover if you are running the correct size carb or not. The same method can reveal some pretty weird action in other vacuum operated systems such as power enrichment at over 3/4 throttle like power valves do. We had some pretty major problems carbing and jetting our more radical AMC race stuff until we were forced to toss some widely held conventional ideas out the window to then pick up spectacular amounts of power. Tell others and you got that look that said they think you are crazy but then you take a 390 inch AMC motor to whip the daylights out of a 454 inch one and the tongues did waggle. Even worse when the opposing car was a true 426 Mopar hemi.

Here's one for you...............We know that any changes mess CV carbs up. If a given that paper air filters are more restrictive than low restriction ones like K&N then why is it the lower restriction messes carb opening to open slower or not open up all the way? It also flies in the face of thinking that says if I allow denser air from low restriction to enter the carb more fully then the denser air should apply MORE pressure at the direct bottom of slide entry point (at relatively low pressure) to increase the acceleration of mass past the slide holes to then lift the slide more. I mean, doesn't atmospheric pressure actually fill a cylinder since vacuum is technically NOTHING? Something is seriously wrong there and where CV tuning tactics have to change away from direct lift carb ones.

I tossed that big clash around in my head for a good while until doing research on my own to come up with a workable answer. They won't teach you that in any books I've seen.

You can ignore any videos where people film slide action to 'disprove' the slide does not open fully, it being wrong. Yes, my eyes see the same fully open slides yours do. It is in no way that simple.

The U in the rear pipe thing = nothing, the engine won't see it. The only true restrictions in exhaust pipes are sharp corners and pipe size changes. U turns in pipes are often found on the best high hp. pipes there are. As long as the pipe is still round the exhaust pulses do not really see a turn. Straight is always better but in many cases not needed. Per testing done WAY back in the 'Scientific Design of Exhaust and Intake Systems'. Look at Formula 5000 spaghetti pipes and how they snake around.
 

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You can ignore any videos where people film slide action to 'disprove' the slide does not open fully, it being wrong. Yes, my eyes see the same fully open slides yours do. It is in no way that simple.
Didn't know those videos even existed. I guess that means I've been ignoring them the whole time.

S F
 

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Discussion Starter · #12 ·
UPDATE

So today I am getting somewhere, I decided to tear apart the carbs and inspect the floats,,,,I set the rear float as close to spec as I could, the diaphram and needle looked good, I cleaned all passages, removed the mixture screw, cleaned and reset,,,,HOWEVER, this time I was able to read the rear MJ and it was a 165! Someone put that in there, I knew It was an issue,,,,I had some spare jets and decided on a rear 120MJ and put it all back together,,,,NOW the bike has more power and more midrage torque, I got it up to 78mph no issues,,this bike was sputtering and topping out at 70 since,,,,so I know Im on to something,,,,I was out of time so next time I will inspec the front carb closer,,,given the OEMs for this bike are 90 and 100 MJs with the no snorkel K&Ns spacer Jim says 120 or 130 MJs,,,,,,today was a big win as I am on to something
 

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Steps of 30 are still pretty big and you may still be too big. Bear in mind that too rich often runs FINE at first doing it but after a time the engine tune 'colors in', or settles more in place and commonly what you thought was great can later show signs of not being so great.

Now you like so many others grasp why everybody thinks they are lean when they aren't necessarily.
 

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Discussion Starter · #14 ·
Yes, only time will tell, spacer Jims fourm has Marauder folks with K&Ns and exhausts running all types of jetting 125 135,,,,etc,,,,Its a huge jump, but maybe its something fickle with this bike and those filters,,,Ill just have to wait and see, I have not even seen the MJ on the front carb,,,,,that fact that just doing this was a big difference Im headed in the right direction,,,,,once I dial in the fron carb jetting I will ride for a few days, then take a step down and see what direction it goes,,,,,I almost fell backwards when I saw the 165 in there, but makes sense, this bike would not go past 70mph and would sputter doing so,,,a huge MJ would cause this exact issue,,,,,the plan from here is tune and set the front carb jetting and float,,,,,then go up or down accordingly
 

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Discussion Starter · #16 ·
UPDATE

So today I tore the front carb apart and woulnt you guess, at 155MJ with OEM 40 pilot,,,,so this bike was running 155 - 165MJs,,,,,I cleaned all the passage ways and the float was measured way lean and moved it into spec, the needle valve passage way was gummed up a bit with all types of debris, maybe even corrision, not sure,,,,,,IM out of jets so I put in a 105 MJ in front and 120 in the rear,,,I took it for some high speed runs and hit 80 with more to spare, the power is there, but I think I can go richer in the front MJ maybe 110,,,,,2 issues

1. Now the temp light is coming on, I did a full collant flush and replace month ago and the light was coming on before that, but never after the flush, any ideas why that light is coming on now after carb clean and lower jet size? could I possible be too lean?

2. The idle is a bit eratic and fast\surgy at times and takes slightly longer to return to idle upon rev,,, what do you think? is it time to sync the carbs, I imagine its never been done,,,I sprayed carb lean on boots to check leaks but didnt see any, any ideas?

TY all
 
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