SXR Fine Tuning Carb Bottom End

[rocknice2]

I have stock carbs jetted to Factory Wet Pipe recommended jets. See below for all mods.
Pop Off Spring = stock
Pop Off Valve = stock
Pilot Jet = 80
Main Jet = 152.5
High Speed Screw = 1/2 out

Mid and top end are crisp, plug is light brown/tan when run wfo.
When riding around at low to mid speeds the plug comes out wet and black. I'm running a quality syn. oil @ 60:1

If I turn low speed screw : [1 turn out recommended]
@ 1/4 out it idles better and smokes less with the plug staying much drier. Throttle is better from idle => full, but not as snappy I'd like.
@ 1 turn out I need to increas idle speed to make it run but the 1/4 => full throttle is better.
Actually I can turn the low speed screw to ZERO out and it idle good.

I was thinking a stiffer pop off spring and maybe a bigger pilot jet to compensate for 1/4 throttle response.

 

[rollin5150]

Here in AZ I am running a 2.0 NS and a black spring. I believe my popoff is about 21 psi. Right now I am running about 1/4 out on my low. Usually I am about 3/4 out but with the hot summer upon us I had to turn it in. Are you using a tach for the top end RPM?

 

[rocknice2]

No I don't have a tach yet but am planning on getting a Tiny Tach.
What is the stock seat and spring combo?

 

[Mark44]

t

No I don't have a tach yet but am planning on getting a Tiny Tach.
What is the stock seat and spring combo?

Tint tach will not work, they don't repeat fast enough. You need to go on Watcons site and get a tach from him, this is the cheapest tach I have found.

Mark44

 

[rocknice2]

every 1/2 second is not fast enough?
The Pet 2100 DX is over $200

 

[rollin5150]

The tiny tach will get you close if you have real smooth water to tune on. To do the job correctly, you need one similar to the one Watcon sells.

 

[Crab]

check your actual popoff with a guage or your just spinning your wheels, on my 750 it didn't run right till I got it at about 35-38 psi with those carbs, depending on the engine hours yours could have dropped too low causing the over rich just off idle.

 

[Mark44]

t

every 1/2 second is not fast enough?
The Pet 2100 DX is over $200

Depends how much a fine tuned motor is worth to you, $200 bucks is cheap to me when I am tuning a couple grand + motor.

Mark44

 

[fastony]

I have stock carbs jetted to Factory Wet Pipe recommended jets. See below for all mods.
Pop Off Spring = stock
Pop Off Valve = stock
Pilot Jet = 80
Main Jet = 152.5
High Speed Screw = 1/2 out

Mid and top end are crisp, plug is light brown/tan when run wfo.
When riding around at low to mid speeds the plug comes out wet and black. I'm running a quality syn. oil @ 60:1

If I turn low speed screw : [1 turn out recommended]
@ 1/4 out it idles better and smokes less with the plug staying much drier. Throttle is better from idle => full, but not as snappy I'd like.
@ 1 turn out I need to increas idle speed to make it run but the 1/4 => full throttle is better.
Actually I can turn the low speed screw to ZERO out and it idle good.

I was thinking a stiffer pop off spring and maybe a bigger pilot jet to compensate for 1/4 throttle response.

Epoxy in the cross over tube in the intake manifold and then adjusted your low speed screws, you will tell a big differents on idle to 1/4 throttle response. This will make your jetting a little richer too.

 

[rocknice2]

I have stock carbs jetted to Factory Wet Pipe recommended jets. See below for all mods.
Pop Off Spring = stock
Pop Off Valve = stock
Pilot Jet = 80
Main Jet = 152.5
High Speed Screw = 1/2 out

Mid and top end are crisp, plug is light brown/tan when run wfo.
When riding around at low to mid speeds the plug comes out wet and black. I'm running a quality syn. oil @ 60:1

If I turn low speed screw : [1 turn out recommended]
@ 1/4 out it idles better and smokes less with the plug staying much drier. Throttle is better from idle => full, but not as snappy I'd like.
@ 1 turn out I need to increas idle speed to make it run but the 1/4 => full throttle is better.
Actually I can turn the low speed screw to ZERO out and it idle good.

I was thinking a stiffer pop off spring and maybe a bigger pilot jet to compensate for 1/4 throttle response.

Epoxy in the cross over tube in the intake manifold and then adjusted your low speed screws, you will tell a big differents on idle to 1/4 throttle response. This will make your jetting a little richer too.

OK so I finally recieved a selection of jets , needles & springs. I spend the last two days tuning and slamming my head on the work bench.
I was surprized with what I ended up with.

#2 Needle seat
95 gram spring
Low screw 1_1/2 out
75 Pilot
152.5 main
High screw 1/2 out

The 75 pilot jet made the mid range really good. It hit much harder than with the 80.
The low screw has best idle @ 1 out , but acceleration was best @ 2 out so I put it at 1.5 out.
It seems that no matter what combination I tried 2 turns out on low speed screw was the best for acceleration. I didn't think the low screw had that much influance over acceleration but it does.
I even tried a # 1.5 seat with 115 gr. spring & 82.5 pilot, that just plain sucked.

Final results.
0-1/4 throttle riding = Kind of blubbers/studders but has more power than before. [ this studder kind of bugs me a bit but the rest is good ]
Mid range = really good , lots of power, much more than before
Top range = same good power didn't change a thing
Idle to Full Throttle = Strong
After a whole tank of riding @ all speeds but mostly playing, the plugs were a light tan with no deposits. Still wet but a good colour.

I'm still running the crossover. That is the next thing I need to do. I guess it should have been the first thing.
What do you guys use? ...... JB Weld??

 

[fastony]

JB Weld works fine, but when you do this it will make your lowend richer so you might have to do some more jetting.

 

[rocknice2]

Do you fill the whole tube or stuff in a plug like aluminum foil and then fill the last 1/2" or so ?

When I was jetting I found that the pilot had greatest effect on mid range and [this is the wierd part], the low speed screw setting. The pop-off had a greater effect on acceleration.
Which is opposite to everything I've read.

I was a little worried running 2 sizes lower pilot but it didn't sieze after a full tank of riding, plus it's making good power.
Should I be worried or are the Factory Pipe recommendations and safe ball park?

The other thing I noticed was that the carb bores don't line up with the intake bores. They were out by about 2mm.
Should I grind the intake bore to match the carb bore and then blend it to the stock intake bore 3/4" further down tract. Would this be gasket matching?
I would simple enough but just checking so I don't do something foolish.

Thanks for the help fastony

 

[Waternut]

I filled my entire crossover with JB Weld. It looks like a lot but it doesn't take that much to fill them. I just put tape over the ends so it doesn't seep. Then just take some sand paper attached to a piece of glass to get it all smooth. If it's not smooth, it could cause an air leak which will make tuning even harder and could potentially cost you your engine.

I've never had any luck tuning with tachs. I even have the commercial style tiny tach which updates a lot faster than the regular one. It's just really difficult to get any kind of reading off of an ever changing digital readout with 4 numbers.

To my knowledge, plug reading is only good for the high speed circuit. When you're on the low speed circuit, there's too much fuel getting dumped in the cylinder to get an accurate reading. This would also explain why your plugs always look wet when you're looking at them while trying to get the low speed circuit tuned. Lastly, in order to get an idea of exactly what's causing the problem, it might help to know exactly what parts of the carb control what. Carb circuits only care about throttle input but a poor mixture can be masked by higher rpms. Pop off works with the low speed circuit from idle to 1/4 throttle. From 1/4 to 1/3 is only the low jet (the adjuster doesn't come into play in this range). 1/3 and up is the high speed circuit. So if you can figure out where the issue is, you can narrow down the problem.

Some of the guru's may correct me on some of this and if so, great as I'll know better from here on but this is what I've always heard/read.

 

[rocknice2]

Pop off works with the low speed circuit from idle to 1/4 throttle. From 1/4 to 1/3 is only the low jet (the adjuster doesn't come into play in this range). 1/3 and up is the high speed circuit. So if you can figure out where the issue is, you can narrow down the problem.

Yea that's sort of what I've read but that wasn't my experience when tuning. I'm wondering if the crossover isn't throwing a monkey wrench into the tuning.

 

[Crab]

Carbs will be way more touchy when tuning, a small adjustment will be more noticible, on mine 1/8 turn went from ok to ballistic.

 

[Waternut]

Filling the crossover should make tuning a little easier but you'll have to add a second pulse line if you don't already have one.

 

[Watcon]

The lower the P.O. the better the accelleration. Dont worry if it feels a little ratty at steady RPM.. its just the extra fuel needed for accelleration. Try a #80 low speed and turn the low speed screw back in, so you are on the taper of the needle.. The ratty feeling should be better.. Take a look at the Watcon tuning tips on the site here somewhere, but your approch is right on the moneY!!
This is my favorite epoxy, as its "non-metallic" like JB weld.. http://www.watcon.com/Catalog_Pages/AB_Putty.htm

Regards,
Randy

 

[rocknice2]

Why is that? Is the pulse cut in half and therefore the fuel pump flow is cut also.
Would I need a second fuel pump on the other carb? Or can I merge the two pulse lines into one fuel pump?