QT50 and SHA slide tuning

Real first name Real last name /

So i dont think SHA carbs are a favorite on kitted QT50s but thats what im rocking with and was hoping to find others similar setup that can tell me what they have going on. On the entire internet this site is the only place that even talks about slide tuning for these carbs that ive found and they are old ass threads with nothing to do with QT50s

Yz60 kit

MLM side bleed

Dellorto 15:15 carb

Cone mesh air filter

Thats my ride. Its rich on the low end and at idle and im trying to figure out which slide is right. I cant really figure out the jetting till i get this sorted out as changing the slides requires rejetting. Running a 61 now and it 4 strokes when the temp is below 320. Being in a residential area I'm not always going full throttle so this is quite annoying when when the engine cools to 290-310 as I give it gas. I have all slide that are available on treats, 1,2,6,7,9 and the stock plastic one. 10 is outta commission.

Screenshot_20220423-222959_Chrome.jpg

I read on here that the slide angle leans the mixture out by creating a nozzle effect and the the greater the slide cutaway number the leaner the transition off idle. The reviews on treats about some of these slides conflict with the information offered on dellorto thread. As you can see, not all the slides are angled but have a funny shaped cutaway instead so im not sure where to start with the information on this site as the dellorto thread is old and some slides mentioned dont exist on the market anymore and theres new ones at this point in time.

I have a tachometer coming in the mail so i can get my idle to 1,700 RPMs as advisied in the owners manuel and will go from there with slide tuning. As of now I've been tuning to where the back tire starts to barely move and then I back it off but the idle is really really high and it sounds ugly and unhealthy when I do this.

Re: QT50 and SHA slide tuning

Well, for starters, the exact idle rpm would be a function of the carb choice to a certain degree, don't sweat that, set the idle high enough that it won't die and low enough that it won't grab the clutch.

As far as the slides go, you already have them so try them and see. Inside the carb there is a emulsion tube that runs vertical with holes in it, the different slide shapes are trying to reduce vacuum (increase pressure) on that tube by slowing down the air velocity at 0-30% throttle give or take. Reducing the vacuum causes less fuel to flow.

Based on your temps it sounds like you're already tuned pretty well, at low load the temp will definitely drop. Head Temp isn't really a good tuning tool the way you're talking about it here, it's only a warning light duty something being way wrong.

Re: QT50 and SHA slide tuning

Jack Rutherford /

what temp gauge are you using?

Re: QT50 and SHA slide tuning

Real first name Real last name /

Its a trail tech from treats with the spark plug washer

Re: QT50 and SHA slide tuning

Real first name Real last name /

Ive been relying on my temp gauge because it helps me indicate if i will 4 stroke when i open the thottle all the way. Less than 320° i will 4 stroke but over 320° its usually fine however 320° is not my usual operating temp. Ill warm her up nice and hot before riding and blast off but as i ride at slower speeds in the duratation of my ride the temp goes down and i 4 stroke.

Re: QT50 and SHA slide tuning

Jack Rutherford /

61 seems like a small jet for your setup. I would think 70-75. You don’t seem to be at altitude.

I would try slide 6 or 7 and see what that does for your idle and low end. (edited)

Re: QT50 and SHA slide tuning

Dirty30 Dillon /

Yeah, the temp gauge is not indicating 4t'ing. My bikes typically warm to 320 and I don't wanna see them drop below that, under anything other than inoperation.

The issues you are seeing are specifically why people go multi circuit carb.

Re: QT50 and SHA slide tuning

Real first name Real last name /

Ill give that a shot tomorrow, got 12hr shift today. But i was thinking the same thing about the jet but i kept going down so it wouldn't 4 stroke at lower temps. Now that i think about it, it makes sense my engine wont hold the heat at 1/4 thottle if the slide is letting in too much gas to begin with but when frustrated you dont think logically

Re: QT50 and SHA slide tuning

Bump your timing or compression.

Re: QT50 and SHA slide tuning

Real first name Real last name /

Most people understand the concept of jetting. To me it seems these carbs arent popular as upgrades cause theres not to many threads about tuning the low end so they get overlooked or skipped . Im willing to put in the time to figure out how to get it running optimally. When i post on reddit it seems no one is aware of how slide effects performance which makes sense because when they come stock on bikes like a tomos theres no need to fiddle with slides because the manufacturer took care of that beforehand

Re: QT50 and SHA slide tuning

Real first name Real last name /

QT50s timing cannot be adjusted unless i get a $300 CDI kit from treats. As for compression, the 60cc kit was put on around late August and crankshaft seals were replaced as well so i dont think Compression should be the problem either. I recently went form a bp4hs plug to a bp6hs

Re: QT50 and SHA slide tuning

so ok, a #2 slide and #9 slide have the same cutaways. the #9 is just physically shorter and clears the whole venturi on the larger bore SHA carbs (14:14-16:16)

a #1 slide and a #10 slide have the same cutaways and the #10 is physically shorter and clears the whole venturi too, but is not available really anywhere.

i’ve modified #7 slides to the same cutaway as a #1 slide and it opens the full way and is a good stand in for a #10 slide.

having the carb open the whole way is super important to getting the carb to settle back to idle nice and smoothly.

09438755-FCD2-4C19-932A-881E7D0E21DC.jpeg

number 9 slide

2EEBA025-36DF-4932-858D-B23DFB9BC2C5.jpeg

number 2 slide

Re: QT50 and SHA slide tuning

I went a tad ott and cast my own

20211214_133523.jpg

It's a #7 and #2 love child with added boost holes to lean off idle to ½ throttle.

Re: QT50 and SHA slide tuning

Jack Rutherford /

They make an offset woodruff key for the pw50 that will work. Depending on how you install it, it will advance or retard timing about 3.5 degrees (relying on memory here as to timing degree change)

Re: QT50 and SHA slide tuning

Real first name Real last name /

Now this is some really good info to have. Im assuming since i have a 15:15 i dont have to modify my slides to much or even use the shorter ones, is that correct? Or would the shorter slides lean out the mixture more than than longer one a the 15:15? Bernoulli's principle or something? I failed chemistry

Re: QT50 and SHA slide tuning

Real first name Real last name /

That's good to know about I only assumed that the CDI was the only option for QT50s. What would the benefit of changing my timing be in this situation? Seems drastic at this point in time

Re: QT50 and SHA slide tuning

you need to use the shorter slides.

Re: QT50 and SHA slide tuning

Get Tom's slide. Sha game changer. Seriously. Adam, get one from him. My Sha has never felt so alive!

@OP: Sha carbs are not tuned the same way other carbs that contain multiple jets for controlling different throttle positions and have needles with tapers. The only thing that controls everything is the slide. The issue with the low end is the lack of adequate fuel and air due to the majority of the vinturi being blocked by the slide. Tom's slide helps with this by having some boost windows in the wall of the slide. You can make your own with a very fine drill bit, or grab one from Tom. I also tried the 3d printed one, but it was not as easy to tune.

The benefit of this style of slide was that it allowed me to make sure I was jetted properly for the top end but did not bog out my low-end. It let me go up a couple jet sizes as well.

The other important thing on Sha tuning is their screen pack. It is important. But you can remove screens to find just the right mix of air. The only other filter that will work if you want to ditch the screen pack is a good foam filter. But too dense of foam and it will never get enough air. The mesh screen filters do not offer enough air restriction on their own so you still need to run the screen pack.

Lastly. Shas have an air leak at their clamp you must have an o-ring behind the shim that goes into your intake. The o-ring is the only way to stop that air leak.

Re: QT50 and SHA slide tuning

Real first name Real last name /

The o-ring was one of the first things i did before puting on the carb. As for my air filter i have a short compact one similar to this

16508984858722874848009522724825.jpg

i do have a screen pack im not using but i can easily pop that in behind the airfilter. Is the short filter okay? If not i might as well ditch it and grab a foam one as you said and if thats the case which would you recommend?

As for the boost holes, which number slide would be best for trying to add them to? Could i do that to the plastic one?

Re: QT50 and SHA slide tuning

Real first name Real last name /

Hey tom, could you post a photo of that slide sids by side with a #1, I have a bunch of #1s so that'd be the side I'm most comfortable trying to modify

Re: QT50 and SHA slide tuning

As I said in my previous post, the slide mods are changing how much air goes past the emulsion tube or bypass it.

Bernoulli's law says that the faster air moves, the lower pressure it has. The lower the pressure the more fuel gets pulled in from the emulsion tube. There are 3 small holes in the tube that give you idle, midrange and full throttle jetting.

If you want to make the carb suck up less fuel (leaner) figure out how to make the air going past the emulsion tube go slower. Adding bypass holes is one way, making the cutaway angle steeper is another way.

Since you're tuning everything with one jet, you also want to make sure that you are giving it as much advantage to be rich at full throttle, having a little air filter restriction means more pressure drop at higher rpm which means you can run a smaller main jet and be leaner at idle.

Eventually you get tuned to a point where the progression of the fuel delivery is too extreme for a Sha. Big porting and big pipe need a lot more fuel at wot and are much more load sensitive so you end up going to a multi circuit carb... Like the OEM one you removed, lol.

Re: QT50 and SHA slide tuning

Real first name Real last name /

The with the #9 the clutch catches before i can turn down the idle enough before stalling so im gonna give #7 a go

Re: QT50 and SHA slide tuning

Real first name Real last name /

So I've added the screen pack in between the air filter and the carb, put in the #7 slide, I've tried jets from 75 to 65 but I can't get the clutch to stop grabbing before it stalls. Scratching my head here Do I need to keep going lower on the jet?

Re: QT50 and SHA slide tuning

Real first name Real last name /

In a side note, this is opposite to my previous issue where i had #2 slide and 60 jet the clutch would not engage untill a very high idle

Re: QT50 and SHA slide tuning

Real first name Real last name /

Well it looks like #6 was the ticket. I thottle is much more responsive on the low end and no more 4 stroking Most importantly. Didn't want to use #6 because it didn't clear the venturi all the way but it's only a couple centimeters and I'll just have to grind down a little bit. Got a 65 in jet in there and my top speed is now 34 mph hoping maybe I can get another mile or 2 after I modify the slide. Thought my mods would put me in the 38 mph range but every bike is different I guess.

Thank you all for your feedback and I am glad I made this thread for other people who decide to a SHA on their Yamahopper

Re: QT50 and SHA slide tuning

Real first name Real last name /

Welp nevermind.... I guess I must have ruined the slide or something. I had it almost perfect and I'm just so pissed off right now. After filing it down I started 4 stroking again so I went And tried my jets all the way down to 58 so now I am bogging and then 4 strokeing. I am just at a loss I was so close just should left the damn thing alone. I am done for the day. I guess I'm just going to order another #6 slide and just leave it the fuck alone. Fuck

Re: QT50 and SHA slide tuning

Ah man that's a bugger, I know your pain tho, I scrapped a few before I decided to cast my own (then if I messed it up I could just melt them down and start again). Don't remember the hole placement exactly, I'll dig the drawings out when I'm back at work tomorrow, but I guess a #6 does a similar thing. How many #1 do you have to play with?

Re: QT50 and SHA slide tuning

Real first name Real last name /

I know i have 3, possibly 4. Are you selling your casted slides? Definitely seems like its worth a try. I did go ahead and order the 3D printed one with the #6 from treats but ill to bet yours will operate better. Ive got venmo and zelle

Re: QT50 and SHA slide tuning

Oh my. So going back up to your filter. I am going to say that your filter is not a great one for a Sha. It has restriction built into it that can not be adjusted and I do not think it is playing well with the Sha. If you really want to use it, you can try removing screens from the screen pack one at a time until you remove all the screens and then it is just your screen filter again. I would first ditch that filter and just use the screen pack with the original plastic cover.

I would also start off with something close to a 65 jet in it, but probably something like a 68 or 70 might be the one.

If it seems like it is muddy and too rich, just remove a screen from the screen pack. You will notice some screens are finer than others. You can combo them up to get the right amount of airflow. It is like a puzzle and can be kind of fun.

I save all of my screens, I have so many Sha carbs that I have a bunch of these screens left from past tunings, but sometimes need one for a new tuning.

Get it tuning real nice with the screen pack and black cap then see about replacing the cap with that mesh filter if you want to try that again. My mesh filter is really just an open screen, just designed to keep larger objects from entering my forward facing carb. The screen pack controls my air restriction and adds finer filtration of debris.

Re: QT50 and SHA slide tuning

Also, everything that Graham said is exactly what you need to know for planning to modify your own slide. And I think that is what times design did best was have the way for the air to push past the emulsion tube at lower throttle positions. Just mark some holes to the edge of the slide that you can visibly see in the carb when it is all the way down. Make one on each side at one of the lowest spots you can see. I will see if I can get some pics of how Tom's slide looks at rest.

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