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  #1  
Old 07-12-2004, 09:05 AM
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Default How to de-restrict Suzuki LT50 quad

Hey everyone,

A friend of mine is trying to de-restrict a Suzuki LT50 quad for another friend of his. He's found, and removed, the restrictor plate in the intake tract and has gone over the exhaust system looking for restrictions (none were found). We figured it might use an exhaust restrictor like the Yamaha PW50s do.

Prior to the de-restricting surgery, the quad ran fine, if you can call the wheezing almost total lack of power fine, but at least it ran. It had also developed a fuel leak from the carb (probably a stuck float) so that was the original reason for the disassembly. De-restricting it along the way was just an added bonus. The fuel leak didn't keep it from running, it just caused it to go through fuel at a pretty rapid rate (several tankfuls in an afternoon, which is a lot for one of these).

At any rate, he put it back together and now it won't even fire. No changes to the jetting were made or anything else. The pipe was cleaned out and the restrictor plate was removed and that's it. Does anyone know if a jetting change is required? He'd really rather not put the restrictor back into the intake as the quad can't climb the slightest grade with a small child on it in that condition. Living in PA, that rules out most riding areas around here. We're thinking that it might need richened up a good bit, considering that the restrictor plate covered probably 80% of the intake area and it flows a lot more air now with it removed, but we don't have any documentation to go from on it.

Any help would be most appreciated.
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Old 07-12-2004, 10:35 AM
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Default Re: How to de-restrict Suzuki LT50 quad

The carb uses stacked pilot jets, once de-restricted you need to remove the first pilot jet. Also, the main should be a 55 stock, without the restrictors you should start at a 65 and work from there. These motors are extremely low compression, milling 0.020" off the head provides a noticable gain without any drawbacks. In fact, you could go as much as 0.040" without problems or being required to run better-than-pump gas. There is a lot more a person could do, but this is a good start.
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Old 07-12-2004, 11:15 AM
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Default Re: How to de-restrict Suzuki LT50 quad

Faded,

Thanks MUCH for the info! My buddy was thinking exactly what you said on the pilot jet deal, but we didn't try it since we were not sure if that was the way to go or not. I'm not sure if we'll know which of the two is the "first" pilot jet, but we don't have much to change if we guess incorrectly.

The main jet will be a bit more of a challenge as he's only got main jets down to 74 (I think) on hand. He's got a Dynojet dyno in his garage so he's got a fair assortment of jets in the cabinet. So I guess we'll give a 74 a whack and see what happens. Or see if the local dealer has any mains smaller than the 74 he's got right now.

And since I've got a milling machine in my shop, we've always got the head milling bit as a back-up plan. But I don't think we'll do that as a first pass. It IS for kids, after all, we just want to make the thing run well enough to climb the hills in the field where they always ride. When you can walk up the hill faster than ride, it kind of takes the fun out of it.

Looks like some rejetting is in order this week! Thanks again.
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Old 07-12-2004, 11:46 AM
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Default Re: How to de-restrict Suzuki LT50 quad

No problem. The "first" pilot jet is the one that would be removed first, the second one will need to stay where it is. A 74/75 main would be okay to start with, and with a dyno at your disposal you'll make short work of the jetting.

The stock exhaust is also restrictive, you can pull the end cap off and drill extra holes through the exhaust baffle and then replace the end cap.

I think you'll find that even without the restrictors and proper jetting, it won't take to the hills with authority. The head milling will definately help, but to doing it in progressive steps will help you realize the gains.

If it's being ridden on short, tight trails and the rider would be more comfortable with short gearing, it might benefit from being in first gear rather than second. The JR/LT 50 motor is stuck with only finding second gear from the factory, but there is a 1st gear in the box. If you pull the side cover off the left hand side of the bike you can see the shifter mechanism. There should be an oblong cutout that the shifter rides it...if you'll notice, it only allows you to shift up, not down. If you remove this stop plate and remove enough material to allow the shifter to shift down, you'll find 1st gear.
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Old 07-12-2004, 01:20 PM
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Default Re: How to de-restrict Suzuki LT50 quad

It's actually a LTA50, not an LT50. It's one of the new yellow jobbies with suspension and all the rest. Not sure if it changes the transmission picture or not. I didn't see any "shifter" to speak of on the engine when I was looking at it, but we didn't open it up either.

I don't think we'll be dyno testing it, since his isn't set up to run ATVs. "Dyno testing" will consist of backyard laps to evaluate the changes. That should get us in the ballpark though.

I'm not sure how much performance they're actually looking for out of this thing. The big one right now is it will barely climb many of the hills on the farm where the kids frequently ride. Put an adult on it and forget it, it's downhill or flatland only. Yeah, I know, it's a kid ATV but my ATC70 is a hoot to ride around the yard. Looping wheelies on it don't hurt like they do on my CR250. Or at the very least, I don't intentionally loop the CR like I do the ATC.

Is the "first" jet the smaller of the two or something? Or is there some other way to determine which is "first" to remove? OK, I think I'm getting it, the two pilot jets aren't side by side, but one on top of the other. You remove one, the smaller of the two, and there's a larger jet behind it. So the smaller jet meters the fuel and the second does nothing. Then you remove the first one and the larger, second pilot jet now does the metering? Is that right? I didn't see the carb innards myself, I only heard about the "two pilot jets," so forgive my ignorance. But from the way you worded it, it sounds like it's obvious which is which so I'm guessing that I'm correct.

If the 74 main is too big, I think the exhaust drilling will help on that front, so we might have no choice but to open up the stock pipe like you said. Sure, we could get a smaller main jet, but what fun would that be?
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Old 07-12-2004, 02:47 PM
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Default Re: How to de-restrict Suzuki LT50 quad

Quote:
It's actually a LTA50, not an LT50. It's one of the new yellow jobbies with suspension and all the rest. Not sure if it changes the transmission picture or not.

I'm not sure either, I know they were all the same from the mid-80s up till just recently...not sure on the new ones though.


Quote:
Is the "first" jet the smaller of the two or something? Or is there some other way to determine which is "first" to remove? OK, I think I'm getting it, the two pilot jets aren't side by side, but one on top of the other. You remove one, the smaller of the two, and there's a larger jet behind it. So the smaller jet meters the fuel and the second does nothing. Then you remove the first one and the larger, second pilot jet now does the metering? Is that right? I didn't see the carb innards myself, I only heard about the "two pilot jets," so forgive my ignorance. But from the way you worded it, it sounds like it's obvious which is which so I'm guessing that I'm correct.
You're getting it...they're stacked on top of each other, in order to get the 2nd one out you'll need to remove the 1st.

Sounds like you have it under control, have fun! :
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Old 07-12-2004, 04:34 PM
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Default Re: How to de-restrict Suzuki LT50 quad

Yep, I just talked to my buddy and he filled me in on the stacked pilot jet so we're good to go on that front.

He's also got Dynojet jets, not Mikuni ones, so the 74 might be OK after all since I think they run smaller than the stock numbers. Either way, we'll see what happens.

Thanks again for the help.
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Old 07-12-2004, 04:41 PM
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Default Re: How to de-restrict Suzuki LT50 quad

M,

Be sure to post back and let me know how it goes...it's always good to hear the outcome of these things, ya know?!
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Old 07-12-2004, 04:50 PM
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Default Re: How to de-restrict Suzuki LT50 quad

Will do. It will probably take a few days as he's got to order an exhaust gasket for it. The pipe is now leaking at the head so that's got to be dealt with first. But once we get it running up to snuff, I'll post the details on what it took to do it.
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Old 07-12-2004, 04:53 PM
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Default Re: How to de-restrict Suzuki LT50 quad

Cool deal :, can't wait to hear what you think of it when you're done.
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Old 07-18-2004, 01:17 AM
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Default Re: How to de-restrict Suzuki LT50 quad

Hey, what's this about a first gear? I have an 85 LT50. Are you saying it has a lower gear? There is no shifter on the outside. It is just gas and go. It would be awesome if there is a way to shift it down.
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Old 07-18-2004, 07:24 PM
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Default Re: How to de-restrict Suzuki LT50 quad

Quote:
Originally posted by 91CR500
There is no shifter on the outside.
Might want to look for one, maybe yours broke off? : There were only minor changes from '84 untill '02...
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Old 07-19-2004, 09:29 PM
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Default Re: How to de-restrict Suzuki LT50 quad

I took a good look at mine. There is no place on the outside of the case for a shifter at all. Are you talking about the LT50 four wheeler? That is what I have and I see no place for a shifter. I have not pulled the side cover off yet. Might have to try that.
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Old 07-31-2004, 10:25 AM
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Default Re: How to de-restrict Suzuki LT50 quad

The final verdict on the LTA50 was to remove the first pilot jet and leave the rest of the jetting stock. He tried a larger main jet, but the airbox lid had to be removed to make it work. It was going to need some more tuning, as well as jets he didn't have, to make it work so he put the stock main back in and left it that way. It still runs better than it did with the restrictor plate in the intake. There's more to be had in that engine, but tuning the crap out of it really wasn't the idea so that's how it was left.
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Old 08-02-2004, 07:10 AM
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Default Re: How to de-restrict Suzuki LT50 quad

An update:

The LTA50 got a workout yesterday from it's pint-sized rider and it seemed to run pretty well for him. I told his grandfather that we could still make it faster for him but he said it's quite fast enough as it stands. At least until we can break him of the habit of not looking where he's going on it. He tends to look at us and gas it, rather than where the quad is pointing, so faster probably isn't better just quite yet. But removing the restrictor made a big improvement as the quad will now climb hills for the boy at will.
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