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Discussion Starter · #1 ·
Working on a 2008 750 Teryx. After installing the Cylinder Works 860 Big Bore kit, we are struggling big time with getting it to run right. Although the timing and valve adjustment can be confusing, seems like we've got that right now.
Put 170 main jets in the stock carbs, shimmed the needles, and upped the pilot jets to 48.
It starts okay and idles good. With the plenum off, the vacuum slides DO move or pulsate some (fluttering), but both are doing it the same amount. Earlier, the rear slide wasn't fluttering, but the front one was - alot. So in trying to sync the carbs, we ended up with both of them fluttering. Hooking up a vacuum gauge, the gauge is un-readable due to needle flutter on the gauges as well.
So let me back up. This thing came in with incredible dirt ingestion due to the plenum falling off. The stock cylinders were junk. Thus the big bore kit. However, there seems to be no support from Cylinder Works as far as what other changes need to be made to support the higher displacement, such as jetting.
Okay, so by changing the carb sync screw, the rear carb slide stopped fluttering, but nothing stops the front side from fluttering. I've read all the posts about this that I can find. One person had a diaphram that wasn't seated, solved his problem; and one guy had the same exact problem, and solved it by re-adjusting the valves. We've been over and over it. The new valves were lapped on the front cylinder, so they should be sealing good. The valve guides have not been touched on either cylinder head. If the problem were valve guides, though, it should affect both, and not just the front.
So. 48 pilot jets. 170 main jets. 0.030" shims under needles.
Last test drive, it was bogging down really bad, until we pulled off the plenum, and then it just took off. Ran waaay better, but still popping some at full speed, and not quite running right at full throttle. Could be running too rich, thus the increased performance by pulling off the plenum and giving the carbs all the air they can take. Planning on doing a snorkel, and bought the K&N air filter for it.
Sorry this is soo long, but somebody out there HAS to have experienced some of the same things that we are going through..... HELP!!!!! :rocket1:
 

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Call Hunterworks. Todd was the first guy on the scene working on making the 2008's run the best they could with carb and airbox tuning. Do not over tighten your plenum clamps it will make it pop off. They used to make billet plenum rings you might be able to find some in stock at UTVInc that fix this issue. Tighten the boots on the carbs first then do the plenum and make sure they are pretty loose, or it pops off.

Todd is your man to talk to. Also, if you haven't already, get an air/fuel ratio meter and tune by it. Every machine is a little different.
 

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48 pilot seems large. But... Like said above, get your hands on an air fuel meter. ONLY way you will get it tunes correctly. Going to be interesting to see how the BBK works with stock cams.
 
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hell yeah. 48 is insane. these need a 40 max.

Not sure how your airbox is setup, this will make a huge difference. a 3x3 intake square will allow you to be around 160-170 range

use 160 KEIHIN main jets. BE SURE THEY ARE REAL OR THE SIZE WONT FOLOW SUIT.

Teryx Dynojet needles, second clip down shimmed/braced with a #4 washer above and below the Eclip. 2.5 turns out on the af screws.

Best bet is the afr meter. tune EACH carb individually.

don't use the sync tool method unless you have a vent able gauge. these will pulse so you need a breather hose to crack open until it smooths out
 

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Discussion Starter · #9 · (Edited)
Can't believe this is new territory

I still find it pretty amazing that there are no Dyno runs or anything for the cylinder works big bore kit, where they have determined what jetting to use with stock or aftermarket parts. It probably would only take a day and a bench full of aftermarket parts to come up with some real data, that we could use. Somewhere I saw that one of the big bore kits actually includes Jets based on the stock or aftermarket parts on the UTV. I saw on one of the forums, a formula, to determine the maximum jet size for a carburetor. According to this guys mathematical calculations, multiplying the carb diameter in millimeters, times five, gives you the maximum jet size that the carburetor will flow enough air for. So in other words, if you went with Jets larger than that, you are only increasing the richness of the AF ratio. So, a 34 mm carburetor can only benefit from a jet up to a number 170. In all actuality, there does seem to be some validity to this. By going with larger Jets, you're only pumping more fuel in to a maximum amount of air that will flow through that venturi.
In the interest of getting this thing back on the road in a timely manner for my customer, we are going to try to go back with basically the stock Jets and stock plenum, and just see if we can make it run that way. We did get the billet plenum rings and have installed them. Even if it compromises the performance that we could have gained from the big bore kit, the owner of this Terex just wants it back on the road, so that has to be our primary concern at this point. We had no idea when we jumped into this that there was no support for the carbureted 2008 version of the Teryx. This thing is the red headed step child, apparently. We will find out tomorrow what happens when we go back with the stock main jets. It does actually run really well on the low-end, with the big pilot Jets. However, it's painfully obvious when you drive it with the big jets, that the stock plenum cannot even come close to supplying the amount of air that this thing needs. After working on these things for years, this thing has made me feel like a total idiot.
 

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Because it is so dependent on altitude, what air filter you are running, if you have done anything to your airbox or drilled the carb slides what cams you are running (I did not know you could even run stock cams in a BBK as I did not think they could flow enough air to make it work) I am no engine expert but I have tuned 3 2008 Teryx machines, one with STD bore kit.

Did you try to contact Todd ar Hunterworks and see what he had to say about it? He is the man to call and I would bet he would talk to you about it.
 

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Discussion Starter · #11 ·
Thanks

Thanks to everyone who replied. We are going to work on it a little bit more this weekend, but if we don't make any major gains on it, then I will call Todd at Hunter works on Monday.
 

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I still find it pretty amazing that there are no Dyno runs or anything for the cylinder works big bore kit, where they have determined what jetting to use with stock or aftermarket parts. It probably would only take a day and a bench full of aftermarket parts to come up with some real data, that we could use. Somewhere I saw that one of the big bore kits actually includes Jets based on the stock or aftermarket parts on the UTV. I saw on one of the forums, a formula, to determine the maximum jet size for a carburetor. According to this guys mathematical calculations, multiplying the carb diameter in millimeters, times five, gives you the maximum jet size that the carburetor will flow enough air for. So in other words, if you went with Jets larger than that, you are only increasing the richness of the AF ratio. So, a 34 mm carburetor can only benefit from a jet up to a number 170. In all actuality, there does seem to be some validity to this. By going with larger Jets, you're only pumping more fuel in to a maximum amount of air that will flow through that venturi.
In the interest of getting this thing back on the road in a timely manner for my customer, we are going to try to go back with basically the stock Jets and stock plenum, and just see if we can make it run that way. We did get the billet plenum rings and have installed them. Even if it compromises the performance that we could have gained from the big bore kit, the owner of this Terex just wants it back on the road, so that has to be our primary concern at this point. We had no idea when we jumped into this that there was no support for the carbureted 2008 version of the Teryx. This thing is the red headed step child, apparently. We will find out tomorrow what happens when we go back with the stock main jets. It does actually run really well on the low-end, with the big pilot Jets. However, it's painfully obvious when you drive it with the big jets, that the stock plenum cannot even come close to supplying the amount of air that this thing needs. After working on these things for years, this thing has made me feel like a total idiot.
With stock cams, stock needles and stock exhaust you will be real close to stock jets. And it's almost never needed to change the piolot jet. Deffinetly not in your case.

I played around with stock needles on mine and is what I found was with the tapper on them I had to run a huge main jet to get the fuel I needed on the top end but ran way, way way to rich on the bottom end. But that was also running much bigger cams and muzzy pro exhaust.

Stock exhaust and cams is so uncommon for a big bore I have actually never heard of anyone even doing it. So don't be suprised if it's hard to find tuning info. I used a LM1 wide band a/f meter to tune mine and without it I feel like I would just be swinging in the dark. With so many variables on this engine it's almost a must. Also very rarely will the front and rear cylinder end up with the same jet size.

You seem really bitter that cylinder works isn't holding your hand. Almost as bitter as I would be as a customer who paid a shop to build and tune an engine that doesn't have the tools like a wideband air/fuel meter to tune it properly.
 

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I ran up to 200 jets on my 840 with the correct AFR all through the throttle range. I'm not exactly sure that formula is correct.
 

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Discussion Starter · #15 ·
You seem really bitter that cylinder works isn't holding your hand. Almost as bitter as I would be as a customer who paid a shop to build and tune an engine that doesn't have the tools like a wideband air/fuel meter to tune it properly.
Point well-taken. Admittedly, we are new to the performance upgrading side of this, and certainly accept advice.
 

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I just got done with a 896 kit for my 08 ran a 3" intake snorkel up to a k&n my jetting was 195 in the front and 200 in the rear did the plug tests and jetting is spot on and my elevation is @3500


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