Jetting Issues? Can you perform the jetting procedure on a stand?

[cajones2]

I have 99 600sx with 760 Hauck big bore kit, carbon tech reeds, reed notch, hauck husher triple pipes (simons), 1" predator track with 144 megabites down the middle, 23-40 gearing.

I finally got all my wrenching done, installed the hauck spec on jetting 47.5 Pilots, 160-162.5-160 mains with PTO needle at position 3, middle and mag at position 4. On paper they said this is the spec to 10 degrees. After some short testing in 0 degree temps, the plugs looked perfect. When I got on it, RPM would climb but then drop steadily until i got off the throttle. I thought this was due to the flyweights (48g HH with HH Black primary spring). Thinking it may have been the weights and clutching, I restored it all to close to what was original aside from the top gear, changed plugs and went again when it was in the upper 30's. Tested it again and the problem continued. I then checked plugs, they looked ok, starting to turning a strong tan color. Piston wash on the mag and middle pistons looked good. The PTO side looked wet on the piston crown. Plug looked more damp as well. Checked spark, it is good, took carbs off, cleaned them and also shot some shop air through them, everything looked clean and clear. I called Hauck and they said that their jetting spec is conservative and is good for more like 0 or -10. In about 40 degree temps, it would idle fine, but when you got to 6000 or so, it would get throaty and bog a little bit. As I was on the throttle and the bog came about, i hit the choke..to make it slightly worse so I am thinking i am runing too rich.

My theory is that it is running pretty fat right now. Specifically the PTO cylinder. My next step was going to be to run it again with the airbox screen/filter off to see if that helps. If it improves, I will drop main jets to 160-157.5-160. I will test it again, look at wash and plugs and fine tune by moving the needles.

Now that we have no snow on the ground, can I perform the jetting procedure with the sled on a stand when it cools down? All my clutching has been restored to a close to OEM setup. I did leave in the 23T top gear (was 21T). Surely I wouldn't think that would cause it since the 700sx for that year run that gearing. I would also think that if all three cylinders were firing well, I'd be able to run the HH weights without this type of result.

Is my plan of attack sound reasonable, anyone have experience with this kit/pipe combo or anything else I should be considering?

Thanks!
Craig

 

[Ding]

You cannot simulate load, and airflow on a stand without a dyno and a wind tunnel.

 

[cajones2]

yeah i was wondering about the load. I have heard of people holding the brake down slightly to create that load as well. Fortunately i have a bean field right outside my door i can use....it happens to have no snow on it right now, but it should get me close i'd think.

Any comments on issue & theory from above?

 

[bufalobob]

there's only 2 ways to tune. on the dyno or in the field.
sounds like your motor could be rich. plug color doesn't tell you much by itself. i've seen motors w/ black plugs burn down. reading plugs & piston wash can be difficult even for an experienced tuner. takes lots of "time w/ the tools" to get an accurate read & to understand the relationship between the two!
below are the specs for my bender 800 sxr ( 160+ observed h.p. @ dynotech @ 8800 rpm ). this should be a good reference & starting point for your situation.
mains: 155-155-157.5 ( this is rich, could safely run 152.5-152.5-155 )
pilots: 55 all
needle: #2 - all ( 2nd leanest )

bob

 

[cajones2]

As always, thanks a ton Bob!

I am taking a vacation day tomorrow to do nothing but to do some field testing. It'll likely be on a bare bean field where I can run 600 feet easily. We are expecting a little snow tomorrow night with temps dropping to a reasonable level so saturday i can fine tune it. I will start with that jetting procedure in the tech section. If you have any other suggestions/methods let me know. Thanks!

 

[SXlover]

No load on engine when on a stand. If in a shop, you would also have temp differences.
Check this link in the Tech pages. http://www.totallyamaha.com/snowmob...g a Sled/Jetting a sled and reading plugs.htm
Might want to give a check on your reeds also. Had a reed problem on a 05 Viper Mtn and it would pull up good RPM's then wouldn't hold them. Fought for a while troubleshooting until we found a chip out of one of the reeds. Replace that one and it still wasn't quite right. Found out one of the other ones had only a slight wear spot. Sounds like reed problems are more prevalent in Vipers than others, but it may be worth a look to be sure.

 

[RJH]

Almost impossible to jet online – so…..

If its rich - it will reach a range and burble. You say the rpms drop – this is not consistent with jetting – it either works or it don’t. I would suspect the clutch is too heavy - which can be caused by a ton of things.

Can you go back and change one thing at a time – I would say the pipes last.

10 deg for him may not be relative to 10 for you. For example – the jetting I run here in Ontario is no where the same if it was the same temperature in Michigan. Totally different air. (That would be optimum jetting – it would still run OK normally)

You have small jets – they should be good for a 30 to 40 degree range. Once you get up into the 400’s -you need to change every minute.

Optimum jetting needs to be tested under load….but …you should be able to…from idle…on the stand….blip your throttle and it should run clean to factory recommended rpm. You can make adjustments on the stand to get it clean. When the times comes – run it on the ground and do a plug chop.

Don’t touch the brake.

I would put the needle on the same clip.

In addition – you can run it the ½ throttle and see if it burbles there.

 

[cajones2]

I dug into things a bit and found a couple more suspicious items (one is my own doing). The first thing was I preformed an compression test across all the three. Mag~128, Mid~120, PTO~100. Concerned, I removed the head, the pistons all look good, piston wash looked good from when i last ran it. I turned the crank to confirm the cylinder walls were in good shape, and they were. I did notice that I installed the exhaust flange upside down and was obstructing more the exhaust port on the middle cylinder that it should. I have about 2500ish miles on the big bore kit and think that is a little premature to replace rings, but I am just speculating there. Hauck said the rings would cost me $30 per set, same for the gaskets...sounds pricey to me!

My reeds are brand new but will check them when i have the carbs off here shortly.

I am going to fix my F up there, return the jetting back to spec for a baseline. I have pics of the pistons and such, but they looked good so i didn't bother posting them. The PTO side seems to be running slightly more rich than the others with the needle clip in one leaner setting than the other two...kind of odd, but that is what the spec says...you can always trust the spec right? I'll provide another report soon.

 

[cajones2]

Turns out I installed two exhaust flanges upside down. The flanges didn't have a "T" or "up" on it as well as no indication as to which cylinder they bolted to. Upon installing them I actually called Hauck's and the kid on the phone told me it didn't matter, there may be neglible performance difference. I was able to get it out and it clearly ran much much better. Now I am trying to get the clutching dialed in. It really seemed to run well now.