RPM and boost are low

[nytrozula]

I just got my supercharger back after last years meltdown and was able to get it out on the trails this week; riding in the UP Michigan. The pulley combo(27T/28B) I am using is supposed to be producing 8lbs of boost but I am only seeing 5-6. I have an Ulmer clutch kit installed which was set up for 8lbs on a 128" studded track and 210lb rider.. Primary-O-S-O, Secondary-red set at 6-2, weights-60Y with T1 in the heel, mid and heel are empty, helix =K. I am only seeing 8100rpm's from a 50mph roll to WOT on a groomed trail. It will climb to about 8400. First question is, if I can get my rpms up to 8900 will I get the extra 2lbs of boost I am supposed to have? Second, how do I get to 8900 now that the mid and heel are empty and I cant remove anymore weight? I have a 26 tooth pulley that should give me a little more boost, if I were to change that would it give me the hp needed to get to 8900 rpms? In certain conditions, I would see 8400rpm from a 50mph roll and that extra 300rpm really seemed to make a difference.

 

[nos]

Try taking the tungsten weight out of the heel and replacing it with a few washers. If I remember correctly, the tungsten weights 7 grams so I would start be replacing them with 4(.8grams each) washers and see if you can get the 500 rpm's back. That should 3.2 grams instead of 7 grams at the heel. 4 is the most you can add on each side. Don't overtighten the weights in the primary. The weight should fall freely. I'm sure a clutching guru here can either verify that or give you better advice.

 

[nytrozula]

After speaking with MPI , I think we figured out the blow off valve has a 5 lb spring so I was limited to that. A 10lb spring will hopefully resolve the issue. I'm sure if I get the 8lbs of boost the clutching will be right as well.

 

[scuba_nytro]

I ran 27T and 28B all last season and it will build 8 psi at 8800 ish more on cold day. Did you do the fuel pump/ regulator upgrade? Let me know how you make out.

 

[nytrozula]

I have not done the fuel upgrade. I was told it needs to be done after 10bs so I am trying to stay under, at least for this year. 8 lbs is good but I have the 26 pulley if I need to get to 10. What elevation do you ride at? Do you know what your clutch specs are on the Ulmer kit? Is it the same as what I posted at the start of this thread?

 

[scuba_nytro]

I ride between 500-1000 feet above sea level, I think the fuel system is right on its limit at 8ish psi, I put almost 2000 miles on last winter without any issues but never did any long top speed pulls as I was worried about it leaning out. I have an AFR gauge and found it would creep up on longer pulls. I have the MPI fuel upgrade in a box 1:1 regulator and external fuel pump but haven't installed it yet. The ECU I'm running also has the EVO timing flash. I swapped to Apex weights with MPI 7 gram rivet in the tip and 4.5 gram mid and base, Dalton 43/47 reverse cut secondary, green yellow green primary, pink pink secondary, and primary machined for OD. Played all last winter with clutching and still not done. I like the factory weights and profiles new heavier set out for the utility sleds, find they work best in a wide variety of conditions. Good luck with your setup.

 

[MNBlizzard]

Something sounds messed up in your clutch and/or secondary. Your boost is based on RPM, if you can't pull RPM, you can't build boost. Heat in the engine bay will rob power, I see it occasionally when in the powder versus trail.

I run the Yamaha stock SC with 28/26 pulley combo and run the Ulmer stage two clutch kit. My SC will pull 5-6lbs at about 9000rpms. I can't tell you my whole clutch setup exactly right now, but your added weight seems very light for sea level. I have 1T and 3 washers in the heel, 2 washers mid, and 3 washers in the tip. For 6000-8000', I was running your weight.

Also, what are you running on your GEMS controller? You should have 4's for all four settings at sea level, perhaps you have it too rich. Also, with no AFR gauge I wouldn't run over 6lbs of boost at sea level without a head shim and/or 110 octane and EVO ecu flash.

 

[nytrozula]

I have a head shim, AFR gauge, as well as the ECU reflash from MPI to retard timing so I should be good with the lower octane fuel. My GEMS is still set at factory settings which if anything is running a bit lean. Ulmer set the clutch up for 8lbs of boost so I think once I replace the blow off valve spring I should be getting the 8lbs and my rpms should get up to 8700-8900. Going back up at the end of the month so I'll update with the results then.

 

[nos]

I thought there was a screw at the top of those bov's that should allow you to tighten it up. Or does a 5lb spring mean that 5 is the highest number you can get from it?

 

[FLYBYU]

That's what were wondering also but it makes sense with the spring being only a 5 lb spring

 

[nytrozula]

First of all, the new spring in the BOV didn't change a thing! So I stripped even more weight off the clutch! I'm now running 60 gram base weights with 3 grams in the heel; mid and tip are empty. I'm now seeing 7 lbs at 8400 rpms. I'm hoping if I remove the final 3 grams from the heel I'll see 8-9lbs at 8800-8900rpm. MBNBlizzard? Are your stock weights 60grams? If so, I don't understand why our weight combo is so far off.

 

[MNBlizzard]

Nytrozula- Is the clutching the same or was that new this year? If so, I will stick to my first statement above that you must have something wrong with your clutches (broken/worn out parts), if it all else is the same from when it last ran perfectly. Pulling out weight is not the fix. (And the answer to your original question about missing boost psi, is still to fix your clutching to hit max RPM and your boost psi will follow.) The blower doesn't make the motor "work" less so thinking that the blower would "power" you thru was incorrect. The blower working and PSI produced is actually 100% dependent on the motor RPM.

You see if you were hitting 9000rpms and only seeing 5lbs of boost and your pulleys are supposed to produce 8lbs, then the BOV spring would of made sense although you probably would of heard it dumping the excess air. A stock motor will run 9000+ rpms no problem, yours will not and this is the problem. With the info provided, I do not believe has anything to do with the SC.

I will try to remember to look at all my details and report back later. In the mean time, you should start inspecting the clutches (I'd bet the primary is the issue) and see where the RPMs might disappearing.

 

[nytrozula]

With stock weights, springs, helix, I am clutched at 8900 without the SC. With SC and new Ulmer kit with Tungston and washer in heel, 0 mid, 2 washers in tip, my rpms are way down to 8200. So that clutch combo clearly brought motor RPM down. i guess I don't understand why pulling weight from clutch weights is not the solution. If i need to get the rpms up to get my boost up then wouldn't less weight allow that to happen? When I pulled 5.6 grams from the base it allowed me to get to 7lbs so it definitely helped. Ulmer clearly thought I needed the added weight to the heel and tip with the SC added and I'm sure this isn't the first one he setup. I'm waiting on a reply to an email I sent him for advice. The sled is in storage in the UP until I go back so i can inspect then. What should I be looking for in the primary? Spring and weights are new and rollers have about 4000 miles on them, the rest of the clutch has about 8000 miles on it.

 

[FLYBYU]

I think the 60 gram weights are to heavy. What's mpi use? I believe those are the base weights for my apex

 

[nytrozula]

where have you been! I've been trying to reach you the last 2 days!