Jetting question

[bolty16]

so I went up to Three Creeks south of Sisters here in OR. The elevation I believe starts somewhere close to 4-4500 ft and goes up to about 7000 at Moon Mtn. I brought up my XLT that I have been working on for its maiden voyage back on the snow, I knew it would probably take some trail tuning since where I live is about 500 ft. The motor is a 600XCR with psi triples, I rebuilt the carbs and cleaned them out and went to a 290 main when it calls for I believe a 260 from the factory. The reason being is I had talked to some guys about jetting and that I would need to go larger since the pipes will lean it out a bit and extra fuel would help. The problem is I took it off the trailer and tried to go for a test ride real quick up the road and it wouldnt get out of its own way. would barely move, it would load up and that was the end of it. I also think my clutch weights might need to be changed out. The clutch engages really high in RPM's, so would that mean I need to go heavier or lighter? to get them to engage lower.

Any help would be greatly appreciated.

 

[retiredpop]

290 mains seem pretty fat for that elevation and the temperatures at this time of year even with triple pipes. I looked at the specs for SLP triple pipes for an XCR and they are talking 250 mains for that elevation. I can't see PSI being too far off from that. Do you have the 38mm carbs that the XCR engine came with or did you install the 34mm carbs that were on the XLT? What year of XCR do you have as some of them came with ACCS?. To lower engagement rpm you would need heavier weights or a lighter primary spring. The only problem with doing that is that you may not run at the proper full shift rpm the pipes are designed for. Usually triple pipes were designed to run at around 9000 rpm.

 

[bolty16]

Ok, I am thinking I will drop and few and see how that does. The carbs are the 34mm that are on the XLT. I was not able to get or find the carbs for the XCR600. I hope I can make these work. I really dont want to search all over gods green acres for those carbs. I'm sure they can work with the proper adjustments. The engage rpm of the primary is at I believe 5500 or 6000 right now which seems too high. and doesnt leave much room to ramp up to 9000 for the good powerband. I have the factory blue spring in the primary.

 

[Scott]

First.....clutch weights have nothing to do with your engagement. That would be the first number on your primary spring.

Second...what brand of carbs do you have? Stock Kehins, right?

 

[bolty16]

First... I have not chagned the clutch spring that is as far I know it is stock.

Second... I think they are Mikuni 34 carbs

 

[Scott]

First... I have not chagned the clutch spring that is as far I know it is stock.

Second... I think they are Mikuni 34 carbs

So do I remember correctly....those are roundslides carbs, right?

 

[retiredpop]

Here is the setup we ran in a 95 XLT600 with 34 mm Mikuni roundslides in similar altitudes as you are riding at. We were using SLP triple pipes though instead of PSI. Main jets were 200 for most of the year in all 3 carbs. I think we dropped to 190 in the spring. We ran stock needles with the clip in #3 position. We had to put in 25 pilots instead of the stock 35's in order to get good throttle response. Clutch was stock blue spring with 10MR weights. Secondary was stock red spring in position #3. It ran at 9100 rpm. I can't remember what it engaged at but I think it was right around 5000. Ours worked really well with the above setup.
Hopefully this gives you an idea where to start. I never had anything to do with PSI pipes but I would suspect they should be fairly close to SLP in jetting. By using the 34 mm carbs you have to tune it like the XLT as the only difference in the XCR was the bigger carbs which gave it more power.

 

[bolty16]

see that is the reason I come on here and ask questions that myself being only 26 do not know. Thank you very much for all the info on the setup. ctrl + P and this will be going to the garage with me to sort some stuff our. I wouldve been spinning my "wheels" on this for a while in order to get the set up close and even at that it might have never been the same. I really appreciate the info and as always age and wisdom kicked a$$.