Stock RN Popoff pressure/ spring selection at altitude??

[dirtydrew]

Hi guys,
Picked up my first rn about a month and a half ago. Totally stock 1997. I rode it at sea level, where I bought it, for a whole day. Ran absolutely flawless. Brought it up to truckee, ca where I live. It sat 3 weeks while I installed footholds, new turf, bars, bilge pump. Did not touch the motor at all.
Brought it out to ride at 6200 feet. Did not touch the carbs, anti-tamper caps were still on the screws. It started fine, but at quarter throttle bogged terribly. Was able to ride a little bit and sometime could get it on the main jet by feathering the throttle, but if you blipped the throttle it was very hard to get it to recover.
Took it home, pulled the carbs off and installed t handle screws and a primer kit. Brought it out to ride and set the screws to 1 turn out on the lows and 1.5 turns on the high. Still had the same symptom. Turned the lows in to 7/8 and then 3/4 out. Still the same. Turned the highs to 1.25 and then 1 turn out, no change.
I am assuming I need to check pop off pressure and possibly change springs. What should pop off be on a stock ski? I'm assuming measured pop off pressure has gone up with the increase in altitude and I need to put a softer spring in to bring pop off back into spec? If I put aftermarket flame arrestors on the the pop off needs to be lower psi than stock correct?
Thanks for the help!

 

[X2Kid]

While it is true that at your altitude the jetting would richen up, the symptoms sound far more dramatic.

What you're experiencing could be an exhaust leak. Is there any exhaust smoke present when you pull the hood? Even a minor leak combined with the altitude change could cause the issues you have explained.

Another thing to consider is that modern fuels can congeal in a fairly short period of time. It might be worth stripping your diaphragms to see what is lurking in your fuel circuits. Clean your micro filters while your at it.

I'd be trying to eliminate faults in the fuel system before playing too much with your jetting.

 

[dirtydrew]

There is no exhaust when I open the hood, nor smell of exhaust. Ski ran absolutely fine when I got it for a whole day at sea level. The fuel only sat for three weeks before I rode again. I'm going to pull the carbs and check pop off pressure and take a look at the diaphragms.

 

[Quinc]

Looks like you need to go down one and half jet sizes.
https://www.amazon.com/Mikuni-Pocket-Tuner-MK-550-TNR/dp/B0012TUUHG

 

[dirtydrew]

I pulled the carbs and both diaphragms looked a little suspect. I ordered rebuild kits, 125 mains, 65 slow jets, and 95 and 80 gram pop off springs. Had to drill out the fuel plate manifold screws because they stripped. Anyone know where to find those? With the special coating on them? Also, where is the best place to find a pop off gauge quick??
Thanks fellas

 

[X2Kid]

Jetmaniac (his forum member/business name) should have everything you need. He has a huge range, quality stock, good prices and fast, reliable delivery. His reputation on this forum speaks volumes. View his master parts list to establish what you need.

I have genuine Mukuni pop-off gauge as I figured it would be of comparable quality to their other products. They seem to have gotten a bit expensive of late so you may be tempted to buy/borrow a mountain bike suspension pump/gauge and modify it to suit.

While building up my jet ski-specific tool stash I plumped for the genuine Mikuni tool kit. Be aware that most comprehensive tool kits will have all the tools required to disassemble a carb. I got this as it was cheap and would save me diving into the depths of my (two) tool boxes.

Finally, I sourced the Mikuni altitude jetting calculator and their tuning book. Most of this can be sourced online but I like access to a ready reference in the field.

 

[dirtydrew]

Ended up rebuilding the carbs and rejetting. Probably not necessary to rebuild, they looked pretty decent inside. Went to 65 pilots and 125 mains. 1 turn out on the pilot and 1 1/4 turn out on the main. Put new 115g springs in and pop off is 45-50psi. Runs good now, got rid of the bog and hesitation.