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RXX dies about 4500 RPM

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Jerseyrider60

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So here is the issue.

My RXX dies once I get above about 4500 RPM. I can run at 4000 - 4500 rpm with no issue. Once I try to get over 4500 it will run at 6000-7000 for about 5 seconds then it's almost like its not getting enough gas and wants to dies. It will drop to about 3000 rpm. I can wait a few seconds and it does the same thing. Was fine when I put it away last year and started when I brought it out this year. I have been working on it for about 2 months

I own 2 other RXX and 3 RX so I have been changing all kinds of parts with no change in response
  • Swapped carbs from a working rx
  • swapped selector switch
  • changed all the fuel lines
  • swapped the check valves from the gas tank with know working ones from my rx
  • by passed the fuel selector switch by connecting the inlet to the carb right to the fuel tank
  • changed engines
  • blocked off the oil injection and went to premix
  • changed fuel baffle pick-up
  • adjusted the high speed adjustment screw from 0 to 3/4 (no impact to issue)
  • adjusted the low speed adjustment screw from 1.5 to 3.5 (no impact to issue)
  • pressured the tank and it held the pressure

I am at a loss. Completely baffled.

Any ideas
 
Matt -- this is a standard carb unit no TPS. But thanks

Mickidymac -- if you were closer I would sell it too you cheap. It's bugging me. I like a challenge but this is over the top
 
The carbed 951 uses a tps built into where the throttle cable splits to the carbs and oil pump. If it is not set correct the MPEM wont advanced the timing and you will only get to 6300 rpm.

If I was closer to you I would have water to ride it in too..LOL.
 
I had an extra throttle cable so I put that in as well. and my issue is not that it will not get above 6300. The issue is once it gets about about 4500 rpm for more than 5 seconds its like it's getting too much gas or not enough gas and drops back down to about 3000 rpm. if I ride there for a while I can get it back to 4500 all day or once above 4500 it wants to die again. feels more like being flooded so I am going to try and put the high speed adjuster back to closed.
 
At the plug plush a piece of wire or paperclip into the back of the black wire with white stripe. Connect a DC volt meter to this and ground. With lanyard disconnected push the start button and your meter will read 5 volts push the throttle and at 80% travel the meter should drop to 0. There is a plastic adjuster witness 10mm lock nut up by the steering.
 
I eliminated the tps on my rxx with a reflash. But I haven't put it back together yet still in the works.
 
mikidymac -- thanks for the testing procedure. I will try it later today.

10f500 -- does a dealer need to do the reflash? Could I just disconnect the TPS without the flash?

Thanks
 
No you cannot disconnect the TPS without the flash. This is why conversion builders like 98 MPEM's because they are pre-TPS for 951.

Novi-Tec performs the MPEM service.
 
My 96 XP, I know it's a different beast, had the exact same issue. I changed everything fuel wise etc. Turned out to be the MPEM, problem gone.
 
Did not think of that. I can switch one from one of my other machines to test. Do you know if it has to be a rxx mpem or can it be an Rx mpem. I have a spare Rx mpem but no spare rxx mpem so the Rx one would be easier for me.
 
I have no clue on the RXX models all I can do is dream about that machine. Oh would I love to have one though!
 
mykidimac -- tested TPS and it worked fine.

10f500 -- could you help me understand more about the timing thing. I thought the RX and Rxx have the same engine and the same carb basically all the same components except twin pipes, water box and jet pump. So if I used an RX mpem would it just run more like an RX?

I will swap with one of my other RXX mpems and try that this weekend.

Thanks to everyone
 
The timing for twin pipes is different from stock pipes. The mpem has 4 curves in it the one used is determined by the tps
 
If I understand correctly your saying it will not run as efficient with the RX mpem. Is there a place to get the RXX service manual?

Thanks
 
1of500 do you remember how many turns out on your hide side adjuster? Do you know what the max is?

Did the mpem switch and problem does not go away. I ran 4000-4500 for about 10 minutes the minute I tried to throttle up past 4500 it ran at 6000 for 2-3 seconds then wants to goes back to about 3000.


BTW just for the heck of it I did put my RX mpem on there as well. The good news was nothing bad happened. the bad news is it did not fix the problem.

I am running out of ideas
 
I can try swapping with another coil but it's so predictable. I would think a coil losing spark would be more intermittent? This issue is so predictable. I can ride 4500 rpm forever without a single hick-up. As soon as I try to go higher it gets to 6000-6500 for 2-3 seconds and back to 3500. If i hold the trottle full it will get back to 4500 and that's it. If i release throttle and then push it up again I get to 4500 rpm at about 3/4 throttle. But as soon as I try to go higher it starts all over again.

What on the 951's would allow the system to reduce RPM's even when throttle is wide open? It almost feels like the system is getting a signal that it's going to fast and low the engine down...sort of like limp mode on sleds.

BTW how many turns on my hi side adjustment? I tried 0 and I tried 2.5 and does not seam to make a difference so I want to put it back to wear it belongs.
 
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