1998 gtx rfi stutters at 4200 rpm

[BLand]

Hey guys..I have a 1998 rfi that runs great..except for two minor issues that I'd like to fix if possible. They are tough to troubleshoot..Main one is that if you are just cruising..it misses/stutters around 4200-4300rpm give it a little gas and it flies..let off the gas and it hits that range again and it starts the same..its a perfectly consistent problem. Never notice it unless you go cruising..of course that's the cruising around speed. Last issue is that when it idles ..its like the idle can get to low and Iit shakes hard and sounds like someone is slapping the inside of the ski with a hammer..give it a little gas and it idles perfect.ive searched everywhere and even had motor out and can't find anything loose..can I just turn the idle screw up a little on an rfi?
Thanks

 

[POPPS]

I think the idle is set at the factory,,(3 turns out),and ,may have a cap on top,,,not sure,,,and there may be a tps,,,not sure if this affects the metering if the fuel,,. you may have to reset the tps,,
before you change the idle,,turn the idle screw all the way in and carefully count how many turns there are,,,so you can get to the original,,,
I had a similar situation,,,after a top end rebuild,,,it did nit idle well,,,now keep in mind either the front or rear cylinder cuts out at idle to save fuel,,,i was worried it may nit run right in the water,,,but it kind of found its proper metering.

 

[Dtrain55!]

The same sputter happens to my 98 at the same speed. other than that runs fine

 

[etemplet]

Most times the idle screws on the RFIs are stuck. I've had to drill a couple. You can't set the TPS unless you loosen the idle screw. Throttle has to be closed all the way. You can raise the idle or lower it using the screw on the throttle body. Personally I've never had resetting the TPS do anything for performance or solve any problems for me. I've swapped computers without resetting the TPS and the skis have run just fine. I'm not advocating against resetting the TPS though especially if you have access to a Candoo.

If you are having issues I'd do some checks on the components, Pressure Sensor, Air Temp Sensor, Crank sensor and make sure all the plugs are clean. You could also have an issue where the raves are struggling to open and that is the speed they begin to open. Check your rave solenoid and make sure your raves are not leaking. There is also a check valve in the line that feeds the raves. It comes off the engine block. Make sure that valve is not stuck open. You should not be able to blow back into that line. Do the easy stuff first.

NOTE I also had a rev limiter issue on an RFI where it wouldn't get over 4170RPM. Every now and again it would and it would take off like a bat out of hell. Once I got under 4k it was the same problem all over again. These skis have rev limiter issues sometimes. I replaced the computer with a spare I had and. VIOLA no more problem. Good Luck !!

 

[Dtrain55!]

I read a thread on the forum talking about the rave valve adjustment. Mine were about half way in. the thread said flush was the factory setting. When I adjusted the raves out flush it moved the sputter to a different rpm, But its still there. I would like to get it figured out. I took the caps off the rave and can move the raves up and down with little effort so I think there lose enough and not sticking

 

[Dtrain55!]

Today I cleaned and put new o rings in the raves. They were definately leaking. I changed the diaphrames also with new ones. The diaphrames were marked for a 951 and 787, They were a differenr color and not as plyable as the ones I replaced. When I put it together it wouldnt hardly run! So I put the old diaphrames back in and it ran better than before but still has the sputter. Are the diaphrames in the raves different in the 951 and 787? Im checking some other compenents measurements now. I had a powersport mechanic tell me the rfis are just gonna sputter when the raves open is this True? doesent sound right

 

[burtshaver2021]

I’m not sure if the same diaphragm is used for a 787 and 951 but the part number is different between a 787 carbureted and a 787rfi. Also seen a lot of bad reviews for the green diaphragms sold on amazon and manufactured by JSP ( I think JSP) manufacturing. All the reviews said they were too stiff and the machine wouldn’t run correctly. I think OEM ones are still available.