Running problem after restart

[Ndanger]

I have a great running 21 850 Pro that is perfect in all conditions except when restarting after taking a break. Engine temps in powder are 100 to 108 and after stopping for a few minutes goes to 140 when stopped. On restart after about 30 seconds of idling I go to ride and have a bogging on acceleration and surging at constant speed for a few minutes then all is good after that. It makes it hard to maintain a turn in technical conditions so I try to avoid tight stuff until it smooths out. Curious what that could be? It seems to have started after about 700 miles.

 

[davesilb]

I have a great running 21 850 Pro that is perfect in all conditions except when restarting after taking a break. Engine temps in powder are 100 to 108 and after stopping for a few minutes goes to 140 when stopped. On restart after about 30 seconds of idling I go to ride and have a bogging on acceleration and surging at constant speed for a few minutes then all is good after that. It makes it hard to maintain a turn in technical conditions so I try to avoid tight stuff until it smooths out. Curious what that could be? It seems to have started after about 700 miles.

Most likely over heated fuel in lines causing lean conditions and system trying to correct those conditions

 

[RNO]

I have a very similar problem on a 23 Matryx 850 Pro RMK Slash that coughs and sputters for first 30 seconds or so after restart. It does not seem to bog. Initially thought is was from being in break-in mode. Have been out of break-in for about 50 miles and it still does it. I have not looked at the plugs yet. No one else in my group have had this experience and I did not have it with my new 21 Axys 850 pro RMK.

 

[burnerup]

Have almost exactly the same problem with a 2020 850. After taking 5-15 minute break it's sometimes finicky to restart and surges or stumbles when you maintain a slow speed. Had it in to two different dealers and they have noticed it but have not fixed it. The second dealer put new throttle bodies/tps on and that seemed to help for a day but then it went back to acting the same way. I've been searching for a fix with no luck so far..

 

[Ndanger]

Most likely over heated fuel in lines causing lean conditions and system trying to correct those conditions

I was thinking along the same line, I was wondering if there is a fuel rail that heats up and causes symptoms similar to vapor lock. I wonder if the fuel rail is designed to maintain pressure and if it is not maintaining pressure it is prone to fuel vapor. Is there a system pressure that is maintained in the fuel system when shut off?

 

[Ndanger]

I have an update on diagnosing he problem. I stopped by a shop near Island Park and talked to the mechanic at Golden Spike Powersports. He was very knowledgeable and suggested that it could be the fuel pump. According to him, the pump needs to hold system pressure when shut off and that the reason that he recommends looking at replacing the fuel pump is that it has a check valve that maintains pressure while the engine is shut down. He indicated that the check valve is not replaceable and requires a new pump at 750 dollars. The process to determine if it is the pump is to run it up to 5000 rpm to make sure that the pump delivers full pressure, (which I assume it does) check it at idle for a few minutes and then with the engine shut off to check if it holds pressure. He mentioned that it should not drop more than 1 pound per hour or something like that.

So that is the direction that I am heading. I was told by another shop that it coud be the power valve and or cable adjustment / timing / software flash, but I don't know if that could be causing my problem. Anyone know what the symptons are for the power valve issures?

 

[AdrenalineAddict]

Mine does the exact same thing. After warming up and riding around a bit it seems to go away, I've decided it's just a quirk in the fuel delivery system and just deal with it. I have wondered if it could be a dead spot in the TPS just off of idle, but if others have the same issue, that is more than likely not the cause. Check Valve Hmm?, it didn't begin until about 1,500 miles.

 

[pdaddyvr6]

2020 850. Mine seemed to start doing it right after break in was timed out. At 600 mi or so I turboed the sled and used my own mapping and was able to tune it out. Using a wide band sensor I could watch the thing go crazy lean right before it started cutting out. After a rod failure ruined the engine early this year I put a used motor in it using the injectors, rails, exhaust valves, everything from the donor. Put it back to stock to ride as a backup/loaner, and put the factory flash back in it. Went right back to doing it again, lol. Flashed it again with the same change I made my turbo flash, and its gone. Far as Im concerned its just in the mapping, it has a lean spot when the coolant temp is normal or even heat soaked a bit, and the pipe is cold............... It is strange however that some seem to not do it at all, and some seem to start doing it after some miles are put on it. Cant explain that one, but tweaking the pipe temp modifier in the file worked for me....... Maybe the pipe temp sensors get inaccurate at low temps with some age? I am using the original temp sensor in the pipe, so i dont know, maybe? My .02