4500-6500 RPM at Idle after rebuild

[MoonBeamer]

All,

I was having the High Idle issue on my 390-RRS and so I decided to tear it down and clean it up and so on. I found the following things:

2017 Beta 390 RRS 150+ Hours. Bought used with 98 Hours on it 1 Year ago.(March 2020). Its now Feb 2021

Throttle body was very dirty. Large grease/dirt build up especially around the stepper motor. Looks like dirt was getting past the filter. The O2? sensor on the Throttle body was also very dirty.
A high amount of carbon build up on the piston and valves and exhaust ports, Also some white hard build up, Not sure what that was other than possibly poor quality fuel used.
The Valve Clearances were all tight.
The piston wear indicators on the skirt were almost all worn away.
The diode pack was pretty corroded.

So This is what I did.
New piston and all top end gaskets and o-rings.
New Valve Shims in specifications, now At the loose end of the spec
New Valve Seals (I removed the old ones during the cleaning and they require new ones if removed)
Removed the throttle body and cleaned thoroughly.
Did some light porting on the exhaust, Mostly to get rid of the carbon.
Cleaned up the carbon and white build up on all surfaces including valves.
Ground the valves seats.
I used assembly lube on the top end to make sure things had lube at startup.
I replaced the Diode pack and Capacitor (My bike does not have the wire harness update apparently).

So.. after that I put it all back together. Filled with fresh gas. Then It started right up. Only thing is that it is reving up to 4500-6500 RPM ( can't remember witch right now.

I know about the passive ECU/stepper motor reset/calibration procedure but for a fresh rebuild I am not comfortable with this high RPM at idle right off the bat. Especially when I would like the rings and valves to seat in easy.

I probably need to do a throttle position calibration as well but this was not the issue.

Questions:
How does the bike regulate the fuel?
Is the injector regulated somehow?
Is it OK to let the bike Idle at such a High RPM right after a rebuild?
Should I just let it do the Stepper Motor calibration?
Should I have the wire harness updated?

Thanks for any comments you may have. If I can't figure this out I will be taking this bike to the dealer who can plug in and do their magic.

[MoonBeamer]

With advice I have gotten from several sources I have ordered a new throttle body. I will report back the results. Seems like poor maintenance by the previous owner and probably me that let dirt get by the filter may have contributed to the issues I have had. I am not sure who is more to blame but it doesn't matter. I need this bike to get back to working. I love it and can not wait to get back riding again.



In the future I will be making sure the Air filter is properly seated and I inspect the TB often.

My next upgrade may be the new wire harness.

[warrent]

Regarding air filter seating; a little trick I learned many years ago is to put a smear of grease on the intake boot 'after' the filter. Each time I service my air filter I run a finger through the grease.If I feel grit; I didn't do a good seal the last time and use this as a warning! No grit means a good seal and I don't have to kick myself today.
BTW, I wonder how many people are using the 'FunnelWeb' air filter. I have been using one since 2017 and thnk they are wonderful. funnelwebfilterusa.com
Warren......

[MoonBeamer]

Regarding air filter seating; a little trick I learned many years ago is to put a smear of grease on the intake boot 'after' the filter. Each time I service my air filter I run a finger through the grease.If I feel grit.

That is some good advice. Due to the seating issues with this bike I think I will go this route. I ride a lot in the dusty desert so this is a real concern for me. Especially after what happened to my bike.

[MoonBeamer]

Ok.. So I when ahead and took my Throttle body back of the bike to check the butterfly clearance. That is with a light shining through the other side. So I have(had) lots of air gaps.

I started looking closer and saw that there was an idle adjustment screw. I never loosened or tightened this screw during my rebuild. But I decided to see if I could get it loosed up to have the butterfly close more. I backed it off until The flapper would not close any more. Sorry no pic of this one. After this there was hardly any gap around the butterfly valve anymore. But the valve was sticking a little at full close. I figure this is better than sticking open and after a few throttle blips back and forth it would wear in.

THe bike started right up.. The idle went up and down a bit as I let it warm up and I am sure that was the stepper motor adjusting. I let it idle until the fan came on then let it cool down and did it again.

It is now Idling just fine. But I have already ordered a new TB that should be here Monday. I took the bike for a quick ride down the street and back and it seemed to be doing great.

Problem solved!!!!

See photo here:
https://drive.google.com/file/d/1KKl_Rf ... sp=sharing


I did have a few other issues though. My rear brake wire melted against the exhaust pipe causing the main fuse to blow. Took me just a little bit to find the issue. BETA supplies a few spare fuses and I tried to use one of these.. NOPE. they would not fit in the starter relay Fuse location. They fit on the other component (Not sure what it is) So I had to go out and get normal Fuses (the beta ones are very different looking). Once this was replaces and the brake wire fixed and re-routed all was fine.

I will report back probably next week when my new TB gets here and I install it. I guess I will now have a spare semi working one just in case.

[MoonBeamer]

Update on my 2017 Beta 390 RRS Rebuild:
Replaced Parts:
Piston
Capacitor
Diode pack
Throttle Body
Valve Stem Seals
Top end gasket kit
Battery
Mosfet Voltage Regulator from Yamaha (14+ volts now at battery with all stock items on, Light, fan etc.)

Maintenance performed:
Top end rebuild with new piston
Valves & seats lapped
Excessive Carbon and other deposit build up in head removed.
Light porting in Intake and exhaust
New coolant
New Oil
New Transoil
Filter cleaned and oiled
Lots of other general cleaning


I went for a 40+ mile ride today and the bike performed better than it did when I first bought it. For reference I bought it 1 year ago used with 98 Hours on it. I now have 162+ hours on it. So in the last 12 months I put on ~65 hours.
I need to do a post rebuild oil change on it and check for any filings. I expect there may be a few. I also need to put on a new Exhaust header gasket. It has been leaking around it and I found that it doesn’t have a gasket and I guess never did since I have owned it.

I did some research on lapping Titanium valves and it is not unheard of. Lots of posts about top fuel cars doing it. I am not a racer nor to I drive super fast so I m fine for now. I will take a look at them either Mid year or end of the year to see how they look.

I am very pleased at how it has turned out so far. I will see how the reliability ends up after this riding season.

[Dr Z]

Do not lap titanium valves. The coating is micron thin and they will wear fast if you get to the softer alloy. I have a 2008 RMZ450 I use for a snowbike now and the valves needed adjusted every ride after I bought it. The valves actually had a groove in them from the wear, and that was not lapped, just worn valves as far as I know since I bought it used 2 years ago. I sent the head to Fastheads for a rebuild with new valves and they are staying in spec for the last 2 seasons.