Throttle linkage and LRP ZR.32 idle problems

buschman

Member
Messages
5
Location
New Market, MD
Curious if any of the members can help me. I have a 10 year old XSS. Recently just picked up an LRP ZR.32 to replace my original K4.6 (cracked piston). I'm having a hard time getting the LRP to idle correctly. Couple things I've noticed First the throttle linkage. Never noticed this with the K4.6 and not sure if the LRP has a more narrow throttle body. However, the resting position of the throttle linkage is different depending on whether I'm giving it gas or brake. In other words, If I'm giving the truck acceleration and release the throttle goes back to ,let's say, 15% open. If I give the truck braking and release the throttle goes back to, let's say 5%.

The return spring seems tight, but it almost seems too small for this throttle body. Again, does the LRP have a more narrow TB than the old K4.6?

I remove the servo controlled throttle arm and connected a log rod to the throttle that hangs out the side so i can control it by hand. Even with that I am having a hard time keeping it idling. It will idle for 5 or so second then cut out.

Are others with the LRP ZR.32 having troubles maintaining idle?

Is there a better after market throttle rod that does a better job of getting around engine guard? My current throttle rod has the bend around the frame. I suspect that friction is contributing to this variance in the resting throttle return position.

I appreciate any suggestions that you all might have.

Thanks,
Mike
 

olds97_lss

Well-Known Member
Messages
1,917
Location
Dekalb, IL 60115
Got a photo of your setup? I have an LRP30 in my X, but I don't have the HPI throttle linkage, I made my own with springs/collars as I don't care for the stock split servo horn.
 

Grumpy1822

Savage Owner
Messages
788
Location
Kenner, Louisiana
First make sure youre linkage esp rod to carb is straight with no binding. Then adjust your throttle servo return point. Turn the trim towards brake until its at full idle stop in neutral. You may have to recenter the servo arm to allow adjudtment without throwing the brakes off.

Once you have that straight lean the lsn a bit. You should hear the idle increase.
 

buschman

Member
Messages
5
Location
New Market, MD
Thanks for the responses. Sorry for the super late response. I didn't have time to really dig into the truck. I actually snapped a picture show you all, but then immediately after that I ended up snapping the throttle linkage. I ended up ordering a new one and it sat for a few months. until this weekend I could get into it, replace the linkage and start working through some issues with the truck.

On the throttle servo side I ended up going back to the original servo throttle linkage setup. As olds97 calls it the "stock split servo horn", which is a great description. In my setup, I actually prefer this setup to the more custom setup I had with my old 4.6. A softer throttle response I believe will help tame this big .32.

My major issue I have now is the idle. While I believe I have hashed out the issues with the with the carb and TB opening. Now I have the servo setup so braking is good and when the servo is at it's normal resting position, the TB is all the way closed. One less variable I have to worry about.

I can start the engine and for about 5-10 seconds of the first fire up it idles perfectly. Then I can hear it, the idle starts to slow and until it stalls out. Subsequent starts give me an even shorter period before stalling. if i open the throttle enough to get the engine started and revving it revs fine and will hold as long as I keep a light throttle opening. But it's well beyond a healthy standing idle speed. It's a slow access speed. Thus I can drive the truck around and as long as I don't let go of the throttle it is fine. As soon as I let go, it stalls.

I had this problem with my 4.6, granted it was a really old engine. Served me well for many years, but in the end just wouldn't idle and once the piston cracked the acceleration was not consistent. The LRP is brand new. So I was hoping for a very stable easy to maintain idle. So far not the case.

Because I had this issue with my 4.6 I'm looking for commonalities.

Things I have tried:
  • Glow Plugs(Came with an R5, but have also tried an R3) and replaced gasket
  • Fuel (I have a batch of O'Donnells 30% that is a few years old. Bought some new Byrons 20%)
  • Removed air filter(for testing only)
  • Verified and reseated exhaust gaskets
Most everything was transported from my old engine to the new. So looking for ideas of what my be stalling this engine out. Any thoughts?
 

olds97_lss

Well-Known Member
Messages
1,917
Location
Dekalb, IL 60115
An engine that idles itself to death is usually too rich on the LSN. Pretty much any nitro engine will "load up" as it sits and idles for 20+ seconds and a quick blip of the throttle usually clears it's throat. However, if the LSN is too rich, it loads up too much and stalls.
 

buschman

Member
Messages
5
Location
New Market, MD
An engine that idles itself to death is usually too rich on the LSN. Pretty much any nitro engine will "load up" as it sits and idles for 20+ seconds and a quick blip of the throttle usually clears it's throat. However, if the LSN is too rich, it loads up too much and stalls.
Thanks for your helpful advice Olds97. I will test the LSN out this weekend. Question regarding the Throttle Body opening. Would the preferred idle state to have the TB completely closed? Or should I adjust so it's not completely closed?
 

X

Conspiracy of One
HPISF Staff
Messages
3,244
Location
Minnesota
Thanks for your helpful advice Olds97. I will test the LSN out this weekend. Question regarding the Throttle Body opening. Would the preferred idle state to have the TB completely closed? Or should I adjust so it's not completely closed?
Start by tuning your Idle needle so there is about 1mm gap when looking down your carb. After a little break in you can then adjust accordingly while doing the rest of your needle tuning.
 

olds97_lss

Well-Known Member
Messages
1,917
Location
Dekalb, IL 60115
Thanks for your helpful advice Olds97. I will test the LSN out this weekend. Question regarding the Throttle Body opening. Would the preferred idle state to have the TB completely closed? Or should I adjust so it's not completely closed?
Like @x said, there should be about a 1mm visible gap when you look down the carb throat at idle or full brake. If it's completely closed and still running, then you must be pretty rich. The idle stop screw on the carb is what keeps it open when your at "idle" position on the transmitter and when you apply brakes.
 

buschman

Member
Messages
5
Location
New Market, MD
Like @x said, there should be about a 1mm visible gap when you look down the carb throat at idle or full brake. If it's completely closed and still running, then you must be pretty rich. The idle stop screw on the carb is what keeps it open when your at "idle" position on the transmitter and when you apply brakes.

I wanted to thanks Olds97 and others who gave advise on this one. I think you gentlemen hit the nail on the head. Leaning out the LSN significantly improved the idle on this truck.

After getting it to idle and run reasonably in the neighborhood. i took it up to a large construction site to really test it out. The thing absolutely flys now. I ended up breaking the RWD on it, something I kind of guessed would happen with this LRP motor that's twice as powerful as the old K46. But no bother, I'll take it apart and fix what needs to be fixed. After running it for a while I could sense when pushing into the higher throttle it would cut out. I believe I went counter clockwise to let the HSN out a turn or two and that fixed that. Couple of things to I noticed. Perhaps because of the high speed runs and air flow the temps were not getting over 200 at any point. I was really pushing the speed and doing some dirt hill climbs, nothing too outrageous. I ended up breaking the red trying to do some donuts. Should have known better with this motor on stock drive train.

I did notice after running a bit hard if I needed to stop the truck for a bit to test temps, or reseat the shell, or anything like that. The truck would idle but then die when I tried to accelerate. Even when I intentionally gave very little throttle to get it started. Does this mean I need to lean the LSN out even further?

Thanks again for all the assistance. Even though I broke the drivetrain, it was good to get the old Savage running again and running well. The assistance is much appreciated.

Thanks,
Mike
 

olds97_lss

Well-Known Member
Messages
1,917
Location
Dekalb, IL 60115
Probably still a bit rich on the LSN causing it to build up when it's idling. You may also be too rich on the HSN.

I don't necessarily "tune for temps", but I do use temps as a tuning aid. You can usually hear when an engine is too lean as you will get a bog when you run WOT and then get a high idle for an extended time after making a WOT pass. I look for smoke when accelerating and listen for the lean bog or rich sputter, then adjust tune accordingly and check temps periodically to make sure it's not getting overly hot or running too cool.

Just took my OS 21TM revo out for a bash this weekend. First time since last year. I vaguely remember pickling the engine (excess ARO in the carb/carb inlet/glow plug) for the winter storage, but my tune was way off compared to the last time I ran it. Was lean bogging and wouldn't settle to a nice idle. Took half a turn on the HSN to get it to sound right. My rear diff grenaded on me half way through my first tank, so I didn't get it dialed in yet.

If your turning a HSN or LSN 2 times... that sounds excessive. Usually you adjust by 1/8th of a turn. Much more than that at any one time and your causing problems.
 
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