Running a Reds 521 Sport engine in my MP10T. Has M manifold with 2143 Pipe. I’m having some trouble with it on the track, as I’ve only raced electric for years until now.

Engine Broken in by standard procedure. Used 20/12% Break in fuel.

On track now I’m using 25-30% VP Fuel.
C3 Glow Plug

Here is my issue. I can get it to start fine, I pre heat. I can get it to idle happily on the box and crack the throttle with good response. I set the HSN by doing short WOT’s on the box first. Adjusting it so it was not too lean and over revving out. I set the idle gap roughly to 0.5mm. I set the LSN by cracking the throttle and letting off, seeing if it revved smoothly, bogged, and then I would listen to see if the idle stabilized. Once I drop it on the track, I can make about 5-7 laps. Then randomly when I let off before the end of the straight, or after I jump and let off the trigger, I will flame out. I’ve tried going small increments lean, still an issue. I go small amount rich, and it bogs and loses its umph. Not trying to beat the dead horse, but I’ve watched many videos and read up a lot of guides but I’m still being stumped. As whichever direction I go on my needles I am still fighting this engine. Any help is appreciated.

Did you setup your throttle servo neutral and end points correctly? My guess is neutral is a hair off and it's closing the carb slightly more sometimes.

I think also possible fuel line is too close to the pipe? I vaguely recall that could reduce fuel flow to the carb as the pipe heats up.

I believe I did, but I will re-check just to rule that out. As far as the fuel line that’s interesting, I haven’t heard that. But yes, the fuel line is quite close to the pipe. On my MP10 it runs underneath the pipe slightly down the chassis in designated channels. The exhaust fuel pressure line is laying on the pipe from where it connects and up to the tank lid.

how's the pinch on the engine? I'd try swapping the plug out and run 8% castor fuel on a reds engine

Did you change the plug? It is most common that after break in the plug is not functioning well. Also running 30% I would use a colder plug.

I had one of those model Reds. It was very difficult to tune. Really I never could get it down. I could get it to where it ran well, no pinging, running on, etc. But it would randomly flame out. Another Reds user at the time told me you have to let a Reds idle higher than say an OS or Nova. I feel that person may have been right. I was trying to get the same low idle like my OS. Maybe try raising the idle ?

When the 3 needle carburetors came out I recall watching a video on them by Elliot Boots. In that video he specifically said they allow you to get the lower idle like an OS. From what I see Reds users are having an easier time tuning with the 3 needle carb. If memory serves me correct the 521 has a 2 needle. I could be completely wrong on this. Hope this helps.

I was gonna recommend a slightly higher idle as well and tune the high speed needle so when the carb returns back to idle you get a slightly high idle that hangs for a second. I had a couple Novarossi engines that were like that. Op what is the air temps where you are running? Like Roelof mentioned above, change the plug or even try a colder plug.

How much fuel has gone through it? TS4 plug will help with tuning. What temp is the motor when this happens? Reset your needle settings to factory and start again. Never finish your tune on the box. If it runs perfect on the box, when you put it on the track it will be too lean. Set the high speed needle so the motor almost tops out at the end of the straight. Always stay a bit fat on the bottom. If the high speed needle is to lean, it can affect your idle and bottom end a lot. Check for air leaks and a sticky clutch as well. Nitro has a ton of variables and some are harder to find than others.

Thats what I was beginning to think. That this motor might like a higher idle. Right now where I’ve been running air temps have been between 85-90F.

Thanks for the reply. It’s had about a gallon on it now. I also have ordered a TS4 Plug last night to try next weekend. I’ll be resetting my carb to the manual standard and start from there.

I actually have not changed the plug yet. Right now it’s got the standard C3 Plug. I ordered a TS4 Plug to try next (step colder).

You ordered one plug? Plugs have no long life so you must have a few to have spares.