Trouble with a new F4.6

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pbiscuits

Member
Messages
12
Location
Michigan
I bought a new F4.6 from Jennys RC.

The first couple tanks of break in seemed fine, except it was idling a little high. On the 3rd tank of break in, it was idling very high and I had to turn the lsn out a full turn and narrow the idle gap to like .5mm to get it to not turn the wheels.

After that 3rd tank, I stripped the engine and carb and found everything to be in good condition. No torn o-rings. Everything looked pretty much new. So I put it all back together, only to realize the fuel tank has a decent crack in the bottom.

I bought new fuel tank and lines, but it didn’t change anything, still idling really high unless I narrow to a tiny idle gap and set the lsn super rich.

Other things to note:

- it is only running lean on the low side. The hsn is at factory and I’ve even turn it in a bit and produces lots of smoke and sounds great when I open up the throttle.
- i see some air bubbles in the fuel line from time to time
- the engine primes and starts easily
- doesn’t seem to be anything wrong with my throttle linkage or servo.
- i’m running a brand new stock exhaust, header, coupler, and header gasket.
- i’m using a brand new gallon of vp 20% fuel.
- i’m running the r5 hpi plug that came with the engine.

I’m not sure what else I could do besides buy a new carb or trying sealing the carb/engine. I know a lot of people recommend sealing the carb/engine, but there’s also a lot of people that do not recommend it. I’d rather not seal the engine, but I might have to try it if I can’t figure out another solution.

Any and all thoughts/ideas are appreciated.
 
Last edited:
Yes, I’ve read all of those threads. Sealing the carb/engine is the one course of action I haven’t taken yet. I’d like to avoid it if possible, but will likely be my next step if I can’t figure out another solution.
 
Without the engine in front of me it is exceedingly difficult to diagnose the trouble, guess you will have to find and fix the symptoms in order to find and fix the trouble, Good Luck and please update this thread when you get it running better
 
I ran it yesterday and it was holding a tune decently. Still had to run the lsn 3/4 richer than factory with a tiny idle gap, which is concerning.

I figure there has to either be an air leak or weak fuel pressure. I took some video yesterday and assuming I can’t figure it out, I’ll edit it all down into something watchable.
 
I'd run it with the air cleaner off, so you can see into the carb. Mine was doing something odd when braking which was slightly opening the throttle. (I got mine 2nd hand and the linkages etc were all messed up). And check the trim setting on your transmitter.
 
I will run it with the filter just to be 100% certain the throttle is working properly at all times, but I doubt that is the issue.

I’m pretty sure there is either an air leak or I’m doing something wrong with the tune. If anyone has the time to watch the two videos below (like 7 minutes total), you can get a good idea of what’s going on with the tune.

This video shows the general setup of the carb and throttle:

And this video shows me attempting to tune it:

I get it pretty good by the end of the video, but the engine just keeps getting leaner and leaner as I run it, which I assume is just the good ol HTL issue, but it seems to be pretty pronounced. And the fact that I have the LSN a full turn out and the idle gap pretty close to 0.5mm and it still idles on the high side makes me think something is wrong.
 
Seems like you are making too large of adjustments on your low speed needle. try thinking of the adjustment as a clock face and make 1 hour adjustments also the idle is the same way, make smaller adjustments, my wheels all turn on the stand but stop when on the ground...
 
Seems like you are making too large of adjustments on your low speed needle. try thinking of the adjustment as a clock face and make 1 hour adjustments also the idle is the same way, make smaller adjustments, my wheels all turn on the stand but stop when on the ground...
Word, I’m gonna try tuning it again and keep that in mind.

Is it somewhat normal to have to turn the LSN out 3/4 or a full turn out? I feel like everything I’ve read says that factory settings will make the engine run really rich, so I thought it was weird that I had to richen the LSN further and to that extent.

And everything I’ve seen (in manuals, forums, youtube vids) says you don’t want the wheels turning when the car is idling on the stand because it can cause additional wear on the clutch and the brakes as you drive the car. It also typically means the idle is too high, assuming the clutch springs are in good shape.
 
I made another attempt at tuning the engine and I think I have it running great now. This video shows what the idle sounds like before it’s fully tuned and how it resolves itself once I get it tuned.


Still think the truck wants to idle too high for some reason, but for now it seems like I can tune around it. I’m hoping the idle settles down some more as the engine gets fully broken in.
 

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