Maximo

iTrader: (11)

I might be a bit late to the party here.... But for all out Speed and power nothing is going to match my modified Nova 28-7..... right now I have a few in oval racing and they literally eat the field alive every time out...We have smashed track records by multiple laps....... they have insane torque and the ability to spool well past 40 000 RPM carrying load........

car 1 and 2 are my mod 28-7..they go thru the other cars like pylons...these two cars went 1 and 2 all weekend, smashing track record and winning the event..... they are running against other modified 25's and 28's and just tore em up

+ YouTube Video

howard85may

iTrader: (3)

Thanks Neil, but I went with Murnan Modified Roma.25, started building the car yesterday hopefully i can finish it up today.

howard85may

iTrader: (3)

Hey guys, finally got the car built and running. There's only one problem, with the 42021 header and 9886 pipe I cant seem to get the idle stable it keeps ramping up (novarossi roma 25 / os 21xz-r speed). When I make a pass, it doesnt idle down when i let off the gas. The idle just seems to "hang" until I blip the throttle and it will settle for a second or two then idle back up. I tried two different engines and they both are having the same problem. What gives? I've tried richening the high speed needle, richening the low speed needle, lowering idle.. nothing seems to work I am very frustrated at this point and dont know what direction to go. You guys are my only lifeline. Again, thanks for your help and support.

howard85may

iTrader: (3)

oh yea, with the nova, i tried the wd40 method to check for air leaks and i sprayed it everywhere and noticed no difference until I sprayed it on the front bearing. It would idle down for a second every time i sprayed it so that engine is down for a bearing swap at the moment, but that still doesnt explain why im having the same issue with two different engines? Could it be the pipe? Could it be the flimsy carburetor return spring not fully closing the carb? Im stumped!

TerribleTy

There are a few things I can think of… What are your temps? Get the engine up to temp and then run a tank through it. See how much that changes. Keep the car running if the temps are okay <250F (with body) keep monitoring the temp. If you have an air leak it will be plain as day, one second you’ll be lean and mean and then bam rich. Or this can go the other way as well rich to lean which is never too pretty. Temp is key and will tell you tons about what your engine is doing. As far as air leaks go keep in mind it can be anywhere from the fuel line/tank to the exhaust. Any potential for a change in pressure results in angry engines. One thing we do here is shoegoo the outlet on the fuel tank, if it moves around too much it will eventually leak. Last thought is check your idle gap. This is by far the biggest mistake tuning I have seen and accomplished many times myself. If the Gap is too big you are in for all kinds of frustration and heartache. Gap should be maybe the width of a credit card and then small adjustments (I do maybe 1/32 turns) from there. Remember more gap allows more air into the carb and will cause sporadic idling. Keep you adjustments small, its better to make multiple 1/16 turns than a few ¼ turns. The smaller turns will enable you to find that sweet spot on the engine.
Things I would do
-ShoeGoo the fuel tank outlet nipple
-Replace and check all fuel line (cheap and easy but can cause serious problems)
-Check all exhaust gaskets ( easy to crease or tear one and cause leaks)
-Run car like you would for a few tanks and monitor the temp, monitor how much smoke the car is producing. (this can be tricky, only make adjustments if you car is running hot, if its running cool keep going. If after a tank or more your engine won’t get warm then make adjustments to lean. Try and avoid making adjustments each time you temp, remember we are watching for sudden changes in the engine to indicate the air leak.
-Check you idle gap (make it small and adjust the low speed needle to get your correct idle)

Worst case scenario call Gus Wood and have him listen to the engine… How he knows what to do is sheer experience lol (probably not realistic to actually call..). He and Andy are the ones who have helped me learn many tuning lessons. Andy showed me the idle gap and how important that is. I tune regularly with Gus at the hobby shop on all kinds of engines, many of the tricks I have listed above come from him.

I hope something in this short novel helps you out! I have no experience with modified engines but I’m sure the concepts are the same. Best of luck!

Oh I forgot the easy one…. When you hit the brake make sure your carb stays closed before during and after. If you don’t have everything correct the carb will open and raise your idle speed after you let off the brake!

howard85may

iTrader: (3)

I will inspect for air leaks first. That seems most likely my issue as it can sit and idle then all of a sudden the idle will "jump" up. the seal around the fuel nipple and also around the tank lid dont seem very good to me..

Herrsavage

Check your linkage.. With the engine off, but electronics and radio on.. Gas brake gas brake gas brake, etc.., while looking at the carb..

People always say change fuel line, tank, seal this, that, etc etc.. But usually I find it's something mechanical - bad linkage setup, or maybe a dodgy clutch or clutch bearing.. Or, just bad needle settings.. Always hard to judge these things online, but my first guess would be linkage, and second maybe too lean on the LSN... But yeah, could be a cracked tank or something too..

TerribleTy

Exactly why I wrote it in bold. Especially with the Serpent, the linkage set up is much different from most RC cars. Seen this numerous times, may want to add a little tension to your return spring on the linkage so it always has pressure to be closed.

howard85may

iTrader: (3)

Ok I went back over all my linkages and added more spring pressure to the return side. I will test it later today.

Grinder

iTrader: (2)

It could be that the idle gap is too large. Close it until the engine idles lower, until it almost shuts off. Then run it around, and listen for the idle. If it is good, then idles high the engine is most likely lean on bottom. If it comes in good, and the idle drops its probably too rich on bottom. If the idle stays steady on the bottom it is close. When the idle stays steady, then adjust the idle gap until it is where you want it. It will take some fine tuning from there.

The low speed needle should be just outside of flush with the housing on the Roma.

Both of those engines should drop to a low steady idle.

Feel free to call for more details on tuning.

jneg

In my Cobra I had something silmilar. I turned out to be a clogged tank. All I had to do was to spray the inline fuel filter of the tank with carb cleaner until the fuel flowed easily. After that the motor ran great. Another thing that I have found very useful to have is a Torque screwdriver. Most of use just go by feel on the head and other engine bolts and sometimes we either overtighen or leave loose the motor screws.

howard85may

iTrader: (3)

I went back to factory settings on both engines, it wont even idle at all with a small idle gap. could it be the exhaust gasket between the pipe not building enough pressure?

1FastVW

+1

Grinder

iTrader: (2)

Not likely. Probably too rich on the bottom for the amount of idle gap. Factory settings are too rich.

howard85may

iTrader: (3)

Ok I have the needles in the ballpark and it runs well. It just hangs after a pass once the fuel clears out. I can tell the tune is close getting light smoke trail and nice idle sitting there and throttle response is good. It just hangs after a run for a few seconds then it tapers off to nice idle. I can't seem to tune it out. Even with low idle and slightly rich on both needles it still does it. I may just leave it alone and try to get it to you to look at...