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in need of help on LRP Z.28r SPEC3

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Old 04-11-2018, 09:15 AM
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Lt4-396
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Default in need of help on LRP Z.28r SPEC3

I'm trying to start this lrp .28 spec 3 that has sat for roughly two years, I got it started and drove it around for 10-15min and it was running really rich. I turned both LSN and HSN in until they bottomed out to see where the carb adjustments where and they were both at roughly 2.5 turns out from fully closed, which seems very lean from what i understand LRP recommends 3.5 turns out on each needle for a rough starting point to tune from. The problem now is i can not get it to re start. Its getting extremely flooded and i keep making it leaner by 1/8 turns but it still floods the engine almost immediately to the point i have to take the plug out and turn it over and go threw getting the nitro out of the engine.

Does anyone have a lrp .28 that can tell me where their needles are set so i have a starting point to go from. I tried the factory 3.5 turns out setting and where it was when i took it out of storage 2.25 turns out but both just flood the crap out of the engine. Glow plugs are new, glow plug ignitor is fully charged and i am using the "rotary start" I'm unsure of the actually name but it uses a 7.4v battery and no pull start.

Im wondering if i am over looking something that could cause it to dump so much fuel into the motor, usually a air leak or something of that nature would cause it to run lean, correct?

weather is about 55 degrees F and 50-60% humidity at sea level

Any help would be greatly appreciated
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Old 04-11-2018, 11:59 AM
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Set the high speed to 3.5-4 turns open from lightly seated. Set the low speed so the screw head is flush with the edge of the throttle arm, then turn it in 1/2-3/4 turn. Set the idle gap to 0.5-0.6mm. The idle gap is probably the most important setting. Too wide of an idle gap coupled with an over-rich idle mixture will lead to flooding pretty easily.

Fill fuel tank, prime engine using the pressure line from the muffler to the tank. Blow into the pressure line and watch the fuel go to the carb. Stop blowing a moment after fuel reaches the carb. Light the glow plug and hit the starter. It should fire right up and be rich. Work the low speed leaner just until it will hold a smooth low idle, then set the high speed needle, and return to the idle needle to get the idle and midrange set. You may need to hold the throttle open 20-30% to get it to start if its a little too fat to idle on its own.

Use a medium heat glow plug like an MC8 McCoy.
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Old 04-11-2018, 01:35 PM
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I will try everything you said tomorrow afternoon, but im pretty sure as of right now my settings are leaner then what you are recommending, which is where i become puzzled with this problem. Im not a complete newbie to nitro but obviously i am no expert. Again ill check my settings tonight and report back, and again tomorrow afternoon when i get to try to start it.
I really appreciate the quick response, i always get this part mixed up and when reading about it some write ups say it one way and others the complete opposite. Should i try to tune the LSN first or the HSN first?
Also does the HSN setting have anything to do with the A/F mixture of the engine at idle?

Thanks again,
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Old 04-11-2018, 06:54 PM
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The high speed needle controls overall fuel flow to the engine, but more importantly it basically is the sole fuel metering circuit once above about 1/2 throttle. If the high speed is way way too lean, it will make the idle needle ineffective, but that’s pretty rare. Most short needle carbs - which I believe the RTR type LRP engines have - require the high speed to be set first (because its in a fixed seat) and then the low speed after. The only reason I suggested rough setting the idle needle is only to keep it idling on its own. If the idle gap is too wide and the idle mixture is too rich, it will basically slowly flood the crankcase with fuel and once you pop the throttle, it will douse the plug and you’ll have a flameout. Restarting will be futile because the plug will get drenched again if not already and you’re stuck pulling the plug, draining fuel, and cleaning the plug off. With problem engines - or engines with out of whack settings - ensure you have a good or NEW aglow plug installed as well as a FULLY charged glow driver. You want that plug burning blaze orange.
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Old 04-11-2018, 07:03 PM
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ok i checked where the needles were when i got home today,
HSN was 3.25 from closed
LSN was 2.75 from closed

I followed what you said and have the HSN to 3.5 turns and the LSN is at 1.5 from closed, this was based on making the screw flush with its surround metal and then going in .5 turns and the idle gap is set to a touch over .5mm.
I will try to start it tomorrow afternoon and report back.

so if your recommendations are close that means i originally had the HSN very lean and the LSN very rich... what's even scarier is the last person who tuned it was an "expert"

EDIT: yea i when i would pull the plug it was doused in fuel and when turning the truck over and spinning the engine it would almost leave a puddle, i've never seen a motor this flooded. and like you said as soon as i touched the throttle it would die and sometimes when taking the ignitor off it would stall aka flame-out i believe.

Thanks again for all your help

Last edited by Lt4-396; 04-11-2018 at 07:07 PM.
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Old 04-11-2018, 08:04 PM
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Anytime you notice the rpm drop when you pull the glow driver, either your fuel doesn’t have enough Nitro or your idle
mixture is too rich. Usually the latter.

It’s easy to get an engine to run reasonably well with a needle compensation situation - ie: rich low and lean high. This is where the idle gaps start getting wide “because it won’t idle otherwise”. When you have your carburetor properly set, you will know by the sound of the engine. When you’re “on”, the top end should just howl and the low should give a low lopey idle. It probably will sound like it’s gonna die, but it shouldn’t. Way to check your low speed mixture: run a couple WOT passes and note the exhaust note with the engine at idle. Within 5-7 seconds, the rpm should drop to that nice and slow idle. After about 10 seconds, hit the throttle to WOT; the engine should pickup and clean out virtually instantly. Maybe a slightly heavier smoke trail/cloud at first. Letting it idle for 15-20 seconds and it should burble a little bit, but not flame out. Basically you want it to ever so slightly load up - very slowly. The engine temp should drop 1-2 degrees for every couple seconds of just idling.

Another key to getting a good tune is having the proper fuel. For bashing, I run 20% Nitro with 11-12% oil (castor/synth blend). Fuel with too much oil will be more difficult to tune to and also will run hotter. Don’t use “RTR” type fuels.
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Old 04-12-2018, 01:51 PM
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when you say idle mixture do you mean the idle gap or the LSN?
I tried starting it at your rec. settings and it was close enough to almost start and i leaned it out a touch more and sure enough it fired right up. Its still running way to rich, i only had about 30min all together so i leaned the HSN about 1/4 turn and the LSN about 1/3 of a turn and its running strong but still too rich. Im going to keep tuning and leaning it out an hour at a time tomorrow morning. I really appreciate your help, idk where lrp gets off saying the LSN should be 3.5 from closed... if it wasn't for you and this forum i would be trying to start a ridiculously rich engine that obviously would not have started.

How fast should the temp reach the 200's, when its say 60 outside?

Thanks again
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Old 04-12-2018, 02:08 PM
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Mixture setting changes are made with a needle valve. So idle mix = idle needle valve. High speed needle = main needle valve. Idle gap is idle gap.

New engines tolerate those mega rich conditions much better than a broken in engine. Those “factory settings” are a general starting point where that engine in new condition is guaranteed to start and run. The break-in settings are often very different (leaner).

You should NOT fine tune your carburetor until you’re done with a complete full tank of fuel at reasonably close setting to ensure the engine heatsoaks completely.

Last edited by 1QwkSport2.5r; 04-12-2018 at 02:10 PM.
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