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Old 03-09-2009, 08:05 PM   #1
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Questions?? SH P6-28 Pro Spec with severely aggravating problem

I am only new to the RC world and I have an SH P6-28 Pro Spec with severely a aggravating problem which I think is probably carby related

The engine is in my 1/8 off road buggy.

I run Nitro-X SSS fuel which is good quality fuel here in Australia and it is 25% nitro 11% synthetic oil


Problem is that I cant manage to get it to tune correctly. It will run, no problems at top end, I can tune that, then as soon as I touch my screwdriver onto the LSN it will idle lower and then stalls.

I thought it was the O ring on the LSN so I replaced it 3 times but still does exactly the same thing.

It is like the slide is worn and if I touch it then it moves slightly and changes the needle or something??

I ensured that the LSN and HSN cant move.

The engine is about 2-3 years old but hasnt had much fuel through it, and it has been stored with after run oil.

I have set the idle a touch higher so that the clutch is almost grabbing.

When I removed the carby and stripped it I noted that there was like a stain or wear patch on the slide, the needle looked in good condition.

The motor has great compression, even when hot.

After rebuilding and sealing the carby I began with the factory settings (3 full turns on the HSN and LSN) but no matter what I have tried it just wont idle properly.

Temps are good (usually between 98c and 110c depening on the day)

I live in mid north Queensland so its pretty warm and a bit tropical here so I use the #8 glowplug

I a replaced my tank and fuel lines because I thought that they may have been a problem.


Because of this problem I have rebuilt the carby with new Orings and totally sealed it, including full sealing of the motor with HighTemp RTV and I also completely sealed the rubber boot over the end of the slide but this did not stop the problem......


Any advice??

Is it just these carbys? If so then is there a replacement which is less problematic?

Looking forward to hearing back from someone.

Regards,
Andy,
Australia
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Old 03-09-2009, 08:27 PM   #2
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If you completely sealed the engine up, sounds like its your typical pain in the ass break in When you completely tore down the mill did you check the bearings and internals for free movement, and lube them good before re-assembly? The carbs are good and the engines are easy to go along with, were you the original owner? Mo detail
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Old 03-09-2009, 08:59 PM   #3
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If you completely sealed the engine up, sounds like its your typical pain in the ass break in When you completely tore down the mill did you check the bearings and internals for free movement, and lube them good before re-assembly? The carbs are good and the engines are easy to go along with, were you the original owner? Mo detail
Hi, No I am not the original owner but it only had 2 tanks through it when I got it and Ive followed the guide from my local RC club to run it in properly.

I did check everything and lubed everything when re-assembling.

I noticed the stain / wear on the slide and I also noticed that when I just touch the screwdriver onto the LSN it makes it stall.

I can also make it stall if I touch the carby with my finger. I thought the carby was loose or not sealing so I stripped and rebuilt it, new Orings etc, but that did no difference.
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Old 03-09-2009, 09:00 PM   #4
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Sounds like my STS D30M

Have you checked your linkages, Or tried trimming the radio

And how old is the plug?

Is it fresh fuel?
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Old 03-09-2009, 09:10 PM   #5
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Sounds like my STS D30M

Have you checked your linkages, Or tried trimming the radio

And how old is the plug?

Is it fresh fuel?

Hi, yes I tried trimming the radio, and checked the linkages.

I even tried removing the linkage and ran the motor without it. It still did the same thing, if I touched it with my finger it would stall.

If I idle it any higher the clutch grabs and it starts driving.

I have tried 4 brand new plugs of various brands, 2 were #3's and 2 were #8's.
The fuel is very fresh, only just purchased and I contacted the manufacturer who asked the batch code and confirmed that it was only batched on 10th Feb 2009.

My mate bought a bottle of the same fuel for his racer and it runs perfectly with the same motor and same fuel batch, even when we used it straight from my bottle to eliminate a one off bottle problem.


I also tried another fuel which is mixed at my local hobby store and it is 20% nitro with 15% castor and 5% klotz.

It did the identical thing.
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Old 03-09-2009, 09:14 PM   #6
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Mabye first dude put some worn out carb, or parts?? I dont like buying anything second hand, just me I have been using SH for a long time and dont have much trouble, seal it and forget it, but one time I had a piston crack, started running all ereratic so pulled it apart and had a crack down the side of the piston. It was a new engine send it back and they fix no prob. like other guy says linkage endpoints?? Make sure the idle screw is only 1-2mm open at idle, try to pinch the fuel line if it dies right away wayy too lean, if it goes on forever and ever wayy rich bottom.
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Old 03-09-2009, 09:31 PM   #7
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Mabye first dude put some worn out carb, or parts?? I dont like buying anything second hand, just me I have been using SH for a long time and dont have much trouble, seal it and forget it, but one time I had a piston crack, started running all ereratic so pulled it apart and had a crack down the side of the piston. It was a new engine send it back and they fix no prob. like other guy says linkage endpoints?? Make sure the idle screw is only 1-2mm open at idle, try to pinch the fuel line if it dies right away wayy too lean, if it goes on forever and ever wayy rich bottom.
I was thinking that it must be the carby, I also looked at it for cracks but cant see anything with the naked eye.

I think it must be the carby slide because when I touch it, even with no throttle linkage installed then the engine dies.

When I get it running good at high speed I can keep it above idle but it is driving the wheels, but if I pinch the fuel line it will run for 3-4 secs then stop.

I tried making it really rich to see if that helped, made it 5 full turns out on the LSN, no difference other than more smoke and still stalled at idle when the clutch was just slightly grabing.

I got the engine cause Im only new to RC cars and wanted to make sure it is something I want to do before outlaying a load of ca$h.
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Old 03-09-2009, 10:08 PM   #8
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You sound like you know your way around so I hate to say this. Are you using the idle screw to stop the slide and adjust the idle speed or the radio and linkage? Does it stay running if you push the linkage back cause it touches the slide? When you touch the slide with your finger and it dies are you pushing on it in a different direction than the linkage does? I hope you find the problem.
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Old 03-09-2009, 10:47 PM   #9
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You sound like you know your way around so I hate to say this. Are you using the idle screw to stop the slide and adjust the idle speed or the radio and linkage? Does it stay running if you push the linkage back cause it touches the slide? When you touch the slide with your finger and it dies are you pushing on it in a different direction than the linkage does? I hope you find the problem.
Im using the idle screw to stop the slide,

I have my radio trimmed so that it doesnt push hard once it is at the idle screw (Limiter function)

I adjust the idle screw so that the clutch is almost grabbing, it is idling alot higher than other motors and even my mates same motor (SH 28 prospec) idles alot lower than mine will.

When I push the slide with my finger it is in the direction of the idle position, and if the throttle is already at idle it will stall.

Im not sure how much clearer I can be about this problem, surely SOMEONE must have experienced it???

I think I may just have to spend the $90 on a new carby and hope and pray that it fixes my problem.
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Old 03-09-2009, 11:25 PM   #10
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You may have to trim the radio so its pushing harder against the idle screw. Its got to be pushing it hard enough so that when you push on it it wont lower the idle. At idle with the radio trim is set right it should be compressing the spring on the linkage and leaving a gap on the back of the servo arm of 1 to 2 mm. If you can get that setup so it works maybe with a high idle still.You can move on to see if you got a air leak. If you got a air leak in the engine some place else you can try to find it with some carb spray. Spray a tiny bit between the flywheel and front engine bearing and on the back of the engine if it dies from any of those test in will show where to replace stuff next. If you use too much the fumes will make their way into the filter and affect the running so try to direct the spray away from the filter.
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Old 03-09-2009, 11:30 PM   #11
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You may have to trim the radio so its pushing harder against the idle screw. Its got to be pushing it hard enough so that when you push on it it wont lower the idle. At idle with the when the radio trim is set right it should be compressing the spring on the linkage and leaving a gap on the back of the servo arm of 1 to 2 mm. If you can get that setup so it works maybe with a high idle still. If you got a air leak in the engine some place else you can try to find it with some carb spray. Spray a tiny bit between the flywheel and front engine bearing and on the back of the engine if it dies from any of those test in will show where to replace stuff next. If you use too much the fumes will make their way into the filter and affect the running so try to direct the spray away from the filter.
Been there, tried that. I have had it pushing from mild to hard.

I usually use WD spray to find air leaks, there is none evident on this motor so far but I cant really spray onto the carby.
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Old 03-09-2009, 11:37 PM   #12
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From what I read I thought you might have some time behind a wrench. I gave it my best shot plus Im learning to type faster.
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Old 03-09-2009, 11:46 PM   #13
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I have seen a air plane engine where the lsn was jammed into the spray bar causing it to be bell shaped and limiting the adjustability of the lsn. I thought it may of happened when the dude had the idle screw out. Thats all I got
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