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Old 12-22-2005, 03:47 AM   #1
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nitro newbie need advice

hello to any one who reads this i have just bought an xb8 and have an sh .21 engine in it, but am having trouble keeping it running on the track as it is a tight and lose gravel track i have traction problems any advice there?
but as far as the engine is concerned i can tune it right to run without the body shell cover on it but as soon as i run it with the body cover on it seems to struggle at the bottom end until it hits top end though i need good low end punch for the small tight loose track any engine advice is much welcomed thankyou ..............Aaron.
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Old 12-22-2005, 07:57 AM   #2
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It would help if you were a bit more clear when you describe what it is doing on the bottom. When you accelerate hard off the bottom, does it bog and a lot of smoke come out, or does it stutter a lot, and act like it wants to stall? If number one, then lean the bottom until it idles smoothly and pulls hard after sitting 10 sec with no stuttering.

If no.2, then richen the bottom end until you get the same tune as mentioned above. Try to set the top end first though. Also, make sure you are using a good bottom end pipe like a Jammin JP-1 instead of a top end pipe, which will give you NO power on the bottom.

To cover your traction problems: There probably won't be a perfect tire for a tightgravel track, but I would suggest trying Panther Komodos (just because they are great all-around tires) or any tire with a large aggressive tread that digs on the gravel. If the gravel is very hard packed and the car is sliding, try a Pro Line Crime Fighter tire, because those seem to cure "loose" cars on about any surface. I really don't know what would work great because I've never raced on gravel......
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Old 12-22-2005, 03:54 PM   #3
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I ran the SH .21 2004 Pro XB in my buggy this past summer. Is this the same SH engine you have? I used the Jammin JP1 pipe and it ran great on the bottom with it. I could feel that the engine did seem to want to rev a little more, though. I probably should have tried a mid range level pipe. All in all though, I was very pleased with the combo mentioned.
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Old 12-22-2005, 04:41 PM   #4
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The JP-2 is a top end pipe,it could give you a better powerband though.
A 053 is a good mid to bottom end pipe,I ran one on my P-5 and really liked it.It would probably work well on your SH,since it sounds like a bottom end motor.My Collari is a top end motor,but I run a 086 on it and it is for top end.It has crazy power.The bottom end is there on tap.

For tires you may won't to try some Treadz Jollys,but I don't have a clue about good tire for gravel.
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Old 12-22-2005, 07:56 PM   #5
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hi guys thanks for your help, ok ill do my best to describe everything as good as i can.
ok i will start with engine type which is (as written on the head which is red)
PT 2004 XB does the pt stand for pro or somthing sorry im not sure.
ok now my pipe is an SH MAX TORQUE pipe.
this is what the car was doing last time i ran it ; ok i tuned it so it could run good from idle right through to max speed (but this was with the cover off)
with out stutering or chocking it was smooth.
but now keep in mind that when i put my cover back on it started to struggle after about 1/2 of a lap now the description of what it was doing whilst struggling was it just seemed to be lean (not rich and getting flooded and stutering) it was just struggling to get power as if wasnt getting enough air and fuel but it only done this on the bottom end until it got to mid/high end then it takes of to max speed but with all this being said its still stalling mid tank i have never got a full tank out of it without a stall (on the track)
so i have not only just the bottom end struggling but it will sometimes stall say after i full throttle then brake then accelerate again it seems like its flooded after that.
i seem to tune it right but then put the cover on and then i have trouble's
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Old 12-22-2005, 08:02 PM   #6
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yeah um id have to say option 2 id need to richen it up a little at the bottom end but it still doesnt solve my problem of stalling after full throttle brake then accelerateing i cant get it to just stay going for a full tank like i expect it too in a race so i can accelerate brake then accelerate etc so i can rally it round the corners with max torque and drift, slide etc i just need it to survive when i work the car around the track.
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Old 12-22-2005, 09:23 PM   #7
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I'm assuming you cut holes in your body, correct? Most 1/8th scale buggy bodies fit very tight on the chassis, and if you don't have any holes cut, the engine will starve for air.


Also, you mentioned that the engine seemed to stutter after you returned to a low speed from a high speed. When you slow the buggy down, does it have an unusually high idle for a few seconds, or does it drop so low that it almost stalls?

Other than that, I really don't know what to tell you. I've never heard of anything like this before. Try putting the body on and letting it idle next to you for a little while. Check the engine temps, and notice any changes in engine sound or exhaust smoke.

This one is tough to call!
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Old 12-22-2005, 10:41 PM   #8
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Could it be possible you are pinching a fuel line when you are putting the body on? Or the air filter tube? Have you checked the engine temp when running with the body on?
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Old 12-22-2005, 10:52 PM   #9
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Speedbump57: That's exactly what I was thinking, because he says it stalls about a 1/2 lap later. It could be that the engine is set lean so it can run on the fuel left in the pinched portion of the line? Even for a little while?
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Old 12-23-2005, 12:26 AM   #10
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hi yeah i see what you mean it was a bit crowded on the air filter where the fuel and exhaust lines ran underneath the filter i moved them around and also i cut out the front windscreen of the body shell so it will get plenty of air flow through to the air filter but unfortunately i broke the front left suspesion arm yesterday so i wont be able to run it until i get spares.
out of what i know and what you guys have said i think the low end could do with richening up a bit but i guess through mucking around with the settings i have already been through this process but cant seem to get a good comprimise ill wait till i get the sus arm and ill put some fly screen mesh to cover the windscreen to stop the rocks getting in but still have air flow and then i can go from there but do you guys know how to tune this engine from scratch like what would you do if you had this car and tuned it from scratch?
thankyou for your help.......Aaron oh and yeah when i get the settings right without the lid there is plenty of smoke at the bottem end but not alot at the top end hard to see becuze of all the dust but any richer on top end it will stall.
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Old 12-23-2005, 12:55 AM   #11
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What are your needle setting now from fully closed? LSN & HSN
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Old 12-23-2005, 07:57 PM   #12
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ok i just checked the needles and the high speed needle is about 3 turns out and the low speed needle is about 4 turns out.
also when the throttle is all the way open the low speed needle is about
2.5 -3 mm out from the high speed end opening should i have the low speed needle further in so it doesnt flood after high speed has full open high end and full open air intake i am thinking maybe it should be more even with the low needle coming out of the high end hole like at 1 mm out when full throttle maybe this is why i am stalling it maybe getting to much gas just before full air intake im not sure.
by the way this engines settings are as follows the low end needle adjustment is at the end of the dust cover where the throttle linkage connects to the carburettor and the high speed needle is at the opposite side of the carburettor where the fuel line goes in and the idle adjustment is between them set at 1 mm (credit card thickness)
and to your earlyer question the car did have some rpm after i hit the trigger and let off it would roll on its own and gradually pick up speed so its not trigger responsive when i let off it should not move and idle?
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Old 12-23-2005, 08:29 PM   #13
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Is the engine at full running temperature before you put the body on? If not it may need a pinch assuming you did not purchase the engine new. The engine may not have enough compression after the engine reaches full temp. When compression starts to go it will run very erratic and you will be chasing mixtures. I would pull the head and check the pinch to see how tight the engine is. Just a thought. I would also check for air leaks.
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Old 12-23-2005, 08:55 PM   #14
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Start the car, get it up to operating temps, tune up the top end, and then pick the car up and go full throttle for 3-4 seconds, then release the throttle. The engine should immediately drop down to a low, steady idle. If the RPM stays up for 1-5 seconds and then drops down, your bottom end is rich. If it drops down immediately and after a few seconds goes back up and the car starts rolling, then your bottom end is too lean. Tune the top end so the car gets up to full speed very fast, so there is no stuttering at top end, and so you can still see smoke at wide open throttle, and then richen the top end 1/16th. Then rev it all the way out and see what it does when it is coming back down to idle.

Check for air leaks. Check your fuel tubing for small holes, check the fuel filter (The XRAY XB8 filter will come loose after a while and let air in), check your air filter, and check the gas tank seals.

Check your clutch settings, check your clutch bearings, check your engine gaskets, check compression (rotate the flywheel with your finger: If it is very easy to turn, rebuild your motor.)

Just go over everything in the car, and go back to the stock carb settings and completely re-tune the settings and check for any possibility of an air leak.

Damn, this is a tough one to call.
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Old 12-23-2005, 09:05 PM   #15
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i thankyou once again for advice, but do know, i am just getting familiar with this stuff so bare with me .ok sinse i have bought it second hand all i have been doing is trying to get it going nicely with about 1 litre through it so far and i do this without the cover on and i seem to have got it going great however i do put the lid on once its warm/hot whats the running temperature if you may? (thats the next thing on the list a venom temp guage)
ok so then the lid goes on and it struggles like i explained erlyer but only after say a lap thats when it does this.
now i am not sure what u mean by pinch? i have taken the head off and primed it before though when i first started this engine i had trouble starting it because of high compression so i losened the glow plug to start it and had no trouble starting sinse so i guess the compression is good as far as air leaks i doubt it though how do i check for air leaks?
is there a rule of thumb about the low needle distance from the hole where the fuel enters once in full open throttle?
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