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Old 11-13-2001, 12:55 AM   #1
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Default Engine tuning tips

OK I have been playing with my engine (CX12 slide JP Black) and found the following things:

- Starts and idles fine.
- It idles nicely.
- When you give it throttle it accelerates nicely with a nice plume of smoke (a fair bit actually)
- If you accelerate lightly or in a short burst it will return to normal revs quite quickly.
- If you accelerate for the length of the straight it will run-on with quite high revs for a period (5-10) seconds then drop back down to normal revs. I am used to engines revving high then low but the drop off on this engine is quite significant.

I am thinking that the low end is too rich meaning that I am having to use a high idle to keep it going. When I "clear its throat" it will idle high till it loads up and drops the idle again. The idle slide is open mayby 1-2mm which seems like alot.

I am running about 3 turns on high end needle and 3 1/2 turns in from flush on low end (black) needle. Mid range is flush.

Any ideas????
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Old 11-13-2001, 01:35 AM   #2
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Default Re: Engine tuning tips

Quote:
Originally posted by AMGRacer
OK I have been playing with my engine (CX12 slide JP Black) and found the following things:

- Starts and idles fine.
- It idles nicely.
- When you give it throttle it accelerates nicely with a nice plume of smoke (a fair bit actually)
- If you accelerate lightly or in a short burst it will return to normal revs quite quickly.
- If you accelerate for the length of the straight it will run-on with quite high revs for a period (5-10) seconds then drop back down to normal revs. I am used to engines revving high then low but the drop off on this engine is quite significant.

I am thinking that the low end is too rich meaning that I am having to use a high idle to keep it going. When I "clear its throat" it will idle high till it loads up and drops the idle again. The idle slide is open mayby 1-2mm which seems like alot.

I am running about 3 turns on high end needle and 3 1/2 turns in from flush on low end (black) needle. Mid range is flush.

Any ideas????
what nitro % you run on your engine? seems 1-2 mm openning is too much ! I run like less then 1mm on the idle position.
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Old 11-13-2001, 03:15 AM   #3
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I run 15% nitro, 9% caster and 3% Neo synthetic.
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Old 11-13-2001, 03:36 AM   #4
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Quote:
Originally posted by AMGRacer
I run 15% nitro, 9% caster and 3% Neo synthetic.
check air leakage on the carb. seal the connection area between carb and engine case if possivle with high temp sealent. check leakage on the boot. you need to adjust the idling opening to less then 1mm. it is too wide open for idling with 1-2 mm
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Old 11-13-2001, 03:44 AM   #5
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Yes I agree. I have sealed the engine. When I make the opening down to .5mm it stalls. So therefore I assume the low end is too lean......

Sorry about all the questions but I bought this engine 2nd hand and I have no instructions with it. So I am trying to get some baseline needle settings.
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Old 11-13-2001, 05:11 AM   #6
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It doesn't mean it's too lean when you have the idle stop at .5mm and it stalls. I run all mine at that or less. When it stalls, is it choking? Could be the low end is too rich.
The fact that it'll run at a high rpm after a run then drops significantly when it idles tells me the bottom is too rich.

Air leaks usually gives you inconsistent idle.
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Old 11-13-2001, 06:10 AM   #7
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Quote:
Originally posted by Sydewynder
It doesn't mean it's too lean when you have the idle stop at .5mm and it stalls. I run all mine at that or less. When it stalls, is it choking? Could be the low end is too rich.
The fact that it'll run at a high rpm after a run then drops significantly when it idles tells me the bottom is too rich.

Air leaks usually gives you inconsistent idle.
My dear HKBC is right !!!
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Old 11-13-2001, 04:14 PM   #8
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sorry guys I meant rich
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Old 11-13-2001, 06:42 PM   #9
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No problem.
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Old 11-14-2001, 11:22 PM   #10
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OK new tuning question.......

I have leaned out the low end needle a bit, mayby 1/3 a turn. Weather is a fair bit different today as well. Now after a long burst of throttle the engine returns to a fairly low idle right away then 10-20 seconds later the idle INCREASES. I am thinking that the low end now has gone too lean. Also the performance off the line seems flat. When I clamp the fuel tubing the idle of the engine increases almost immediately.

Man the low end on this thing is touchy.
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Old 11-15-2001, 12:29 AM   #11
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Yes you went too far. When I adjust the needles, I go no more than an hour at a time and see what the engine is doing. I don't turn it 1/3 of a full turn.

When I say an hour, think of the needle as the face of a clock. 1 'o clock from 12 o'clock is an hour. 2 o'clock from 1 o'clock is also an hour and so on.

In your case, turning it 1/3 of a full turn you went from say 12 o'clock to over 4 o' clock in one fell swoop.

Last edited by Sydewynder; 11-15-2001 at 12:33 AM.
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