Pinging Noise - running too lean?

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#1
I recently rejetted my 2000 model KDX200 as suggested by this forum and the notes on the JustKdx website. I changed from the stock main to a 155 (was 160), and the pilot to a 45 (was48). I also raised the clip on the needle from the middle positon to the 2nd from the top.
I rode the bike afterwards on a trial ride, and didn't notice a problem. But yesterday I raced the bike on a fast natural terrain grass track and noticed a pinging noise during my first race ( I mainly noticed it when I was rolling of the throttle and changing down gears to corner. Prior to the next race I dropped the clip on the needle back to the middle position. It seemed better. I may have heard the odd ping, but am unsure as paranoia set in, and it could have been the chain or somthing else clanging.

A few questions:

1. Could this have caused any damage?
2. Is dropping the clip several postions (raising the needle) better than playing with the jet sizes?
3. I have been running Castrol TTS at 32:1. I thought this would be better than 40:1 considering I already leaned the jetting. Is 32:1 best?
4. I assume I would be best of doing a plug test as suggested on the Justkdx site.

Your advice would be appreciated
 

bud

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#2
1, Not likely
2, Not unless the jetting problem is between 1/4 and 3/4 throttle. Check the carb tuning article to see how the different circuits work.
3, There's lots of points of view on this. If I understand things correctly, the main reason to run more oil is for the extra power you may get if your jetting is spot on, and unless you use race gas, don't bother trying. I don't know what tts is, but with any reputable brand of synthetic, 50:1 is fine, unless you ride wfo with a heavy load for hours on end. I personally use 66:1 with mobil mx2t.

Also, keep in mind more oil means less fuel, effectively leaning your jetting.

4, yeah, can't hurt :).

Another thing to think about is the fuel you run. Not sure how things are in Qld, but here in vic, there is some difference between pump fuels. Eg, 2 regular pump fuels (same octane, supposedly) from different suppliers require quite different jetting. As far as I know, regular fuel was relatively similar, at least to jet for, until recently. When I had my kdx, the jetting recommendations here were spot on. I don't think they would be now. Just something else to think about :).
 

Mac

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#3
Are you sure the noise your hearing is pinging?? I have the same bike (almost) with the same jetting. Sometimes when I let off the throttle and the engine RPM is dropping I will hear the engine fire once or twice but I dont think this is the "pinging" that destroys engines.

If at WOT you hear pinging then STOP because your main is too lean but a 155/45 combo should be close to perfect in that bike.

I would put the needle clip back in the #2 position and do a WOT plug chop, if the plug is a nice tan then dont worry about it.

Also, what plug are you running? What gas are you running??
 
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Hi Bud,

I use premium unleaded as it has a higher octane than the standard unleaded. However I didn't get the fuel from my usual supplier. So whether that will have made much of a difference I don't know.

Castrol TTS is a full synthetic race oil. They recommend mixing it at 50:1.

The fuel / oil mix has always confused me a little. I understand that 32:1 is running the bike leaner (on fuel) than 40:1 does. But if an engine siezes because the bike is run too lean at WOT, isn't it due to a lack of lubrication of oil? Therefore if you have leaned the jetting and don't want to run the risk of siezing the engine at WOT, would you put more oil to fuel in your pre-mix (ie run a leaner mix)? :think

Does that make sense?

Hi Mac,
I'm not sure if you'd call it pinging, or knocking. But it was certainly making a noise I haven't heard before.
Any noises concern me. What's the back fire noise caused by?
I think the standard plug is an NGK 8 ES or EV? I'd have to check.
 
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bud

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#5
Grinch, my local mechanic tells me some or all brands of premium unleaded now have additives that do more harm than good, leaving deposits behind, and will require different jetting. Your fuel might be different than what we get in vic, but personally I'd use either regular or race fuel or a mix of the 2. I'd bet if you switch to regular, the justkdx jetting recommendations will be pretty close.
 
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#6
I'll have to check that out bud.

Does anyone else out there use race fuel with the same jetting?
 

Mac

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#7
Race fuel is not required in your KDX unless you had the head modified, use 92 octane or better.

Engine seizure by running lean is due to excessive heat and lack of lubrication , using more oil will fix the lack of lubrication but the heat due to lack of fuel will still seize the engine.

The only way to know if your too lean on the main is to do a plug chop!!

P.S. how does your bike run with the 155/45 compared to the 160/48
 

Canadian Dave

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#8
Seizers at WOT are often the result of a lean main jet. Why does the piston seize in its bore? As the piston's temperature increases it expands. If the main jet is too small/lean two things can happen: the engine may receive less lubrication than what's required which causes additional friction/heat but more often its receiving less fuel than is required to keep piston temperatures within the normal operating range. The incoming charge of fuel quenches the piston cooling it. Even if you're running a high oil ratio, say something like 20:1 and your engine is getting all the lubrication it needs if an adequate amount of fuel isn't supplied the piston over heats and grinds to a halt.

David
 
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#9
Ahh ha. That now makes sense. Thanks for the explanation Canadian Dave.

Mac, The bike is definately more responsive down low and up top, since I rejetted it. You just have to ask a friend of mine who helped with his opinion before and after the change. I rode it first after I rejetted and noticed that the bike was more responsive. I told my friend this prior to him testing it. He soon found out how much of a difference it made when the front wheel suddenly lifted and the rear end fish tailed before he ended up going down with the bike in a pile. (my nice new unscratched bike! - not anymore :( )

In regard to the octain rating: Caltex Australia say "A highly refined, premium grade unleaded fuel for spark ignition engines blended to meet the requirements of modern automotive engines fitted with catalytic converters and designed to run on unleaded petrol. It has an octane rating of 95 minimum which makes it ideal for imported vehicles which require unleaded petrol with octane ratings higher than the commonly available 91. It is also ideal for those cars which experience engine knocking or run-on problems when using 'regular' unleaded petrol.
A recent development is Lead Replacement Petrol. A petrol specially formulated for cars with engines designed to run on leaded fuel where Leaded Petrol is unavailable. It contains an additive to prevent valve seat recession and has the same 96 octane rating as Leaded Petrol. It retains the characteristics of easy starting, quick warm up and full power under all climatic conditions of Leaded Petrol. Environmentally it is an advance on Leaded Petrol, having a lower maximum benzene content and exhibiting lower vapour losses to the atmosphere during summer months. It is coloured red."

Ampol say that the octane ratings of petrol in Australia at the present time are as follows:

Super (leaded) 96
Regular (unleaded) 91
Premium unleaded 95

Long winded, I know. Just thought you may be interested. I'm not sure how American fuel rates.

I've been using Premium unleaded. I know some people who run Super(leaded) due to the higher octane rating, or a mix of both Super and unleaded. There doesn't appear to be much difference.