Fouling plugs

T

timtune

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Starts first or second pull. Runs great. Punch it and there is no lag it just goes.
However if I'm not on the throttle it will foul up pretty quickly. Following someone slowly fouled the plugs. Waiting too long at a busy road crossing will do it too.

Is this fouling plugs on the low end just the price to have it run so well at the top end or could a change in the heat range help? I'm running 9s now.

Any help appreciated.
 
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If that motor was also used in a motorcycle, that should also cover it since the question is about the motor and not the sled.
 
timtune said:
Starts first or second pull. Runs great. Punch it and there is no lag it just goes.
However if I'm not on the throttle it will foul up pretty quickly. Following someone slowly fouled the plugs. Waiting too long at a busy road crossing will do it too.

Is this fouling plugs on the low end just the price to have it run so well at the top end or could a change in the heat range help? I'm running 9s now.

Any help appreciated.
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What premix are you running 50:1? Most 2 strokes don't like to be idled but yours sounds extreme adding a bit more oil will lean it out a bit. Are you getting spooge if so you are probably slightly rich. But you really don't want to go too lean and blow it up.

Sent from my Pixel 5 using Tapatalk
 
With half the nonsense on this forum any "motor" related question should be welcome and encouraged.

Now back on track.

Typical Causes of fouling:
Rich fuel mixture: Too much fuel being injected into the cylinder can lead to excessive carbon buildup on the plugs.

Incorrect spark plug heat range: Using a "cold" plug for the engine can cause incomplete combustion and fouling.

Excessive oil consumption: Oil leaking into the combustion chamber can also contribute to fouling.
 
weak ignition coil(s) ? sometimes coils fail when they heat up-but otherwise work before heated...have any spare coils to try? .my DT200 idled and ran well at 30 to 1.
 
It's been a number of years since I've tuned carbs, but if it runs well at near-full throttle then it sounds like your main jet is good. If it's only fouling at part throttle then that sounds like needle position and/or needle jet. Changing the clip position on the needle is free. I think you'd raise the clip (lowering the needle) to lean things out at partial throttle. If that helps but doesn't solve it, grab a couple smaller sizes of needle jets from Winner's Circle and try those out.

See the "needle jet tuning" section here: Kevin Cameron Explains How To Tune Carburetors
 
Thanks all.
Doesn't run pre-mix it's oil injected.
 
wondering if this engine is oem stock? sled? yes. sometimes just setting the carb back to
ALL STOCK works - float, pilot jet(s), main jets. float height.
most times the engineers have them set up pretty good from the factory.

simply moving the needle jet one position can make an engine run like cr@p. or vice versa,-and it flys...lol
for this idle, low revs situation Im guessing pilot jet(s).

I miss my old 2 strokes; street 500 gamma, rg250 racebike, to rotax and yamaha dirt bikes..thx for the 2S memories ! please keep us wanna be tuners informed.
best luck !
 
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boyoboy said:
wondering if this engine is oem stock? sled? yes. sometimes just setting the carb back to
ALL STOCK works - float, pilot jet(s), main jets. float height.
most times the engineers have them set up pretty good from the factory.

simply moving the needle jet one position can make an engine run like cr@p. or vice versa,-and it flys...lol
for this idle, low revs situation Im guessing pilot jet(s).

I miss my old 2 strokes; street 500 gamma, rg250 racebike, to rotax and yamaha dirt bikes..thx for the 2S memories ! please keep us wanna be tuners informed.
best luck !
Click to expand...
It has a set of velocity stacks. ( I have not changed anything since I got it - it may have been jetted for the airbox removal - stay on the juice and it runs top notch)

Could raising the needle one slot lean it out enough to cause damage?
 
Last time I played with vintage sleds was when they were not vintage. I did play with lots of sleds in the 70s-90s.

Any chance you're running Mikuni Powerjet (Econojet) carbs? They are hard to dial in if you remove the airbox-- rejetting isn't easy for experts. If you have these carbs, replace the airbox or add some pod filters to correct low speed vacuum, or change to regular VMs. Use the stock 15 or 20 pilot jets at 1.5 to 2.5 turns out on the air screw. If it tunes at less than 1.5 turns, use the 20 jet. More than 2.5 turns, use the 15. Check the idle, it should be 2500 RPM. The engine might sound fine idling at 1200, but those machines need the stock 2500RPM idle to keep from fouling.

I never got into tuning performance sleds, I stuck with stock stuff and used factory service manuals. Once and a while I had no choice -- I remember trying to setup the stock econojets on my 93 MZX triple. Never worked. I had a few buddies that played with performance sleds -- they couldn't get them going either. Popped the airbox on and all was good.
 
They may be Powerjets. Sled came to me w/o the airbox so I don't have one to put back on.
I might drop the needle one clip, but I'm hesitent to do much since it runs so well the other 98% of the time.
Was out yesterday and it never missed a beat.
 
The power jet doesn't "kick in" till 1/3 throttle... but if it IS a power jet VM it has a air bleed, which can clog and do weird things at low RPM.
With a 30 year old motor... do you have the basics? Low compression will do that, sacked main seals will do that, clogged jets will do that. Ever do a leak down test?
 
Don't know how to do a leak down on a 2 stroke.

All I really know is it starts first pull, goes like a cut act when you peg and brings a huge smile to face when "on the pipe".

If you're not on the gas or on the brakes you're just wasting time. Changing plugs seems like penance for time wasted.
 
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