Lean running condition.

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Ratt_Bones

Ratt_Bones

New Member
Aug 2, 2013
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Appleton, Wi.
I can't seem to figure this out........
Keep burning up spark plugs left and right. I got tired of this, and decided to go through everything, and make sure the entire engine is set stock. I even replaced the fuel, emptied the tank/carb, and started over. I am running 20 to 1, and the leanest for the GT-5 according to Grubee is 25 to 1, with 16 to 1 being the break in.

This seemed to work right away. All was going nice and smooth, had a good sound, smooth idle, etc. The bike felt like new. Then, out of no where while rounding a corner (long flowing corner), the engine seemed to go into turbo, the sound got louder, and the bike went faster. A LOT faster!!!

Now I know it's running lean, and I went over everything again, and nothing is different. I have no clue why. I also know this is not good. Though, I enjoy the mid 40mph range, I would much rather achieve it through proper means.


I have three spark plugs that look like this. Worst part is, it's only taken me a month to do it. Any help or suggestions would be greatly appreciated.


Thanks guys!
 

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KCvale

KCvale

Well-Known Member
Feb 28, 2010
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Phoenix,AZ
This is usually a lean running condition due to an air leak but what is the heat rating on your spark plug?

The heat rating is the number between the letters in the middle, usually in the range from 5 to 8, the lower the number the LESS heat the plug body will transfer to the head and the hotter your engine will run, the higher the better until it won't run hot enough to burn off plug deposits.

Here in Arizona we run 7's and the 2-stroke plug I put in every new build is an NGK BPR7HIX Iridium (stock number 5944), you'll be hard pressed to burn one of these up and they come in a 5-8 heat range.

http://www.ngk.com/product.aspx?zpid=9496

SBP has them as well but for me anyway I put one in every new engine and never have to dick with it again.
 
2door

2door

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Staff member
Sep 15, 2008
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Littleton, Colorado
Possible fuel starvation? Vibration can also foam the fuel in the bowl and cause a lean condition. Is the engine mounted securely, solid to the frame? Remove the fuel line from the carburetor and see how well the fuel flows with the petcock wide open. It should be a nice steady stream. If it isn't steady, or drips, the petcock or in-tank filter might be dirty and restricting the flow.
A sizable air leak in the induction system, intake manifold or carburetor can also cause a lean burn but you'd see evidence of that at low rpm also. A fast, uncontrolable idle is a symptom of an air (vacuum) leak.
My guess is fuel flow or jet size. Typically the jets are on the large side, not too small so unless you've soldered your jet and redrilled it, jet size probably isn't your issue.
Check that fuel flow and let us know what you find.

Tom
 
rustycase

rustycase

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May 26, 2011
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I do not have all the facts...

IMO
It would seem to me there is a lot of ash deposit down on the plug.
Leads me to believe too much, or cheap mix oil.
Then I read about your 20:1 mix ratio...
IMO
That is too much oil!

Fact. Too much oil displaces some of the gasoline, causing a lean burn!

I would only use that much oil for a beer can's worth on the very first run of the engine round the block. Then I'd go 30:1 for the first tank and 40:1 thereafter... for any kind of reasonable two stroke oil.
... a super-duper synthetic or that Opti-2 stuff? Well, I'd follow THEIR directions.


and, IMO
The air cleaner may not be doing it's part.

Last, but not least, two more things...
The float may be adjusted improperly, to run out of fuel, creating a lean run condition, in a long sweeper like you described.

Question...
Do you have a nice fuel filter on there, since day one?

Could be grit from the tank partially, or intermittently plugging the float valve or the jet.

and I'd get a 2nd opinion on anything I say!
:)
rc
 
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Ratt_Bones

Ratt_Bones

New Member
Aug 2, 2013
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Appleton, Wi.
The plugs I have been running were recommended to me by a local guy here, the NGK B6HS. So these are the ones I've been cooking up. Right now I have the stock plug in (which I was told was junk), the LD Z4JC three prong. This is the plug that comes with the GT-5 kit. I took it out (per advice), and replaced it with the NGK B6HS plug, but those have been failing miserably.

I have all brand new fuel line, and filter. I'm also running a brand spanking new speed carb. I recently cleaned/flushed (properly) the tank as well. I see no evidence of frothing, and no bubbles in the line.

Tomorrow I'll take the head off and inspect the piston for build up. If it's bad, is there a proper way to knock it down, clean it off?
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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I agree with rustycase, 20:1 is too much oil. I run 40:1 in all my two strokes and have been doing so for decades with no problems. Just use good quality two stroke oil (NOT outboard!)
Once you have the ratio right, you can tune much easier by reading the plug.
Right now, you cannot tell what the engine wants because of the oil deposits and ash on the plug.
Lean your oil mix and then try tuning.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
Most people here seem to like 32:1 but I stick with what I know.
Been running 40:1 in every china doll I ever owned. Never had a engine failure of any kind (aside from wet mag coils)
 
rustycase

rustycase

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May 26, 2011
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RB, I might suggest you NOT remove the head for inspection and cleaning.

IMO
it will not get you anything...

There IS carbon and buildup on the piston.
that's the way it goes!
and removing it does nothing except to lower the compression ration by some un-measurable amount.

You can take off the exhaust pipe and using a small flashlight, look in the sparkplug hole and the exhaust port to see whats going on in there.

If you must scrape carbon buildup, a popsicle stick is popular to prevent scratching the piston crown.

If you pull the head you risk stripping the bolts and case, may need new gaskets, may knock chunks of carbon buildup down into the rings, etc.

IMO
it's just not worth it.
She's a chinagirl!
She's got compression, or not.

If she goes WAY lean and seizes, or holes a piston, it's still cheaper and EZr to buy a new motor than work on em!
Until that changes.... well...

IMO
Perhaps you might try drilling the main jet open just one size if everything you described is in good order.

Good luck
rc
 
rustycase

rustycase

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May 26, 2011
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Ratt_Bones said:
I was actually running 40:1, but was under the initial impression that this was too lean, and that was the cause.
Click to expand...
That's pretty much the idea we all began with.

However, 'lean' is a description of the fuel/air ratio.
The 40:1 part is a description of gasoline fuel to lubricating oil ratio.

If it's not fuel, it's making the engine burn leaner.

(they really DO run better on straight gasoline. Just not very long!)

To further muddy the waters, optimal fuel/air ratio changes, depending on temperature, and demand placed on the engine.
It's never a perfect world.
Which is where a chinagirl fits in... just right !

:)
rc
 
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2door

2door

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Sep 15, 2008
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Littleton, Colorado
As always Rustycase is correct.
Lean refers to the fuel to air mix. The oil content, or ratio does have an effect on the mix because the less gasoline you have (more oil) gives you a leaner fuel to air mix. That sounds backwards I know but it is a fact. Oil isn't figured into the combustion equation because it isn't a fuel. It doesn't actually burn and produce power. It's only there to lubricate so the more oil you add to the mix the less gasoline there is to mix with the air. Therefore you end up with a lean combustion condition.

The 32 or 40 to one fuel to oil ratio works for a great majority. The kit recommendation of 16 or 20 to 1 will give you a lean burn but will leave deposits on the plug, piston and combustion chamber as well as the exhaust system.

I'm still not clear on what you mean by, "burning up" your plugs. Could you define that for us? Deposits or oil fouling is not really burning a plug. It is simply fouling them in which case they can be cleaned and reused. However if you're still running a 20:1 oil to fuel ratio your plugs will probably continue to look like the one you show.

Tom
 
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