Detonation (pinging)?

[newmaac]

On my 80 SG, I find that I RARELY use more than about 1/2 of the throttle. It has enough power, that with very little patience, I can get to a speed that gets my attention.

I do find though, that when I open the throttle harder, I am getting the classic "baby rattle" pinging that one would usually connect with poor gas or incorrect timing in a car.

I typically use a mid-grade gas (89 octane), as I think I have seen this reccommended in earlier posts.

Any input from others?

[John]

Pre ignition (Pinging) can be caused by a few different things, One, is the base timing correct? Not too far advanced? Two, Carbon build up on pistons and combustion chambers. Carbon will retain heat and will ignite the fuel before the plug fires. Three, bad fuel. You said you used a midgrade octane. The higher the number the less likely the the fuel is to detonate, and it takes longer to complete it's burn. That is where the power gain comes from. Lower octanes ignite at lower temps, and burn quicker. The wrong spark plug heat range. If the plugs tips don't cool properly, they can ignite the fuel just from their residual/retained heat. Is the airflow across the engine blocked or restricted? That can cause the engine to run hot, causing pre ignition. Do you keep the air filter clean? Running rich can cause carbon build up.
If you only use 1/2 throttle, then chances are the combustion chambers are carboned up. I tend to not to twist mine up very tight, but every now and then you need to 'blow the carbon out'.
This may sound funny, but spraying water into the carb inlets while it's running at a high rpm will help to break up the carbon by creating steam pressure in the combustion chamber. Use the mist spray from a Windex bottle or similar type, Remove the bottom of the air box. Run the bike at about 3000 rpm and just spray away. You'll be able to tell if you are introducing too much water, and can scale back on the amount of water you are spraying. I've done that with a few engines at work. A lot of our stuff is goverened down to 2800rpm and just can't blow the carbon out.

[chevy45412001]

water spray

That is a good tip. My Father used to do that on cars . He said to use ice cold water though. Really ice in the pitcher and all, but dont actually put the ice in the motor.Kind of hard to pour water into our carbs,never dawned on me to spray it. Thanks

[newmaac]

Actually I learned that trick in High School auto shop. I haven't tried that in years!
One key part to using this method, as I recall, is to make sure that you keep the revs up during and after misting the cold water into the intake.
You want to make sure that carbon, that flakes off fo the head, doesn't get a chance to lodge in a valve seat.

I hadn't thought of the carbon build-up, but it sure makes sense.
I will try it.
Thanks for the input.

[pgg]

The cranckcase would end up full of milky sludgy oil would it not? I'd be inclined to lift the head and scrape the pistons and chambers spotless.

[John]

There won't be any water getting into the oil because it will be vaporized and turned to steam under the combustion temps. The resulting steam will be expelled with the exhaust gasses. Rermember, there will only be a small amount actually injested by each cylinder. You would have to flood the cylinder to get it past the rings and into the oil. Sludge usually comes from condensation, or in the case of a blown head gasket or cracked head on water cooled engines. Many older jet engines used water injection to increase the pressures inside the combustion chambers of them to spin the compressor sections faster. That was accomplished by the steam pressure reacting against the turbine blades in the exhaust section of the engine.

[pgg]

I'm not too sure on this one John! You must be right but how many bucketloads of water do you need to shovel through the motor to zap all this evil carbon and how long would it take? Do the pistons come out clean and shiny? Would dishwash liquid help? Can I run my bike on steam only? Sorry. Sorry. Ignore those last two. Put it this way - if a workshop told me they'd been pumping water through my precious engine I'd have some choice words to tell them! Am I being over dramatic? ( mind you, would never take the bike to a workshop anyways - too many rip-off merchants - I get rooked and rogued more than enough by car workshops ) Cheers.

[newmaac]

PPG
I know that most of what you just said was just for fun, but I still don't think that you get what John is suggesting.
Stop thinking "water" and think "cold mist".
The water,(very cold), is not poured into the carb, but a mist is sprayed in the area near the throat of the carbs.
The cold mist is sucked in with the air.
The way that it was explained in school, what actually clears the carbon, is the quick change in temperature. I don't recall any mention of steam, but that WAS before this old bike was even made!!

[pgg]

I think I'll stick with sandpaper Newmaac.

[graybird78]

pining ?

hi newmaac.
i to had the same problem. my bike is also 80 SG. my solution to this problem was to try and eliminate the carbon in combustion chambers. what i did was to use a fuel additive called BG44K. we use it on cars at work with good results. add to gas at fill up.then would drive bike on interstate and give her a few quick blasts at full throttle. will stink like you know what. after a few tank fulls, i noticed not pinging as bad. so to futher help i installed 1 heat range colder plugs. this also helped. this last week i pulled my carbs off to clean and to fix a couple of problems with carbs . I looked inside combustion chambers on intake sides and carbon is almost gone.they look like new. last summer i had carbs off and all i could see was carbon deposits. big difference the BG44k made in just a few tanks off gas. so this was my solution to this problem. did make big difference for me.