What causes goop??

[bedell99]

When a person tunes jetting he/she adjust's the Air/Fuel mixture in his/her engine to ensure a complete burn. This I understand. What I don't understand, is what is the goop? Is it unburned fuel or oil?? Is it fuel that isn't atomized, etc.?? How does using different gas/oil effect goop, etc etc???

Erik

 

[ML536]

My understanding is that it is principally oil that did not burn because the temperature in the combustion chamber was too low due to overly rich jetting.

The fuel mixture entering the combustion chamber has a cooling effect, I think because of evaporation. When there is too much fuel for the quantity of air passing through the engine (a rich condition), the temperature in the combustion chamber drops too low to completely burn all of the oil. The excess oil is blown out the exhaust as spooge. (I'm not sure, but I suspect that at least a small percentage of the spooge can be unburned components of the gasoline itself).

When there is less fuel entering the engine for the quantity of air (a lean condition), there is less of a cooling effect, raising the temperature in the combustion chamber. This is one of the reasons why engines will seize when they are too lean, but generally will not seize when they are too rich.

As to fuels, gasoline is a mixture of hydrocarbons and other chemicals, some of which will vaporize more readily than others. Although they vary widely in their intended application, a properly-chosen race gas will have a distillation curve that is tailored to your application. Plus, it will be a more-consistent blend of hydrocarbons than pump gas, which will allow you to jet it more sharply without risking becoming too lean. The end result is that it is easier to eliminate a spooge problem by jetting the bike to run on race gas than on pump fuel.

As to oil ratio, if the bike is jetted properly, all the oil will burn up regardless of the oil ratio used. A bike, properly jetted, could be running 20:1 and not spooging while another bike, improperly jetted, may spooge running 50:1.

 

[Faded]

My understanding is that it is principally oil that did not burn because the temperature in the combustion chamber was too low due to overly rich jetting.

Answer me this...does the oil actually burn? :think:

 

[MikeT]

I think Rich should step in on this one.

I think there are several causes for spooge. I think that the oil does burn and if you get an oil that burns at a higher tempreture than your cylinder achieves, you get spooge. Also if you introduce too much oil due to improper jetting, that can also cause spooge because the excess won't burn.

I will qualify that last statement with JETTING changing the amount of oil, NOT changing your mixture. I firmly believe in running 32:1. I have run 26:1 in the past with good results (no spooge) but switched back to save some $$. 32:1 is tried and true.

 

[ML536]

I think that the oil does burn and if you get an oil that burns at a higher tempreture than your cylinder achieves, you get spooge.

Yes, I believe this is the case as well.

I think Rich should step in on this one.

I would, too.