On some glow plugs I have noticed some have a idle bar and some dont what are the advantages and dis-advanteges?

Here is a link to some answers to your question http://www.rcuniverse.com/forum/m_34...tm.htm#3467875 Hope it helps

Idle bar plugs were advertised to help our engines idle. The idea is that raw fuel might get into the combustion chamber and quench the plug's coil. Actually, the bar is supposed to help keep the engines from dying on idle.

Engine and carb design has improved a bit over the years. Nowadays, most times an engine quits on idle is simply a low-speed needle or airbleed that needs adjusting. Our fuels are a tick better and the engines are a bit better and the carbs are a lot better.

You very probably don't need one nowadays. If you're experiencing poor idle performance, it's probably not the plug being washed out. Do a pinch test at idle before you bother the plug. But if that doesn't work, try one.

Disadvantages?

They sometimes cost more.
The bar has been known to come loose and ruin the piston/sleeve. (Fox idlebars won't do that.)
They don't always fix idle problems. (Which are more often carb lowspeed adjustments problems.)

Idle bar plugs are for people who can't properly tune their engines. The one exception MIGHT be an inverted mounting.

Dr.1

The idle bar plugs were a Duke Fox invention to aid in maintaining ignition on the old cross flow head designes (the state of the art back in the 50's and 60's) and generally are not needed any longer on modern engines.

Cool thanks for all the info.