SU carb's

[XYZ]

Can anyone tell me where the fluid in the resevoirs for the carbs goes? These are round-top carbs. Does it evaporate or leak out somewhere, burn up? How often should those things be topped off? I'm mostly a weekend driver so it's not getting daily use.

Thanks

[Royce]

If you overfill them then the excess will be forced out over the top of the reservoir and into the carb then burnt in the engine. Not a bad way to make sure they are filled all the way! Otherwise, if you are using proper oil it shouldn't go anywhere. You should probably check them every 6 months or so just to make sure everything is up to snuff. If you are using something like maybe jack oil, shock oil or sewing machine oil than I suppose it could evaporate from the heat. The manual calls for straight 20w, use oil intended to be used in an engine. You don't want to use anything too light or you will get a lean condition when you stomp on it.

Have fun!

[XYZ]

What about something along the lines of transmission fluid?

[Marty Rogan]

A lot of people use ATF. I use Marvels Mystery Oil in mine. Both are supposed to give you better throttle response.

Marty

[bryantatem]

I have always used ATF. Works GREAT & CHEAP!!!!

[XYZ]

I'm glad to hear ATF is acceptable. It's weird, but it seems on occasion when I put fluid in my carbs it initially fills and then after a few seconds it seems to dissappear and look as if they need to be filled again. About 4 or 5 months ago I was refilling the resevoirs and I must have filled them 3 or 4 times each and they finally started to appear like they would hold their levels. I looked all around the bottoms of the carbs to see if they were leaking but nothing. Perhaps they were just really low. Would this phenomenon indicate an potential oncoming problem?

[bryantatem]

when you fill it there is a bubble created and it has to pop. Therefore it will now be low.

[beandip]

They only need about a tea spoon full each. There are variables that can change the need of different weights of oil. Recommended by the factory 20w. ATF and Mistery oil I have tried and found to be too thin, in my area because it is to warm here in Ore. and it causes me to set the carbs too rich so I can have a smooth acelleration from the start. I have heard of people trying brake fluid, and things all over the board. At least here in temps from 40 f to 110 f the 20w works the best. You hear of faster throttle responce but what thin oil does is cause the piston and needle to rise quicker and so doing it leans the mixture at first because more air is let in and not more fuel untill the air speed causes the fuel to increase. the thicker oil richens the mixture for that moment and then the fuel mixture is increased as the air increases in volicidy and draws the gas out of the jet . With a carb that has no accelerator pump to squirt an ammount of fuel into the throat when the butterfly is openned to add rich mixture this how it is accomplished. I use fork oil from a cycle shop and have been for a couple of years now and all is good. There is a lot of missunderstanding in this area as how these things work. But this is the stright poop.

[XYZ]

Thanks guys. One last question - if you are running a particular type of fluid in the carbs and I want to change to something else can I simply start adding new over old or is there a process of flushing the units and then adding the new?

[JEFF]

Adding new over the old is fine in my opinion

- Jeff

[beandip]

That should not be a problem the excess will just be burned in the engine, remamber it only takes about a tespoon full to fill the unit, if you look closely on the plunger that is attached to the black plastic nut, you will see a line that is the fill line. Gary