L18 problem

[zed]

Driving over the mountain this morning, my Hardbody with L18 and Nikki carb slowly lost power on hills, then died. Didn't jerk like when plug wires or condensor go bad - only ran with less and less power, then died. This happened twice. Each time I waited 10 seconds, and it started and ran again, no problem. Now at home - it's running fine. I'm wondering about flooding - because when I stopped at home the fuel level in the carb was a few mm above the line on the carb glass. I pulled the plugs - they were black/sooty - maybe unburned fuel? Does this seem like flooding? Seems strange that the motor would flood while running hard - surely it would just burn the extra fuel? For what its worth I changed cap, points, plugs, condensor, fuel filters. Blew down the line to the tank. I know nothing about carbs ... Any advice would be appreciated

[DanielC]

The fuel level must stay on the line on the sight glass on the carb. The carb is calibrated to that level. If it is too high, too much gas runs into the engine. That will turn your plugs black, and it also wastes a lot of gas.

 

Is the float itself brass looking, or a black plastic? if it is brass, it is hollow, and may have some gas inside it, from a leak. Also the needle valve and seat may be bad. Sometimes a small piece of dirt will get caught in the needle and seat, and hold it open.

[H5WAGON]

So this only happens on hills?

 

Check your float level in the carb.

[zed]

the float in the carb is brass. The motor died on hills, but lost power downhill too. Surely it would burn the extra gas?

I built this motor - but I have never opened a carb. Am afraid to screw it up. Is there an easy way here? What about taking off the aircleaner and spraying carb cleaner into the carb? thanks for the replies

[Farmer Joe]

welll, the nikki, is it like a hitachi of later years?

 

do you have a pic of the carb?

 

it shouldnt be that hard to adjust the float on the nikki.. im not too familiar with them tho.

[H5WAGON]

If you know what the eccelerator pump looks like, it may leaking?

 

Can you post a picture of carb with air cleaner off?

[zed]

I know the accelerator pump - like a small leather cup on the end of a brass rod. I'll have a look at it. I'll get some photos tonight. thanks

[DanielC]

An engine can burn gas from about a 12 to one ratio to about 15 to one ratio. 12 parts air, 1 part gas. More gas than that, and the mixture does not burn. Not enough air. Less gas than 15 top 1, and again, there is not enough gas to burn, it "misfires". This condition is called "lean misfire".

 

Your carb is basically a pipe, that air goes through, with a pinhole on the side, that gas goes through. The float, needle and seat, and float bowl hold the level of the gas just below the pinhole in the side of the pipe the air is going through. When the engine draws air through the pipe, it sucks a little bit of gas through the pinhole, and if everything is calibrated properly, the engine runs good. This system even adds more gas when more air is drawn through the pipe.

But everything is calibrated to the precise level of the gas in the float bowl. That must be correct.

 

"What about taking off the aircleaner and spraying carb cleaner into the carb?" This will clean gunk out of the "air pipe", but will not get to the float system. The float system is outside of the air pipe.

 

"The motor died on hills, but lost power downhill too. Surely it would burn the extra gas? Too much extra gas is too much extra gas. It will burn up to a limit, but especially going down hill, it is hard to open the throttle enough to allow enough air to burn the extra gas. Too high of a float level, will,be more of a problem going down hill.

 

The carb is not impossible to fix. You can do it, be careful, and watch for very small parts. take notes, or pictures of it before you start. An old egg carton makes a good holder for small carb parts.

 

"but I have never opened a carb. Am afraid to screw it up. Is there an easy way here?" The float system is one of the more accessible systems on the carb. Look at your carburetor, and where the fuel line goes to the carb. The rubber fuel hose goes to a pipe on the side of a round thing held to the carburetor with a bolt. This is called a banjo fitting.

take the fuel hose off the fitting, by loosening the hose clamp. Twist the hose, and then pull it off. Some gas may leak out. No smoking while you are doing this.

After the hose is off, remove the bolt on the top of the banjo fitting. You may have to remove a retainer held by a screw next to the banjo fitting.

Lift the banjo fitting straight up. There might be a screen in there. After removing the banjo fitting, and the screen, you will see another hex right next to the carb body. It also unscrews. This is the needle and seat. It could be bad, or it could just have some dirt stuck in it. wipe as much gas off it as you can. If you look at the bottom of it, there is a small pin that moves up and down. The float pushes this pin up into the seat, and shuts off the flow of gas. Blow gently through the top of it, and gently push the pin into the seat. It should stop air being blown through it.

Do this with your mouth. Compressed air is way too much, it may just blow every thing apart, and scatter small parts all over the garage.

 

Put everything back together. See where the gas level is on the sight line.

 

If is is still too high, there are three screws that hold the cover for the sight glass on the carb. Remove these screws, and the cover. There is a paper gasket under it. The glass will probably still be stuck to the carb body. Carefully remove the glass. There is a little brass spacer on the pin the float pivots on. Remove it, and then you can slide the float off the pivot. if the float has any liquid in it, it is bad, and needs to be replaced.

[zed]

thankyou for the detailed post. I will give this a careful try

[ggzilla]

Don't take the carb apart! First, look at the fuel level. There is a sight glass on the side (Nikki or Hitachi). If the level is correct (or close) don't take it apart.

 

 

The problem could easily be ignition system . if it was fuel it wouldn't run good but have less power. It would start running rough.

[zed]

got the needle & seat out last night - first time I ever opened a carb. Enjoyed it! even got to see the jets for the first time. Found a ridge on the steel needle, polished it very gently with 1200 grit, cleaned and re-assembled, and did a 50 mile trip this am, running sweetly. will now get a new needle and seat to replace. Thanks to Ratsun, once again

[DanielC]

Good job! Now that was not so hard, was it?