Doctor, Doctor! I need a diagnosis!

Here are the symptoms.

Oil level raised after I drained and refilled the oil, and it smells like gasoline. The oil and gasoline are mixing in the crank case.

Blue smoke. The fuel is burning with oil, it is very very rich.

Black spark plugs. Brand new plugs, just put in, and they are caked with black gunk.


There's too much fuel getting pushed through the engine. Way too much. Enough so that the fuel is leaking down past the pistons and into the engine. I'm thinking that maybe the fuel pump is wrong (it was replaced, It's not the original pump) and it is sending too much fuel through the carbs. Does anyone else have any other ideas? Has anyone had this problem? The pilot screws are set at the factory standard as per the owner's manual. Basically, I need to figure out how so much fuel is being sent through the engine. Any ideas are welcome.

Thank you all,
--Bill G.

 

Did this issue only start after you replaced the pump? If so then you may have too much fuel pressure... If not it could be your rings.

 

I'm thinking it's the fuel pump.. There's so much fuel that the plugs don't even have a chance to burn it all. If a new pump doesn't work, I'm getting new rings. By the way, anyone have any idea what the fuel pressure should be?

 

Sounds like you have a sticking float (or one w/a hole in it) in one of the carbs. Rebuild those carbs and change the oil, then all will be well.

 

A sticking float will do that if you don't turn the fuel petcock off, or if you also have a bad fuel petcock.

 

Replace the Float-valve needles too. Go with Honda OEM for the needles if you can . . .

 

My Yamaha 400 did the same thing. Stuck float needle valves.

Looks like a carb rebuild is in your future.

 

I put the new fuel pump on, and it seems to run better... It still smells really rich, and my spark plugs are jet black. One of them was wet when I took it out, and they're all caked with thick black burnt fuel.

Also, when I rev the engine, the RPMs don't go back down to idle speed. It gets stuck right around 3-4,000 RMPs and I have the idle speed right around 1200. After a little while it returns to normal, but I can never tell when. It just happens.

I've checked all the floats, there are no cracks in them, they seem ok. I checked the float needles. The rubber is still soft and flexible on all of them, and they seem to move just fine. I took the carbs off, took apart the float chamber and tipped them upside down to simulate it's position on the bike, and pushed up the floats to simulate the filling of the chamber. Everything seems to work. Did I perhaps miss something?

Does anyone have any other ideas as to what's causing both the jet black plugs and the high idle speed? You guys have been very helpful, and I really appreciate your input. Thanks again!

--Bill

 

This could possibly be a bad carb sync. Did you bench synch the carbs? If so, how?

Did you check the float level? Are the jets stock?

 

I don't know exactly what the procedure is called, but when I had the carbs on the bench I used the owner's manual to set the openings on the air intake to the specified level. I didn't tune the pilot screws on the bench. I checked the float levels, they're all where they should be. The jets are the ones that came with the carbs. As to whether or not they're the original ones that came with the bike, I have no idea.

 

I'm guessing you checked, but might one of the float bowls leak/have fuel in it?

 

Bench syncing the carbs accurately is very hard to do by eyeing it.

Another method is to use a 3/32" slip of copy paper as a feeler gauge.

1. Set your idle on the #4 carb, snap a the throttle a couple times
2. Open the throttle and insert the slip of paper under the throttle plate - centering it in relation where the plate hits the bore.
3. Pull out the paper and remember how it felt. If you can't remove the paper, up the idle a little more.
4. Open the throttle and insert the paper into the carb throat of #3. Pull out the paper and compare it to #4. Adjust the sync screw until both #4 and #3 feel the same. Snap the throttle shut a couple times and re-do to verify it is the same feel.
5. Repeat step 3 and 4 for carbs #2 and #1.

Note: The paper is sensitive to where you place it in relation to the bore and throttle plate. Make sure it is in the same spot on every carb.

 

Another thing to check is that your brass choke valves are working smoothly. When the choke is closed, you should not be able to push the valves in at all. If you can, either the cable is too tight, or the choke valves need cleaning with #0000 steel wool.

 

I checked the floats, they all seem ok. I'll try that procedure when I take the carbs off again. I'm getting to the point where I might just get new float needles. I'm thinking maybe they are sticking somehow. Would the slightest failure of the needle to close all the way cause the high idle speed? Would gas just be flowing past the needle if it got stuck as it was closing?

 

The gas is getting into the crankcase when it's stopped, not while it's running. If there were that much fuel in the cylinders it would flood the engine and stall it or bend a rod. It's probably a small amount and it could be causing the idle issue. Replace the float valves and all should be good.