Carb issues

[Crusty Snippets]

I forgot to ask. What have others found to be the best way to run, if the original air filter box, and filter has been removed?

[Patrick1980]

The issues continue for me. I had it running well today after putting a 2x4 under the front tire. I think that may have been luck because then I started it later and it wouldn’t rev up with a quick throttle turn. So I thought maybe it is float height even tho I’m 99.99% sure I have it at 23mm. And also again I took off the pods and saw that gas was coming up through the emulsion tube and over flowing in the carb tunnel behind the butterfly valve. So I thought maybe I should take off the carbs again and try the clear tube method for checking the bowl level. And now I’m even more confused because it looks like the level is super low. I’ll leave a picture of what the first I had time to look at today appeared. So are the float needles that came in my rebuilt kit maybe the wrong size and the float level is not right for me because the oem float needle is different? And again I don’t know how if my float level is low than why am I getting gas coming out as well. Btw it is hard to see the gas level in the line but it is right in front of the black fuel line if you zoom in you can see where it stops

[bikerphil]

I don't know if this has been discussed, but is it possible that you have the type of late carbs that require the use of the rubber plug over the pilot jet tunnel? Is there a passageway between the pilot and main jet tunnels? Carbs get replaced on the rack over time and one may differ from the rest.

[Patrick1980]

I do not believe I have that on any of the carbs but when I change the float height I’ll take out the pilot jet and shine a flashlight and see. Would I be able to see with a flash Light or maybe dragging a pick in there to see if there’s a hole through to the emulsion tube/main jet? I do doubt that this is the case because I did have it running pretty well about a year ago. Also I’m still stumped on my float height and why the 23mm that the service manual calls for is not accurate at all for mine because I heard it should be up to where the bowl meets the carb for gas level.

For the float height I think I’ll just adjust one bowl until I get the gas up to the right spot on the carb then go back in measure the new float height and apply it to the other 3.

[DEEBS11]

Pat, you mention a carb "kit". That does not sound like genuine Mikuni parts to me. Mikuni makes no such kit. Rebuilding a carb with real Mikuni float seats is not cheap. The market is flooded right now with cheap Chinese carb kits that are causing havok with every brand of motorcycle and lawn equipment. What you end up with is a bike that will run but it will never run right.

[bikerphil]

Would I be able to see with a flash Light or maybe dragging a pick in there to see if there’s a hole through to the emulsion tube/main jet?

[Patrick1980]

So I went back again to check some things out
1: I was still confused about my floats so I checked the pressure coming out of my fuel hose to the carb and it was barely any, so I took off the paper in-line filter I had and put in a mesh one I had laying around and then checked the fuel level and it was dead on. On all 4! However it did want to creep up past the correct level on a couple so I need to check the seats and the o ring. Even though they are pretty new.

2: I did go in and check the pilot tower on one of the carbs I was having issues with and it looks like there is no passage.I’ll leave a photo.

3: I saw a YouTube video about the little tab on the float that keeps it from dropping too far when empty so I’ll mess with that too and see if that helps anything. I’ll leave photo.

so the next thing is I’ll take out all the seats agian and the float needle and make sure it’s clean. Should the o ring be greased or oiled?
once I do that I’ll blow air in from the T and see if I’m getting anything passed the needle seat/needle.


I meant to add this earlier but when the needle slide is just sitting there and the needle is in the emulsion tube. Should air be able to get through the main jet into the venturi tunnel or when the slide is all the way down resting is the main jet supposed to be completely blocked off by the needle allowing no air to pass through the emulsion tube?

[bikerphil]

Should the o ring be greased or oiled?

A little motor oil won't hurt anything if it helps the o ring slide in easier. Make sure there isn't any built up crud down there where the o ring sits.

[DiverRay]

Motor oil can cause an early failure on some rubber bits. I like to use a silicon grease, or Dielectric grease. just smear a SMALL amount on the parts before inserting.

[bikerphil]

Maybe silicone spray would be ok too.

[Patrick1980]

An update:

When I was blowing through the straw and slowly rotating the carbs till the floats close I noticed 2 and 4 were sealing not completely and then when fully upside down it would finally seal. It turns out the angle of the floats inward and outward from the middle matters quite a bit. It’s a variable I did not think about before. So then I put the float bowls on once I was happy and checked again for leaking after slowly rotating carbs till closed. And then again different ones we’re doing the slow leak then sealing. So a couple were rubbing on the float bowls and I had to go back in and change the angles again very minimally. And then it was good with the bowls back on.

The other issue was a little stupid on my part but the combination of my tank having barely any fuel in it and the restricting filters I wasn’t getting much fuel into the carbs which made it never run right.

I just took it on the second test ride and it seems pretty good. My after market tach is not yet delivered but I believe when I get to about 4k rpm the power seems to increase a lot. Not sure what that means. The other thing is I get a little burbling after releasing the throttle and engine braking. But as stated by I forget who, that could be an exhaust leak so when the pipes were still hot I tightened them and the lower inside Allen nuts were pretty loose. The akward angle may have stopped me from tightening originally but not they are nice and tight. We’ll see if that changes anything.

Im posting incase anyone has similar issues in the future, make sure nothing is hanging up your floats and you actually have gas!

[Radioguylogs]

It's expected to feel a power surge at 3500 RPM, especially with the '78 and '79 models.