Running rich

[BLOWCLVL]

OK I have searched this site from top to bottom and found good info. Just not the answer I'm looking for I guess.

So here is the deal. 1980 xs1100 midnight special. I have a custom 4 to one intake I made myself, and custom 2to1 exhaust with baffles. The bike is running extremely rich. How do I know this? Spark plugs are black and sooty and exhaust smells of un-burnt fuel not to mention id be lucky to get 100km on a tank. When I removed the carbs I see that my main jet was a 120 across all 4 carbs. So I decided to clean the carbs the correct way and drop down a size on the mains. tried running again and same deal. I now have 105's as the main on all 4 and still running rich. what exactly can I do to lean this bitch out.

[Bonz]

Is it running less rich with the 105's? 110's are stock on those carbs, so someone had been in the carbs if you found 120's initially. Regardless, something is not right with some part of the set up if 105's are rich. However, the header system could be a wildcard in this and throwing things off. I do not have any experience with custom headers.

As jettng example, I have a 1980 special and live at 7200' of elevation. I have 107.5 mains in the carbs and that works great in this thin air with stock exhaust.

How many turns out our your pilot fuel screws, and what is the float height? Do you know if the jets are genuine Mikuni or ones from another source you got aspart of a carburetor rebuild kit? Let's start there.

The rest of the collective will be along shortly...

[BLOWCLVL]

Runs way better with the 105's pilot screw is 1 turn out. and Float height is around 26 I believe that's stock height. Carbs jets are genuine Mikuni.

[BLOWCLVL]

here is a pic of the bike not that it matters lol

[DiverRay]

OK, so we'll start with the intake. Looks like a side filter into the 4 carbs. How is it connected to the carbs? Is there a lip or something that may be intruding on the intake bell? have the carbs been properly dialed in, ie sync, adjust idle mixture, and re-sync. Has the float level been set properly for the carb type/year?
Almost seems like high fuel level or poor vents.

[Bonz]

Pilot screw one turn out with stock pilots would barely be any fuel at all. Do you know what size pilot jet you have in there, 42.5 is stock.

The questions DiverRay asked are key as well, let us know.

With that said, what are you judging the bike running rich by with 105's, are the plugs still black and sooty? In the grand scheme of things you are only down two main jet sizes from stock with a one-off header and intake system. I bet there is not another one like it on the planet. That's a pretty cool bike!

Keep in the back of your mind, it isn't out of the realm of possibility that you might go down another one or two jet sizes and be just fine, again with a totally custom intake and exhaust like you have.

[BLOWCLVL]

OK, so we'll start with the intake. Looks like a side filter into the 4 carbs. How is it connected to the carbs? Is there a lip or something that may be intruding on the intake bell? have the carbs been properly dialed in, ie sync, adjust idle mixture, and re-sync. Has the float level been set properly for the carb type/year?
Almost seems like high fuel level or poor vents.

Intake box is smooth and connected to the carbs using the stock rubber mounts. Carbs have been synced. Carb level is stock height across all four carbs. Runs the same if I remove the intake completely.

[BLOWCLVL]

Pilot screw one turn out with stock pilots would barely be any fuel at all. Do you know what size pilot jet you have in there, 42.5 is stock.

The questions DiverRay asked are key as well, let us know.

With that said, what are you judging the bike running rich by with 105's, are the plugs still black and sooty? In the grand scheme of things you are only down two main jet sizes from stock with a one-off header and intake system. I bet there is not another one like it on the planet. That's a pretty cool bike!

Keep in the back of your mind, it isn't out of the realm of possibility that you might go down another one or two jet sizes and be just fine, again with a totally custom intake and exhaust like you have.

Stock pilot jet. plugs are black and sooty. Hard crack of the throttle produces large amounts of black smoke. Bike looses power in the higher RPM range. I have not adjusted the slide needle height yet. That is what I'm doing tonight before I drop main jet size again.

[Bonz]

The needles on 1980 model carbs are not adjustable to my knowledge. Is there a jet kit in there? With that said, do you know what position the clip is in on the needles right now since you indicate they are adjustable? That changes things quite a bit it could be needle positioning is the culprit and not so much jetting.

Hard throttle giving black smoke... Does it bog down when you cwhack the throttle, what does it accelerate decently until it gets to higher RPM where it slows down? Another thing to check is the diaphragms themselves do not have holes. That would slow them lifting and cause rich running.

[BLOWCLVL]

The needles on 1980 model carbs are not adjustable to my knowledge. Is there a jet kit in there? With that said, do you know what position the clip is in on the needles right now since you indicate they are adjustable? That changes things quite a bit it could be needle positioning is the culprit and not so much jetting.

I haven't looked at the needles yet. Yamaha dealer said they are but I think they are not. The jets were all replaced by PO with stock mikuni ones.

[BLOWCLVL]

Just had a look at the package the pilot jets came in and they indicate a #45. should they be smaller?

[DiverRay]

YES! If you main jet is smaller than stock, then the pilot should NOT be larger than stock. I'd try a 42.5 first, but you may need to go to a 40.....

[skids]

You made the pipes? Is there anything at all in the tail cone for a muffler? You can try to fiddle with the carbs to compensate, but straight through exhaust can be a problem. Usually 4 into 1's require you to increase mains, but I had a Jardine that went the other way...

The other thing is to find out is which carb circuit (i.e. throttle position) causes over rich conditions. I understand it, you tune the carbs by starting with the mains to color plugs, make adjustments and work down to the pilots. If you didn't use stock rubbers for the inlets, make sure they are not blocking any holes in the carb inlet bells.

[BLOWCLVL]

You made the pipes? Is there anything at all in the tail cone for a muffler? You can try to fiddle with the carbs to compensate, but straight through exhaust can be a problem. Usually 4 into 1's require you to increase mains, but I had a Jardine that went the other way...

The other thing is to find out is which carb circuit (i.e. throttle position) causes over rich conditions. I understand it, you tune the carbs by starting with the mains to color plugs, make adjustments and work down to the pilots. If you didn't use stock rubbers for the inlets, make sure they are not blocking any holes in the carb inlet bells.

Custom pipes but have baffles. It was stock rubbers used and they are not blocking anything. I just ordered a set of 100 mains plus a set of #40 pilots.

[skids]

You said 26 for the floats? You may want to check that again if it is an 80SG.