Bike running really rich, needles all the way down...

[leggers]

Like the title says.

Ive got a 1975 xs, with stock BS38 carbs. Stock air filters are back on but it had pods when I first got it. PO must have also fucked with the exhaust because its loud. It has full length pipes but I'm assuming its been carved out. She idles like a dream.

Only during take offs, or higher rpms (only on the road) I'm experiencing a sputtering or choking from the bike. At first I thought it might be gasping for gas, but looking at the plugs after a good ride around, I knew right away its running super rich (plugs were black as fuck) its gasping for air...

So I dialed down the needles a notch, things improved. I moved them all the way down (circlip at the top notch of the needle), things improved even more but not completely resolved. I can no longer adjust the needle to reduce the gas mix.

With the carbs synced, timing correct, and cam chain adjusted, I thought maybe its time to mess with the fuel mix screw?

The thought also crossed my mind that if I just put the pods back on it could solve all my problems... Thoughts anyone? Huge thank yous in advance, I've been reading a lot of material on the carbs from the carb section, but not sure how to proceed.

TL;DR: bike chokes up when accelerating, running super rich, needles adjusted all the way down, and I think my pod filters could fix the problem

 

[5twins]

I would check and record all the jet sizes. The P.O. may have jetted way up (too much) for his mods. Putting the pods back on may help a little but airbox to pods is not a major change. I would also inspect the condition of the needle jets. Are they all hogged out and worn oval inside or textured like sandpaper?

 

[leggers]

looks like it has stock jets for a 75.

Z-6 Short main
45 Pilot

Aside from discoloration, needles appear to be in good shape too:

 

[ProSimex]

Hows your spark? weak spark=bad burn=black fouled plugs. Lets see your bike BTW, I havnt seen it ridable on DTT yet

 

[leggers]

Hows your spark? weak spark=bad burn=black fouled plugs. Lets see your bike BTW, I havnt seen it ridable on DTT yet

Well this is the other xs that I have, I did post a vid of me kicking her over a few weeks ago shes pretty rough around the edges but I couldn't resist for 200 bucks. LOL

Spark looks strong on both sides:

 

[ProSimex]

That seems right. It may be possible that the needle has worn grooves inside that is allowing too much fuel to pass. Ive hear of it but never seen it.

 

[Ccrider]

I have the same issue. Stock 75 (bs38's) pipes gutted by PO, (sounds great).
I chased my jetting around, tried k&n pods, now have uni pods (thanks for the tip 5Twins). I'm back to stock jetting with uni pods and needle clip at #2 clip. Right cyl runs rich, left cylinder running good. My next step will b new pipes

 

[gggGary]

What size is the main jet? POs sometimes drill jets larger instead of buying different sizes...............

 

[Ccrider]

Good point, Im going to check this out. I was going by the stamped # on the jets

 

[glennpd]

Check your float height with the depth gauge on your caliper. Make sure your floats are not damaged.

 

[XSLeo]

In post #3 the Z-6 is the needle jet, not the main jet. The main jet is in the float bowl, under the drain plug.
The 75 should have a 127.5 main jet, a 45 pilot jet, the Z-6 needle jet, a 4N8 needle clip in the #4 slot from the top, 25 mm float hieght, 3/4 turn out on the idle mixture screw.
Looking at your pics the needle jet is the Z-6, the pilot a 45 and the needle a 4N8.
Have you read the carb guide.
Leo

 

[leggers]

In post #3 the Z-6 is the needle jet, not the main jet. The main jet is in the float bowl, under the drain plug.
The 75 should have a 127.5 main jet, a 45 pilot jet, the Z-6 needle jet, a 4N8 needle clip in the #4 slot from the top, 25 mm float hieght, 3/4 turn out on the idle mixture screw.
Looking at your pics the needle jet is the Z-6, the pilot a 45 and the needle a 4N8.
Have you read the carb guide.
Leo

I've read the guide, thanks, yes I mis labled that needle jet. I've had the main jet off and cannot read the stamp but I'm assuming that it is a 127.5 I don't have anything to compare the diameter of the jet either, but its possible PO drilled it out. Everything else looks stock/not messed with.

I did put the pod filters back on, and tried leaning the mix screw as a last ditch effort, but that hasn't seemed to change anything . I'm going to order smaller (main) jets from mikes.

http://www.mikesxs.net/products-38.html#products

I'm just going to work my way down in sizes from the stock size (127.5) looking at starting with a set of #125 and #122.5 main jets unless there's a reason to start with even smaller sizes.

 

[XSLeo]

How about float level? Should be 25 mm measured from the carb body to top of float, not from the gasket but where the gasket sets. There is a small ridge in the sealing surface, measure just beside it.
If it is off even 1 mm it can make the bike run too rich or lean.
I'd check that before changimng jets.
Yes, the po could have drilled out the jets. If your buying jets I might suggest buying the stock size. Try that and go from there. Often with pods and an open exhaust you need to go one bigger on the pilots and two up on the mains, but every now and then that doesn't work and smaller does. It takes some experementing.
If you can find a local repair shop that works on ATV's and dirt bikes as well as street bikes they might have an assortment of slightly used jets. Save some cash and they might but back the extras.
Maybe if you took the bike there and they might let you swap jets till you find what works and only charge you for the ones you finally use.
On the jets, a light polishing with steel wool or very fine sand paper can clean off the crud from the surface and leave it in the numbers, this might help you read the size.
Leo

 

[5twins]

Honestly, I wouldn't buy jets from Mike's, they're knock-offs. The beveled part leading into the metering orifice is different than a genuine Mikuni. There's no way to know for sure if they flow the same. They might if you could be assured of exact quality control from one jet to the next but that is not a strong suit of Mike's. I have used his jets in the past when they were like a dollar cheaper than the real deal but now they cost the same. There's no reason not to use the real Mikuni jets.

 

[leggers]

How about float level? Should be 25 mm measured from the carb body to top of float, not from the gasket but where the gasket sets. There is a small ridge in the sealing surface, measure just beside it.
If it is off even 1 mm it can make the bike run too rich or lean.
I'd check that before changimng jets.

You're right, I'll check the bowls first before going forward.

Honestly, I wouldn't buy jets from Mike's, they're knock-offs. The beveled part leading into the metering orifice is different than a genuine Mikuni. There's no way to know for sure if they flow the same. They might if you could be assured of exact quality control from one jet to the next but that is not a strong suit of Mike's. I have used his jets in the past when they were like a dollar cheaper than the real deal but now they cost the same. There's no reason not to use the real Mikuni jets.

Where is the best place to order online?

 

[leggers]

when setting the float level

- setting the float

the guide reads: Holding the carburetor with the floats up, lower the floats
gently onto the float needle, taking care not to compress the float needle spring. Since
the reading is taken with the carb upside down, raising the float level will lower fuel
level, and conversely.

does this mean that I should not let go of the floats after the instance where the tang contacts the needle spring. Because I see the weight of the floats move the needle spring lower after I release it.

 

[XSLeo]

It might be tough holding the floats and measuring. Usually just setting on the pins is ok. If the floats move much after pin contact, as in compressing the spring. Set the carbs on your bench. Tip the carbs over toward the floats untill the floats move away from the pins, rock back and forth a bit to find the point the floats just touch the pin. Hold that position. Measure the height. Some where around 15 degrees from level.
Leo

 

[5twins]

I think the manufacturers take into account that slight pin compression from the weight of the floats when they figure the specs. Pretty much all instructions I've ever seen for setting floats, no matter what type or brand of carb, show this upside down measuring technique. What they don't usually mention, but what I consider important, is to measure from both sides. Many times a float can be twisted or bent on it's mount so that one side sits higher or lower than the other. You must measure both sides to catch this.

 

[weekendrider]

+1 5twins. I think the spring action on the pin is figured and bounce the floats off them to make sure they work. If stuck in or out they won't be working correctly and may cause a false measurement? And sealing problems.
The pita way of measuring floats on an angle, you gotta pay Harley money to have that pleasure.

 

[XSLeo]

I have not worked with as many different carbs as %twins and other carb guru's. I mentioned tilting the carb because thats how Harley tells you how to in the repair manual for my '03 Harley.
Leo