Carb tuning. Did I go too big on my pilot. Am I better or worse

Ok. This is on my TX750. But it's my 72 XS2 carb's. I'm running pod's and a po cut off the pipe's. But the baffle's is still in there.

I'm trying to dial out some popping/crackling out of the exhaust. It does it mainly at idle, or low rpm.

The carb's are fresh. I just did butterfly seals too. From what I understand, this sounds like a pilot jet issue?? I've went from a #42.5, to #45, to #47.5. It did get a little better each time I think. It was hard to tell by the seat of my pants.

The bike has always started easy, and run strong under WOT. But I've had that little popping I'm trying to get rid of.

So today I put in a #50 pilot. Now it's hard to start, and spitting out of the carb's when I try to start it. I didn't get a chance to go on a far enough ride to really get on it to tell how it pulls.

I checked the plug's and they are black as can be. Real sooty looking.

I have my needle's set in the 4th position from the top. Do I just need to change that now. I'd have to say the popping is gone now. But again, it was a very short ride.

I have to have a special wrench for this dang thing to get the valve adjust cap's off. It's on the way. So I'm on vacation next week and will address that. But it has always run very good I think. Except for that little popping.

Am I any closer,, or farther away than I was before. Does it sound like I'm too big on my pilot now. Or do I just need to change my needle setting. Thanks.

Just want to add.

I just went for a ride. I rode it hard. Still runs very strong all the way up to red line. And red line is something you don't want to do with a TX750.

I am now getting some hanging rpm. It takes a while for the idle to come down. It was never like this before. Plug's look good now. I must have fouled them before.

I know there's no love for the TX750. But can you guy's take pitty on a fool.

They're at least XS2 carb's I'm workin on.

My money's on "Too rich".

When I had my panhead, I left the manual spark advance intact, except cable. (Left handgrip controlled spark advance on originals). Rather than locking it at full advance, like most would do, I left it rotatable like stock, and used my right heel to control the advance housing. I'd heard about a 'gee/wow' trick done by the old timers. They would close throttle, retard spark, and get loud pops. Fast forward: Running open dragpipes, nighttime, doing 70 with riding buddies. Close the throttle, heel-shove advancer to full retard, and 3-foot long backfiring massive blue/yellow flames would explode out those dragpipes. Bikes scattered, cars ran of the road, heart attacks, mass hysteria...

I guess backfiring is out of vogue now.

TwoManyXS1Bs said:

My money's on "Too rich".

When I had my panhead, I left the manual spark advance intact, except cable. (Left handgrip controlled spark advance on originals). Rather than locking it at full advance, like most would do, I left it rotatable like stock, and used my right heel to control the advance housing. I'd heard about a 'gee/wow' trick done by the old timers. They would close throttle, retard spark, and get loud pops. Fast forward: Running open dragpipes, nighttime, doing 70 with riding buddies. Close the throttle, heel-shove advancer to full retard, and 3-foot long backfiring massive blue/yellow flames would explode out those dragpipes. Bikes scattered, cars ran of the road, heart attacks, mass hysteria...

I guess backfiring is out of vogue now.

Click to expand...

Are you saying I'mm too rich on the needle's??

If so. Do I need to move the clip's up a groove or two??

Sounds like too rich on the pilot if the plugs are black at idle... Better wait for someone with more knowledge, I'm struggling to learn this right now myself. Moving the clip up on the needle leans it.

Take Warning15 said:

Sounds like too rich on the pilot if the plugs are black at idle... Better wait for someone with more knowledge, I'm struggling to learn this right now myself. Moving the clip up on the needle leans it.

Click to expand...

I wouldn't say they are black at idle. I went for a short ride. I'm thinking it's more in the tuning now,,,, I hope.


Before I put the #50 pilot in, the left side looked like the plug was new,,,which it was. What I mean is the porclein was very white. The right side looked a bit oil dirty.

They both look the same now. I burnt of the soot with the last run. They now have a golden look starting on them. I only rode it a couple of mile's though. So still to early.

Apparently the best way to tell is by getting it up to cruising speed and cutting the ignition. Then look for the color on the insulator. Sounds like you're getting there though with the golden color.

Take_Warning15, DAYUM! You're getting it! Carb thinking engaged...

Ummm. So then do you guy's think I'm close on the pilot now, and just need to trim the needle's.

I just wrote a long dissertation on this, net is getting clobbered, lost it all, get back on this late tonite...

Cal, Takewarning15 is also going thru carb tune. See if you can find his thread, and read the 'systematic approach' post. This should get you in the ballpark.

Short post, don't trust the 'net'...

I watched one of your videos of this bike and noticed it started easily with the choke but stalled when you turned the choke off. When the bike starts idling rough, or "8 stroking" as it's called, with the choke on, that's an indication that it's time to take it off. It seems you can't do that or the bike stalls. I think your pilot circuit still has some blockage. The fact you're going so big on the pilots is also indicating this. One or two sizes up on the pilots is usually the norm.

5twins said:

I watched one of your videos of this bike and noticed it started easily with the choke but stalled when you turned the choke off. When the bike starts idling rough, or "8 stroking" as it's called, with the choke on, that's an indication that it's time to take it off. It seems you can't do that or the bike stalls. I think your pilot circuit still has some blockage. The fact you're going so big on the pilots is also indicating this. One or two sizes up on the pilots is usually the norm.

Click to expand...

Thanks for the reply 5t.

Technically, I guess I only went up 2 sizes. The original pilot size for the 73 TX750 is #45. So I went from 45-47.5-50.

The #42.5 was the size for the 72 XS2. So that one doesn't even count really.

These carb's have been dipped in Berrymans 2 different time's. I then used carb spray.

I will heed your advice and dip them again. This time I will try running a wire or something, if I can find something small enough,,, through there. Then I will blow it out with air. I didn't use air before because I don't have a compressor. But I will borrow one this time.

Thanks again.

So what would you guy's recomend for some type of wire to run through there.

Would a guitar string work maybe.

Hey Cal,
How about post detailed closeup of carb bowl and underside/inside of carb body?

TwoManyXS1Bs said:

Hey Cal,
How about post detailed closeup of carb bowl and underside/inside of carb body?

Click to expand...

Boy. You know how to hurt a guy. There will be no picture's from me for awhile.

Watch the second video.

http://www.xs650.com/forum/showthread.php?t=26988

TwoManyXS1Bs said:

Hey Cal,
How about post detailed closeup of carb bowl and underside/inside of carb body?

Click to expand...

Are you thinking I have a mis-matched bowl and carb body??

You shouldn't need to dip them. I sort of frown upon that and use it only as a last resort. Just do some more cleaning on the pilot circuit, that seems to be the trouble spot. Yes, you need compressed air to do a proper job. A rubber tipped blow gun works well too. Pressed into the openings of passageways, it seals to them and directs a good, full force air blast through. I actually use two, the other being one with a long needle tip. This one is ideal for getting into long, deep passageways, like where the choke jet resides .....



Start with the bowl. Remove the pilot jet. Leave the main and the plug in the bowl bottom. On the side, near the bottom of the "tower" that the jets mount into, you'll notice an inlet hole. This feeds fuel from the bowl to the jets. Cover the main with a finger and blow carb cleaner through the pilot jet hole. It should exit out that inlet hole into the bowl. Now pull the bottom plug out. Cover the main and that inlet hole on the side of the tower. Blow carb cleaner through and it should come out the pilot jet hole. When done, repeat using something mild like WD40 or kerosene to flush all the carb cleaner out.

Now move onto the circuit through the carb body. The fuel/air mix from the pilot jet is fed into the main bore through 4 tiny holes. Three are clustered together and the 4th is off to the side. The three holes flow the mix directly from the pilot jet. The 4th hole comes from the mix screw. The pilot mix goes to (and is metered by) the screw and then out that single hole. That means you have control over roughly 25% of the flow from the pilot jet. That's why mix screw adjustments can only help so much and pilot jet size changes are needed to implement a larger change.

OK, back to the cleaning - remove the mix screw. Dribble or spray some carb cleaner into the pilot inlet on the bottom of the carb body .....



Block the mix screw hole with a finger and blow the cleaner through. Watch for it to exit out the 4 small holes in the main bore. All 4 must be clear for the pilot circuit to operate properly .....



Now add carb cleaner to the mix screw hole. Block the 4 ports in the main bore and blow the cleaner through. It should come out the pilot inlet on the bottom of the carb body. By alternating back and forth, and blocking alternate outlets, you can usually blow things clear with no poking or probing required.

Oh Cal, ohno, ohno! Man, sorry about your camera!

What I heard of your engine noise makes me want to run out there and go all over that thing with a mechanic's stethoscope. I don't like that sound! I could try to walk you thru using stethoscope, or maybe there's already a well detailed doc online, showing the various subtleties and tricks. You can also pull the plugs and rotor cover, and listen closely while slowly forward/reverse rotating the crank a few degrees at a time. My first thoughts were camchain driveline and/or primary driveline. From my experience, wristpin knock is a little different.

Ditto 5twins on the 'choke' observation. The engine should be revving a little higher than that, then start '8-stroking'.