1976 Running Rich

[Wilsonsk]

Tried the 127.5s this morning, definitely an improvement, the stumbling moved up and covers a narrower RPM range. I switched to the 125s, I'll try that at lunch time, getting there.

I know you (5twins) are not a fan of either end of the 5 groove range on the needle, but given the probability of my needle jets being worn/eroded. I may try that at some point and go back up on the main. Right now I want to stabilize on a decent running combination and just ride for a while and focus on continuing to cleaning up 26 years of shed grunge.
This thing is a true survivor, my favorite kind of old vehicle. I have a 1941 Ford Tudor Sedan that had a '49-'53 flathead put in it in the 70s and was painted at that time, otherwise all ratty and original. Its a daily driver for me. I also have a 1930 Erskine (Studebaker) that had paint and seats done in the 60s but otherwise original, original 107,000 mile 205 inline six. Also a daily driver (my father in law has that now) although top safe speed is about 40 so you can drive it daily, but not far).

 

[Wilsonsk]

125s are really close, still just a little stumble around 5,000. I think I’ll try the 122.5s. The needle is leaned 1 groove from stock. I’ll see how 122.5s work with that and I may try dropping the needle 1 more 1/2 step and put the 125s back in (jets are a lot faster to change than needle height).

 

[Raymond]

I'm just coming in here to say this thread gives good vicarious guidance on setting up a set of carbs. Reading what changes are made, how that affects things, further changes then tried out. I'm enjoying this and just hope I can remember some of it when I need to.

 

[Wilsonsk]

Thanks Raymond, I'm glad someone else is learning, this is my first time attacking tuning carbs, I've avoided it in the past. I've learned a LOT in this process, I'll be coming back to this down the road to review my notes. 5twins has been very patient with me and immensely helpful.

My wife isn't real happy about the process, no matter how much I bathe and wash, I smell like gas.

 

[5twins]

Tell her to look on the bright side - it's keeping you out of the bars at night, lol.

 

[Wilsonsk]

Tell her to look on the bright side - it's keeping you out of the bars at night, lol.

Haha, I'll see how that goes, or may be go to the bar until I don't smell anymore? I try wearing rubber gloves but I always wind up getting frustrated and tearing them off.

 

[Wilsonsk]

I got out and tested the 122.5s, runs about like it did before I started the process, a little misbehaving above 5,000, kind of intermittent, kind of flat, but generally better I think. For a while I will apply the Italian tune up (ride it hard) and run some MMO and/or seafoam through it. I haven't gotten any real miles on it running at speed for any length of time.

 

[Wilsonsk]

I’ve been riding around town, just general riding, runs great, still pulls well on the bottom end. I’m riding it to my property tomorrow, 35 miles over there. I’ll put in fresh plugs and see how they look when I get back.

 

[Wilsonsk]

Forgot to change the plugs and I haven’t looked them yet since I got back. 78 miles 60-65 mph, ~3,500-3,700 rpms. Ran great, still stumbles a little starting around 4,500 through 5,000 or so. Very happy running at 60-65 and has a little something there to pull away without downshifting. I put in a few ozs of MMO and filled the tank with non-oxy. Maybe it’s my imagination, but maybe the MMO is cleaning some crap I missed? It seems like it is running better and stumbling less after the ride, probably more likely that I’m just riding around the issue, either way, runs pretty darn good, shoulda bought one of these 40 years ago.

I’ll pull the tank and drop the needles a half groove with a washer tomorrow, see what that does.

 

[Wilsonsk]

I couldn’t wait til tomorrow, moved the clip to top groove, used 1 .5mm washer. So here is the current configuration.

122.5 MJ
25 PJ
Stock needles and needle jets, clip on top groove, .5mm spacer under clip

The stumble is ALMOST gone, just a hint, it is running by far better than it has since rising from the grave.

So, next step?

1. Remove .5mm washer, drop needle to most lean position
2. Replace existing, old, blackened 122.5 MJs with new Mikuni 122.5 MJs.
A. Maybe the varnish has eroded them and they are a little big?
3. Replace existing, old, blackened 122.5 MJs with new Mikuni 120 MJs
A. Seems hard to believe that’s where I should wind up, but by 5twins process (which has tracked perfectly so far) I should have tried that before dropping the needles another half groove, but I don’t have new 122.5 or 120 MJs.

Next step???

 

[5twins]

Well, I'd consider replacing the needle jets as well. If they're eaten away inside and richer than they should be, that may be why you have to lean the needle so much.

 

[Wilsonsk]

Can you buy replacement Z8 needle jets? Are these the right ones?

 

[5twins]

No, that's the wrong style. You need ones that look like this .....

I thought Niche sold reproductions but I'm not seeing the Z-8 size listed. But it looks like XS650Direct has them .....

https://xs650direct.com/products?show_all=true&category=161&page=4

 

[Wilsonsk]

Awesome, thanks! I ordered 2 needle jets and 2 needle jet o-rings (looks like rotten needle jet o-rings could contribute to this too). Needles are out of stock but I believe less likely to need replacement?

I also ran out and checked the plugs, dark chocolate brownie brown. I took the washers out from under the clips, I’ll get out later tonight or tomorrow and see what it does.

When I get the new jets, should I start with stock middle slot clip position?

Dumb question: Does the needle jet come out up through the bore? Or Down through bowl?

 

[5twins]

The needle jet pulls out from the bottom. It's just a push fit into the bottom of the carb body. You'll notice in my pic that the o-ring groove is very close to the lip that hits against the carb body (on the Z-6 and Z-8) when the jet is installed. For this reason, the jet and o-ring may not want to go all the way in. That's OK, lube it up real good and install the float bowl. That will press the jet all the way in and eventually, the o-ring will work it's way in as well.

Yes, with new jets, I would go back to the stock needle setting (#3 slot).

 

[Wilsonsk]

I took a quick spin, needle is as lean as it can get, clip in top groove. Better but still a slight stumble 4,000-5,000. If I shift in that range it will "burp" when I get back on the throttle, very brief, more audible than anything. I'll get my new needle jets in when I get them, I'll ride it in the mean time. It has maintained or even improved the torque through this process, really happy at 2,500-4,000, nice comfortable power. Big grunty thumper dirt bike.

 

[Wilsonsk]

Went on a 10 mile ride, it is sooooooo close, just the tiniest hint of a stumble around 5 grand. hopefully the new aftermarket needle jet is close to what the stock one is supposed to be, it would be nice to put all back to stock setup and have it work. The pilot must be right on, is close to 90 here, it needs the choke on to fire but you have to turn it off immediately after it does, it will idle just fine, cold, no choke, somewhere around 700 rpms. What a fun bike to ride, probably the best stock seating position of any motorcycle I've ever ridden, I've always wound up moving the pegs back 2-4 inches. I built a 2000 1200 sportster into a scrambler, it had been forward control, I made center controls that were 5 inches back from the stock center controls, no small feat on that horribly asymmetrical motor unit. got it done though. Was a fun project, looked awesome, couldn't gear it down enough for off road and those sportsters don't like to lug so it was a cool looking tall street bike. It sold well anyway. This 650 feels as fast and handles way more nimbly, even though after I got done, the sportster maybe had 20 lbs on the 650, those big heads way up high made it a bear at real low speeds.

 

[5twins]

Yes, most of these require the choke for a cold start, even in warm weather. But as you mentioned, it doesn't need to be on for very long. The bike needs that initial shot of rich mix for a cold start. Although you can run the idle low, it's not really a good idea. The bike won't be charging much (if any) and it will just up and stall at stops randomly. You want to stick to the factory spec of 1100-1200 RPMs hot. It's the nature of the beast to idle lower when cold, and that's OK, just set it so once hot it will be in the 1100-1200 range.

The fact that your old stock pilots are working OK with the needles set so lean without having a flat spot just off idle is telling me that they are probably eaten away and now larger (richer) than their #25 stock size.

 

[Wilsonsk]

Personally, I don't like to run the needles at their extreme ends (last slot) but you could try it I guess. Yes, 5K is the upper part of the midrange to main transition area. Usually, when the main gets too big, you will get break-up in this area (4 to 5K) but only under heavy or full throttle applications. It will usually run through the range OK using light throttle. That's why for testing, you have to use lots of or full throttle. You won't normally ride like this but for testing, you need to do it. These CV carbs are rather forgiving and will mask over small jetting "glitches" unless pushed hard.

This break-up in the upper midrange is usually the limiting factor on how big a main you can run. You "fix" it by leaning the needle a step but if you then go up another size on the mains, that usually brings the break-up right back. So, you have to step the main jet size back down.

Tell her to look on the bright side - it's keeping you out of the bars at night, lol.

Yes, most of these require the choke for a cold start, even in warm weather. But as you mentioned, it doesn't need to be on for very long. The bike needs that initial shot of rich mix for a cold start. Although you can run the idle low, it's not really a good idea. The bike won't be charging much (if any) and it will just up and stall at stops randomly. You want to stick to the factory spec of 1100-1200 RPMs hot. It's the nature of the beast to idle lower when cold, and that's OK, just set it so once hot it will be in the 1100-1200 range.

The fact that your old stock pilots are working OK with the needles set so lean without having a flat spot just off idle is telling me that they are probably eaten away and now larger (richer) than their #25 stock size.

I'll move the idle up some, it's been good at stop signs hot, sounds awesome running that slow, but it makes sense to run it a little higher. The charging system WAS a bit of a concern, back in the 80s, every bike I owned got the "weed burner" headlight bulb, 90/100, back then I ordered everything from Racer's Supply. I ordered the weed burner from Mikes for my XS a couple weeks ago, at that low idle it was 11.9-12.0, at 3,000 rpms on the road, 13.0-13.1, it was keeping up - barely. I ordered the

AUXITO H4 LED Light Bulb Motorcycle, 9003 HB2 LED Light 3000LM 6000K Cool White for Hi/Lo Beam 1860 CSP LED Chips, Pack of 1​

Off of amazon based on a couple of threads on here, VERY bright, VERY white, but I'm now at a solid 13.0 at my sub-1,000 rpm idle and 13.8 at ~3,000 rpms. I just got it today so I haven't ridden in the dark with it yet, but in the dark garage it is pretty impressive. I also have an LED tail/brake light, and I use trailer tail light adapters so my rear turn signals (red lenses) are also brake lights, just like converting a the tow vehicle that has amber, When I use the brakes all 3 light up, I like to be seen as much as possible. I've done this on all my bikes for the past 10 years or so. I also replaced my reflectores with the cheap LED illuminated round reflectors, they are dual so they light up with the running lights as well as brake lights and turn signals, I did the amber ones up front too.

 

[5twins]

Well, if you keep the bike, some charging system upgrades are a good idea. Ideal charging output is in the low to mid 14's, and you're a bit low. Mine was like that when I got it but I never had battery issues, it's enough to keep it charged, it's just not the ideal value. If you still have the original voltage regulator, it's adjustable and maybe that's all that needs doing to bring your max charge rate up a bit. That's all mine took. But eventually, I replaced that "antique" with a more modern automotive regulator (VR115) and now get a nice solid 14.2 volt output.