Tuning carbs after rebuild

[Peanutbutter Nma]

Hey yall,

Looking for some advice before I just start sinking my teeth into this. Sorry for the long write-up but I've tried to keep it coherent.

The bike ran alright but the exhaust temps were definitely different at idle last fall when I got it. Last ridden like 10 years ago, garage kept since. I pulled the carbs and found some pretty awful gore; broken post which I repaired last year, cracked fuel and vent T's, the gaskets turned to dust when I pulled the bowls... It was a mess. Reinstalled the carbs, I could get it to idle but it would slowly lose power and then die. I'm working outside on my porch and the cold was getting to be too much so I stopped for the year.

I started trying to run it again on the first warm day but she wouldn't catch idle. I pulled the carbs to clean them again, just out of diligence and I'm glad I did.

Problem #1: the #1 carb had the idle screw broken off. Don't know if it was like this and I missed it, or if I did it when I was reassembling. Managed to extract the tip, but upon inspection I realized that all of the idle screws were a little deformed and none of them were exactly alike.

Problem #2: the #2 carb's float had fluid in it. I don't know how I caught it, but I noticed the sloshing. It's got a little ding in it, presumably where it leaked.

I got through all the trig I needed to machine a new idle screw when I realized that even if I make it exactly identical, it would be in better condition than the other 3 and I'd have to make all 4 of them to them same level of precision. Instead, I bought this chinesium kit that I though best matched the pictures on the Yambits site without being prohibitively expensive for a full set of floats and idle screws.

https://www.ebay.com/itm/335068202815

My thinking is that the idle screws and floats should all be identical across the carbs, then balanced from there. If I bought an OEM it wouldn't match what's in there. Checking with calipers, it seems like the geometry of the new parts matches with the old but the floats are a little different in weight(9g vs 11g).

I'm replacing all 4 idle screws and all 4 floats. Keeping the same jets. I've never touched a carburetor except to tear one apart off an old mower when I was a kid. No clue what the hell I'm doing, but I'm at least a competent mechanic.

So here's my plan:

-Set float heights dry
-Set idle mix screw
-Bench sync with bread tie
-Float heights wet
-Vacuum sync
-Colortune
-Ride
-Read plugs for more detail


Questions:

I have no idea what the main idle adjustment was set to. Does anyone have a ballpark for the normal gaps under the butterflys?

A lot of the guides and my Clymers say to start at 1 or 1.25 open on the idle mixture screw, but I think that would be a bit lean? Wouldn't I want to start a little rich and lean it out if I'm going to be sitting there fiddling with it for a while?

Anything I'm missing?

Thanks in advance yall, I'm so stoked to get this beauty on the road. If I'm confident she's running well I'm gonna try to bring her to Williamsport in the summer, I'm not too far away!

[DEEBS11]

PBN yes, those kinds of "Unbranded" kits are pure Chinese counterfeit parts with jets that are drilled improperly. Very low quality parts. As far as pilot screw settings I always start with 2 turns out on a fresh carb rebuild and then use the Honda drop method to fine tune once the engine is fully warmed up (15 minute short ride type warm).

P.S. look at how many sold. 20 more sets of ruined carburetors. It's an epidemic in all brands of motorcycles.

[DiverRay]

Please put year and model of your bike in the "auto signature" feature, it helps us a lot.
You have about everything correct in your list EXCEPT the starting point on the idle mixture screws. They should be 2.5 turns out to start.
For the vacuum sync, do you have a 4 gauge set or just a single gauge? I have the 4 gauge set, but still use 1/4" "T" fittings and a hand vacuum pump to set all 4 the same every time I use it.
With a fan cooling the engine, get it started and let it warm up a bit, so you can keep it running without the enrichment circuit.
Set idle speed to 1100 RPM, and then starting at #1 carb, turn idle mixture screw in SMALL amounts until you get the most RPM's from it. I do it by ear, but I've been doing this for about 55 years.
When you're done with #1, do the same with #2, etc. Do blip the throttle a little after each adjustment to settle the idle speed. As you go along, the idle should get higher, so you may need to turn it back down to 1100rpm after every adjustment.
Once done, you then sync carbs with the vacuum gauge, all 4 at the same level. I ALSO check vacuum at about 3,500rpms, to verify all 4 carbs are working together.
You are now done. Give it a ride and see how well it runs. I do not use a clorortune, so I can't say anything about it.

[DEEBS11]

Ray perfectly describes the Honda drop idle method. It works great.

[DEEBS11]

OEM pilot screws.

[Peanutbutter Nma]

Yeah, I don't really trust most of the stuff in the kit... Floats and pointy screws, all of which need adjusted from install anyway? I'm hoping I get away with it lol

I don't have gauges yet. I was thinking of making an octopus contraption with some valves to connect between all the ports. Could you explain what you mean by the hand pump? I thought you hook the gauges up and adjust the sync once it's warm before doing the mixture screws?

Also, where do you guys set your main idle adjustment? Is the bread tie sufficient gap to just throw it on and bring up to 1100 from there?

[Larrym]

Details/Data...... and a Plan??? NOICE!!! (^_^)

1. "The bike ran alright "

THAT's the tell I use to determine iffin a bike already HAS the chinee carb parts/jets installed. ( ・・)

When things are right these bikes are absolute BEASTS. Cliff notes version is that it's likely that the owner BEFORE you bought and installed the Taiwan Kit(s), found out it wouldn't run right, and then gave up tryin' to figure out WTF wuz wrong. That's not "speculation" on my part. Please consider it a "working Theory" until you provide the evidence imma WRONG 'bout it. (-_-)

Translation- ALL JETS GOTTA COME OUT and be replaced with the CORRECT GENUINE MIKUNI fOaR yur make/modle/year. (*ﾟｰﾟ)

2. "Keeping the same jets."

Refer back to above issue #1. (•‿•)

3. "I'm replacing all 4 idle screws and all 4 floats"

Even tho they's chinee the Idle screws have the feature that they's adjustable after the install and have the possibility of working. I wouldn't go so far as to say you could set them to a certain number of turns and then fugget about it. ┐(´ー｀)┌

The four floats have the same feature- adjust after install. That is iffin wut you actually get/got is anything CLOSE to the glossy photos shown before the sale. Provided they ain't got holes in'em and SINK insteada floating the "WET" fuel level checks/adjust should get the fuel levels in the bowls right. Just don't count on the float heights "recommended" by the repair manual being any wheres CLOSE to wut they end up being IRL.

Translation- Build the Carb Pagoda and get set up with the clear fuel lines and fittings in the float bowl bottoms. ┐(´～｀)┌

4. "So here's my plan:

-Float heights wet"

Conspicuosly missing is the 'swap out the old float needles/seats with the NEW float needles/seats." (O_o)

THIS is where the chinee junk parts hit you below the belt. ლ(ﾟдﾟლ)

I swapped installed 4 needle/seat pairs and only 2 actually were capable of sealing/stopping the fuel. The other 2 didn't. DIDN'T stop the fuel at all. ┐('д')┌

Translation- Giv'er a go and be prepared to buy 4 (FOUR) K&L Kits from JetsRus just to get the working float needles/seats that WILL stop the fuel but WON'T actually set the fuel level correct in the bowl(s) when they're adjusted to the proper float height per the repair manual. (ノ_<、)

5. "I'm at least a competent mechanic."

Then get the tools out beforehand to deal with stuck jets. (^_^)

Heat Gun, Propane torch, Ez-Outs, Left Handed Drill Bits, Penetrant, compressed air, AND a special set of scredrivers where you've filed or ground down the ends to the right shape. (O_O)

No translation needed here, right? (O_o)

[Peanutbutter Nma]

All of my jets have the little "square inside a square" stamp which I'm pretty sure is Mikuni right? I've already pulled all the jets and cleaned them before hitting them with compressed air. Unless the brass got damaged in some way, I don't think they'll give me any problems right?

The ONLY things I'm using from that kit are the float and the idle screws. Should I expect that some of the stock floats will leak?

[DEEBS11]

You should have a factory manual. It will help.

[DiverRay]

You can buy a hand pump from Harbor Freight that is for bleeding brakes, etc. that is what I use. The tools are not cheap, but the correct tools can shorten a job buy hours. Look for tools at pawn shops, as you can save money and still get good tools.
Pictures of my bike running with the 4 gauge set.

The plastic "jar" behind the gauges is the fuel supply for the sync.

[Larrym]

All of my jets have the little "square inside a square" stamp which I'm pretty sure is Mikuni right?

The ONLY things I'm using from that kit are the float and the idle screws. Should I expect that some of the stock floats will leak?

Taken frum the JetsRus site-


If true that all are Genuine Mikuni AND the correct size/style jets fOaR the make/model/year of your carbs AND untampered/unmolested with then I, personally, don't see the harm in seeing if they'll wurky. (O_O)

In my own experience, I haven't had the floats themselves go bad as in like develop holes/leaks on their own but I HAVE seen them perforated accidentally. Most often encountered the brass floats SQUISHED by the tech who picks'em up wrong (OR uses compressed air to blow into the bowl to "blow out gunk") and then crushes the sides. THEN they don't have the same volume needed to actually "FLOAT" above the fuel as high as they should. (>_<)


Imma "speculating" that one or mOaR of the float NEEDLE/SEAT pairs will give you trouble and leak. (●︿●)

But you'll catch that before you actually RE-install the carbs iffin you do a benchtest/fuel level test of the carbs using the carb pagoda. ( •̀ᴗ•́ )و ̑̑

[Hecky 48]

PBN yes, those kinds of "Unbranded" kits are pure Chinese counterfeit parts with jets that are drilled improperly. Very low quality parts. As far as pilot screw settings I always start with 2 turns out on a fresh carb rebuild and then use the Honda drop method to fine tune once the engine is fully warmed up (15 minute short ride type warm).

P.S. look at how many sold. 20 more sets of ruined carburetors. It's an epidemic in all brands of motorcycles.

Hello everyone. I come from Germany and have built in this Repair Kit and cannot share the opinion that the scrap is. My XS 1100 with sidecar runs with this kit without any problems. Greetings Horst

[DEEBS11]

I'm glad that your happy with them. What did you do with all the stock Mikuni parts?

[Peanutbutter Nma]

Ah, another benefit of doing the floats on the bench, that puts me at ease. Yeah, I can see exactly where a hole got poked in mine.

Thanks boys, that was exactly what I needed! I'm going out of town this weekend, but I'll definitely be driving with the carbs and my little setup in the trunk. Shouldn't be too much longer now!

I feel like I have access to some ancient arcane knowledge by having you guys as a resource. The guys who can do this kind of work are getting harder and harder to find, people just throw parts at stuff. Thanks again for sharing what you know.

[gtem]

I feel like I have access to some ancient arcane knowledge by having you guys as a resource. The guys who can do this kind of work are getting harder and harder to find, people just throw parts at stuff. Thanks again for sharing what you know.

These "old school" web forums are absolutely worth their weight in gold. Speaking as one of the younger(?) guys here at 36 years old, the older guys that have been around these bikes since they were new are an invaluable resource, sad to say many are of the age that they are passing on now. None of the FB groups or reddit groups etc come anywhere close. I absolutely treasure the "gurus" on here, and hope to glean atleast 10% of what they know!

To echo what others have said, just bite the bullet and buy the good quality OEM Yamaha/mikuni carb parts. You'll just end up chasing your tail until you finally break down and buy the "good stuff" sooner or later anyways. Consider the value of your own time in all of this.