The last mile.... tuning help

[Ccitis]

At the risk of being annoying, I think I have talked about this before... my bike runs really well when hot... but pops and backfires with enrichener on full and half... seemingly out the left side. Then off choke she idles well, but when cold pops and backfires a bit until it is warm. On the throttle under 3500 it burbles and pops a touch. It pulls really hard to red line and runs otherwise... would just love to iron out the popping and backfiring on the enrichener and when cold. I feel like I am so close. The carbs have been cleaned a whole bunch of times. Including making sure the enrichener bypass ports are clean. I feel like it could be electrical... anyone know the gap for the pickup coil sensors? I did have that apart to repair the wires... could it be a bad coil?

Any help is much appreciated, you folks have been instrumental in getting this old gal back on the road. Here is the video of it running after start and backfiring. https://youtu.be/bkD0g2hx2Tk

[DiverRay]

You probably have a vacuum leak, and also need the idle screws adjusted to the bike. Find and fix vacuum leaks first, if you can.
Ride the bike to warm it up, then park on the center stand with a STRONG fan blowing over the engine.
Starting at the left side of the bike, turn the adjustment screw on the top front of the carb clockwise, S-L-O-W-L-Y until the idle speed starts to drop. Then turn counter clockwise 1/4 turn.
Repeat for the next three carbs, adjusting the idle to keep it about 1,000 to 1,100 RPM.
This should get you closer, until such time you purchase a set of vacuum gauges and can set all four carbs the same.

[DEEBS11]

Ccitis, I'm not sure if you mentioned syncing the carbs. Ray mentions the "Drop Idle Method" of adjusting the pilot circuit which will work fine on the fuel adjustment screws but I don't remember if you lined up all the throttle plates at idle with a synchronizer tool.

[DEEBS11]

The procedure that Ray mentioned. Those of you with Honda V4's will remember this page out of the manual.

[cajun31]

At the risk of being annoying, I think I have talked about this before... my bike runs really well when hot... but pops and backfires with enrichener on full and half... seemingly out the left side. Then off choke she idles well, but when cold pops and backfires a bit until it is warm. On the throttle under 3500 it burbles and pops a touch. It pulls really hard to red line and runs otherwise... would just love to iron out the popping and backfiring on the enrichener and when cold. I feel like I am so close. The carbs have been cleaned a whole bunch of times. Including making sure the enrichener bypass ports are clean. I feel like it could be electrical... anyone know the gap for the pickup coil sensors? I did have that apart to repair the wires... could it be a bad coil?

Any help is much appreciated, you folks have been instrumental in getting this old gal back on the road. Here is the video of it running after start and backfiring. https://youtu.be/bkD0g2hx2Tk

If you plan on keeping the bike you might want to consider buying the tools, if you don't already own them, for doing the job right. The Morgan Carbtune gauges that Deebs has a picture of above is a great tool for synching. I have owned mine for over twenty years which is a testament to it's durability. morgan carbtune pro for sale | eBay Another tool that I have owned for about the same amount of time is the Colortune. Gunson 10mm COLORTUNE #4072 Fuel System Diagnostic Tool - SHIPS FROM USA | eBay. There has been a lot of discussion on this forum over the years and many like it and many don't. I am in the camp of liking it. Ray and Deebs have both explained and illustrated the DROP method. That will get you close as Ray explained. The Gunson product lets you dial the pilot jet screw in. Of course like Ray stated, in order for it to work correctly you have to make sure that you do not have any vaccuum leaks. Leaks make it virtually impossible to get the carbs tuned in. I always rebuild the carbs on all the bikes I acquire. That includes replacing the butterfly shaft seals and I also remove all the intake manifolds to make sure there are no paper gaskets and if there are I remove them. I clean both surfaces on the engine side and the manifolds then apply a coat of yamabond. That ensures there are no leaks. I then use the Gunson Colortune and set each pilot screw to just the hint of an orange flame. That indicates just a tad on the rich side. Makes the bike run a little cooler.

[Larrym]

Right! The running but popping/spitting video! I remember. (ʘ‿ʘ)

Well....like I commented on the vid befOaR, seems to be acting just like a LOT of XS'es I've seen/heard. (_Oo)

AFTER you've confirmed that any and ALL jets in EVERY carb are genuine Mikuni and not the cheeepee Taiwan copy-cats from E-bay? (O_o)7



I call it the "Carb Pagoda". Takes a lot of the clumsiness outta what GOTS to be done. ๑(◕‿◕)๑
(Carbs are wire-tied to the Pagoda and securely attached....)



Seen other ways but....THIS is the way I does it. (◠﹏◠)

I mean it's a "What cannot be shunned must be embraced" situation, right? ¯\_(⊙_ʖ⊙)_/¯

Otherwise yur XS is gonna be HaUnTeD by the popps/barks of the PO's Taiwan parts and fuel levels that IN-NO-WAY are the correct level in the bowl even though they've been double/triple checked fOaR float height wit' a digital caliper. (つ﹏<。)

I mean the Waste-Spark ignition on these engines WILL ignite the unburned fuel left over in the cylinder from a carb with a overflowing/high fuel level and/or an Idle jet that Dribbles/drops the fuel instead'a a fine mist/spray in the correct ratio. (ㆆ _ ㆆ)

That waste spark (and ignition of the left over overly rich mixture) is at he WRONG moment mechanically and can have the engine try to run BACKWURDZ for an instant. ヽ(O_O )ﾉ

Additional photos below show what I FOUND my fuel levels to be. O'course they're set right NOW. ( ‾́ ◡ ‾́ )

[oldyam80sg]

Not mentioned is the vacuum caps- they do split over time and can cause that popping sound-its annoying to hear. Look at them closely-they can be cracked.

[Ccitis]

You probably have a vacuum leak, and also need the idle screws adjusted to the bike. Find and fix vacuum leaks first, if you can.
Ride the bike to warm it up, then park on the center stand with a STRONG fan blowing over the engine.
Starting at the left side of the bike, turn the adjustment screw on the top front of the carb clockwise, S-L-O-W-L-Y until the idle speed starts to drop. Then turn counter clockwise 1/4 turn.
Repeat for the next three carbs, adjusting the idle to keep it about 1,000 to 1,100 RPM.
This should get you closer, until such time you purchase a set of vacuum gauges and can set all four carbs the same.

Carbs are synced using vacuum tool. I hear no change when moving the screws. It is very strange. First bike I have ever worked on where there is no apparent change, even with large movements of the screws.

[Ccitis]

I will search for vacuum leaks. Intake boots are new, as are the carb vacuum caps. There are no apparent leaks. I will keep looking.

[DEEBS11]

Carbs are synced using vacuum tool. I hear no change when moving the screws. It is very strange. First bike I have ever worked on where there is no apparent change, even with large movements of the screws.

Which screws? The pilot screws? If so, your Idle is too high. Lower it so you can get some adjustment. Your throttle plates are open too much and letting in fuel through the emulsion tube/needle. This is why you have no adjustment.

[Larrym]

Carbs are synced using vacuum tool. I hear no change when moving the screws. It is very strange. First bike I have ever worked on where there is no apparent change, even with large movements of the screws.

Yup, Right there with ya as in BTDT. (☉_ ☉)

FoaR the record, my 79 Special ran like the Super bike it was s'posed to be. THEN the "series of unfortunate events" which required I not just clean the carbs but actually re-kit. My bad was to buy/install the cheeepees ones from Ebay. ╮(╯_╰)╭

Ran JUST like shown in your vid and like 4 other XS'es I had the pleasure to ride with in my travels. (☉౪ ⊙)

Just like you, no change or improvement when gauges connected and going thru the motions. (ノ﹏ヽ)

After verifying the ignition parts/systems (list of tests and actions as long as yur arm...) NO faults found. (⩺_⩹)

THEN....I broke out my Test bank of carbs (KNOWN good runnerz!) and swapped them- SuperBike was BACK! \(^_^)/

Ordered the Genuine Mikuni jets, installed in carbs instead of the cheeepees, installed carb bank and THEN the adjustments began to have an effect. (´◡`)

BUT the popping/sneezing was still present at Idle and in the 1.5 to 3.5 Rpm range during the test ride(s). ლ(⋋·⋌)ლ

I had expected the cheeepee float needles/seats to wurky like the OEMs did. WRONG!
（＞д＜）

They did pass the bench leak tests where one inverts the carbs with the bowls off and fills the lines/Tees with fuel. (*´_ゝ｀)

But they did NOT end up setting the fuel level correctly in the bowl in "normal" operation when adjusted to the proper height (25.4mm). ಠ╭╮ಠ

That issue fixed by measuring and viewing the actual/TRUE fuel levels with the carb pagoda with sight tubes. (๑˘︶˘๑)

Just sayin' that after YEARS of enjoying my superbike running like a superbike, I finally encountered the dreaded situation you and so many others are in and suffering from.
( ﾟ，_ゝ｀)

Sharing the way out of it too. (´◡`)