slight 'pop' to the exhaust after carb rebuild

Okay guys. I Just rebuilt my carbs, and im very happy with how it turned out!! My number 4 carb was not running before the rebuild so the 4th cylinder was doglegging. I got them all teared down, cleaned and rebuilt and the bikes hauls on the quick ride i took it on. I can not even believe how quick my bike is now!

The only problem i'm seeing at the moment is the exhaust has a very slight 'pop' at idle. It isn't even that audible. The only reason i found it was i held my hand over the exhaust and every 5 seconds or so there's a 'pop' of air thats greater than the idle air coming out.

This is on the exhaust which is linked to carb's 3 and 4. (the problem carb before the rebuild) Is this just because the cylinder wasn't running before that it might just be rough on the strokes of that 4th cylinder?

 

light popping usually means lean. does it pop more when you decellerate?

 

If the Pop is pretty regular ... you ought to be able to Tune it Out.

Tweak the Pilot Mixture OUT ... listening to the rpm's.
If the rpm's INCREASE ... continue tweaking OUT.

Control the Idle with the Idle Adjustment Rod.

Bring the Pilot Mixture Screw OUT until the RPM's NO Longer Rise.
The Exhaust Note should be constant without misfires.
Once the rpm's No Longer rise ... there is a Plateau before further tweaking OUT causes misfire from too Rich.

Tweak each Hole to get Max rpm's ... While controlling the rpm's with the Adjustment Rod if they rise above 1050.

If you arrive at the Plateau and the Bike is Idling steadily without --> Poppity-pop-pop ... Poppity-pop-pop ... leave it there and work on OFF IDLE

When you wrist it open ... if it delays ... it needs a bit more Richness.

 

Thanks rick, I'll give that a try when i get some time.


And to skeeter, Yes it was poping a bit when I decellerate. I'm guessing hat mean's its running lean?

Hopefully I'll be able to tune it out like rick said. I'll give it a shot when the weather improves.

 

yep - the popping means lean. bear in mind, rick's advice is spot on IF you're carbs are CLEAN and your carbs are jetted correctly. however, trying to tune away an air leak or plugged pilot circuit will eventually make screwdrivers fly across the garage.

 

Carbs are squeaky clean, you could eat off them. All stock jettings as well.

 

so where exactly is the pilot mixture screw at?? the top, side or where? I know theres probably a cap plugging it,but i just wanna make sure i get the right on.

 

hmm - if you don't know where the pilot screw is at, then there's some carb parts that didn't get cleaned.

from the factory, there is a little cap installed on them. if the xj550 carbs are similar to my xj750 carbs, then the pilot screw is on the top - directly above the top of the butterfly (when it's closed) if that makes sense.

also stock jetting is good - IF you have stock airbox, airfilter and stock exaust, also.

 

Hiding under here:



You have to Drill the Plug
Its soft Brass
The Screw Head is RIGHT beneath it.
DON'T let the Drill touch the Screw Head

It's better to start a hole ... stick s Drywall Screw in it and Yank that Plug right out of there.

 

Thanks once again, Rick. I took a look at my carbs and the caps are already removed. I know the PO took the bike to the shop to get tuned up every so often.

Now I'm still a little shy about turning these screws. How do I know which one of the carbs needs to be tuned on the pilot screw? how big is the 'sweet spot' that im looking for before i go to far into rich? Quarter turn, half turn?

Still waiting for weather without rain so I can take care of this. I'm just trying to get all my knowledge before I tinker.

 

tuning carbs is like tuning a guitar - there is only one perfect, but the range of "good enough" is up to you.

looking at your spark plugs will tell you what (if anything) to do with each of the screws. search "plug chop" on here and you'll find plenty of reading to do.

before you attempt to turn those screws, you want to sacrifice a screwdriver and grind it so that it will fit the heads of the screws perfectly. you do not want to strip the head out of that screw. i used a screwdriver with a wooden handle so i could saw a mark into the handle to help keep track of exactly how far i've turned it.

to figure out where you're at currently you just turn the screws in until they bottom out, counting the turns and back them out the same number of turns to get where you were.

i believe rick also uses a "deptch gauge" method to measure the current depth of the top of the screw and uses that to return/adjust the screws position (if that makes sense to you)

remember - be careful when you turn those screws, they're a pretty soft metal.

 

Chacal sells a tool that precisely fits these adjustment screws and allows super fast & accurate adjustment. I bought that with the colortune plug from him and I'm completely satisfied.

 

Screw moved easily. I turned out the 4th carb screw 1/2 a turn and the popping went away at idle. took the bike out for a spin ( in the rain ) and there was no popping on decelleration.

The only thing i noticed was when i got her back to my garage and gave it a quick twist, it didnt seem to come back down to idle as fast as before i turned out the screw. just SLOWLY came back to idle speed.

 

During the Dialing-In Phase ... Any movement pf the Pilot Screws --> OUT will effect IDLE.
The Pilot Mixture Screw is an AIR Adjustment, Primarily.
You are allowing more AIR into the Engine ... which ... Draws-up some Pilot FUEL Jet supplied gas ... because the Passages are married.

Obtain the Highest IDLE you can by adjusting the Pilot Mixture Screws OUT.
IF, ... as you turn the Pilot Mixture Screws OUT ... the IDLE Increases ... LOWER the IDLE to 1025 rpm ... (((Or a little bit lower ... if the Bike won't stall))) ... And you will be "Right On The Money" Tuning wise.

Perfect has about a 8 ~ 12 Degree limit where YOU select the Ideal Mixture for the way you want the Bike to run.

A)>Harmful Critical Lean<<<
|High Performance Lean
||Fine Tuned
|||Cruise
||||Long Haul Cool Running Rich
B)>Too Rich Bogging Out>>>

The Vertical Lines before each situation are just-about how much of a Tweak you have to do to change things ... once you're Tuned-up and want to play with it.
The Total distance is about the width of 2 Nickels ... maybe a bit less.

Monkey-choking Dialed-IN!!!

 

Thanks, AGAIN, Rick! Will work on it. I'm just satisfy now that I'm not popping on deceleartion .I'd imagine i'm somewhere between cruising and long haul. Will work on getting it FINE TUNED with time. Just glad i'm running all 4 cylinders now!

 

Ricko: My 1981 550 Maxim runs like a frieght-train[as in great] carbs are all done,and run spot on for acceleration ete. The bike [550] idles smooth at about 1,000-1,100 r.p.m. .mileage is good too----BUTTTT I will still get some popping and burbling in 2nd gear[only] when decellerating. Any thoughts? I check the plugs all the time and they're normal. Otherwise the 550 runs great. P.S. I really don't mind the popping too much ,as it sounds kinda cool-old school. Thanks

 

this thread was VERY helpful, thanks