Minor backfire on downshift?

[KnoxSwift]

Hey-Ya!

I got my 86' out for the first time since the big rebuild. She purrs and runs EXCELLENT. Real smooth and great power throughout the bands. Everything works and I'm pretty sure I can now pass inspection. I have one issue that I'm a bit stumped on and wonder if this is sort of normal on a GL1200? (This is my first goldwing build).

I however have what I call a Minor Backfire on downshifting and only once in a while it's not every time. I wonder if I have my mixture set wrong? I thought about the Anti Backfire Valve or whatever that thing is called? But I would assume if I installed that wrong it should backfire all the time? It doesn't pop and spit on decel like a bike that is running lean either? It's really weird it's just once in a while one pop or "puff" kind of noise and that's it? Usually happens on downshift from highway speed into an exit or something like that.

I have the carbs set 2 turns out right now, the carbs are synced no smoke like when I first got this bike it was totally set up wrong when I first got it and ran extremely rich, so much so the plugs would foul. So that's sort of why I'm wondering if I have it set lean though it doesn't have the symptoms I normally associate with a lean mix? I really hope I don't have that valve screwed up I kind of don't want to have to pull the carbs again, LOL! But really any help from you all that are way more experienced would be great!

[neoracer]

do you have any minor exhaust gasket leaks?

[KnoxSwift]

I don't think I have exhaust leaks. I replaced all the gaskets on the exhaust and checked it out when doing the rebuild. I didn't see any holes and believe it or not only minor rust...well, I saw two holes but I was told those were "Weep" holes for water? Since your post I made sure all my bolts were to "Spec" as per the Haynes manual and the torque is OK.

I did NOT replace the Slides when I did the carbs because they didn't look dried out or cracked or anything. I read here and there about the Chrome tops and problems. I do have the chrome tops from the previous owner but I don't have any "Standard" ones to try.

How would I know if it's a slide or chrome top issue?

Thanks!

[bluewing]

My bike also has a slight popping sound on down shift at times but I think it is a normal sound. I did have some backfiring on down shift until I synced the carbs and it went away. A friend of mine had the chrome carb tops and it caused a performance issue with them but no backfiring.

[KnoxSwift]

Thanks, I don't have any performance issues (Right now). I think I might search for "Regular" carb tops on Ebay. I'm not sure if my slides are a problem and Randakk only sells the diaphragms so I'm a little leery of changing those out right now? Also since I've personally never experienced a slide issue on any of my bikes I'm not really sure of the symptoms if what I have is worth changing out those parts.

I know the carbs are synced pretty well, if not as close to perfect as I can get them because before the rebuild of the carbs there was a terrible stumble in the power band. It would even stall, Now it is smooth throughout. ALso the bike would run 4 bars on the temp gauge before and now it's 3 bars and 4 only on the hottest of days...

I'll have to keep tinkering to see if I can rid the backfire but if others keep chiming in that it's pretty normal I'll have to maybe not obsess about it as much, LOL! :oops: :-SS

[admin]

You might want to check for minor vacuum leaks in the hoses under the intake manifold.

[KnoxSwift]

Yeah, I'm starting to think I have to pull the carbs again...OY!
I commuted to work today (60 miles one way) and it ran really really well 95% better than when I got the bike. But my gas milage is not close to anything people are posting here? I'm probably around 35mpg. OR maybe I was just to heavy on the throttle (What is the average RANGE per tank on a GL1200?)? I actually had NO pops or backfires on the way to work this AM. I wonder if it's temperature related? I'll find out on my commute home this AM was 70* home it should be 90* again...

I tell you 4 carbs is tough to set up! I've only worked on single carb bikes up until this GL1200...

THANKS!

[admin]

I can go approximately 350 Km or about 220 miles on a full tank of gas. Brake drag, tire pressure, throttle use, engine state of tune, elevation and wind drag can all affect gas mileage. Also, check the vacuum hose that runs from #4 carb to the ECU to make sure that it is in good shape, if leaking you can lose vacuum advance wich will decrease fuel economy.

[garyft]

My gas mileage can range anywhere from about 33 mpg to close to 50, depending on throttle use.

[KnoxSwift]

Hmmm, I wonder if I'm just being heavy on the throttle. People do drive like MANIACs here in NJ and you have to keep your speed up...Average to work would be 75mph...

I think I need to take a weekend ride all backroads and see how my mileage does. i'll check those vacuum hoses when I get home tonight.

All three brakes have been rebuilt, checked, double checked and triple checked because they all were frozen when I got the bike and I'm super nervous about breaks.

Tires are brand NEW. I'm currently running them at 34 front and 38 back...I need to play with tire pressure I'm sure. I'm going off how I like my other bike to ride? What is the general consensus on pressure here? The max on the tires I have is 42psi. Tire balance is good. Shocks and forks are NEW and ride like a dream.

Wind drag...Wasn't too windy this AM.

State of tune this is where I'm second guessing myself. I'll check those vacuum hoses and get a few tanks under my belt.

OH, ONE more question. THere is a label on the bike that states it recommends 91 Octane or better no ethanol. As we all know ethanol is here to stay. I have no choice, BUT as for the 91 Octane Mother Honda Contradicts herself in the manual it says you can run 87? What are everyone's opinions on this? This would effect milage too right? I'm currently running Super (92 or 93 I think).

THANKS!

[neoracer]

87 Octane is correct,anything else you are just wasting money

if it pings alot on 87 it means that you probably have to decarbonize your motor,there are several ways that can be done

your tire pressures are about right

your mileage is probably pretty good for 75 mph,your actual speed is probably about 68/69 if you have the typical wing speedo they are usually off about 10 %

[KnoxSwift]

LOL!, Yeah I think the speedo is off. My GPS keeps crashing so I really couldn't compare..GD Garmin and their crappy software updates!

Anyway, I will go 87 on next fill up and see what happens.

THANKS!

[KnoxSwift]

OK, thanks again all for your suggestions.

I checked all the hoses and vacuum stuff this early AM. I didn't really find anything loose or cracked or missing.

I'm on my second tank of gas (87 octane w/ seafoam) and she's running real nice.

I've also done more research and it seems that when the engine is COLD my symptoms are somewhat normal? that the engine will run rough and pop and sputter when cold?

Also it seems the backfiring is subsiding "some". I've been running SeaFoam through the bike. Is it possible I have a carbon buildup problem from years of no use and just idling? What suggestions do people have for cleaning the combustion area's? I DON'T have a compression gauge to check this "Hunch"? If I wanted to go buy one what size adaptor would I need?

My commute this morning was FUN! This bike is so much FUN and runs soooo smooth and fast above 3000RPM and when it's warmed up...I mean it really really is amazing! I'm so glad to have been able to find this project bike I think the project is coming along...

[KnoxSwift]

Update:

Still need/could use some help? :YMPRAY:

SO , I've gone through everything I can without removing the carbs again...

I've 100% traced the backfire to Cylinder 2 ONLY. And I'm pretty sure it's a backfire through the carb and not exhaust now. It happens mostly around 2100RPM +/- a few hundred on the bike tach (I don't have a shop tach).

SO, The question is, what did I mess up on the carb build?
Or what else can it be?

The bike runs superb compared to when I got it. Smooth and wines through all gears and RPMS quick and powerful. The heavy smoke I had is all gone I might be running just a touch rich, however, The plugs look great! Not black anymore. No oil on them either. No coolant leak either. so don't think head gaskets are an issue. Tank 1 I got 41.6mpg tank 2 I got 37 MPG. I'm on the third tank now and will see what I get for milage...

I can guess a vacuum problem but that comes back to what might of I messed up on just cylinder 2?

Could it still be ignition related? OR carbon related?

I've ordered the wires recommended here by neoracer. I'm also going to continue to run SeaFoam or maybe some Techrcon through it. I'm starting to think NOT carbon build up because it is only one cylinder.

[neoracer]

sounds kinda like same problem i had

wait and see what the sparkplug wires cure

you'll have the wires tomm if you ordered today early enough