Small carb pops at steady speed. LOTS OF INFO!!!

[Skyboy8950]

Ok guys,

Last time we try to diagnose this and I am including ALL that I know.

1982 GS850G(Z)
V&H 4-1 exhaust
Dynojet stage 3 jet kit (165 main jets)
K&N Pods
Valve adjustment 6 months ago (checked yesterday and still good!)
Synched (but noticed a spark plug wire fell off halfway through, may not have changed anything)
Used colortune to set mixture screw (on one cyl and set the others to match turns out from bottom).

When I initially did the valve adjustment, many of them were tight enough I couldn't get the .04mm gauge in there. I believe most of these were on the intake side. Ended up with 5 shims I had to buy.

On decel, the muffler pops.

On start, it starts up almost immediately. I put it on choke for 30sec-1min and then it will run just fine.

At low RPMs, when I twist the throttle really far, it doesn't have as much kick as it does +3500 RPM (may be normal).

HOLY CRAP DOES THIS THING ACCELERATE!!! When accelerating hard, nothing bad happens. It is smooth and powerful.

All pipes are hot (just look at my fingertips without fingerprints). They are all firing.

But! When at a steady speed dancing the line between acceleration and deceleration, I get the occasional pop through the carbs. What gives? Why is it doing this? Also, when warming up, I hear a pop or 3. It was worse at one point, seems to be getting better, but certainly not gone.

The only thing I can think of is that the valves were damaged from the valve adjustment being so tight. Is this a likely suspicion? Maybe there is just carbon built up in the valves that is slowly going away with the correct valve adjustment. What do you guys think it is?

Thanks for taking the time to consider my situation.

[reddirtrider]

The carb experts will be here in a few, but my guess is you're running a bit lean. I'd raise the needle one notch.

As for not having the kick at low rpm's when the throttle is opened - that's natural.

[Skyboy8950]

As for not having the kick at low rpm's when the throttle is opened - that's natural.

That's what I thought.

I was suggested to increase jet size one or two sizes up, just FYI.

[reddirtrider]

That's what I thought.

I was suggested to increase jet size one or two sizes up, just FYI.

You may need to do that. Check your plugs after a full throttle chop. That will tell you if they are sized correctly. If they are, and you're still running lean at partial throttle you need to raise your needles.

[Skyboy8950]

Ok, could you explain this:

Needle height adjusts: _________
Main jets adjust: _________
Mixture screw adjusts: ________

I think I know, but I want to hear it from someone who knows for sure.

[reddirtrider]

Ok, could you explain this:

Needle height adjusts: part throttle
Main jets adjust: full throttle
Mixture screw adjusts: idle

I think I know, but I want to hear it from someone who knows for sure.

There are plenty more who know a great deal more than me. I'm not a carb expert. I know just enough to get into trouble and sometimes out of it.

[Stefnwolf]

Ok guys,

Used colortune to set mixture screw (on one cyl and set the others to match turns out from bottom).

I personally would colortune all 4 pots, as there can be differences in each carb, inlet tract, valve, compression etc. that can affect the burn.
Having said that, I don't think it will solve your problem, I just like to be thorough.

Can't hurt though

[Gimpdiggity]

Ok, could you explain this:

Needle height adjusts: _________
Main jets adjust: _________
Mixture screw adjusts: ________

I think I know, but I want to hear it from someone who knows for sure.

Needle height adjusts your mid-range throttle fuel mixture. On a high RPM bike, it will typically adjust about 2k to 7k. However, it's not actually measure in RPMs, it's measured in percent of the throttle used.

Main jets adjust your full throttle fuel mixture. It's what is doing the work when you have the throttle yanked all the way.

Mixture screws adjust the low range throttle fuel mixture. Probably from like idle to maybe 1/8th of the throttle.

All are integral to having the bike run correctly, and the correct way to go about tuning them is to find the correct main jet, then work down to the idle from there.


With all of that said, popping on deceleration is a bit of a different story. When it pops, is it coming out of the exhaust or out of the carbs?? This is important because the two different places are two different issues.

I chased popping out of my exhaust on my Ninja for, quite literally, months before I finally figured out what was wrong. I jetted, and rejetted, and jetted, and rejetted. Probably about 18 different settings, and none of them could fix the problem.

What happens on a bike with pods and such is that when you're accelerating you're letting a TON of air into the engine. When you start to decelerate, those throttle plates in the carbs close and that causes a vacuum to form throughout the rest of the engine. That vacuum is trying to suck air in from anywhere that it can.

What was actually causing the problem on my Ninja was....drum roll please...a bad exhaust gasket.

Yup, I jetted the bike for probably at least 50 hours worth of work and all I needed to do was put in new exhaust gaskets.

See, what was happening was when the engine was flowing during acceleration or steady speed, the whole system was pumping air through it at a constant rate, or an increasing rate when accelerating. However, when I'd let off the throttle and those plates shut, the vacuum would start and it was pulling just a small amount of air through that bad gasket and into the exhaust pipe. That air was mixing with the unburnt fuel that was coming out of the exhaust and igniting in the exhaust, causing the popping sound.

I replaced the exhaust gaskets and put the jetting back to where I originally had it and have never had another pop since.

[chef1366]

The Colourtune was lean for me so I'd take out the idle mixture screws equal turns until the popping on decal stops.
On the popping during riding/Could be a rich condition and unburnt fuel igniting in the exhaust on the redundant spark stroke or lean as mention but I doubt the you'd be lean enough to create a pop (it would create a surging first)
Take a good picture of the spark plugs and it will tell the tale.

[Skyboy8950]

Ok, the small pops at steady speed are through the carbs.

The popping through the exhaust is on decel. I screwed the mixture screws in with the colortune, that is when the popping started.

[chef1366]

It can also pop out the carbs if the intake valve is open during the off stroke spark.

[Skyboy8950]

That is why I thought the valves may be damaged.

[Skyboy8950]

So here is what I need to check:

Going to re-sync tomorrow.
Plug chop at full accel.
If good, plug chop at intermediate level. Might need to raise needle.
Re-visit mixture screw issue after all that.

[Billyboy]

See, what was happening was when the engine was flowing during acceleration or steady speed, the whole system was pumping air through it at a constant rate, or an increasing rate when accelerating. However, when I'd let off the throttle and those plates shut, the vacuum would start and it was pulling just a small amount of air through that bad gasket and into the exhaust pipe. That air was mixing with the unburnt fuel that was coming out of the exhaust and igniting in the exhaust, causing the popping sound.

I replaced the exhaust gaskets and put the jetting back to where I originally had it and have never had another pop since.

This post is awesome!
My bike started popping on decel yesterday and really bad this morning. I just checked my header bolts and the were all loose! Thanks!