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Here goes:

The sulphur yellow '76 that has been my winter project is oh, so close. After getting things all "buttoned up," I noticed the popping. Occasional decel pops are one thing... It seems to occasionally pop at idle, but up around 3k+ I'm getting a fair bit of popping. The bike is not on the road or under load - yet.

I have read through Tory's thread on popping and a later GL1000: https://www.ngwclub.com/forum/viewtopic ... 35#p821935.

• Carbs are '76 period, split, cleaned, and rebuilt with a Randakk kit.

• Vintage but great condition horseshoe muffler bolted on.

• I synced the carbs on the bike - while running. I'm not 100% happy with it, as I struggled to get any vacuum on any cylinder at idle. I did use Pistol Pete's method for static sync on a rack, which has worked for me on a few other GL1000s.

After noticing the popping problem, I went back almost to square one:

• Rechecked plug gap

• Rechecked/set ignition timing (points, btw), using a split timing method to get as close as possible on both 1/2 and 3/4.

• Rechecked and tighted header bolts.

• Made sure intake boot screws were tight - on hot boots.

• Messed with air/fuel screws, running them in to seated and slowly back out to 2 turns (as recommended). Then I headed back to 1.5 to lean it out a bit, thinking that perhaps unspent fuel was igniting.

I'll check one more thing BEFORE pulling the carbs again:

• Valve lash once engine is again dead cold.

• I should also try to pay more attention to which side has the popping, which might aid in troubleshooting.

I've read about the collapsed header pipe phenomenon, which could be in play.

I do NOT recall popping back around November/December, when I bolted up a GL1100 rack to make sure the bike would run. So that's a thing.

Other ideas?

I would do a compression check and recheck valve lash. I would also make sure the spark advance mechanism is working properly and smoothly. I had an intermittent pop on my '76 GL1000. I set the valve lash 0.001" over the shop spec. I also rebuilt the decel air valve that is attached to the carb plenum. This solved my popping problem.

A stuck valve (intermittent) can cause popping as well. An air leak at the exhaust manifold to cylinder head can cause popping upon deceleration however it should not do this at idle or under load.
-P.

Cliff. Thanks.

I think the rack needs to come off.

I stepped way back to try to move forward:

• Rechecked cam belts. Good.

• Rechecked valve lash and set at .005. Some were pushing .006, which should be ok. But I closed the gap.

• Rechecked plug gaps.

• Rechecked points gaps and timing. I don't think they can be more spot on.

• I removed the top of the air cut valve to make sure I had things in the right way. Confirmed that my hose running from #1 bowl to the cut valve is attached and in good shape.

• Went back and followed Pistol Pete's static initial carb sync instructions (https://www.facebook.com/pistolpetesser ... 573310943/), which have worked well for me on 3 other GL1000s.

• 3 turns out on fuel/air screws.

• Rechecked intake boot screws - tight when rubber is hot.

• new o-rings at the bottom of intakes, with bolts snugged down well.

• Hooked up my carbtune pro and coaxed vacuum pretty close. My hoses kept popping off, as is known to happen.

No popping at idle, so I think that's some progress. But the pops up at/above 3-5k are pretty frequent and seem to come from both pipes. The pops happen while holding steady at 3k, 4k, 5k. They aren't decel pops.

Here's a possible additional clue: I've never seen the vacuum draw as low as it is with this rack. Again, I really did follow Pistol Pete's guide to get #3 set and bring the others somewhat close to 3.
I had to play around a bit blipping the throttle to get the gauge to show much vacuum.

Roll-on throttle response is good, with no notable hesitation. Off-throttle response is also good. (This is my first v. early Wing, and I was expecting an obvious flat spot off idle given all I've read about the value of correcting it. But maybe that'll be something to experience when pulling away from a stop light.)

Unless there are other bits I've clearly missed, I think I've done what I can to isolate the carbs as the likely issue in the pops - or maybe it's collapsed header walls.

I don't want to remove a rack from one of my other GLs to test, but I think I'll want to do that before digging into the just-disassembled-cleaned-and-rebuilt-with-Randakk-rubber '76 rack.

Another update:

• Compression isn't great at 140-145. Bike has 8k original miles and had sat dormant for nearly a decade in an unheated, dirt-floor garage on the Maine coast. Lower numbers are also not unexpected for a motor that has sat for so long, as I understand. 150-165 would be better, but I'm not seeing sub-120 or a notable gap between cylinders.

• I went back and reworked Pistol Pete's bench sync instructions, perhaps with more of an eye on the "slight" movement at #3.

• I also paid attention to guidance about some of the possible weaknesses in the Carbtune device. When I hooked things up this time, I was able to get recordable and stable vacuum at all 4 right away. (It wasn't hard to bring them all to 17-19 cm/Hg on the gauges.) Even if that tool isn't so great/accurate, it appeared to enable me to bring all 4 carbs into alignment. Before, I could swap hoses and struggle to get more than a minimal reading at #3. My guess is that perhaps a combination of pinched hose and inexpert "feel" on the #3 bench sync conspired against me.

At 3k+, I'm still getting about the same amount of popping. I think it's coming out both sides of the bike, but I cannot be certain.

I can also report that a couple plugs do seem to report good-to-lean, while a couple had the black look of a rich condition - even with all 4 air/fuel screws at 3 turns out. I don't hang a lot on what plugs show in a 20-minute run on the center stand with a bit of high revving, but they are definitely two different colors. I may be getting different fuel delivery values through those needles.

I harvested 4 air/fuel needles from another early Wing rack. I'm going to install those in place of the seeming aftermarket ones, set them to 3 turns out, and hear what's what. I don't expect much change.

NotSo, 140-145psi isn’t what I would call bad and am pretty sure the majority of the 75-79 wings would be an improvement with that,,,, particularly after sitting for 1k or so years, it will improve with miles. My 76 from new ran between 135-145psi and remained there pretty much until I advanced the cams +4 degrees and milled .040in off the heads. I wouldn’t worry about it !

On the Carbtune, as I’ve said before I’m not a fan at all ! The OE hoses are pure crap and they have restrictions in them so you don’t need any needle valves for restriction. I believe that the internal restrictions are part or all of the problem. On mine I removed the oe hoses and threw them away and put new vacuum hose on it using the normal fish tank type of needle valves so I can adjust the vacuum pulses down. The next big issue is that the tubes get residue in them which causes the rods to hang up and respond differently and even after cleaning them thoroughly if you connect all the hoses up to a common vacuum manifold and apply a vacuum source to it the rods should all read the exact same but they rarely do,,,,junk gauge in my opinion…. I should sell mine but I feel like I’d be screwing whoever bought it. So it just sits in the storage closet.

Problem Solved!

Culprit: Frozen mechanical spark advance behind the points plate.

I thought I had checked it way back in about early December. Clearly, the advance mechanism didn't like sitting still in a not-climate-controlled environment for a decade.

It took me pulling a good set of GL1100 carbs off my '82 and mounting them to the '76 and hearing the same pops to be firmly convinced that it was NOT a carb issue.

After cleaning up the advance, it worked like a charm. I then spent the requisite 30 minutes dialing in the split timing on 1/2 and fiddling over and over to dial in 3/4.

I started the bike up, and she ran well. After a brief warm up, I rolled on the throttle to 3k and she was smooth as could be. A few minutes later, we rolled on to 4k. Same.

Thanks for all the recommendations, as always.

Now I just need to extract the GL1100 rack and reinstall the one for the GL1000.

*

NotSoLilCrippseys wrote: ↑Sun Jun 01, 2025 8:23 am Another update:

• Compression isn't great at 140-145. Bike has 8k original miles and had sat dormant for nearly a decade in an unheated, dirt-floor garage on the Maine coast. Lower numbers are also not unexpected for a motor that has sat for so long, as I understand. 150-165 would be better, but I'm not seeing sub-120 or a notable gap between cylinders.

Excellent troubleshooting there finding the ignition advancer issue.


If you are utilizing a schrader-type valve checked 14mm hose to 12mm spark plug threads reducer-sans a check valve- I feel you are seeing pretty good compression test cylinder pressure readings. Why?

When I desired to check my '75 GL1000 engine's individual cylinder compression around 2013, I had only my circa late 1960s Fox Valley compression tester. 14mm adapter only. As far as I knew, the new to me engine ran 'good'.. just ride it now

Eventually, after I first time (mid-2015) engine idle speed synchronized the brike's carburetors with the vacuum gauge panel I obtained from robin 1731, I searched ebay and purchased the used snap-on set I have now.
It, of course, came without a 12mm hose. A very good 0-250 psi gauge assembly, several 14mm hoses and an 18mm hose or two populated the slots in the red storage case. This sucks...
what to do now?

I then acquired the go-to set of three aluminum spark plug threads adaptors from amazon to adapt the snap-on 14mm hose to 12mm spark plug threads reducer. With all intake and exhaust valves set at 0.004 inch, my individual test results were 135-ish psi for cylinders 1,3 and 4. To this day I don't understand why cylinder 2 has always recorded ~10 psi greater than the other three cylinders;145-ish psi. At that moment, I was seeing approximately the same often reported 140 psi test results. The engine ran 'good' and variation between all 4 cylinders was 'good', too. okay...forget it and ride

When I unexpectedly discovered the very affordable ebay 12mm snap-on hose, with all 8 valves set at 0.004 inch, cylinders 1,2,3 and 4 compression test results had increased an average of 20psi. 155-ish for 1,3 and 4....165-ish for #2.

Finally, we test at the Nixon recommended 0.006 inch. With the 12mm snap-on hose, cold engine cranking with a fully charged battery, etc, etcetera, et cetera
Cylinders 1,3 and 4 results were 165-170 ish and the cylinder 2 tested multiple times at 179 -ish. At that time, I was testing many times and had noted, especially with the overachieving #2 cylinder, as the pressure was climbing on the gauge face each successive pressure pulse incremental increase was getting smaller. The needle would fluctuate a few times, then suddenly stop advancing any further. After recognizing it had stopped moving, I released the starter button.
I didn't understand why, but it was repeatable. anyways...

I don't have any historical documentation of what 'performance enhancements'
might have been added to the cylinder heads to influence cylinder 2 to outshine its other three mates.
Maybe reworked camshafts (Weber Cams, somewhere in California might have been a source?)
There in a coconut shell is my 2 bits worth of questionable value to most readers

gltriker: no hijacking from my vantage point, so please don't delete.

It's been a hectic couple weeks. And I'm still not happy because I have a '76 that should be on the road but sits in the shed because of this ongoing issue! (It's good that I have more than a few - too many - other bikes to ride.)

Here's the latest:

• I found "a problem" with the timing advance, to be sure. Fixing that calmed down the popping considerably by, umm, eliminating it entirely.

• Thinking I had solved the issue because the bike was just running well, I pulled my 1100 rack and installed the '76 GL1000 set. No joy!

• I have a lazy #1 that is slow to start firing from a cold start - with the GL1000 rack. The header will warm and get there mostly or sort of. I'm using the highly sensitive wet fingers test and not an IR gun.

• Popping is way, way less now, but I'm getting it out of what I think is the right exhaust (#1 misfire 5k lets fuel ignite in the header? Hmm.)

• And I have a wholly new-on-the-scene difficulty coming down when rolling off throttle. It hangs up.

This last issue has me thinking air leak somewhere. I went back to check my intake boots to make sure I had them cinched down. I checked the bolts to ensure a good snug fit to the heads - yes, new Randakk o-rings that aren't pinched. I got out my propane tank and tried spraying it around the intake to see if I could goose the RPMs with a bit of propane. Nothing. Could a slide stuck in the up position be a culprit? The surfaces were cleaned and polished with light aluminum foil. Hmm.

Thinking misfire may be ignition, I again checked spark, again checked timing, again checked the advance mechanism. Plugs are new and good. I trimmed the #1 wire a bit to get a good bite from the end cap. I sense no misfire on #2 and can't see a half-failed coil in a wasted spark arrangement. I see no obvious issue with the #1 wire up to and into the coil.

I pulled some hair out, wiped off some tools, and decided to reattach the GL1100 carbs. I'm trying desperately to ISOLATE things - fuel/air? ignition?

OK. 60 minutes later and the GL1100 carbs are bolted on. Pull choke, turn key, push start. She roars to life.

• #1 header warms up right alongside #3, again using the wet fingers temp gauge. It is immediate.

• Choke off, and she's idling nicely. I could tweak the adjusting screw, but there's no need.

• After the temp gauge moves up out of cold, I start twisting the throttle.

• Immediate throttle response. I run up to 5k. No popping whatsoever.

Great. I have a problem with the carb rack. Couple questions:

• Aside from the intake boots and attachment to the heads, where else might I find a "new" air leak that causes the bike to hang up at 3k? There are lots of possibilities, but it wasn't doing this a couple weeks ago when I was chasing the pops.

• I'm going into the rack again to check my jets carefully to make sure I have OEM Keihin and really inspect #1. I don't know that #1 is my culprit, but the slow to awaken symptom points me there.

• Let's talk air cut valve and the vacuum there. I rebuilt the valve with Randakk's kit, so the rubbers and spring are new. I'll really look into the float bowl end of things when I'm back in there, but is there any reason to think that valve could be a factor here?

NotSoLilCrippseys wrote: ↑Thu Jun 19, 2025 8:04 pm gltriker: no hijacking from my vantage point, so please don't delete. Alright, I'll leave it be

WoW! That's quite the report. So much to compare and weigh in those paragraphs.
Yes, I am leaning towards your suspicion the #1 carburetor is somehow affected/affecting the idle speed behavior of/in the #1 cylinder.

Put your Carbtune engine vacuum synchronizer back to work, again. Won't commit to saying it will discover anything, but you never know. It's a diagnostic tool. Perform another cranking engine cylinder compression test on #1 cylinder, as well

To eliminate concerns of the integrity of the air-cut valve, itself, pull the small diameter air-cut valve actuating vacuum hose completely off its downwards pointing hose barb fitting on the #1 carburetor body fuel bowl.
Cap off the hose barb fitting.
Nixon states its not required anymore when all 4 carburetors' air/fuel pilot mixture screw is set at 3 full turns out from lightly seated.

last thing
I trust you have utilized this remedial information at least one time before now. Just checking
viewtopic.php?t=78104

Cliff. Thanks!

With the rack off the bike now, I think I'll open it up and have a peek inside before going back into some of what you suggest.

I've not seen that Pistol Pete tip, but it sort of seems like what I experienced on the high idle. I appreciate the link to the link, with photos to boot.

After I get the rack installed again, I'll do a re-sync and keep reporting back.

My youngest son (a newly minted graduate with a BS in Mechanical Engineering) reminded me last night that isolating it to the carbs is good because bouncing from fuel/air to ignition as possible causes just leaves too many variables floating around. I think his words were, "That's progress."

Some might recall that he was a reason I joined NGW back when he was in high school: we had bought a dead-to-the-world GL1100 as a winter project (the Blue Phoenix) and used the centuries of wisdom on this forum to help us resurrect it and get it back on the road. We documented the daylights out of that project, and the bike is still going strong! OK. Digression.

Congratulations to your son (and you, too) for his academic success.

I have this topic stirring in the back of my mind while I'm engaged in finding other information re: ignition coil installation details.
The man (you) states he is double-triple checking the breaker points ignition timing. hmmm...

Eventually, I came across something, again, that ties in with a properly grounded contact breaker points assembly and condenser mounting tab/case contribution to the Kettering type ignition system design.

https://www.randakksblog.com/gl1000-con ... denser.pdf

https://www.randakksblog.com/wp-content ... denser.pdf

This bike is still rockin' the OG points/condenser rig. A better ground is easy enough to implement, so thanks. My '79 GL has a Dyna set up, mainly because it had one when I dragged it out of the PO's yard.

I'm just getting into the '76 carb rack but can confirm that the jets for #1 are OEM spec, according to Randakk's table, posted to his Early vs. Late GL1000 carb mixing post.
There's nothing obviously amiss with the #1 carb - jets are clean, emulsion tubes are clean, etc. Float was pivoting smoothly on its pin.

*

NotSoLilCrippseys wrote: ↑Thu Jun 19, 2025 8:04 pm

• Thinking I had solved the issue because the bike was just running well, I pulled my 1100 rack and installed the '76 GL1000 set. No joy!

• I have a lazy #1 that is slow to start firing from a cold start - with the GL1000 rack. The header will warm and get there mostly or sort of. I'm using the highly sensitive wet fingers test and not an IR gun.

DSCN0604 (2) numbers 1 and 3 exhaust headers (1).JPG

DSCN0599 (1) numbers 2 and 4 exhaust headers.JPG

• Popping is way, way less now, but I'm getting it out of what I think is the right exhaust (#1 misfire 5k lets fuel ignite in the header? Hmm.)

Unloaded engine, 5,000rpm, the throttle shutter is only slightly open

Low liquid level in carburetor fuel bowl/lean fuel-oxygen rich mixture's slower rate of combustion in a cylinder is more likely to promote 'popping' in the header when its exhaust valve opens

Great. I have a problem with the carb rack. Couple questions:

• Aside from the intake boots and attachment to the heads, where else might I find a "new" air leak that causes the bike to hang up at 3k? There are lots of possibilities, but it wasn't doing this a couple weeks ago when I was chasing the pops.

• I'm going into the rack again to check my jets carefully to make sure I have OEM Keihin and really inspect #1. I don't know that #1 is my culprit, but the slow to awaken symptom points me there.

I don't suggest loose float bowl screws are present. Please, examine this area, too.
https://ngwclub.com/forum/viewtopic.php ... 17#p826017
and
https://ngwclub.com/forum/viewtopic.php ... 25#p826025 idle discharge port jet
https://ngwclub.com/forum/viewtopic.php ... 27#p826027 #35 slow fuel jet