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Discussion Starter #1
Hi all!

I've been troubleshooting this problem for almost a year now. The bike runs, and I have found a few problems which I've repaired along the way. But here is the overall problem I've been having.

No matter what gear you are in, with the RPM under roughly 2,000, give or take a few RPM's, the bike begins to jerk with 1/2 to full throttle. I've test ridden other GL1500's and none of those bikes possessed this symptom. Once the RPM climbs high enough (above 2,000), the bike takes off like a bad out of hell. If you are cruising along in OD, and partial throttle, the bike accelerates very good. But as soon as you turn the throttle towards half, she begins to jerk until RPM's are high enough. And then I can sometimes smell a very rich exhaust emissions. But to me, I suspect it is a lean condition causing spark knock, especially when using low-grade 87 octane fuel. I've tried using 93 Octane fuel and it improves, but still jerks, although not as bad. It is my theory that I have a lean condition which is causing pre-ignition.

Here is what I have replaced so far:

1. Rebuilt Carbs from Ethanol blended fuel damage (likely caused by BTEX ingredients)
2. Replace a few leaking vacuum lines
3. Replaced secondary air filter which was missing
4. Recently replaced failed Intake Air Shot Air (IASA) Valve due to failure in holding a vacuum per the manuals troubleshooting procedures
5. Replaced air filter

I've also performed the following vacuum tests:

1. PAIR Valve operation - passed
2. Carburetor Control Vacuum test (suspect this might be bad at high vacuum as bike runs very rough when a manual vacuum is applied)
3. Carburetor Sync and Idle Mixture Screw adjusted to about 2.5 turns each - all set appropriately
4. AJ2 and AJ3 Vacuum test - passed
5. PAIR Valve Solenoid Vacuum test - passed
6. Spark test - passed and looks clean and new for a bike with only 39,000 miles
7. Plug Wire Test - passed

At this point, I am completely stuck and cannot seem to figure out why my bike is jerking under 1/2 to full throttle load below 2,000 RPM's.

I noticed also that the PAIR Valve vacuum line that is attached to the intake filter box has a constant vacuum. Place your finger on the vacuum line that is attached to the filter box, and the PAIR Valve intake tube stops making the burrrr noise. Is this normal? Is the PAIR Valve intake tube (attached the front ride side of the filter box) supposed to make a gurgling sound while at idle? And when I close the vacuum hose connected to the PAIR Valve, the gurgling sound stops and no more vacuum can be felt from the PAIR Intake tube (on the filter box)?

Is it possible my intake box is not sealed correctly and causing the carb-slides not to pull back far enough under low RPM?

I am all out of guesses at this point?

The bike has stock mufflers, but previous owner sawed off the baffles, and installed custom end-caps. So the bike sounds like crap and is too loud. Without the back pressure in the exhaust, will this cause jerking or possibly a lean condition? Or as with some of the V-Twin bikes, will the carbs have to be rejetted to a larger size (idle jet maybe) due to the free-flowing exhaust? Could this be causing the jerkiness?

I hope someone here with extensive Goldwing experience can help me out with this. I'm a great mechanic (aircraft and automotive), but this bike has me completely stumped. Even the Honda Dealership couldn't figure it out as they assumed it was the carbs, which have since be rebuilt but to no avail.

Joseph
 

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Those symptoms are more akin to secondary spark. Plug wires, leakage, cracked insulation. If it were a 1200, I'd say you were lugging it. But the 1500 should pull decently even at those rpm's. Connect a timing light to the plug wires and see if the signal gets erratic or goes away.
 

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Discussion Starter #3
Those symptoms are more akin to secondary spark. Plug wires, leakage, cracked insulation. If it were a 1200, I'd say you were lugging it. But the 1500 should pull decently even at those rpm's. Connect a timing light to the plug wires and see if the signal gets erratic or goes away.
Ah!!! Interesting that I never performed that test. So you think perhaps the spark could be jumping from one wire to the next? Wouldn't this also be felt at higher RPM's? Also, I know the bike has never had the timing belts replaced. I wonder if that might be it.

Here is another symptom I've noticed. When I replaced the IASA valve, there are three hoses attached to it; one side has a large vacuum hose with plenty of pull; the other large hose pulses. The 3rd hose is a very small vacuum hose. I believe constant vacuum from the small hose is applied to the valve keeping it closed. But when you snap the throttle closed, the momentary drop in vacuum pressure moves the switch in the open position, thereby allowing exhaust gases to temporarily flow back into the left and right intake manifolds; this allows for a reduction of fuel delivery from the carbs to high RPM deceleration, and also reduces the chances of rear wheel lockup. Once you come to an idle or stop, the IASA valve closes and the engine then receives fuel from the carbs.

Is it normal for the large lower left hose (as indicated on the pic) to pulse the way it does? Meaning neither vacuum nor push is happening from the lower right hose of the ISAS valve....refer to the picture for reference, although the valve depicted in this picture is facing backwards in relation to its actual position when installed. In the bike (installed), the single sided port faces left, and the double ports (small and large) would actually be on the right.

The small vacuum port allows for opening and closing of the valve. The single-port on the left side (in the picture) is the vacuum flow, whereas the large port on the right side is the hose in question that pulses yet neither pushing nor pulling air; just pulses. Is this normal?

I just replaced this valve 2 days ago, and the bikes pulls much harder. However, I'm still jerking below 2,000 RPM under 1/2 to full throttle load.

Joseph
 

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Here is another symptom I've noticed. When I replaced the IASA valve, there are three hoses attached to it; one side has a large vacuum hose with plenty of pull; the other large hose pulses. The 3rd hose is a very small vacuum hose. I believe constant vacuum from the small hose is applied to the valve keeping it closed. But when you snap the throttle closed, the momentary drop in vacuum pressure moves the switch in the open position, thereby allowing exhaust gases to temporarily flow back into the left and right intake manifolds; this allows for a reduction of fuel delivery from the carbs to high RPM deceleration, and also reduces the chances of rear wheel lockup. Once you come to an idle or stop, the IASA valve closes and the engine then receives fuel from the carbs.

You're close but off the mark. What that valve does is allow extra air into the intake on high vacuum situations, i.e. deceleration to keep deceleration from being too harsh. If it wasn't closing it just wouldn't idle and if it didn't open you would probably learn to refrain from closing the throttle too quickly.
 

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Discussion Starter #6
You're close but off the mark. What that valve does is allow extra air into the intake on high vacuum situations, i.e. deceleration to keep deceleration from being too harsh. If it wasn't closing it just wouldn't idle and if it didn't open you would probably learn to refrain from closing the throttle too quickly.
Thanks for the correct. In fact, that was my problem before replacing the valve which had a slow vacuum leak from a crack on the bottom side of the valve. I was going to simply epoxy the crack until I noticed it failed the vacuum pressure test according to the maintenance manual. Using a small vacuum pump, the first test requires vacuum pull be applied to the lower port and the vacuum should hold; it did not hold and leaked down after about 2 to 3 seconds. The second test is to apply vacuum to the upper (smaller) port and apply 5psi pressure to the lower port; when vacuum is released, the valve should open and the 5psi air blows out the opposite side large port on the other side of the valve. The cracked valve functioned but was too intermittent. So I was lucky enough to find a fully functional one on ebay for $24 bucks (new one unavailable/discontinued at $160 bucks), and I tested it before installing the used one; it checked perfect. So now the bike idles much better, whereas before it would fluctuate dramatically between 800RPM to 1000RPM. So replacing the valve solved that problem and also improved acceleration.

Unfortunately, I am still having the jerky problem under 2,000 RPM at 1/2 to full throttle all gears.

Also, before I replaced the valve, you are quite right; I learned that snapping the clutch on high-vacuum RPM causes the rear tire to lock up while in a turn...this happened to me and was quite scary. LOL Since replacing the valve, this does not happen anymore, and in fact my deceleration is very smooth. I do not know what to do if this valve goes bad because I had a hell of a time finding this one. And Honda cannot get a new one because they do not manufacture these valves anymore.

Thanks for the inputs bro. I'm actually learning quite a bit about this bike. Despite what most would believe, I think Honda makes some of the best cruisers on the road; especially the Goldwing which in my opinion is superior to the Harley's. Don't tell that to Harley fans though. LOL I've blown 4 Harley Davidson's off the road so far with my Goldwing; actually beat an Ultra Glide, a Road King, and even a Screaming Eagle.

Long live the Goldwing!

Joe
 

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Discussion Starter #7
Have you checked and cleaned your pulse generators?
I had not considered that yet. Wow! So thanks for the question. I will check that this evening! It's my suspicion however that either I have a sticking intake or exhaust valve on the left head, or possibly the left carb slide may be sticking and not opening far enough (or perhaps too far) under 2,000 RPM. I got it to backfire in the intake yesterday while snapping the throttle open and close several times when jerking. And then POP! Left intake manifold backfired. This seems to suggest a vacuum leak or a sticky intake or exhaust valve. The only reason why I'm suspecting the left carb-slide is because that slide has scratches and gouges on it. When I rebuilt the carbs, I noticed that the left slide doesn't transition in and out smoothly with a sticky point. I wonder if that could be the problem.

Any thoughts?

Joe
 

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You can run the engine with the air filter out and visually check the slide travel while snapping the throttle. If you have a sticky slide hit it with a few shots of silicone spray and work it back and forth with a finger.

When I first bought my 1500 years ago it had a terrible backfire and stumble. Took it to a Honda dealer who charged me $137 for supposedly lubing the enrichment valves (yeah sure) and of course no change. They then said the next step was a carb out service at around $1000. I went home and learned my way around the bike and first thing i found was a broken spark plug insulator. Not noticeable till you rotated it in your hand and watched as it moved. Cracked at it's base it would slide up the electrode and snuff out the spark, cylinder filled with unburned fuel/air then next cycle pop bang. New set of plugs and problem solved. I learned to start simple and pay attention to small details.
 

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Despite what most would believe, I think Honda makes some of the best cruisers on the road; especially the Goldwing

Joe

A Goldwing is not a CRUISER, it is a touring bike.
 

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Discussion Starter #13
Accelerator pump on left carb probably not working correctly. That would give a lean snap accell. And a backfire.
That was my original thought as well when I first troubleshot the problem. Both the left and right accelerator pumps are working as far as I could tell. Both nozzles squirt quite heavily, but the slower you rotate the throttle, the less fuel is sprayed; a sudden twist of the throttle and fuel squirts out.

Joe
 

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Discussion Starter #14
You can run the engine with the air filter out and visually check the slide travel while snapping the throttle. If you have a sticky slide hit it with a few shots of silicone spray and work it back and forth with a finger.

When I first bought my 1500 years ago it had a terrible backfire and stumble. Took it to a Honda dealer who charged me $137 for supposedly lubing the enrichment valves (yeah sure) and of course no change. They then said the next step was a carb out service at around $1000. I went home and learned my way around the bike and first thing i found was a broken spark plug insulator. Not noticeable till you rotated it in your hand and watched as it moved. Cracked at it's base it would slide up the electrode and snuff out the spark, cylinder filled with unburned fuel/air then next cycle pop bang. New set of plugs and problem solved. I learned to start simple and pay attention to small details.
I removed all of the plugs and they looked brand new....and expensive. LOL All appeared to be brass or gold colored. I checked visible areas of the plug wires which all looked good, but was unable to view the wires deep in the engine bay. I suppose I should check that too. But all plugs were torqued properly after reinstalling them, so no leaks. Something is telling me that I still have a vacuum leak that I must have missed. I sometimes wonder if the PAIR Valve (hate the damn thing to be honest) might be either leaking or not functioning correctly. Perhaps I should do another PAIR Valve test.

Joe
 

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Discussion Starter #16
Have you sprayed water on the plug wires?

That will show leaking spark problems fast.

Use a small mister spray bottle.
Gonna try that tonight. I'm also going to make a video and post it on YouTube so everyone can see what it's doing.

Be back soon!

Joe
 

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Discussion Starter #17
Okay folks! Here is a short video of the problem I'm having. I hope you are able to hear what the bike does below 2,000 RPM. I know it sounds like I'm lugging the bike, but keep in mind that it's only 1/2 throttle. And with the cheap fuel that's in it, I noticed the full power doesn't kick in to close to 3,000 RPM on a 90 degree day. Had I filled it up with 93 Octane, it would not have jerked or stumbled as much. This is why I continue to believe this to be a lean condition at or below 2,000 RPM, give or take.

https://www.youtube.com/channel/UCpSc6XQl0XwrhPHLkQbdVww

Let me know what you think guys....

Joe
 

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Good video, beautiful and super clean bike.

When you check the vacuum hoses make sure to squeeze, bend and manipulate them as some splits and cracks may not be visible otherwise.
Also pay attention to hoses that have a preformed bend as they can collapse along the inside radius of the bend.
 

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Discussion Starter #20
Sounded like water in the carbs to me.
Certainly the way it's acting, you would think so. But Carbs are great and clean fuel, non-ethanol. I'm still thinking it's a vacuum leak in the left intake, but I can't seem to find it. Might also be a bad PAIR Valve, so I'm actually thinking of deleting the thing since it's only purpose is to help burn off residual fuel in the exhaust system.
 
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