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Old 03-04-2013, 06:04 PM   #1
bmwhacker OP
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Location: MONTANA NATIVE from NATIVE MONTANA
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Honda GL 1000 "Backfire" Mystery

Anybody got some Cheese that I can have with my Whine?

History -
Bike: 1977 Honda GL 1000 - 43k miles. Engine rebuilt a few thousand miles before I acquired it last Winter. I've ridden it about 3000 miles. Runs great, starts instantly, smooth as silk. 36 - 44 mpg. No smoking or oil use. No problems until.....
During a trip through the mountains / Yellowstone last summer, the bike started "popping" through the right exhaust, especially during decceleration. Occasionally during a constant throttle position it will also "pop" through the right exhaust.
I made some inquiries on a "Gold Wing" forum and got lots of advice. So far I've:

1) Checked exhaust valve clearances. They were dead on...I opened the exhaust valve clearances an extra .001 from spec. for good measure.

2) Replaced the (still as new) spark plugs, the plugs which were in place were gapped at .035. Stock gap is .026 with points. regapped a little wide @ .032 due to Dyna electronic ignition as recommended by the Gold Wing "Experts".

3) Checked & tightened all the clamps / bolts / connections / hoses in the intake system. sprayed ether around all the connections prior to removal / after retightening. No RPM change noted. All the rubber intake tubes look to be new.

4) Loosened / retightened all the exhaust manifold nuts, then removed the right side and replaced the right side copper exhaust manifold o-rings. The old ones looked good.

5) Removed the "Air Cut - Off Valve" (which everyone was telling me was the problem). The valve consists of a diaphragm / small spring and 2 o-rings. Everything there looked as new, and the small vacuum line to it looks good. Maybe I should replace it even though I can't find anything wrong with it? It was probably replaced when the bike was rebuilt a few years ago. The bike went through a frame - up restoration.

6) Bought a decent compression gauge and checked cylinder compression. All were from 140 psi - 145 psi.

7) Ran some "Sea Foam" through with a few tanks of gas...no change....also ran some "Marvel Oil" for a few tanks, no change.

8) Readjusted the idle mixture screws to "2 turns" or highest idle as recommended.

9) Finally after 2 months of fruitless tinkering, bought some better ear plugs to dull the "popping" sound. Drove 1000 miles in 2 days. The bike starts easily cold, runs fine, normal engine temperature, no smoke, no oil use, no leaks.

What am I missing here ???????
I'm getting frustrated and pissed off at this Honda.

Maybe I'll just start over again and re-perform all the things I've already done., Can't think of anything else to do.
The one thing I haven't done is mess with the timing. Don't have a special device needed for that.
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bmwhacker screwed with this post 03-04-2013 at 06:20 PM
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Old 03-04-2013, 06:20 PM   #2
SOS
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Quote:
Originally Posted by bmwhacker View Post
History -
Bike: 1977 Honda GL 1000 - 43k miles. Engine rebuilt a few thousand miles before I acquired it last Winter. I've ridden it about 3000 miles. Runs great, starts instantly, smooth as silk. 36 - 44 mpg. No smoking or oil use. No problems until.....
During a trip through the mountains / Yellowstone last summer, the bike started "popping" through the right exhaust, especially during decceleration. Occasionally during a constant throttle position it will also "pop" through the right exhaust.
I made some inquiries on a "Gold Wing" forum and got lots of advice. So far I've:

1) Checked exhaust valve clearances. They were dead on...I opened the exhaust valve clearances an extra .001 from spec. for good measure.

2) Replaced the (still as new) spark plugs, the plugs which were in place were gapped at .035. Stock gap is .026 with points. regapped a little wide @ .032 due to Dyna electronic ignition as recommended by the Gold Wing "Experts".

3) Checked & tightened all the clamps / bolts / connections / hoses in the intake system. sprayed ether around all the connections prior to removal / after retightening. No RPM change noted.

4) Loosened / retightened all the exhaust manifold nuts, then removed the right side and replaced the right side copper exhaust manifold o-rings. The old ones looked good.

5) Removed the "Air Cut - Off Valve" (which everyone was telling me was the problem). The valve consists of a diaphragm / small spring and 2 o-rings. Everything there looked as new, and the small vacuum line to it looks good. Maybe I should replace it even though I can't find anything wrong with it?

6) Bought a decent compression gauge and checked cylinder compression. All were from 140 psi - 145 psi.

7) Ran some "Sea Foam" through with a few tanks of gas...no change....also ran some "Marvel Oil" for a few tanks, no change.

8) Readjusted the idle mixture screws to "2 turns" or highest idle as recommended.

9) Finally after 2 months of fruitless tinkering, bought some better ear plugs to dull the "popping" sound. Drove 1000 miles in 2 days. The bike starts easily cold, runs fine, normal engine temperature, no smoke, no oil use, no leaks.

What am I missing here ???????

Now, I'll just start over again and reperform all the things I've already done., Can't think of anything else to do.
The one thing I haven't done is mess with the timing. Don't have a special device needed for that.
I have a 1976 GL1000 with a lean pop on the left side. I have not eliminated it yet and I'm curious to see what comes up. The air cut off valve on these bikes will affect all the cylinders, no one side or the other.

One item might be that one of the pilot jets got clogged. Mine only does it on deceleration. If yours does it at throttle it could be a piston slide haging up. Maybe the piston or possibly the air jet or vacuum lines.
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Old 03-04-2013, 06:30 PM   #3
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Quote:
Originally Posted by SOS View Post
I have a 1976 GL1000 with a lean pop on the left side. I have not eliminated it yet and I'm curious to see what comes up. The air cut off valve on these bikes will affect all the cylinders, no one side or the other.

One item might be that one of the pilot jets got clogged. Mine only does it on deceleration. If yours does it at throttle it could be a piston slide haging up. Maybe the piston or possibly the air jet or vacuum lines.
I'm pulling my hair out! (what little I have)
Mine will "pop" sometimes during warmup at idle, and then while running from time to time. Gets worse after running down the road and getting to the hotter running temps. It's my only currant solo bike so I'm running it with the issue anyway.
Back to the drawing board.
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Old 03-04-2013, 10:47 PM   #4
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Decided to purchase a new "Air Cut Off Valve" since many of the Honda "experts" say to replace it, regardless of its' physical appearance. It is a fairly cheap part, under $25.00, and replaces all the o-rings, diaghragm, and spring. Grasping at straws and this is an easy replacement. .

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Old 03-04-2013, 11:06 PM   #5
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Check that side's carbs. Partial blockage or diaphragm tear sounds possible.
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Old 03-08-2013, 07:32 AM   #6
LonerDave
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On my '77, seem to recall shimming needles up a bit with a washer or two in order to cure off-idle stumble. The stumble occurred as a result of a lean condition, so maybe that's what's causing popping? Shimming needles is Randakk's idea and worked for me.

Just my 2 cents.
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Old 03-10-2013, 07:11 PM   #7
sraber
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No experience with your Gold Wing but I have had popping on deceleration from a open vacuum line on a Hayabusa. It's worth a check with a vacuum gauge to isolate a possible leak. Good luck.
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Old 03-10-2013, 07:21 PM   #8
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Quote:
Originally Posted by sraber View Post
No experience with your Gold Wing but I have had popping on deceleration from a open vacuum line on a Hayabusa. It's worth a check with a vacuum gauge to isolate a possible leak. Good luck.
Thanks for the input...got a new "Air Cut Off" valve but haven't installed it yet.
I visited on the phone with a top notch independant Honda mechanic the other day....he kind of chuckled when I described the problem. I know that he knows exactly what the problem is....but I'll have to pay him to fix it. No free info. from him! I was hoping he would give me at least a little hint...no such luck.
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Old 03-10-2013, 08:31 PM   #9
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...good riddance "Old Blue"....after over 60 hours of labor.

This old GL1100 belongs to an aquaintance of mine. One of his $250.00 finds. I told him I would "help" him bleed his brakes. Well, that led to complete over hauls of both master cylinders and all three calipers, which were completly "stuck" and full of dirt...Then he asked me to get it running for him, saying it "ran like a sewing machine" when he started it a "while" back.




Tried to start it and found the fuel filter clogged with rust...pulled the tank float assembly and saw nothing but rust in the tank.
Pulled the carbs off and lo and behold: No way this thing has run for years....



Since he is dirt poor, no carb rebuild kits. I pulled each carb apart and cleaned up every thing as best I could. One slide was "gummed" up tight but actually the carbs weren't too bad considering.
I reassembled with no new parts and rigged up a remote fuel supply. The bike fired right up but still has idle issues. Probably more "crap" in an idle circut somewhere.



Pulled the fuel tank, which is not a real "friendly' job on a Gold Wing. Flushed the tank with a LOT of water. Dumped a handful of big angular rocks in the tank and shook til I was blue in the face....more flushing...more shaking. Then filled it to the brim with vinegar. vinegar works pretty good eating away at the rust. Flushed and refilled a few times. Ended up with a fairly clean looking tank, although the "reserve" line is still plugged with debris.
Reassembled to the state you see in the first photo. Actually rode the thing around the neighborhood a few times.

Moral of the story:

Beware of volunteering to adjust someones brakes.
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bmwhacker screwed with this post 03-11-2013 at 09:58 AM
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Old 03-11-2013, 06:52 AM   #10
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Popping on decel can be from something as simple as the internal baffles in the exhaust rusting/burning out. Most standard mufflers mute popping to pretty unnoticeable levels, but once the baffles start to go it becomes noticeable. Is the bike any louder? It doesn't have to be much, and it looks like you've checked all the usual culprits. Popping on deceleration or overrun is normal for many engines, but you simply can't hear it with factory exhausts.
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Old 03-12-2013, 05:15 PM   #11
Andyvh1959
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+1 to the previous answer. Popping is normal, more normal now than ever. I perhaps missed it, or maybe you detailed it, but is the exhaust stock or has the exhaust been modified in any way that the bike "breathes freer" than before. As in, a more open exhaust?

Most all exhaust mods, intentional or age induced (rot holes) tend to lean out the fuel mixture going through the combustion chamber. Popping, or an increase of popping is the result. Modded exhaust without sufficient volume/baffles to "dampen" out the popping means you hear more of it. Now, if the popping on decel stops immediately when you pull in the clutch and coast, then you know it is simply a closed throttle/decel lean condition which is not harmful to the engine in any way.

Now, gimme a minute to climb up on my soap-box and rant. Lean condition decel popping is NOT backfiring, never has been and never will be. To decribe it as backfiring is incorrect because that defines it as a condition correctable by correct timing (ignition and valve) or fixing an ignition/timing issue. REAL backfiring is the engine spitting BACKWARDS out the intake. Its almost totally unheard of these days of modern ignition systems, and is only related to ignition timing or valve issues.

There, rant done, climbing down. An air leak on the intake manifolds can cause excessive popping. Same for rotted/modded exhaust. Install a Dynojet or K&N jet kit, and the bike will start easier, warm up quicker, runs STRONGER, not pop in closed throttle decel, and still get great gas mileage. The lean condition on decel is all done to suit emission regulations. So, richen up the fuel to air ratio and bye bye pop!
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Old 03-15-2013, 09:41 PM   #12
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Quote:
Originally Posted by Andyvh1959 View Post
+1 to the previous answer. Popping is normal, more normal now than ever. I perhaps missed it, or maybe you detailed it, but is the exhaust stock or has the exhaust been modified in any way that the bike "breathes freer" than before. As in, a more open exhaust?

Most all exhaust mods, intentional or age induced (rot holes) tend to lean out the fuel mixture going through the combustion chamber. Popping, or an increase of popping is the result. Modded exhaust without sufficient volume/baffles to "dampen" out the popping means you hear more of it. Now, if the popping on decel stops immediately when you pull in the clutch and coast, then you know it is simply a closed throttle/decel lean condition which is not harmful to the engine in any way.

Now, gimme a minute to climb up on my soap-box and rant. Lean condition decel popping is NOT backfiring, never has been and never will be. To decribe it as backfiring is incorrect because that defines it as a condition correctable by correct timing (ignition and valve) or fixing an ignition/timing issue. REAL backfiring is the engine spitting BACKWARDS out the intake. Its almost totally unheard of these days of modern ignition systems, and is only related to ignition timing or valve issues.

There, rant done, climbing down. An air leak on the intake manifolds can cause excessive popping. Same for rotted/modded exhaust. Install a Dynojet or K&N jet kit, and the bike will start easier, warm up quicker, runs STRONGER, not pop in closed throttle decel, and still get great gas mileage. The lean condition on decel is all done to suit emission regulations. So, richen up the fuel to air ratio and bye bye pop!
Excellant Rant!
You hit it right on, as it is not a "backfire" per say. I'll look into the "lean condition" scenario.
The exhaust is definately a more "open" system than stock , even though it is baffled and fairly new.
I have been "baffled" by the fact that the condition didn't start until after I had ridden the bike for a couple thousand miles after purchasing.
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Old 03-16-2013, 01:25 AM   #13
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Originally Posted by bmwhacker View Post
I have been "baffled" by the fact that the condition didn't start until after I had ridden the bike for a couple thousand miles after purchasing.
It will be the pipes. They get crackly once the packing in the cans starts to settle in after a few thousand miles.
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Old 03-16-2013, 07:00 PM   #14
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Popping

Sounds like a lean mixture. Where did the bike come from? What is the altitude? Is it at the same altitude now or when the popping started. If lower altitude all main jets may have to be changed. Mixture is leaner at low altitude. Constant velocity carbs can be a pain. Make sure all carbs are synchronized whenever you adjust valves or do carb work. Have you checked the vacuum piston on the top of the carb under the dome? See BikeBandit for a schmatic of the parts. http://www.bikebandit.com/houseofmot...1838#sch404909 I had a similar issue with an airhead beemer. Detonation at 900 ft, ran like a banshee at 3000. Wound up going up two sizes on the main jets, Bing CV carbs. Problem cured, the detonation issue at 900 ft. is gone. Course, if I go back to CO the bike will run way rich at altitude, but the jets are easy to change on an airhead with Bings.
Good luck and keep us posted on findings and progress.
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Old 03-16-2013, 07:09 PM   #15
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Originally Posted by Jimbo4001 View Post
Sounds like a lean mixture. Where did the bike come from? What is the altitude? Is it at the same altitude now or when the popping started. If lower altitude all main jets may have to be changed. Mixture is leaner at low altitude. Constant velocity carbs can be a pain. Make sure all carbs are synchronized whenever you adjust valves or do carb work. Have you checked the vacuum piston on the top of the carb under the dome? See BikeBandit for a schmatic of the parts. http://www.bikebandit.com/houseofmot...1838#sch404909 I had a similar issue with an airhead beemer. Detonation at 900 ft, ran like a banshee at 3000. Wound up going up two sizes on the main jets, Bing CV carbs. Problem cured, the detonation issue at 900 ft. is gone. Course, if I go back to CO the bike will run way rich at altitude, but the jets are easy to change on an airhead with Bings.
Good luck and keep us posted on findings and progress.

The bike was built / set up by the PO in the desert at low elevations....I take it to MT. and higher elevations in the Summer. "Popping" started while going through Yellowstone last Summer. Now I'm back in the desert and low elevations and the issue persists. Back to MT. and higher elevations (3500 - 4500) in a week or so.
Haven't touched the carbs other than to reset the idle mixture screws once.
Guess I need another bike. Leave one at each elevation.
I've made up some sheet metal "plate" baffles to install in the Jardine mufflers. Not quite done with them yet and will need some imagination to install them as the mufflers are real shallow at the outlet, with the existing packed baffles close to the end. .

Like you, I carry multiple jets with my BMW. Ran into troubles in real high (12k +) elevations in Co. a few years ago. Can change out the Bing 40mm carb jets in 10 minutes. Honda Carb. changes will be a major hassle, definately not a quick road side affair.
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bmwhacker screwed with this post 03-16-2013 at 07:15 PM
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