slight popping at 2500 r.p,m,

[Flounder]

After buying this 84 1200 which did not run, I just finished rebuilding the carbs with randakks kit.
They synced up just fine and it runs strong and smooth but there is a slight popping at 2500 r.p.m. Since I never got a chance to run or ride it before rebuild I'm not sure if it existed before.
Weather in neutural or while riding this happens. New plugs, fuel and air filters. Any ideas? Thanks

[Roleketu]

When I had popping, which sounded more like a bang, it was a bad head gasket. Do you get any white smoke in exhaust? Check condition of plugs and do a compression test.

[PanMan75]

I used to have a carb "cough" at 2500rpm as well. Mine has been solved since I rebuilt the carbs with Randakks kit.

[BigBro]

I had a popping coming from the Carbs at idle and when running especially when not fully warmed up.

Rebuilt the carbs with a Randakks kit did a bench adjustment of the carb balance as best I could.
Charged the carbs with fuel to check leaks, etc then put them on the wing.
It started up really easy and sounded great on first start except the slight popping was still there although less and softer through warmup.

Thought well still chasing a problem but kept at it to finish the carb overhaul.

Once the carbs were sync'd the popping went away.

[neoracer]

there is always the possibility that you may have a weak ignition wire or the ngk caps may have a problem,could be a lean spot in that point before it gets out into the main circuit of the carb

[Flounder]

Thank you everybody, I have some testing to do. I just recalled while I was calibrating the sync tool the rubber plug on the #1 cylinder vacuum tube adapter shot across the driveway after a pop so the problem is most likely at that cylinder. The other thing I forgot to mention is that this is a California model. Could this be a reed problem???

[bs175dths]

Thank you everybody, I have some testing to do. I just recalled while I was calibrating the sync tool the rubber plug on the #1 cylinder vacuum tube adapter shot across the driveway after a pop so the problem is most likely at that cylinder. The other thing I forgot to mention is that this is a California model. Could this be a reed problem???

Although it sounds like you may have isolated the cylinder experiencing the popping, the culprit still needs to be identified.
May I suggest swapping spark plugs between cylinders number 1 and number 3. If there is no change, swap the spark plug boot between number 1 and number 3.
If still no change, and this will be harder, swap the coil leads between number 1 and number 3.

The idea here is to swap one part at a time with a known good part to see if you can get the problem (in this case the popping) to move from one cylinder to another.
If at the end of it all the popping is still coming from number 1, then you have eliminated the plug, boot and coil wire.

Another thought is to recheck the intake O-ring(s). Make sure it is not pinched and is properly seated in its groove before tightening.

Some things to remember however, the coil leads have been routed in their position for a long time and don’t like bending differently, ie, the inner core may crack and cause an open or a ach generating gap.
Also recall, one coil operates two cylinders (but only one is ready with a charged cylinder) so if you are experiencing similar problems with two cylinders, check the coil.

All GL1200 carburetors systems utilize the reeds. The California Carbs. have that additional purge control valve which should not cause your popping problem. It is a vapor purging device (SMOG reducer)

As part of the carb. rebuild, did you inspect all those little vacuum lines under there? They all looked good? All ends are on tight and the hose ends are not dried or cracking?

Just another avenue.

Good Luck.

-Ride On

[Flounder]

Thank you everybody, I have some testing to do. I just recalled while I was calibrating the sync tool the rubber plug on the #1 cylinder vacuum tube adapter shot across the driveway after a pop so the problem is most likely at that cylinder. The other thing I forgot to mention is that this is a California model. Could this be a reed problem???

Although it sounds like you may have isolated the cylinder experiencing the popping, the culprit still needs to be identified.
May I suggest swapping spark plugs between cylinders number 1 and number 3. If there is no change, swap the spark plug boot between number 1 and number 3.
If still no change, and this will be harder, swap the coil leads between number 1 and number 3.

The idea here is to swap one part at a time with a known good part to see if you can get the problem (in this case the popping) to move from one cylinder to another.
If at the end of it all the popping is still coming from number 1, then you have eliminated the plug, boot and coil wire.

Another thought is to recheck the intake O-ring(s). Make sure it is not pinched and is properly seated in its groove before tightening.

Some things to remember however, the coil leads have been routed in their position for a long time and don’t like bending differently, ie, the inner core may crack and cause an open or a ach generating gap.
Also recall, one coil operates two cylinders (but only one is ready with a charged cylinder) so if you are experiencing similar problems with two cylinders, check the coil.

All GL1200 carburetors systems utilize the reeds. The California Carbs. have that additional purge control valve which should not cause your popping problem. It is a vapor purging device (SMOG reducer)

As part of the carb. rebuild, did you inspect all those little vacuum lines under there? They all looked good? All ends are on tight and the hose ends are not dried or cracking?

Just another avenue.

Good Luck.

-Ride On

Thanks I will do that. I replaced all vacuum hoses with new and even put little zip ties on them.
I was very careful that the intake o rings were seated properly but will double check them, I imagine that would cause more of a problem at idle where vacuum is higher.
Just to be clear , does the coil fire both #1 & #3 plugs simultaneously and the non charged cylinder is fired at the end of the exhaust stroke where it has no effect?

[bs175dths]

One coil will fire two spark plugs at the same time.
Off hand, I don’t recall which two cylinders are tied to which coil, (I understand one of the repair manuals out there is incorrect) but yes, two plugs will fire at the same time, from one coil.
But only one cylinder is on the compression stroke (waiting to continue to enhance our thrill in the saddle, A.D.D. – sorry about that) while the other cylinder is on its exhaust stroke.

Did you ever notice the one, two and three cylinder bikes have one, two, and three coils, respectfully?
When you get to a four cylinder bike, there are two coils – some automobiles have one coil per cylinder, plug directly into the spark plug, and can run up to and past the $200.00 mark. EACH!!!
Times 4, 6, 8 or 10!! How many cylinders do you have??? Ouch, that hurts to replace all the coils at once if one or two are failing. (A. D. D. again - sorry)

Air leaks can cause problems throughout the rpm range.
True, the intake O-ring will cause problems in the lower rpm range, but a hole in your exhaust (in the muffler area) can cause a back-firing when letting off the throttle. A defective diaphragm in either the SLOW AIR CUTOFF VALVE or ANTI-AFTERBURN VALVE under the carburetors will cause the same effect.
The thing to remember is to identify the symptoms your bike is displaying…. Run through your knowledge of what might be causing these symptoms, check those first and if the cure isn’t found, there must be another way the bike is causing these symptoms, but in a similar way as if you had a defective device.
Example 1: a defective diaphragm in the slow air cutoff or a small hole in the muffler – both can cause a back fire at throttle down
Example 2: excessive carbon dust, lack of lubricant or in need of proper grounding of the starter motor, OR you have a discharged battery – both will cause the starter to rotate slowly
Example 3: failing to replace the timing belts or failing to put oil in the engine - both cause the engine to stop!!!! LOL

BTW, when I went through my carburetors, I too destroyed those little hose clamps and since I had it available, I used safety wire for these small hoses. Making the same number of rotations around each hose then twisting them in similar fashion does the job of the OEM hose clamps, but to me, looks COOLER.

I hope this helps… answering some questions and causing you to think of other questions…..

-Ride On

[Flounder]

One coil will fire two spark plugs at the same time.
Off hand, I don’t recall which two cylinders are tied to which coil, (I understand one of the repair manuals out there is incorrect) but yes, two plugs will fire at the same time, from one coil.
But only one cylinder is on the compression stroke (waiting to continue to enhance our thrill in the saddle, A.D.D. – sorry about that) while the other cylinder is on its exhaust stroke.

Did you ever notice the one, two and three cylinder bikes have one, two, and three coils, respectfully?
When you get to a four cylinder bike, there are two coils – some automobiles have one coil per cylinder, plug directly into the spark plug, and can run up to and past the $200.00 mark. EACH!!!
Times 4, 6, 8 or 10!! How many cylinders do you have??? Ouch, that hurts to replace all the coils at once if one or two are failing. (A. D. D. again - sorry)

Air leaks can cause problems throughout the rpm range.
True, the intake O-ring will cause problems in the lower rpm range, but a hole in your exhaust (in the muffler area) can cause a back-firing when letting off the throttle. A defective diaphragm in either the SLOW AIR CUTOFF VALVE or ANTI-AFTERBURN VALVE under the carburetors will cause the same effect.
The thing to remember is to identify the symptoms your bike is displaying…. Run through your knowledge of what might be causing these symptoms, check those first and if the cure isn’t found, there must be another way the bike is causing these symptoms, but in a similar way as if you had a defective device.
Example 1: a defective diaphragm in the slow air cutoff or a small hole in the muffler – both can cause a back fire at throttle down
Example 2: excessive carbon dust, lack of lubricant or in need of proper grounding of the starter motor, OR you have a discharged battery – both will cause the starter to rotate slowly
Example 3: failing to replace the timing belts or failing to put oil in the engine - both cause the engine to stop!!!! LOL

BTW, when I went through my carburetors, I too destroyed those little hose clamps and since I had it available, I used safety wire for these small hoses. Making the same number of rotations around each hose then twisting them in similar fashion does the job of the OEM hose clamps, but to me, looks COOLER.

I hope this helps… answering some questions and causing you to think of other questions…..

-Ride On

Thanks again, I will let you know when I get into it next. Buy the way I like the A.D.D. rants!
Cheers

[wallbrad]

New to this thread....

The behavior you describe sounds EXACTLY like what was happening on my 85 Interstate. The pop would happen on both acceleration and deceleration at around 2500 RPM.

I think your problem is the SLOW AIR CUTOFF VALVE. After I replaced mine (which requires a complete carb removal, so you might as well re-examine that rebuild again...) all the popping went away!

I wish this damn valve had been located INSIDE the air plenum instead of outside, 'cuz it sure would have been easier to replace!!!

Good Luck!
-Brad

[Flounder]

Thanks for the tip Brad, I was planning on taking carbs off real soon and I will check out the cut off valve. The ignition system tested good , I then brought it up to 2500 to cause the popping and sprayed brake clean in different areas looking for vacuum leaks. When I sprayed the area around the bottom of the reed valve housing it smoothed out completely. I did not replace the air hoses from the reed valves to the heads as they looked in good shape with tight connections. I will replace those. If the diaphram in the cut off valve is torn the circuit still would not be exposed to outside air would it? All other vacuum hoses are new.

New to this thread....

The behavior you describe sounds EXACTLY like what was happening on my 85 Interstate. The pop would happen on both acceleration and deceleration at around 2500 RPM.

I think your problem is the SLOW AIR CUTOFF VALVE. After I replaced mine (which requires a complete carb removal, so you might as well re-examine that rebuild again...) all the popping went away!

I wish this damn valve had been located INSIDE the air plenum instead of outside, 'cuz it sure would have been easier to replace!!!

Good Luck!
-Brad

[wallbrad]

Flounder: As it turned out on mine, the diaphragm rubber was OK, but the spring had flattened out. Be extra careful when you take it apart to observe which side (up or down) the diaphragm goes with respect to the throttle body, or else the thing won't work properly.

[Flounder]

Thanks again. It's hard to tell on the fiche, is the slow air cut off valve item #13? It just says "spring" I of course would want to replace the diaphram too. Where did you get your spring from and how would I get a new diaphram?

---

Flounder: As it turned out on mine, the diaphragm rubber was OK, but the spring had flattened out. Be extra careful when you take it apart to observe which side (up or down) the diaphragm goes with respect to the throttle body, or else the thing won't work properly.

Forgot to give the fiche link.........................
http://www.shspowersports.com/fiche_sect...veh=132497

[wallbrad]

I got mine off of Amazon. Do a search on GL1200 cut-off valve, and you will see the K&L cut-off valve kit.

I have to say, I never did figure out what the little o-ring was for... It will probably screw me later that I didn't.