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Popping on Deceleration and rough at light/neutral throttle

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Popping on Deceleration and rough at light/neutral throttle

Old 04-09-2017, 10:36 AM
  #1  
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Popping on Deceleration and rough at light/neutral throttle

Hello, I am new to the group having purchased a 1998 SuperHawk with 17,000 miles. It's the US/non California model. I have been searching the forum and it just gets more confusing because there are so many ways to go when approaching the issue of popping on deceleration. I assume this symptom come from incomplete fuel burn igniting someplace past the exhaust valve and well down the exhaust. My bike has the PAIR in place, Yoshi RS3 exhaust, stock air filter. I do not know the history of changes to carbs (if any) from stock condition. My objective is a street capable bike. I'd happily forgo some performance for smooth operation.

The bike runs and pulls hard past 3000. It is hard starting but the choke circuit does get the job done with some occasional BANGS out the exhaust while cranking until a start happens. My bike is not happy unless accelerating. When decelerating there are lots of bangs out the exhaust. When running at slight throttle on level ground I get some popps out of the exhaust and jerky (within the lash of the transmission and chain) snaps that sound like pre ignition or back fires through the intake. It's hard to tell but I suspect back fires. For ease, test runs with cowling off and the temp is in the bottom third of the range. The coolant hoses feel right. I've spent good time and money on all the service stuff (brakes, chain, sprockets, forks) but I'm not sure where to head next. Do I next take off the carbs and determine all the jet and needle and screw adjustments? Do I block off the PAIR?

By the way I followed the honda service manual instruction for the PAIR inspect and service. Using a vacuum gauge a brake bleeder, I can verify that the raw PAIR air input does cut off at 15" vac but engine at idle makes 8" vac under each carb (front for PAIR valve) so there is no way the PAIR shuts unless under decel from speed the vac goes way up to 15". I'd have to plumb a vac gauge and ride. It's hard to test carbs when the tank is removed, maybe I need to set up long vac and fuel line so the tank can be off while working on carbs? Is that what you all do to avoid tank remove replace for each warm up and test after change?

The last owner got stymied because of a faulty fuel valve leaking fuel down the vac line and or down through carbs with (possibly) bad float valve pin rubber points. I have new float pins in hand, just in case.

SO. Block Pair? Remove Carbs to get the facts?

BTW the voltage is spot on and I will do the CCTs while Carbs are out.

Knowns with instructions I can deal with unknowns are tricky. Does anyone have a flow chart for a new owner with unknown bike history? The factory service manual is ok but it assumes nobody changed anything. I did look at 8541Hawk carb guide that speaks about shims under slides and pilot sizes.

Cheers, Peeb
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Old 04-09-2017, 01:44 PM
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The main issue you are having is the PAIR system. Then it also sounds a touch lean on the bottom end, but you can't really tell with the PAIR hooked up.

So the bike will pop & bang on decel as long as you have a PAIR system.
As for the jetting, they are really close stock.
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Old 04-09-2017, 02:30 PM
  #3  
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Popping on deceleration and rough at light/neutral throttle

OK, so there is no negative drivability consequence to PAIR being disabled? I use a motorcycle infrequently so a little added discharge does not make me feel guilty. My understanding is that the PAIR system causes problems when it won't STOP makeup air coming into the area behind the exhaust valve. If it is blocked, there is no issue because most engines don't have any fresh air introduced into the exhaust anyway (other than early 1980s USA cars with the horrid air pumps). Am I correct, no consequence to blocking the pair?

Ive been spending the afternoon getting the carbs out. I discovered the screws that hold the bands which secure the rubber couplings that hold the carbs on were loose or at least not tight. One of the other posts says the carbs best be well sealed to the intake so that may have been a problem also. I'm also going to check/change the float needles because it was flooding the front cylinder when sitting (previous to my ownership) and before I replaced the fuel valve diaphragm.

Hope this fixes it, I'm doing several things at once so no telling which is right. Thank you Mr. 8541!

PeeB
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Old 04-09-2017, 06:36 PM
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I've had mine disconnected for 20yrs now with no issues yet......

Also loose clamps on the isolation boots is not a good thing either.
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Old 04-13-2017, 10:09 PM
  #5  
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Smile EVERYTHING is FIXED !!!

Dear Mr. 8541Hawk and others,

1. Eliminated the PAIR system
2. Switch pilots from #45 - #48
3. Adjusted TPS from 883 ohms to 520 ohms at idle (on bench)

No changes to mixture or balance.

Runs perfectly! Starts on choke in 2 cranks, Turn choke off in 10 seconds, idles nice, drive away! No back fire, no popping and banging on deceleration, runs fine at light throttle, no stalling at stop lights. What an enormous change. All it did before was accelerate well. All the rest was rubbish.

Also did a CCT Stopper Mod and all the services you expect on a 18 year old bike where someone thought oil changes and warm baths were good maintenance.

Many Thanks! PeeB in Seattle
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Old 04-14-2017, 08:22 AM
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Glad it is working well for you.....as for maintenance, the SH I am bringing back to life now didn't even get the warm bath.....
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