Help-right aft or #3 cyl Popping noise

I just bought a 1996 Royal star classic, only issue is a popping noise only on the Right Aft cyl or #3

 

Happens shortly after engine starts to warm up 2min

 

popps at all ranges of rpm but it does NOT back fire (loud bang)

 

Where should I start looking first - vaccum - carb sync ?

 

Thanks

 

Pete

 

ptynning@msn.com

I just bought a 1996 Royal star classic, only issue is a popping noise only on the Right Aft cyl or #3

 

Happens shortly after engine starts to warm up 2min

 

popps at all ranges of rpm but it does NOT back fire (loud bang)

 

Where should I start looking first - vaccum - carb sync ?

 

Thanks

 

Pete

 

ptynning@msn.com

Just a point of clarification - a loud bang would be an afterfire (explosion in the muffler), not a backfire (explosion back through the carb).

 

I do not have experience with your specific model of bike, so it is quite possible there is an easy and common cause of your problem which I cannot list. In general, however, popping at all RPM would most likely be ignition related - either bad plug, plug cap, wire or coil. If it was fuel related, it would almost certainly go away under either low or high throttle since they use different fuel circuits. Even a major vacuum leak would generally become insignificant when the throttle is more than 1/2 open.

Goose

I will start looking at Ignition problems

I do not think an exhaust leak would cause your problems, but I wouldn't rule it out, either. Do make sure the header bolts are tight and any gaskets are in place and working.

Goose

Do the spark plug cap wires pull of the ignition coil or is the wire cap and coil one unit ??

Do the spark plug cap wires pull of the ignition coil or is the wire cap and coil one unit ??

I do not know about the mid-90s bikes. I believe that the 1st gens had replaceable plug wires, but the RSVs do not. The plug cap unscrews from the wire, but the wire is bonded into the coil.

 

Your bike could go either way, but more likely it is like the current bikes. I'm sure someone who knows will jump in and give the right answer soon.

Goose

The configuration of the coils on the original Royal Stars are the same as the Venture, the caps can be removed from the wires, but the wires are molded into the coil.

The easiest test of the full ignition circuit would be to simply swap the rear coils. No need to actually remove them - just reverse the plug wires and the trigger wires on the coils. If you also swap the rear plugs at the same time, you will have conclusive proof in one test for the entire ignition circuit except the ignitor.

 

I do not know of any way to check the ignitor other than either replacing it or using an auto scope to observe the spark curve.

Goose

I also have a 96 RSTD and it does the same thing on the lower left cyl (#1 if I'm correct) when the engine is cold. I don't get the popping above idle, but I do get it on deceleration. I have yet to find anything that will stop the popping. The only thing that I haven't done yet is a valve adjustment. I'm not sure if that will fix it but I need to do the adjustment anyway. I'll let you know what happenes when I do the valves. BTW, thanks for the info on the plug wires. I was wondering if the wires could be changed without changing the coils.

 

I also own a 96 Royal Star and have had the same problem with #3 cylinder since I purchased the bike 3 years ago. I will list what I have done and my observations and maybe we can track down the cause.

The popping is only on cold start up and is worse with the choke on. In the summer when no choke is needed there is little or no popping. As soon as the choke can be pushed right in the popping stops and there is nothing the rest of the day.

On my bike this cylinder is slower to warm up than the others, carefully touch the header pipes with your finger and see if this pipe is warm when the popping is present. The pipes get very hot so use care!!!

So far I have cleaned the spark plug caps, done the coil swap (no change), new plugs, replaced the vacuum caps on the sync ports, checked vacuum hoses for leaks, removed and cleaned the carbs, checked float levels, checked and adjusted the valves, synced the carbs and played with different pilot screw settings. So far nothing has eliminated this problem. I have not checked the carb diaphrams since it is an idle issue and I didn't think they would cause this problem.

As Goose said, it could be an ignitor issue but the only way to be sure is to change it, which will probably be my next step. The bike runs fine other than this cold start issue so I haven't worried too much about it during the riding season. All the plugs are burning with a nice tan colour so whatever is causing it appears to be only idle related.

Highway speed riding seems fine but I know these engines run well on 3 cylinders and I don't have another bike to compare it to.

I will probably do some more tinkering over the winter, maybe pull the carbs and recheck the float heights and idle circuits. I am leaning toward a carb issue since it seems to be affected by temperature, use of choke and idle RPMs.

 

Keep us informed on your progress, there is no guarantee that our problem is caused by the same thing but maybe with all the knowledge on this site we can find the answer.

 

Good luck

Doug

Thanks for all the info guys, I will plug away at it !

I first put new plugs in with gaps check to spec - no help

 

I then tried switching spark plug wire/coyles - no help

 

checked air filter/airbox and visual look at carbs/vaccum hoses/caps - they looked okay

 

I then re-adjusted "Pilot mixture screw to factory spec" - no help

 

I then put sea foam in carbs and gas tank and ran the bike a couple of hours - no help

 

Soo ! for me, as Clint Eastwood would say - A MANS GOT TO KNOW HIS LIMITATIONS !

 

Living in SoCal - I took my Royal Star to one of the TOP motorcycle shops - Rancho Cucamonga Yamaha - One of the top Yamaha Mechanics Jay who has 30 years exp.

 

Jay put an exhaust gas analyzer in #3 pipe - then Adjusted the pilot mixture screw - to more rich setting - 2 additional turns ! -PROBLEM SOLVED - NOT MORE #3 CYCL POPPING

 

Jay then recomended Carb Sync and he did a great job ! Sync carbs and tweeking the pilot mixture screws !

 

NOW MY ROYAL STAR RUNS VERY SMOOTH - THANKS JAY !

 

I Would Also like to Thank V7goose and everybody else for helping me !

Thanks for the feedback. I'll have to look into that one, if I can find a guy like yours. The only people around here that I know about are stealers. Did he do the gas analizer on the other 3 cylinders too?

Yes, the machine he used looked expensive. The Royal Star is 15 years old with 28,000 miles.

carb springs/rubber parts and other parts get worn and tweeked over time, thats why jay went way over the 2.5 to 3 turns on the pilot screw for #3

 

With the Carb Sync, bike runs great

Reviving an old thread, chasing a problem.

Last night I noticed the pilot mixture screws were out just about 1 1/2 turns.

Reading another thread I tried turning them out 4turns. Better but still getting a few pops on decel.

Valves done, carbs synched, 42mpg . Bike is running great except for that may explosion on decel.

There was no pop before all the work done.

Last night riding home I had another motorcyclist cone around and say my bike smells like raw fuel. A bad exhaust smell.

What's going on

CARBTUNE! Without a exhaust gas analyzer, kinda hard to know how pilots need to be set exactly, though you can get close.