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Topic-icon '81 R100RT: exhaust burble on deceleration

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1 month 4 weeks ago - 1 month 3 weeks ago #6083 by red horse
Happy Spring,
After working on my 81 R100RT 68k this winter, I took it for it's first ride this year. The bike makes, for lack of correct term, a burbling exhaust noise when not under load such as slowing down or riding downhill. It's not a loud back firing noise, but consistent burbling noise. I worked on the exhaust system replacing clamps where mufflers meet head pipe, and replaced cross over pipe that had rusted pin holes. Checked valve clearances, checked timing, all hose clamps to and from carbs. Everything to specs and tight. Bike starts right up and has good power through acceleration in all gears. Put fresh gasoline in, Sunoco 93.
Is there something I may have over looked?
redhorse
Last edit: 1 month 3 weeks ago by Wobbly.

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1 month 3 weeks ago - 1 month 3 weeks ago #6091 by Wobbly
Replied by Wobbly on topic '81 R100RT: exhaust burble on deceleration
2 things can cause that....

• Air leak at the cross-over tube. There is plenty of un-burned fuel inside the exhaust. On decel, air gets sucked in through cracks and the fuel burns inside the pipes. When you assemble these exhausts you want to install that cross-over pipe with a coating of silver silicone sealer. Sometimes you can successfully add that after the fact from the outside without disassembly. (Look for small exhaust leaks marked by small black marks indicating a hole.)

• Extra-lean on the slow speed jets caused by slight Ethanol clogging. Add 1oz of Star-Tron fuel treatment at each fill-up and see if things don't improve in the next 2 months.

Don't hide 'em, Ride 'em !!
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Last edit: 1 month 3 weeks ago by Wobbly.

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1 month 3 weeks ago #6092 by red horse
Replied by red horse on topic '81 R100RT: exhaust burble on deceleration
Wobbly,
Thanks, I remember reading in another thread, you mentioned the silver silicone. I did that when I put the mufflers back on the header pipe, but I believe I didn't do that when I replaced the cross over pipes. I will check them and apply the silicone. I'll add the star-tron additive and see how that works. Will balancing the carbs correct the low speed issue?
Will check back in a week or so to let you know. Snow in the forecast-aargh. If it's not on thing keeping you inside it's another.
be safe, stay healthy.

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1 month 3 weeks ago #6097 by Wobbly
Replied by Wobbly on topic '81 R100RT: exhaust burble on deceleration
Balancing the carbs is always a good thing. Especially if it's been 5K miles or more since last done. When you're doing that, be sure and twist the idle mixture screw in and out before returning it to its normal 1-1/2 turns out. That helps dislodge build-up too.

I simply recommend the StarTron because the "blockage" is probably no more than a thin varnish-like coating on the jets. You notice it at low speed due to the burble, but if it's there... then it's on everything. And riding around with a cleaner sure beats sitting at home with a bucket and a toothbrush !! :lol:

Don't hide 'em, Ride 'em !!
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3 weeks 6 days ago #6366 by red horse
Replied by red horse on topic '81 R100RT: exhaust burble on deceleration
Finally got some decent riding weather. After applying the silver high temp ATV silicone sealant to the cross over pipes and re-tightening all clamps the burble noise has greatly subsided, although still there. I also replaced the spark plugs with a one step up in heat range, Bosch W6DC.
I can live with the noise and it's not offensive. I just wondering if there could be any long time effects?
redhorse

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3 weeks 5 days ago - 3 weeks 5 days ago #6378 by Wobbly
Replied by Wobbly on topic '81 R100RT: exhaust burble on deceleration

red horse wrote: I also replaced the spark plugs with a one step up in heat range, Bosch W6DC.

Thoughts.....

• What was the purpose in changing heat ranges ? You should be running the heat range recommended by the spark plug manufacturer, unless you've lost a significant amount of compression or burning lots of oil, and simply need the plug to make up for a mechanical fault.

• Was this "one step change" to a hotter or colder plug ? For some manufacturers going to a higher number is "colder", of others it's "hotter". There's not one common numbering system for spark plugs and it can get very confusing.

Don't hide 'em, Ride 'em !!
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Last edit: 3 weeks 5 days ago by Wobbly.

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