Idle RPM dropped after adding Seafoam to gas tank

[WalkingAntique]

Short story;
I added 5 oz of Seafoam to my gas tank.
1997 Harley. The gas was 91 octane before Seafoam was added. After running about 3 gallons of the treated fuel through the engine at hiway speeds, my idle speed dropped from approximately 850RPM to around 550RPM, according to the bike tach.
My question is whether or not Seafoam increases octane, and would higher octane fuel cause slower idle speed??

Then, I filled tank back up and added 4 more ounces of Seafoam. Burned out another 3 gollons or so. The idle slowed down more, to alike 300 RPM. (barely running). So I filled back up, didn’t add any more Seafoam. Ran about 15 miles, and reset my idle to 850 by adjusting the idle speed screw.

Next question is whether or not I need to adjust the idle mixture screw on the carb?
Or just keep burning the treated fuel until gone?
I know what you’re thinking, “That’s the SHORT story??”

 

[repairman54]

Probably just gunk in the idle mixture screw. Seat it in lightly and back out to where it was and test.
Octane has no bearing on idle speed.

 

[Bonz]

What was the reason for the Seafoam being used? Sounds like the idle was good before adding it.

IMO, I would chase it in the next tank or two with Berryman's B12 or Techron or similar.

There are some comparisons on this forum about Seafoam vs XX.

 

[BusyLittleShop]

I've talked with many of the factories and they all say stuff like this...

Gas additives are not a cost effective cleaner because Gasoline is a distilled form of petroleum...
Read the MSDS on almost any fuel additive and the chief ingredient is: Petroleum Distillate at 3 times the cost...

Hirotoshi Honda...

 

[WalkingAntique]

What was the reason for the Seafoam being used? Sounds like the idle was good before adding it.

IMO, I would chase it in the next tank or two with Berryman's B12 or Techron or similar.

There are some comparisons on this forum about Seafoam vs XX.

I got the Seafoam in order to clean carbon deposits. The bike has 137,xxx miles on it.
Around 125,xxx mi it started backfiring loudly sometimes when restart a warm/hot engine. I have had a butt-ton of stuff done to it, in part to resolve this backfiring.
Most recently, I had a well respected local tuner do: leakdown test(8%), rebuild carb, verify single-fire ignition timing(spot on), tune carb, dyno (80”Evo made 65hp).
The machine ran great, and idled smoothly, but that dang explosion still happened.
Someone in a Harley forum suggested that maybe the bang was in a combustion chamber, not in the exhaust/muffler, unburned fuel being ignited by a hot carbon spot.
I’m not sure if the Seafoam eliminated the backfire yet, but my seat of pants dyno tells me it has gained some power.
Thanks for your input.

 

[ZeeOSix]

I would have used Gumout Regane or Redline SI-1 fuel system cleaner. I've always had good results with them.