Honda 750 Popping on Deaccleration

[texas dogman]

Picked up a new ride a couple of weeks ago, Shadow 750. The only mod by PO was a set of Cobra pipes. Engine pops and backfires quite a bit on deacceleration and engine brake.

I have read some write ups on K&N carb rejetting and such, and may consider in future, but for now would just like to get rid of annoying popping.

Is this likely to running carbs to lean? If so, I guess I could try to eliminate by turning out mixture screws a 1/2 turn or so to increase fuel mixture.

Would just adding after market pipes cause this, or is there something else going on.

Thanks.

 

[baxter650]

YUP. Fatten up the pilot jets.
I used header wrap on one of my bikes pipes and that was enough to bring on the poping.

 

[Gumby]

mixture screws ain't gonna do the trick. You need to re-jet.

Nice bike. The wife rides a 750 Aero.

 

[Red Herring]

you probably have to plug the PAIR valve. It is part of the emissions system that pumps air into the exhaust for burning in the catalytic converter. Most aftermarket pipes loose the cats, but if you don't plug the PAIR valve, and solder the wires to close it's circuit, you'll pop on decel.

 

[oro-o]

The time-honored "hack" to fix this is eight #4 (I think) washers from Radio Shack - net cost about $2 in a washer pack from Radio Shack. Since the Shadow is a twin, you will only need four (you normally use two washers per needle). I have done this on all my older metric bikes with great success. This isn't the write up I remember, but this one will guide you through it:

Shims, Springs and Other Carb things...

It is about 95% effective as a Dynojetkit but at 3% of the cost. It should take care of your problem, as well as improve your mid-range jetting quite a bit. Your other solution is to restore the original pipes and restore the proper back-pressure and thus stochiometric ratio the bike was designed to work with.

Slapping on aftermarket pipes on a bike is the fastest, surest way to screw up your bike - I've seen this so many times it amazes me people never learn to do both modifications at once!

 

[dgangle]

Usually this is caused by an exhaust leak. Air is pulled into under deceleration. Find/fix the leak and this popping will go away.

The Radio Shack washer trick is for raising the needle clip position on the jet needle that does not have any adjustability.

 

[SHERMAN FJ62]

Try running some carb cleaner through the bike