MLB

usually fires as soon as it's cranked, but sometimes it won't and will crank for a few seconds after which it will back fire and then immediately start.
??????
I drilled out the the endcap of the stock exhaust last fall. No airbox/filer changes.

shayne

What are your jetting specs?

gboezio

Flodded, make sure that the petcock cuts the fuel flow when the engine is off. Gas smell ??
Fouled plugs, check them.
Misadjusted choke, try using less.

nath981

did you check the TPS? that's probably the first thing I would check since they are notorious for being out of adjustmt. I had to adjust mine after years of varying degrees of popping/backfiring that eventually increased to unacceptable levels. What a difference.

MLB

Stock jetting. I'm not much of a wrench so what's to "check" on the TPS (throttle position sensor?)

No gas smell.

Another "problem", choke is too "tight". When I pull it all the way out, if I let go it pulls back in enough that the bike will stall if cold. Pull it out and hold (what I normally do) and it idles 500 rpm faster (normal cold start rpm)
I assume it needs adjusted somewhere, but where?

Thanks!!

lazn

That's an easy fix. If you pull back the rubber boot directly past the choke **** you will find a plastic nut that adjusts the resistance that holds the choke out. (you don't weaken the spring, but rather increase the friction that holds the choke out)

RickB

Mine does this once in a while, I always attributed it to being slightly lean when starting it cold.

nath981

the TPS is a plastic sensor on the side of the rear carb. it needs to be checked with a multimeter. It is secured with rivets that need to be surgically removed to avoid buying a new one. it's a bit easier if you pull the carbs up and tilt them. There are many references and pics on this forum if you need more info to decide if you want to tackle it. It helps if you have a dremel(cutting disc) to cut slots on the rivets so they can be removed. If you have a buddy that is handy, it might be best to seek help.

shayne

It is possible that your bike is lean. Backfiring is a sympton of this. A dyno tune may fix the problem.

MLB

Thanks guys! I'll fix that choke this weekend.
I've been suspecting lean too, just really surprised that drilling some holes in the end cap with no airbox or filter changes would make that much difference. it does growl nicely though.

nath981

I don't believe it would. I did that exact thing first and ran it quite a while without any problem. get someone to check your TPS if you don't feel confident enough to do it yourself.

fighter hawk

mine backfires under deceleration like no other. its a build up of fuel in my case. if either of your coils aren't throwing spark fast enough may cause this as well. you have more fuel than spark track it down it may just take a lot of trial and error

Fozzy Bear

Is this when starting from cold or hot? Do you twist the throttle much when starting?

I don't think there's anything wrong with your bike, its your starting technique.

MLB

Ok.

Cold only. and not all the time, just a few times. But all since I drilled the endcaps.

Full choke, don't touch the throttle. Just like every other of the 15 odd Honda's I"ve owned over the past 40 years.

Fozzy Bear

Good to hear. When I removed the baffles in my stock cans, about the only difference was that she idled a bit higher. Starting was just the same.