Back firing when hot starting.

a bad plug will cause backfiring when starting

regards

scrap

I had this problem recently, and it was caused by too lean jetting. I had been riding around 9000' and jetted for that altitude, when I got down to 4000 I was having trouble electric starting, but, like you, the kicker worked fine when hot.

Has it been colder lately where you are at?

Have you tried adjusting the fms to improve starting?

And like scrap said, it could be a plug. Are you running the standard DCPR plug, or a fine wire equivalent like the DCPR8EIX?

Hope this helps,

dale, when did we start calling it an "fms". to me that means the squadron i was in during the air force years..."field maintenance squadron" ( which is what taught me how to work on the berg in a field :wink: )

Hiya Ned,

I used the term fms ( I like acronyms anyway) because any people confuse the "fuel" screw with an air screw, and if one doesn't understand this one will be totally screwed up when trying to adjust it richer or leaner. And it's pretty hard to get "air screw" out of fms.

And with the older bikes, the setting of the fms was crucial to getting them to start on the button reliably.

Having good skill is a plus! When I was testing jetting at high altitude last summer I was making needle clip, and jetting changes on the trail. All I needed was the ever available stump to set my tank on and I was good to go. Berger had showed me this cool little motion pro tool kit for changing jets, you can even keep the jets in there too!

Dude,

I am so sorry! I thought I had quoted you and was replying to your last post on your hot starting issue, and I totally erased what you had written beyond what is now left, because I was in edit mode instead of quoting. I can't believe I did that!!

Again I am so sorry.

What I had intended originally was to offer a suggestion on how to set the mix screw.

With the bike warmed up and idling normally about 1500 rpm, put the bike on a stand, turn the fms screw in until the motor starts to slow down, now back it out until the motor starts to slow down again taking note of how many turns it is from the lean slow down to the rich. Set the fms in between these two points, and then go 1/4 turn in. That should get you really close.

Try hot starting it from there with the electric starter. You may need to tweak it a little bit either way to get it just right.

In your reply, the part that I erased you said the temperature was about the same, but, conditions had been a drought, but, now it was wetter and more humid, this would tend to make your mix a little richer.

Logjump used to carry a small screw driver on his bars in a little piece of clear tubing so he could make adjustments when ever he wanted. I had always thought that was a cool idea.

Dale

Just for the heck of it, make sure to inspect the m6 bolts on the intake between carb and cylinder. I recently had an issue with this being loose causing similar problems.

Just a quick inquiry here: would the exhaust valve clearance being a touch too tight also cause a similar situation? My thought being, once hot the valve would be held open just a bit, not enough to release all the compression, but enough to put some unburned fuel into the exhaust pipes, just a thought.

dale

you'll find that thumpertalk and the doc always said PS beofre you even heard of jetting!

"pilot screw" says nothing about air or fuel. so quite why we need you to confuse the issue with "FMS" i don't know?

can we please all stick to what was there all along - PS.

regards

Taffy

I think Bendberg is on to something. Check for leaky valves especially exhaust. On mine found exhaust valves were carboned up and leaking. Bike was backfireing on deceleratoin. thought it was lean. By the look of the inside of the pipes though was way to rich!!!

i hear ya, taffy. fms to me is the field maintenance squadron in the usaf. (usaf= u sure are f...ed :twisted: )

they all carbon up around the exhaust valves and their seats bill. i've not pulled a head off yet that head clean valve seats on the exhaust side. they all clean up and don't look too bad for it afterwards though.

it would be interesting to know if the simply the tappet clearance is wrong on the exhaust side? after all it's the same as the inlets for us but all other bikes known to man have a clear difference. maybe they're being held off their seats when VERY hot?

now we have better cams and some even have better springs it's got to be worth considering?

LARGER TAPPET CLEARANCE ON THE EXHAUST?

regards

Taffy

Taffy said:

dale

you'll find that thumpertalk and the doc always said PS beofre you even heard of jetting!

"pilot screw" says nothing about air or fuel. so quite why we need you to confuse the issue with "FMS" i don't know?

can we please all stick to what was there all along - PS.

regards

Taffy

Click to expand...

Okay, I will try and refer to it as the PS from here on out. I picked up FMS from somewhere that I cannot find at the moment. The Kehin jetting guide http://www.keihin-us.com/tune1.htm refers to it as the idle mixture screw, as does the Husaberg manual.

My apologies for causing any confusion.