350X backfiring, not idling down

[nouseforaname90]

I just got my 350X up and running and it runs great, all except for when I go to WOT (or just rev it up too fast) and it backfires. What would cause this? The guy that had the engine before me said that it ran very smooth and didn't backfire (and I'm using the same engine and carb). It has a 10.5:1 compression piston and performance cam.
Also, I just now noticed this. When I'm going a low speed and I let off the gas, the 350 doesn't slow down/rev down for about 3 or 4 seconds after I let off the gas. It doesn't do this at full throttle or half throttle, just when I'm going slow/not revving it high.. what could do that?
And earlier I was having trouble getting it to idle.. it would idle fine for a few seconds, then all of a sudden it would sound like it didn't fire at all.. then it would idle fine and then it would sound like it didnt fire at all. Sometimes it would shut off when that "didn't fire at all" sound occured. Could the timing be off?
I'm going to try running a higher octane gas and see if it helps out with some of these symptoms, but do you guys know what might be causing this?
Ben

[Tri-ZNate]

clean the slide. That may fix the idleing down issue, fixed mine on my 350 carb. Check the routing of the throttle line too

[84honda200s]

yea try higher octane fuel and check your plugs and timming.

[nouseforaname90]

clean the slide. That may fix the idleing down issue, fixed mine on my 350 carb. Check the routing of the throttle line too

Routing it wrong would make it pull the line when you turned and make it not want to idle down, right? I think that may be the problem. Hmm.. I'll have to check.

[dufrain]

If that cam is very much above stock it could effect the idle.Are you sre you arent floating the valves at high rpm.Do you know if they guy put in stiffer springs for the more radical cam.It does sound like the cable or slide is binding to.

[nouseforaname90]

I bought this engine from a guy who bought it when it was already modded. He said the guy mentioned something about larger valve springs or something along the lines of that.
And what do you mean by floating the valves?
If it is binding, does that mean I should rerout it or buy a new one?

[Tri-ZNate]

reroute it first. Easiest way to check if it is the cable is make sure your throttle has play, then start it up and just turn the handlebars and listen for a change in RPms. If you dont have a change clean the slide and carb

[dufrain]

Floating the valves means at high rpm the valve springs arent strong enough to keep the cam followers in contact with the cam.When that happens the valves are open too long and you will hear a miss.This can happen on a high lift ,high rpm cam ,thats why the stronger springs are needed

[nouseforaname90]

I rerouted my cable because it was routed behind the handle bars and under the tank instead of infront of the bars, between the tripples, and then under the tank. Even though it was routed wrong, it still acts like it did. At idle when its cold, it idles up and down the SLIGHTEST bit and then it idles fine when its warm. Then sometimes I will be going half throttle or above, pull in the clutch and let off the throttle and the engine will just stay at the RPM range it was at for a few seconds, go to idle, and then die.
And if I get into the half throttle or above, then let off the throttle, it will usually backdire if I just let off the throttle and don't slowly let it off....and at almost any Rpm range, it will stay at that Rpm range for a few seconds after I let off the throttle. I have never had a thumper with a clutch..only 2 strokes so that's what I'm used to. Do 350Xs idle down a lot slower than 250Rs?

[slothminx]

Possible air leak. A thumper will rev back down just as quick as the 2 strokes. Check your throttle spring isnt weak.

[TtownJoeShow]

might wanto lube the throtle cable too

[NOS_350X]

I have an insane cam in one of my 350x's right now with stock valve springs,(because at the time i didnt have the money to buy the springs) and it dosent float the valves yet. I probably wont buy the spirngs until i float them now.

Check for an exhaust leak at the head and headpipe. Also check your plug to make shure your jetting is proper.

[nouseforaname90]

Ok well I fixed the backfiring problem. I was missing a gasket between the header and muffler.
Now, it still wont idle down quickly. When I put the throttle cable on, I remember that I had to pull down on the little lever thing in the carb to get it to rest on the idle screw. I'm thinking that the throttle cable is too short? Is there a very slight difference between '85 and '86 throttle cables?
And yet another problem has arose. There is a very small leak coming from the right side (when you are sitting on the bike) exhaust hole thing. I have the header on there as tight as it will fasten down, but its still leaking slightly. Its coming out and turning the frame black by the exhaust (just soot). What would cause it to not fit tightly? I have a brand new copper gasket in there, and I took the header off to check to make sure the gasket was fitting correctly and it was, but it was not smashed down at all. I don't get why it would do that?
Ben

[Mosh]

As far as your high idle,Make sure you do not have the nut on the throttle lever too tight under the throttle cover.If you tighten those up too tight,that will cuase a sticky thumb throttle.The exhuast leak sounds like maybe your head pipe is tweaked.Take it off and put a level across the 2 snouts and make sure they are even.If not you may be able to tweak it back or grind some off the higher snout and get a better fit.

[nouseforaname90]

The thumb throttle isnt sticky. It rebounds quickly.
And I will try that thing with the headpipe.
Ben