After having my motor punched to a 416, I've noticed a new sound that wasn't there when it was stock. The only way I can describe it, is that it's a slight ping...kinda like the pinging sound aluminum makes when it's cooling down. It only happens when the motor is good and warmed up, and under load when accelerating up from about 2,500 rpm in any gear (1/4 to 1/2 throttle position).

At first I thought it might be a loose bolt or something, but I've checked and re-checked every fastener I could find and found nothing loose. Also, since I'm now running a higher compression piston I thought it might be a case of slight pinging, but although I'm running a mixture of four parts 92 octane with one part 111 race gas (effective octane about 96) it still does it. Other than this irritating sound, the motor runs fine (and strong).

I'm not sure if it's a jetting problem or not, but overall jetting seems to be good. Running the needle on the 4th groove may have helped, but on this position I could tell it was running a tad too rich. Anyhow, if anyone has any suggestions I would appreciate hearing them. BTW, I've also listed my recent mods and any other information that might be helpful.

416cc with 10.8:1 JE Piston
Stock head gasket
XR400 cam
39mm FCR carb
Pilot Jet: 50
Jet Needle: 3rd groove
Main Jet: 165
Stock air filter with vented lid
Stock exhaust (internal silencer modified for better flow--stock endcap)
Elevation: 500-600 feet

 

this is just my opinion but i would try raising the octane even higher. here they have pumps that give out 104octane at this one place. i would try a 104octane. it is an easy way to try to fix it so i would. empty most of your gas tank out. and give it time to feed into the carbs.

 

Had the same problem.

I drained my tank completely, it had 92 octane.
And i filled it with 94 and rode this weekend without any knocks!
the previous week with 92 in it knock on every excell.
goodluck
007

 

don't forget that you happen to live in the most emission restricted states in the country. So their pump fuel is tailored for better emissions and not at all for performance. Plus they change it so much for emissions purposes that it would be hard to keep consistent jetting in your rig. I would go for straight race gas at least 100 octane, that way there is no more pinging and you would only have to change jetting for weather changes.
Good luck!

 

I have a 10:8 ro 1 Wiseco (+.040) and I mix 1 part 92 to one part VP C12 (112) and have run as low as 2 parts 92 to 1 part 112 until pinging (spark knock) occured. I would raise your octane level to at least 98 and I believe your problem will be gone. Don't go too high with octane level, your motor will run too hot and you definatley don't want to hurt that 416!

 

NVR2L8, I wonder if you may be lean on your pilot jet and your pinging sound may be related to that. I got a FCR carb from Curtis Sparks and it came jetted like yours. When I received it they had left the air screw turned all the way in. With a the supplied 50 pilot jet I found I had to turn the air screw out four full turns! Normally the air screw would be used at one to two turns out. I called Curtis Sparks about the odd jetting and they say it is supposed to be four turns out. I tend to disagree because at four turns out the tapered screw tip is all the way out of the corresponding seat area. What's the point of having a screw adjustment when the only usable setting is wide open? On top of that they sent absolutely no instructions- so I searched the internet to find some. I found a couple good sites (FactoryPro and Carb Parts Wharehouse) both of which contradict what Sparks claims. They say the air screw should be one to two turns out and that they would normally run a 52 or 54 pilot jet for a modified 400EX. Right now I'm waiting for bigger jets so I'm using the 50 jet with four turns out on the air screw. When I ran the air screw at any thing less than two and a half turns out I had lots of pinging and back-firing.

 

Thanks for the responses... I think everyone has mentioned a few of the things I've thought of. First of all, the gas here in CA is really leaning burning, as even with quality 92 octane gas in a stock machine it's hard to do a plug reading for jetting. FYI...I know I've been rich in jetting yet the plug doesn't show anything at all...not white, brown or black...just clean! I also have a 52 pilot coming in the mail since I think the 50 may be a little too lean, and after several calls (including SUDCO who is perhaps the largest distributor of the FCR), I still can't get an answer where the air screw should be for a normal setting. My guess is that it's about 2 to 2 1/4 turns out. Anyhow, that's what I'm gonna set it to when I get the new pilot.

I'm also going to bump up my premium to race gas mixture so I end up with 100 octane; the race gas I run is the good stuff from Union 76...leaded 111 octane. Alone I would think enough of that stuff would eliminate any pinging. Anyway, besides this annoying pinging sound the motor pulls hard and runs well everywhere else...will post again if I figure out the problem.

 

Where did you guys order the larger pilots for the FCR? My local dealer has ordered them three times and they keep getting the wrong jet. They are still on order but it has been a month or so and I don't think it is coming.

The jetting specs from a KTM 520SX which has the 39mm FCR says the pilot screw should be between 1.0 and 2.5 turns out. I am currently at 2.5 turns out and I still have a slight backfire under deacceleration. Maybe I should try to go to 4 turns out until I get a larger pilot jet.

 

I got mine directly from Sudco--their number is 323-728-5407. Bear in mind they have a minimum $10 order, so you might as well order a few to make it worth the hassle.

Blodg500RX: I'm not so sure you're running lean on the pilot. A little backfire on deceleration might be caused by being a little too rich instead of too lean--I’ve found this condition to be common if you’re running a free-flowing aftermarket exhaust system. What might be happening when the throttle snaps close is a little un-burnt fuel is detonating in your head pipe instead of the engine. I had this problem with a Warrior and White Brothers exhaust system...even after I got the jetting right it still backfired a little bit on deceleration. Also, in my experience backfiring on "acceleration" is caused by a lean condition.

BTW, on an FCR carb what we’re calling an airscrew is actually a fuel screw, so turning it out richens up the pilot circuit. What I would do is install as large as possible pilot jet and adjust the airscrew until you get the best idle and response off of idle. If you have to turn the screw all the way out--go larger on the pilot. Conversely, if you have to go all the way in--drop a size. The point being to find a pilot jet and airscrew adjustment to get the best idle and off-idle response. Also, since the needle and its taper can also affect low throttle position, take a look at it as well. If it’s too rich it can cause the same de-accel backfire condition when the throttle closes.

Anyway, I don't consider myself a jetting expert, but I provided this info in the event it might help. I figure the more experiences and opinions, the better. Right? *L*

 

Adams44,

Not trying to start a fight, but doesn't higher octane fuel make the engine run cooler? Or am I wrong? I thought that it did, but I may be wrong. Can anyone help and tell us one way or the other? Thanks.