PLEASE Help. Dieseling noise at 1/3 throttle

Hey all,

I have a 1996 XR600r and have had it for a year. I have put about 9k on the bike on and off road. The bike runs flawless but for the past month it has started to make a dieseling noise when in the lower portion of the gear range. For example when shifting from second to third and at the low end of third is when it is most noticeable and gets worse in forth and fifth.

The temp is about 110 degrees out here and I am running 87 octane in bike but have also tried 91 octane with no better results. I live in Utah. I have an Edlebrock carb and have thinned it out and richened the mix and it still does it and getting worse. My valves are in adjustment. ANY IDEAS? I am tending to think something is wearing in there and I want to replace it before it breaks other stuff.

Thanks in advance for any help.

Sounds like you are hearing detonation (preignition). If this keeps up, the engine will suffer damage probably in the form of a burned piston and/or damage from the extra heat generated from running a lean mixture and/or low octane gas. What number needle are you running in the Edelbrock and how many clicks out from full lean on the adjuster?

I believe the needle is the 17e and it is 6 clicks to the left from the fully rich position. (All the way in) Right is rich and left makes lean right?

So If I do but higher octane gas in it the problem should go away almost immediatly right?

The Bike does not feel like it has lost power at all. Maybe a tiny bit ont he top end.

If I have damaged the piston will it continue to sound like this? could I have damaged the valves and will it continue to sound like this?

I am really wondering if I haven't already damaged something.

My '92 XR600 with an Edelbrock needed a 19E needle with the clicker adjustment 6 clicks back from full rich. The same carb on a '98 XR628 needed the same needle but 2 clicks back from full rich. I think a 17E is too lean for a 600, especially if it has the exhaust is opened up and an aftermarket air filter fitted.

If it is detonation or preignition You certainly want to try to richen the mixture...What does your plug look like....ride it then right after the ride pull it without letting it idle. Is it white or black, wet, dry.

I'm sure you already know that Lean mixtures burn hotter and if there are hot spots in chamber it will cause combustion before the plug fires...like a diesel glow plug. Richer mixtures run cooler. Pull the plug to see what it looks like...maybe even replace it if it ran hot enough to wear at it. and richen it. If you have 6 clicks to full rich that may be enough to get it or going to the 19 needle would certainly help!

Thanks for all the advice. I really appreciate it!! I think you might be right I will look into replacing the needle. I am concerned that I have maybe done some valve damage but i still have great compression and the valves stay in adjustment, but I am getting more noise from the head than ever.

I was thinking...something I have heard of that also causes preignition. If there is enough carbon deposits in the chamber that when there is combustion it kind of remains like a coal or imber and when new fuel enters it the glowing imber causes ignition before the spark?

Again...I THINK I have heard of this...so still check you plug just in case.

I'm sure when you figure it out you won't have hurt anything!

JT

yeah after you mentioned it I went and read several articals on the topic and I may have some carbon build up. I think my game plan is to makes sure I only put in 91 octane or higher. I try out the 19e Needle instead and feed it some gas treatment with lubricant and cleaner to break up any real carbon build up. I am sure riding this bike in 115 degress might have something to do with it as well. I love my pig and have had soo much fun with it. I will soon be in the Market for a xr650r or a KTM 525.. Still trying to decide.

Thanks

again

XR600Rs that are stock should be fine on 87, because they were designed to run on crappy gas for caring Baja. The compression stock is relatively mild, but try the richer needle anwway, can't hurt. Id also thro in some premium to show yourself it isn't pre ignition. If that cures it all the better, I don;t think it will. Did this problem start when you installed the carb? Or, just rear its ugly head out of nowhere?

i am going to have to agree with most of the peole on hear and say the 17e needle is to lean. i don't think i know anyone who is running that needle it is all the 19 and 21 needle.

I run all my XRs a little on the rich side, they run cooler, especially in hot weather.

This problem just reared its ugly head. I am getting more noise from the head as time goes on. Nothing major just things aren't as quiet as they used to be. The bike is basically stock and does about 82 mph and doesn't cut out and seems to have great power. I have the Edlebrock and an E series WB exhaust w/K&N filter. I did put 91 octane in and richened the mix and the problem is almost gone. I heard just a tiny but when really getting on it in when trying to do a corner slide out on a dirt road. I richened it up 2 more clicks but then at full throttle it cuts out on me so I put it back one click.

So far so good.

I run all my XRs a little on the rich side, they run cooler, especially in hot weather.

What kind of gas mileage do you get running with a 19 needle and a little rich?

This problem just reared its ugly head. I am getting more noise from the head as time goes on. Nothing major just things aren't as quiet as they used to be. The bike is basically stock and does about 82 mph and doesn't cut out and seems to have great power. I have the Edlebrock and an E series WB exhaust w/K&N filter. I did put 91 octane in and richened the mix and the problem is almost gone. I heard just a tiny but when really getting on it in when trying to do a corner slide out on a dirt road. I richened it up 2 more clicks but then at full throttle it cuts out on me so I put it back one click.

So far so good.

Sounding good so far, I had a little noise like you describe, turns out I had no screen in my air filter, put in a new Twin Air and cage, no mo noise! It was mostly between shifts or at low RPM.....also, if you took out the backfire screen, put it back. Itll lead to a bog when the bike gets hot and make the intake tract noisy...

Just to clarify, Doharris90, you are running the XR600 right? I think you are doing what you need to. by richening the mixture if it truly is predetonation. What did the plug look like before vs now?

JT

Just to clarify, there are two separate abonormal combustion phenomenon. They are preignition and detonation. Predetontation is not a term in this context. Preignition is mostly silent (until you burn a hole in the middle of your piston and destroy the engine). Preignition can destroy an engine in seconds. Detonation is a completely different phemenon and is not silent--it produces the tell-tale "pinging" and "knocking" noises. Most engines can withstand a certain amount of deto before something finally gives way (usually it's the piston's top ring land).

Good Call! You are correct in that detonation is what I should have been saying instead of the other which was wrong so I won't say it again. Thanks Hawk

JT

What kind of gas mileage do you get running with a 19 needle and a little rich?

Mileage varies with how I am riding the bike. Tight technical trail riding with a few fast sections usually gets me 75-85 miles with the stock tank. In open fast riding, especially in sand, I have gotten as little as 60 miles on a tank.

Thanks for the education.

Well with the 17 needle I put in some 91 octane and richened up the mix and the problem is gone. I do wonder a little about the backfire screen as I don't have one and the guy who sold me the bike had already removed it. I have a K&N Filter and a sock on the filter. I think I am going to find a UNI sponge Filter as the K&N seems to get too dirty way to fast. I do almost a100% desert.

Well thanks again for all who posted!! My problem is solved and I know alot more now. I may switch to a 19 needle but I am heading to CO. at 11000 feet and may need to keep the lean mixture.

Cheers!!!

Don't worry about not having a backfire screen. My experience with K&N is that they do not do a good job, I've been using UNI and Twin Air for several years with good results. The last time I rode my XR600 in CO (Taylor Park area) I left the 19E needle in and leaned the clicker a few clicks, it ran fine.

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