99 XT600 Severe popping under acceleration
 

Have you checked the rubber intake? and there is a filter inside the carb did you clean this? sounds to me like the problem is when you need more fuel and its not getting the right mixture.

A very long shot but a sticky inlet valve could explain it -it might allow the mixture in the inlet/carb to ignite under certain circumstances. This would clear them of combustible air and account for the bog down.

Perhaps a cheap start would be some redex and an oil change?

Timing is electrical and very hard to get wrong. You are much more likely to get no spark than one at the wrong time/place.

I agree with Bandit127, to get the popping through the carbs might require a stuck valve or timing way off. Slipped timing chain?? The cdi defaults to the early advance stage I believe or quit outright. Are you sure the poping was from the carbs?
I had a V8 car engine with high miles that the valve springs were getting weak and as the rpm hit 4500, the things would start to pop, crackle, flames out the side pipes, from floating valves. Broken spring a slight possibility, but definately check the "normal" stuff, like Mezo's suggestion, hate to overlook the simple:oops2:

The link below shows how the carbs looked when I rebuilt the top end about a year ago. the only thing I didn't pull apart was this diaphragm valve cause it was pinched in place.

Motorsports Forum - Carb Inspection/Cleaning

Mezo do you mean the coasting enricher ? what should I be looking for ? I remember the diaphragm was in good shape last time I pulled it apart but I didn't remove the brass pin below it since it was pinched in place I wasn't sure if I should play with it.

http://i879.photobucket.com/albums/a...8a512x384x.jpg

Shouldn't be a sticking valve I just a did a valve job 2500km ago and the two exhaust valves are new.
extrock the rubber intake boots were starting to seperate from the aluminum but those have been cleaned up and resealed with silicone and are still looking good, when I had the carbs apart the only filter I remember is the course foam filter for the air coming into the secondary diaphragm (top of carb) otherwise the fuel tank has screen filters on both petcocks and an inline fuel filter between the tank and the carbs.
It does sound like it's coming from the carbs and sounds a lot like the pop you sometimes hear when first starting the bike, the one that blasts out the left side of the carb, I'm getting lazy I don't wanna pull the carbs out/apart again if it's not an obvious electrical part going bad but I guess I might have to.

Yamaha XT600 1990 1992 Carburetor Rebuild Kit 00 082 | eBay

Dont know if you have same but as you see on pic there is a small filter, and i had same problem when this was full of dirt.

Thanks for that link xtrock, I can't recall if my carb has that screen or not, I noticed some of the rebuild kits include the screen while others don't, I'm not sure if it's a fuel starvation problem just yet but I'll check if my carb has that screen and see what it looks like.

Well the search is back on, I pulled the carbs and gave them a thorough cleaning, inspected every part except the coasting enricher and didn't notice anything obvious in the secondary carb, threw the bike back together and went for a short snort only 5 minutes into it the bike was popping like crazy, it seems to be getting worse with each ride cause on the previous ride it took half an hour to begin popping this bad, I'm wondering if it's an electrical issue ? would appreciate any suggestions.

I noticed the carb was sucking unfiltered air and discovered the original hose clamps even when bottomed out were not clamping tight enough, didn't take much effort to pull the rubber boot off the carb, will use another style of clamp that tightens more.

http://i879.photobucket.com/albums/a...pse75e7935.jpg

All that dirt:eek3: , it is likely that some has plugged up at least one of the air intake passages. That secondary can get stuck down with all that dirt or if the diaphragm isn't getting vacuum to pull it

What did the did filter look like inside the carb?

Filter looked good fairly clean, it's only got 2500km on it.

To eliminate a few more possible problems I drained the fuel tank/carb, pulled both of the fuel petcocks off the tank, removed the screen tubes and blew everything clean with compressed air, the screens were surprisingly clean and the tank only had a few grains of sand inside, refilled with fresh premium and installed another spark plug, hit the magic button and no spark :funmeterno: now I'm wondering if this issue is related to the original popping under acceleration problem ? any and all help would be appreciated with what to do next !

Be logical and don't jump to conclusions
 

It rarely is, IMO.
I had a similar experience years ago with a TTR600 and that turned out to be the spark plug wire connected to the coil - I had pulled on the plug so many times, checking the spark, that the connecting wire had developed an air gap inside its connection.

Basically, I suggest you check the high tension side of the ignition for continuity.
If not that, then it will be something pretty simple associated with the latest work you've done on the bike.

Done that as well!

For me was when I was putting the fuel tank back on the frame, some part must've gotten caught on one of the cables going to the ignition coil and unplugged it..

Here are the results of some testing with an Ohm meter. I would appreciate any suggestions as to what to check out next, should I have the Ignitor checked out if I can find a service that does that ?

Ignition coil, primary: 4.5 (spec is 4)

Ignition coil, secondary: 14.0 (spec is 13)

Stator coil: 0.6 (spec is 0.65)

Pickup coil: 243 (spec is 230)

Sparkplug cap: 00.0 (spec is 10k)

Sparkplug wire: 00.0 (spec ?)

So with your numbers, are you actually getting spark to your plug when it is under compression? O.O when the speck is 10K sounds like that setup isn't quite right. Sometimes even though a plug is sparking when out of the head, it doesn't or has sporadic spark under compression. Do you have another plug wire and cap to try?

No there's no spark at all, I tried another plug wire and cap from a set of automotive wires I had in the shop, they don't have the copper wire like the original but still I thought it would do if the plug wire/cap were the problem, still no spark.

You'll have to check for juice getting to the coil and see if the cdi is sending it in the first place. Start from there and work back.

Did you take the coil off the frame and scuff up the mount surface plus shine up the ground wire and all touching surfaces. You want good grounding to start with. Not just clean but physically sanded and made positive contacts.

Just an FYI. Your decel valve looks like it has been replaced already. The 3 little marks are factory marks. Mine had that too. I just grabbed the lip on the brass and rocked it a little and it came out easily. Might be worth a try. Normally this circuit is held open with the spring behind the cover of the diaphram. High vacuum from the secondary in front of the butterfly valve over rides the diaphram spring and closes the air off of the pilot jet causing a richer condition.

You mentioned popping under acceleration. I don't believe this circuit will cause this as it is to enrichen the mixture to the point it will not burn in the muffler and cause a backfire.

Is your spark good and robust? Really snap? If not, if it is a weak spindly spark your CDI could be dying. I had that happen to me, then it quit altogether.

Steve

I pulled the coil off and scuffed up the mounting surfaces but still no go, can you explain the procedure for checking for juice to the coil ? I set my tester to 200 AC and placed one of each lead to each of the wires going to the coil, turned the engine over but the meter remained at zero, I've searched all over for stator output numbers going to the coil but nothing is coming up, can't find anything in the various XT600 service manuals I have on pdf files either, I'm probably not testing it right.

Thanks for the info Steve I appreciate that, except for the extreme popping under acceleration the bike has been running excellent, starts right up runs great right up to 3500 when the popping starts, then suddenly no more spark.

Before my CDI quit altogether the bike got to be hard to start and backfired quite often. I think the CDI "CAN" die a slow death. Since yours starts and runs ok up to a certain RPM may be an indicator of CDI problems.

I did test my stator output and trigger coils for output. I did not measure the actual output values as I have a digital meter that is not a good indicator of short burst of voltage. I just wanted to see if there was AC output when spinning over to verify my stator and trigger was working.

A better meter to use if you are concerned about the amount of stator output is an analog meter or an oscilloscope.

Steve brings up a good point, can very well be cdi or the trigger coils. There is two signals a 12 degree and a 34-36ish. It may be that only the 12 degree signal is being sent or received. I have a spare cdi if it is compatible your welcome to try to see if it's you cdi. I don't have a pulse generator yet so no help there.

I doubt if the coil itself is bad, those don't fail very much plus it would probably effect low rpm also, but you can pick up new ones for relatively cheap.

Since we are on the subject of CDI's, I have been in communications with the engineer for the new CDI he is making for the XT. He is working on a starting function that MAY have an anti kickback function. He is measuring the starting RPM and adjusting the function from that. It would be adjustable as some bikes could be harder to spin over due to the rider's strength or very high compression or perhaps the decompression cable has broken. I have asked for a bypass of this function that can be done in the field if you have a decompression cable break and you cannot kick it as fast as normal. This is still in testing phase so could change or not be implemented at all. The stock ignition does retard during starting so this is being looked at and made adjustable so it could be customized by you or eliminated.

I am very excited to see this manufacturer take such an interest in these old bikes. Hopefully there is a market for a programmable and reliable CDI so he can recoup his development costs.

Stay tuned...:clap::clap:

Steve

Problem solved ! a guy by the name of webmonstro over at ADV suggested I check for broken wires at the connector for the TCI where sure enough I found a broken green/white.

This photo was taken before I started testing components, the
green/white wire looks perfectly intact.

http://i879.photobucket.com/albums/a...ps993333e9.jpg

After pulling the connector from the TCI the wire popped out.

http://i879.photobucket.com/albums/a...pse6bbeae3.jpg

Broke clean off at the spade connector.

http://i879.photobucket.com/albums/a...pse04c37ad.jpg

Lengthened the wire by an inch and installed another spade connector, the bike fired up immediately and ran perfect with no popping at all, my thanks to Mezo, xtrock, Bandit, jjrider, Walkabout, becardi and steveloomis for all your help and suggestions, thanks also jj for the offer of your spare CDI, the beast is back ! bier

http://i879.photobucket.com/albums/a...ps7a4138e6.jpg

:thumbup1: A happy ending is always good news.

You might as well take a look at the other connectors while you are there.