Help needed, SRX dropping cylinders under load.

T

Theicor

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I just got back for a trip out west with my SRX700 powered mtn. sled and I was having some peculiar issues with it. The engine was just freshened and had Mega power heads installed along with some custom Hauck pipes. Other than that the engine is stock. I am running a stock airbox with the ATACC and jetted at 157.5 straight across with 45 pilots and screw out 1.5 turns and needles on third clip with both washers underneath the clip. I did two throttle chops with it, once in the midrange and once wide open. Both yeilded, gourgeous plug readings. Now the issue is when I am on the trails or on hardpack the engine pulls like a banshee. Once the engine gets into a climb with heavy snow or a lot of load and I go to grab a handfull of throttle, one of the cylinders will start dropping off and eventually will quit all together if I don't back out of it, when i do back out of it, all of the cylinders eventially light back up again as long as I don't go for wide open. This occurs on all cylinders randomly. When a cylinder does go down, I change out the plug and away I go. The mag checked out good and the coils checked out good at the Yamaha dealer. Is there a chance that I am jetted too fat in the main but my needle setting is lean enough that I can't see an issue until I go WFO? I am kinda confused. :o| If it is indeed a jetting issue, should I raise my needle and go smaller on the main a couple of sizes? Any help would be appreciated!
 
I have an srx based mod as well with the atacc my baseline jetting is 147.5,147.5, 148.8 but I live at 3000' and ride between 6000 and 8000'. I think I am going to go down one size all the way accross based on my egt and plugs. The atacc should be good for 10000' of adjustment but with temp and barometric pressure changes you may be asking it to do too much. Could it be a clutch bog?
SRXM5
 
That was something I was beginning to wonder too, if the ATACC was running out of range. I am jetted to 1000' at -20* and was riding from 6700' - 10000'+ in 30* temperatures. the clutches are dead on and there is no powder in the airbox, heck, there wasn't even any powder to be found during the whole trip... :o|
 
we were out this last weekend and I noticed that my sled was running cool egt's compared to the last few colder drier days (it was warm and wet). The sled wasn't blubbery but it was on its way to being that way.I think you may a little fat on your jetting. Just remember that where you unplug that hose on the atacc is where your baseline is. So if you are in your 70 degree shop thats where the atacc thinks you want to ride so you need to adjust your jetting accordinly.
SRXM5
 
So are we leaning in the direction of saying that this is a jetting isssue I am having, not something else?
 
I honestly couldn't say that is your problem for sure I'm just saying that its possible your on the upper end of the range that the atacc can handle so that is one place to maybe look for some improvements.If its randomly dropping cylinders its not likey a coil issue. Bad ground somewhere?
 
Still looking for other opinions. Even without the ATACC, does this sound like a jetting issue, ore something more involved?

Thanks!
 
droping

i just fixed mine as the problem sounds the same as what i had drop 1 cyl then a differnt one it turned out to be a bad stator. i run a open air box bender stage one moter and 157 mains you could see this on the egt running from cly to cyl
 
Awesome!!!

That is awesome to find someone with what sounds like the same problem, I got the jetting stuff figured out and dialed in, and I was starting to lean towards swapping out the stator as we head into the new season, but now it is confirmed. It has been a while since I have visited, thanks black john for the info, and I am going to swap out my stator, hopefully it works. ;)!
 
I had the ATACC on my 00' srx and I burned it down twice so when I rebuilt it the second time I took the ATACC off and the sled ran great, so I threw the ATACC in the garbage.
 
My 700 sx did this after I put my peak head on it. never did it before that. Are you sure it is not the head doing it. maxdlx
 
Although I do not use jet compensation devices(just can't bring myself to trust them)there are another couple of options you would be wise to consider.Check your fuel filter,pump and lines for a MINOR restriction which will cause fuel level in one or more carbs to drop too low only under high fuel demand causing cylinder cut-out until the throttle is backed off and the fuel level can recover.
 
Keep it coming...

Thanks for the added info. I have been in the habit of replacing the fuel lines from the pump to the carb every year since it is easy to do when I clean the carbs anyway, but I can give a check to the lines running from the tank to the fuel pump. I should add though that when the cylinder dies the plugs are pretty wet, and when the cylinder does go down, whatever one it may be it usually doesn't recover as one would expect if there was a lack of fuel, but point noted. I am a little confused how the head could create this condition, I would like to hear more on this one. And, yes I do agree that compensation devices do seem a little hokey, but I have had this one for a couple of years now and I have so far been pleased with the operation of it... Knock on wood... ;)!
 
I had to dig this back up...

Well, it is a new season and I haven't cured the issue. Before the season started I went through the entire ignition system, replacing the stator, coil packs, wires, caps etc. I had the ATACC recalibrated and updated by Holtzman. I started off with my 1000' baseline at 155 mains, needles on fourth clip with one washer under. Sled started acting up again the first day, after the third day of jetting I ended up with the ATACC disconnected with 140 mains (7000+ ft), and needles at third clip no washers under, and BR9ES plugs, since they didn't seem to foul as bad as the ECS, that and I had already burnt through all the plugs I had, more than a box.

Needless to say the sled is in the shop again. I pulled the heads, and the wash looks nice, slightly lean on the mag cylinder but allright, and I am looking in other directions.

I am thinking that the CDI may be getting weak and the three cylinders are fighting for spark, this reason being that on one particular day when I was heading back down the trail back to the hotel with two cylinders running, I literally watched the dead one and one of the live ones fight back and forth to run, I would drive a couple of miles and the dead one would start to light up, and as that one built up temps, one of the other cyls would drop off almost simultaneously until the the dead one was running 100% and the live one went completely dead. These two cylinders fought back and forth four times like that until I got home. So I have pulled the CDI and I am hoping to try it this weekend on my other '98 SRX to see if it will act up.

I am also going to check the power valve adjustment, and the reeds. I am pulling my hair out on this thing. :o| Help! I would like to get one good year out of her before I have to part with her...

Much thanks to everyone...
 
Are you still jetting for 1000@-20 and riding at 7000+@30ish. Because if you are you are have pretty much maxed out the ATTAC. It will handle the 8-10 thousand feet of elevation change with no temp change not 8-10 and 50 degrees warmer.

That being said it does sound like you probably have electrical issues as well.
 
When I recalibrated the ATACC last year, I had them set the screw to 0 degrees to get some more range and I jetted for that, So I originally started off at 1000' and 0 degree baseline. It was still acting up though with the ATACC disconnected and straight jetted with 140s in. We are getting snow here now today, hopefully it keeps on coming so I can do some testing this weekend...
 
If this is a 98-99 srx, the cdi could be your root of all evil, they fire all 3 plugs at once and have a common problem of not cycling the power valve servo motor. When firing all plugs at once its more of a voltage strain on the cdi box signal going to the coils, that same signal supplys juice for all 3 coils to fire, so if it became weak, your coils cant produce peak voltage, and wide open requires the most amount of voltage to the plug. The sled could run ok sometimes but wont cycle the valves and sometimes DO have intermittant spark problems, the 2000-02 dont have the problem, with the 3d ign system they fire only 1 plug at a time and I have never had to replace one for a servo problem. I would try a cdi and see if it cures the problem, I dont think jetting is your problem, if it was so rich it would drop a plug on and off it would have the piston tops washed clean, bright silver.
 
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I apologize for not mentioning this earlier, but yes the sled is a '98 model. I am thinking the exact same thing that you are MrViper, all the way from the jetting to the CDI. With all three coils firing they are fighting for spark with a weak CDI. Can you explain to me about the power valve cycling issue? It may be another way of verifying the poor CDI. When you mean cycle the valves, is that during normal operation, or cycling during startup and shutdown?

BTW, does anyone have a 98-99 SRX700 CDI to part with if that is the problem?

Thanks!
 
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