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Discussion Starter · #1 ·
I have an '87 Phazer that my kids ride. It's been a great sled but developed a miss last year that starts in the midrange and gets steadily worse as the you try to build RPM's. It idles perfect.
I've been through the entire ignition system. (stator, coil, CDI box)
I'v thoroughly cleaned & checked the carbs sevaral times, including the chokes.
The motor is pretty fresh,(New pistons, rings & crank seals)
I just opened up the pipe as I was suspecting an exhaust obstruction, but it was fine. About the only thing that I haven't changed is the labrynth seal and the wiring harness.
Anybody got any ideas or experience with somthing like this?

HELP!
 

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ZR rider
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How does the belt look? Does it do it with the rear end elevated?
 

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intermittent miss under load?

definately in the motor and not the drive?

have you checked the coils and the plug caps and wires? you would be surprised what a new cap or clipping the wires back to a non coroded contact point will do when you need the most spark.

next thing i would check is for rust on the flywheel or any corrosion or dust on the ignition contacts under the flywheel.
 

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Discussion Starter · #4 ·
The Coil and plug caps were all replaced and are new. It runs the same as before I changed them. I have had the flywheel off and inspected it and the pickups which are clean & rust free. It's not really itermittent it does it every time, it just doesn't do it at very low RPM. It will idle perfect, & take off OK. If you run it at very low throttle openings it runs pretty good, as soon as you try to increase speed by opening it up more it begins to miss & run on one cylinder (Mostly) If I have the rear end off the ground with it wide open it will keep runing if I pull the left plg cap but will stall if I pull the right. (Yes it does this when I raise the rear end off the ground & pin it also)
I've also inspected the reeds which look perfect. I wil be trying to isolate the motor from the wiring harness this weekend. Maybe a wire is shorting.
 

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ZR rider
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Hmm... are you sure the left plug is definitely firing under pressure? Is the plug dry when you pull it out, in other words?


Take the airbox off and give it full throttle while watching the slides in your carbs. Is the one on the left definitely rising as much as it should be?
 

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Discussion Starter · #8 ·
Well,
I was able completely isolate the entire wiring harness running the sled with only the igition system hooked up and it still runs the same. (With a new set of plugs also, which have been changed several times) I went ahead and did a compression test, and both cylinders are at 110 PSI according to my gauge. Keep in mind that new pistons were just recently installed. I am sus[ecting caburetion again as I have pretty much ruled out anything in the ignition system. Althoug I have had the carbs apart several times and everything looks good. I does seem to be jetted rich, although this is the same jetting that has been in the sled since I've owned it. (Many years) and it's always run great.
Is it possble that main jets can suddenly wear out & become lager (Richer)?
The other thing I'm unsure about is the labryth seal. (The crank seal between cylinders) does anybody have any practical experiecs as to the symptoms of a bad labryth seal?
Please let me know. I've already spent too much money on this old beast but I really want her to run strong again!
 

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the main jet would not be able to oversize itself. if someone ran the wrong item through it during a cleaning process, then it could have been reamed larger. the main jet wouldnt necessarily affect the mid range problem.

you can confirm the float level is set correctly on both carbs and the rubber caps installed in the proper locations, as well as the butterflies being in sync.

my experience with labryinth seals is when they fail they usually spin on the crank or in the case and you will know it by the noise or the broken crank.
 

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ZR rider
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I'd be more concerned that your jets are too SMALL. I had a problem a lot like this on my zr this year and I found out that the previous owner had set it up for warmer weather with smaller jets (350's, should have been 370's). I replaced those and it helped me out a lot. My other problem was that my carb boots were held on by crappy sealant and I was getting a vacuum leak. I replaced that sealant and between the jets and that it started running great again.
 

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Discussion Starter · #12 ·
I did make sure the plugs were gapped correctly. As I have each time Ive replaced them. Please keep in mind that this condition developed when I owned this sled and no work had been done to it until after it began to run irratticly.
With regard to the carbs, iI have checked the float levels on each occasion that the carbs have been off (Several) but I do want to re-check the rubber plug positions, as I can't swear I remember that the jets having the plugs over them, as I have read in other threads that there should be. There must be some other path for the fuel to get to the jets.
If anything though. the jetting seems rich as the plugs are black & wet after running WOT for a short time. I've never had this much difficulty diagnosing an engine issue before.
The only reason I questioned the labvryith seal was I was wondering the effects of excessive pressure leaking from one side of the crankcase to the other.
Everyones comments are much appreciated.
 

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Discussion Starter · #14 ·
They do seem rich & fouled, but why? The jetting has not been changed, and the sled always ran great for many years with the same jetting!
 

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I'd say you narrowed it down to that seal then.
 

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Discussion Starter · #16 ·
I went ahead and moved the rubber plugs to the pilot jets as has been suggested by some of the treads I've read. The sled now runs much worse. (This really never made any sense to me anyway) it will now only barely idle, and if I give it some choke/enrichment I can get it to rev a littlte but it sounds like it's only running on one cylinder then after 10-20 seconds it wants to die, and will only Idle again.
I noticed that I've got 145 mains and 56 pilots in it. From what I've read, the 145's are definitly on the rich side.
I think I'm going to unplug the pilots and try a little leaner main jet. If the labrynth seal is the culpret, that will be an expensive and labor intensive ordeal.
 

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I've got the same exact sled dooboy, and it was a real struggle to get it jetted properly. It runs well now, I've got the rubber plug over the pilot jets, size 125 mains, and 95 pilots. It was originally over the other hole, leaving the pilot jet uncovered. It runs a helluva lot better now. I ride at pretty high altitude though, 6000-10000 Ft. I downloaded the free manual here:http://www.snowmobileforum.com/yamaha-snowmobiles/39584-1984-1989-yamaha-phazer-manual-pdf.html

I'd use the jetting chart in the manual as a guide, and go down on the mains, and up on the pilots. Sounds to me like you could be too rich on the mains and too lean on the pilots. Stock jetting on the '87 Phazer is 143.8 mains and 95 pilots. Yamaha jetted these sleds for sea level from the factory, so unless you ride at or near sea level, you're definitely rich with those 145's. I don't think you should have to change the pilot jets from the stock 95's no matter what the elevation is, so I'd try installing the stock 95 pilot jets.

The rubber plug placement on these Phazer carbs seem to be a common source of confusion; the manual tells you to leave the pilot jets uncovered, yet most people's opinions suggest plugging the pilot jets. I speculate that the proper plug placement might vary based on elevation because this factory document that depicts the pilot jet plugged off and has been used to refute the manual's instruction is titled "High Altitude Recalibration Program":

[/IMG]

Maybe unplugging the pilot jet and plugging the other circuit according to the manual's instruction is correct if you ride at low elevation?

Another suggestion: been told that you can remove the float bowls and access the main jets without pulling the carbs if you remove the secondary clutch first. Won't help with swapping the pilots (for that you'll still have to remove the carbs to get at them, but for moving the rubber plugs, or changing the main jets it should do the trick and save you some hassle).
[/IMG]

Good luck man, I hope you fix it soon.
 

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dooboy, my 87 phazer is doing the same thing. I have a possible scenario and question that needs to be asked of a Yamaha Mechanic, not just the counter person.
Did Yamaha put a low oil ignition cut-out in these sleds? If they did and the sensor in the oil tank is bad, it would allow the engine to run perfect up to a certain rpm, allowing you to get someplace you can get more oil. (not leave you stranded)

I KNOW Yamaha did this on their outboard motors all the way back in the eighties. On the outboard I know how to bypass this circuit to test but have no idea on this sled.
My problem is I don't have a Yamaha dealer/mechanic I can talk to. That is why I'm on this site...
Let us know what you find out.
 

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Jack, message yamadad4.
 
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