compression readings - Snowmobile Forum: Your #1 Snowmobile Forum

polaris_indy22 · 12-23-2012, 12:47 AM

Today i did a compression reading on my 1991 indy 650 rxl efi now i have a few questions.

1. As i was pulling the plugs from clutch side to water pump side i notice that the plug on the clutch side look normal but the other two look dark and oily. what could this be from?

2. I took the compression readings with WOT and the readings were from clutch side to water pump side 130-125-115. All the readings should be close to 130 right? also i have heard that the readings should be within 5psi of each other. is that right? Obviously mine arnt so what does that mean?

Clutch side to water pump side

**RJ Gleason** · 12-23-2012, 06:33 AM

That would be 10% of each other, which you have.
Was that warm or cold test?
The one plug looks perfect color.

polaris_indy22 · 12-23-2012, 09:09 AM

so u think that those are good numbers? i thought they seemed kinda far apart. it probably wouldnt hurt to rebuild it next year would it? and that was a cold test. on the plugs what do u think is causing thoes two to be really black? i talked to my dad this morning and he said it sounds like it its getting oil fouled. he has never really looked at it and he doesnt know much about snowmobiles but he knows his engines.

Any ideas??

ClassicIndy600 · 12-23-2012, 12:33 PM

are all three plugs the same?

**RJ Gleason** · 12-23-2012, 03:57 PM

What I would recommend is that you do a seal test.
Start it up and spray some carb cleaner or starting fluid at the crank seals and the throttle body mount flanges. If the rpms go up, there is an air leak.

**BC_Dan** · 12-23-2012, 06:04 PM

I agree, the left plug looks perfect. If I were jetting a carb sled, I would jet more like the right one, so there would be a bit of fudge factor when riding in colder weather. But for EFI, they should all be about like the one on the left.

The center one does look more oil-fouled than the right one. Not much you can do to change either the fuel or the oil. It's better to have a bit too much oil and fuel than not enough! As long as the sled isn't continually fouling plugs and runs fine, I wouldn't worry too much.

I would run a half can of SeaFoam with the next tank of gas, that may help clean out the fuel system a bit and give more precise metering. But I do a half can on the first tank on all my sleds, just because. I really should buy stock in SeaFoam and WD40

polaris_indy22 · 12-24-2012, 10:52 AM

yes all three plugs are the same only had two runs on them. i will get some carb cleaner from my dad and test the crank seals. we have a 79 enticer 250 thats going to need crank seels im pretty sure.

also i was wondering if i could remove the oil injection system and just premix the gas 32:1 that way it cant inject more oil than it needs. if i cant do that how would i fix the oil fouling. bc i really want the top end back.

i have already Put seafoam in the tank i use seafoam in all my toys

could having different plug wires cause anything?

musicfreako · 12-24-2012, 11:05 AM

Check your plug gaps also

polaris_indy22 · 12-24-2012, 11:08 AM

what should they be gaped at?

white lightning · 12-24-2012, 11:18 AM

.028 I think - WL

**BC_Dan** · 12-24-2012, 05:37 PM

Keep the injection. At idle, it's giving you 150:1. At wide open, maybe 32:1. When the throttle varies, the oil delivery does, too. If you were to mix 32:1, your plugs would be even worse.

meburdick · 01-08-2013, 04:24 PM

Quote:

Originally Posted by BC_Dan

Keep the injection. At idle, it's giving you 150:1. At wide open, maybe 32:1. When the throttle varies, the oil delivery does, too. If you were to mix 32:1, your plugs would be even worse.

Not to mention that at least some EFI machines specifically say to NOT pre-mix and run the oil through the fuel injectors.