1st time cleaning carbs, pilot screw was all the way in?? - Snowmobile Forum: Your #1 Snowmobile Forum

edski · 11-07-2009, 04:23 PM

Hi, i just bought a 92 Skidoo Mach 1 with a 670 twin. The guy said he never cleaned the carbs so i decided to try cause it wasn't running good. The carbs are Mikuni and were VERY dirty.
I looked at the tutorial here and it said to turn in the pilot screw to know how far out it is. Well both of my pilot screws were turned all the way in. Is this right?
I also have to clean the rave valves on this sled. How do i do that? Sorry for all the noob questions.

**smallengineguy** · 11-07-2009, 06:06 PM

Turn the air bleed (pilot) screws out one turn from seated. The RAVE's can be checked first by moving them in and out. They should move quite easily. If they have any resistance, clean them.

Here's a link:

Snowmobile Exhaust RAVE Maintenance - Ski-Doo Tech - Snowmobile at Off-Road.com

Are you sure it's a 670 and not a 617? There should be a tag on top of the recoil that will say what type of engine it is.

**BC_Dan** · 11-07-2009, 06:36 PM

If someone was adjusting the carbs and adjusted the air screw for best idle and it ended up having to be in all the way, that would indicate plugged fuel passageways to the pilot jet, or the pilot jet is clogged. Usually, cleaning the carbs and paying attention to the air and fuel passageways to the pilot jet helps. Then set the carb as SEG suggests.

TwinsofMLB · 11-07-2009, 08:11 PM

This is a 93, I have both a 93 670 and a 92 617.

edski · 11-08-2009, 06:16 AM

are we all talking about the same screw? It's the small screw next to the main jet, it is pretty small.

Ultrafrozen · 11-08-2009, 06:16 AM

1992 Formula Mach 1 (type 643 engine), Pilot Air Screw = 2 turns out
1993 Formula Mach 1 (type 670 engine), , Pilot Air Screw = 2 3/4 turns out

From Ski-Doo 1990 to 1995 Clymer shop manual

TwinsofMLB · 11-08-2009, 09:39 AM

Manual's wrong

Mine is best at about 1, like SEG said.

edski · 11-08-2009, 11:51 AM

alright, i turned the air screw 1 turn out. I started it up and it ran for about 5 minutes. It would idle at about 2,500 RPM, then would shoot up rapidly to 3,000 RPM. It even dropped to 1,500 RPM for a little. Don't know what's up with that?

Oh, by the way it is a 617, the guy i bought it from said it was a 670.
Also, i took the cap off the rave valve, there is grease all over the inside of both of them. Is this normal? I loosed the nut on both and they both move freely in and out.

**RJ Gleason** · 11-08-2009, 02:00 PM

Time to check for air leaks at the crank seal and carb mounting flanges.

edski · 11-08-2009, 06:55 PM

i forgot to mention that the plugs keep getting wet also.

**smallengineguy** · 11-08-2009, 07:39 PM

Wet RAVE's means that the rubber bellows are cracked. Easy to replace.

YamahaSS440 · 11-08-2009, 07:50 PM

My sled did the same thing where it would idle high, then drop like 500-1000 rpms, My problem was the carb idle screw were way out of wac and not synced. I thought it might of been the crank seals but it wasnt.

edski · 11-09-2009, 06:10 AM

my rave valves weren't wet, it looks like someone greased them below the cover.
Also, which screw is the carb idle screw?? How do you sync these carbs?
I guess i will have to look up the carb. model # and get some schematics so i can find these things. Sorry for being such a noob.

**smallengineguy** · 11-09-2009, 06:12 AM

I'm trying to remember if there are weep holes in the rubber bellows. Take them apart and clean the RAVEs and see if everything is OK.

edski · 11-09-2009, 06:14 AM

Quote:

Originally Posted by smallengineguy

I'm trying to remember if there are weep holes in the rubber bellows. Take them apart and clean the RAVEs and see if everything is OK.

ok, i'll do that, thanks for your help. I might need some more so be prepared. lol!

Now i just read something about grease being on the engine. Could this mean crankshaft seal is bad? This engine has grease all over it. The rave valve covers have grease all over them too.

edski · 11-09-2009, 05:16 PM

It started up good today and i let it run for about 5 minutes, it is running around 3,000 rpm. When i gave it a little throttle soon after it boggs out and the plugs get wet. What does that mean?
The screw on the side of the carb. is the air jet right? I have that turned 1 turn out. What is the tiny recessed screw next to the main jet? I have that all the way in.
Sorry, but i cannot find any #'s on my carb. besides a #4 then looks like 40, then 49 underneath.

**RJ Gleason** · 11-10-2009, 07:13 AM

The pilot jet air screw is the small one, the idle speed is the one with the spring on it.

edski · 11-10-2009, 07:18 AM

Quote:

Originally Posted by RJ Gleason

The pilot jet air screw is the small one, the idle speed is the one with the spring on it.

See this is where i am getting confused. You keep telling me pilot air screw, in the tutorial it shows the pilot JET is next to the main jet.
I have 2 screws with springs, a big one with phillips head, and a smaller one to the left with slotted screw. The smaller one to the left is the pilot air screw that you are talking about right? What about the pilot jet, next to main jet, how should that be set? I am so confused.

**RJ Gleason** · 11-10-2009, 07:31 AM

Then you do not have the standard Mikuni carb.
Is it a rack set up?
Can you show a picture of it?

edski · 11-10-2009, 08:05 AM

RJ, i am pretty sure it is a standard Mikuni Carb. I was wrong on previous post. The big phillips screw i am assuming is the idle screw, right? On the other side of the carb is another screw that is slotted with the spring inside. I am assuming this is what you are calling a pilot air screw?
The tiny screw under the bowl next to the main jet is called the pilot jet??? That is the screw that was turned all the way in. Is that where it's supposed to be?
Don't know what a rack set up is.