685 flooding on cold start

[Kmitch1971]

Hello, looking for some help with a jetting issue I’m having with my 685. Long story short last summer I bought what I thought was a mint low mile (~1,700/117 hrs) 2007 600 HO RMK 155 with some nice goodies on it (Ice age rails, full Holz suspension and spindles with Floats up front and zero pro’s in the rear, Simmon’s flexi skis, big wheel kit, cable scratchers, full SLP single pipe/can, SLP air horn, extra air plenum venting, the works). Turns out it’s a 685 with 42mm carbs, also had a Boondocker nitrous manifold in the airbox and button on the bars but no bottle/solenoid. Compression was low at ~100 psi each hole when I bought it and I planned to do a full rebuild.

The engine has Indy Specialty TMX685 cylinders with gussets. Indy specialty confirmed they originally did the crankcase/cylinder/exhaust valve work but not the head.

I decided to have Indy Specialty do the HG7 cylinder hone, inspect/balance/true the crank, balance and rebuild both clutches with a full clutch kit.

The engine was reassembled with new ProX ART pistons, full gasket kit, new water pump seal, carbs cleaned and rebuilt with genuine Mikuni parts (with the exception of the choke plungers which look to be in good shape). Oil pump/lines properly bled per Indy Specialty guidance.

All nitrous parts have been removed and carbs are vented to air box.

Broke in per Indy Specialty guidance with 50:1 premix (half 92 non-oxy half 110 race fuel) at 1,000’ (my local MN elevation). The 110 was because I was a little concerned about the tight squish of 0.050” and possible DET. Turns out 0.050” is the bottom end of the spec for a 2007 600 HO.

Compression is even at 160 psi/hole cold (uncalibrated compression tester).

Current set up:
92 non-foxy premium fuel
440 mains (450 during break in)
55 pilots
145 starter jet
#2 clip position
9DGN6-57 needle
1.0 out on fuel screw
0.9 air jet
TPS 4.0 volts @ WOT
Needles/seats hold 5 psi
Throttle slides/cable set per Polaris manual
Choke cable has proper slack


I ran this setup in West Yellowstone for 5 days (Very close to Carl’s specs):
350 mains
55 pilots
145 starter jet
#3 clip position
9DGN6-57 needle
0.5 out on fuel screw
0.9 air jet

Here is my issue, ever since getting the engine back together I struggle to get it to start when cold. Instantly floods with no choke. The only thing that seems to work is a shot of ether in each cylinder, fires right off on first pull and then ~5 seconds of light shots of ether to the air box.

Once it is warm I can stop/start dozens of times a day-although it still seems fat at idle. Will barely start with no throttle, starts much better holding the flipper open about 1/4”.


I love the motor once it is running, quick revving, lots of low end grunt, pulled 70 gram Indy Specialty adjustable mountain weights/clutch kit out west to 8100 rpm, absolutely rips and will run with (and embarrass some) 800’s all day long. Gets about 8-9 mpg being hammered on.

I know, I spent a-lot of money to rebuild a 15 year old IQ RMK but I only spent $2450 on the sled. Fits my needs for my one trip out west per year.

I’m considering progressively going smaller on the starter jet, pilot air jet and turning in the fuel screw to try and resolve the issue.

Is there something else I’m missing here?

Any help/insight would be appreciated.

 

[triedit]

Hello, looking for some help with a jetting issue I’m having with my 685. Long story short last summer I bought what I thought was a mint low mile (~1,700/117 hrs) 2007 600 HO RMK 155 with some nice goodies on it (Ice age rails, full Holz suspension and spindles with Floats up front and zero pro’s in the rear, Simmon’s flexi skis, big wheel kit, cable scratchers, full SLP single pipe/can, SLP air horn, extra air plenum venting, the works). Turns out it’s a 685 with 42mm carbs, also had a Boondocker nitrous manifold in the airbox and button on the bars but no bottle/solenoid. Compression was low at ~100 psi each hole when I bought it and I planned to do a full rebuild.

The engine has Indy Specialty TMX685 cylinders with gussets. Indy specialty confirmed they originally did the crankcase/cylinder/exhaust valve work but not the head.

I decided to have Indy Specialty do the HG7 cylinder hone, inspect/balance/true the crank, balance and rebuild both clutches with a full clutch kit.

The engine was reassembled with new ProX ART pistons, full gasket kit, new water pump seal, carbs cleaned and rebuilt with genuine Mikuni parts (with the exception of the choke plungers which look to be in good shape). Oil pump/lines properly bled per Indy Specialty guidance.

All nitrous parts have been removed and carbs are vented to air box.

Broke in per Indy Specialty guidance with 50:1 premix (half 92 non-oxy half 110 race fuel) at 1,000’ (my local MN elevation). The 110 was because I was a little concerned about the tight squish of 0.050” and possible DET. Turns out 0.050” is the bottom end of the spec for a 2007 600 HO.

Compression is even at 160 psi/hole cold (uncalibrated compression tester).

Current set up:
92 non-foxy premium fuel
440 mains (450 during break in)
55 pilots
145 starter jet
#2 clip position
9DGN6-57 needle
1.0 out on fuel screw
0.9 air jet
TPS 4.0 volts @ WOT
Needles/seats hold 5 psi
Throttle slides/cable set per Polaris manual
Choke cable has proper slack


I ran this setup in West Yellowstone for 5 days (Very close to Carl’s specs):
350 mains
55 pilots
145 starter jet
#3 clip position
9DGN6-57 needle
0.5 out on fuel screw
0.9 air jet

Here is my issue, ever since getting the engine back together I struggle to get it to start when cold. Instantly floods with no choke. The only thing that seems to work is a shot of ether in each cylinder, fires right off on first pull and then ~5 seconds of light shots of ether to the air box.

Once it is warm I can stop/start dozens of times a day-although it still seems fat at idle. Will barely start with no throttle, starts much better holding the flipper open about 1/4”.


I love the motor once it is running, quick revving, lots of low end grunt, pulled 70 gram Indy Specialty adjustable mountain weights/clutch kit out west to 8100 rpm, absolutely rips and will run with (and embarrass some) 800’s all day long. Gets about 8-9 mpg being hammered on.

I know, I spent a-lot of money to rebuild a 15 year old IQ RMK but I only spent $2450 on the sled. Fits my needs for my one trip out west per year.

I’m considering progressively going smaller on the starter jet, pilot air jet and turning in the fuel screw to try and resolve the issue.

Is there something else I’m missing here?

Any help/insight would be appreciated.

Are you sure it is flooding not out of gas in the carbs . If it is truly flooding then start with float level floats should be level with carb upside down or a little bit higher than level choke plungers leaking by if rubber is hard . I had a bad fuel pump that would leak fuel into the crankcase . Reeds if they are not sealing could give you those symptons

 

[Ox]

Interesting that you say that the seats hold 5psi.
Never heard of anyone actually check that before...

I would agree with the float levels in most cases. I could never understand it, but Pol sleds have always had flooding issues if parked pointed downhill.
It always seemed like Pol must'a opted for a cheaper needle/seat combo, but I think that I heard that Pol has their float levels set higher.
So if downhill and hot was the issue, then I'd say to adjust float level down, but it sounds like your issue is different.

But if you are dead sure about it being flooded at cold start, then I don't know what it could be other than needle and seat leaking past.

On the other hand, having to give it a snort to start, and a cpl more to keep it running, does sound like a dry float bowl.

IDK how big of an issue this is on that chassis, but have you ever just took the plugs out in the morning and opened the throttle, and yanked it over 3-4 times, and then put the plugs back in?
If it is actually flooded, you should see it blow gas right out the plug holes, and it should then start right up.

I think that the first thing that is easy and cheap, and will help rule out one issue - is to pick up a fuel shut-off valve and plumb it in. (Dennis Kirk) Back in the round slide days, Doo used to run these as stock, but Pol never seemed to. But Doo quit it when they went to flat slides. I think that they said that the newer pumps had a valve inside of them that acted as a shut-off valve? Not sure how that would work (possibly like a hydraulic chuck actuator on a lathe?) but I have never had this issue on my flat slide Doo's, and we ran them lots of years. Still have one or two...

I guess that I don't know from your post if you are running rounds or flats. But a shut-off valve closed up overnight will keep the static pressure in the tank from pushing past the needle and seat overnight, and then you can see if that really is the issue.

I know that you said that they hold 5psi, but ...

[late thought]
Doo you have a fuel filter inline?
Any chance that you got some Schidt in the needle / seat?
I'm sure that your 5# test was on the bench, not after having issues - right?
[/late thought]

Not sure if there was any point in typing this in as it appears that you (original poster) hasn't logged in since the day that you started this thread.
But you may get e-mail notices so ...

 

[jim]

New float needle and seats might help. Verify its flooding and explained above. Good plugs at proper gap? How is the cold start? And you can easily rule out flooding or lean at start with using choke.

 

[Kmitch1971]

Long overdue update, my problem is solved. I went back to Indy Specialty (Cannon Falls, MN) to get some advice from them. After explaining my issue/settings/specs it took less than a minute for him to suggest that my TM-38's bored to 42mm could be the source of my starting issue. His theory was that the boring altered the dimensions between the bottom of the carb bore and the slide cutaway enough to impact starting. Suggested that I get a stock set of TM-38's and try that. I ordered up a set from ebay, rebuilt them with genuine Mikuni parts and now it starts cold in 1-3 pulls. I can't tell any difference in overall performance from the 42's. Also had him build a low elevation pump gas head with interchangeable domes I can't say enough good things about the quality of Indy Specialty's work, customer service and willingness to help figure out an issue on an older machine. Even the way they package their parts for shipping is first class.