07 RS Viking (973cc Carbed) - Hard Starting/Backfiring

[John B]

Good morning everyone, I've got an 07 RS Viking, with the 973cc carbed engine so I thought I would just post this in the RS thread shere since my issue it likely isn't unique to the Viking and this might catch a wider audience.

I've owned the sled for ~6 years, and it has given me zero starting problems. Historically, my starting routine when cold has been full choke, turn key, it would start immediately, I leave full choke on until the temp light shuts off, slide off the choke, and it is good to go.

But this year I have had issues with it starting when cold. I have to crank it over to the point the battery is starting to die before it starts to sputter/backfire and eventually it will start. Once it starts, it runs fine, no hesitation no issues whatsoever. But when it cools off, it usually starts hard again.

Things I have done:
- Cleaned carbs (I always run non-oxy, and the carbs were very clean)
- New Plugs
- New Coils
- Pumped out the gas (it was 50/50 mix of old and new gas)
- Put in fresh non-oxy gas with some seafoam in it.
- Installed new battery

One odd thing I noticed that "might" be related so I thought I would mention it:
Yesterday, I cranked it over to the point the battery was getting weak, I attached my little jump pack and it started immediately when I turned the key.
Today, it cranked over and wouldn't start, it didn't get to the point of backfiring yet, and the battery was still turning it over just fine. But just for fun I attached the jump pack, and it started up.
The jump pack has a quick connect, and the leads are attached directly to the battery.

Anybody have any thoughts as to what I should look at next?

Thanks in advance for any help, I really appreciate it...

 

[DGZRT]

I would start with a new battery first ! might cure all your problems ....

If it has carbs the bowls might be dry if it's been sitting for a while . You can crank forever sometimes and it won't start . You can blow air into the Vent line . located in left foot well . Small line with a spring around it going into the Support bar of the foot well. I take a air compressor and turn it down to 20# and blow just a little air up the line you can see the gas cap rise just a little . Have a clamp ready and clamp off the hose to keep the air in the tank. wait 2 mins and start cranking . Should fire ! then replace the line on the fitting . Once you have done it a few times it only takes a min. Once bowls are full you should never have to do it until next year .......
I posted this the other day . I have two carbed Vectors and do this every year .

This product is far superior to Sea foam for getting dirty carbs clean . I use one in both sleds at the start of the year .

This product is the best thing ever! Drop them into your tank and your fuel stays good for years . I have them in all 4 of my sleds .

And last clean your starter relay ... Located under the air box next to the oil tank side of the battery. Make sure all the green stuff is gone .

 

[Roger]

I had a 2008 rs Venture, carbed, not starting properly, and actually dying on the trail, when I let go of the throttle!
The engine was defective! It had a cracked exhaust valve, so it wouldn't hold enough compression to start it properly.
My dealers first response once they completed a "leak-down-test", "let's see if Yamaha will cover this under warranty!"
My response to that statement was, "if they don't, you can keep the f...ing sled!"
Apparently my engine was the first 4-stroke Yamaha engine to fail, suuuure!
Anyway, it was fixed under warranty, and I traded it two years later, to the same dealer, as I was starting to have starting issues again!

Sure hope this isn't your issue.

Good luck!

 

[John B]

Thanks everyone for the advice so far.

Unfortunately I dont have a leak down tester. I did a quick compression test, engine was cold but it was consistent across all 3 cylinders (~180 psi).

I also have a borescope and looked at the pistons when I replaced the plugs, everything looked OK.

It does seem like it turns over easier than it used to when I try to start it, maybe it is something with the exhaust...

 

[BACK COUNTRY YAMAHA]

Are you getting in codes? Sounds like your battery is getting drained, some of the earlier pros had issues with the voltage reg up in the nose, if the sled was operated in a corrosive environment , basically the pins on the reg would rot off thus no longer charging your battery. Pull up the rubber flap upfront and unplug the plugs and look at the pins on the reg and sockets in the harness. Cheers!

 

[John B]

Are you getting in codes? Sounds like your battery is getting drained, some of the earlier pros had issues with the voltage reg up in the nose, if the sled was operated in a corrosive environment , basically the pins on the reg would rot off thus no longer charging your battery. Pull up the rubber flap upfront and unplug the plugs and look at the pins on the reg and sockets in the harness. Cheers!

Havent gotten any codes, but will check those connections. The battery was getting weak, but it was in the sled when I bought it, probably 10 years old.

I ordered a leakdown tester, supposed to get it tomorrow. I will post any results from that.

It seems to start easier if I dont use the choke as well,

 

[74Nitro]

Why did you change the coils?

 

[John B]

Why did you change the coils?

Mainly because I am an idiot throwing parts at it. One of them had a cracked connection but still worked so I decided to just get a new set.

 

[DGZRT]

Sorry should have read the first post again.
New plugs
coils
batteries

I would say clean the carbs again and Sync them .

 

[74Nitro]

Mainly because I am an idiot throwing parts at it. One of them had a cracked connection but still worked so I decided to just get a new set.

Ok, so the problem existed before changing coils.

 

[Confused]

Havent gotten any codes, but will check those connections. The battery was getting weak, but it was in the sled when I bought it, probably 10 years old.

I ordered a leakdown tester, supposed to get it tomorrow. I will post any results from that.

It seems to start easier if I dont use the choke as well,

If the battery is potentially 10 years old, certainly replace it. 3 years is all I ask of a battery.

 

[grizztracks]

Hard cold starts can be an indication that the valve clearance is out of spec. I'd replace the battery first due to it's age and if that didn't correct the start issue then I'd pull the valve cover to check valve clearance.

 

[John B]

Whelp. Just did a leak down test. Which it appears to have failed miserably. I have never done this before, this was what I did so let me know If I did anything wrong (fingers crossed I did it wrong and everything is fine):

• Got it started, same issue cranked over forever, backfired, etc.
• Ran fine once it was started, however I did have to adjusting the idle speed a couple of times.
• Let it run ~10 minutes until it was warmed up before performing the test.
• Removed plugs/coils and the airbox.
• Turned crank over, cylinder top dead center (Chinese takeout chop sticks finally came in handy)
• threaded test hose into cylinder.
• Hooked compressor hose to leak tester, set pressure to 100 psi.
• Attached the hose that was threaded in the cylinder to the leak tester.

It didn't hold pressure at all in any of the cylinders. When I lift up the slide valve on the carb and open the throttle I can hear it leaking out the intake side of the engine.

Despite my hands on approach I am definitely not a mechanic, so I'm not sure what my options are at this point. These sleds are super hard to find, and this one only has 2,400 miles on it so I would definitely like to fix it. I only use this machine for ice fishing, before I had it the DNR used it to groom cross country ski trails, so it has spent most of its life travelling at pretty low speeds.

 

[maim]

sounds like time for a valve set or a bore scope look at the intake valves and see if there is carbon on them holding them open.

 

[grizztracks]

You might have been testing at TDC overlap which occurs between the exhaust and intake strokes. At this point both exhaust and intake valves are slightly opened.

Top Dead Center refers to the piston being at the very top of its travel in the cylinder. On a four stroke, TDC will occur at the top of the compression stroke and the top of the exhaust stroke. The test needs to be done on Compression TDC.