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Surging idle on a 350 Rancher, with a weird twist

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My neighbor has a 350 Rancher.  He bought it a few years ago, and I went through the engine.  New timing chain, all new seals, cleaned everything out, and at the time money was tight so I just honed the cylinder and put new rings on it with the hopes that it would be ok.  He rode it a bit and it started smoking again, and by that time I was neck deep in my own stuff, kids, wife etc, so he ordered a cheap top end from Amazon and put it on himself. 

 

Yesterday he asked me to stop by and listen to it because it was making a weird noise (which turned out to be a one-way going bad on the clutch).

 

Bike runs good with the new top end on it, and doesn't smoke, but it is belching oil into the airbox until it gets towards the bottom of the dipstick and then it stops (If I recall from one of the other boards, @toodeep said that wasn't unusual on the 350 Ranchers, and just to run it). 

 

The really weird thing was it was surging at idle, which to me normally says air leak.  He had a can of starter fluid there and if I shot the head to carb boot with starter fluid, it would die (I'm used to it revving up when I do that and there's a leak).

 

I repeated the process several times.  Start it up, hit the intake boot with a shot of starter fluid, and it would die every time.

 

Anyone tell me what's happening there?

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A bad air leak. I wonder if the oring fell out between the intake an the head. Quite a few 350s would force oil out until it was about half way on the dipstick (going through the proper checking procedures on a cold motor) but I haven't had any take it to the bottom mark.

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On a hunch do they make a later model 350 engine that bolts in his frame cause sounds like he got an early rancher engine, that shouldn't be doing that, sounds like to me the air leak is less of a concern now, id figure out why it's pushing oil like that.  IMO

Edited by F250 guy

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It's an 02 Rancher. 

 

I asked him about the O-ring and he said he put it in.  It actually drives around pretty good all things considered, but doesn't want to idle without the choke on, and then you have the weird "dies with a shot of starter fluid" thing.

 

The oil level was low on the dipstick right after shutting it off.  If you let it sit a minute the level would come up to about 1/2 way on the dipstick.

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I would check the oil level on a cold engine to see exactly where it stabilizes at. I would also inspect the intake since something is not right there leaning it down. I usually use carb cleaner so I'm use to it killing the motor when there is an intake leak.

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Be careful with using starting fluid, pretty sure it can be harmful to these engines with extended use.  As stated carb cleaner much better choice.....

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On the surging thing, it probably needs some carb work and reseal the intake boot to the head. The valve lash may have tightened up a bit tight too. I'd check the lash for sure, since a new top end and gaskets was just put on it, the gaskets may have taken a set and tightened up the valve lash. Valves should be readjust after heat cycling a new top end anyway, cause everything is in motion during that first hour of runtime and first couple cooldowns.

 

On the oil blowing into the airbox thing I'd suspect a plugged screen, worn out scavenge pump, or a blown o-ring on the pickup pipe. The 350 is a dry-sump oiler and has multiple screens inside the case. It also has a two-stage oil pump design, one stage scavenges the other stage pressurizes, so its a lot more complex than a wet oiler. It should not blow oil out the vent hose, it can be fixed. I'd yank the front cover and the oil pump first then decide whether the cases need to be split to clear the screens.

 

 

oil-pump.png

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2 hours ago, retro said:

On the surging thing, it probably needs some carb work and reseal the intake boot to the head. The valve lash may have tightened up a bit tight too. I'd check the lash for sure, since a new top end and gaskets was just put on it, the gaskets may have taken a set and tightened up the valve lash. Valves should be readjust after heat cycling a new top end anyway, cause everything is in motion during that first hour of runtime and first couple cooldowns.

 

On the oil blowing into the airbox thing I'd suspect a plugged screen, worn out scavenge pump, or a blown o-ring on the pickup pipe. The 350 is a dry-sump oiler and has multiple screens inside the case. It also has a two-stage oil pump design, one stage scavenges the other stage pressurizes, so its a lot more complex than a wet oiler. It should not blow oil out the vent hose, it can be fixed. I'd yank the front cover and the oil pump first then decide whether the cases need to be split to clear the screens.

 

 

oil-pump.png

Your on point bud, but I'm confused as to why it's doing the oil and intake things, sounds to me like a design issue with the engine like I said earlier in the thread. 

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Its a great motor & transmission design, the 350 motor has proven to be very durable. Dry sump oiling is far superior to the cheaper and common wet sump oilers. Honda spent a lot of money on the Rancher 350 motor design. The only design issue they had that I can recall is the '00-'01 FM models were prone to shift drum breakage. But they fixed that issue in 2002 and newer models.

 

99.9999% of all faults can be traced back to operator neglect, shoddy workmanship and/or abuse. Its humans that fail the machine.... not the machine failing the human....  🙂

 

 

 

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12 minutes ago, retro said:

Its a great motor & transmission design, the 350 motor has proven to be very durable. Dry sump oiling is far superior to the cheaper and common wet sump oilers. Honda spent a lot of money on the Rancher 350 motor design. The only design issue they had that I can recall is the '00-'01 FM models were prone to shift drum breakage. But they fixed that issue in 2002 and newer models.

 

99.9999% of all faults can be traced back to operator neglect, shoddy workmanship and/or abuse. Its humans that fail the machine.... not the machine failing the human....  🙂

 

 

 

I may be wrong but i said what I did with good reason. 

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I wasn't calling you out or doubting your intent or being personal in any way. I apologize.

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2 hours ago, retro said:

I wasn't calling you out or doubting your intent or being personal in any way. I apologize.

No need my family some are engineers so I when a problem like this comes up I think ok is it a design flaw or lack of care. 

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The last time I read about oil blowing into the airbox on a 350 Rancher the problem was solved by replacing the oil pump and cleaning the pickup screen. But that was probably more than a year ago, maybe two years ago. That thread might be difficult to find. I hesitate to guess because there is more than one part in a 350 motor than could cause oil to blow out. Its gotta be torn down for inspection.

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42 minutes ago, retro said:

The last time I read about oil blowing into the airbox on a 350 Rancher the problem was solved by replacing the oil pump and cleaning the pickup screen. But that was probably more than a year ago, maybe two years ago. That thread might be difficult to find. I hesitate to guess because there is more than one part in a 350 motor than could cause oil to blow out. Its gotta be torn down for inspection.

I agree teardown needed. If it's like I think it may be " geo roator pump like a diesel, split the cases for metal debris, that's what I'd do if I was this fella, if is the pump type I'm thinking of. 

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In My humble opinion, the motor has a VERY bad air leak if the shot of starter fluid killed the motor, without a doubt !  Fix that first.

 

As far as the oil in the air box I might suspect the china top end kit that was installed even though, You do not see it smoke !    If it was in My small garage, I would do a leak down test on the motor before tearing anything down.

 

Again just My opinion.

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Thanks for the input guys.  I send my neighbor a link to the forum so hopefully he'll sign up.  Figured I'd start a thread for him so he'd have some ideas right off the bad.

 

 

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