Oil leak 1985 suzuki 250

[Mhatayas]

So I noticed there is no crankcase vent hose, does the hose that's supposed to run there go to the air box or up under the dash ? 

 

I'm talking about the one on the right side crankcase just beneath the fender 

[Gwbarm]

That vent hose routes under the seat and comes out close to the main air intake not sure on the 85 this is from a Yamaha the two holes are for the vent lines.

[Mech]

If the engine burnt as much oil as you are saying it does, then it wouldn't run.

I've seen exhaust valve guides loose, or leaking between them and the head, and/or worn exhaust valve seals, let heaps of oil straight into the exhaust, and make a huge amount of smoke, but the engine run quite well because the oil wasn't getting into the combustion chamber. Those suzukis have the head tilting forwards and the exhaust valve guide and seal gets deep in oil.

If there is oil getting to your valve gear then the oil pump is fine.

I doubt the engine is meant to have three litres of oil in in..

 

[Mhatayas]

7 hours ago, Mech said:

If the engine burnt as much oil as you are saying it does, then it wouldn't run.

I've seen exhaust valve guides loose, or leaking between them and the head, and/or worn exhaust valve seals, let heaps of oil straight into the exhaust, and make a huge amount of smoke, but the engine run quite well because the oil wasn't getting into the combustion chamber. Those suzukis have the head tilting forwards and the exhaust valve guide and seal gets deep in oil.

If there is oil getting to your valve gear then the oil pump is fine.

I doubt the engine is meant to have three litres of oil in in..

 

Says 3500ml . I filled it until the oil was between the marks on the sight glass 

When I took the top off  a bit of oil poured out. There's oil in the combustion chamber since I see it on the spark plug. 

 

If I flush the engine with Diesel or kerosene think that'll help me ?

[Mech]

Well I don't know where you got the 3.5l oil capacity from but I've never seen an LT250 that took more than two litres, and they definitely aren't meant to overflow back out the fill hole.

No I don't think it needs flushing with diesel or kero.

[Gwbarm]

Is your fill plug toward the back of the engine under the exhaust and next to the shock! Kind of hard to get to. If so it does take 3500 cc of oil with the filter change, but if you can see it in the sight glass it shouldnt come out the fill hole. I think the z250 only takes the 2200cc of oil. Just wondering if your engine might have been changed or does it say 3500cc on the engine.  

[Mhatayas]

7 minutes ago, Gwbarm said:

Is your fill plug toward the back of the engine under the exhaust and next to the shock! Kind of hard to get to. If so it does take 3500 cc of oil with the filter change, but if you can see it in the sight glass it shouldnt come out the fill hole. I think the z250 only takes the 2200cc of oil. Just wondering if your engine might have been changed or does it say 3500cc on the engine.  

Yup thats the spot, hard to get to, says 3500ML right next to it. I filled it until i seen it in the sight glass, ran it for a bit and filled again till i seen it was between the two marks in sight glass. it burnt so much oil in juat a tank of gas there was just about a litre left, as well didnt stop smoking till there was practically none left in there..

[Mhatayas]

4 hours ago, Mech said:

Well I don't know where you got the 3.5l oil capacity from but I've never seen an LT250 that took more than two litres, and they definitely aren't meant to overflow back out the fill hole.

No I don't think it needs flushing with diesel or kero.

Possible that carborator i have, the diagphram that isnt meant for the engine causing this ? i dont understand. I have a nibbipe30 carb and electric fuel pump ordered for it anyway, so ill be selling these oem carbs when i get the chance. I was dumb and gave away the old slider carb i had for it

[Mhatayas]

4 hours ago, Mech said:

Well I don't know where you got the 3.5l oil capacity from but I've never seen an LT250 that took more than two litres, and they definitely aren't meant to overflow back out the fill hole.

No I don't think it needs flushing with diesel or kero.

Just to make sure we are on the same Page mech, im not talking about my 2wd chain driven lt250

im talking about the LT4WD bike i recently obtained. with the high low and super low 15gear transmission.

[Mech]

Oh..  I'm stupid..  haha. When did we start talking about this one..  kidding.. I do remember you coming back with a new bike now..  I should pay more attention..

 

Ok, so it does take about 3.5L..  And after a run (to circulate the oil and leave a bit in the head {which holds quite a lot  [especially around the exhaust valve] }, and other places, and with the bike off, the oil should be half way up the sight glass.. And if you undo the filler cap, no oil should come out.

[Mhatayas]

2 minutes ago, Mech said:

Oh..  I'm stupid..  haha. When did we start talking about this one..  kidding.. I do remember you coming back with a new bike now..  I should pay more attention..

 

Ok, so it does take about 3.5L..  And after a run (to circulate the oil and leave a bit in the head {which holds quite a lot  [especially around the exhaust valve] }, and other places, and with the bike off, the oil should be half way up the sight glass.. And if you undo the filler cap, no oil should come out.

Correct, oil was halfway in the sight glass, none came out the filler cap, just burning it like crazy. Wonder if i didn't install the rings correctly? i tried to make sure the gaps weren't lined up with each other. This is so frustrating and annoying

[Mech]

You should have checked the valve seals, and possibly for leaking between the guide and the head when you had it apart.. The exhaust valve sits in a puddle of oil and if it leaks the oil goes straight down the exhaust pipe and gets burnt.. That could be your problem.. I understand it's getting oil into the cylinder too, and that could also happen once the engine is stopped, then the oil can drip off the valve and into the cylinder. It's also possible that the new rings didn't bed in, and that could let some oil get up into the combustion, but for it to burn as much oil as you are saying the rings would have to be really seriously damaged. Just having the ring ends aligned or not, doesn't really make that much difference. Repositioning the rings alone won't cure the problem.

For it to burn that much oil in one tank of fuel it should have fouled the spark plug several times over.. I'd have to suspect the exhaust valve over your ring fitting job as being the culprit.. Were the ring gaps correct ? Did you de-glaze the bore a little ? Did the barrel slide down over the piston nicely ? If yes to all those then the rings shouldn't be letting that much oil be burnt..

If you have the cylinder head off again, take the valves out and block the head up so the exhaust valve guide is pointing up, and you should be able to make a small puddle of fuel around the guide, but not deep enough to run down the guide..Leave it and see if fuel leaks down the side of the guide. If you can't get the puddle deep enough like that you could put the valve in and test the guide and the seal at the same time.

[Mhatayas]

54 minutes ago, Mech said:

You should have checked the valve seals, and possibly for leaking between the guide and the head when you had it apart.. The exhaust valve sits in a puddle of oil and if it leaks the oil goes straight down the exhaust pipe and gets burnt.. That could be your problem.. I understand it's getting oil into the cylinder too, and that could also happen once the engine is stopped, then the oil can drip off the valve and into the cylinder. It's also possible that the new rings didn't bed in, and that could let some oil get up into the combustion, but for it to burn as much oil as you are saying the rings would have to be really seriously damaged. Just having the ring ends aligned or not, doesn't really make that much difference. Repositioning the rings alone won't cure the problem.

For it to burn that much oil in one tank of fuel it should have fouled the spark plug several times over.. I'd have to suspect the exhaust valve over your ring fitting job as being the culprit.. Were the ring gaps correct ? Did you de-glaze the bore a little ? Did the barrel slide down over the piston nicely ? If yes to all those then the rings shouldn't be letting that much oil be burnt..

If you have the cylinder head off again, take the valves out and block the head up so the exhaust valve guide is pointing up, and you should be able to make a small puddle of fuel around the guide, but not deep enough to run down the guide..Leave it and see if fuel leaks down the side of the guide. If you can't get the puddle deep enough like that you could put the valve in and test the guide and the seal at the same time.

Thanks ... The piston did slide up white nicely, and I used a cylinder and piston and rings from another bike that DIDNT SMOKE , so i knew it was good. I never gapped them or checked the gapa but everything honestly looked as it should. Cylinder still had crosshatch on the bottom half not so much up top, but it didn't smoke. 

 

When I put the parts from the bike that didn't smoke on the bike that did, the bike still smoke! 

If timing was off a little bit , would this cause smoke? It might be off by a tooth when I put it together.I'm sure valve guide seals are good because the other bike didn't smoke. 

 

I'l take it all apart AGAIN I guess. I am getting so frustrated with it at this point. This is my second plug that oil fouled by the way . No oil =no smoke , I drained it (the litre that was left in there ) and let the bike run and no blue smoke . Go figure. 

 

I got a new set of rings ordered anyhow 

 

[Mech]

Ha..  Very good. 

You said you used a barrel and piston and rings off another bike that didn't smoke..  Then later you say you think the head must be good because the bike didn't smoke.. So you did swap the head off the other bike too ?

The cam timing being a tiny bit off wouldn't make it smoke.

[Mech]

You could check the engine breathers. They generally run from the crankcase to a branch where one hose goes up the front, around the fuel filler and then down a little, and the other branch goes onto a restricted vent into the air box. The restricted vent in the airbox is only to stop water getting drawn up the main breather if you drive into deep water. it breaks the vacuum. They also often have a short branch going down the bottom of the bike somewhere with a plug on it, that's to drain water out if any does get drawn in. The main vent hose can get blocked by dust and oil, and then if you undo the filler while it's running there will be pressure. You could test that and/or check the main vent hose going up front and high is clean..

If the filler plug gets pressure, the vent isn't clean.

[kingkw54166]

On 2/9/2024 at 8:44 AM, Mhatayas said:

Thanks for the response , I ordered a new filter and it comes with the 2 o rings needed (one small in behind the filter one large in front ) , should be here by Wednesday, pretty excited 

 

do you have any clue on how much oil my bike should take ??

I entered the information that you provided and Google says It should take at least 3.5 litres of oil without a filter, and 3.8 litres with a filter. Also, when doing any oil change your quad should be on as level ground as possible or the level could read to much or not enough 22, 2016"

[Mhatayas]

6 hours ago, Mech said:

You could check the engine breathers. They generally run from the crankcase to a branch where one hose goes up the front, around the fuel filler and then down a little, and the other branch goes onto a restricted vent into the air box. The restricted vent in the airbox is only to stop water getting drawn up the main breather if you drive into deep water. it breaks the vacuum. They also often have a short branch going down the bottom of the bike somewhere with a plug on it, that's to drain water out if any does get drawn in. The main vent hose can get blocked by dust and oil, and then if you undo the filler while it's running there will be pressure. You could test that and/or check the main vent hose going up front and high is clean..

If the filler plug gets pressure, the vent isn't clean.

yup swapped heads as well. one breather isnt hooked up for sure, one on the right transmission side just beneath the fender, dont know which hose is which. At this point mech, im just waiting till i get the new parts and testing the waters there, i pause the work on it for now before i get totally frustrated. Ill wit till next month . In other words, see ya in a months times LoL

[Mech]

Yeah ok. So when you get the new rings, check the holes in the back of the oil groove are clear, check the side clearance of the rings (that's the clearance top or bottom of the ring), and check the ring gap of course. When you get the bike together, check it all over before you start it, then when you do start it, check the oil is getting to the head, then start riding straight away, don't let it sit idling, and when you are riding it, put a heavy load on it until it's built up about 3/4 revs, then let the throttle right off till it's slowed to just above idle revs then give it about 3/4 throttle again and keep it there till about 3/4 revs.. repeat that cycle about ten minutes or so and the rings will bed in.. That first few minutes is more important than hundreds of miles of careful running in.If you bed the rings like that, the engine doesn't need any running in. Let it sit idling and the rings might never bed in.

The rings have to have a heavy load on them in the first few minutes.. That means letting the engine labour slightly..

[Mhatayas]

Ok folks! After a new set of rings , installed with the gaps away from eachother, it seems, it's no longer smoking blue! Can't even see any exhaust! 

 

Very happy. But get this , I installed a Chinese nibbi pe30 carb, and electric fuel pump. The overflow hose on the carb is extremely long and just happened to drop fuel onto my exhaust during a backfire! You can guess what happened next. (This was right after the new rings installed and tested out. It did smoke blue for the first 30Seconds to a minute. But now no longer! )

 

 

In panic mode, I pushed the ATV out of my shed and pulled it out further into the snow where it wouldn't catch my shed on fire. I started throwing snow at it and luckily after a minute or so it went out . Phew, only burnt a bit of the overflow line off. 

 

I have up for the night and went back at it tomorrow. It seems the pull cord is too easy to pull over than it ever was, and it's hard to start with e start even. Though it idles and runs perfectly when it's going. 

 

I'm gonna change plugs anyhow because it's possible oil fouled . 

 

And the only problem now besides the starting issue, is anywhere past half throttle, it bogs and runs rough. Stutters. Seems like it's getting too much fuel or something. 

 

I May fiddle with the carb set the needle height, what do you think? 

It didn't do this at first when it was smoking blue .

 

To confirm the smoke problem is gone , I added another quart of oil bringing the grand total up to 2l (still need another 1.5l

 

 

 

Forgot to mention I'm going to do a compression test on it too now. But the main problem is thankfully solved !

[Gwbarm]

Great you got the rings installed and no smoking, sorry to hear about the fire bad luck there. You might check closely and make sure non of the electronics were burned. Did the hard starting occur after the fire or didnt really run it long enough to notice it and the fire didnt really cause anything.

Its very possible that the aftermarket carb is causing your running and starting problems, but because of the fire i think i would take it apart to make sure nothing in there got hot enough to caause damage.

[Mhatayas]

On 3/1/2025 at 12:07 AM, Gwbarm said:

Great you got the rings installed and no smoking, sorry to hear about the fire bad luck there. You might check closely and make sure non of the electronics were burned. Did the hard starting occur after the fire or didnt really run it long enough to notice it and the fire didnt really cause anything.

Its very possible that the aftermarket carb is causing your running and starting problems, but because of the fire i think i would take it apart to make sure nothing in there got hot enough to caause 

  Alls well there thankfilly! The fire was near the rear left tire, where the exhaust joins together. But today I figured something out snf why it's hard starting. Was running good for about 5min beforehand

 

I setup a nibbi pe30 carb on my 87 quadrunner, paired with a low 1-2 psi electric fuel pump. Problem I'm having (i think) is the float needle/seat is not sealing properly and allowing fuel to pass it. whenever I turn on the key the pump keeps pumping fuel through and it overflow and leak through back of the carb. 

 

I tried adjusting the float tab to multiple different positions and it either would do one of the two , overflow or not flow enough fuel at all to let the bike run. 

 

Trying to figure out all potential issues here , fuel pump too high pressure causing fuel to force the needle/seat open and float not able to seal it on its own , or debris possible stuck in there ? Note that it worked good for about a minute before I noticed the bike bogging past half throttle, go to look at carb and it's leaking a constant trickle of fuel out the back . Any help is appreciated

[Mhatayas]

Ok so , I got the float tab vent upwards near 45 degrees, and turns out there was a bit of crud in the needle seat. Ran good for 5mins of riding then it seemed like it starved itself for fuel. 

 

What should I do to the carb now , should I set needle height? I don't know yet if it's running lean or rich . I will have to get a new spark plug and check it out 

[Mhatayas]

Ok. After a through carb clean  I'm still having the same issue. Either too much or too little fuel depending on float tab setting. THERE IS NO IN BETWEEN!!!  Seriously flustered with it all. It seems the needle/seat won't seat correctly. The vacuum port I drilled is up in the Intake manifold, used a presta valve from bicycle. Works well. Would it be too much pressure though? The carb seems to be spat out from the manifold at times with the back pressure? Is this possibly why the needle seat wont seat ? 

 

 

As much as I don't want to , I think I might just have to find another carb or buy one and use . Sucks . Wish I could take the rig for a run already. 

 

 

 

[Gwbarm]

Its hard to Judge whats really going on. Not all chinese carbs are built the same and not being familiar with the one you have is difficult. I set the float level as the factory setting suggests which means the float is parallel with the float chamber lip. Then adjust it out from there with the air fuel mixture screw..The only time i vary that adjustment is if gas is still overflowing from the float chamber  which theoretically shouldnt happen unless there is a discrepancy in the needle and seat.  If you bought this carb new i am assuming it is right one for your quad. If not i would not spend much time on a aftermarket carb. The cheapest solution would be to get another aftermarket carb, my expierience is some work great but most dont. If i was doing it and wanted it up and running quickly i would try the cheapest solution, but continue to look for an OEM carb to rebuild and get it back to factoruy specs with oem jets and needles.

[Mech]

You almost certainly have too much fuel pressure.

I'd try to keep the original gear.. The fuel pump and the carb were made to operate together. Gravity fed carbs have bigger float needle jets than carbs with pumps.

You should set the carb float to specs if it's a carb recommended for that bike (bikes with tilted carbs have different float settings than flat mounted carbs), or to a setting that will have the fuel at the right height if it is tilted, and then try running it with a temporary gravity feed.

 

[Mhatayas]

Hey folks, thanks for the responses. I've since gave up on the Chinese carb. Went back to the original fuel pump, drilled hole put valve in intake Boot etc.. still same troubles.

 

I'm back to the regular OEM slider carb now, the original that is supposed to be on the bike. I got it from a friend, he's been using it on his ATV (same year and model as mine) for years with no issues. 

 

I put it on mine, it worked perfectly, for about 20mins riding. Then it started flooding when I would let off the throttle. It would sputter and sometimes almost cut out before it picked up again. But this is only after about 20mins of riding in 4th and 5th gear on a road throttle nearly wide Open. As soon as i let off, it seems it wants to sputter and flood out. 

I went and cleaned the carb inspection the needle and seat etc, cleaned tank replaced fuel petcock... New fuel filter. 

 

Still same issue.

 

Do you think I should set the needle height a little lower? Or the float tab a little higher? The float tab is at about 35 degrees as it is . 

 

Is there some other type of issues I can be overlooking? Already tried adjusting the air fuel screw, still didn't make any difference. 

I should note, that the intake boot is from a newer model Suzuki lt4wd bike. It's a tad bit larger diameter than the old slider carb boots. That being said , I cut off about 1/2 inch of the boot, since there is an inner lip that's smaller diameter than the outside of the boot where the carb fits. The inner lip seals perfect with the older carb accompanied by a hose clamp. No leaks, sealed great, as well the rear boot is sealed great too. 

 

Don't think that could cause an issue would it ? 

 

I know it's a carb flooding issue because the overflow tube leaks gas when this happens, and it cut out once or twice and wouldn't start after that , plug soaked. 

 

Kind of boggled, since it was taken off the same type of bike working fine, and now doesent want to work properly on mine. 

 

 

[Mech]

Are you sure the fuel isn't leaking between the float needle seat and the carb body ?

Does that bike have a fuel pump originally ? Is that carb made to run with a fuel pump ?

If not, then the carb on it will have big float needle jet, and it will struggle to seal against even one pound of fuel pressure.

The normal pressure for a bike with gravity feed is only about, er.. probably a quarter pound of pressure. Water gives 0.4Lb of pressure for every foot of height, and most fuel tanks are only a few inches above the float needle jet, and, fuel is lighter than water and gives less pressure.. The fuel pressure is very low. You can get different sized float jets for carbs and depending on the fuel pressure they are designed to operate with. the size of the jet can vary by a factor of three or more. Using the wrong size float jet can cause flooding or fuel starvation..

If you are sure the seat to carb body is sealed, then I'd recommend resetting the float height to specs and rigging up a gravity fuel feed temporarily(without the pump), to see if that cures the problems

 

Edited March 30 by Mech

[Mhatayas]

On 3/30/2025 at 4:11 PM, Mech said:

Are you sure the fuel isn't leaking between the float needle seat and the carb body ?

Does that bike have a fuel pump originally ? Is that carb made to run with a fuel pump ?

If not, then the carb on it will have big float needle jet, and it will struggle to seal against even one pound of fuel pressure.

The normal pressure for a bike with gravity feed is only about, er.. probably a quarter pound of pressure. Water gives 0.4Lb of pressure for every foot of height, and most fuel tanks are only a few inches above the float needle jet, and, fuel is lighter than water and gives less pressure.. The fuel pressure is very low. You can get different sized float jets for carbs and depending on the fuel pressure they are designed to operate with. the size of the jet can vary by a factor of three or more. Using the wrong size float jet can cause flooding or fuel starvation..

If you are sure the seat to carb body is sealed, then I'd recommend resetting the float height to specs and rigging up a gravity fuel feed temporarily(without the pump), to see if that cures the problems

 

I've since switched to another carb,I've read online a lot of people switched to smaller carbs due to flooding issues. This worked for me . Switched from the original vm34 to a vm32 from my 85 2wd bike. It was running perfectly, UNTIL, get this :

 

Bike runs for 15mins or so till it gets hot. Then it backfires a bit and makes popping noises through the carb. Then it spitters and cuts out like it don't wanna run . Let it sit for a bit to cool down then starts back up like nothing happened. don't know if this is a fuel pump issue or some sort of electrical or mechanical  issue? 

 

Man I thought I finally had this bike ready to take on a run. Guess not 

[Mech]

Well the circumstances should be considered here..  It takes about 20 minutes before the trouble starts manifesting..

A blocked fuel tank breather could cause problems like that. A blocked vent normally causes a fuel shortage as the tank starts to get a vacuum in it and the fuel stops flowing. It can happen though that a blocked vent can cause the carb to flood, but it's normally when the bike gets parked in the sun and the tank pressurises. It is possible though that in this case a blocked vent, despite the fuel being taken out of the tank as the engine runs, is actually letting the tank pressurise as the engine or sun warms the tank up.

Check the fuel tank and the carb breather hoses are attached to the right place, and that they are clear.

[Mech]

When a carb starts backfiring it's normally because the mixture is too lean. It can be caused by badly retarded ignition timing or tight valve clearance, but mostly it's a lean mixture, especially if it does it more as you open the throttle more.

The flooding out the overflow is a different problem..