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Discussion Starter · #1 ·
Hi Guys, first post here always been a fan of the forum. Not sure if this is the right forum to post, please let me know if this should be moved.

I bought a 1 tone mini-ex from china with LCT 420cc gasoline motor. Its an LCT CMXX commercial series engine 420cc. The engine is 6 months old and has 23 hours on it, from day one we found that when the gas tank is full "up to the red fill line" in the basket strainer. It begins to surge and loses power, sometimes it catches itself and sometimes it stalls out. It looks like it's very lightly puffing smoke from the exhaust when its surging. We found when the gas tank is half full it runs okay. I was wondering what the tube is that comes off the top of the tank and goes into the carb? I'm in no way a small engine pro, is this vent tube for the gas tank? usually the vent is in the fuel tank cap?

Screenshot of tube:
Automotive tire Motor vehicle Light Wheel Automotive design



Could this tube be drawing up fuel and flooding the carb? I also have a video of the engine surging see link: Video of Engine Surging

I'm sure someone will know what it is, like I mentioned earlier it seems to happen more often when the tank is full, if we leave it half full it seems to run just fine.

MODEL # OF ENGINE: PLMHS231300178EGHJKPQTUVY61EE2S

Any info would be greatly appreciated.

Looking forward to hearing from you, thanks in advance.
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I'd unclip it from the nipple and see if it runs any better. It looks to me like an overflow line but I would expect it to be longer with a small one way vent in it to prevent a vacuum situation.
 

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Discussion Starter · #3 ·
I'd unclip it from the nipple and see if it runs any better. It looks to me like an overflow line but I would expect it to be longer with a small one way vent in it to prevent a vacuum situation.
Thats a great idea, thanks for the advice. I will let you know what the out come is will try it later this week. Is it normal for an overflow line to go right into the carb?
 

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Could be a return line if that is a fuel injected engine. There should be a "T" at the carb if that is the case, one from the fuel pump and then the return.
 

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Discussion Starter · #7 ·
would need a better picture but does that hose not go to a shut off valve?
No shut off valve that's on the hose that comes out the bottom of the gas tank.

Here are a few pictures, I tried my best but it's super tight and I didn't have time tonight to rip all the panels off.

Hood Automotive lighting Motor vehicle Automotive tire Tire


Hood Light Automotive lighting Fluid Barware

would need a better picture but does that hose not go to a shut off valve?
 

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it looks like an emissions measure... looks like it goes to the air-filter?....
it basically sucks up any fuel vapour in the tank, when the fuel heats up - so that the hydrocarbons don't vent to the atmosphere.....
Surging normally happens when there is a vacuum leak but by the sounds of your explanation that's probably not the cause here. If that vent line was actually sucking up liquid fuel, you'd get a rich burn condition... smoke etc...
To test it, fill the tank and make it surge for a few minutes... then stop it and remove the spark-plugs - see if they are dark (rich burn) or not.

You can also take a look inside the fuel tank, to see if the vent inside the tank reaches down at all into the fuel... it should not.
The puffing from the exhaust could just be the throttle opening and closing....

You mentioned that the issue doesnt happen with half-tank... did you drain some fuel to get to that stage?... or run it for the duration to burn it down?... Am wondering if the surging stops "after a certain amount of time elapsed", and the engine is good and warmed up... not "when the tank is half full"?...
You could run it for a while - when the surging stops - top the fuel off right away and re-start and see if it does it for just as long?... or if it goes away after a minute or two....

Try disconnecting that line - it should not affect normal operation....unless that line goes to the vacuum side of the carb - which it sounds like it doesnt
 

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Discussion Starter · #9 ·
Did a web search but could not find much out. Any manuals come with it?
Hey Ariens, I downloaded the manual from the LCT site, I noticed there can be many option thrown on this engine, I couldn't find what that tube is for in the exploded diagram.

Here is the link to their parts catalogue: LCT Service Parts Catalog

Model: PLMHS231300178EGHJKPQTUVY61EE2S

then just punch in the model number and the exploded parts diagram shows up.

I've also attached the manual for the engine downloaded right from there site: https://lctusa.com/ , ive emailed LCT I will keep everyone posted what the say about the surging.
 

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Discussion Starter · #11 ·
it looks like an emissions measure... looks like it goes to the air-filter?....
it basically sucks up any fuel vapour in the tank, when the fuel heats up - so that the hydrocarbons don't vent to the atmosphere.....
Surging normally happens when there is a vacuum leak but by the sounds of your explanation that's probably not the cause here. If that vent line was actually sucking up liquid fuel, you'd get a rich burn condition... smoke etc...
To test it, fill the tank and make it surge for a few minutes... then stop it and remove the spark-plugs - see if they are dark (rich burn) or not.

You can also take a look inside the fuel tank, to see if the vent inside the tank reaches down at all into the fuel... it should not.
The puffing from the exhaust could just be the throttle opening and closing....

You mentioned that the issue doesn't happen with half-tank... did you drain some fuel to get to that stage?... or run it for the duration to burn it down?... Am wondering if the surging stops "after a certain amount of time elapsed", and the engine is good and warmed up... not "when the tank is half full"?...
You could run it for a while - when the surging stops - top the fuel off right away and re-start and see if it does it for just as long?... or if it goes away after a minute or two....

Try disconnecting that line - it should not affect normal operation....unless that line goes to the vacuum side of the carb - which it sounds like it doesn't
Hey Wally, ya it has to be some sort of Emissions addon as when I bought the excavator, I had two options of gasoline engines as the the diesels they had did not meet EPA standards. Your right too that tube is going right into the air-filter box. It only does this weird surging when the tank it full so I just assumed it was sucking fuel down that tube and i guess dumping fuel into the air-inlet of the carb, when it happens you can smell fuel and it was puffing a light smoke.

I will try that spark plug method you suggested to see if its running rich, I haven't look in the tank but I will feel if its hanging down into the fuel, your right pictures online are showing it shouldn't be hanging in the fuel.

I just let it run and then once the fuel was down it seemed to run okay, no issues, so I have just been filling the tank to half. The surging actually starts happening when the engine is warmed right up and been running for 20-30min, it doesn't do it right away. I actually thought it was an overheating problem at first, but again I really dont know much.

I'm going to try and disconnect that line and see if that helps.

Thanks again for your suggestions.
 

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ok thanks... so question: if you only fill to half full - does it run just fine "all the time"?... or does it surge after the 20-30min, even with the tank half full?....

Surging after a warm up - it may be ignition.... or spark plugs...
it may be thermal-expansion around the carb, so as to create a vacuum leak... check the tightness of the bolts that attach the carb onto the manifold... etc
 

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Discussion Starter · #14 ·
ok thanks... so question: if you only fill to half full - does it run just fine "all the time"?... or does it surge after the 20-30min, even with the tank half full?....

Surging after a warm up - it may be ignition.... or spark plugs...
it may be thermal-expansion around the carb, so as to create a vacuum leak... check the tightness of the bolts that attach the carb onto the manifold... etc
Hey Wally, yes if I fill it half full it runs fine all the time. If the tank is completely full to the red max fill line it will run for 20 - 30min then start this surging. I will check the tightness of the bolts that attach the carb to the manifold. As for spark plugs / ignition what am I looking for?
 

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Discussion Starter · #15 ·
Are you following the fill instructions on page 13?

Refuel in a well-ventilated area with the engine OFF and cool. Avoid spilling fuel. Do NOT fill above the fuel strainer marking.
Hey Ariens, yes I read that on page 13, it not being filled past the red fill mark on the strainer. I actually heard back from LCT support yesterday... this is what they suggested to check, the tube coming off of top of the fuel tank to the airbox is a "Roll over valve" just for everyone's information.

LCT's Response:
" Here are a couple of things to look at:
1. The hose coming from the roll over valve goes to the air filter and not directly to the carb. You could disconnect the hose from the ROV and see if the run ability corrects.
2. What is his elevation? – you may need a High Altitude Jet
3. To confirm its not vapor locking, when surging remove fuel cap. It should be venting through the fuel cap but just to test and confirm it is operating correctly.
Let me know if any of these correct the surging issue"


1) I'm not sure how a ROV - Roll over valve works (i've asked LCT) especially why it would go into the air box and how it would shut off the engine if thats even what it does. I'm thinking if you roll t he machine it locks the fuel from pouring out with some sort of air lock? not sure too sure.

2) My elevation is 872feet about sea level, so I'm assuming I do not need a a high altitude jet.

3) I left the cap off by accident when I was only filling it half tank and it started surging right away, when I put the cap back on it was fine no surging. I haven't tried to operate it with a full tank cap off, I may have some time today to try it out.

Thoughts?
 

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the roll over valve is a ball / cage valve like in your shop-vac, so that fuel does not start to flow out of the tank if the machine rolls over. Otherwise, it's open to the airbox to collect HC emissions from the tank.
You could totally close off that hose and the machine won't care... all that will happen is that it will no longer be emissions-compliant. You can try that to test it.

As for surging with the fuel cap completely off - that just doesn't make any sense. Hmm.....
 

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Discussion Starter · #17 ·
the roll over valve is a ball / cage valve like in your shop-vac, so that fuel does not start to flow out of the tank if the machine rolls over. Otherwise, it's open to the airbox to collect HC emissions from the tank.
You could totally close off that hose and the machine won't care... all that will happen is that it will no longer be emissions-compliant. You can try that to test it.

As for surging with the fuel cap completely off - that just doesn't make any sense. Hmm.....
Thanks again for the reply Wally, I'm thinking the first thing to try is just take that tube off as you suggested. Am I taking it off the valve or the air-filter box? and do I need to plug the hose or tape it off or something.

Yah that's what I thought it doesn't make any sense, I refilled the tank half full and forgot to put the lid on as I was in the middle of lifting some armor stone, fired the machine up and with in seconds it started surging, I couldn't believe it as I was certain this was only happening from filling the tank to full. I put the cap back on and it ran fine, this rabbit hole is getting deep 😳
 

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yea when you remove the hose it needs to be closed off on both ends... just to make sure.
Queston - does the fill-cap have a vent?... if not, this hose could also act as a vent to prevent a vacuum from building up in the fuel tank.
If the fuel cap is vented, then just close off the hose on both sides....
 

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LCT says the cap is vented in their reply. Don't understand why they bothered with a roll over valve if the cap is vented. Unless there is also a valve in the cap.
Went back and read everything again. Does this surging happen at idle or at equipment run speeds?
If installing the cap at idle stops the surge and the surge begins at run speed I am wondering if there is not two problems at play here. 1. extra idle enrichment to keep it running with the cap on. 2. starvation at equipment run speeds.
Would be interesting to know just what type of vent is in the cap.
 

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the vent in the cap will not allow spillage on tipping. it requires slight vacuum or slight pressure to release. When the machine tips no fuel leaks out because there is neither slight pressure nor slight vacuum in the tank.

But the emissions vent tube does not have the same kind of vent mechanism. So if the machine tips, fuel will leak out the tube into the airbox... out of the airbox and onto the hot exhaust. So the tip valve is there to "close that tube" in case of tipping.

To be honest I'd be surprised if the fuel cap is vented... with the emissions tube in there, it's not required.
 
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