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  #1  
Old 11-03-2018, 04:20 AM
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Default LT50 - Newbie Problem

     

Hi team,
Have recently purchased a LT50 2000, not running but assured it Ďit would be fineí.... Iíve got minimal experience on bikes and none on LT50ís.
I replaced the plug and gave it a new tank of gas, this allowed it to start but ran on half choke and not idling well.
So I stripped the bard down and cleaned out the jets with a wire brush strand. Putting it back together the bike will only start with the choke on and then dies and wonít start at all with the choke off.

Looking at the plug it is wet/dark and can be wiped down but guess this means too much fuel into the engine?

To add to the scenario the tank has a little rust in it and the gasket between the carb and engine is split in two (needs to be replaced soon).

Iím assuming the rust could be causing issues for the carb however the petcock filter still looks good enough.

Iím scratching my head as to what to look at next and any help would be appreciated.

Cheers
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Old 11-03-2018, 07:39 AM
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The split carb boot may be making it too lean to start.

Paw Paw
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Old 11-03-2018, 01:35 PM
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Thanks Paw Paw will get that done this morning and report back.
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Old 11-03-2018, 08:23 PM
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Right, got the gasket sorted with some gasket paper and got it as about as good as I could.
It ended up starting and then dying, same old.

With the airfilter off I placed my hand over the air intake and it fired up, no for long but off choke and ran for a while longer than previously with the choke on.

I tried this again however noticed a bit of petrol on my hand I.e appeared to be getting too much fuel.

Took the carb off and undid the bowl to adjust the float cut off. I bent the metal tab that triggers the cut fuel cut off up so the float didn’t have to get so high before stopping flow.
(Previous day I had tested the float simply by removing the bowl, leaving the fuel line attached to the carb and seeing if the fuel would stop as I moved the float up and down - it worked, however not to say it does when operating under normal conditions).

I put it all back together and it started up, no choke, and it ran, however it seemed to be reving a bit high/not what id deam an idle. It ran for say 5 seconds and then died.

Tried starting it again however no joy. I then checked the plug to find it wet again (cleaned it at the start of the day).

I looked down the carb from the air filter to check the needle seating in the jet, it appears ok to my untrained eye, moves freely in and out.

From the above, restricting airflow seemed to work, so does this mean too much petrol is getting into the carb? And therefore the needle possibly isn’t seating correctly?

Am I also right in assuming the jets must be clear if too much fuel is getting in?

Thanks
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Old 11-03-2018, 08:46 PM
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The jets have nothing to do with the fuel flow to the carb, but rather the fuel flow to the engine. The reverse flow of fuel onto your had is normal as this does not have a reed valve.
Sounds like you may still have an air leak and a fuel supply issue.

Paw Paw
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Old 11-03-2018, 08:55 PM
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Thank you will relook at the bowl and see where else the air could be getting it.
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Old 11-04-2018, 01:36 AM
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Had a couple of goes writing this reply as the phone died.
Went back, and looked around for any air leaks that jump out to me, tightened up the bolt that clamps the carb to the elbow leading to the head, but only slightly.
Tried starting again, no luck.
So checked the bowl and dumped fuel out of there but no fuel came out, so undid the carb for the ?th time today to adjust the float, did this a few times until got fuel running out of the drain plug for the carb.
Then the better half came out, still didn’t start after multiple attempts.
Better half left, not encouraged by my progress.

So I thought about the air, and covered the air filter with my hand and it started. Revved up and then died as I took my hand off the airfilter. So I tried it again and left my hand on the filter for a while longer and low and behold back into life.
Took my hand off and as it started to die I half covered it and away it went.
I left it running for a bit on the jack and altered the throttle screw bringing the revs down a bit.
I left it running, revving it a little for a couple of minutes. I then stopped it and easily started it again with no hand on the filter. So got my daughter to have a go around the backyard and was able to restart it easily.

However I left it a couple of hours and it was back to being stubborn.
Not starting at all.
So I dumped the fuel from the carb, out it on prime briefly and then back to run, it would fire but not run
Eventually I put a rag over the air filter as couldn’t get my hand on it due to the plastics, stuffed it as tightly as I could and it started.....
It ran for a bit then died so I did the same again and away it went. I had no time to keep playing with it however getting an idea that blocking the airfilter to start it works until it’s warm, then once warm we are away.
I can’t put my finger on why it’s apparently working when starving the airfilter.
Does this allude to an air leak somewhere still?

Daughter loved it when it was going, the dog not so much, ohh well.

Cheers
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Old 11-04-2018, 08:01 AM
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It still sounds like an air leak to me. When you place the rag or had over the air filter you are starving the engine of air and thus makes the mixture rich, as needed for cold running.
You may want to totally clean the carb using a carb soak.

Paw Paw
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Old 11-04-2018, 12:38 PM
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Thanks Paw Paw, I'll strip it down and give it a good soak.

Cheers
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Old 11-06-2018, 03:37 AM
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Very wuickly, I stripped down the carb completely, taking off the choke component and the rubber seals. I got a can of carb cleaner and basically emptied it into a container deep enough for the carb to sit and submerge the area the main jet sits and the central cylinder of the carb (sorry technical words escape me) as there was a bit of crap in there. Also took apart all the jets for them to soak.
I let it sit over night and took a toothbrush to it, cleaning out the main cylinder.
It was hard to start for a couple of times then I again blocked the airfilter but it was a lot easier than previously to start.
I turned it off and restarted, again easier.
I’ll report back in 24hours, leaving it a day and seeing how it is.

My wife’s sceptical of the results...
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Old 11-07-2018, 02:15 AM
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Hmm still not 100%.
It is a lot easier to start however still holding my hand over the filter for it to finally tick over/keep running, otherwise it’ll start, rev and then die - starving the air seems to still get it there.
The parts making up the carb were dirty, there’s a bit of filth at the bottom of the container from the soak and using brush.

Am I right in saying it is leaning more towards an air issue rather than fuel?

If that’s the case is it better to buy a new carb than fix the problem? I’d rather fix it, I might try another gasket on the carb/engine previously replaced and check the airfilter.
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Old 11-07-2018, 02:37 PM
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How is your air/fuel screw set? 1.25 turns out would be a good place to start.

Check the intake manifold bolts (attaching it to the cylinder). I have a KFX50 (same as the LT-A50, same engine as the LT50), I started modding it by removing the restrictors and damaged the intake manifold gasket in the process. I was not able to restart the quad until I had the new gasket sealing perfectly.

If its starting by restricting the air, that would be making it richer. If you have the fuel/air screw tight in, you would be limiting the fuel flow under a normal circumstance. Worth checking out.

Videos on youtube about setting the air fuel screw. essentially you will need to jack up the rear, back off (unscrew) the air fuel screw until you hear the idle speed increase all the way, then make small adjustments based on how reactive the motor is to throttle blips. you will find a spot where the motor shows no hesitation when its set right
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Old 11-08-2018, 01:28 AM
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Gotcha, two good points - the gasket seal has been bugging at me as a possible issue.

The air screw is wound quite tightly in (how I got it), it is not even 1/4 of a turn (clockwise) until the screw is right in. I’ll have a go with that and look into the YouTube video.

Will report back!

Cheers
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Old 11-08-2018, 10:32 AM
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Yes, very much you need to back that air fuel screw out. I just checked Cyclepedia on my kids 50 and the stock spec is 1 1/8th turns out.

I do not know exactly where my kids is at the moment, but Im guessing it is a bit over 2 turns out with its current set up..

I did take notes on a YT video discussing air fuel screw settings. The video made the suggestion that if your motor runs best at less than 1.5turns out, your pilot jet is too rich, and if it runs best at more than 3 turns out, your pilot is too lean.

Ive removed all the restrictors, piggy back jet, shaved the head, cut off the spark arrestor, and opened up the air box a bit, added a 67.5 main jet. It would seem to be consistent that I have leaned out the mixture (at low rpm at least). My quad is not perfectly tuned, but its close, and I can tell you for sure that when I was adjusting the air fuel screw, I would almost kill the engine getting within less that a full turn of the air fuel screw.

---------- Post added at 10:32 AM ---------- Previous post was at 10:27 AM ----------

I hope this isn't against forum rules, but this video helped me understand a bit. Our Suzuki 50's have a "fuel" screw

I need more posts apparently before I can link videos
search
Idle mixture adjustment (air or fuel screw adjustment)
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Old 11-11-2018, 07:15 PM
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Hey, sorry I haven't posted for a couple of days.
Have been, and continue to be slammed by work so am not going to investigate the problem further for a week or two.

So I started the bike via my new method of covering the air filter and letting it warm up (l'll come back to my thoughts on this).
Then once 'warm enough' I started winding out the fuel screw to around the 1.25 - 1.5 turns from completely in. It is better at idling and without the brake on will just sit there ticking over - an improvement on before which i'm happy with and response is OK as well.

However the starting was still problematic.

Thoughts on air leak (and remember not a mechanic), bike is a pain to start without blocking air, metal expands when hot and bike is a lot easier to start once it has been running, i.e. one pull and we're away. Hell it'd be a weak pull too.

My question is this, is it possible that there is a small leak that is mitigated with choke on and covering air filter until the engine/carb is hot enough and the metal expands to 'plug the gap'?

Also, where the two bolts connect the carb to the head, the area where the top bolt screws into seems to have chipped, I can see part of the bolt thread. This is possibly my issue. Or one of them.

I've got to follow up the jetting line of query, maybe even a cheap kit of aliexpress...

It didn't come with the throttle screw so I made one up with a bolt and three nuts, to date works OK and my daughter was able to use it without hitting full throttle (and I could run beside her).

I'll try get photos up when I can.
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  #16  
Old 11-13-2018, 11:02 AM
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Good to hear.

My kids Bday is this weekend, therefore I will not have to hide the quad and can tune in the open. Hope I can help a little more then.

If you think your intake manifold is wonky, I did notice that new ones are cheap, and some of them do not have the quad's restrictor (not sure if the old LT had one or not). Honestly for all the time and $ I spent trying to JB Weld and Porting the JB, I could have just bought a 10 dollar restrictor less intake. The best part about this engine is the availability of parts and info when you start searching the JR50/KDX50/LT50/KFX50/LT-A50

If it does run well enough for your kid to ride, maybe adding some seafoam to the gas will help clean the carb as she rides.

And for what its worth, my kids is a pain to start cold, then runs great warm and restarts easy. I think I need to turn the fuel to Prime for a bit before I even attempt to pull.

Next step for me is to eliminate the oil pump and run premix. I have a feeling Im over oiling (especially since I have it up on a jackstand free spinning) the majority of the time. The oil is driven off the drive side.
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