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Old 02-25-2020, 01:58 PM
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Default 110cc atv engine acting up

I got a 110cc atv and put a new carb on it
at first, it would idle really high no matter how I adjusted the idle screw.
I assumed the issue was the carb spacer, that there was an air leak. So I made 2 gaskets to go on either side of the spacer.
It still idled high.
Then I adjusted the air mixture screw (on the side by the air filter) and got it to idle down. It will idle and will run good...but sometimes when you slam on the brakes hard the engine will die.
The air mixture screw had been set to 1.5 turns out from the factory. I have it set to only a half turn from fully set for it to idle right.
I can't find any combination of idle screw and air mixture screw that will allow it to idle low enough not to move without throttle input, but also stay running no matter how hard someone hits the brakes. Also, when in neutral if you rev it up it doesn't always return as low as it should go...sometimes it does, others it doesn't.

This is a new carb, I double checked for a vacuum leak...frankly the only other thing I can think of is if the idle jet is just too small? If it is too small, then that could explain why I have to block off more of the air mixture screw than would normally be required.

Any other thoughts or ideas?
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Old 02-25-2020, 02:00 PM
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Can you post pics of the machine and motor in question??...
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Old 02-25-2020, 03:04 PM
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It's an Ice Bear, 110cc, with reverse
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Old 02-25-2020, 04:37 PM
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Check to see if you didn't install the carb slide wrong.
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Old 02-25-2020, 06:59 PM
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Quote:
Originally Posted by Texan View Post
Check to see if you didn't install the carb slide wrong.
It can only go in one way. And if it were in wrong, it wouldn't be able to idle down at all. I have it idling good and it drives good...just sometimes the rpms don't drop down as low as they should when you let off the throttle (it will hang a couple hundred rpms high for a few seconds) and sometimes under hard braking the motor will stall.

I am going to try putting thick foam around the air filter. That should limit the amount of air going it, and thus enrich the mixture. If that works, then I will see if I have a slightly bigger idle jet to put in it.
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Old 02-25-2020, 08:48 PM
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online bough carb I assume
ebay or amazon I assume
"fits 90cc, 110cc and 140cc engines" I assume..

chances are it's the wrong main jet
(sounds too big for me)

get the mainjet from the old carb, clean it, install it to the new one
readjust and try again

'sid
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Old 02-25-2020, 10:13 PM
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Quote:
Originally Posted by itsid View Post
online bough carb I assume
ebay or amazon I assume
"fits 90cc, 110cc and 140cc engines" I assume..

chances are it's the wrong main jet
(sounds too big for me)

get the mainjet from the old carb, clean it, install it to the new one
readjust and try again

'sid
I should have mentioned that the old carb was acting pretty much the same way. It was a bit worse with the old carb, because there was a tiny bit of extra air getting in by the intake spacer. When I put on the new carb, I added gaskets I made. This did make it not rev up as high on start up like with the original carb, but it was still too high until I adjusted the air mixture screw in.

I am curious that you think the main jet is too small. Wouldn't it be an issue with the idle jet? It can take off from a dead stop with no problem. If the main jet were too small, I would think it would either hesitate off the line, or bog down at higher rpms.
Even if the main jet is too small, I could try raising the needle (assuming it can be raised) first.

I've fixed many of these 110cc quads, and generally the cheapo amazon 90-125cc carbs work just fine. Only other times I've had an issue with a new carb, is when I tried to reuse the old slide/cap and one time where the main jet had brass shavings stuck in it from the factory. But most often, they bolt on and work just fine.

I put some 1" foam (like seat foam padding) around the air filter...will see tomorrow if that helps it. I've done it once in the past (due to running in colder temps) and it helped. Plus, those stock air filters don't look like they filter much anyway...so the foam padding will act like a pre-filter.
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Old 02-25-2020, 10:35 PM
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I cannot help you at all with your problem, but I have a Suzuki EN125cc motorbike, and the bike behaves exactly like yours....with the idle staying high for a few seconds (or sometimes for longer) once the engine has been revved. I have even tried a different carb, but it still acts the same.

Some of the things the bike shop tried was lubricate the throttle cable (they thought it might be sticking), as well as carb cleaning.

I just thought it was interesting that your quad does the same
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Old 02-25-2020, 10:48 PM
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you might have misread..
I said "too big" not "too small"

here's my thinking behind it..
if the main jet is too big there's too much fuel in the idle mix..
thus the idle needle must be threaded way further in to level that mix out as good as it can...

Ideally, just get a plug reading and show us what your spark plug looks like atm.
I'd say it'll be pretty dark and maybe even wet when afer the engine just stalled.
And I'd say that's more than likely a fuel issue here (too much of it in the mix)
not oil..

And at higher revolutions the only cause for that could be the main jet really.

it'd also expain why the engine tends to stick on higher rpms when you let off the throttle
(still enough combustible accumulated in the manifold and combustion chamber)
and why it tends to stall after a sudden stop...
if the plug isn't allowed to dry (at low rpms) the spark gets weaker and weaker..
a dramatic increase is fuel will render it nearly useless and the engine stalls

So yeah too big main is my call from what you're saying;
a plug reading can certainly give us a clue at least.

side air would cause a too lean mix (usually),
resulting in a light to white maybe even pitted plug..

the exact opposite of what I'm thinking you plug will look like

'sid

PS sticky return can cause such indeed.. but usually that is the easiest test of them all..
with a non running engine twist the throttle and let it snap back, if you hear the carb clicking* the return should be fine (*slide or butterfly hitting the endstop)
and while an overheated plug can cause a menacing engine (revving too high nearly unstoppable)
that too can easily be judged by looking at the plug itself.
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Old 02-26-2020, 10:29 AM
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Quote:
Originally Posted by itsid View Post
you might have misread..
I said "too big" not "too small"

here's my thinking behind it..
if the main jet is too big there's too much fuel in the idle mix..
thus the idle needle must be threaded way further in to level that mix out as good as it can...

Ideally, just get a plug reading and show us what your spark plug looks like atm.
I'd say it'll be pretty dark and maybe even wet when afer the engine just stalled.
And I'd say that's more than likely a fuel issue here (too much of it in the mix)
not oil..

And at higher revolutions the only cause for that could be the main jet really.

it'd also expain why the engine tends to stick on higher rpms when you let off the throttle
(still enough combustible accumulated in the manifold and combustion chamber)
and why it tends to stall after a sudden stop...
if the plug isn't allowed to dry (at low rpms) the spark gets weaker and weaker..
a dramatic increase is fuel will render it nearly useless and the engine stalls

So yeah too big main is my call from what you're saying;
a plug reading can certainly give us a clue at least.

side air would cause a too lean mix (usually),
resulting in a light to white maybe even pitted plug..

the exact opposite of what I'm thinking you plug will look like

'sid

PS sticky return can cause such indeed.. but usually that is the easiest test of them all..
with a non running engine twist the throttle and let it snap back, if you hear the carb clicking* the return should be fine (*slide or butterfly hitting the endstop)
and while an overheated plug can cause a menacing engine (revving too high nearly unstoppable)
that too can easily be judged by looking at the plug itself.
interesting...
well, once I run it with the foam around the air filter...thus reducing air flow we should know. If it acts worse, than your thinking of a main jet too big will be proven.
But in my past experiences, these chinese 110's usually run on the lean side from the factory. So even though the carb is one of those sold as being for 90-140cc...I think it is still more likely to be lean than rich. Lean mix can cause it rpms to "hang", and my thinking is the stalling when you chop the throttle and brake is that you get a slight load on the motor while the mix is too lean.

I'll know which after I test with the added filter foam.
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Old 02-26-2020, 10:35 AM
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not really no..
a foam filter reduces airflow, yes.. but reduced airflow ALSO reduces drawn fuel through the jet
so there shouldn't be much of a difference with or without foam
(the actual ratio shouldn't change too much)
the only time the ratio changes is by the plunger setting
(it relies more or less on the main jet according to throttle position adding idle as needed)

check the spark plug instead

'sid
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Old 02-26-2020, 01:09 PM
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Quote:
Originally Posted by itsid View Post
not really no..
a foam filter reduces airflow, yes.. but reduced airflow ALSO reduces drawn fuel through the jet
so there shouldn't be much of a difference with or without foam
(the actual ratio shouldn't change too much)
the only time the ratio changes is by the plunger setting
(it relies more or less on the main jet according to throttle position adding idle as needed)

check the spark plug instead

'sid
hum...it works very well on 50cc moped...when it gets around 45-50 degrees they run much better when I partially block of the inlet to the air filter. But then, those bikes have a carb where you control a butterfly..and not the throttle slide directly.

I did just have my son ride the quad, it ran pretty much the same as before.

I am going to try adjusting the needle height tomorrow.

I did look at the plug, it looks pretty good...in thinking it was lean I expected to see it white or gray, but it was dark. Not wet, nor bad enough that I would think it would cause it to stall.

The mixture screw that I had to adjust in on this bike is an air mixture. If it were a fuel mixture (on the engine side) then I'd be more inclined to think it was running with too big of a jet. But since I am reducing the air mixture at idle, that is why I'm thinking it is running lean. The way it hangs just above idle rpms sometimes also seems the same as if it were lean. If the main jet were too big or too small...I'd think it would have more trouble running than it does. It drives great...the only problem is it sometimes stalling after heavy braking and sometimes having the rpms hang when you chop the throttle. Going do the road, it sings nicely.

Anyway, I will see tomorrow if adjusting the needle up or down makes a difference, and which way it prefers. I'm hoping that it only needs a small adjustment, rather than a different sized main or idle jet.
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Old 02-26-2020, 01:20 PM
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Dry black is carbon, indicating rich mixture.
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Old 02-26-2020, 01:48 PM
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Quote:
Originally Posted by ghost civic View Post
It can only go in one way. And if it were in wrong, it wouldn't be able to idle down at all. I have it idling good and it drives good...just sometimes the rpms don't drop down as low as they should when you let off the throttle (it will hang a couple hundred rpms high for a few seconds) and sometimes under hard braking the motor will stall.

I am going to try putting thick foam around the air filter. That should limit the amount of air going it, and thus enrich the mixture. If that works, then I will see if I have a slightly bigger idle jet to put in it.
Yeah, they can't be put upside down, but some Carb Slides can still be oriented 180 degrees off. I know some do have built in stops that don't allow that to happen, but some don't.
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Old 02-26-2020, 06:43 PM
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Quote:
Originally Posted by Texan View Post
Yeah, they can't be put upside down, but some Carb Slides can still be oriented 180 degrees off. I know some do have built in stops that don't allow that to happen, but some don't.
yeh, these ones have a thin slot on one side, and the slot with ramp on the other for the idle speed screw...so they can't go in backwards.

JTSpeedDemon, that is what the plug looks like, dry and black.

So what has me confused...the mixture screw looks like a air mixture, as it is on the intake side. I thought that if the mixture screw is by the intake...it controls an air circuit...and if it is by the engine side, it controls a gas circuit...and that either way, it mainly effects idle and just off-idle mixtures.

SOO, if the main jet is too rich, why does lowering (turning in) the air mixture screw lower the idle speed? That should be making the mixture more rich right?

Tomorrow I can see if the needle can go lower, if the mixture is rich, then lowering the needle should help.
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Old 02-26-2020, 10:29 PM
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On a four stroke carburetor it's actually a fuel screw (motor side of venturi), on 2 strokes it's a air screw (airbox side) so its sounding like you have a 2 stroke carb on it to be honest... Best way I've learned to set the mixture whether it be a 2 or 4 stroke is to start at 1-1/2 turns out from lightly seated then turn in until idle drops (pay attention to how much you've turned it, return to 1-1/2 then turn it out until idle drops and split the difference. You're trying to achieve the highest idle with the mixture screw and then adjusting your base idle. If you're past 2-1/4 turns out or under a 3/4 turn to achieve that highest idle then it's time to resize your pilot jet. If your emulsion tube is the threaded type you can run without the main jet as a test, the jet needle controls roughly 1/4 -3/4 throttle and the main jet only fully comes into play past 2/3-3/4 throttle once the jet needle is fully out of the needle jet (which is the main fuel nozzle that sits on top of emulsion tube and often protrudes into the venturi). Dont forget that in a slide style carb that the pilot circuit is working from idle to WOT, it has the most affect at idle and slowly tapers off but always plays a minor role. Heres a Mikuni chart that should help you visualize it, disregard the "cutaway" as it only applies when you're talking about major modifications and racing. Sorry for the lengthy post. Brian
•MERGED•
Sorry forgot to upload it! Lol. I know it says "pilot air screw" (it's a 2 stroke chart) but the principles are the same.
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Old 02-28-2020, 01:15 PM
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I tried adjusting the needle height today

first I set the C clip all the way up, to allow less fuel.
Bike wouldn't start.
Tried playing with the mixture screw a bit, only got an occasional pop.

Then set the C clip on the needle all the way down, to run richer. Still not able to start.

Put the C clip back where it was...in the middle and once I had the mixture screw back where it as it started up and idled.

But while doing all this I did notice that the muffler has a leak where the exhaust pipe attaches to it. I wonder if the lack of back pressure could be causing the idle issues or at least the tendency to stall under hard braking?
Either way, I need to weld it up to quiet it down. So the next step is to fix that pipe and see if that helps any. I think it is at least possible that allowing more exhaust flow could hurt it more at low rpms and not be an issue when it's actually driving around.

If that doesn't fix it, then I think I will try different size idle jet.
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Old 02-28-2020, 01:33 PM
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Screwing the mixture screw in leans out the mixture. Usually the screw closer to the intake is the idle circuit fuel screw.
But I have not personally used a Mikuni yet. Soon, though!
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Old 02-28-2020, 03:16 PM
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welded up the muffler, no change in engine performance.
Idle still hunting, if I adjust the mixture screw and idle speed screw so the idle is good, then it misses (either rich or lean) when you mash the throttle.
Set it so the throttle is a bit high and can hang when you let off the throttle, and she revs right up nicely.
Going to have to pull the carb and try different pilot jets next. Hopefully the one in it will have a number...sometimes they dont!
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Old 02-28-2020, 10:29 PM
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after trying to adjust the needle height, the quad was harder to start but could get going. I just took the carb off to clean it, thinking maybe something from the tank partially clogged the pilot jet, I also considered dropping in a larger pilot jet...but the one in it had no size # on it
and now it doesn't want to start. I keep getting pops from the intake. Not 100% sure why.

One of the things I did when I bought a new carb is get one that didn't come with the plastic spacer. So I'm using an old spacer but I added 2 fiber gaskets. I can't imagine that air could be getting past, but maybe since I have now had the carb on/off a half dozen times they are no longer sealing completely?

The bike is in way better shape than most I buy, so I think I will try buying another carb off amazon...this time one with a new spacer. I have a couple other 110's I recently bought that are in rough shape, so if the carb/spacers I have turn out not to be the problem, I can always use them on one of the older quads.

The only other time I had this much trouble with a cheapo carb was when I put one on a yamaha breeze. The float wouldn't shut off flow, I tried adjusting but that made the bowl level just a tad low.

And with any cheap carb, the more you take it apart, the lower the chance of it going back together. The bowl gasket especially tends to stretch out when exposed...then you can't get it to sit back in the grove.
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