Quadrunner LT4WD Running too Rich?

[Jd101506]

Hi all!  

I've got a 1988 LT4WD that I am working on.  It sat for almost two decades in a shed, so I replaced both the carb and the fuel pump (Pump was rusty, carb was ok, but had a pin hole in the bowl itself?).  Now, I went el cheapo and I replaced BOTH with Chinese aftermarket Carb and Fuel pump.  Now is where it gets confusing:

So I did this SAME thing on my other Quad, a 1988 LT300E.  They take the same PN carb, and a similar fuel pump, (One has a 90 degree bend in the vacuum port).  I've been battling the four wheeler a bit with some electrical issues, but I noticed that at idle it runs GREAT when I gravity feed fuel from a burp can into the fuel bowl of the carb... But as soon as I put it on the fuel pump from the tank, it idles EXTREMELY low and smokes a little.  To me, this indicated that the carb itself was running rich.  I adjusted it a little on the LT300e, but I could never seem to get it right, it still will slowly die at idle when warm, but ironically if I CHOKE the motor, it'll start up and run.  I dont know if this is because the RPM increases?  But the quad will run around the yard great at RPM and then die at idle.  

Now, the LT4WD.  I ended up with a faulty fuel pump for my second (I think the spring isn't seated inside as I can hear one rattling around) so when I installed it it WOULD NOT pump fuel.  So I ended up swapping the LT300 pump onto the LT4WD.  Boom, pumps fuel.  I put it all back together and got my tires on.  I ran it around my yard and it exhibits the SAME symptoms as the LT300e!  It will run around at RPM, but it will not stay running at idle, it drops realllllly low RPM and will start smoking a little as if its running rich.  Again, when I ran it with the fuel pump OFF I didn't have this issue. 

In my head I'm thinking it would be a mixture screw OR float issue... But the mixture screw doesn't seem to help me on either, and the bowls are not over flowing (I checked both overflow lines).  Is there something I'm missing here thats obvious?  Is there a vacuum line or something I missed? Maybe some configuration or something I missed? I reviewed the manual and nothing stood out to me.  

Conclusion:  Two different Suzuki fourwheelers, two different carbs (Both are chinese Ebay carbs) that BOTH run well when I mainline fuel from a drip can INTO the bowls, BOTH do not keep idle and seem to run extremely rich as they run great at RPM but slowly die at idle.  Adjustment screws, idle screws be damned.  

I ended up ordering a new Suzuki OEM fuel pump for ~90$ just to have it and see if it makes a difference.  Any advice here though would be SUPER appreciated!  

Edited July 31, 2023 by Jd101506

[Jd101506]

Update:  The carb is DEFINITELY wayyyy too full of fuel.  I pulled the carb out of the LT4WD and there is literal fuel pooled in the intake boot.  

At this point: Is it possible for the pump to pump TOO much fuel into the bowl?  Is it just the needle that stops the fuel from getting pumped in?  Would adjusting the float prevent that?  I pulled the float, and I'm confused about the float adjustment in the screen shot.  The needle has a TINY spring in the back side of it, where should the tang be resting on the needle to measure from the bowl to the float?  Or should the tang not be pushing on anything on the needle?  I realized that I have the same exact carb on both, so it stands to reason BOTH are set the same way, ie, too rich.  

If I measure from JUST at the point where the tang touches the needle while seated, i get a .87in measurement.  In the manual it states .92 to 1.00in.  Is that my issue?

[Mech]

Most those sprung float needles you hang the float down from it's pivot till it just rests lightly against the sprung loaded pin in the float needle. You have the carb body tilted on it's side.

Try testing it for pressure. Old carby things with mechanical fuel pumps the fuel pressure was about four pounds give or take a pound. That though is probably meant to be way less. Gravity from a regular bike to the carb would be about a half a foot of height, and water at half a foot only has about point two of a pound.. and fuel will be less. If you can just feel pressure with your finger it's probably enough..

And so both carbs do the same problem, so not a damaged O ring under the float needle seat..  And probably not the tap..

Well.. They have a diaphragm with a big washer on each side that're sort of riveted in the center, and it makes a seat for the spring.. If that leaks fuel can go down the vacuum hose..  If you suck gently on it you might get a whiff, or a mouthfull of fuel.. The fuel tap can do the same thing..

It's a good idea to check your engine isn't filling it's sump with fuel..

[Jd101506]

As a side note; mine are both slide carbs. 
 

I double checked. The needle jet is set in the 4th postion, aka ‘rich’ condition. Would I be running rich like this if the needle was set that low? I’ll probably pull the OEM needle out and see what that was set to and try to match it. It’s just still weird to me they both seem to run well when the pump isn’t running… is there any adjustment to these mechanical pumps? 
 

thanks!

[Mech]

No adjustment. Well the float, as you know, is meant to maintain a steady level of fuel, and it sounds like that works with a foot or two of head to the fuel level. It runs ok with the jury rig.

The float needle's seats are made with different sized orifice to suit the pressure they are meant to be working under. A smaller hole is a smaller area and the float manages to seal the needle in the seat easier with a smaller hole.

I've never taken much notice of the seat sizes in different bikes, but it's possible that that same carb body, set-up for a bike with a gravity feed fuel system, has a larger hole in it's seat than a carb designed for pump pressure has.

If you have a gravity feed carb it might get the needle forced off it's seat if the orifice is too large for pump pressure. Or, if the new pump is pumping too much pressure. A parts place online might say what size float needle seat they are meant to have, or the service manual should.

If you aren't sending the other pump back you could take it to bits and put the spring in the right place. Then try that one. Or revert back to an old pump and try it.. 

I can tell you how to assemble the pump if you want to look inside it. And I can tell you how to test a fuel pump if you want to check the old suzuki ones.

And no the slide needle shouldn't make any difference since both carbs ran fine with a jury rig fuel supply.. which I think had lower pressure than the pump has.

I think fuel pressure is causing your problem.. Too much for the carbs.

[Jd101506]

New data point! 
 

I had ordered a second Kipa fuel pump from Amazon (A refund/replacement for the broken one, the ball from the ball valve inside the inlet was loose inside the pump) arrived today. The so now I have three of these things at the house. 
 

I installed this new pump on the LT300e… and magically, it runs perfect. Like, this thing hasn’t run this well yet. I took it for a spin around the yard, no stalling no stutter, nothing. It runs like an absolute top. I left it running in my driveway for a bit and it ran for about 2-3 mins untouched and popped right into gear and sped away when I jumped back on it. 
 

So… the old Kipa, the ‘working’ one that I swapped from the 300 to the LT4WD, might be my issue. Works well enough to pump fuel, but doesn’t work well enough to maintain. This was the one that was in the 300 and it ran like crapola, then on the Quadrunner and it ran like crapola. 
 

I’ll wait until I get the new OEM fuel pump here and installed on the 4WD before I make any final decisions but so far it seems like this may have been my issue or at least partially. while I was spending money I ordered a ‘name brand’ carb from Amazon (easy returns) to see what the needle clip and default settings are. Reviews were very positive about it being a plug and play so I’ll likely swap it and see what happens. 

[Mech]

So what's the update..  Short version..

[Jd101506]

Installed the OEM pump, and I have the same issue. It will run around the yard at RPM with random stumbles but will slowly die at idle. It will smoke a bit as well as I let it sit and idle. The mixture screw seems to make very little difference on the carb. 
 

So I installed the KIPA new carb from Amazon. When I first put it in, it just wants to run at an extreme rpm, all the time. I couldn’t slow it with the idle adjustment and the slide needle (thisnis a slide carb not a CV) didn’t seem to make much difference. 
 

While I was bored I rebuilt the old LT300 carb and swapped the jets from the LT4WD into that carb with all new seals. I installed that carb and it did the SAME thing where it ran really fast rpm. Couldn’t figure it out. As I was standing there… it suddenly dropped rpm and then went back to the same old behavior it used to have where it would idle and then slowly kinda die and run like junk. 
 

So now I’m back to square one. I’d like to think the fuel pump is good and it just seems like it’s letting too much fuel in. At this point I’m going to pinch off the pump and mainline fuel into the carb again to see if it still runs ok. If it does… it feels like a float issue… across three different carbs. But I don’t have much else at this point to go on. 

[Mech]

I explained earlier that fuel pressure in a fuel tank has very little pressure and a fuel system with a pump will have quite a bit more quite likely.. The carb for the pump system will quite likely need a smaller float needle to prevent it flooding.

That's my guess.

[Jd101506]

So your suggestion is to change float needles or adjust the float?

It just seems impossible that over four different Quadrunner 250 carbs I would have all four not be able to hold fuel pressure. Doesn’t it? Hell even the rebuilt OEM carb isn’t. 
 

I haven’t been able to locate a clear instruction on how to adjust the float on these carbs as yet. I debated trying to restrict the fuel pump somehow to test but I haven’t figured that was a worthwhile test long term. 

[Mech]

Ma I misspoke.. It might need a smaller sized float needle's seat. if you look in the service or spares list it might tell you what size it should be.

[Jd101506]

More data! Definitely running way too rich. Fuel in the crankcase I think, the oil level is higher than I remember it being and smells a little bit like fuel… 

But the big clue is the plug, pictured below. Black as night. 
 

I took a video of the fuel pump off the carb. The quad runs really well in this way, so I think Mech you are right that something isn’t seating. QUESTION; does that fuel pump look like it’s pumping correctly? From descriptions I’ve seen it seems fine but I want to be sure. (I’m adding a YouTube link for the video because it’s larger than the attachment limit) 

 

vidoe here: 

It’s amazing to me this could be traveling across 4 different carbs.. but here we are! Is there anything else I can check on this? I took the bowl off the two carbs previously and both floats were .97 and .98. Unless I’m measuring wrong, the spec is .9 to 1.0in. I would assume thisnis ‘fine’ but I could adjust it more aggressively. 

[Gwbarm]

It is definately running rich by the looks of your plug, but engine sounds good, idles good and doesnt sound rich, no popping or run issues that i heard, is it blowing black smoke when revving, i also agree that if gas is getting into your oil it is probably leaking past the float valve.

[Jd101506]

1 hour ago, Gwbarm said:

It is definately running rich by the looks of your plug, but engine sounds good, idles good and doesnt sound rich, no popping or run issues that i heard, is it blowing black smoke when revving, i also agree that if gas is getting into your oil it is probably leaking past the float valve.

When I run it with the fuel pump it struggles pretty bad, runs a little rough and definitely will stall over time. Without the fuel pump you can see how it runs so I’m near positive it’s just pushing too much fuel and flooding the carb. I’m going to adjust the float fairly aggressively and see if that might help. Right now it’s within spec, but I wonder if I need to just go a little more aggressive. 

[Gwbarm]

Hopefully that helps, but if it’s within specs , I doubt it will. Tell me about the carb that’s on it, is it the correct OEM carb for the bike with OEM jets or kit jets, and if it’s running the same with 4 different carbs, there is something else wrong, I know you have done a lot to it, I’m going to read through all your posts to see if I can figure it out. 

[Jd101506]

ok so a new data point! 
 

I messed with the carbs a bit today. I tried using the carb that I had on it previous and tried to pump fuel into it to flood it. I couldn’t get it to flood! No matter which way I turn it or anything it will not flood. I tested this by taking the old carb, pre filling it with a little bit of fuel, and cranking the engine over with the plug wire off. It pumps fuel like it should, and I can’t make it flood. 
 

Now here’s where it’s getting interesting. I noticing my oil level was a little high so I went ahead and I pulled some oil out. After I said screw it let’s try and ride it around a little. Now I left the air box cover off and I left the breather tube for the carb off. 
 

it ran around great. Like, how it should. I was astonished! 
 

that’s when I realized I forgot to put the oil cap back on. I panicked. Stopped the quad and ran back inside and grabbed it, screwed it back in and started it back up… Wellnit ran great again for about a minute… Now it is doing the same thing as before and the carb has fuel burping back out of the breather! 
 

im attaching a video. 
 

it got me thinking though… where is the crankcase breather on these? Maybe mine is plugged and as it generates heat and runs it slowly pressurized and pulls fuel hard from the carb and dies? Is there a way to test this? I noticed one breather is missing the little snorkels they come with. 
 

and @Gwbarm the carb that is currently on here is from a LT300e that I have. It’s a known ‘good’ carb but I installed the Shink rebuild kit with proper jets for the LT4WD. So far it’s functioning the same as the eBay carb, which I tested on the LT300 and that works fine. 

[Mech]

That pumps pumping enough fuel to keep the bike running.. but that's not the issue here.

If the float needle seat has too bigger hole in it then the fuel pressure pushes too hard on that larger diameter and area of needle and overcomes the float.. A smaller float needle seat has a smaller area and so the float closes off the fuel pressure easier..

It's the pump causing the problem with those carbs.. they run fine you say under gravity feed. The pump has more pressure than gravity fed fuel does.

And if they warm up with fuel in the oil, the fuel starts evaporating and pressurising the sump bad, and trying to run the engine on fumes..

[Gwbarm]

I see where i got confused, you have the LT4WD which is a 250, you put the carb from your LT300 on it but jetted with the correct jets from a Shindy carb kit for the LT4WD. From what you described it does sound like the crankcase needs to breathe better. Still doesnt explain why you are getting gas into the oil, only way is if leaking by float needle and intake valve is not seating completely.

[Jd101506]

46 minutes ago, Gwbarm said:

I see where i got confused, you have the LT4WD which is a 250, you put the carb from your LT300 on it but jetted with the correct jets from a Shindy carb kit for the LT4WD. From what you described it does sound like the crankcase needs to breathe better. Still doesnt explain why you are getting gas into the oil, only way is if leaking by float needle and intake valve is not seating completely.

Did you happen to see the video I posted? Any idea about why the fuel would be coming out of that breather? 
 

Mech is right. The crankcase may be part of the issue but it doesn’t explain the fuel. Unless the crankcase is causing extreme vacuum somewhere? 
 

Anyone have any idea where the crankcase breather is on these LT4WD? 

[Mech]

They vent up near the front of the tank and into the air box. But the problem is the fuel in the cranckcase..  It gets warm and evaporates causing the pressure.

Your problem isn't with the vent, it's that fuel is in the oil !

You need to stop the fuel flooding the carbs.

The carbs run fine with low pressure gravity feed you tell us, but flood when the fuel pumps, even the genuine OEM pump, is connected..  The carbs are the problem.

[Jd101506]

I guess at this point I'm just not sure how to do it.  Four different carbs and they all seem to do the same thing.  I guess tomorrow I will pull the OEM carb and check the floats again.  

The tang on the float, I assume I bend it TOWARDS the needle to increase the amount of pressure on the needle?  It just seems impossible to me that all four carbs would have the same symptoms but from a technical standpoint it does make sense that the needle isn't doing it.  I MAY swap my eBay carb back in because I can adjust the tang and test it outside the ATV using the vacuum from the other one.  And the ebay one and the OEM one seem to function identically.  

One question: The needle itself on the slide of the carb.  Would any adjustment to that needle help me?  I noticed that the KIPA carb would run at high RPM and my throttle cable was tighter using that than the ebay or OEM... I assume that needle ONLY impacts RPM and not the mixture/how much fuel is going into the engine?  

[Gwbarm]

The crankcase vent is on the top of the crankcase where mech said just to the left of 21

It appears there were 2 different carbs that came on the 88 model depending on the model letter this is a diaphram model it had a 122.5 main jet and a 40 pilot jet with a 160 air jet.

This one had cable actuated slide it had a 100 main and a 22.5 pilot no air jet listed

This is the one from the 300e with cable slide 112.5 main and 20 pilot.

I dont know if this helps at all because like mech said fuel getting into the crancase is the problem, we have to figure that out.

 

[Mech]

#21..  The problem is that too much fuel is getting into the bowl, not the jets or the slide needle.

No amount of adjusting the float height is going to cure a fuel pressure that is too high and forcing the float needle off it's seat.

[Jd101506]

Super, thanks.  I'll take a look at the vent and see what I can see.  

And yep, I have the slide carb in the middle diagram.  The shindy kit I had replaced the jets with exactly the ones you mentioned.  100 and the 22.5.  

@Mech Ok, just wanted to check and make sure I wasn't missing something.  So to confirm:  At this point you would adjust the tang on the float needle to be more aggressive to prevent the flooding?  

[Mech]

No Jd, that's just the opposite to what I said.

If you look up parts for all the various carbs availiable for that bike, you will see they all use different float needle seats, with different sized holes where the needle fits..  You need the right float needle seat..

[Jd101506]

I’m using the needle and seat that came with the shindy kit for the LT4WD. 
 

I’ve never used anything but the proper needle and seat which is why I’m confused as to what you are asking. 
 

 

[Mech]

I'm saying some of those models you are mentioning have a fuel pump and some don't.

They use those CV carbs on lots of different suzuki bikes, and some of those bikes have pumps, and some don't.

But you've confused the issue even further by using other non suzuki carbs which we have no idea whether they are set up for a pump or no pump.

I think you should go back to the start and re read what I've been saying repeatedly..  It should be very easy to understand. Not all carbs are the same, not even if they are the same make and model.

Or, find the original carb for each bike you have there, and clean and set them up to specs.

[Jd101506]

I have the original carb for the LT4WD. 
 

All of these LT4WD models from 85-98 have fuel pumps. They have to, there is no way to gravity feed any fuel to them. I also removed an original Mikuni carb from this LT4WD when I started working on it because it was seized. I know for 100% fact this Suzuki has and needs a fuel pump. 
 

I also know for 100% fact that I have the right jets and needles in this carb because I matched the new Shindy ones to the ones that came out of the Mikuni from this bike that wasn’t salvageable. 
 

im using Suzuki parts warehouse to buy said parts. The part number for the eBay carb, Amazon carb both pulled from my bike, my year page that was mentioned in screenshots above. I’ll add my vin in here so you can double check I’m not horsing you around. 
 

For what it’s worth my LT300 is running great with an eBay carb and a Kipa fuel pump. I don’t know if it was a lightening strike or what, but both machines have and require the same style of carb (Slide style, NOT CV) and both use a variation of the same fuel pump.
 

Im not trying to be an idiot here, I just can’t get this thing to not overfuel itself no matter what I do.
 

I just got bored and pulled the slide out of the Mikuni and man, there’s fuel just sitting in the top there. Wild. Added a photo.  Side note; what’s a sure fire way to test for fuel in oil? I’m second guessing if I smell fuel in it or if I’m just smelling the overflow from earlier. 

[Mech]

Yeah but what if the carbs you have bought are set up for a bike that doesn't have a fuel pump ?  Then it will have a bigger sized hole in the float needle seat to suit low pressure gravity fed fuel.

If you've used several different carbs, and checked the float needle tip, and the seat and the O ring under the seat, and adjusted the float level, in all of them, and they all keep flooding with the fuel pump, but not with gravity feed, then surely it's the pump causing the trouble. And you've tried several pumps, including an OEM, and they all cause the flooding, so it's not a/the pump, it's all pumps... Or all the carbs are now set for gravity feed systems with low pressure fuel.

If what you've been saying is correct, and your work has been careful, then that's the only conclusion I can come to..

If the oil level has gone up, or it smells like fuel, or is making the vent system overload when it's hot.. and filling the airbox with oil.. those are all signs there is fuel in the oil..  It's quite common if the fuel tap isn't closing off.. or in a case like this where the carbs are dribbling fuel.

Fuel can get into the oil because of a hole in a diaphragm in the pump or tap, or a leaking tap, or a bad float, bad float needle, bad float needle seat O ring, or badly adjusted float level.

[Mech]

#12.. The manuals I've been looking in say that there are two different float levels, one around an inch and the other around a half inch.  What exact model of carb do you have ? It could be a BST or a Vm, but both models have some other numbers on them if they are OEM, like 19BA or 39DO.. 

I also noticed that those crankcase vents only vent into the airbox, no branch to the front near the fuel tank..  Where that hose fits to the front of the airbox there is probably a restrictor, or it might even have a restrictor inside that rubber hose.. some did. They get blocked with gunk and can cause crankcase pressure..  but again, it's not your main problem..