Linhai 250 CC, carburetor float valve

[maydog]

Hello,

I spent some of the summer and most of the fall trying to fix a fuel delivery issue on my RoadRunner 250 race. I removed all restrictions, and I still get stumbling holding full throttle for an extended period.

I tried a small fuel pump, but it simply had too much pressure - a regulator didnt help. The cycle would run fine at full throttle, but would barf at idle.

I had the carb off a few times and tried to adjust the float valve, but that didn't help the flow.

I am pretty convinced that it is this valve causing the restriction, and want to modify it - but I would like a spare on hand. I contacted roadrunner a few times to get a parts list and prices for the valve, with no response.

I found a YP250 parts list and the part number is 4HC–14390–00, but havent found any where I can actually order it.

Does anyone know where I can get these parts?

If this doesnt work, I may remove the valve altogether and use some the electronic fuel solenoid to control the bowl level.

Thanks

[Andi]

What spark plug are you using? Mine came with a NGK DR8EA.

Shortly after I finished an extensive PDI, I couldn't get it started as it kept flooding the plug, changed to a new NGK DR8EA plug and it fired right up. I now got 120 km on it and after an oil change today I got the same problem again, it wouldn't start so I changed the plug again, had to use my old Lifan OEM plug (same as the NGK but non-resistor type) and it fired right up.

Its a little early to tell, but either something keeps spoiling (fouling) the plug or maybe it is the resistor in the plug. I have read somewhere once that the resistor plugs can cause this exact problem, I will get some non-resistor types the NGK D8EA tomorrow and see how it holds out. Only difference is that it may cause interference to radios etc.

I'm not sure if this is your problem, but not getting a proper spark will also cause the problem you described, maybe its not a lack of fuel, but rather a lack of proper spark. Maybe a component in the ignition system is causing the premature failure of the plug.

Andi

[maydog]

Hi,

I am pretty sure it is a fuel supply issue, I have checked the plug on several occasions - it looks fine. The stumbling is correlated to throttle position - not necessarily speed. The problem shows up as slower speed when riding into a headwind or uphill (more throttle) .

The pump did take care of the problem, but made other - worse - problems. I thought about adding a switch that would turn on the pump at WOT, but I want to keep it simple and decided to try to increase the flow without the pump.

I want to try opening up the float valve a bit - but want spares on hand in case i screw something up.

[scooterollie]

Maydog;
There is really no "opening up the float valve a bit" adjustment. The float height is either correct or it isn't. The float valve either works properly or it doesn't.

When you remove the top of the carb., turn it upside down. If the float is level with the top, it is adjusted properly. Many of these carbs have plastic floats in them that cannot be adjusted. They are molded in the proper shape to allow the bowl to fill with the correct amount of gas.

Remove the float valve and visually inspect it's tip. Should be clean and not damaged. Many, if not all, have a tip covered with a type of rubber that allows it to seat better, shutting off the gas flow. If possible, blow compressed air through the opening.

Did you check the slide (accessed from the carb. top) to make certain it is moving up and down freely and that the diaphragm isn't torn? Sometimes it helps if you can swap the carb with one known to be OK. My suspicion is that the carb. is OK and you have a fuel delivery problem TO the carb.

[monty57]

I have to agree with both ollie and andi. The float needs to be set where it is supposed to be set, there is no tweaking it. The problem you describe is what I would cause "misfire under load". This is usually caused by the speak plug. There is no it looks "OK" test for this one.

I have had the issue on both my 50cc scoot and my two cylinder generator. Missing under load. In both cases I felt there was a fuel issue and messed with both carbs for several hours only to to find out that changing the spark plugs cured the problem in both cases. And in both cases the plugs "looked" great. Clean, properly gapped, etc. Cleaning and re-gapping did not cure the problem either. The cure was a fresh new, out of the box, spark plug.

I can't explain it nor will try but when I hear that "misfire under load" symptom now my first step if a fresh plug.

[maydog]

Thanks all for the replies,

I have had the carb and float valve out of it several times for inspection. The problem is with fuel delivery - adding pressure cures the problem. The valve will not - however - will not deal with the extra pressure and overflows at part throttle.

I have troubleshot this several different ways and I keep coming back to fuel delivery. It will run fine a wot for a while and then bog down until I back off the throttle and let the bowl refill a bit, in theory at least.

Since I cannot peer into the bowl while running, I want to increase the flow of the valve (ie drill it out slightly) and see if the problem goes away - I am 80% sure it will. I want to be able to cover the 20% of doubt by having backup parts available.

What I am really looking for is a source for the part.

I suppose when -if- I order it, I can get a new plug as well.

[scooterollie]

IMHO, you will be making a mistake drilling out the float valve orifice. Unless your carb. is undersized, maybe for a 50cc or something like that, fuel volume through that orifice should be sufficient. It is, however, your call.

The O.E. vacuum fuel pumps have been known to be weak and cause fuel delivery problems on some scoots. Also, since the pump is operated by vacuum and engine vacuum drops off at WOT, there is often less fuel delivered to the carb. because of this phenomenon.

[monty57]

I'm sorry if I lead in the wrong direction with my previous post but that happens when you are not actually there to see/hear/experience the problem. I also know how frustrating some of the issues can be. As I described in my earlier post the plug issue drove me crazy for a couple of days.

Once again though, I have to agree with Ollie. The float, valve and orifice is designed to work together with the carbs main jetting. Drilling out the opening, even slightly, could cause irreparable harm to the crab. The openings are machined which allow for very smooth surface and good flow. Drilling will cause scarring and the will actually inhibit flow. Not as much as if you did it to a jet but still IMHO, not a good idea.

If you could see into the crab you will see that the fuel flow into the float bowl is designed to out pace the usage through the jets. If that was not the case there would be no need for the float and valve. I have heard of similar tales of running our of fuel at high speeds and wide open throttle and as Ollie said the culprit is usually the fuel pump. There is a higher quality vacuum replacement pump available and there is a low volume electric pump available from NAP. If you search through some of the older Threads here you will find info on both.

[maydog]

I did try to remove all sources of restriction, including the vacuum petcock. Besides pressurizing the fuel supply nothing helped. I did use a small fuel pump from checker, but the pressure is too high - a regulator just caused flow problems. Currently I have an electronic solenoid valve in place of the petcock and larger diameter hoses. The flow is good.

The valve body itself is removable, and if I had a spare - I wouldn't worry about messing anything up. The opening in the body is much smaller than the cone of the needle - if one did a good job, they may be able to increase the opening.

The problem is, of the US suppliers I have searched - none carries parts for this type of scooter.

If I cant possibly get my hands on the part, then I may try some sort of low pressure pump (windshield washer?) Or remove the valve altogether and modulate the fuel solenoid - though I would like to keep it simple.

[maydog]

Here is the parts guide for anyone interested.

www.ekoinstal.com/skutery/katalogi%20czesci%20YAMAHA/YP250%205SJ9%202003.pdf

[Andi]

The scooter model really doesn't matter, you have to look for someone that carries parts for the engine or the carburetor. The Linhai 257 cc engine and likely the same carb is used on a good few Chinese 250's now. Try the seller for parts, I purchased mine at EVO Sales and have had a few little issues with the scoot. I found Rony and Moises to be very responsive, within less then 2 weeks they send me a few parts I needed, under warranty and I'm located in the Caribbean. Bandit Motorsport sells the YP250 clone with the Linhai engine. Try Stan at Oregon Vintage, he also ownes (or owned) a Race 250, he maybe able to help.

I own the same scoot and don't have any of the problems you describe and quite frankly think your wasting your time re-engineering the fuel delivery, but I will give you the benefit of doubt as I have only had mine out a few times and not put any significant miles on it yet.

- First of its a gravity feed system so a fuel pump is really not required. If the bowl really runs out of fuel at WOT then the bowl is to small (which I doubt) or your feed is restricted somewhere in between the tank and carb.
- Check and preferably change the fuel delivery and vacuum lines they are known to cause problems on the Chinese bikes.
- Maybe at high demand it creates a vacuum in the tank, so try at 1/2 to 3/4 tank if you still get the problem with the gas cap off.
- Try bypassing the vacuum fuel delivery valve and see if that corrects the problem.
- Check you carb for any blockage, contaminants or damage. Inspect the main jet and atomizer, but be carefull not to poke anything through as it may damage. Check the operation of the slide for full movement, I've seen them stick already.
- I would guess you have the same Vacuum style carb as I have on my Race 250. They offer great throttle response, but are finicky to tune. Having too much air flow through the airbox reduces the pressure that lifts the slide or lack of sufficient vacuum when at WOT.
- Humor all of us and try a new sparkplug , get the non-resistor type NGK D8EA, Champion A8HC or Denso X16EP (I think those are the correct cross references to the NGK). If it isn't the problem its always good to have a spare plug anyways.

You mentioned you have troubleshot this several different ways, remember if you are looking at the wrong thing from several different angles its still the wrong thing.

Good luck

Andi

[Andi]

I thought I had this info some where:


VACUUM-STYLE CARB JETTING.

One of the hardest carbs to jet is the vacuum slide style carb. These are found on a lot of sportmachines, including the z400, kfx400, dvx400, raptor, and even utility quads. They are great forthrottle response. Unfortunately, they are not the best high- performance carbs.With a vacuum carb its best to not open up the airbox right away. Get your main jet set correctlyfirst, which in most cases will be one to two sizes bigger than stock. After that, if the machine isbackfiring when you let off the throttle, you can turn the fuel screw out one or two more turnsthan stock. After that if the machine is backfiring when you let off the throttle, you can turn thefuel screw out 1 or 2 turns than stock. If this does not get rid of the problem, you will have to goup on the pilot jet size and turn your fuel screw back (leaning it back down).Once you have these set, if you now want to open up the air box, you’ll often have to change theneedle. Several companies offer jet kits with needled.As you open up the air box, you lessen the pressure that allows the slide to lift, so you need torichen the mid range up with a thinner needle. A thinner needle allows more fuel to pass into theintake tract. This can be a trial and error process of learning.

Hope this helps.

Andi

[maydog]

It seems as if I am going in circles - I do appreciate the feedback though I think that some important points stated previously are overlooked.

All of the original hoses, filters and pumps were replaced. Long before posting, I searched this and other forums for known issues and remedies - I have tried or at least considered most before coming to this point.

Upping the pressure via fuel pump clears up the issue, thus far, only this has corrected the issue.

Upping the pressure via fuel pump also makes the carb overflow- so this cannot be a long term fix.

I am looking for a spare part to try to troubleshoot futher. For several weeks, the supplier, EVO sales, has been unresponsive to my multiple parts requests.

Maybe I didn't explain the issue right. The scooter more or less dies completely at prolonged stretches of full throttle and doesn't come back to life until letting up. The harder I stay on the throttle the longer I have to let up for it to recover.

Maybe I am having the issue since I am taller (6'4") and have more wind resistance than most other riders and that I take it on a fairly long commute (20 miles one way, engine has 3000 miles on it) with several long stretches where I sustain 60-65 mph. The problem occurs at all temperatures (both engine and air) and is very consistent. Its possible that it is a spark/cdi issue, but adding pressure to the fuel eliminates the problem - that is why I am pursuing this.

I hope that someone that visits the board would be able to point me to a parts source, I will try Stan and Bandit Jim to see if they can acquire it.

From parts diagrams in the link I posted previously, image D2 shows a fuel pump. Could it be that this carburetor was not designed for a gravity feed application? Do other scooters that use this engine employ a fuel pump? If so, maybe there is something really wrong with the float valve since it seems that it cannot hold back anything more than the gravity feed pressure.

Is there anyone else out there dealing with this? I thought I saw some posts a while back.

[monty57]

First, where is your gas tank?. If it is below the floor between your legs, you have a fuel pump. If it is located above the engine, it is gravity flow.

If you have a fuel pump, I' ll will bet this is your issue not the carburetor. If the float bowl is running dry, it is a supply problem not a float/needle valve issue. The opening in the seat is always much small than the end of the needle. That is to shut off the fuel with minor pressure the float exerts. If the new fuel pump overrides the float then it is too much pressure. The electric pump many have used is a very low 2 or 3 psi pump. If your pump is more than that, it will override the float.

If you do not have fuel pump but rather a vacuum valve on the tank, that most likely is the issue.

I don't want to seem like I'm preaching but you did say you are going in circles and that my friend is because I think you are barking up the wrong tree.

If you want to find out for sure, get a small tank or bladder that you can hang higher than the carb. Hook it directly to the carb and give it a try. If this works then you know for sure it is the fuel delivery system and not the carb.

[scooterollie]

Maydog;
Most Chinese scoots that have fuel pumps have the vacuum type. Just because your scoot uses the Linhai/Yamaha engine does not mean it has the electric pump used by Linhai on their scoots and the ones they make for Yamaha. Your model does have the fuel tank in the rear, above the carb. level so you may well only have a fuel tap. However, only inspection will determine this. I wonder if they still install a pump on this model because it has the larger carb. & engine? Since you tried an electric pump and it seemed to eliminate the problem, I would still bet on a restriction somewhere or something else which reduces fuel flow to the carb.

[Andi]

maydog said:

From parts diagrams in the link I posted previously, image D2 shows a fuel pump. Could it be that this carburetor was not designed for a gravity feed application? Do other scooters that use this engine employ a fuel pump? If so, maybe there is something really wrong with the float valve since it seems that it cannot hold back anything more than the gravity feed pressure.

Is there anyone else out there dealing with this? I thought I saw some posts a while back.

The parts diagram you supplied is for a Yamaha YP250 otherwise known as Majesty. The only similarities there is that Linhai cloned (actually copied) the engine form the Majesty. The Linhai is a 257cc engine, the Majesty was 249cc, 1 mm less diameter in the piston bore. The YP 250 parts manual is a nice reference, as the engine is the same in design so it seems is the carb, but I doubt you could use any of the parts. You may be able to use the Majesty carb, don't know if its jetted the same way though.

Your fuel tank is above the rear wheel behind and above the engine, the Race 250 does not come with a fuel pump. I'm not sure why adding the extra pressure seems to help your problem, but its not much of a fix if it overflows. Are you sure that your engine isn't overheating? Maybe it gets so hot at prolonged WOT that its boiling the fuel out of the bowl? Check with a infra red thermometer if available.

I changed the coolant on mine before I ever rode it. I took of the hoses and noticed that the outlet on the water pump and the inlet at the engine was half closed from corrosion, big chunks of white corrosion deposits had formed, surely inhibiting the flow. I cleaned it all out and flushed it through several times, before refilling with quality coolant.

Check your engine compression cold and right after you've experienced the problem.

I would ask EVO for a new carb and try that, don't know the cost, but may well be worth the aggravation you are going through.


And o gosh, unless you've done so, please change the spark plug already, to rule that part out . Your total investment there is like 3 US or so, you are starting to sound like the guy that measured 3 times and its still to short.

Andi