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Discussion Starter · #1 ·
Hi All,

I have a 1993 LT-4WD that idles fine (20 minutes no problem) and revs easily when sitting still and in neutral but stalls and is almost impossible to restart after a 30-second ride around the yard. It usually takes pouring gas down the intake tube to get it restarted. My first thought is fuel pump, but I don't know how to test it or what else could cause the problem. Any suggestions are appreciated.
 

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Sounds like the carb need to be fleshed. So I would first start by thoroughly cleaning the carb then installing a carb rebuild kit. For kits I highly recommend Shindy. And we to the Forum.
 

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Discussion Starter · #3 · (Edited)
Thanks for the suggestion and the kit recommendation. I disassembled the carb and cleaned out a bunch of white crud that looked like it was blocking the fuel inlet, then cleaned everything up so it was spotless and installed the Shindy carb kit. I also replaced the fuel lines and flushed the fuel tank in case they were the source of the white stuff (I think the fuel lines were the original ones). The engine now starts immediately which is a big improvement. It also idles well, and revs easily in neutral like before but as soon as I put it in first gear or reverse, the engine struggles to rev beyond idle. I can usually feather the throttle and get it to rev enough to move, but there's no part-throttle. It's either idle or almost wide open. Any suggstions for what to check next?

Thanks in advance.
 

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Verify your float height, more critical on these CV carbs than on normal slide or butterflies.

Make sure the slide is not sticking at all. It uses vacuum to move up and down and even a slight drag can cause it to open slowly. The diaphragm under the cup is easy to twist slightly and that will make the slide not operated correctly.
Your symptoms point to the slide. At idle the slide is mostly closed and is fine. At full throttle there is enough vacuum to overcome any stickiness. Mid range suffers.

I battled my 1990 CV carb for a long time and finally figured out the slide issue. I replaced the diaphragm and the spring and then was very careful not to twist the diaphragm while putting the cap on. Ran like a champ until the carb boot between the motor and carb failed and it leaned out. One last rebuild and it is running better than ever.
 

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Discussion Starter · #5 ·
After doing some research it seems the float height should be .51±.02 inches. I checked mine with a dial caliper and it was exactly .51 inches. You were definitely onto something with the diaphragm. The slide moved smoothly but I had installed the diaphragm/slide assembly turned 180°, so the little bumpout on the one side of the diaphragm was not seating in its corresponding recess on the carb body. Once I turned it around and reassembled everything it ran flawlessly... for about 30 minutes. While it ran, I alternated between riding it around the house a few times with a few minutes of idling. On the second or third stint of idling, it died and would not restart. On a whim, I pulled the fuel line off the carb and only a couple drops came out. I grabbed my Mityvac and easily pulled gas through the fuel line. I reinstalled the line on the carb and with a little starting fluid, it fired back up and ran for a couple minutes, then stalled again. The gas tank is at least 3/4 full. Should I expect the fuel line to be full or at least partially full? Any ideas for the next thing to check?
 

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I think I'd pull the petcock off the gas tank and see if it is clogged up or maybe the rubber seal is deteriorated to the point that it is plugging up the screen.

Now that said, there are two types of Petcocks. One is manually operated and the other is vacuum. Manual will only have 2 fuel lines, vacuum will have the 2 fuel lines and a 3rd line coming out that is typically rigid fuel hose.

Might just drain the fuel tank and with just about a cup of gas left in it, shake it up really good and then drain it out. You might see some odd colors come out.
 

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to check the fuel flow,
disconnect the line that goes to the carb from the fuel pump,
start it and see how much fuel comes out into a jug with ON and RES
if any hiccups or no fuel, thats your problem.
perhaps the fuel pump diaphragm is broken inside.
 

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Keep in mind that when testing the fuel pump fuel should pulsate out not continuously flow out.
 
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Discussion Starter · #9 ·
I drained the fuel tank and pulled the petcock. The screens were clean, though if it matters my petcock only has one hose instead of the two or three mentioned above. I sprayed some carb cleaner on both screens just to be sure. I also shined a light down in the tank after draining it and there wasn't any residual crud in the bottom. I was able to get enough fuel in the carb bowl through a separate tube to get the engine to run a couple times, once for about 20 seconds and once for about 40 seconds. With the 20-second run I got about a thimble full out of the hose from the fuel pump. The second time, I got exactly nothing. Sounds like this might be the problem. Is there anything else I need to do to confirm? Is the fuel pump rebuildable?

Thanks for all the help with this.
 

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I drained the fuel tank and pulled the petcock. The screens were clean, though if it matters my petcock only has one hose instead of the two or three mentioned above. I sprayed some carb cleaner on both screens just to be sure. I also shined a light down in the tank after draining it and there wasn't any residual crud in the bottom. I was able to get enough fuel in the carb bowl through a separate tube to get the engine to run a couple times, once for about 20 seconds and once for about 40 seconds. With the 20-second run I got about a thimble full out of the hose from the fuel pump. The second time, I got exactly nothing. Sounds like this might be the problem. Is there anything else I need to do to confirm? Is the fuel pump rebuildable?

Thanks for all the help with this.
is the pump electric or is it on the petcock if it's elec make sure you are getting power to it and clean conn and remem some of these carbs have a screen before the float valve seat that may be a prob hope this helps
 

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Discussion Starter · #11 ·
There is a screen in the carb before the float valve seat. When I took the carb apart to rebuild it the screen was caked with white stuff and almost completely blocked. I put the screen and the rest of the disassembled carb in an ultrasonic cleaner for a while and everything was pristine when it came out. As for the fuel pump, I want to be sure what I'm looking at is what I should be looking at. In the picture below, what I'm calling the petcock is at the bottom right and has the lever for on,off, and reserve. What I believe is the fuel pump is at the upper left (five-sided silver cover). There is a large hose coming from the fuel tank petcock into the left side of the pump, a large hose going from the right side of the pump to the fuel inlet of the carb, and a smaller hose going from a small plastic fitting on the carb to the back of the pump (not shown in picture).

IMG_9864[1].JPG
 

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The valve with On/Off/Res is your fuel petcock. That style fuel petcock is non vacuum activated. Meaning you need to manually turn the fuel supply On/Off. In the top left corner of your pic is the fuel pump. The main fuel line feed goes from the fuel petcock to the fuel pump, then from the fuel pump to the carb. The smaller line on the fuel pump that you stated isn’t visible in your pic is a vacuum line. It goes to a vac port on the carb. Your carb should also have a line that runs up and under your shift panel. That line is simply a vent line and is typically connected to a T fitting. And just a note, the fuel petcock has fine screen pick up tubes inside the tank designed to filter out any crud or sediment before fuel leaves the tank. Sometime these fine screens on the pick up tubes can become clogged preventing proper fuel flow to the fuel pump.
 

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exactly like he said and after you have cleaned the petcock screens hook your hoses back up and with the motor cold not been started unhook your battery take the vacume line loose of the fuel pump and i hate this next part cause it sounds bad but blow and suck on the hose and have the hose unhooked from the carb and when you blow and suck the line the fuel should rush out of the hose in bursts hope that gets you going if it doesn't rush out the pump is bad or your pet is still not suppling it
 

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Discussion Starter · #14 ·
I tried a version of that with my Mityvac on the vacuum hose and nothing came out of the fuel pump outlet. When I inherited the Quadrunner it came with an extra fuel pump but no one knew why because the engine ran fine. It is a little different shape but has the two fuel lines and vacuum port. I pulled the extra one apart and everything looked good (no crud buildup, diaphragm intact, spring in place, etc.) I put it back together and installed it. While feeding fuel to the carb through a separate hose, I started and ran the engine and voila!, gas came out of the fuel pump outlet. I'm not sure what was wrong with the pump originally installed, but the other one works, so I'm happy. I've done the extended idle/ride around the yard/extended idle thing several times and it runs like a champ.

Thanks for all the help diagnosing this. I'm sure I saved at least a couple hundred dollars by not taking it to a shop.
 
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