1991 suzuki quadrunner 4WD carb fitment issues.

[Joeguy]

Hello, i just bought this quad and i think the carb that came with it is either wrong or i am very dumb and cannot figure out how to install it ha. The bottom of the carb hits the wire boot on the starter before i can get it to seat into the boots, i measured it with calipers and its about 6.1 inches long. The ones that i see on ebay for it claim 5.72 inches for length, i assume that will fix my issue but just wanted to double check before buying. The carb that is in it right now has no numbers or anything on it for me to reference.

Edited August 5, 2024 by Joeguy
messed up picture

[Mech]

https://www.partzilla.com/catalog/suzuki/atv/1991

There are four 1991 quadrunner's listed, and several models of carb. Some of the carbs are similar to that one you have except they don't have that enrichener valve that hangs off the bottom of the bowl. Check carefully though because there are several different jetted carbs, each for a different market, for different fuel, altitude, climate and possibly engine.

It appears your carb isn't availiable, but, if you identify your model bike, then choose the correct carb in the listing and double click on the part number, it will take you to a page where, if you scroll down a bit, you will find a list of all the other models that carb fits. One of those other bikes may still have it's carb availiable, or you google search for the original part number for an after-market carb.

[Joeguy]

According to my VIN its an LT 4WD and there are 2 carbs that fit i guess, does the J in my VIN also mean model J for the carb? If not ill just guess with an aftermarket one and see if it will even fit.

[Mech]

Did you notice that they didn't have that diaphragm on the bottom of the bowl ? Would that make the difference between fitting and not fitting ?

I'd suggest sending that carb that doesn't fit back, and cleaning the old carb. Unless the idle mixture screw is seized in, or there is huge amounts of play between the slide and body, then it will be the best option.. the aftermarket carbs hardly ever run right without some adjustments and work anyway.

[Joeguy]

I do believe the one with no diaphragm would fit due to where it is hitting the starter when i try to install the one i have already. I have not bought anything yet the one that doesn't fit is the old one that came with the quad, i bought it not running. Its weird to me that it wouldn't fit at all, i mean i get there are different models but you would think either would fit but just not run right. Honestly im about to just remove the starter and get this one i have in it to make sure it will run before putting more time in.

[Gwbarm]

Its different from OEM, waas it on the bike when you got it.

[Joeguy]

18 minutes ago, Gwbarm said:

Its different from OEM, waas it on the bike when you got it.

Yes it was on it when i got it, i figured it was the wrong one or i was just dumb and not installing it right somehow, came here to double check before buying anything.

[Gwbarm]

If it was on it when you got it it should go back on, might take a little finagiling, like turn it to the side get it started in the rubber connection and then turn it to where its straight the rubber should give a little bit so you can get it in there. If you prefer to get another one i have had good luck lately with aftermarket ones, i prefer OEM but a good used one is hard to locate, i have tried on several of my projects.

[Joeguy]

Ah my bad, it was not actually fully installed when i bought it, it just came with it. The carb was just loosely set in place not actually in the boots but the cables and fuel line were connected. My carb looks alot like one of the OEM ones but is over a quater inch longer by my measurements. Think im just going to order the similar looking aftermarket one and we shall see how its goes, atleast they dont cost a whole lot. 

[Joeguy]

Well new carb seems to fit atleast, there is a vacuum line was not not sure what to do with but it looks like it pushes air into my gas tank to add some pressure and push fuel if that sounds right, its the one on the "back side" of the carb on the engine side not the airbox. Also is there guides on here for checking valve lash? I got alot of smoke and some of it coming from the intake so im hoping they are just out of spec and letting some exhaust come up through. Also dies after like 15 seconds of running with a high idle.

Edited August 10, 2024 by Joeguy

[Gwbarm]

Not sure which vacum line you are referring to vacum line off the carb or off the engine, if its off the carb it may be there for a vacum petcock and yours may not have that but the carb fits many different models.

For checking the valve lash remove the valve cover, turn the engine over until both rockers are loose, use a feeler gauge to check the clearance have looked at your manual but should be intake 002 and exhaust 004 or somewhere in that range.

[Mech]

Have you adjusted the idle mixture Joe ? Are you sure the choke's going right off ?

Valves don't cause smoke. I'd recommend leaving those alone at the moment. They are very particular about their clearances and you need to allow for the wear when you are setting them. If you get it wrong it will be adding a complication to checking and adjusting the carb. The smoke might clear after the bikes had a run and been warm for a while.

Those bikes originally have two vacuum lines, one to the fuel pump and one to the automatic vacuum operated fuel tap if it's still fitted. I think that carb will have the vacuum port for the fuel tap on the front(near the engine) right, and the bigger vacuum hose for the pump comes off on the left and about in line with the slide I think from memory, or perhaps a little forward of that. The bowl breather will be right rear and the fuel inlet left rear.

 

[Joeguy]

Ok, long story short i basically had to re do the whole fuel and vacuum system. They had bypassed the fuel pump for some reason and that was confusing me pretty bad, thats why i was doing weird stuff with the vacuum, honestly still not 100% sure i have all the lines right because this carb is a little different than OEM it seems. Anyways now its all hooked up and i can get it to run for as long as i want with a little throttle input, so still a bit of tuning to do. Im going to put new fluids in it now that i now it will actually run. Oh and the smoking has gone away quite alot already so i figure some new gas and running it a while will fix er up. Only a few more posts then i can download the manuals and stop having to ask everything ha.

Edited August 12, 2024 by Joeguy

[Mech]

The fuel pumps are fussy about their vacuum. They need thick walled vacuum hose because if you use thin walled hose it partially collapses and dampens the pulsing effect the pump works on. If you attach it to the wrong vacuum port they can get too steadier vacuum too and not pump properly. They also don't work as well when going up a hill because the vacuum drops when there is a load on the engine.

They might have disconnected the pump because it wasn't working properly going up hills. Here's how to test the pump...

 

To test the fuel pump you lay the fuel hose to the carb into a bottle. Lay it on it's side with the hose laying flat. If the hose is dangling down you won't see the fuel pumping out properly. Then suck hard two or three times on the vacuum hose going to the pump, and then let the vacuum off suddenly. You should see a single slug of fuel come out of the fuel hose. The slug should be full diameter of the hose and about ten mills long. If that works then your pump is ok and will work if it's getting good pulsating vacuuum.

To test the vacuum you reattach the vacuum hose and start the motor and let it idle. It should pump fuel out of the fuel hose into the bottle at full diameter of the hose and slugs about eight mills long. If that works then the pump is working and it should start and idle at east.

Then you need to check the vacuum is still strong enough when the motor is under load. To check that you leave it all as is but sit on the bike, put the brakes on hard, engage first gear and open the throttle until the motor starts straining against the centrifugal clutch. As the motor starts to labour the pump will likely slow down it's delivery of fuel, but it should keep pumping some. If it stops pumping then you have weak vacuum or a malfunctioning pump.

The vacuum has to be strong, and pulsating when it gets to the pump. If the vacuum hose has been swapped with some soft thin walled stuff the pulsations can get lost as they suck the vacuum hose flat and then let it out again. Low vacuum can be caused by low compression, tight valves, or air leaks. Low vacuum at high revs can be caused by a blocked exhaust.

 

[Joeguy]

I did replace the line as they had some tiny little thin one attached and i saw fuel when i sucked on it. Didn't do a full proper test like you are saying though i will have to go check that out when i got time for sure. Waiting on new air filter and a boot for the airbox, because i feel like tuning with no air box even connected is sorta redundant, not sure if these engines are sensitive to it but figured its a good idea either way.

[Mech]

If fuel is getting into the vacuum lines it means the diaphragm in the pump, or tap, depending on which vacuum hose it is, has a hole in it.

And yes some are quite sensitive to their airbox and filter... Some other bikes, it doesn't seem to make a lot of difference. I always make sure the filters all oiled and wrung out correctly before adjusting the carbs.

[Joeguy]

I meant saw it pumping fuel, not coming from the vac line my bad. Should have er going this weekend hopefully once this all comes in. Then i gota fix the plastics on it, you know any glues that work? I have an epoxy for thermo set plastics i was going to try.

Edited August 15, 2024 by Joeguy

[Gwbarm]

I have used numerous different glues and techniques to restore plastics. It can be melted back together, they make a plastic welder that actually uses a curved wire and melts into the plastic to hold it back together, then you can go over it with epoxy colored to the existing plastic to repair. Or bondo if you are going to paint it. Fiberglass can be used, messy, with a colored top coat to match. If its not a very bad crack i have used E-6000 it is a very flexable glue that does a fairly descent job. I have also used Epoxy made to finish Granite countertops, but it dries kind of brittle and would probably break if it was rolled over or hit a tree.

[Joeguy]

Its actually like a 8 inch oblong hole in the fender im going to try and patch with like a red harbor freight bucket to at least kinda look normal ha. Might try out that plastic welding with some extra glue to cover.

[Gwbarm]

The welder will work better for replacing missing pieces. Harbour freight bucket, great idea.

[Joeguy]

Ya ill order it and then post pics of how it comes out when i get er done.