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Discussion Starter #1
Hey Guys,
Been searching around a lot on this site and thought it might be best to just post some pics and ask. First off, I have a 1985 VN700A, so it may be a slightly bit different. My bike was leaking gas from around the location of the air cut-off diaphragm on the left side of the bike. I'm not sure if this was the only place but I know it was from at least there.

Now, I don't believe this should be possible as gas shouldn't get past the petcock into the carbs as there shouldn't be a vacuum right? So there's likely a problem with that. I have a Res, On, and Pri on my petcock and if I open the drain valve in any of the 3 spots gas will just come out non-stop.

Also, I opened up where it was leaking and saw that the diaphragm seemed pretty shot. It felt more like paper than rubber and when I looked behind the diaphragm the rubber was all cracked and pretty shot. The one on the right side of the bike looked and felt great (pics attached for comparison.) Also, the left side was pretty dirty while the right was pretty clean. You can see in the one pic of the caps, the one on the left was after I had already cleaned it a bit! I didn't touch the right side.

So I'm looking for some feedback, what do you think I should do? I've already drained most of the gas so I'm thinking that removing the tank and pulling the carbs is probably in order. Seeing how gunked the air shut off area is the rest of that carb is probably pretty bad. Should I also look into taking apart the petcock? If gas is flowing freely something probably needs replacing there, just not sure what. Should I try to rebuild it? Can it be replaced? I took the bike out for a ride before it started leaking bad and it honestly ran like a top.

Thanks!
 

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FREEBIRDS MC CENTRAL NY
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the petcock shouldn't work on" off"period."on" should flow only with vacuum and" pri" is to prime the carbs if they run dry,so that is always on.as for the leak,try replacing the diaphragm

Sent from my LGL34C using Tapatalk
 

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Discussion Starter #3
Mine doesn't have an off, just RES, ON and PRI and when I opened the drain valve on the bottom of the carb gas ran free in any setting.

I'm definitely going to get the air shut off diaphragm, already found one on ebay around $21. Would the petcock diaphragm cause the gas to flow freely if it was bad? Looks like the seal kits are pretty inexpensive: Petcock Repair Kit

I'll probably open the petcock up when I get home to see what it looks like either way.
 

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FREEBIRDS MC CENTRAL NY
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ok res and on should only flow with vacuum. pri flows all the time.and yes a bad petcock gasket would make the petcock flow all the time

Sent from my LGL34C using Tapatalk
 

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The needle valve in your carb should cut the flow of gas into the carb (except of course if you have the drain screws open)
So yes, make sure the petcock doesn't flow fuel in the ON or RES position...PRI it should.
Then clean the carbs and make sure the the needle valve in the float bowl is working.
 

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FREEBIRDS MC CENTRAL NY
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can use a Yamaha tw200 petcock.it's not vacuum operated so would need to plug the vacuum opening. get the OEM one,not the Chinese knock off,as they are crap

Sent from my LGL34C using Tapatalk
 

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Discussion Starter #7
The needle valve in your carb should cut the flow of gas into the carb (except of course if you have the drain screws open)
So yes, make sure the petcock doesn't flow fuel in the ON or RES position...PRI it should.
Then clean the carbs and make sure the the needle valve in the float bowl is working.
Ahh so having the drains open would make gas flow? How would I test if gas was getting into the carbs without the drains open, I do not have clear lines. Sorry I'm pretty new to all of this and learning as I go.

Thanks for the tip on the petcock OleDirtyDoc, I'll take a look at the gasket on mine when I get home.
 

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can use a Yamaha tw200 petcock.it's not vacuum operated so would need to plug the vacuum opening. get the OEM one,not the Chinese knock off,as they are crap

Sent from my LGL34C using Tapatalk
X2 on the tw200. Works great and simplifies things a bit.
 

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Ahh so having the drains open would make gas flow? How would I test if gas was getting into the carbs without the drains open, I do not have clear lines. Sorry I'm pretty new to all of this and learning as I go.

Thanks for the tip on the petcock OleDirtyDoc, I'll take a look at the gasket on mine when I get home.
If the drain screw is open under the carbs the float bowl won't fill up...the needle valve attached to the floats won't be able to seal....this of course should only happen when the petcock is in the PRI position. When set to RES or ON, fuel should not flow into the carb (This of course all being done with the bike NOT running)
Once you start the bike, engine vacuum opens the diaphragm in the petcock and lets fuel flow to the carbs.

If fuel is overflowing your carbs WHEN THE MOTOR IS NOT RUNNING, you have two problems...
1. The petcock diaphragm is not shutting off the fuel as it should
2. The needle valve(s) in the fuel bowls are not sealing either.

To test the petcock...just pull the hoses off the petcock (make note where each goes) if fuel is leaking out (In RES or ON) your petcock is bad. If you turn it to PRI...fuel should flow.
If the petcock seems to be working, then you need to clean or replace the needle valves in the carbs...
That help?
 

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Discussion Starter #10
If the drain screw is open under the carbs the float bowl won't fill up...the needle valve attached to the floats won't be able to seal....this of course should only happen when the petcock is in the PRI position. When set to RES or ON, fuel should not flow into the carb (This of course all being done with the bike NOT running)
Once you start the bike, engine vacuum opens the diaphragm in the petcock and lets fuel flow to the carbs.

If fuel is overflowing your carbs WHEN THE MOTOR IS NOT RUNNING, you have two problems...
1. The petcock diaphragm is not shutting off the fuel as it should
2. The needle valve(s) in the fuel bowls are not sealing either.

To test the petcock...just pull the hoses off the petcock (make note where each goes) if fuel is leaking out (In RES or ON) your petcock is bad. If you turn it to PRI...fuel should flow.
If the petcock seems to be working, then you need to clean or replace the needle valves in the carbs...
That help?
Very much so! Thanks! New to working on bikes and would rather learn it myself than pay someone to do it. Replaced all my plugs and wires last year thanks to everyone here.

I wasn't able to tear into it at all last night, slipped my mind that it was Halloween so the lady had my handing out candy to the kiddies that come by.

From the sounds of it, the problems are definitely starting with the petcock. When I opened up the drain at the bottom of the carbs I was able to empty fuel non stop no matter what setting the petcock is in. Then I'm assuming since the petcock was shot and the lovely ethanol gas was sitting in the carb, it turned the air cut off diaphragm in the left side (since the bike leans that way when on the stand) to a cracked piece of crap that resembled paper instead of rubber causing the leak.

So sounds like some petcock work and replacing that cut-off valve diaphragm for sure. Going to start using the non-ethanol gas at the station near my new house, costs more but for the size of the tank won't barely notice it.

Thanks all, will keep you posted.
 

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Discussion Starter #11 (Edited)
Alright, got the tank off and the petcock pulled and the bad cut off diaphragm out, it was worse than I thought. Also hear some gritty crap in the tank so that'll need cleaning.

The petcock o-rings all looks in really good shape, but the gasket by the knob and the diaphragms were a bit off. Looks like the gasket had stretched a bit away from the small posts, probably letting gas by. The inner diaphragm looked rough, but the outer one wasn't bad.

I was looking at some of the TW200 petcocks and I only see one nipple for a fuel line instead of two, so searched around and saw a T or Y split would be needed, for now I think I'll just rebuild the current one, it's lasted 31 years so why not.

Since I have everything off though I was considering switching to clear fuel lines. Thoughts? I saw one post that 5/16 was the correct size and another that it was 1/4, which is correct? I would be clamping/zip tying them on either way. Half the tube ends on my bike had these clamps you press together to open (not sure the name) and half were zip tied. Strange.

Pics below of the removed junk.
 

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Discussion Starter #12
Here's another interesting find, after taking the diaphragms out of the petcock assembly I noticed there wasn't a spring inside my petcock, per the manual it looks like there should be one. Any idea if I don't have one being a VN700 with ON RES and PRI (instead of OFF)? If I need one any idea where I can get it?
 

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Fuel lines are 5/16" (ID) Clear is a good choice. Not sure why you're missing the spring, but you do need one. Not sure if they sell these seperately.

Yes you need a "T" fitting for the TW. (Or a "Y" really) might be easier to find than the spring...;)
 

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Discussion Starter #14 (Edited)
Fuel lines are 5/16" (ID) Clear is a good choice. Not sure why you're missing the spring, but you do need one. Not sure if they sell these seperately.

Yes you need a "T" fitting for the TW. (Or a "Y" really) might be easier to find than the spring...;)
I was wondering that too, unless it flew out when I was taking it apart, but I looked all over my work bench and the floor. How small is the damn thing? It definitely explains why gas was getting right past the petcock though if it WAS missing.

I found it online, part # 92081-1240, but the shipping is more than the spring. Might try to look at my local hardware store for something comparable or check some local Kaw dealers, but I don't have anything for comparison.

You might be right on that one, just need to see which is actually cheaper. I'd prefer to stay with the stock petcock (I can see myself forgetting to turn the TW off) and not sure how I feel about plastic fittings for a Y. Metal might be expensive.

Thanks!
 
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