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Discussion Starter #1
Hey all, I have a 2000 Honda Magna VF750C2, I had not ridden in a month or so, I went out to start the bike just to let it run for a little while and noticed there was a leak on the left side while it ran, it had a pretty good flow. I didn't get a chance to work on it for a a couple weeks but went back out to check it and it wasn't leaking anymore when running, I road around to test, maybe 5 miles or so and it didn't start leaking. Well, recently I went out to go for a ride and it was leaking again. I decided it was time to pull the carbs and check the float needles (not sure the technical name for them), they all seemed to move correctly when lifting and letting the floats fall back to position. I replaced all float bowls. Bench synched the carbs, and checked the pilot screws, because the bike had been back-firing when reducing speed before the leak. 2 pilot screws were screwed out at about 2 1/2 turns, one was 1 turn, the other was 2 turns out. I returned each to 2 1/2 turns out, like it says in the repair manual. Replaced the carb bank (anyone that has every done this on a Magna knows how much fun that is!! ), after a few tries the bike started, had to adjust the idle a bit but she ran pretty good, sounded better than before. And the leak was gone. I ran the bike for about a half hour, didn't have time to ride very far, to the corner and back because I had been working on it all day and had other engagements. That was last weekend. Yesterday I went out to start her up and let her run for a little while and the leak is back, coming from carb no 1, it looked, at first, like it was coming from the bowl over flow, I tuned the overflow screw and it increased. I traced the best I could where the leak was coming from and it looks to be coming from the top of the carb. Any ideas where up at the top it could be coming from?
 

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Does carb #1 have a vacuum port that leads to the petcock?

If so, disconnect that tube at the carb and leave it in a jar, check it often, and see if it fills with gas...if so, the petcock is defective...or it could just have a piece of crud stuck in it...you can use an air hose with LOW pressure (10psi) to backblow it.

A vacuum line from the petcock to the carb is there to shut off the flow of gas if the engine is not turning over..there's a spring mechanism in the percock...when the engine turns over, the vacuum pulls back the spring allowing fuel to flow...if the seal on the spring in bad, you'll have a week vacuum and be sucking gas which causes a high idle when the bike is warm.
 

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Your case sounds like a classic case of the float needle and seat sticking.
I have a first gen 750,and it may not be the same as yours,so i can only offer general advice. One piece of specific advise is to test the carbs for leaking while they are off the bike by rigging up a slave tank maybe 3 feet higher than the carbs. I feel you on how difficult carb R&R is on these bikes

My first gen magna had to have some O-rings between the carbs replaced [fuel tubes that connected them] Since the first generation Magna has a fuel pump, it had to have new O-rings to hold back the pressure of the pump. The slave tank test was not enough pressure to reveal my problem,but i am fairly certain that later Magnas do not have pressure fuel pumps
 

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If your petcock has on/res/prime it probably is the petcock that is faulty. I had the same problem. Sent the carb out to the best carb guy in the nation, imo. Still had the same problem. Everyone said the same thing, float, needle, and seat. Which is logical, because 95 percent of the time it is. I was sitting here stomping my feet practically having a babies temper tantrum cause I knew darned well that Kurt would not miss anything. This guy is absolutely a genius when it comes to carbs/throttle bodies. It turned out to be the petcock that was faulty. Changed that, and I havent had a problem yet. I went with the Yahmaha Raptor 660 which is a normal non vacumned fed petcock, on/off/res. Just have to remember to turn it off....and back on lol!! 450Suki was the only person in the world who believed in me about the petcock. Even my own friends thought I was just a dumb blonde for thinking it was the petcock. Who's the blonde now?

If your's is a vacumn fed petcock, there will be a vacumn line for it. Take it off. Suck on it, if any gas comes out, well there's your problem. You can even leave the line in a jar like suki said, you may see gas come out of it. If so, that petcock is definetly bad.
 

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Discussion Starter #5
Thanks for all the replies, I will have to check to see if it has the vacuum port, I have also ordered some o-ring float bowl gaskets to replace just in case, they should be here tomorrow. I've never replaced a petcock, how difficult is it?
 

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Its easy as pie. I suck at mechanic work and I did it. On mine it was just unscrewing two screws. I drained the tank cause I wasnt sure if gas would leak out. But I was told I didnt have too. Theres a rubber cap that u will need to by to cover the vacumn port on carb if u decide to go with a non vacumed petcock.
 

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Discussion Starter #7
Great, Thank you! I am fairly mechanically inclined and if I've never done something I do quite a bit of research on the internet before diving in so I think I'll be ok replacing the petcock. I am researching prices for new petcock now. A couple weeks ago when I pulled the carbs I did notice the tank was leaking a little on a towel that it was sitting on now that I think about it. I will change the o-ring float bowl gaskets and replace the petcock and go from there.Thanks again!
 

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I you use a petcock with a vacuum port, then get a new hose and use it...gas hose is best...fuel won't flow if there is no vacuum on the petcock vacuum port.
 

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Discussion Starter #9
450zuki, I don't believe there is a vacuum diaphragm directly on the petcock from what I remember, I'm at work right now, but there is one under the tank, mounted on the frame. I will check it out when I get home.
 

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gas lines are probably leaking, one of the connections might be loose, or one of the tubes might be broken. Also check the underside of your tank for pin holes.
 

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Discussion Starter #11
Well, a quick update, the petcock was leaking when in the off position, I replaced with new OEM petcock, so it no longer leaks from there. I also replaced the float bowl o-rings but there is still a leak :-( . This week end I will be checking all fuel lines, the hardest part, I think, will be me being able to see in between the carb bodies to check all of the lines.

Here is a video of her running though, sorry about the quality, taken with my iPhone.


youtube.com/watch?v=jZaN2v6j92I (you'll have to add the h ttp:/ /www to it, because I had less than 15 posts, the site wouldn't let me post a link :-/)
 

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Hi BryB912,



I know this thread is a few weeks old, but I had this same issue with an intermittent carb leak on my 97 Magna.

Basically, my problem was one of the o-rings on one of the plastic fuel tubes that bridge the carbs. When the bike sits too long one of the o-rings gets dry and shrinks. When you start it and leave it running for a few minutes the o-ring gets wets again and expands stopping the leak after a few minutes. You can replace the o-ring/s if you want or just make sure that you start the bike every so often to keep the o-rings wet so that they don't dry out letting fuel leak past them.

**Well, I tried to post a picture of the the o-ring location but the forum won't let me because I haven't made enough posts yet. I give up.***

In any case,I hope that helps. Maybe if you PM me, I can send you a link to the exploded view taken from the OEM user manual and show you what needs to be replaced.

Hairfarm
 

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Discussion Starter #13 (Edited)
Hi Hairfarm,

You are exactly right, I found that the leak was at the plastic tube going into carb 1, I actually worked on it yesterday and got the o-rings replaced but, unfortunately I popped a c-clip on the linkage off just as a gust of wind blew leaves into my garage so I am not exactly sure where the clip went :mad: ......I will be searching the garage floor this weekend carefully so I can get the carb bank put back together and on the bike. Wish me luck!
 

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BryB912,

It's too bad you had to keep removing those carbs again and again. But now you're a pro at it, I bet.

Please keep me updated and let me know if that o-ring swap worked for you. I also have to do the same procedure on my Magna except that I have the dreaded California-type fuel system...with all of the hoses.:mad:

Get your self a proper "C" clip removal tool. It will hang on to those C clips after they're removed. Then you can drop them into one of those pill organizing trays. You know, the kind that have a separate compartment for each day of the week. And the pill organizer has lids to keep the parts in too! I have written on four of the compartment lids with a sharpie pen, Carb1 - Carb 2 - Carb 3 etc. They make pretty good organizers, especially for carb parts.

Keep updating!

thanks,

Hairfarm.

Ok, only 13 more posts before I can add links and pics...OMG!:thumbsup:
 

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Discussion Starter #15
This is getting frustrating, I found the clip, turns out it popped off into the #2 carb throttle body, I just happened to turn the carb over and it fell out :). I replaced the o-ring on the tubes between carb 1 and 3 (i think that is #3), got it put back together and it is still leaking, looks like from #2 and 4 now :mad: , revving high and backfiring( I think the carb synch screw may be screwed in too far) ...I hate to give up at this point and take it to a shop, that could be pretty expensive. I guess I have until spring to decide though.
 

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The first mod most people do is to adjust the carbs to correct the stock lean condition. In stock trim, the low end torque is a bit anemic and there is a mild flat spot between 5k and 6k RPM (visible in the above dyno chart). The low end lean condition can be fixed simply by adjusting the pilot mixture screws. In stock trim they are around 2 turns open. Setting them all to 2 5/8 turns will eliminate part throttle lean surging and smooth out the throttle response. Doing this will require a special "D" shaped screw on an "L" bend wrench.


Hope that helps.
 

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Discussion Starter #17
Hey all, been awhile since I posted...I got the o-rings in on the tubes between carbs, got it back together and now the linkage is too tight, the bike idles waaaay too high and the idle adjustment screw does nothing...I took it to a shop and they told me it would be $600-$700 to replace 2 carb boots (+$42 a piece) and the screw is stripped or the cable is broke, that's why it's idling high and it wont adjust. I know better though, it's the linkage hanging up. They said it would be $500 for labor at $72/hr, I had the money to have them do it but, it was obvious to me when I talked to them, that they weren't sure what was making it idle high and that if they worked on it, they would keep tacking charges on. I also know from experience it does not take almost 9 hrs to take the carbs off, change the boots and cable or screw and put it back together. I've had those carbs off at least 5 times and I can do it in less than 3 hrs, with a break in there somewhere LOL, they also said it needed a carb job and that'd be another $530...I just rejetted it, put new float bowl gaskets and cleaned the carb last year....So I loaded the bike back up, ordered the boots and a fuel line, that I saw a tear at the end of last time, myself and am waiting patiently for my parts to come in....I will get this fixed this time, I will take my time and do it right, I refuse to go another year without being able to ride it.
 

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My high idle experience is limited....
you will have to ask the right questions...

Try turning the cable holder over when you put back together.
That solved my high idle problem superfluously! I had put the cable adjuster in upside down, and then mounted the adjuster on upside down because I knew it didn't go on that other way...
 

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Discussion Starter #19
Update

Thanks for all the advise everyone! I installed the new boots (easiest the carbs have ever gone back on!)and fuel line, got the idle down a little bit but it still seems a little high to me, around 12-1300 RPM at idle. I think I might also try adjusting the pilot mixture screws, I didn't think about checking them when I had the carbs off but I did a quick bench sync using the drill bit between the butterfly plate and the throttle body method. The throttle also does not spring back like it should, I have new cables, I will try them this weekend but my question is, could it also be the grip sticking and making it so the throttle doesn't return? OH YEAH! And also, no more leak, it just disappeared LOL!! WOOHOO!!!
 

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The throttle also does not spring back like it should, I have new cables, I will try them this weekend but my question is, could it also be the grip sticking and making it so the throttle doesn't return?
It's possible. That often happens with out training bikes when they have an unfortunate tip-over. If they are the rubber type, you can try pulling them away from the control housing and see if that helps.
 
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