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xv750 running rich and stalling

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xv750 running rich and stalling

PostAuthor: robbietobbie » Wed Sep 12, 2018 2:47 am

Hi guys, hoping you have some good tips for me since I can't find a solution.
Got a '95 xv750 a couple of years ago that was literally lying in someone's backyard. Got it back to running pretty easily after cleaning out the tank and carbs and getting it a fresh battery and new tires. It ran fine for a year or two.
At the end of last year I took it out for a ride, parked it in my garage and noticed a little later that almost all of the gas had leaked out (my girlfriend was not happy with that smell).

Since it was leaking from the carbs I figured that must be where the problem was so I took them off and cleaned them again without having found anything troublesome. I then discovered the issue was the petcock so I got a new one. The good news is that it hasn't leaked since, the bad news is that it hasn't worked right either. Also changed the oil and filter since the gas had gotten in there too.

When I start the bike up after not having driven it for some time it will initially run and idle just fine. Then after a couple of minutes it stalls when I let the RPM drop and will not start up again. After a couple of minutes I can get it running again as long as I don't use the choke but again it will stall if I let the RPM drop.
I tried increasing the idle rpm but that didn't help. Figuring I messed something up with the carbs I took them off again, cleaned them and put them back in. That didn't fix the issue. I took the carbs off again and checked the float height which was perfect.
The sparkplugs are pitchblack. The engine dies pretty much immediately if I use the choke. I found no clogs or anything in the carbs

Would love to hear some suggestions to what I can do next! Thanks in advance for any input and advice you can offer.

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Re: xv750 running rich and stalling

PostAuthor: bstig60 » Wed Sep 12, 2018 8:46 am

Did you replace the O rings in the Pilot Screw? If they are flattened out or cracked, that will allow the idle fuel flow to run full Rich with no way to control it.... Pilot screw settings are 2.5 turns out from a soft seat and then adjust each cylinder for the best idle. Did you sync the carbs?
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Thu Sep 13, 2018 6:28 am

Thanks for your advice. I never touched the pilot screws so I was hoping that would rule them out. Decided to give them a go anyway and noticed that the previous owner must have fiddled with them too since the heads were ruined.
They were impossible to turn so I decided to gently drill them out which worked pretty well on the first one but on the second one the part of the carb where the pilot screw goes in just snapped off completely. I have no idea how that happened since I hadn't put any pressure on it yet...

So yeah I'm screwed now, will have to see if I can find a replacement carb or try to switch to a single carb.

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Re: xv750 running rich and stalling

PostAuthor: bstig60 » Thu Sep 13, 2018 8:32 am

I would look for a set of stock Mikuni carbs. They are not inexpensive, but if they are set up correctly, your bike will run perfect. IMHO, the cost of going to a single carb will be just as expensive. If you choose to go that route, don't use an old carb that you were already having problems with. Bite the Bullet and get a new Mikuni carb.....
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Thu Sep 13, 2018 11:46 am

Would you recommend getting a set of bst 40's or will others do? Since the bst40's are hard to find in my area. And if I do find them, will they fit the same as the old ones? Because the ones I can find look slightly different than mine and the diagrams in my Haynes manual.

Again thanks a lot for taking the time to help me out!

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Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Thu Sep 13, 2018 4:07 pm

I've found two mikuni bst 40's for cheap, thing is though they're single carbs so there's no brackets to link them. Having a hard time figuring out what the difference between my current stock bst 40's and these are. They look completely different to me (i have the ones with the copper "top" and these have black ones if that clarifies).
Getting pretty confused :roll:

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Re: xv750 running rich and stalling

PostAuthor: bstig60 » Fri Sep 14, 2018 8:17 am

Do you have a link to the ones you found? I would recommend the BST40 MIkuni's. Theres a bracket that holds the two carbs together on the back and at the top.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Fri Sep 14, 2018 9:08 am

This is one of them https://www.marktplaats.nl/a/motoren/on ... e=whatsapp

This is the other one: https://www.marktplaats.nl/a/motoren/on ... ousPage=lr

Guy says he doesnt have any brackets and i'm guessing the ones from my carbs won't fit?

Are there in fact two types of mikuni bst40's? The ones like that guy is selling and my stock carbs?

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Re: xv750 running rich and stalling

PostAuthor: bstig60 » Fri Sep 14, 2018 3:43 pm

Yes, there are two types of bst40's. The one's in your link are for KTM, Honda 650 and others single cylinder dual sport bikes and they are different externally, but similar inside. Here's a link to a guy that rebuilds them, he may have a set he can sell or he may be able to rebuild yours. https://www.ebay.com/itm/Virago-Profess ... XQVT9TDYms
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Mon Sep 17, 2018 3:00 pm

Thanks for your help, i'm going to look into that link you sent me.
I've decided to try glueing my carb back together with heat resistant epoxy glue since that would be an inexpensive fix.

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Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Wed Sep 26, 2018 3:52 pm

Update: looks like the glueing went well! Throughly cleaned everything and got a rebuild kit. I can't figure out where one piece goes though. Got a similar kit to this one : http://www.nrp-carbs.co.uk/shop/index.p ... uct_id=261

Where does the thick ring on the bottom left go?

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Re: xv750 running rich and stalling

PostAuthor: Flyingdog » Thu Sep 27, 2018 12:46 am

That 0-ring is part of the pilot screw assembly. Maybe this will help show the order of the parts for the pilot screw stack.

Make sure the "old 0-ring" is not stuck in the pilot screw tower, before putting the new assembly in.

Good idea to make sure the 'new' 0-ring is "seated squarely" in the tower.

As you can (kinda) see, the order is from bottom-up (as in pic): 0-ring, washer, spring, pilot screw. Then that silver plug, if you want to use it. Better just to leave it out, for future adjusting.
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Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Thu Oct 04, 2018 3:41 pm

Thanks for the diagram, looks like the mix screws were installed wrong before.

I got the bike running again but it is still running rich, even with the mix screws softseated. It is running less rich than it was with the mix screws at 2,5 turns out but something must be wrong if it is still running now right?

Thinking about taking the carbs off again and lookong at the choke plungers. Not sure they're going to be the problem though since the choke still works (using it instantly kills the engine). Any others things I can check while the carbs are off would be greatly appreciated. Float heights are ok, checked those before.

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Re: xv750 running rich and stalling

PostAuthor: bstig60 » Fri Oct 05, 2018 9:00 am

When you check the float levels, check both sides of the float. They must be the same.... The chokes could be the problem, but I doubt it would be the same on both cylinders unless you have the choke cable maladjusted... I would suspect the jets sizes are either incorrect or the needles are not seating correctly in the main jet causing it to leak fuel past the needle jet at low RPM or idle.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

SERVICE MANUAL DOWNLOAD LINK
http://viragotechforum.com/viewtopic.php?f=220&t=31501#p279545

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bstig60
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1982 Yamaha Seca XJ750RJ w/factory touring package (sold)
2003 Honda Goldwing GL1800 Touring
2007 Honda ST1300A
Sex: Male

Re: xv750 running rich and stalling

PostAuthor: robbietobbie » Fri Oct 05, 2018 4:28 pm

I rechecked the floats, on both sides this time and they are spot on.
Choke plungers are in perfect condition as well. The jet sizes are the factory defaults, so are the needles. At least they should be, i'll doublecheck tomorrow just to be sure. I'll also try to let it run without an air filter again, haven't tried that since replacing all the jets. Who knows right?

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