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1983 XV500 Choke problem

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1983 XV500 Choke problem

PostAuthor: daveolywa » Mon Feb 12, 2018 7:02 pm

Hi everyone, I am new to the forum. I have looked extensively through old threads but I cannot find this particular situation. If I've missed it I apologize. I picked up an 83 XV500 that someone had started a bobber project with. They had also tried converting (poorly by the way) to a single carb set up. I could not get it to start. Thanks to the forum and some luck with another bike I found for parts nearby I have managed to get the original carb on it, figure out fuel and vacuum hose routing (that was rough), oil and filter change, new battery and put a new (to me) petcock on. It starts and idles great. Revs great. Rides great. So here's the issue I have not yet solved.

I start it choke open, fires right up. Let it warm up and close choke it idles fine. Choke closed rev it and at about 2500 rpm's it starts to bog and sputter just a bit. Choke open it revs fine. When riding it needs choke open about 1/2 way or it will bog and sputter a bit. At higher rpms like 3000-4000 even with choke open it bogs a sputters a bit. Every now and then it will backfire.

I have found several threads with this issue but in all of them the bike won't idle with the choke closed. This idles just fine. I do not believe a have a vacuum leak but I can check closer. I am new at all of this, I have some experience with car engines etc but not motorcycles.

Any help is GREATLY appreciated!

Dave

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Re: 1983 XV500 Choke problem

PostAuthor: Flyingdog » Tue Feb 13, 2018 2:24 am

First off..might be good idea to get everyone on the same page as to the interpretation of: Choke being: On vs Off, open vs closed, engaged vs disengaged. A good way to think of it is a choke is like a window or door. You open it and fresh air can get in. You close it and you choke it. You restrict the air flow and the richer mixture assists with starting. As the engine warms up, you open the choke. Pushing the choke lever in the direction of the arrow (if you still have one) is "closing, engaging," the choke. Or in simpler terms..the choke is "On".
Your statement here: "I start it choke open, fires right up. Let it warm up and close choke it idles fine", is what led me to think someone may get atad confused. JMO
May or may not happen..more of a "just in case" thing.
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Re: 1983 XV500 Choke problem

PostAuthor: Jake » Tue Feb 13, 2018 8:09 am

The choke on a Virago, is not a choke in the conventional manner. It does not use less air to get the job done, but instead it adds extra fuel via the starter circuit.

Pulling the choke lever back with your thumb ( towards your elbow ) is choke on ( more fuel ), pushing it forward with your thumb is choke off .
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Re: 1983 XV500 Choke problem

PostAuthor: Flyingdog » Tue Feb 13, 2018 9:41 am

Yes..it does not operate as a normal choke...aka: no use of a butterfly, probly why the technical term would be a starting enrichment circuit. My reason was solely for interpretation toward helping the poster....different operations to get the same end result..as in who's interpretation whether it's ON or OFF. Same a a clutch being engaged or disengaged..but that's a different story for another time.
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Re: 1983 XV500 Choke problem

PostAuthor: ivanhienas » Tue Feb 13, 2018 11:26 am

Hi Dave,

As a recent single carb modder, I would strongly suggest giving up dual carbs. Tweaking is much easier (by being half the work hehe) along with access to the carb (in my case, a XV400 - it was painful to put them back in).

As stated above, choke on a virago is an enrichment system, that said, we can assume you're running lean, hence why you need the enrichment system on otherwise it bogs (assuming you have the stock carb with no vacuum leak, cleaned up and stock jets).

Having 2 carburetors is having 2 headaches, IMO. Unless you have the proper tools to find out if both cylinders are getting the proper mixture ratio, it is difficult to tune up and synchronize them.

I used this when tweaking my single carb but it helps giving you an idea about carbs in general (specially the drawing at the bottom left):
Image

Cheers,
Ivan

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Re: 1983 XV500 Choke problem

PostAuthor: daveolywa » Tue Feb 13, 2018 9:09 pm

That info on the enrichment is very helpful thank you!

Ivan, I have heard single carb is much easier. I'm not too familiar with how to go about it. I went back to all stock because it seemed an easier place to start because of the petcock being part of the vacuum system and the fuel pump being vacuum as well. A gravity feed petcock I dont think will work well because the bike has been lowered and the petcock is now lower than the carb but I could be wrong. What carb and manifold did you end up using and how did you deal with fuel system?

Thanks!

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Re: 1983 XV500 Choke problem

PostAuthor: Flyingdog » Wed Feb 14, 2018 2:53 am

daveolywa wrote:I have heard single carb is much easier.


Well, that depends on how you hold yer tongue and which way the wind is blow'n. :r:

Not to dis-sway from the way you want to do your bike. Just another approach to an end. Never been a fan of single carb conversions. Yes..they do reduce the amount of tinkering, cuz you're only doing one carb. And I suspect, in the back of their minds, it gives that "Bad Boy Look". But the way I see it..two cylinders=two carbs. Just like any 4 cylinders, you'll see 4 carbs.. or 6 for 6. All you really have to do is take a good look how harley's carb worked. The key here is, how long it took "them" to get it right. And... that's with 45° cylinders, with intakes equally apposed from each other. Don't remember, but think it was 2007 or so, they went to EFI on their big twins. Only remember this cuz of my harley buddies spout'n off bout what a miracle it was. Until they can't tune them, themselves. Now, with our carbs & intakes, there's a whole new ball game. Feeding each hungry side what they need. These cylinders require different feeding habits, so to speak. And ya just can't satisfy two scream'n mouths with one spoon. Hence..that's why each carb is setup differently (jets & needles). Not too many single carb intakes with equal runners out there, either. And even if they were equal, you still have to deal with lot of other factors, such as heat, air densities, inertia, intake off-set, blah blah blah. But like everything else..give & take...give & take. And..again..I can't say this enough, for those it works for, that's great, just my way of look'n at it.
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Re: 1983 XV500 Choke problem

PostAuthor: ivanhienas » Wed Feb 14, 2018 10:51 am

Hey Dave,

I decided to give up on the stock carb after figuring out I would spend quite some money to get mine repaired (full repair kit for each was $80) plus the friggin headache it was to put the carbs back on (along with the air intake boots)

I wanted to keep it simple so I used a suzuki DRZ400 carb (since mine is a XV400) and copper fittings to do the manifold - 1 1/4" Tee with a 90elbow glued on top with jbweld (had to trim a bit of the tee to fit the shape of the intake boots) - also helps that I found a DRZ carb with a dynojet kit for sale on a decent price - so I had jets to play around with

https://imgur.com/a/9ZL6g

And with the single carb I was able to put the left pod contents (electrical for my bike) inside the frame and get rid of both chrome pods the virago has on the sides.

It is just an idea since you seem to be having problems getting the stock carb working - I just think rather than restoring yours, it would be easier and even cheaper to go singlecarb.

At least this way you will know if the carb isn't working properly, the bike won't work. When I was troubleshooting my stock carb, the only way I could check if a cylinder was working or not was by it's temperature (putting my hand on it) or taking out the spark plugs (see the work it was?)

Cheers,

Ivan

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Re: 1983 XV500 Choke problem

PostAuthor: Jake » Wed Feb 14, 2018 11:14 am

Ivan, maybe you missed something. The bike had a single carb setup when he bought it and he went to the expense of buying a pair of originals. Going back to a single would not be cheaper.

Also, I might add, some people never get a single carb to work properly for them. There are cases here where people went back to dual carbs for that reason. It's great it worked for you, but it's not for everyone.
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Re: 1983 XV500 Choke problem

PostAuthor: ivanhienas » Thu Feb 15, 2018 1:35 pm

Jake wrote:Ivan, maybe you missed something. The bike had a single carb setup when he bought it and he went to the expense of buying a pair of originals. Going back to a single would not be cheaper.


I didn't miss it - in my case I said it was cheaper to get the single carb than repairing the stock carbs (proper rebuild kits and jets - repair kits at $80 a piece + tax in Canada + whatever the jetting would be).
I managed to find the DRZ400 carb with a dynojet kit which cost me $120 and I made the manifold for another $50.

Cheers,

Ivan

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Re: 1983 XV500 Choke problem

PostAuthor: daveolywa » Tue Feb 20, 2018 5:29 pm

Thanks for the input from everyone. So I pulled the plugs, font (closest to front wheel was a tad black and wet, rear looked just fine. A couple of other details, the previous owner had cut the exhaust down and fabbed some kind of manifold that they both went into. When I figure out how to insert an image i will post a pic. download/file.php?mode=view&id=44104

Also realized that I filled it with premium which I have now read may make these bikes run like crap.

So as far as front cylinder appearing to be running a little rich would I adjust that on the pilot screw located behind the V.I.C.S. box at the bottom of each carb? I don't want to mess with anything without being sure cuz this is as close to getting this bike running as I've come so far lol.

Also do you think either the fuel or the exhaust would be causing the issue?

lastly I found this interesting. I put new plugs in, cross reference AC/Delco, had NGK in before, it ran worse, more sputtering etc, definitely as less steady idle. Put old plugs back in, back to normal (i.e. as normal as I've seen it run so far.)

Thoughts?
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Re: 1983 XV500 Choke problem

PostAuthor: ivanhienas » Wed Feb 21, 2018 2:59 pm

Hey Dave,

Is that custom exhaust completely open (ie no baffle)?
I had my bike sputtering too but it was stock exhaust with baffles removed - installed new baffles and now runs like a charm.

As for the front cylinder being rich - adjusting the mixture screw only helps to some point, just for idling (check the image I posted). Make sure you have the right jets or that you didn't mix up the jets as the cylinder 1 (back cylinder) has a slightly bigger jet than the front one (cylinder 2) but usually we think cylinder 1 would be the front one.

Cheers,

Ivan

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Re: 1983 XV500 Choke problem

PostAuthor: Flyingdog » Wed Feb 21, 2018 7:28 pm

ivanhienas wrote:As for the front cylinder being rich - adjusting the mixture screw only helps to some point, just for idling (check the image I posted). Make sure you have the right jets or that you didn't mix up the jets as the cylinder 1 (back cylinder) has a slightly bigger jet than the front one (cylinder 2) but usually we think cylinder 1 would be the front one.


Well, kinda. What's right.... Pilot screw adjustments only effect A/F at idle. Also causes smooth transition from pilot circuit to needles.
But..#1 carb (rear) will have the smaller jet. Conventional wisdom(?) likes to put the larger jet in the rear carb. 99.9% of the reasoning will something like this: " Oh, that cylinder runs hotter, it needs the larger jet for more fuel for the cooling effect". That's wrong. The rear cylinder uses the smaller jet cuz "Hot" air is less dense and does not flow as well. Less air, combined with larger jet? Nope..that's wrong. Hence, the smaller jetting (mixed with less air than the front gets) to keep the A/F mixture in balance with the front. AFAIK, there's only one Virago that "states" a larger jet in rear carb. That's some 920. I think that maybe a type0. My 750 says both jets the same. But after lotta trial and errors, runs so much better since I've changed the mains and needles. I always cringe alittle with I hear people saying: You need to change the jets. That's true to a point, but we're not on the track and spend 99% of our riding not even coming close to being on mains. We're on the needles. You'd have to be WOT all the time to be on the mains. Changing jet size won't hurt, but changing needle size and/or height (and along with jets when needed) will definitely give ya way more actuate results. Now, these carbs being in the horizontal position? If that plays into something. I wouldn't think so. I haven't looked at how the air is plumbed.
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Re: 1983 XV500 Choke problem

PostAuthor: daveolywa » Tue Mar 06, 2018 5:07 pm

OK, here's something I hadn't thought about. Reading a different thread made me think about it.

The previous owner had done some modifying to the bottom part of the air box trying to accommodate the single carb set up he was trying. The air filter and lid to airbox are currently not on it. Could this affect the vacuum (basically like a big vacuum leak)? I had just figured the more air the better but with the vacuum system it may be a major cause of my symptoms? It would make sense why having the fuel enhancement (choke) thing open lets it run better until it gets to a high enough rpm that it starts to starve for fuel. what do you guys think?

Thanks!

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Re: 1983 XV500 Choke problem

PostAuthor: Flyingdog » Wed Mar 07, 2018 8:41 am

Probly a pita, but some pics would be helpful. Haven't studied that style of intake system, just know they sit "ontop" of carbs. But...yes... if it's completely open, it can effect the A/F mixture to a point. Kinda like putting individual pod style air filters on. You usually have to have some back pressure on the intake side. It can be quite a balancing act changing things out. Specially intake & exhaust. That usually entails changing jets & needles. Cuz adjusting the pilot just won't do it, as that circuit doesn't come into play when you're riding. Only at idle> barely off idle. This will show roughly what's going on:
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Re: 1983 XV500 Choke problem

PostAuthor: daveolywa » Wed Apr 25, 2018 3:01 pm

Thanks for all the feedback! Flyingdog I think the airbox/vacuum leak is on the right track. I got on the freeway today behind a semi, drafting it it which changed the airflow around me completely. Immediately I had more power, no sputtering, right up to 6500 rpms. I realize there is less resistance behind the truck but was such a dramatic difference. It's like as the wind resistance gets greater and the demand for power/fuel increases then that's when I have issues. I'm going to try fabbing some kind of floor for the airbox (which was removed) see if that helps. The only other thing I can think of is some kind of spark problem....? Or fuel pump problem. Sometimes when it's warming up the front(closest to front wheel) head goes quiet. If I rev it it comes right back up but blows some exhaust out the pipe and then is fine. It's fine after it warms up.


Side note, all of the described above is with the fuel enhancer/ choke thing all the way open (pushed to the left) If I run it with it shut(all the way right) I have all the same issues just at a much lower rpm.

These bikes seem to be pretty complicated. I'm getting bummed out a little that I haven't figured it out yet cuz it's a fun bike to ride. I've got it running decent but not great. I may think about selling it cuz this issue may be beyond me.


Thoughts?

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Re: 1983 XV500 Choke problem

PostAuthor: daveolywa » Fri May 04, 2018 4:42 pm

OK, update. So I sealed the floor of the airbox, Cleaned up the spark plug connectors etc. and it runs great now with the fuel enhancement thing off all the way up to 70 80 90 mph. However still at Low speeds it seems like the front head is intermittently going on and off. Now at high-speed’s it runsGreat! But if I come from a dead stop and accelerate it has limited power until about 2500 RPMs and then suddenly the Front cylinder kicks in and everything is fine. It seems like a spark or a fuel supply problem, or could the carbs needs syncing? I don’t know that it would cause this kind of problem…

Any help with this problem now would be much appreciated!

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Re: 1983 XV500 Choke problem

PostAuthor: daveolywa » Fri May 04, 2018 4:45 pm

A couple other threads I’ve read that said it could be a TCI box problem. Anybody have any thoughts about that?

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Re: 1983 XV500 Choke problem

PostAuthor: daveolywa » Mon May 07, 2018 7:50 pm

Solved, TCI box replaced and it runs like a dream now! Several issues had to be addressed but major ones was sealing the airbox bottom that PO had removed and replacing TCI box. Thanks for everyones help.


Dave

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