Hello all you Yamaha experts. I own a 79 xs650 special. My son and I restored this bike from the ground up and made a cafe racer out of it a few years back. I did not rebuild engine but did take it down to the case and installed all new gaskets. She was a really bad leaker. She never has idle correctly. I replace the carbs with VM34's hoping that would help, bike did not change. My idle got worse. So bad that I thought I had a timing issue. Spitting back thru carbs and some back fire, I have adjusted cam chain. Went through the valves. Adjusted points per manual. and set up timing. Still no change. Getting very frustrated. Well I pulled the trigger and went all pamco electronic ignition with the e-advance. Guess what? bike still idles like crap. Bike's rpm's also take off on it's own. Revs so high have to just shut it down. I have check the intake for leaks. The Vm kit that sudco sent did not come with intake gaskets. I called them and ask if i should use some and they said no. I removed intake and found that the brand new intakes developed cracks and one looked like it had a melted spot in it. I installed gaskets and there was no change. I'm out of know how. I know this is long but i'm tring to give good description. So I'm hoping you experts can give me some more feed back.
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can't get bike to idle correctly
- Thread starter Tony Hurd
- Start date
Your mixture must be too lean. Perhaps there is air leakage around carbs/manifolds.
http://www.amckayltd.com/VM34-36.pdf
http://www.amckayltd.com/VM34-36.pdf
Should you use a gasket with the Sudco Rubber boot that they send? I read most of the article you just sent me. So I pulled boots off and had damage on the inside of the boot so I installed gaskets. Felt that it would seal the damage. It wasn't to bad. I would have thought that they would have been sealed at that point.I would like to check for leaks but can't get bike to idle own its own to long enough to check.
I pulled pilot jet and the number on it is a 15 which is what Sudco sent in the carbs. They also sent a 12.5. So I take it that 15 is to small to start out with?
Here is what is in it. I could be missing something so bare with me. Do I need to buy a jet kit?
Pilot 15
Needle jet ?
Needle 6F9
Main 175
I can't help you with jeting or tuning VM carbs, because I have never used them and I know nothing about them. However, there are very knowledgeable lads here that can help you. First thing they will want to know, is what exhaust you are using, and are you using stock air box or pods.
Hang on to the stock carbs you took off, as they are very good carbs.
Hang on to the stock carbs you took off, as they are very good carbs.
There's no such thing as a jet kit for the VM carbs. You just change individual jets as need be. What you need is a "baseline" to go by, a list of jet sizes that have worked for these carbs on this bike. The link RG gave you provides that, and according to it, I think your big problem is your pilots are too small. Your symptoms also reflect that. Try some in the 20s.
To identify your needle jet, you'll have to remove it. The numbers are stamped on the side and hidden from view when it's installed. Hopefully you'll find a P5 or P6 in there. Also make sure the air jet is removed.
To identify your needle jet, you'll have to remove it. The numbers are stamped on the side and hidden from view when it's installed. Hopefully you'll find a P5 or P6 in there. Also make sure the air jet is removed.
TimeMachine
SeventyEighte
Idling question ? If XS is "well tuned", how slow will an XS idle before it stumbles and dies ? Mine yesterday would die at 900 rpm.. I was expecting to get it even slower. -RT
A lot of people try to get these bikes to idle very slow, then complain the battery goes dead. The book calls for 1200 rpms.
Leo
Leo
There's no such thing as a jet kit for the VM carbs. You just change individual jets as need be. What you need is a "baseline" to go by, a list of jet sizes that have worked for these carbs on this bike. The link RG gave you provides that, and according to it, I think your big problem is your pilots are too small. Your symptoms also reflect that. Try some in the 20s.
To identify your needle jet, you'll have to remove it. The numbers are stamped on the side and hidden from view when it's installed. Hopefully you'll find a P5 or P6 in there. Also make sure the air jet is removed.
Does that have an orfice as well? Do I replace it with a different size?There's no such thing as a jet kit for the VM carbs. You just change individual jets as need be. What you need is a "baseline" to go by, a list of jet sizes that have worked for these carbs on this bike. The link RG gave you provides that, and according to it, I think your big problem is your pilots are too small. Your symptoms also reflect that. Try some in the 20s.
To identify your needle jet, you'll have to remove it. The numbers are stamped on the side and hidden from view when it's installed. Hopefully you'll find a P5 or P6 in there. Also make sure the air jet is removed.
TimeMachine
SeventyEighte
Usta could get a BMW boxer airhead , say R80, or even R69 to idle quite slow ! Guess these parallels need a few more rpm to stay running ?
Idle set at 1200 rpm and they're still not charging. Get closer to 1500rpm and there ya be. Installed voltmeters will tell the tale.
Yes, they do. When I first got mine, I thought the 1200 idle speed sounded a bit to "busy". I too have airheads and was used to a slower idle on a twin. So, I tried it with the 650. Random stalling at stops was the result. It would just up and quit sometimes. You really need the 1100 to 1200 idle speed on these. I've grown used to it now and it sounds normal for the bike.
Tony, do you replace what with a different size? The air jet, no, you just run without one. The needle jet, maybe, depending on what size you find in there. Ideally, you want a P5 or P6 in there. One of these sizes combined with no air jet is what most run. That air jet feeds the midrange and main circuit. Using one restricts the air flow too much and makes that area too rich, so you just take it out completely.
TimeMachine
SeventyEighte
There we go ! the idle speed challenge to my bike yesterday was all about the tune, not the charging.. So 1100 is a purring for an XS.. thx, -RT
I will pull carbs back out and take a look. Sudco sent several 2 or 3 different main jets but only one size if pilot jets and they are smaller. I take it that the needle jet is the post I see in the center and it pushes out from the bottom?
Yes, the needle jet is in the center and is what the main jet screws into. It's a push/slip fit into the carb body from the top. The main jet holds it in place. Once you remove the main jet and the brass washer under it, this is what you'll see. This is the bottom of the needle jet. Tap it up and out of the body, into the main bore .....
Once removed, the jet will look something like this .....
Once removed, the jet will look something like this .....
Here is what in the carbs.
Needle jet 159 P6
Jet needle 6F9
Pilot jet 15
Main 175
Air screw 2.0
My engine will idle down as low as about 600 rpm, but its not desirable or wise to do so. 1200 rpm is the place to be when idling, as it gives the oil pump enough volume for good lubrication at idle. Also if your bike still has the original style flasher unit, if you lower idle below 1200, the flasher does not have enough current flow and the flashers will stop. That's a real safety concern.
Charging concerns.................these bikes do not charge the battery at 1200 rpm. That's just a fact of life. They were never designed to do that, because there is no need to charge while idling. Your engine spends >95% of its time at rpms above 1500 rpm, and that is where the battery is charged. If your bike shows 14.1 volts to 14.5 volts as it drives down the road, your battery will always be charged. (unless you let the bike sit in the garage for months ! )
Well I removed air screw. Little better. Guess I'm going to need to buy some jets
What size slide does it have. 2 or 2.5 if 2.5 you will need at least a 25 pilot, I like 30 for a stock xs .
I just helped a guy that had left and right carbs and had the slide in the wrong carbs. so that the cut out was facing the front, it needs to be in the back. The can be turned around.
I just helped a guy that had left and right carbs and had the slide in the wrong carbs. so that the cut out was facing the front, it needs to be in the back. The can be turned around.
you talkking about the cut away and is that the slanted portion of the slide?
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