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Scenario: 75 Yamaha XS500 CV Carbs, Timing set with light, carbs synced, upjetted main jet. Overheats in city stop and go traffic. Short stop, backroad cruising, occasional red light it is fine. Frequent stop lights and stop signs starts to overheat.
Anyone an expert at tuning a Yamaha TX/XS500 with CV Carbs or comparable bike? I pretty sure I have the main jet figured out and runs a little rich with no problems.
I get the impression that I am running to lean on the on the idle jet. Could this explain the over heating I experience when riding stop go in the city?
I can't be sure from personal experience, since my bike has only run with VMs- not the original Keihins- since I've had it, but it sounds logical that running lean is running hot. I'd step up on the pilots. You might be able to richen it up a bit with the air screws, but hard to say if it'd be enough.
What pilot jets are in it and where did they come form? The reason I ask is that those carbs do not usually take a stock VM series slow jet (some do) and it they need a BS series pilot jet, they look the same but are very different in the way they flow.
What pilot jets are in it and where did they come form? The reason I ask is that those carbs do not usually take a stock VM series slow jet (some do) and it they need a BS series pilot jet, they look the same but are very different in the way they flow.
I haven't be able to find an upjetted pilot jet on the internet. So they are stock. I never questioned the engine oil but I use Shell Rotella T 15w-40. It's meant to handle high temperatures. Maybe it provides too much resistances to the engine to pump and push through?
I read an article on finding the right idle air mixture. Apparently after setting the engine to the slowest idle then counting how many turns richer till it starts to die, then count how many turns lean till it starts to die and find the inbetween. do that sound about right?
Another question? Has anyone tried opening the air flow hole on the CV slide where the needle is? I read a bunch of stuff that says that it will allow the slide to lift fast when throttling through mid range.
How do you know it's overheating? What symptoms are you getting that led you to this conclusion?
Also, Rich, throttle position plug chops only work on slide carbs. CV carbs are RPM dependent, so you do the plug chops at different RPMs to check different parts of the carb circuits.
How do you know it's overheating? What symptoms are you getting that led you to this conclusion?
Also, Rich, throttle position plug chops only work on slide carbs. CV carbs are RPM dependent, so you do the plug chops at different RPMs to check different parts of the carb circuits.
Because it begins to smell, idle starts to drop and becomes increasingly harder to maintain. And at one point it was literally smoking. This only happens when I ride in the city. :\
The reason I ask is because it's pretty darn hard to overheat an air cooled engine.
That said, the TX500 has been known to suffer from that problem. If I remember correctly, many folks even got cracks in their heads (perhaps related to the heat?).
I think your 15w-40 is a decent choice for oil (especially the Rotella) and installation of an oil cooler on your model of bike is not unheard of. It's probably the route I would pursue.
Running a bit rich on fuel and/or retarding the timing a couple of degrees will also lower operating temps, though both will adversely affect power.
Obviously there's not much you can do when you're stuck in traffic and idling, but try to avoid blipping the throttle. When you are able to move, avoid WOT and let the bike rev high before shifting. Keep RPMs up and use the throttle at little as possible.
CV carbs are not like slide carbs but there's a pretty c lose correlation that we can work form. Order a pair of one size larger pilot jets from MikesXS.com http://www.mikesxs.net/products-39.html#products you need BS30/96 jets and not VM 22 style.
Then raise the needles one clip position - Clip goes DOWN and the needle moves UP. and tray that. It's pretty easy to overheat an air coolded motor at low speed without sufficient air past it, but anything over about 15-20 mph it should cool OK
Avoid drilling anything at this stage. but do check every jet to make sure a/ you know what's in there and b/ you are 110% sure they are all clean. Main and pilot jets are mounted in the bowl and get blocked easily.
Also, Rich, throttle position plug chops only work on slide carbs. CV carbs are RPM dependent, so you do the plug chops at different RPMs to check different parts of the carb circuits.
New Question: I played around with the idle air/fuel mix pilot screw today. Had gotten the bike running nice and smooth at about 3-4 turns out with no back fire pops. Assuming that I needed to run richer I backed it out to about 5 screws. The bike runs a little less smooth at idle. Meanwhile I have been measuring and monitoring the engine head temp. And it doesn't level out while idle. It keeps climbing to around 290F/300F and slowing becomes a little bit hesitant on the idle. Sounding like its on the verge of maintaining and stalling out.
My hunch is that I need to step up the main jet just a few more. I am running #135 main.
Anyone think I am in the right direction? I didn't do a plug chop this time around but that would be my next step.
I was assuming that you have Mikuni BS32/34 carbs but maybe they are Keihin.
From what I have seen on line, early model TX500s came with Keihin carbs similar to a CB450 honda or CB900F. XS models appear to have been fitted with Mikuni BS34 carbs similar to Yamaha XS650. Which are on that bike?
edit: I just went back to your thread and they are Keihin carbs, so please ignore my previous comments about Mikuni parts.
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