Hot QUICK!

[savag454]

So I got my 74 tx650 pretty much wrapped up. I cleaned the carbs real good and starts first kick. The problem I'm having is I have a 2 into 1 exhaust with no baffle. When I start the bike the right header at the head gets smoking hot in like 10 seconds. Is this caused by right side carb running too lean? Even though I have the mix screws set the same is it okay to just adjust it a little richer on that side? Will it cool down that header? Thanks Ryan

[yamacette]

Try resetting your valves.

[5twins]

Mix screws should be set for best (fastest and smoothest) idle. There's not much leeway there, maybe 1/4 turn either way from optimal. The idle speed will start dropping off after that which is telling you the setting is not ideal. I don't think that 1/4 turn or so richer will help you much.

These bikes normally run a bit hotter on the right, it's just one of their quirks. If you didn't rejet for the 2-1 header, that may be amplifying this quirk. Check your idle speed. Your carbs have an idle speed adjustment screw on each carb. The right one may be set faster than the left one.

You say the right pipe gets "smokin' hot" within a few seconds. It's normal for a pipe right up near the head to become too hot to touch within seconds of starting. What about the left pipe? Is it staying cold? If so, the problem may be with that side, not the right.

[tomterrific]

5twins solves the problem in the last paragraph (I'm guessing). There isn't enough difference to note in the temperature between cylinders.

The exhaust pipes get hot enough to burn off any oil film and smoke. It is not normal for a pipe to be not that hot. So many folks think their engine idles fine when it is only idling on one cylinder.

If you are still running points. Pull the cap off the right side as the engine idles and see if it runs on the left cylinder. Do this quickly as you don't want the engine to blump-blump away with the plug cap pulled.

Look to the idle/pilot jet in the left carb. It is most likely plugged with dirt and needs poked through with a thin wire. Spray with carb cleaner and one poke is all it needs. There can be other reasons but the idle jet seems to be the culprit most of the time.

Tom Graham

[savag454]

Okay thanks. I might have worried me cause it was smoking or burning off oil or whatever. The pipe started to blue though. The left side isn't very warm (after 10 or 15 sec didn't let it run that long) It deff could just not be running on the left cylinder. I'll try the plug thing, and then clean the left carb again. Which jet is the idle jet? The main jet (?) that the big needle seats in is slightly squished like someone tried to take it out and pressed too hard with the pliers. It is only slightly out of round and seems to be idleing good and starts first kick cold. I have the original spare carbs for my 70' xs will they do to replace them? Also the big needles are set with the C clip on the second adjustment from the bottom. Is this too far down?

I bottomed out my mix screws and turned them out .75 (1974 tx650) per the carb guide on here. Should I go another 1/4 either way? Also does anyone know how to properly adjust the idle screws to a standard starting point? Thanks a ton Ryan

[5twins]

Idle screws should be set the same amount of turns in from just touching the stops. That opens the butterflys an equal amount in each carb so they run at the same speed. With the motor off, back the idle screws out until you can see light between them and their stops. Now turn them in until they just touch. This can be achieved by using a thin piece of paper between the screw and stop as a "feeler" gauge. Set each screw so you can pull the paper out with the same amount of drag. Once that is done, turn each screw in one full turn. Start the bike and adjust to desired idle speed (1200 RPM). To make changes in speed but to keep the speed the same on each carb, you must adjust BOTH screws the same amount. Turn only one and you'll be mismatching the speed between carbs.

Next, set the mix screws. That 3/4 turn out is just an initial starting point. From there, you need to work the screw in/out to find where the cylinder idles best (fastest and smoothest). Pick a direction (in or out) and start turning the screw 1/4 turn at a time. Wait a few seconds between changes for it to have an effect. Keep going until the idle speed starts dropping off or it starts to stumble. Note how many turns you're at and start working back in the other direction until the same thing happens. Best setting will be somewhere between those two points. Farther out on the screw would be richer, farther in leaner.

Last setting is sync. Adjust the freeplay in the two throttle cables so they match exactly. This will make the throttle butterfly arms begin to open at the same time.

Study the second entry in the last post of the carb guide. That is an exploded cut-away drawing of a similar carb to yours. It will show you where the main and pilot jets are (in the float bowl) and what that damaged jet is (needle jet). The damaged needle jet shouldn't effect starting and low speed operation but may impede fuel flow at higher RPMs. All the fuel delivered by the main jet passes through it.

Needle clip positions are counted from the top down. That means yours are in the #4 slot which is correct for your model.

[savag454]

Okay I cleaned the carbs again and the pilot jet was slightly clogged at the bottom. I reinstalled them and started it. I pulled the left plug cap and it ran fine, pulled the right plug cap and it stoped immediately. Could this still be a fuel issue? I don't think I have the mix screws adjusted properly yet. What else might it be? Thanks a ton, Ryan

[5twins]

Sounds like you haven't set and matched the idle speeds yet. That must be done 1st before setting mix screws or sync. Turn the speed up on the left cylinder so it will run when you pull the right plug.

[sevens0n]

Have you checked the timing with a timing light? On each cylinder separately? I ask because I ran into a similar (One cylinder HOT) trouble. Come to find out with dual points it is possible to get one cylinder timed incorrectly and that will cause it to run very hot. Too far advanced I believe. I have one blued pipe to prove it. This may also explain having trouble with the carb setting.

[tomterrific]

If you did not poke a thin wire through teh pilot jet then there is no help.

Pull teh left plug from teh head lay it on teh head and see if it fires when you kick. The plug could be fouled so buy a $2 replacement if you are out.

Swap the coil wires to see if there is a break in the left wire the spark can't jump. This shows to replace the SP wires and SP caps.

The points may have worn and closed up. Check teh left side point.

You can easily see if you have a fuel issue by spraying some carb cleaner or starting fluid or even straight gas into the carb mouth of the left carb while the engine runs on the right cylinder. If the left side fires off then you know it is not getting gas. Go back to poking a thin wire through the pilot jet.

Tom Graham

[savag454]

Okay I'll try all these things. I did adjust the idle screws first using paper and then about 2 turns in. Should I adjust the right one only until that cylinder fires or stay with keeping both matched? I did poke the pilot jet with a wire. A striped twisty tie. I could need an external fuel filter though because it was plugged when I checked it again. Thanks everyone, I'm going to go down this new list of things. Ryan

[5twins]

Keep the idle speed screws matched. That's the basis for all the other carb settings. If one side isn't running with the screws matched, as mentioned you may have an ignition problem, not a carb setting problem (or your idle jet has plugged again). If your idle jet keeps re-plugging, you may need to clean your tank and petcocks. There should be filter screens over the feed pipes of your petcock. If those are missing, any crud in the tank can flow right into your carbs.

This or any bike needs to be tuned in a certain order or sequence because one setting can effect the next. This is the order things need to be done in ......

-set cam chain tension
-set valves
-set points gap
-set timing
-set carbs

You can't skip ahead on the list because if an earlier item is off, it can affect the latter one. Notice where carb setting falls on the list - yep, dead last.

[savag454]

Okay thanks for the run down. I'll do that. It is running on both cylinders now. I'm not sure if it was a carb problem or an electrical gremlin but the points were good. It's running good but now there is a rattle in the top end. I am going to go through the list 5Twins just posted. Thanks for everyone who's helped me get this sorted out. It was in the middle of being worked on by who knows when I got it. I will keep you posted after I go through the list. Ryan

[savag454]

Okay, my cam chain tension was fine but the valves are pretty big. The rocker arms have quite a bit of play at TDC. I will adjust the clearances tonight and hopefully my problems are solved untill the next set. Thanks everyone. Ryan

[savag454]

Alright, thanks everyone who helped me out. I adjusted the valves and got the carbs sorted out and she runs like a top. Took her down to the Hoe Down with the local Iron Mustangs here in Detroit and not a problem except losing my kickstand on the express way. Really thanks again, Ryan.