If you take any picture of the float bowls, try some from an edge-on angle, looking for warpage.
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Bike runs good until it's warmed up, then terrible
- Thread starter Rexxis
- Start date
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- carburetor engine
Okay, your plate is full. Will wait until pictures arrive...
To check the choke plungers, there's no need to remove the housing. You can just pull the plungers out the top. Many times when I clean or rebuild a set of carbs, I don't remove the choke housings, just the plungers. The passageways through the choke system are quite large by carb standards and rarely get clogged.
Correct bowls for you '78-'79 carb set would have no hose nipples on the bowl bottoms and no overflow brass tube inside the bowl. The air feed for the pilot would travel across the top and feed the top of the jet as illustrated here .....
Correct bowls for you '78-'79 carb set would have no hose nipples on the bowl bottoms and no overflow brass tube inside the bowl. The air feed for the pilot would travel across the top and feed the top of the jet as illustrated here .....
Rexxis
Almost there...
Ok I will check all of this when I get home.
What do you mean two many, when you ask if I can hear when the left cylinder is running?
I barely use any gasket sealer when I apply it. Just little dots, then I kinda tap it around with my finger until it covers all of the surface and it leaves the sealer kinda bumpy looking and slightly tacky, then I apply the gasket. Should I not use sealer on the choke plate gaskets?
What do you mean two many, when you ask if I can hear when the left cylinder is running?
I barely use any gasket sealer when I apply it. Just little dots, then I kinda tap it around with my finger until it covers all of the surface and it leaves the sealer kinda bumpy looking and slightly tacky, then I apply the gasket. Should I not use sealer on the choke plate gaskets?
Use no sealer at all, doesn't play well with fuel, especially silicone sealer.
See in 5twins pics how flat the top bowl surfaces are? Make sure yours are flat as well.
Also, check the mating carb body surface, should be flat, not warped.
Check the four corners where the bowl screws are. I've run into several cases where a PO torqued the bowl screws before fully seating the bowl, warping it, allowing leakage around the needle jet area.
If/when we get to the running/riding stage of the diagnostic, you'll need to listen to the left exhaust.
This is part of the black art of wrenching.
Experienced/blessed/gifted/cursed mechanics can tell quite a bit of what's goin on by just listening to the exhaust.
You've taken your first steps down this rabbit hole. It gets deeper.
Do you want the blue pill or the red pill?
See in 5twins pics how flat the top bowl surfaces are? Make sure yours are flat as well.
Also, check the mating carb body surface, should be flat, not warped.
Check the four corners where the bowl screws are. I've run into several cases where a PO torqued the bowl screws before fully seating the bowl, warping it, allowing leakage around the needle jet area.
If/when we get to the running/riding stage of the diagnostic, you'll need to listen to the left exhaust.
This is part of the black art of wrenching.
Experienced/blessed/gifted/cursed mechanics can tell quite a bit of what's goin on by just listening to the exhaust.
You've taken your first steps down this rabbit hole. It gets deeper.
Do you want the blue pill or the red pill?
Rexxis
Almost there...
Haha, I'll take the red. Both my exhausts come out on the right side of the bike, near the back so it may be difficult.
Okay, we'll try this anyway...
The bowls hold about 35cc each, together about 70cc. That's about 1/55 gallon.
If, during this slow speed test, you get about 55 mpg, then there's about 1 mile of fuel in the bowls.
What you're gonna do is take the bike out, turn on the fuel for about a minute to fill the bowls.
Then turn the petcocks off. All this will be done on bowl fuel only.
Start the bike, ride around at the low throttle setting that's giving this trouble, till yer outta gas.
While riding, you'll need a good sense of time, and be able to hear that left cylinder.
Various scenarios will occur, for example:
Left side stumbles for 10 seconds, clears-up, runs fine till empty.
This may mean that the fuel level was too high, or fuel was entering leakage at bowl top.
Left side stumbles for 30 seconds, then just dies.
This means it's dumping fuel irreguardless of fuel level, maybe enrichener circuit.
There are many more, but I hope you get the idea. Think "carburation theory" while doing this...
The bowls hold about 35cc each, together about 70cc. That's about 1/55 gallon.
If, during this slow speed test, you get about 55 mpg, then there's about 1 mile of fuel in the bowls.
What you're gonna do is take the bike out, turn on the fuel for about a minute to fill the bowls.
Then turn the petcocks off. All this will be done on bowl fuel only.
Start the bike, ride around at the low throttle setting that's giving this trouble, till yer outta gas.
While riding, you'll need a good sense of time, and be able to hear that left cylinder.
Various scenarios will occur, for example:
Left side stumbles for 10 seconds, clears-up, runs fine till empty.
This may mean that the fuel level was too high, or fuel was entering leakage at bowl top.
Left side stumbles for 30 seconds, then just dies.
This means it's dumping fuel irreguardless of fuel level, maybe enrichener circuit.
There are many more, but I hope you get the idea. Think "carburation theory" while doing this...
Boy, I swear, wrote up a full procedure, net crashed, lost it.
Get about 10-20 net crashes out here, frustrating. AT&T hates me...
Get about 10-20 net crashes out here, frustrating. AT&T hates me...
Rexxis
Almost there...
I got so involved in working on the head last night, I forgot to post the pictures.
Here's the thread where we identified my carbs. I think I am wrong in thinking I have a set from '78-'79. I think they are '76-'77's. One thing I noticed though, the slide needle has the snap ring, that started in '78 though right?
You can see where I got confused in post three of my thread. "Yep, I've definitely got a set from '77-'78 then." This will change my jetting quite a bit and explain why it ran better on the jets I had in it previously.
http://www.xs650.com/forum/showthread.php?t=23881
The bowl tops and mating surfaces look to be good.
Take a glance here:
What's the verdict? Need more pics? I can take them w my phone and upload them on the fly if needed.
Oops, I just realized I never looked at my choke plungers, I'm gonna go do that right now.
Questions:
1. So I should use gasket sealer in areas like the backside of the advance cover, tappet covers, head gasket? Basically all the gaskets on the engine but none on the carbs?
2. As you can see, I have new float valves and needles but you said to check them to see if they seal. How does a guy do that?
Here's the thread where we identified my carbs. I think I am wrong in thinking I have a set from '78-'79. I think they are '76-'77's. One thing I noticed though, the slide needle has the snap ring, that started in '78 though right?
You can see where I got confused in post three of my thread. "Yep, I've definitely got a set from '77-'78 then." This will change my jetting quite a bit and explain why it ran better on the jets I had in it previously.
http://www.xs650.com/forum/showthread.php?t=23881
The bowl tops and mating surfaces look to be good.
Take a glance here:
What's the verdict? Need more pics? I can take them w my phone and upload them on the fly if needed.
Oops, I just realized I never looked at my choke plungers, I'm gonna go do that right now.
Questions:
1. So I should use gasket sealer in areas like the backside of the advance cover, tappet covers, head gasket? Basically all the gaskets on the engine but none on the carbs?
2. As you can see, I have new float valves and needles but you said to check them to see if they seal. How does a guy do that?
Yeah bodies are the earlier not 78-9 style.
Rex, if you're feeling confused, congrats. You just upped a notch. I think, therefore, I'm confused...
Okay, one at a time here.
Take-off the carb gasket, put a tiny dollip (use toothpick) of grease on the float bowl in that little flat spot between the mainjet hole and the brass idle hole. You have a felt-pen marker line there. Then carefully place the bowl fully on the body, then remove. If the body and bowl are flat, that little grease dot will be flattened. You can adjust how big a dot to use to determine just how far out of flat they are. Real tiny dot undisturbed means out-of-flat is at least the height on the dot. Do both carbs, interchange float bowls to confirm. You get the idea...
Those two slots that run from the main to the side, and from the brass idle to the other side. Those slots admit air to the jets from the air bleeds in the carb body. Is it me, or is there no matching hole in the carb body, matching the location of the hole(s) in the gasket? Or is the gasket upside down?
Okay, one at a time here.
Take-off the carb gasket, put a tiny dollip (use toothpick) of grease on the float bowl in that little flat spot between the mainjet hole and the brass idle hole. You have a felt-pen marker line there. Then carefully place the bowl fully on the body, then remove. If the body and bowl are flat, that little grease dot will be flattened. You can adjust how big a dot to use to determine just how far out of flat they are. Real tiny dot undisturbed means out-of-flat is at least the height on the dot. Do both carbs, interchange float bowls to confirm. You get the idea...
Those two slots that run from the main to the side, and from the brass idle to the other side. Those slots admit air to the jets from the air bleeds in the carb body. Is it me, or is there no matching hole in the carb body, matching the location of the hole(s) in the gasket? Or is the gasket upside down?
Hey gggGary, do you see any air bleeds on that body?
Ketis, never seen them available individually, might have to get salvage carbs...
Do we have a bowl/body mismatch here?
Okay, these are idle/air carb bodies, the idle air bleed goes to the idle air/bleed screw on the side of the carb. But, there should be an air bleed passage leading to the mainjet area, I don't see it.
The air bleed restrictors are press-fitted into those 2 little holes on the outside edge of the card inlet bell. You could blast carb cleaner into those air bleed inputs, see where it comes out. The smaller bleed goes to idle screw, larger to mainjet.
The air bleed restrictors are press-fitted into those 2 little holes on the outside edge of the card inlet bell. You could blast carb cleaner into those air bleed inputs, see where it comes out. The smaller bleed goes to idle screw, larger to mainjet.
Okay, the other questions,
The float valves/seals can be checked 'shop-style', the fast/easy was we used to do it.
We would just drop the bowl, turn on fuel, finger the float up/down, checking for height and leakage.
Messy, but fast and never failed.
Gaskets: Factory sez no sealer except for yamabond between case halves.
Over time, solving unique problems, using aftermarket gaskets, or ease of service, has produced a plethora of sealing recommendations. You may not like this, but I personally like the old racer trick of coating gaskets with a very thin film of grease. A little bit on the fingers, spread around real good, just enuff to make gasket slick, not too much to make a mess. Generally helps to hold gasket in place, later disassembly real easy, gasket can be re-used. The old original gaskets of the `70s were made from a composition of asbestos, fibers, and reclaimed oil. Hence, compatible with the thin grease trick. They never leaked, but would leave a telltale dark line along mating surfaces. Comes off at car wash after you're convinced you won't be disassembling any time soon. But not good to discerning customers and show bikes.
The float valves/seals can be checked 'shop-style', the fast/easy was we used to do it.
We would just drop the bowl, turn on fuel, finger the float up/down, checking for height and leakage.
Messy, but fast and never failed.
Gaskets: Factory sez no sealer except for yamabond between case halves.
Over time, solving unique problems, using aftermarket gaskets, or ease of service, has produced a plethora of sealing recommendations. You may not like this, but I personally like the old racer trick of coating gaskets with a very thin film of grease. A little bit on the fingers, spread around real good, just enuff to make gasket slick, not too much to make a mess. Generally helps to hold gasket in place, later disassembly real easy, gasket can be re-used. The old original gaskets of the `70s were made from a composition of asbestos, fibers, and reclaimed oil. Hence, compatible with the thin grease trick. They never leaked, but would leave a telltale dark line along mating surfaces. Comes off at car wash after you're convinced you won't be disassembling any time soon. But not good to discerning customers and show bikes.
The air bleeds are there, I think it's just difficult to see them because of the angle of the photo .....
So, you have '76-'77 carbs. I was under the impression you had '79 carbs because your bike is a '79 and, well, you said you did. The jetting you mentioned then is not stock but richer, pilots up one and mains up 5.
What may be causing the problems is the slides. You say you have the type that retain the needle with a snap ring. Those would be '78-'79 slides. They would have had 5O2 needles stock. The '76-'77 slides had 4M1 needles, much shorter (by 5mm). I'm not sure 5O2 needles would work right with the stock '76-'77 Z-8 needle jets or if the 4M1 needles would work in the '78-'79 slides.
What needle jets and needles do you have?
So, you have '76-'77 carbs. I was under the impression you had '79 carbs because your bike is a '79 and, well, you said you did. The jetting you mentioned then is not stock but richer, pilots up one and mains up 5.
What may be causing the problems is the slides. You say you have the type that retain the needle with a snap ring. Those would be '78-'79 slides. They would have had 5O2 needles stock. The '76-'77 slides had 4M1 needles, much shorter (by 5mm). I'm not sure 5O2 needles would work right with the stock '76-'77 Z-8 needle jets or if the 4M1 needles would work in the '78-'79 slides.
What needle jets and needles do you have?
Rexxis
Almost there...
There are 5 holes in the center of the gasket. Take two away, the big one centered over the main jet and the one that the overflow tube passes through, that leaves us 3 other holes. One is over the end of the slot connected to the main. The other two are over each end of the slot connected to the pilot. You can see their corresponding holes in the body in the second picture. It all lines up.. I think..
What is this that you're calling the air bleeds? The three tiny holes in the throat, right by the bottom of the butterfly plates?
Wow, look at the other side(R), this gasket is glued down on the body side and has been on there since I first rebuilt the carbs over a year ago. You can see the pathway in the gasket.
What is this that you're calling the air bleeds? The three tiny holes in the throat, right by the bottom of the butterfly plates?
Wow, look at the other side(R), this gasket is glued down on the body side and has been on there since I first rebuilt the carbs over a year ago. You can see the pathway in the gasket.
Rexxis
Almost there...
One sec, checking needles and jets now.
