New to this, bike cut off and now wont start.

[peanut]

This makes me want to definately check the torque of my own head bolts. These engines vibrate alot. If i ever have to do a big tear down.. i"ll be considering a rephased crank.

rephasing sounds like a good option . I don't know anything about these engines yet having never ridden one but if they are anything like the BSA Spitfire I once owned, my hands were numb after just 5 miles !

I'm beginning to wonder if a lot of the vibration could be due to engines being out of tune . Incorrect timing and poor fuel mixture/delivery

 

[peanut]

well you'll know immediately if retightening the head cures the problem!

you'll need to do another compression test which will tell you.

Try and do the compression test thoroughly, there are plenty of guides on youtube and elswhere on the web such as this one.
http://www.dansmc.com/compression_test.htm


You cannot run this bike as it is ,unless torqueing the head cures the huge compression loss and the oil leak,.... which I doubt.

Such a huge difference in compression between the cylinders with such a low mileage engine is a sure sign that something is seriously wrong with that cylinder which needs fixing sooner not later.

When i suggested checking your valve gaps I didn't mean you to just adjust them like a maintenance job....
I am saying that you must check your gaps to see if there is a fault with one of your valves that is causing this whole problem !....This is a diagnostic check not a routine maintenance adjustment.

If one of your valves is sticking open or binding or just not seating properly due to lack of the correct gap then the edge of your exhaust valve will burn away which will give you the huge loss in compression .

The oil leak could still be due to a damaged valve guide or missing oil seal.

I may be wrong on this but a simple check of your exhaust valve gaps will confirm it one way or the other . I cannot understand why you still have not done this ?

 

[MFJustin]

well you'll know immediately if retightening the head cures the problem!

you'll need to do another compression test which will tell you.

Try and do the compression test thoroughly, there are plenty of guides on youtube and elswhere on the web such as this one.
http://www.dansmc.com/compression_test.htm


You cannot run this bike as it is ,unless torqueing the head cures the huge compression loss and the oil leak,.... which I doubt.

Such a huge difference in compression between the cylinders with such a low mileage engine is a sure sign that something is seriously wrong with that cylinder which needs fixing sooner not later.

When i suggested checking your valve gaps I didn't mean you to just adjust them like a maintenance job....
I am saying that you must check your gaps to see if there is a fault with one of your valves that is causing this whole problem !....This is a diagnostic check not a routine maintenance adjustment.

If one of your valves is sticking open or binding or just not seating properly due to lack of the correct gap then the edge of your exhaust valve will burn away which will give you the huge loss in compression .

The oil leak could still be due to a damaged valve guide or missing oil seal.

I may be wrong on this but a simple check of your exhaust valve gaps will confirm it one way or the other . I cannot understand why you still have not done this ?

Except I did though, a few posts back I said I checked the gaps on the exhaust valve with the problem and it was out of spec, I could get .006 to fit as the manual calls for but I could also get .008 to fit. Anything larger than that was a no go so they are not tightened correctly based on the fact stuff larger than .006 would fit.

 

[5twins]

Well, being off a couple thou like that really shouldn't hurt anything. And you found it loose, we were thinking it may have been too tight. Too tight would cause the compression loss, not too loose.

All you can do is fire it up and see if the re-torque helped any. It will still smoke for a bit even if it did. There's lots of oil in there to burn out. Run it for a short time and then check the compression. You get better readings on a warm engine.

 

[MFJustin]

Gentleman I'm back but this time with a slightly different approach to this.

When I took the bike to my mechanic friend to get it timed after installing the Pamco, he pointed out that my left side inline fuel filter was leaking. I figured it might have a small crack or something so I cut the lines a bit shorter to get fresh unstretched material and installed new inline fuel filters with new hose clamps. I noticed that when I turn the petcocks on it still leaks pretty steadily from the left side. Instead, I shut off the left petcock and opened the right one and for some odd reason it still fills up the left side fuel line and starts leaking because I can see gas entering the fuel filter.

I kept the left petcock closed and barely cracked the right one and the bike ran, I even completely closed off both of them and the bike continued to idle like it was getting plenty of fuel.

At this point I'm kind of puzzled, I dont know if any of this is related whatsoever and I REALLY apologize if you guys start bashing your head off your desk because it seems like I'm jumping around but I did read in another thread (trying to find it now to link it) that a leaky petcock caused excessive white smoke from the exhaust.

I tried to take it out for a ride but with it leaking fuel like it is by just simply opening the petcock a bit I dont even want to risk it. I'm just curious if maybe theres some link, like somehow gas is getting in with the oil and thats whats causing it to smoke so much. With the left petcock closed and the right one open it was like gas was flowing down through the carb and up into the other fuel line. Almost like my carb is overflowing and causing oil to be washed out the cylinder or something???

Update: Unplugged the fuel line from the left side filter, cracked open the right petcock and sure enough gas seems to be flowing through the carb and up through the left side fuel line where it then pours out.

 

[Square Circle]

Gentleman I'm back but this time with a slightly different approach to this.

When I took the bike to my mechanic friend to get it timed after installing the Pamco, he pointed out that my left side inline fuel filter was leaking. I figured it might have a small crack or something so I cut the lines a bit shorter to get fresh unstretched material and installed new inline fuel filters with new hose clamps. I noticed that when I turn the petcocks on it still leaks pretty steadily from the left side. Instead, I shut off the left petcock and opened the right one and for some odd reason it still fills up the left side fuel line and starts leaking because I can see gas entering the fuel filter.

I kept the left petcock closed and barely cracked the right one and the bike ran, I even completely closed off both of them and the bike continued to idle like it was getting plenty of fuel.

At this point I'm kind of puzzled, I dont know if any of this is related whatsoever and I REALLY apologize if you guys start bashing your head off your desk because it seems like I'm jumping around but I did read in another thread (trying to find it now to link it) that a leaky petcock caused excessive white smoke from the exhaust.

I tried to take it out for a ride but with it leaking fuel like it is by just simply opening the petcock a bit I dont even want to risk it. I'm just curious if maybe theres some link, like somehow gas is getting in with the oil and thats whats causing it to smoke so much. With the left petcock closed and the right one open it was like gas was flowing down through the carb and up into the other fuel line. Almost like my carb is overflowing and causing oil to be washed out the cylinder or something???

Update: Unplugged the fuel line from the left side filter, cracked open the right petcock and sure enough gas seems to be flowing through the carb and up through the left side fuel line where it then pours out.

I'm definately not an expert or guru but I believe the carbs fuel lines are connected via that cross over tube just under the barb nipples. A back flow of gas into the other non fed line makes sense , What doesnt make too much sense to me is how liquid gas would flow into the cylinder. If the floats are set at the specified equal heights, how can gas get past the float needle without the demand vacume discharging the level of fuel in the bowls? When the engine is not running, will a gravitational push of fuel from open petcocks force more fuel than required into the float bowls and overflow into cumbustion chamber? I've been making sure my petcocks are off when not running reguardless.

 

[MFJustin]

I'm definately not an expert or guru but I believe the carbs fuel lines are connected via that cross over tube just under the barb nipples. A back flow of gas into the other non fed line makes sense , What doesnt make too much sense to me is how liquid gas would flow into the cylinder. If the floats are set at the specified equal heights, how can gas get past the float needle without the demand vacume discharging the level of fuel in the bowls? When the engine is not running, will a gravitational push of fuel from open petcocks force more fuel than required into the float bowls and overflow into cumbustion chamber? I've been making sure my petcocks are off when not running reguardless.

My petcocks are always off as well when the bike is not running.

The only reason I bring this up is just to see if any of this could be related or just totally coincidental. To recap the bike was running fine a few weeks ago and then just bogged down and cut off on me on the highway one day. Before this there were zero leaks when both petcocks were open but after the whole incident it does what I described today, as soon as I open the right petcock with the engine running and the left petcock closed completely it starts overflowing out of the left side fuel line even with the engine running. I don't know what condition my carb internals are in, float levels or anything like that, I'm just attempting to see if I could put it all together and see if somehow something like that was related to my issue of smoking exhaust and a right side cylinder that's looking and acting like that and not be related to something wrong with the aforementioned items we've already brought up as a potential cause.

 

[Square Circle]

My petcocks are always off as well when the bike is not running.

The only reason I bring this up is just to see if any of this could be related or just totally coincidental. To recap the bike was running fine a few weeks ago and then just bogged down and cut off on me on the highway one day. Before this there were zero leaks when both petcocks were open but after the whole incident it does what I described today, as soon as I open the right petcock with the engine running and the left petcock closed completely it starts overflowing out of the left side fuel line even with the engine running. I don't know what condition my carb internals are in, float levels or anything like that, I'm just attempting to see if I could put it all together and see if somehow something like that was related to my issue of smoking exhaust and a right side cylinder that's looking and acting like that and not be related to something wrong with the aforementioned items we've already brought up as a potential cause.

When you say "overflowing out of" the left side fuel line... do you mean leaking? still need to fix that broken fuel filter? I think your blown head gasket has nothing to do with your fuel delivery. you probably need to pull carbs..clean and check the float heights.

 

[MFJustin]

When you say "overflowing out of" the left side fuel line... do you mean leaking? still need to fix that broken fuel filter? I think your blown head gasket has nothing to do with your fuel delivery. you probably need to pull carbs..clean and check the float heights.

I thought the fuel filter was broken so I replaced it. New filter and new hose clamps to make sure everything was squared away. What I'm saying now is that when the left petcock is closed and the right one is open, even with the engine running gas is flowing through the carb and leaking out the fuel filter on the other side. Not because the filter is cracked but because it's like it fills up that fuel line and because the petcock is close has no place else to go but force it's way out. The only reason I'm asking if any of this is related is because a few weeks ago the bike ran, it cut off on the highway and now I'm having all of these symptoms at once. A little fishy that all of this stuff would appear and not somehow be related right? At this point in time I think I just need to pull everything apart and start from square one.

 

[MFJustin]

Another update, went out to the garage to do another compression test after I retorqued the head yesterday because I forgot to do it then.

Right side plug removed, compression gauge screwed in, throttle rolled all the way open.....I can kick it in about 5 kicks right up to 150. I switched over to the left cylinder and same results. Hopefully I did the test the way it's supposed to be done but at least I know I have good compression again. Now I need to solve why it's smoking so bad and what's up with my carbs. Right side spark plug, the cylinder with the original problem is black with oil/gas on it. Left side spark plug is actually white like its running lean.

For what is worth, when I pulled the plugs after the bike died on me that one day they were both the coffee and cream color of properly burning plugs. After replacing the plugs and getting the bike running again I am now seeing a difference in what the plugs look like. Now that my compression numbers seem to be back up is it safe to say this whole problem or at least what I'm facing now is definitely carb and fuel related?

I think tomorrow I might put together a quick video to physically show what I'm talking about. I really appreciate the help you guys are giving me, learned a hell of a lot the past few days and I feel like I'm quite a few steps closer to figuring this whole thing out.

 

[5twins]

Yes, it's probably time you had a look inside your carbs. In particular, inspect the condition of the floats and their setting. These brass floats can develop leaks. That makes them heavy and you get too much fuel in that carb. An improper setting can do the same thing. As I mentioned before, that excessive smoking should taper off as you burn all that excess oil out of the cylinder, it's just going to take some run time and a few miles.

 

[XSLeo]

If you are having fuel leaks in the left side even after replacing a filter I might replace the fuel lines. If very old they get hard and can crack very easy.
As 5twins said it time to clean your carbs. The carb guide is a good read, it will help you get your carbs right.
Not only burn the excess oil from the cylinders but the exhaust pipe and muffler too.
Leo

 

[MFJustin]

Pulled the carbs tonight, setting them aside to work on them tomorrow.

For now I'm going to read, read, read this carb guide as many times as I can to try and make sense of it all before I start pulling it apart.

 

[5twins]

Here's an exploded parts diagram with stock jetting specs. Your jetting may have been changed for the mods you have. Record the jet sizes you find in there. It's possible it was over-jetted and that's the cause of the rich running and carbon build-up. Many go too far with their jetting. These bikes don't need huge increases in jet sizes for mods like some seem to think.

http://www.boats.net/parts/search/Y...-006/CARBURETOR XS650 E006501- - F/parts.html

 

[MFJustin]

So still working on taking the carbs apart, taking my time as I go along just so I can learn as much as I can since carbs are new to me.

Took the float bowl apart, everything looks really clean no varnish or anything. Brass floats look to be in good condition, the pin that holds them in came right out and I shook them to see if they sounded like they had any gas in them which would indicate a leak from what I read. I'm going to check the float height later once I pick up a proper measuring device.

5twins as far as mods go my bike came with straight pipes and UNI Pod Filters. According to the excellent tech info, the 38's for a 79 came with a 135 size Main Jet, I pulled the Main Jet on mine which came out quite easily and it was a 137.5 so obviously the PO upgraded it. Is that a sufficient size or do I need to go with something bigger or richer or whatever its actually called haha. Also the pilot jet is a 27.5

I'm going to continue on with what the carb guide says but first impression is that I don't see anything out of place or dirty that could be causing the problem. I held both main jets up and could see light through them so they look to be clean.

 

[nj1639]

Test the floats by immersing them in warm to hot water....needs to be warm so's to expand the air in the floats. If there's a hole in them it'll show by a small stream of bubbles...guaranteed fool proof method. Shaking for sound just doesn't do it all the time.

 

[MFJustin]

Test the floats by immersing them in warm to hot water....needs to be warm so's to expand the air in the floats. If there's a hole in them it'll show by a small stream of bubbles...guaranteed fool proof method. Shaking for sound just doesn't do it all the time.

I'll go test this out right now, thanks for the tip.

 

[5twins]

You're one size up on the mains. That may be enough but you might need another size or 2 up. Only road testing will tell you that for sure. You're also going to need to check your needle clip position and your pilot jet size. Here's the usual scenario for re-jetting - you increase the mains until you get some break-up or stumbling under heavy throttle applications in the upper midrange. You lean your needles a step to correct that. That also leans the upper idle circuit which usually requires a larger pilot to correct.

What you have to understand about the '78-'79 carb set is that the upper midrange is right on the verge of being too rich from the factory. ANY increase in main jet size usually pushes it over the edge and requires leaning the needle. If the P.O. didn't lean it, that could be the cause of your rich running.

You're also going to want to carefully check (and adjust if need be) your float levels. They can also cause rich running if the fuel level is set too high. I find the easiest tool for this to be a 6" steel rule graduated in MM on one side. Since the mains mount in the bowl on the 38s, there is no main jet "tower" sticking up between the float "bulbs". This allows you to place the ruler on the far side and sight across the tops of both "bulbs" to get a measurement. You want to look directly across the tops so both are in line or you'll get an incorrect reading. You also want to measure twice, once from each side. Many times the floats are twisted on the mounting bracket making one "bulb" sit higher or lower than the other. You won't catch this unless you measure from both sides.

Here's a set of '76-'77 carbs set to their spec of 25mm .....

Here's the same set when looking from the wrong angle. As you can see, you get an incorrect reading that way .....

 

[MFJustin]

I was attempting to pull the needle to check its clip position but I happen to have the snap ring clip that holds it in and at the moment cant find my snap ring pliers. Once I can find those I'll be able to pull it out. Also the pilot jet size is 27.5

 

[5twins]

OK, your pilots are stock. That probably means the needles haven't been leaned because if they were, that would create a flat spot just off idle. Very annoying and easily cured with #30 pilots.