79 GS1000L backfiring, sometimes r-pipe smokes at start-up

[KEITH KRAUSE]

The intake leak will obviously cause a lean condition by the excess air entering and less vacuum to draw fuel through the jets. Lack of fuel will cause poor combustion (colder pipe).
I've always bought the manifolds from the dealer. You can probably get them from Bikebandit or Dennis Kirk...
Be sure to replace all four manifold o-rings. I suggest replacing the manifold bolts with Allens so you can torque correctly to 6 ft/lb. Also apply a coat of hi-temp' bearing grease to the o-rings to increase service life.
After the intake leak is fixed, let us know how it runs.
Also, do yourself a favor and get some plug reads at 1/3 throttle. If the bike is otherwise tuned well, I still think the jet needles are set lean. But what your test says is what matters. Don't assume the jet needle is jetted correctly. Mark your throttle grip and housing and test. Be careful. 1/3 throttle in top gear is hi-speed. Chop off for most accurate reads.

[gwhunran]

update

All,
Update on GS1000L. Put the bike in the shop to check compression and possibly have valves adjusted. Ended up finding #3 manifold/boot leak causing #3 header to be much cooler than the rest.
Obtained four new boots from cycle/recycle. Cycle/Recycle sold me Kaw. boots that work on GS1000s, with minor tweek to bolt holes. These boots have built in vacuum tubes and don't use O-rings for seal. Now I have two vacuum tubes per intake manifold.
Compression test went as follows 1-4: 110,110,140,140. Mech. then did valve check when bike was stone cold and found valves within tolerance so did not adjust. He said that a couple of the exhaust measurements were towards the tight-end of the scale but still okay. The carbs were rechecked and found to still be synced . I checked the sync myself when I arrived home, and found them to be close. The mech attributed the differences in cylinder compression to 1&2 being more worn, than 3&4. The bike ran okay. I think the idle is high, and tinkering with single idle adjustment knob would not bring it down lower, I will have to look deeper at idle settings later in the week. I don't think my mpg issue has been resolved. I will have to drive it more to get mpg measurements. I have been getting around 25mpg.

[KEITH KRAUSE]

Your bike should idle at 1,000/1,100 rpm. If it doesn't and you say it has nothing to do with the idle adjuster knob underneath, then the carbs are not vacuum synched correctly or you have sticking slide(s) or bad cable adjustment. Take off the pods and you should be able to feel with your finger nail tip any slight sticking as you seat each slide with the throttle grip. You may also use a mirror and see this or remove the tank and carb tops to watch them. Check throttle slack, which should have been done before any synch work.
I don't know about using the Kaw manifold instead of Suzuki. How does it seal without the o-ring? On the inside, does it also have the "built in" o-ring that allows your carbs to "pop" in? How does it seal?
Take some plug reads at 1/3 throttle for the jet needle and minimal throttle tests for any pilot circuit adjustments needed. But be sure the carbs are synched correctly first/find the reason for the idle problem. Your jet needles are still at position 3?
Exactly what rpm is it idling at? Does the rpm rise as it warms up?

[gwhunran]

Attempting to post picture of carb with new boot and one with old boot. and

I have to go back to the shop and pick up my haynes manual that I forgot yesterday. I intend to ask the mech about the idle. My tach is not perfect. When I bought the bike the tach glass was broken, and while I was attempting to remove broken glass shards, I managed to break the needle. I glued it back on and it works but is not perfectly straight, so I can't depend on the tach for 1000-1100 setting. Its just not that accurate. I have won an ebay auction finally for a used one that I am supposed to get by this coming weekend. I am mainly going by ear when saying its idled too high. Before the boot change out the idle sounded "right" to me.
and going by my current tach it is between 1000 and 1500 rpms. It still is between those two readings but seems higher.
The new boots do not have any O-ring. Rob at Cycle/Recycle told me that it didn't need one because of the way it mounted. The mech said the carb to boot fit was very tight and I am wondering if some of that "very tight," is part of the problem.
I will write more later after I go talk to the mech again. I may have to bite the bullet and learn to break the carbs down to parade rest myself to ensure that everything is right with them.

Richard

[KEITH KRAUSE]

I can't really see the pic' that good. Looks odd to me.
I can't see how this Kaw' manifold could seal if it has no o-ring to seal between the head and it's flat metal surface. The two "flat" surfaces simply will not seal enough without an o-ring. I wouldn't have bought these. Suzuki only in this case. I'd have to see them in person to tell, including the surface that meets the head and the inner molded o-ring that needs to fit into the groove on the outer part of the carb inlet.
Also, those carbs aren't stock. Your model/year uses a choke pull cable mounted on the bars. These replacements have a thumb choke. But both carbs are otherwise the same. VM26.
But just to mention it, I couldn't see the bottom of the bowl in your before pic'. Kinda shadowed. I think I see a drain bolt (brass/angled out) which would mean VM26, but if that shadow is really a main jet access bolt (larger/directly underneath), those carbs would be VM 29 smoothbores...whole different story then. I think those are stock VM26 though. You said mains were DJ 138 and that would be VM26 mains.
Maybe a better pic' or compare them to my close up pic's at my website by clicking the www symbol below.
I really question that manifold fit, unless I can see them better, including insides. I just don't see how they're sealing correctly.

[gwhunran]

After new non-Suzuki boot/manifold install bike did not run "right" on the way home. I suspected something to do with the new boot because that was the last thing touched. Yesterday my new used tach arrived courtesy of an ebay auction. After putting it on, the needle did not move, but it lit up, the gas gage worked, and it had good glass. My old one sorta worked but the glass was broken and I broke the needle trying to pull out pieces of broken glass. I had glued it back on but it was not perfectly straight anymore and I had a piece of plastic taped over the top to keep water out. Anyway on my commute to a seminar today the new one started working perfectly and worked right the rest of the day. On my way home, I had to go by the cycle shop that put the new boots on. I decided to stop by and see if they could determine why it was running like crap after the new boot instal. The mech and I went over everything. The carbs seemed to be set okay, the boots positively were not leaking, and we were pretty much stumped. One more item, I failed to mention. Header one is pretty cool, header two hot, header three not as hot as two, header four hot. We decided to check spark again at plugs, it turns out that the plugs were firing but acting funny, if boot firmly attached to #1 cylinder running weak, if boot a inch or so off plug cylinder ran strong, if farther off cylinder dead as it should be. We decided to change the pretty new plug with new plug and guess what??? Bike runs great all cylinders running as they are supposed to. Drove bike home from shop, about 15 miles fast interstate, heavy traffic, and it ran super. I am very pleased.

The mech said that the Kaw. manifold boot seals strong the way its designed. The guy (Ron or Rob) at Cycle/Recylce said the same thing about that boot for the GS series year of my bike. He said he had sold many of them and had no problems. Only thing necessary is to oval out the screw holes a little with a rat-tailed file and the fit is perfect. Mech confirmed what Cycle/Recycle said about fit and function. I don't know how to explain the design without the o-ring but a rubber area mates up withe the motor intake as part of its design.

Richard
Richard

[gwhunran]

update

I almost have the bike fixed to my satisfaction. Thanks to Jeff at Z1 Enterprises I was able to eliminate one possible cause of my #3 header being cooler. I had recently installed a Dyna-S ignition, Dyna Coils, and new Dyna plug wires. I got the Dyna-S and wires at Z1 Enterprises. I did not have the cool header before installing the parts. Jeff was good enough to send me a replacement set of wires. I thought he was sending me some known good used wires to troubleshoot with. I was pleasantly surprised to get a new set of dyna wires in the mail.

I changed out the number three plug wire, no joy, still had cool pipe. I then went back into the timing and still had 1&4 dead on but I wasn't happy with 2&3, and couldn't get it perfect with throughout the range of adjustment with the pick-up, so I went back to the gross adjustment on the plate and moved it, and then readusted 1&4, then was able to get 2&3 to be perfect. Still had cool #3 header.

I decided it was time to take the plunge and tear all the carbs down to "parade rest" and clean them using the Dip, then rinsing, scrubbing, and poking, and air blowing. I then replaced the o-rings from a R. Barr kit. I even managed to put it all back together and reinstall it on the bike without breaking anything, and it even cranked right up, but would only run with the choke engaged until I fiddled with the air screws some. Then I synced with the morgan carbtune. Now all the headers are nice and hot. I still haven't got the carbs all adjusted perfectly(air/fuel mix), but I am pleased with what I accomplished. I wasn't too confident before I turned the key.

Note: I moved the spacer on the needle jets to the next to last richest position due to Keith K's prior suggestion that the dead middle postion might not be rich enough. Don't know yet if its right, not enuough riding yet.

The bike continues to be pretty powerful. Getting into it pretty hard, it lifts the front wheel several inches going from 1st to 2nd, and from 2nd to 3rd. I didn't know the old bike still had it.