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1978 R100/7 Flat top Carburetor Rebuild

After a warm up run, and synchronizing the carbs at idle (and leaving the idle mixture screws at the recommended setting: 1/2 turn), I still get some popping, during decelleration. .

The 1/2 turn out of the idle mixture screw is merely a starting point. Try to isolate which carb is doing the popping and then come OUT perhaps 1/8 of a turn on the mixture screw.

While you have your sync device on, you are adjusting your idle with the mixture screws to where they run the best with the idle screw set for the speed or RPM? Turn the screw in till the cylinder falls off a bit, then back out to where it runs the best, then the plus 1/8 turn refered to above.........I DO NOT ALWAYS DO THIS TURN THOUGH........I wait for if it shows up in a test ride......

A downgrade at idle really is a good place to check this out. My driveway/road is 1/2 mile long on a 12 to 18 degree grade. It really tells me when I have things spot on in relation to the no throttle popping situation..............

One will have a great sync and then bang zoom on the test ride this popping shows up and one just pulls over, gets out a small screwdriver, makes the small adjustment to the idle mix and that big smile grows even wider.......God bless.......Dennis
 
One will have a great sync and then bang zoom on the test ride this popping shows up and one just pulls over, gets out a small screwdriver, makes the small adjustment to the idle mix and that big smile grows even wider.......God bless.......Dennis
Ah, okay...Man, this learning curve is sorta steep for a first timer....idle mixture screws, throttle adjustment screw, throttle cable adjuster...float level... Why the hell can't I just put my shiny restored carburetors and just RIDE the damn thing! ha ha ha...! Well, I know I'll get it. I've read all the advice, but just like riding a bike I'm just gonna have to tinker and tinker until it clicks in my head. "Monkey skills" we used to call it in aviation...muscle memory. Like adjusting the valves yesterday: that was quick and relatively easy because I've done it quite few times now. I WAS able to get the popping to go away for a bit today fiddling with the cables (turns out the right one was slightly twisted and I relieved the pressure)...
Thanks again, everyone!
 
Now what?

The "float parallel to the body" setting might be a starting point, but Dennis referred to the proper way. You want a certain height of fuel in the bowl. Fill the bowl, turn off the petcock, and then drop the bowl. Snowbum says to measure the height of the gas right in the center of the bowl. For the 32 mm carburetors, use 24 mm fuel height.
For the 40 mm carburetors, use 28 mm fuel height.

DSC_0007-1.jpg


DSC_0001.jpg


I've checked the valves...The float level is 24mm using the method mentioned above...the carbs have been synchronized both at idle and at 3000 rpm.
None of this has any effect on the annoying burbling backfire coming out of the bike. I cannot isolate which side either. it seems to be coming out of both sides.
One note: this was NOT happening before I rebuilt these carburetors, so it has to be something I changed, or did not adjust, I'm thinking. The needle height is the exact same as before...the innards are brand new and clean.....

What now?
 
Kurt,

I tend to agree with the previous posts...

Try turning each one of your idle mixture jets clockwise about 2 screwdriver blade widths. The idle mixture srew is the one under the carb and right next to your vacuum take-off port with the small screw and fiber washer. Sounds like you may have a bit of a rich mixture. I like to adjust my idle jets to the point where the cylinder just begins to stumble or reduce in rpm, then back off the idle mixture jet turning counter-clockwise only enough for the idle to pick up, about an 1/8th of a turn. You'll get it! Takes a little time and patience. Make small adjustments at one time.

Make sure the bike is fully warmed up from about a 10 mile ride.

Are your air intake tubes sealing well? While the bike is idling take some brake cleaner or carb cleaner and spray it on the ends of the tubes around the clamp area. Does the idle change when you do this?

Let us know how it turns out.
 
Check the timing?

Recheck the idle mixture screw.

Beyond that, it's timing and tight connectors between carb and head.

Did you recheck the timing? Then follow Kurt and Tom's advice on setting the idle mixture screws. Mine was doing a bit of "popping" after my rebuild, rechecked everything, starting with the timing, valves, carb adjustment and idle mixture per the Bing book. The left carb idle mixture screw was off a bit, causing that one to run rich. Follow the procedure in your Bing manual - should do the trick, unless you have an air leak as mentioned above.

Just a thought.
 
Thanks, Mike/Don

Okay guys, I'll try the idle mixture again, and Mike, I'll try the carb cleaner experiment. The air intake tubes are brand new, as well as the clamps, so I didn't do the "fine toothed Comb" inspection on those, assuming brand new parts and tightened clamps do the trick. (There's that word...."assume"!! Always gets you in trouble, doesn't it?).
Don, the timing is the electronic Brandsen Mark III unit, and I didn't mess with the sensor at all: left the timing chain cover on for my restoration, and saved the timing chain for another garage interval in the future. So once again...I'm Assuming! That the timing is still fine. Pretty confident of that assumption because the bike did not backfire before I rebuilt the carbs.
I would say I'm skeptical, because I spent about two minutes with a warmed up, synchronized bike fiddling with these screws, bringing them down 1/8th of a turn each time, bringing them up and 1/8th each time, and revving the throttle, after each turn, seeing no change whatsoever in the burble. But I also know I tend to get like a bull in a china shop when I get frustrated. Will try again after the weather clears here in Southern California, and I can get her out on the road to warm her up...
http://www.youtube.com/watch?v=-pyC7WnvLT4
 
Kurt,

I tend to agree with the previous posts...

Try turning each one of your idle mixture jets clockwise about 2 screwdriver blade widths. The idle mixture srew is the one under the carb and right next to your vacuum take-off port with the small screw and fiber washer. Sounds like you may have a bit of a rich mixture. I like to adjust my idle jets to the point where the cylinder just begins to stumble or reduce in rpm, then back off the idle mixture jet turning counter-clockwise only enough for the idle to pick up, about an 1/8th of a turn. You'll get it! Takes a little time and patience. Make small adjustments at one time.

Make sure the bike is fully warmed up from about a 10 mile ride.

Are your air intake tubes sealing well? While the bike is idling take some brake cleaner or carb cleaner and spray it on the ends of the tubes around the clamp area. Does the idle change when you do this?

Let us know how it turns out.

No effect whatsoever. I tried small turns, tried leaner than 1/2 a turn, richer than 1/2 a turn....tried 1 whole turn (which the Bing book recommends for the other carbs that are similar to mine)...Nothing changes the popping sound. Also tried carb cleaner on the intake tubes...no effect.
Marc said it might have something to do with the fact that I don't have standard exhausts on the bike...could that be a factor? These are the aftermarket non-stainless steel pipes that have the end opened up a bit more than standard, it looks like.

I would continue with the idle mixture theory, but there is absolutely no change in the symptom no matter what I do there...the popping sound on reduced throttle is consistent throughout the troubleshooting.
DSC_0064-3.jpg
 
Sorry that it is just going on and on. How is it running besides the popping?
I do like the color of your exhaust. Is the other that color? That light grey is what one is after and indicates a good mixture. By chance are your plugs a tan to brown color?..........

For me, The mixture screw is a definate cause as outlined above; but knowing YOU, I beleive you when you say you have tried to fix it and the air screw is not your problem.........ON AND ON.......My driveway is 1/2 mile long up a mountain and down the other side. The slope is 12 to 18 degrees. The popping for me, really shows up here. Anyway, going down hill, if I just crack the throttle barely without effecting engine speed, I can get that popping. If I just roll off that 1/32 of a turn on the throttle and let it idle it goes away..........Works for me.......Other than that........I just ride.....Kinda like my 5th wife: beautiful, fantastic cook, could mmmmm do fantastic things with that great body; but the mouth just had to be ignored..........God bless Bud.........Dennis
 
Not turns!

No effect whatsoever. I tried small turns, tried leaner than 1/2 a turn, richer than 1/2 a turn....tried 1 whole turn (which the Bing book recommends for the other carbs that are similar to mine)...

Kurt, NOT turns, screwdriver BLADE widths when adjusting the idle mixture.

These are VERY fine adjustments!!

Good luck,
 
The exhaust may have an effect

You mentioned that you have a more open and free flowing exhaust than stock. Less back pressure will affect the way the bike runs and performs particularly with CV carbs. You might even need to put a smaller or bigger idle jet in because of the exhaust and then tune from there.
 
One more suspect...

Dennis/Dan/Mike: Yep, I got it, I'm with ya. I've been turning screwdriver widths, tiny, tiny adjustments and revving between each one. My post didn't really get that across.... I turn on the fans, open the garage door a bit so I don't asphyxiate myself, and just move those infernal screws a tiny bit each time...over and over...
and over....and over.... Did I mention I do this over and over? And the popping continues, just as steady as ever, like a metronome from Hell itself...... But I digress.

Mike V. helped me troubleshoot over the phone last night and I've got two more culprits to investigate. One is the choke lever. Now, back when I put the carbs on the bike, this is how I did it:
1) Ensure the choke lever is closed
2) Ensure choke levers on the carbs are completely in the down position.
3) Tighten up the nuts connecting the cable to the carb
4) Put the carb on the bike
....notice something wrong with that process?
Yep, the choke levers on both carbs were raised just a bit, probably due to the fact that I completely seated the choke lever before the carbs were in position. So, I reconnected the cables and ensured there was some lower play (the bike's choke lever is just a tad open when the carb levers are closed...gives me an actual feel to when the carb levers hit bottom and seat). I started the bike up with fingers crossed...

pop pop pop pop.... The devil is laughing at me, I swear...:banghead

Which leads me to the second...the exhaust. But not that the aftermarket exhaust isn't "tuned" to the carbs, per se, but that there's air leaking into the system. I had seen some blow by when I first restored the bike on the right exhaust at the header/muffler joint, and for those of you who followed my restoration thread...I put the mufflers on the wrong side. So, in the course of swapping them out, I made sure I really tightened the muffler clamp down on the right side. But last night, as I am once again experimenting with the idle mixture screws after I had eliminated the choke levers as a possible cause, I was feeling exhaust squirting out of that joint still. The left exhaust is fine, but the right exhaust is definitely leaking...
Just so happens I swapped the mufflers right around the same time I rebuilt the carbs..

My solution is going to be pulling the muffler tonight, spreading the tube a bit, and inserting a band of aluminum from a coke can to fill the little imperfections that are obviously allowing the gas to get past that clamp.

Any thoughts out there? Hopefully, this little saga will help someone else out there.
 
Kurt,

I'm optomistic. Now that the chokes are completely closed during idle I think we can start the (fine) tuning process. I think what's important to remember here is; through process of elimination - this only started after your 2nd carb rebuild. So we have to revisit the areas that were performed during that time...carbs, exhaust. And from what you tell me the bike runs and performs great through all it's range and circuits. Just popping during decelleration. My recommendation would be to complete that muffler attachment and make sure the individual choke operations are closing and correct as we discussed on the phone last night. Take the bike for a nice spirited ride and let's make the idle and balance adjustments for the carbs together.

If that doesn't solve the problem... (?)

-Mike V.
 
Kurt,

I'm optomistic. Now that the chokes are completely closed during idle I think we can start the (fine) tuning process. I think what's important to remember here is; through process of elimination - this only started after your 2nd carb rebuild. So we have to revisit the areas that were performed during that time...carbs, exhaust. And from what you tell me the bike runs and performs great through all it's range and circuits. Just popping during decelleration. My recommendation would be to complete that muffler attachment and make sure the individual choke operations are closing and correct as we discussed on the phone last night. Take the bike for a nice spirited ride and let's make the idle and balance adjustments for the carbs together.

If that doesn't solve the problem... (?)

-Mike V.

Well, if that don't do it, Zeff65's post above and my neighbor Marc's advice about changing the jets to equal the exhaust might be the next step. However, that probably needs more expertise than I have in my head: and some specific equipment like a dyno and a CO2 and O2 sensor...
Since I have to swing by Dave's place anyway for the transmission, I'll just ask him about it then. But, I'll cross my fingers, and let you guys know tonight what happens with the exhaust...I'm optimistic too.
 
Blue flames...

Well, both mufflers are off, and the popping now is blue flames coming out of the header pipes. Sounds cool though! :laugh
Don't have more time tonight to troubleshoot, but thought I'd let you guys know the mystery continues.
I tried several times to get the joint between the muffler and the header to seal, but no luck there either. even with an old clamp ratcheted down until it almost broke, I can't get the exhaust gas to keep from escaping. But now, that's another problem to solve. The popping still is something to do with the carbs.
 
popping

How are the connections at the crossover pipe? That was leaking on mine and popped till I replaced the headers and the two crossover pipes on my '82 R100.
 
How are the connections at the crossover pipe? That was leaking on mine and popped till I replaced the headers and the two crossover pipes on my '82 R100.

Those connections are clean: no soot or discoloration. The headers and the crossover pipe are brand new and stainless. I'll try exhaust wrap in the joint between the muffler and the header pipe next time, see if that works, and add a spacer between the clamp and the muffler to give the clamp some more umph... Amazing that exhaust gas still comes out of that joint....Of course, a 600$ Visa bill would solve this problem with brand new SS mufflers, but I'm just not there yet!
 
Stuck...

Bike is warmed up, the exhausts are sealed, and the idle mixture screws have been turned a million times....floats are 24mm fuel depth, jets are the same size as the original, all the o-rings are new, no leakage by the cylinder head...
I'm stuck.
Here's a quick video so you can hear that popping...although now it's a bit less pronounced than it was before, it's still very irritating gurgling down the road...
http://www.youtube.com/watch?v=9eHKe4t63Ts
 
Engine noise

Kurt,

I think you should fill her up with fuel, pour in 1/3 can of Chevron fuel injector cleaner (black bottle available at Wally World for ~$5.00) and the remaining 1/3 at each fill up until the bottle is empty), pack for a few days, put your riding gear on, and come on to Colorado!! By the time you get here she will be running GREAT!! When you get here I'll fire up the RS and we will chase each other through the mountains for a few days :banghead. If it isn't cured by then, you will be having so much fun you will NOT care :brow.
 
Bud.........If you don't take Don up on his riding offer, take SOMEBODY up on riding or just get out there. I really hate to hear and see you doing what you are doing in the video to that fine machine.

Ride it. Yes, one can get very anal and obsessive but RIDE IT dont sit there and REV IT............God bless........Dennis
 
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