carb balance with spark plug extenders

[hotwheels22]

hi all,

new owner here with one more question. i just finished sorting a r100gs and actually at the last step had to take it to a mechanic to get the timing set and to balance the carbs.*

i am wondering if anyone would mind walking me through a carb balance with the spark plug extenders from northwoods. i bought these (i don't have a harmonizer) with the idea that if i am in the middle of nowhere i will have a good way to balance the carbs.

anyway, i have done a ton of reading on this and it is time to take a stab at trying this. to /some/ extent i almost think i could ride the bike and tune the carbs by iteratively continuing to turn the mix screw in on the side of the bike that the mirrors are wobbling. anyway, i tried it by ear and i am close but i would like to try the spark plug extenders.

it does seem like there are three different methods for doing this and having the opportunity to discuss it with someone would be super helpful.

thanks in advance.

- jon

*actually i think i was able to get the timing set but i was not able to get the carbs to get the bike to idle. for some reason one side had to be turned out much farther than the other to get them close to balanced and things were sounding somewhat clunky. then i got a big backfire and since i had just done the top end i thought i better bring it in.
anyway, i /think/ that basically i was trying to get the carbs to sound balanced in the garage (which they did not) and that next time i will open the mix screws all the way up to two full turns out and take it out on the road and /then/ balancing the carbs by turning the mix screws in as the engine heats up. not sure if that makes sense but it would also be great to get a little info on how to get the carbs up and running just after you have set the timing, adjusted the throttle and enrichener cables, and set the idle set screw...

 

[dieselyoda]

I am not going to make this difficult but what you want is a shop job, fans, good synchronizer and on she goes. You want a bush fix, pretty easy, pull the plug wire from the opposite cylinder you want to adjust. Make sure the plug wire is grounded. Adjust the idle enrichment screw until you have an idle that stays. Repeat the other side.

Crack the throttle to 3K, adjust the cables until it gets smooth.

That will get you home to have a proper shop job and if it's a proper shop job, you won't need a bush fix.

 

[dennisdarrow]

Not knowing about these extender things you have, Diesel Yoda is pretty much spot on. The only thing I can think of is that perhaps the "proper idle" he says would be, for me, for that one running cylinder, start out with the idle set high enough for it to be running and then back off using the mixture screw and the idle screw to get it running so that it just barely chugs. Or even when you start it, that it will chug just a few revolutions and then die...........

THAT BEING SAID...........Before you do ANY carb adjustments to WARM UP THAT ENGINE by riding it for 10 or 15 miles...............

Then do the above adjustments but with LOTS of ventilation moving across those cylinders. Otherwise this is an all morning affair by: starting, make a very few adjustments, let it cool, adjust some more, then cool and on and on............

 

[20774]

I'll add that with the extenders in place, use long plastic handled screwdrivers on each side. Put the blade end of the screwdriver solidly on the engine fins and then firmly, one at a time, move the shank of the screwdriver against the extender. Note RPM of the non-shorted cylinder, then release the screwdriver shorting. Let engine settle. Repeat shorting on opposite cylinder...note RPM on running cylinder. It's important that you make firm contact with the extenders, moving on/off sharply.

This process is used to set the idle RPM and the throttle cable tension to synch each carb with the other. The idle mixture settings doesn't use the extenders. You turn each idle screw from your starting point to find the spot of maximum RPM for that cylinder and then go an 1/8th turn richer. Starting on one side, turn the mixture screw one direction until the engine begins to stumble. While counting the turns, turn back the opposite direction until the engine stumbles. Find the center between these two points...and go 1/8th turn richer. On your bike (R100GS?), these screws are in a gas circuit, so richer is CCW.

 

[hotwheels22]

I'll add that with the extenders in place, use long plastic handled screwdrivers on each side. Put the blade end of the screwdriver solidly on the engine fins and then firmly, one at a time, move the shank of the screwdriver against the extender. Note RPM of the non-shorted cylinder, then release the screwdriver shorting. Let engine settle. Repeat shorting on opposite cylinder...note RPM on running cylinder. It's important that you make firm contact with the extenders, moving on/off sharply.

This process is used to set the idle RPM and the throttle cable tension to synch each carb with the other. The idle mixture settings doesn't use the extenders. You turn each idle screw from your starting point to find the spot of maximum RPM for that cylinder and then go an 1/8th turn richer. Starting on one side, turn the mixture screw one direction until the engine begins to stumble. While counting the turns, turn back the opposite direction until the engine stumbles. Find the center between these two points...and go 1/8th turn richer. On your bike (R100GS?), these screws are in a gas circuit, so richer is CCW.

hi all,

thanks for the great help. Kurt can I just walk through the this a little more?

i have "mixture screw" (points straight up with head facing down) and where CW leans the mix and CCW richens the mix. I also have an "idle stop screw" (bing just calls this an "idle screw") which faces at an angle a bit and simply keeps the butterfly cracked open a little bit to set idle.

0. use fans for first couple of attempts.
1. engine off, pull cap on HT leads, place plug extenders on both plugs, replace HT leads.
2. start bike.
3. place long handles screwdriver against fin and short out one side while hearing how the other side is running. INCREASE or DECREASE mixture screw on /non-shorted/ side (?) to get it to a point where it it is basically running the fastest and cleanest
4. then one method is to turn mix screw in on that side until the engine stumbles and once you find that spot turn mix screw half way out again (between the two) to get that side set.
5. then do the same for the other side.
6. try not to let engine die and simply restart bike if it does.

A. do I try to set the idle /before/ I do this sync but after the bike is warmed up or set idle /after/ carbs are synced? all this is done at idle so I would assume setting the idle up correctly would be important but I'm not sure...
B. am I correct in thinking the spark plug extenders are very helpful mostly because it is hard to do this by ear when you have two sides of the engine working.
C. am I correct in thinking that for a newbie it is also a good idea to do a final check by shorting out each side to see that they die at roughly the same time? this way of one runs longer than the other with the screwdriver shorting it out you know you have one side too rich?
D. have you heard of some riders who set the mox screw at "lean best idle" and just get the engine side running smoothly, add an extra 1/8 turn and call it a day?

thanks and big apologies if i butchered any of that. I read up on it a lot and just having a brief conversation will let me get on it with confidence.

- jon

 

[James.A]

hi all,... with the idea that if i am in the middle of nowhere i will have a good way to balance the carbs....

It seems to me that if the bike got you to "the middle of nowhere" it would be highly un-likely that you would need to balance the carburetors. Still, knowing how to do these things is valuable knowledge.

 

[20774]

0. use fans for first couple of attempts.
1. engine off, pull cap on HT leads, place plug extenders on both plugs, replace HT leads.
2. start bike.

OK.

3. place long handles screwdriver against fin and short out one side while hearing how the other side is running. INCREASE or DECREASE mixture screw on /non-shorted/ side (?) to get it to a point where it it is basically running the fastest and cleanest
4. then one method is to turn mix screw in on that side until the engine stumbles and once you find that spot turn mix screw half way out again (between the two) to get that side set.

No shorting is required for setting idle mixture. You should be able to turn the mixture screw CW and CCW to find the stumble points. Then find the middle and enrichen by 1/8th turn.

5. then do the same for the other side.
6. try not to let engine die and simply restart bike if it does.

OK

A. do I try to set the idle /before/ I do this sync but after the bike is warmed up or set idle /after/ carbs are synced? all this is done at idle so I would assume setting the idle up correctly would be important but I'm not sure...

First thing is to put the idle mixture and idle speed in their nominal settings...the Bing manual has the number of turns for the mixture screw. You want slack in your throttle cables so that cable tension is not masking the initial synch settings. Once in the nominal settings, go for that 20-25 minute ride...the bike should run, maybe not the best, but should be reasonable. Then pull in front of the fans and begin the synching process.

B. am I correct in thinking the spark plug extenders are very helpful mostly because it is hard to do this by ear when you have two sides of the engine working.

Some can do it by ear...I never could. Duane Ausherman talks about going behind the bike and putting your ears between the exhaust pipes and using your ears to hear the differences. You'll need a helper unless your arms are 6 feet long!

C. am I correct in thinking that for a newbie it is also a good idea to do a final check by shorting out each side to see that they die at roughly the same time? this way of one runs longer than the other with the screwdriver shorting it out you know you have one side too rich?

My goal is not to have the engine die when one cylinder is shorted. This means that your idle speed (not lean/rich) is too low. Dennis had a good suggestion which is to have the engine run on cylinder at a given RPM...make them the same RPM on one cylinder. When both cylinders are working together, the idle speed might be too high...just turn each idle speed screw down exactly the same until you reach your desired idle RPM...I shoot for 1000-1100.

D. have you heard of some riders who set the mox screw at "lean best idle" and just get the engine side running smoothly, add an extra 1/8 turn and call it a day?

Have not heard that.

There are three aspects to carb synching:
- idle mixture
- idle speed
- cable tension

The first two interact with each other, so you may have to go through the steps multiple times.

You haven't mentioned synching the throttle cables. They need to pull consistently to get the best performance and smoothness...after all you spend >95% of your time on throttle, not idling. Once you've completed the first two steps, you need to elevate the engine RPM, say 1500-2000, and then short out a cylinder. Watch the RPM. If you have a difference in RPM, always (I stamp my foot!) slow the fast cylinder down. The reason you loosen tension is that you don't want affect the slack you had during the first synching steps. If you increase tension, you might reduce the slack and then your bike won't idle well.

 

[hotwheels22]

OK.

No shorting is required for setting idle mixture. You should be able to turn the mixture screw CW and CCW to find the stumble points. Then find the middle and enrichen by 1/8th turn.

OK

First thing is to put the idle mixture and idle speed in their nominal settings...the Bing manual has the number of turns for the mixture screw. You want slack in your throttle cables so that cable tension is not masking the initial synch settings. Once in the nominal settings, go for that 20-25 minute ride...the bike should run, maybe not the best, but should be reasonable. Then pull in front of the fans and begin the synching process.

Some can do it by ear...I never could. Duane Ausherman talks about going behind the bike and putting your ears between the exhaust pipes and using your ears to hear the differences. You'll need a helper unless your arms are 6 feet long!

My goal is not to have the engine die when one cylinder is shorted. This means that your idle speed (not lean/rich) is too low. Dennis had a good suggestion which is to have the engine run on cylinder at a given RPM...make them the same RPM on one cylinder. When both cylinders are working together, the idle speed might be too high...just turn each idle speed screw down exactly the same until you reach your desired idle RPM...I shoot for 1000-1100.

Have not heard that.

There are three aspects to carb synching:
- idle mixture
- idle speed
- cable tension

The first two interact with each other, so you may have to go through the steps multiple times.

You haven't mentioned synching the throttle cables. They need to pull consistently to get the best performance and smoothness...after all you spend >95% of your time on throttle, not idling. Once you've completed the first two steps, you need to elevate the engine RPM, say 1500-2000, and then short out a cylinder. Watch the RPM. If you have a difference in RPM, always (I stamp my foot!) slow the fast cylinder down. The reason you loosen tension is that you don't want affect the slack you had during the first synching steps. If you increase tension, you might reduce the slack and then your bike won't idle well.

hi kurt. many, many thanks for this.

i think i almost get this. the terms are maddening though and the bing manual does not clear it up well. and referring to their diagram is fine but there is no good name associated with some of them. anyway, this may be part of the issue i have been having.

when you say "idle speed screw" and "idle mix screw" you are talking about the one (?) slotted screw at the bottom that is visible when the float bowl are on. i have been calling this just a "mixture screw" with the understanding that there aren't really any other /mixture/ screws where i can adjust mixtures (can you correct me if i am wrong)? also, you are calling the "idle speed screw" (what i think i am calling the "idle stop screw") and this is the one that turns and acts as a stop for the throttle cable so that the butterfly valve is propped open a tad (at idle), yes?

if so - you are saying that setting the "idle mixture screw" should basically be a trivial process (CCW by 0.5 turns on the 32 mm carbs i think) then find the stumble point, then the best mix and set it mid-point between the two? then i set the "idle speed screw" (bing says to just contact the stop i think and to then turn in by half a turn to just prop open the butterfly).

can i just ask what you would say to do if after doing that the two cylinders sounded radically different in terms of performance? i made the mistake of trying to get the idle mixture screws adjusted at this point (before a ride) by - well i /guess/ i was trying to get them to "best lean mix" or something where they were both revving "clean" with no radical difference between the two. and ended up at a half turn out on LEFT side and then about two turns out on the RIGHT side to get them to sound close. the default settings sounded really pretty bad.

then at that point because the default settings didn't sound good at all i was opening up the RIGHT side carb and checking for blocked passages and then replacing the IDLE JETS. then after having almost got there with all the work i had to take it in to a shop about an hour from here because she started backfiring and i got spooked.

anyway, when i get to shorting these things what do you mean when you say "My goal is not to have the engine die when one cylinder is shorted. This means that your idle speed (not lean/rich) is too low." are you saying that at whatever you have for settings for idle mixture screw and for idle speed screw that they should be close and that you basically want to have the engine ALMOST die when you are shorting one side and then the other?

and you increase the idle mixture screw when it somehow sounds like it is dying from not enough fuel and you increase the idle stop screw when it sounds like it is dying from not enough RPM at idle, or something? i mean, if i wanted to understand it and hear it i am basically trying to get the engine on one side to "purr" like the engine on the other side to a large extent since they are really acting independently and will sound different until you adjust them for balance...?

THANK YOU

 

[20774]

For me, "idle mix screw" and "mixture screw" are the same. There's only one screw that controls the mixture which happens to be in the idle regime of the carb. Note there are three overlapping regimes of the carb - idle, mid-range, and wide open throttle - the Bing manual describes them.

"Idle speed screw" and "idle stop screw" are the same. It does act on a stop but controls the speed at idle.

"...you are saying that setting the "idle mixture screw" should basically be a trivial process...". Yes, it can be that simple.

"can i just ask what you would say to do if after doing that the two cylinders sounded radically different in terms of performance?" I'm not really following the "best lean mix" description...you don't want the carb to run lean. In the situation you found yourself, the best thing to do is start all over and go through the process again.

I said "my goal is not to have the engine die when one cylinder is shorted." That was probably pretty confusing. What I'm saying is that IMO if you proceed to balance the carbs so the engine stops quickly when the either cylinder is shorted, when both cylinders are back running again, I think the RPM is going to be too low, probably below 1000 RPM. The oil splash falls off a little bit when the engine is just barely ticking over. Best to keep the idle above 1000 RPM. On the /2 machines with no tach, this is about all you could do. Short a cylinder and count the number of beats before it stops. Do the same for the other side.

I wouldn't overthink this too much. You do have essentially two engines connected by a common crankshaft. You want each to pull at the same level as the other one. Just do the individual steps of synching - mixture, idle speed, throttle cable tension. If you have the best mixture for each side, the idle speed drops to the same level when cylinders are shorted, and the RPM is the same when shorting under slight cable tension, you should have the best balanced engine/carbs.

 

[hotwheels22]

For me, "idle mix screw" and "mixture screw" are the same. There's only one screw that controls the mixture which happens to be in the idle regime of the carb. Note there are three overlapping regimes of the carb - idle, mid-range, and wide open throttle - the Bing manual describes them.

"Idle speed screw" and "idle stop screw" are the same. It does act on a stop but controls the speed at idle.

"...you are saying that setting the "idle mixture screw" should basically be a trivial process...". Yes, it can be that simple.

"can i just ask what you would say to do if after doing that the two cylinders sounded radically different in terms of performance?" I'm not really following the "best lean mix" description...you don't want the carb to run lean. In the situation you found yourself, the best thing to do is start all over and go through the process again.

I said "my goal is not to have the engine die when one cylinder is shorted." That was probably pretty confusing. What I'm saying is that IMO if you proceed to balance the carbs so the engine stops quickly when the either cylinder is shorted, when both cylinders are back running again, I think the RPM is going to be too low, probably below 1000 RPM. The oil splash falls off a little bit when the engine is just barely ticking over. Best to keep the idle above 1000 RPM. On the /2 machines with no tach, this is about all you could do. Short a cylinder and count the number of beats before it stops. Do the same for the other side.

I wouldn't overthink this too much. You do have essentially two engines connected by a common crankshaft. You want each to pull at the same level as the other one. Just do the individual steps of synching - mixture, idle speed, throttle cable tension. If you have the best mixture for each side, the idle speed drops to the same level when cylinders are shorted, and the RPM is the same when shorting under slight cable tension, you should have the best balanced engine/carbs.

OK. thanks for the time letting me get that sorted. i think i can tackle it.

CHEERS and thanks

jon

 

[cycleman2]

It would be a lot easier if you had somebody near you show you how to do this. Its not complicated.

A big thing to keep in mind that if your carbs are set at one altitude, like close to sea level, then you go for a ride in mountain passes, like Colorado, where the elevation is much higher, the bike will not idle as smooth as it did at sea level and likely be down on power. Humidity, temp, elevation, different gas etc all affect the carbs. So to make a long story short. When on the road, unless it won't run at all you are usually better off to leave things alone, because the next hour, next day it will run fine. You can really chase your tail around on this stuff, and like others said if the bike got you into the bush it should get you out.

Also be very careful about shorting plugs on electronic equipped bikes. If not grounded properly, you can destroy the ignition. Pulling carb boots and shorting them worked fine on the points equipped bikes but can cause issues on electronic equipped bikes.

 

[PAS]

CAUTION you dont kill your electronic ignition! Better do some research. Just as stated in the above post!

 

[20774]

CAUTION you dont kill your electronic ignition! Better do some research. Just as stated in the above post!

It's not an issue as long as you are firm and steady making the short to the engine case. Just give the spark energy a path to ground and all will be fine.

 

[hotwheels22]

It's not an issue as long as you are firm and steady making the short to the engine case. Just give the spark energy a path to ground and all will be fine.

hi kurt,

it is sort of interesting the various methods for setting up the carbs. each seem to do it different enough to have different results (cutter, bing, northwoods etc).

on the plug extenders, the issue is to make sure that the screwdriver stays firmly planted against the fins so that when you do contact the plug to short - it goes directly to ground, yes? otherwise you do risk allowing it to take an alternate (harmful) path?

jon

 

[hotwheels22]

It would be a lot easier if you had somebody near you show you how to do this. Its not complicated.

A big thing to keep in mind that if your carbs are set at one altitude, like close to sea level, then you go for a ride in mountain passes, like Colorado, where the elevation is much higher, the bike will not idle as smooth as it did at sea level and likely be down on power. Humidity, temp, elevation, different gas etc all affect the carbs. So to make a long story short. When on the road, unless it won't run at all you are usually better off to leave things alone, because the next hour, next day it will run fine. You can really chase your tail around on this stuff, and like others said if the bike got you into the bush it should get you out.

Also be very careful about shorting plugs on electronic equipped bikes. If not grounded properly, you can destroy the ignition. Pulling carb boots and shorting them worked fine on the points equipped bikes but can cause issues on electronic equipped bikes.

aok. thanks. hope to make out ok and point taken on the altitude etc

 

[hotwheels22]

CAUTION you dont kill your electronic ignition! Better do some research. Just as stated in the above post!

got it. thanks for the heads up.

 

[cycleman2]

CAUTION you dont kill your electronic ignition! Better do some research. Just as stated in the above post!

True as long as the ground is good, otherwise you will likely fry it. That's all that was said in my post.

 

[20774]

on the plug extenders, the issue is to make sure that the screwdriver stays firmly planted against the fins so that when you do contact the plug to short - it goes directly to ground, yes? otherwise you do risk allowing it to take an alternate (harmful) path?

It's relatively straight forward. Put the blade of the screwdriver onto the engine in a good spot, such that you can easily swing the shank of the screwdriver onto the extender. That's the key...always have the blade grounded and move the screwdriver shank on and off the extender. That way, the spark will readily travel down the screwdriver to ground...that's the path of least resistance.

 

[hotwheels22]

True as long as the ground is good, otherwise you will likely fry it. That's all that was said in my post.

thanks again. it's a helpful reminder....

 

[hotwheels22]

It's relatively straight forward. Put the blade of the screwdriver onto the engine in a good spot, such that you can easily swing the shank of the screwdriver onto the extender. That's the key...always have the blade grounded and move the screwdriver shank on and off the extender. That way, the spark will readily travel down the screwdriver to ground...that's the path of least resistance.

ok, got it. thanks