Post your favorite carb adjustment method.

[Dark Jedi]

I adjust mix on my carbs by idle. it is an arduous process, but works well.

Adjust fuel/air to fastest idle speed on the #2 carb. Reduce idle back to normal, and tweak again, until it all works out. The syncronize the rest to #2.
Rinse, repeat until it all works out.

How do you do it?

[Detman101]

For my bike....

Start at 1/2 a turn out and adjust from there based on the way the exhaust smells.

I can't read plugs too well so that is the only way i know.

:?
Dm of mD

[AOD]

reading plugs is like reading this forum, once you know how to do it.

[Anonymous]

previously, i would have wanted to put the bike on it's centerstand, disconnect the battery, remove tank, then pull the carbs, and find a decent shop press, and crush the f^(*$#'s!!! But i got a clymers, and the carb-cleaning link and now she runs peachy....(is there anyway to switch a 78 gs750e to EFI?)

[KEITH KRAUSE]

Re: Post your favorite carb adjustment method.

I adjust mix on my carbs by idle. it is an arduous process, but works well.

Adjust fuel/air to fastest idle speed on the #2 carb. Reduce idle back to normal, and tweak again, until it all works out. The syncronize the rest to #2.
Rinse, repeat until it all works out.

How do you do it?

I set all four carbs for the highest rpm's and then turn the idle adjuster knob to the correct idle rpm.

[Anonymous]

Through prayer and fasting I beseech the great Earl and whatever he saith shall be right in our eyes.

8O 8O 8O

Seriously, I take Earl's tuning tips. I started with all mixture screws at 2.5 turns out, as I couldn't find the supposed sweet spot. I balanced each throttle for 10 in Hg, starting with #3, #2, #1, #4. Return idle to 1100 rpm with stop screw. Ride for 20 mins. Let bike cool. Check spark plug colors. Adjust mixture screws for the Earl-prescribed slightly rich condition. Repeat final tweaking if necessary. Recheck. Idles great. Flies well. Sounds oooohh so nice.

I did this about a week ago. Got rid of my popping on decel. Haven't checked whether I still have the richness at full throttle, but I'll check it sometime and start another thread.

Michael

[Detman101]

Aye!!! Earlfor KNOWS his stuff!

I went through 3 weeks of trying to get my bike running. With his advice it took 2 days to get right.


Dm of mD

[KEITH KRAUSE]

Through prayer and fasting I beseech the great Earl and whatever he saith shall be right in our eyes.

8O 8O 8O

Seriously, I take Earl's tuning tips. I started with all mixture screws at 2.5 turns out, as I couldn't find the supposed sweet spot. I balanced each throttle for 10 in Hg, starting with #3, #2, #1, #4. Return idle to 1100 rpm with stop screw. Ride for 20 mins. Let bike cool. Check spark plug colors. Adjust mixture screws for the Earl-prescribed slightly rich condition. Repeat final tweaking if necessary. Recheck. Idles great. Flies well. Sounds oooohh so nice.

I did this about a week ago. Got rid of my popping on decel. Haven't checked whether I still have the richness at full throttle, but I'll check it sometime and start another thread.

Michael

OK. You're talking about a carb sinc followed by a mixture screw sinc. The topic asks how do you adjust the mixture screws by idle. You're supposed to adjust the mixture screws before you sinc. This is even in the instructions for many carb vacuum tools.
And when you adjusted the screws for a slightly rich condition, why did you wait? Why not do this adjustment first, since you ended up doing it as part of a plan anyway? I just don't understand this procedure.

[earlfor]

OK Keith, I'll give it a shot at explaining why I do it as I do. Any way one can accomplish the task with the desired results is fine with me, so lets just call this my OPINION through deductive reasoning, a dash of experimentation and a sprinkle of practice. :-)

Certainly, you can adjust the mixture screws before you synch, however, it is not possible to adjust them correctly before you synch. You can only get them in the ballpark. The reason is that mixture screws do not control the mixture directly. Every range/operating stage in the carb is controlled by one thing. That is induction velocity.

Mid and upper range mixture is controlled by needle, slide position and jet size. It can be implemented to a small degree with the mixture screws, but that is not the purpose of the mixture screws.

At idle rpm 1000-1200, the mixture screws are effective and being applied in their intended operating range. I initially set mixture screws only if the mixtures at idle are so far out that I cannot maintain a 1000-1200 rpm idle with the idle control knob. If I have torn down a carb stack for cleaning, on reassembly, I will usually arbitrarily set the mixture screws in mid adjustment range so the engine will run at idle. Normal range is from 0 to 3 turns out (more or less) I just set 1 1/2 to start with.

I then synch the vacuums keeping the rpm exactly the same between each adjustment to vacuum. If rpm varies, then velocity will vary, and if velocity has varied, then venturi effect has changed and consequently fuel flow has changed. This makes it impossible to meter fuel flow accurately with a mixture screw before vacuum is stabilized.

Also, it appears that the designed flow characteristics (stoichiometric ratio) of the Mikuni carbs is matched to the stock jetting when flow rates are between 8 in Hg and perhaps 16-18 in Hg. The higher ranges produce more fuel flow and give richer mixtures which will provide more power, until a ratio of aproximately 10-12:1 is reached. At that point, plugs will start fouling. SO........... I pick intake velocity/vacuum for an rpm and synch to that. Once a uniform vacuum level is set, then I finalize the mixture screw settings. I determine highest rpm just like everyone else, then I richen them up 1/4 turn or so. My reason for that is that on startup, if the idle mixtures are at the upper edge lean, it makes the engine a little bit more peaky to start. I dont like to have to use choke, because choke is excessively rich and constant choke use fouls plugs (my opinion again)
My bike is set up such that I do not need the choke at all. I can leave it for a week untouched, turn the pingel on, wait 15 seconds for the float bowls to top off and touch the starter button. It starts in less than 1 second, immediately idles at 1100 rpm and will take the throttle being snapped to wide open instantly. No hesitation, no pop, just perfect response.

Earl

OK. You're talking about a carb sinc followed by a mixture screw sinc. The topic asks how do you adjust the mixture screws by idle. You're supposed to adjust the mixture screws before you sinc. This is even in the instructions for many carb vacuum tools.
And when you adjusted the screws for a slightly rich condition, why did you wait? Why not do this adjustment first, since you ended up doing it as part of a plan anyway? I just don't understand this procedure.

[Detman101]

OK Keith, I'll give it a shot at explaining why I do it as I do. Any way one can accomplish the task with the desired results is fine with me, so lets just call this my OPINION through deductive reasoning, a dash of experimentation and a sprinkle of practice. :-)

Certainly, you can adjust the mixture screws before you synch, however, it is not possible to adjust them correctly before you synch. You can only get them in the ballpark. The reason is that mixture screws do not control the mixture directly. Every range/operating stage in the carb is controlled by one thing. That is induction velocity.

Mid and upper range mixture is controlled by needle, slide position and jet size. It can be implemented to a small degree with the mixture screws, but that is not the purpose of the mixture screws.

At idle rpm 1000-1200, the mixture screws are effective and being applied in their intended operating range. I initially set mixture screws only if the mixtures at idle are so far out that I cannot maintain a 1000-1200 rpm idle with the idle control knob. If I have torn down a carb stack for cleaning, on reassembly, I will usually arbitrarily set the mixture screws in mid adjustment range so the engine will run at idle. Normal range is from 0 to 3 turns out (more or less) I just set 1 1/2 to start with.

I then synch the vacuums keeping the rpm exactly the same between each adjustment to vacuum. If rpm varies, then velocity will vary, and if velocity has varied, then venturi effect has changed and consequently fuel flow has changed. This makes it impossible to meter fuel flow with a mixture screw before vacuum is stabilized.

Also, it appears that the designed flow characteristics (stoichiometric ratio) of the Mikuni carbs is matched to the stock jetting when flow rates are between 8 in Hg and perhaps 16-18 in Hg. The higher ranges produce more fuel flow and give richer mixtures which will provide more power, until a ratio of aproximately 10-12:1 is reached. At that point, plugs will start fouling. SO........... I pick intake velocity/vacuum for an rpm and synch to that. Once a uniform vacuum level is set, then I finalize the mixture screw settings. I determine highest rpm just like everyone else, then I richen them up 1/4 turn or so. My reason for that is that on startup, if the idle mixtures are at the upper edge lean, it makes the engine a little bit more peaky to start. I dont like to have to use choke, because choke is excessively rich and constant choke use fouls plugs (my opinion again)

My bike is set up such that I do not need the choke at all. I can leave it for a week untouched, turn the pingel on, wait 15 seconds for the float bowls to top off and touch the starter button. It starts in less than 1 second, immediately idles at 1100 rpm and will take the throttle being snapped to wide open instantly. No hesitation, no pop, just perfect response.

Earl

Amazing...simply amazing. God I wish you lived closer.


Dm of mD

[earlfor]

I'm only as far as your keyboard. :-) :-)

Earl

God I wish you lived closer.


Dm of mD

[Nerobro]

previously, i would have wanted to put the bike on it's centerstand, disconnect the battery, remove tank, then pull the carbs, and find a decent shop press, and crush the f^(*$#'s!!! But i got a clymers, and the carb-cleaning link and now she runs peachy....(is there anyway to switch a 78 gs750e to EFI?)

yes... Off the top of my head I can think of three or four sane methods.

First, is take the EFI off of another bike. I would reccomend another 4cyl bike, but that's the only "reccomendation" I'd make. The closer the EFI bike's engine is to the construction of the GS the better. But if you don't mind hard starting you could get away with even using harley EFI and using batch injection.

the biggest deal is getting the injectors matched properly. So long as you're running the right injector "any" Efi will do. (it's just a matterof dumping the right amount of fuel)

Now, there are also aftermarket efi systems available. Expect to pay upwards of two grand for a setup that will run a 4cyl bike.

There is also the option of DIY-EFI. Which is an open source project that is actually running several vehicles right now. So it's proven, but will take a lot of elbow grease to work it out.

You could also make your own. With some clever circutry you could probally get away with a 555 timer, a tps, and a crank trigger. (you could drive that off the camshaft ;-) or something convienant like that, and yes this thought has crossed my mind)

If you dont' want EFI, mechanical FI is available too. About the only thing that imediately comes to mind for me is somehow adapting chevys 50's FI system to the bike... it "should" work ;-)

and now that I'm completely off topic, I'll conclude my post!

[Anonymous]

Question About the Idle Speed Screw

Earlfor, Is there a starting point for the throttle stop screw to begin these adjustments. Should it be all the way back (throttles completely shut). Or open some? thanks, Doug

[earlfor]

Re: Question About the Idle Speed Screw

I find that with the mixture screws set about 1 1/2 turns out, the bike will usually at least start and run. I turn the throttle stop screw in about 3 turns as a starting point. You could find you initially need 5 or 6 turns. That part is flexible. Whatever you need to keep the bike running long enough to start with adjustments. Like the auctioneer said, it aint where you start, its where you end up. :-)

Earl

Earlfor, Is there a starting point for the throttle stop screw to begin these adjustments. Should it be all the way back (throttles completely shut). Or open some? thanks, Doug

[Joe Nardy]

Buy a fuel injected bike (FJR1300), get a Power Commander, do all your tuning with a laptop!