1977 GS750 (now 850 ) VM26SS Carbs / replacement jet question.

[zed1015]

I have no experience with re-jetting where you restrict or decrease air flow at the entrance of a jetting circuit as a way of compensating for increasing air flow because you added free flow filters and a pipe.
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And THAT says it all really.
Why keep insisting that main air jet correctors don't or can't work correctly when you now confess to actually having absolutely zero experience of them ?
Maybe you should apply for a position at Mikuni and see how it goes explaining to them how they ( and other major carburettor manufacturers) have got it so terribly wrong in using the exact same method to rectify the exact same issue for the past 40 years and more.

[KEITH KRAUSE]

I have no experience with re-jetting where you restrict or decrease air flow at the entrance of a jetting circuit as a way of compensating for increasing air flow because you added free flow filters and a pipe.

And THAT says it all really.
Why keep insisting that main air jet correctors don't or can't work correctly when you now confess to actually having absolutely zero experience of them ?
Maybe you should apply for a position at Mikuni and see how it goes explaining to them how they ( and other major carburettor manufacturers) have got it so terribly wrong in using the exact same method to rectify the exact same issue for the past 40 years and more.

I made that statement because I re-jet the right way. I don't practice backwards jetting and that's why I have no experience with it. If you increase air flow through a circuit, you have to equally increase fuel flow. That makes more power, power that can be used safely and not lean/over heat the engine. If you install pod filters that obviously increase air flow, and obviously lean out the mixture, you don't place an air restrictor at some point to try to achieve a proper mixture. If you did, you just defeated the whole reason to install the pods in the first place. The air flow is then back to where it was and you gain zero power. All an engine is, is an air pump. If you increase air flow, you increase power. If you decrease air flow, at any jetting circuit, you lose power somewhere. Would you install pod filters and then wrap them 90% in electrical tape in an attempt to achieve the proper mixture? That's what your air corrector is doing. The circuit, because you've increased air flow and power, now needs more fuel flow to achieve a proper air fuel ratio so you can use that extra power safely. Your air correctors reduce air flow. Reduced air flow equals reduced power. Get it? Would you also install a 4/1 free flow exhaust and then install a restrictive device so restrictive that it now flows the same as the stock exhaust? Again, that's what your correctors do.
And as far as "confessing" to having no experience with air correctors, what experience do you need to understand your air corrector is no more than a restrictor? You don't install an air restrictor when the circuit in this situation needs more fuel flow.
Again, I'll use what works. If it takes a little more work then that's the way it is.
You go ahead and preach your BS to someone else. You're here because you want to make some money and it makes you mad if someone points that out.

[zed1015]

I have no experience with re-jetting where you restrict or decrease air flow at the entrance of a jetting circuit as a way of compensating for increasing air flow because you added free flow filters and a pipe.

I made that statement because I re-jet the right way. I don't practice backwards jetting and that's why I have no experience with it. If you increase air flow through a circuit, you have to equally increase fuel flow. That makes more power, power that can be used safely and not lean/over heat the engine. If you install pod filters that obviously increase air flow, and obviously lean out the mixture, you don't place an air restrictor at some point to try to achieve a proper mixture. If you did, you just defeated the whole reason to install the pods in the first place. The air flow is then back to where it was and you gain zero power. All an engine is, is an air pump. If you increase air flow, you increase power. If you decrease air flow, at any jetting circuit, you lose power somewhere. Would you install pod filters and then wrap them 90% in electrical tape in an attempt to achieve the proper mixture? That's what your air corrector is doing. The circuit, because you've increased air flow and power, now needs more fuel flow to achieve a proper air fuel ratio so you can use that extra power safely. Your air correctors reduce air flow. Reduced air flow equals reduced power. Get it? Would you also install a 4/1 free flow exhaust and then install a restrictive device so restrictive that it now flows the same as the stock exhaust? Again, that's what your correctors do.
And as far as "confessing" to having no experience with air correctors, what experience do you need to understand your air corrector is no more than a restrictor? You don't install an air restrictor when the circuit in this situation needs more fuel flow.
Again, I'll use what works. If it takes a little more work then that's the way it is.
You go ahead and preach your BS to someone else. You're here because you want to make some money and it makes you mad if someone points that out.

You clearly cannot comprehend how main air jets work and you keep calling these air jets mine which they are not.
Instead of continually hijacking other peoples threads to persue this sad little personal vendetta of yours why don't you go do your homework and you might actually learn something or maybe just go join the flat earth society where you should fit right in.
As i've asked previously and you have never given a rational answer to, If they are BS then please explain why Mikuni themselves use them to tune out the same fueling off idle flat spot anomally that occurs on their performance carbs that are designed to run open..
Funnily enough the part number for the Mikuni air jets is BS30/97 so your rantings have actually inadvertently got part of the facts correct.

[KEITH KRAUSE]

It would probably be easier to explain the anomaly going on in your head. You'd fit right in with SpongeBob and Patrick.

[JONJONJON]

Thanks for this. What is the method to bench sync the slides?

Zed likes to believe his air correctors replace the need to raise the jet needle position to achieve a good air/fuel ratio at 1/4 to 3/4 throttle positions on the VM carbs.
Some owners might like the idea of installing a jet at the carbs throat instead of what should be done, which is make the necessary adjustment to the jet needle position.
Free flow pods and exhaust greatly lean out the mixture. Raising the jet needle or replacing it with a needle such as from Dynojet allows more fuel to compensate for more air. Zed's "fix" is instead of increasing fuel to balance out the increased air flow, his air correctors actually reduce/restrict air flow to the jet needle and needle jet. This is his way of compensating for more air flow at the jet needle.....by reducing air flow where it first enters the carb. This not only is backwards jetting, it also compromises proper fuel atomization at the needle jet because now you've reduced the air flow. With less air flow into and around the needle jets several small ports, how can proper atomization be achieved?
I don't post here much anymore but when I see something like this I have to add my two cents. I commented quite awhile ago at another thread and Zed got *@%^$*@%^$*@%^$*@%^$ed off because I prefer to re-jet the way it should be done.
I have no experience with re-jetting where you restrict or decrease air flow at the entrance of a jetting circuit as a way of compensating for increasing air flow because you added free flow filters and a pipe. Trying to be open minded, maybe the final mixture could result in no obvious lean or rich mixture issues such as surging or bogging, and a lot of owners would think their bike is running well, but you won't have a properly increased mixture of both air and fuel and you won't gain the performance you should from those mod's.
I'll stick with what I know works and what makes sense. I have no problem with taking the carbs apart to adjust the jet needles. My '79 GS1000 has run great for 42 years now with V&H 4/1 and K&N ovals and a 1085 kit. I've shared what I know with the GSR since 1999. A lot of other 1000 owners have said the jetting that works for my bike works well for theirs too. 850 and 750 owners have made similar jetting changes and replied their bikes run well.
I'm not going to get into another argument with another member trying to make money so please don't bother.
As for JONJONJON, with quality pods and 4/1 pipe, you do not need to increase pilot jet size. The #15's are fine. Even Dynojet says so in their stage 3 jetting kits. As for stalling at 1,000 rpm's, that's the factory recommended idle rpm and your bike, if in good condition and properly tuned, will idle well at 1,000 rpm's. The pilot circuit WILL need richer adjustments at the pilot fuel screws underneath/engine side. Factory setting is generally around 3/4 turns out from LIGHTLY seated. Try 1 to 1/2 turns out and test. Then follow the "highest rpm method" to adjust your side air screws. Start at 1 1/2 to 2 turns out and make small adjustments in either direction to reach best idle per carb. 1 3/4 to 2 turns out often works as a final setting. Poor idling is often a result of the carbs not being vacuum synched well. You must first carefully manually bench synch the slides, then fine tune them with a vacuum tool. Remember, each time you disturb the jet needles, you must re-synch. Also, to avoid fuel starvation, especially when riding in cross winds or higher speeds, REMOVE the two float bowl vent lines and leave the ports open to breath better. Dynojet recommends this on their stage 3 jetting kits. You'll also need to raise your stock jet needles approximately 2 positions richer and test. The jet needle adjustments are the most work but because the bike is most often operated between 1/4 and 3/4 throttle positions, it's important to jet it right. For the main jets, I have not personally re-jetted an 850 but something close to 125's should work or get you in the right direction. Also, be careful to adjust float levels correctly and never mix up the float needle valves and their valve seats because they wear as a unit and if you don't keep them as a set you'll experience leaking.

[KEITH KRAUSE]

Thanks for this. What is the method to bench sync the slides?

I don't have a factory manual for your exact model. The procedure varies a little compared to a 1000 for example. I'm sure if you search or make a specific topic, someone can help.
Basically, there's a "nick" in the slide that you can use to get the slides APPROXIMATELY in synch. Turn the carbs so the nick faces you, loosen the adjuster holder nuts above of the slide assembly, then slowly turn the adjuster screws to get the slides uniform. Once uniform, tighten the holder nuts. A bench synch in my opinion is only to allow the bike to start up in preparation for a proper vacuum tool synch. Yes, a careful bench synch is better than nothing, but as I found out decades ago, you can bench synch all you want but it's no substitute for a vacuum synch. There's almost always at least one cylinder that will be off compared to the others. The vacuum level even effects the mixture entering that cylinder. One cylinder will run richer or hotter than the others, etc. Once you do a good vacuum synch you'll be amazed at how much smoother the bike idles, cruises, etc.
As for bench synch specifics, there are differences so I can't tell you 100% what you need to know. For example, I believe the factory manual mentions the '77 carbs have a "master" carb that needs to be synched first and you match the others to it. Also, your specific carbs may need to be synched not only for the closed position, but also for the fully opened position. Yes, a slide can be adjusted too far "up" also.
I use a Carbtune vacuum gauge. It works very well and there's no more mercury to deal with. It uses metal rods. It's been awhile since I bought mine but mine was about $110 about 3 years ago. The VM carbs will gradually lose their synchronization especially when ridden hard. I'm guessing the factory manual says to inspect or synch them every 5,000 miles or so? If you keep the bike or expect to have other bikes with multiple cylinders, the vacuum tool will be a solid investment over time. It can be used for 2,3, or 4 cylinders, even fuel injected bikes.
Just be sure after bench synching to adjust the idle control knob that lifts all 4 slides a few turns after you see the tip make contact with the throttle pulley. If the slides aren't up a reasonable amount at start up, the bike won't start or will stall. Warm the bike up fully, use 1 or 2 fans to avoid over heating, then adjust the side air screws using the highest rpm method with a base idle of 1,000 rpm's. Set the pilot fuel screws as I said earlier as a starting point. Vacuum synch on the center stand. Enjoy.