78 GS750 Carb Rebuild - VM 26 (a few questions)

[Forden]

Happy new GS owner here, I’m about to embark on a full clean of my carbs for the first time, and looking for advice on a few points before I break them down completely. I’ve read the sticky threads (and others) here, been watching various videos and grateful for the help (the amount and variety of opinions can be daunting). I’ve ordered a set of O-rings from Barr and need to order at least one replacement pilot jet, for one that broke (I’ll share how I got that out separately in case it helps someone else).

Why I got started with the carbs: bike was running consistently and well enough (as far as I could tell) before, but after I had it running one day, #2 started dumping fuel intermittently out of the breather tube after the engine was off—the root cause of which I figured out (quickly!) was that the petcock valve was not closing properly, so it was dumping fuel into the carbs continuously, at probably about half the rate of the priming setting. BUT I assume #2 float valve was also not closing properly, hence the overflow. So I pulled the bank and after inspecting decided to give them a complete clean and rebuild. Start from a good baseline, right?

I do also plan to check/adjust valve clearances as advised, though that will be a first time for me as well.

Current Setup notes:
--‘78 GS 750, stock VM26 carbs
--Alpha Moto pod filters (I gather a lot of people hate pods, but please don’t judge I inherited them...and everything else on the bike)
--Exhaust: appears stock in configuration but tailpipes are aftermarket (see pics)
--Jets are stock: 102 mains, 15 pilots
--general, pre-breakdown: despite the combo of pods and stock jets, the plugs (and smell) indicated that all four cylinders were running rich.
Please feel free to answer any of these individually—numbered for ease.

1. Could #2 have overflowed because the float sank, not because the valve stuck or didn’t seal? I have been told the new gas can cause that to happen to old floats (in outboards etc.) I haven’t seen this in in my other old machines, but worth asking.
2. Pods: Should I ditch the Alpha Moto pods for another brand, or are they decent? Hope I’m not inviting trouble here…
3. If I can keep them without sacrificing too much, what’s a good starting point for rejetting (mains particularly, I gather I can probably keep pilots stock)? This link in the sticky recommends 4 sizes up for adding pods. Alternately, if I really should get another type of pod, any recommendations for a jet / pod combo for an otherwise stock engine. (I cannot afford $160 for K&N’s at the moment though, honestly)
4. Is the fuel rail as hard to re-seal as I have read? Barr includes O-rings but I gather the sealing bulge may not be a separate o-ring but incorporated into the tubes themselves.

Thanks everyone! Looking forward to the journey with this machine, I’m in love already after only a few weeks of riding her.

[chuck hahn]

http://members.dslextreme.com/users/bikecliff/

look on right margin. also use the early 8 valve service manual

http://cycleorings.com/

orings and intake orings here

[chuck hahn]

composite floats dont sink. check that the floats are perfectly straight...on both float in each carb. also move them up and down to see they clear the bowl gaskets sufficently. ive had to trim gaskets before.

[Big T]

1. Probably the float valve
2. Not familiar with those
3. Keep the pilots stock, raise the needles one notch and 4 sizes may be too much. Depends on your pods
4. This has been debated to no end. I fall into the soak and use camp. Get a small jar, fill with gas and drop all 3 in during the carb cleaning. They should fit very snugly when installed. I'm still using the originals on my 78

[zed1015]

For pod use.
Use only good quality K&N, S&B, APE, UNIFILTER etc.. Cheap Moxi, Emgo, HiLevel etc are know to be restrictive, cause rich running and power loss).
Fit air corrector jets ( see Ebay link provided ).
leave pilot jet size and needle position etc stock...
Increase main jet a couple of sizes.
Air corrector jet kit. Suzuki GS1000,GS850,GS750.MIKUNI.LEDAR.PODS,K&N,FILTERS. | eBay
Check out the seller feedback .

[Forden]

Thanks everyone. I do have the original service manual already, and Clymer's. Have read the early one front to back at this point. O-rings are on the way.

@Zed1015, what you say may explain why the bike was running rich across all four cylinders, if these pods are restrictive. I just haven't found much in the way of reviews etc about them, so thought I'd ask here.
cheers

[chuck hahn]

You can turn the side air screws OUT to lean the carbs out too. Normal starting off setting is around 1 1/2 turns out from seated. A colortune is the ideal tool for setting up VM carbs. How heavily oiled the pods are can be an issue too.

[zed1015]

@Zed1015, what you say may explain why the bike was running rich across all four cylinders, if these pods are restrictive. I just haven't found much in the way of reviews etc about them, so thought I'd ask here.
cheers

Those Alpha Moto pods are just cheap generic pods sold by Alpha Moto and not made by them.
Most likely Chinese or the like with their logo stamped on the end cap.
Most of their stock is rebranded Chinese/Taiwanese budget stuff that you will also find under numerous names on Ebay and swap meet tool stalls.
I would ditch them and buy good quality K&N's ETC..
They do cost more but there's a reason why and they are money in the bank long term.
You get what you pay for.
While you have the carbs apart make sure the air bleed holes in the needle jet tube are clear.
If these are blocked they will also cause rich running.

[Forden]

I ordered the K&N RC-2454 pods--found a way to reduce the cost--so welcome tips on sizing main jets for those pods particularly, since I'm sure many of you have direct experience with them. The installation sheet specifies about 15% increase, or six sizes up, which is a bigger increase than I've seen recommended anywhere else.

Also, 14mm colortune kits seem in short supply stateside (except gauged prices on ebay)--anyone know if they are still in business?

[zed1015]

I ordered the K&N RC-2454 pods--found a way to reduce the cost--so welcome tips on sizing main jets for those pods particularly, since I'm sure many of you have direct experience with them. The installation sheet specifies about 15% increase, or six sizes up, which is a bigger increase than I've seen recommended anywhere else.

See my previous post regarding jetting and air corrector jets to avoid bottom end rough running and off idle hesitation .
Six sizes up is way more than you will need with just the pods and no other mods.
That recommendation is just K&N being over cautious so you don't sue them for engine damage from running too lean.
You should end up around 110 on the mains.

[Forden]

Question about the throttle slides: in Paul Musser's excellent rebuild guide, the picture of the slide assembly has some parts my carbs don't have: two plastic washers, a spring, and what looks like a gasket or seal (all circled in the attached picture). The original service manual diagram (p. 66) doesn't show these parts either. Did some carbs have them and some not?

Screenshot 2021-07-18 at 12-01-18 VM Carb Rebuild - vm_carb_rebuild pdf.jpg

[zed1015]

Question about the throttle slides: in Paul Musser's excellent rebuild guide, the picture of the slide assembly has some parts my carbs don't have: two plastic washers, a spring, and what looks like a gasket or seal (all circled in the attached picture). The original service manual diagram (p. 66) doesn't show these parts either. Did some carbs have them and some not?

[ATTACH=CONFIG]63054[/ATTACH]

Correct! Some have them , some don't.
The lifter arm is also different between the two types where they screw to the slide.

[allojohn]

Correct! Some have them , some don't.
The lifter arm is also different between the two types where they screw to the slide.

... learned something new there.

[Forden]

1. Probably the float valve
2. Not familiar with those
3. Keep the pilots stock, raise the needles one notch and 4 sizes may be too much. Depends on your pods
4. This has been debated to no end. I fall into the soak and use camp. Get a small jar, fill with gas and drop all 3 in during the carb cleaning. They should fit very snugly when installed. I'm still using the originals on my 78

Does it matter how long you soak the tubes in gas? Will the rubber swell at all? Also wondering if applying Permatex #2 could help prevent any leaks from those tubes--anyone have success with that?

Also, there were the short vacuum hose pieces between 1&2 and 3&4--none between 2&3 (in the middle), should there be one there too?

Last (I HOPE!), my throttle shaft was missing the stopper plate--I thought I could fabricate something--the Musser rebuild guide mentions something about a pin on that plate, can someone explain what that is, or maybe send a pic of the stopper plate so I can reproduce it?

[allojohn]

Does it matter how long you soak the tubes in gas? Will the rubber swell at all? Also wondering if applying Permatex #2 could help prevent any leaks from those tubes--anyone have success with that?

Also, there were the short vacuum hose pieces between 1&2 and 3&4--none between 2&3 (in the middle), should there be one there too?

Last (I HOPE!), my throttle shaft was missing the stopper plate--I thought I could fabricate something--the Musser rebuild guide mentions something about a pin on that plate, can someone explain what that is, or maybe send a pic of the stopper plate so I can reproduce it?

Some on here (and me) have purchased aluminum fuel T set from Z1Enterprises, and Cycle O-rings package includes o-rings for this set.

Those are not vacuum hoses, they are rubber spacers between the carbs.

No idea...