?'s about pilot screw o-rings ..77 gs750 (vm26ss?)

[Hiccup]

What started off as a fuel bowl tube overflow drip has turned into more than I planned on..The drip I think I have covered with polishing up the needle and seats but while reading up on these carbs here I thought I would dive in further..So after reading about the chance of fuel pilot tips breaking I thought I would remove the screws and check them out..I had 3 good and 1 broken off and lodged..I know I have to somehow extract the bad tip but my other concerns are the condition of the o-rings..they are pretty rough and was wanting to know what the part#s are or the original dimensions? ..and are the pilot fuel and pilot air o-rings the same size? ..and finally, should the pilot air screw have a spring with it?

 

[Nessism]

Suzuki still sells the pilot air and pilot fuel screw O-rings. They are about $4.50 each. 13246-43010 is the PN for the fuel screw O-ring.

As you might imagine, 46 years for a rubber part to live, while covered in gasoline, is a long time. You would be smart to preemptively change ALL the O-rings at this point, since failures could be eminent.

You can buy a complete O-ring kit for $20 shipped through a forum member here. Check my signature for details.

​

 

[Hiccup]

Thanks for the part number for the fuel screw..I have considered age for reasoning but the other o-rings look pretty good.. I am concerned my pilot air screws have no springs..I have seen teardown images showing springs.

 

[Rich82GS750TZ]

It's ......twenty..... dollars. To replace all the 46 year-old orings in your 4 carbs.

 

[Nessism]

Thanks for the part number for the fuel screw..I have considered age for reasoning but the other o-rings look pretty good.. I am concerned my pilot air screws have no springs..I have seen teardown images showing springs.

Yes, they need springs. Have you looked down into the carb passage? Could the springs be hiding there?

 

[Hiccup]

It's ......twenty..... dollars. To replace all the 46 year-old orings in your 4 carbs.

Actually..about $10-$12 bucks..5-packs are available online for $3-$4..you just gotta know the dimensions..

 

[Hiccup]

Yes, they need springs. Have you looked down into the carb passage? Could the springs be hiding there?

Nope..they are MIA..I found the part#s though from a vm26 parts diagram..
https://www.partshark.com/oemparts/a/suz/50d3ffa5f8700230d8b4e016/carburetor-gs750n-en

Crazy but I actually cant find the pilot fuel screw assembly on there

 

[Rich82GS750TZ]

Actually..about $10-$12 bucks..5-packs are available online for $3-$4..you just gotta know the dimensions..

Which further begs the question - Why wouldn't you?

 

[Nessism]

Actually..about $10-$12 bucks..5-packs are available online for $3-$4..you just gotta know the dimensions..

Sounds like a cheap solution. Good luck with that.

BTW, there are six different size O-rings in the carbs.

 

[uk gs nut]

Look for Centurion motorcycles here in UK. Brian sells all the parts for vm and CV carbs.
https://www.ebay.co.uk/itm/12318016...uI3BN7oSvy&var=&widget_ver=artemis&media=COPY

 

[Hiccup]

Ok..was able to to get the broken fuel screw tip out of the carb, clean out the carbs and passages and all back together with proper orings and springs. Set the pilot screws..fuel screw at 3/4 turn out..air at 1 1/2 turn out. Filled the bowls with fuel before mounting just to make sure no over flow tubes leaked..Well had one carb leaking still so took off the bowl and right away noticed the overflow tube split out ever so slightly. Must have had water in bowl over winter months so I then pressed a sleeve over it and sealed it so no leaks now. Time to mount carbs and start bike..did that and by time I found the best air screw settings I have them turned in nearly all the way in but it runs fantastic..no bog, quick throttle response..hardly any choke to start up..Dont understand the air screw thing but i think the carbs were worked years ago..they have a 110 jet and 15 jet..4 into 1 pipe..never did I look at the needle position on the slides..Plugs look at bit sooty also but she had never run this good in some time..Any thoughts..?.Do they get idle air other than the screw?

 

[unfocused]

Ok..was able to to get the broken fuel screw tip out of the carb, clean out the carbs and passages and all back together with proper orings and springs. Set the pilot screws..fuel screw at 3/4 turn out..air at 1 1/2 turn out. Filled the bowls with fuel before mounting just to make sure no over flow tubes leaked..Well had one carb leaking still so took off the bowl and right away noticed the overflow tube split out ever so slightly. Must have had water in bowl over winter months so I then pressed a sleeve over it and sealed it so no leaks now. Time to mount carbs and start bike..did that and by time I found the best air screw settings I have them turned in nearly all the way in but it runs fantastic..no bog, quick throttle response..hardly any choke to start up..Dont understand the air screw thing but i think the carbs were worked years ago..they have a 110 jet and 15 jet..4 into 1 pipe..never did I look at the needle position on the slides..Plugs look at bit sooty also but she had never run this good in some time..Any thoughts..?.Do they get idle air other than the screw?[/QUOTE

Mines engines not stock so my settings won't apply to yours.

I have the same year engine, correct # carbs and such. I have my lower screw about 3/4 turn out and the upper screw 2 turns out. As I ride it more and more ( fresh top end ) everything is getting better and minor adjustments are needed to the upper screw. I started at 3 turns out.
My pilot is drilled out and my mains are 115.
Oh, and I learned a lesson about those springs.

Unless a hesitation is noted :
The lower screw - set and forget - mostly. 1/2 turn on the lower should be enough for yours.
Upper screw - 1.5 to 2.5 should be the range - stock air box? might change it a little.
Your pilot jet is fine, main jet will need some testing but might consider a 105 or 107.5 - stock for the 77 750 was 102 and lean

Also - my carb bodies are actually warped and I run dual float bowl gaskets. Adjust the floats down ( up if upside down ) to compensate for the float bowl dropping.
I actually played match the float bowl to the carb to get the best fit. Chrome float bowls are hard... lol

The air screw adjust the air crossing over the pilot jet and mixing with the fuel. This is why you might need to adjust this screw from time to time.
The fuel screw adjusts this mixture going into the engine, this is why you set it and forget it.
I have a set of VM26SS Kawasaki carbs and they only have 1 mixture screw (air bleed ) and are better in this sense but to sync them - lol oh my.

 

[Hiccup]

Ok..was able to to get the broken fuel screw tip out of the carb, clean out the carbs and passages and all back together with proper orings and springs. Set the pilot screws..fuel screw at 3/4 turn out..air at 1 1/2 turn out. Filled the bowls with fuel before mounting just to make sure no over flow tubes leaked..Well had one carb leaking still so took off the bowl and right away noticed the overflow tube split out ever so slightly. Must have had water in bowl over winter months so I then pressed a sleeve over it and sealed it so no leaks now. Time to mount carbs and start bike..did that and by time I found the best air screw settings I have them turned in nearly all the way in but it runs fantastic..no bog, quick throttle response..hardly any choke to start up..Dont understand the air screw thing but i think the carbs were worked years ago..they have a 110 jet and 15 jet..4 into 1 pipe..never did I look at the needle position on the slides..Plugs look at bit sooty also but she had never run this good in some time..Any thoughts..?.Do they get idle air other than the screw?[/QUOTE

Mines engines not stock so my settings won't apply to yours.

I have the same year engine, correct # carbs and such. I have my lower screw about 3/4 turn out and the upper screw 2 turns out. As I ride it more and more ( fresh top end ) everything is getting better and minor adjustments are needed to the upper screw. I started at 3 turns out.
My pilot is drilled out and my mains are 115.
Oh, and I learned a lesson about those springs.

Unless a hesitation is noted :
The lower screw - set and forget - mostly. 1/2 turn on the lower should be enough for yours.
Upper screw - 1.5 to 2.5 should be the range - stock air box? might change it a little.
Your pilot jet is fine, main jet will need some testing but might consider a 105 or 107.5 - stock for the 77 750 was 102 and lean

Also - my carb bodies are actually warped and I run dual float bowl gaskets. Adjust the floats down ( up if upside down ) to compensate for the float bowl dropping.
I actually played match the float bowl to the carb to get the best fit. Chrome float bowls are hard... lol

The air screw adjust the air crossing over the pilot jet and mixing with the fuel. This is why you might need to adjust this screw from time to time.
The fuel screw adjusts this mixture going into the engine, this is why you set it and forget it.
I have a set of VM26SS Kawasaki carbs and they only have 1 mixture screw (air bleed ) and are better in this sense but to sync them - lol oh my.

Thanks for the info about your settings..I ended up with 1 turn out on the fuel screws and zero turns out on air screws..If I open them 1 to 2 turns up evenly at all the engine sputters and pops..If I crack just one a half turn the motor dies ..It just doesn't make any sense at all..I think they have modifications that I don't have the experience to notice or maybe I got some race carbs on there. I bought the bike many years ago and it was a cafe racer project with bobbed fenders and it had always run good every season with fresh plugs..I only got into the carbs because of fuel coming out of an overflow tube..Unfortunately I removed the idle air screws without recording turns in but I did turn in the fuel screws and thats when I discovered a broken tip lodged..I have had the tank off during this whole screw setting process so I add fuel to the bowl with a small transparent hanging container..I can actually see the fuel level drop as it idles or revs..but no black smoke out of pipe and plugs have a medium brown color..I dont have the bike licensed for the street and only on occasion take it up the road and back so it suits my needs for the time being but it would be interesting to see the range of the bike on a full tank..

 

[unfocused]

Just a thought. If you have the air bleeds closed I would be looking for two things...

Vacuum leak at the intake manifold o-rings
Plugged pilot jet possibly.
You're getting air from somewhere.
Remember the upper rear is ONLY air and the lower front is air/fuel mixture. If you've closed the air screw, no fuel is present at the mixture screw so any adjustment shouldn't change much if anything.

Right now after tinkering with my carbs over the weekend, I've returned to stock main jet and clip position so I can retest.

Easy check to see if the pilots are rich or lean - drive the bike at 2000 rpms, if it surges you're to rich, spits and sputters, to lean...

Look at your carbs. The front flange - upper left part of the flange has some numbers - you canverify these against the service manual for the correct #. Also, you can measure the throat (engine side of the carb) in milli meters and this should be 26.