carb starting problem

[chuck hahn]

There ARE springs on both the pilot and mixture screws. He should have regular VM26 carbs.

[JTGS850GL]

Lack of vacuum as you describe points to a clog that's preventing the motor's vacuum from reaching the fuel bowl.

Now that's a novel idea... NOT.

He doesn't have a vacuum problem he has either a fuel problem related to clogged passages or an ignition problem. So far I haven't seen any verification of ignition and no confirmation that the carbs have been THOROUGHLY cleaned as in the manual. Seems like the OP likes to beat his head against a brick wall.

[chuck hahn]

When 4 or 5 people tell you the carbs are dirty one would think to pay attention.

[hannibal]

Vacuum in the fuel bowl is necessary to draw fuel out of the bowl and into the carb, isn't it?

I never suggested his motor wasn't making vacuum, just that that vacuum wasn't reaching the bowl. I was trying to tie his observation of no vacuum in the bowl to the recommendations that a thorough cleaning would allow this vacuum to reach the bowl and suck up fuel.

Please correct me if I'm misunderstanding the way carbs deliver fuel.

[chuck hahn]

When the piston goes down on the intake stroke it sucks air into the face of the carbs. This makes a low pressure center inside the venturis..which in turn lets the fuel come up via the needle and needle jets. The vent nipples allows atmospheric pressure to now push fuel up thru the carbs.

There isnt any vacuum produced in the bowls..its all in the carb throats via the low pressure formed there. You have low pressure in the carb bores and high pressure going down the vent tubes. The high pressure just pushes the fuel out of the bowls..its that simple.

[chuck hahn]

Read all this page...

http://members.dslextreme.com/users/bikecliff/images/carb_sync_notes.html

[hannibal]

Thanks for the explanation and link on the mechanics.

There ARE springs on both the pilot and mixture screws. He should have regular VM26 carbs.

I couldn't find springs for any of my pilot (bottom) screws. I see them in the GS850 carb rebuild writeup but I assumed the GS750 carbs were different. Are all Suzuki VM26's identical?

I guess it's time for me to locate some new springs.

[chuck hahn]

A VM26 is a VM26....What condition are the tips of the pilot needles?? Nice sharp points? if they are flat or jagged better look down the holes with a light to see there arent tips broke off in there. Shine the light into the back of the carbs throats while looking down the pilot screw holes..you should see a pin point of light in the hole.

[JTGS850GL]

As Chuck said, the springs are there, just not externally visible. That's assuming you took them out to see and no PO screwed them up in the past.

[chuck hahn]

Note the side mixture screw springs are a different size thann the bottom pilot screws. You have the side screw springs???

[chuck hahn]

i make a bend in a paper clip wire and use that to fish out springs.

[hannibal]

I used my little LED keychain light to peer down into the pilot (fuel) screw hole. Thought I saw a spring so I tried Chuck's paper clip trick. After having no luck, I concluded I was looking at the screw threads. I obviously didn't want to damage them so I stopped scraping and dipped the carbs without getting the springs out. Not a single spring came out, either when disassembling or after dipping. I guess the PO took them out.

The pilot needles were in great shape (very sharp point and not cracked or broken). I was very pleased to get them back in and seated, then backed out without breaking anything. The side mixture screws have springs on them. Those are only springs I found when taking the carbs apart (besides the choke plunger). I'll try shining a light into the carb throat and looking for light in the pilot hole but I'm convinced these carbs are missing the springs on the pilot screws.

[chuck hahn]

You for sure need springs on the pilot screws..the tension applied by them keeps them from vibrating out when the engines running. Glad to hear the tips hadnt been snapped off..thats a good thing.

If the spring where in there they wouldnt be very far down so you probably were seeing the threads.

[JTGS850GL]

Use the carb cleaner and spray it into each of the passages. You should see fluid emerge from every location that the passage goes to.

[hannibal]

Yes i quickly learned there are a bunch of little passages and the carb cleaner would come out of unexpected places. I've tried to follow the passages shown in diagrams but get overwhelmed. I'll give it another shot.

I originally thought I could get by without the springs, but it makes sense needing springs to keep the screw from backing out. The pilot screw isn't listed on the parts diagrams so I don't know what size I'm chasing. Might just bring a carb and screw to the store to find a spring that fits. Thanks for the help.