VM Carbs rebuild question

[bill_face]

Hey all,

I'm trying to fix a long running hard starting problem with my GS 550 1979.

A little background. I brought the bike with airpods and modified jets in, so I enlisted the help of a local bike mechanic to get the requisite stuff to take it back to stock (airbox and orignal sized jets), which he did. It ran better but had this hard starting issue.It also had a bit of low compression so I have since had the cylinder head skimmed and fixed that. Valves clearances have been checked multiple times. So I'm back in the carbs which I currently have apart with a new set of o-rings at the ready.

My main question is about the setting of the pilot fuel and air screws: I've found some info (via Nessism) that 'the pilot fuel screw, on the underside of the carb, can be set to 7/8 of a turn from lightly seated, and the pilot air screw, on the side of the carb, about double that'. What are we calling lightly seated? there is a spring on both of these so presumably as I screw in and start to feel resistance is that lightly seated? If i screw them all the way in the spring buries itself into the the orifice and needs at tap to get it out. Also what is the purpose of the spring? I'm presuming to act as a bit of tension to stop the jet vibrating out over time.

On my carbs, the two springs on these two jets are slightly different sizes, and the longer spring is on the pilot fuel screw (which is the shorter screw). Is that correct?

Any other things to look out for during the rebuild that might influence this hard starting behaviour?

Cheers

Phil

[Nessism]

With the choke plungers removed, put the straw tube of a can of carb cleaner into the small round hole on the bottom of the choke cavity and shoot. You should see carb cleaner shoot out the end of the brass pickup tube on the bottom of the carb. Also, shoot carb cleaner through the choke pickup passage in the float bowl. All these passages must be open in order for the choke to work properly.

[bill_face]

Two further questions:

1) I was rebuilding the carbs and realised I was missing a pilot jet for carb 3. I initially thought I must of misplaced it, but was being very methodical (for me) incorporating egg boxes etc. Having done a thorough search of the area I had been working in and realising at no point had I knowingly dropped anything, it dawned on me it might not have been there when i was dismantling. I was dismantling carbs 3 & 4 together and as I had a vague idea what I was doing from the experience gained on 1 & 2, I was just 'taking bit out' and putting them in the egg cartons so I might not have realised something was missing. Then I did a Google search for the symptoms of a missing pilot jet and #1 is hard starting. Could this have been my problem all along? It tended to idle OK. I would like to know how much jip to give the lovely chap that rebuilt my carbs for me, and so I know how thoroughly to audit the floor of my workshop

2) When i was putting the carbs back together I put a few screws on and forgot the springs, when I got them back out I noticed the o-rings were a bit mangled. Is this a symptom of lacking a spring? I didn't think to lubricate the o-rings which might have been an idea? Will i need to order new o-rings? See pic of the worst one PXL_20250419_140536554.jpg

[Nessism]

Always lubricate the O-rings before installing into the carbs. They crush down as they move into position, and if not lubricated, then can snag and tear. Regarding the photo, showing the torn O-ring, that O-ring looks way too big. Where did you get the O-rings?

[bill_face]

I got them from a member here at GSResouces: Cycle O-rings. Seems like he has now ceased training, but when i ordered back in 2019 he sent me two sets and I've had this set ever since.

Just looking around for more o-rings? Do GS550,750& 1000 use the same o-rings? An eBay listing I've found suggests they do

https://www.ebay.co.uk/itm/123180162761?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=CDD5i3SoTJG&sssrc=4429486&ssuid=PUHR61Q1SWO&var=&widget_ver=artemis&media=COPY:

[zed1015]

Just looking around for more o-rings? Do GS550,750& 1000 use the same o-rings? An eBay listing I've found suggests they do

Yes! All the VM series of carb banks for the road going Suzuki GS and Kawasaki KZ aircooled fours share variations of the same components and items such as gaskets 'o' rings etc are the same .