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VM carb rebuild

  • Thread starter Thread starter Rodman
  • Start date Start date
R

Rodman

Guest
Its getting close to happening and I have read many posts including the tutorials at Basscliffs site but have concerns, more like beginners cold feet because I really don't know what the heck I'm doing. I know that even if I follow the instructions to the tee there can be issues. Right now my biggest fears are issues getting the pilot circuit correctly tuned, seems many have a problem with this. Another is needle shimming, is this a regular issue or realistic concern? I have Morgans carb tune pro and Gunsons colortune. Is the colortune all its hyped up to be or just a novelty and waste of money? If not, can the colortune take the place of the trial and error adjustments with plug reads or should it be used in tandem to narrow down the fine tuning with the road tests. Any input is appreciated.

Thanks
Rod
 
Is the bike stock or modified Rod? If stock, tuning the carbs is easy and nothing to worry about. Just set the fuel screws at 7/8 of a turn open and the air screw at 1.5 turns. Most likely the bike will run fine right there. Worst case is play with the screw setting within a limited range (1/4 turn) from this point. VM's are pretty simple and you can't really mess anything up too bad.
 
You worry too much. ;)

Between the Morgon and the color tuen you have, you should be able to nail that thing, before it ever leaves the shop.

Is your bike modded in any way ie, pods, pipe, Zip Tie on the grab rail?


You beat me to it, Ed !
 
With VM carbs the colourtune works as advertised. With vacuum style carbs, not so much.
Personally, I find the VM carbs easier to tune because you have independent control over air and fuel in the pilot circuit. Why are you changing the needle position? What sort of intake and exhaust set up are you going to run?
 
You can do it

You can do it

I did my first tear down and refresh a few months ago, I didn't know squat. Everything I learned was from here, the tutorial, and trial and error. If you don't impose a deadline, take your time, be organized, and be thorough, you can do it. If you dip, poke the all the passages REALLY good, replace orings, and set the fuel and air screws to factory settings, you'll run good enough to tune. Colortune and carbtune are helpful. Colortune isn't magic, it's just gives you visual feedback (confidence) of what you're thinking, if it runs better a perfect blue, so be it, if it runs better with a little orange flicker every once in a while at idle, that's ok too, just keep reading your plugs.
 
Why are you tearing the carbs down?
Is the bike running incorrectly or carbs leaking/clogged?

VM's are very easy. Oldschool and reliable.
(The CV's tend to be more picky in my experiences)
My VMcarb settings were ALL over the place, and the bike Still fired up....it just popped and ran rich, so I just reset all the fuel and air screws, and tweaked it slightly while the bike was running...easy!
 
Thanks to everyone for easing my concerns. This bike is bone stock except for the charging system, thanks Ed! The bike is not running as well as it was last season and slightly leaking fuel from bottom gaskets on every carb. Considering what it takes to replace these gaskets, might as well do it all. The cover screws have been buggered up some, so someone has been in there or at least tried, but I have a set of JIS drivers and a dremmel if it comes to that. After a valve adjust I'll be in the carbs. I'll keep you posted on my success and or problems. Thanks again for all the great input.

Rod
 
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Those VM carbs are no problem at all. The one thing I would add would be to verify that all the jets, needles, shims, etc are the SAME across all carbs. The jets and needles are all stamped with numbers. Verify that the sizes are what they are supposed to be and that they're all the same, in case someone has toyed with it before. Check the needle positions and any shims. Again, just make sure they're all the same.
 
Just did the ones on the 79, was pretty easy with instructions from Basscliff site. Might take some pics. as you tear carbs apart just in case you can't remeber like me sometimes. My son's bike has never ran so good. Bench sync. them as close as possible and won't have to do much adjustment when syncing on bike. terrylee
 
My only real issue w/ doing my VMs was the pilot fuel screws. I'd suggest pulling those out BEFORE ordering gaskets/rebuild kits. If you have any that are broken off in the body, you can either sharpen them or buy new ones. If you want to buy new ones, they come in the rebuild kits for GS750. If you don't need the screws, then just order the gaskets.

I also had an issue setting my float heights, but that was just me not being very careful w/ measuring.
 
Pendulum said:
My only real issue w/ doing my VMs was the pilot fuel screws. I'd suggest pulling those out BEFORE ordering gaskets/rebuild kits. If you have any that are broken off in the body, you can either sharpen them or buy new ones. If you want to buy new ones, they come in the rebuild kits for GS750. If you don't need the screws, then just order the gaskets.

I also had an issue setting my float heights, but that was just me not being very careful w/ measuring.
Click to expand...

Z1 now stocks the fuel screws, so you don't have to waste money on a kit anymore

The cleaning is easy, just take your time,take some photos, have an organizer (an 18 egg carton is great) and go to it
 
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