Surprise, I'm a VMAX owner now!!

[Super Jimmy]

Hello everyone. I am so very happy to have a reason to be apart of this forum.
About a week ago I was helping a co-worker drop some trees in his yard. After finishing cutting them all up he said to me, "you know how I could pay you for helping me, I'll give you the vmax!" And just like that, I was the proud new owner of a 1991 Vmax!! Now, it is a mechanic special and it wasn't running at the time but my #1 hobby is working on 70s-80s bikes, so its right up my alley. I do still have a lot of questions and hopefully I can get some seasoned advice and some good answers here! V4 for life!

 

[Super Jimmy]

Its a little rough around the edges and needs some TLC but im very exsited to get it going!

 

[ga_max]

You came to the right place. The people on this forum know there stuff. Welcome.

 

[Super Jimmy]

Thanks man!
I'm literally struggling with an issue right now that I'm hoping to get some good advice on.
The bike idles but runs like crap. As I was trying to get it wormed up I noticed that when I shut it off, fuel squirts out one of the jet holes in the top of the carb.
So I'm going thru the carbs and checking to see what if anything is wrong with them and looking at the service manual as I go. I'm replacing all the float needle valves, that should take care of the flooding. But now I'm looking at the jets to make sure someone hasn't made changes to it. This is where the problem comes in. The manual says that cyl #1 & #3 should be a #152.5 and cyl #2 & #4 should be a #150. All the threads I've read are saying put the same size in all the carbs, the carbs I have, all have 152.5 in them. Dose anyone have any thoughts on this?

 

[Fire-medic]

Welcome. You can learn a lot by looking at the factory service manual, of course. Sounds like you've been in it. You should remove the jet blocks, the rubber plugs and the jets behind the rubber plugs. Your pilot jets: probably some or all are plugged. Remove them using a small narrow tight-fitting slot blade screwdriver.

You really should disassemble them and give them a carb soak, I prefer an ultrasonic cleaner.

https://www.vmaxforum.net/threads/new-vmax-owner-faqs-new-members-please-read.21240/
https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf
https://www.vmaxforum.net/threads/ready-for-reassembly.52239/#post-526320
Since you're a student of 1970's/'80's Japanese bikes, you know that CV carbs need to be clean, really-clean to work well. That goes for all carbs, but a VMax sitting unused for a few months, with 10% ethanol/90% gasoline of 87 octane, is probably going to need carburetor cleaning if the float bowls were not drained, or the engine wasn't run until it quit, w/the gas off.

You're in MI, run the carbs on stock jetting but for the mains, use 150 or 147.5 Mikunis. The bike will run crisper with a bit smaller jets. But the carbs need to be spotless! If they're not clean and all passages unobstructed, you're going to be back on here, asking why isn't it running well?

Look at that thread I posted and use that to set your floats, dry, and you can check them wet according to the carburetor section in the factory service manual.

A 1991 bike will probably have hard, not pliable boots from the airbox to the carb bellmouths, or to the VBoost manifold from the bottom of the carb bodies. You can try boiling them in water to soften them, and quickly putting them in-place, for either the airbox to bellmouth or to the VBoost from the bottom of the carb bodies. Use a bit of water-soluble jelly, like KY or equivalent, to help things slide-together. Make sure that you tighten the clamps properly, all-around.

If you want to make things easy, buy new boots, top and bottom. However, to see if it's worth spending $ on it, I'd attempt getting the engine to run reliably first and then go into upgrades.

A tip on a no-$ way to seat the carbs and the airbox:
See post #2. Got a carb question

You should feel a 'give' as the carbs seat into the boots, and as the airbox seats into the upper rubber donuts. Look at the casting marks on the carb bodies to ensure they're fully-seated. Take a look at the carb clamps for the rubber boots, and you can see the clamps have 'stops' built into them, to keep you from over-tightening the clamps.

If you want to get the best bite, use a JIS standard 'Japanese-phillips' screwdriver for the X-head fasteners.

 

[CaptainKyle]

Congrats and welcome!

 

[Super Jimmy]

Welcome. You can learn a lot by looking at the factory service manual, of course. Sounds like you've been in it. You should remove the jet blocks, the rubber plugs and the jets behind the rubber plugs. Your pilot jets: probably some or all are plugged. Remove them using a small narrow tight-fitting slot blade screwdriver.

You really should disassemble them and give them a carb soak, I prefer an ultrasonic cleaner.

https://www.vmaxforum.net/threads/new-vmax-owner-faqs-new-members-please-read.21240/
https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf
https://www.vmaxforum.net/threads/ready-for-reassembly.52239/#post-526320
Since you're a student of 1970's/'80's Japanese bikes, you know that CV carbs need to be clean, really-clean to work well. That goes for all carbs, but a VMax sitting unused for a few months, with 10% ethanol/90% gasoline of 87 octane, is probably going to need carburetor cleaning if the float bowls were not drained, or the engine wasn't run until it quit, w/the gas off.

You're in MI, run the carbs on stock jetting but for the mains, use 150 or 147.5 Mikunis. The bike will run crisper with a bit smaller jets. But the carbs need to be spotless! If they're not clean and all passages unobstructed, you're going to be back on here, asking why isn't it running well?

Look at that thread I posted and use that to set your floats, dry, and you can check them wet according to the carburetor section in the factory service manual.

A 1991 bike will probably have hard, not pliable boots from the airbox to the carb bellmouths, or to the VBoost manifold from the bottom of the carb bodies. You can try boiling them in water to soften them, and quickly putting them in-place, for either the airbox to bellmouth or to the VBoost from the bottom of the carb bodies. Use a bit of water-soluble jelly, like KY or equivalent, to help things slide-together. Make sure that you tighten the clamps properly, all-around.

If you want to make things easy, buy new boots, top and bottom. However, to see if it's worth spending $ on it, I'd attempt getting the engine to run reliably first and then go into upgrades.

A tip on a no-$ way to seat the carbs and the airbox:
See post #2. Got a carb question

You should feel a 'give' as the carbs seat into the boots, and as the airbox seats into the upper rubber donuts. Look at the casting marks on the carb bodies to ensure they're fully-seated. Take a look at the carb clamps for the rubber boots, and you can see the clamps have 'stops' built into them, to keep you from over-tightening the clamps.

If you want to get the best bite, use a JIS standard 'Japanese-phillips' screwdriver for the X-head fasteners.

Wow. Thanks! Thats the kind of insight I was looking for.
I forgot to mention I also replaced the boots below the carbs. They were so cracked that I'm surprised it hadn't burnt a piston or two. I also check the compression to make sure it hadn't melted any rings or something terrible like that.
Ultra sonic is definitely the way to go. I got me one a couple of years ago and now I practically put everything in there. Do you have any idea why the manual would have you put different jets in alternating carbs? Is there a down side to making them all the same size? I plan to drop them to 150 assuming I got the all clear from some vets out there. From the threads I've found, sounded like dropping to a 150 was the way to go.
I was hoping not to have to take off the sub-assembly for the pilot jet. The bowl looks so clean, no varnish at all I thought I might get away with not doing that. But you probably right, I should take it apart and clean it.

 

[Super Jimmy]

Congrats and welcome!

Thanks man!! I'm sooooo looking forward to the first ride!

 

[user 80813]

Welcome! Nice bike you got there.......I would cold some serious amount of wood for that one.

You'll get her running soon enough. My 89 Vmax sat since 2011 when I bought it in October. With the forum's help, CaptainKyle's expertise (he rebuild my carbs), a lot of elbow grease and a fair amount of cash I got a great running and fast Vmax now. She is almost done.

 

[mckzx9]

Welcome to the addiction

 

[Super Jimmy]

Welcome! Nice bike you got there.......I would cold some serious amount of wood fr that one.

You'll get her running soon enough. My 89 Vmax sat since 2011 when I bought it in October. With the forum's help, CaptainKyle's expertise (he rebuild my carbs), a lot of elbow grease and a fair amount of cash I got a great running and fast Vmax now. She is almost done.

Thanks man! ya dude, 2 trees. Like, a total of 4 hours. I was just helping a buddy out. No exspectations of getting payed. Crazy! I'm realy hoping all it needs is some tender loving and a good once over on the carbs and she'll be ready to burn down some tires!

 

[Super Jimmy]

Welcome to the addiction

O dude, 1 week in and I'm already feeling the VMAX fever!
I might have a problem. 3rd road bike in the garage.

 

[Super Jimmy]

If anyone's interested, I have a YouTube channel. Its mainly about by other 2 bikes but the VMAX might have to make an appearance. LOL

@akaSuperJimmy

 

[Fire-medic]

I suggest a 150 or a 147.5 Mikuni. The bikes are set rich from the factory, because rich is better than lean, in terms of 'hurting' an engine. Anyone who's owned a 2-stroke, and who worked on it/them, will know about that.

Sean Morley [email protected] has a Morley's Muscle kit for the intake system, including a replacement filter installed top for the OEM airbox. His product is proven through the many members here who have used it. Plus, you can contact him if you have an issue with your installation, Sean is 'The Man' when it comes to working on our bikes. There are also other members on here who can do repairs, dannymax [email protected] specializes in carburetor rebuilding . CaptainKyle [email protected] repairs bikes, sells parts, and also rebuilds carbs. His painting is often featured in his posts, you want flip-flop, fades, stripes, flames or scallops, or just a smooth stock color finish, he can do it. Sean does paint too, and also sells new and used parts. I've done business w/all of these members, and you will be happy with the outcome if you do too.

Yes to removing the carb jet blocks. Yes to removing their brass jets, and I suspect you'll find dirty, obstructed pilot jet(s) one or more. One thing I suggest is ordering a T-shape rubber fuel hose (#65, below) to replace the one in there, which is probably over 30 years old. It isn't uncommon to have them disintegrate when you attempt to split the carbs.



I use Ron Ayres Yamaha for parts. I've used them for decades, and have never had an issue. If something isn't in stock, you can leave it 'on-order' with them, and they will ship it when it arrives. Sean Morley also sells OEM parts, and keeps them in-stock for many of the commonly-needed pieces.

Ron Ayres Yamaha may not always be the absolute lowest price, but their service is really-good.

1991 Yamaha V-MAX 1200 (VMX12B) Carburetor | Ron Ayers

Numbers 42 (pilot jet) and 44 (main bleed pipe) are the brass jets in the jet block. Numbers 43 and 45 are the different-sized rubber plugs which go into the ends of the jet block. I suggest you order four of each, when rebuilding your carbs, because they need to be there for the CV carbs to function. Keep the old ones for spares.

You'll find that buying the individual parts from Yamaha can get expensive, but if you read the posts about the K&L kits, you will see that their kits can save you considerably. Also, if you can do the work competently you can save $$. If you're not an experienced carb person, then using the services of one of our members is a satisfying way to go. Bolting on a refurbished set, and doing the synch yourself, and having the bike start, idle, accelerate, and return to a smooth idle is one of life's great satisfactions. At least for we who ride and do some wrenching!

 

[Woody]

Welcome, Enjoy the max.

You might want to research the cobra exhaust. Before trying to tune the carbs.

 

[Fire-medic]

Welcome, Enjoy the max.

You might want to research the cobra exhaust. Before trying to tune the carbs.

I know that's so!

 

[Trail Ride]

Welcome to the forum.

 

[Super Jimmy]

Welcome to the forum.

Thanks!!

 

[Modaguy818]

Congrats and that’s a hell of a way to get paid for any type of work 4 hrs or 40 lol. Enjoy it man and you’ll have a blast.