Rebuild carbs??

VMAX  Forum

Help Support VMAX Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Active Member
Supporting Member
Dec 29, 2020
Reaction score
Charleston sc
Long story short I bought an older vmax that had more problems than was immediately apparent. I/e-I impulsed purchased it as a project bike, paid too much probably, and Am now trying to weigh my options. Thanks to a lot of help on this great forum it’s running, but not like I hoped, and I’m trying to decide if I should cut my losses. Biggest apparent issues-1) 2nd gear is stripped out. By all accounts that would be too much $ and effort to put into a ‘98. 2) -I’ve got it running and can ride it briefly but hesitates and backfires around 50-60 mph. ( I cleaned and sealed tank, changed fuel filter, did a “pea-shooter” type carb clean…still not running right. Main question is should an amateur bike mechanic attempt to rebuild these carbs? I’ve been told to run sea foam through for a few tanks and if that doesn’t work-to “trade it in on something else”. I love the bike but it’s not really fun to drive right now. Very frustrating. Would it be better /safer to pay for a rebuild?- is that crazy expensive? This is my dilemma
Depending on if your 2nd gear is actually toast or maybe just the pins are causing the issue would determine your cost to keep the bike.
If the 2nd gear is actually shot you would probably be better off finding another complete motor and swapping it in for the sake of cost.
everything else is fixable. Inquire to Sean Morley here on the forum he can point you in the right direction for sure!
Main question is should an amateur bike mechanic attempt to rebuild these carbs? Would it be better /safer to pay for a rebuild?- is that crazy expensive? This is my dilemma
Depends on your experience and ability but taking the carbs off is just a sequence of undoing bolts and screws, some of which are more difficult than others.

The pilot jets get blocked due to the tiny hole in them so I don't see how seafoam or any of chemical can unblock them as it needs to flow through which it can't.

Price I've seen for an exchange set of rebuilt carbs is $650.
Rebuilding the carbs is easy. It costs around 150 dollars to do it. There are guides online that will walk you through it. The only X-factor you'll have is syncing your carbs after they're rebuilt. That requires a set of gauges. Typically you can buy a set for around 100 dollars.

On 2nd gear, as stated you need to see what that actually is before you trash it.
FYI, dannymax is one of the members on-here who repairs carburetors. You might be confused by the two prices above, "well, is it $150 or $650?" I'll provide an example. The carburetor CV (constant velocity) slides have rubber diaphragms which with time, can become less-elastic, and deteriorate. The OEM CV slides come w/diaphragms attached. There are aftermarket replacements available for the rubber diaphragms and for the combined slides and diaphragms. However, be advised that replacing the diaphragms takes a gentle hand! The plastic of the slides is prone to breakage, especially on a 20+ year-old bike exposed to gasoline for the life of the slides! The CV slides complete with the diaphragms are still available from Yamaha, but their price for four new ones, could easily exceed the $500 point. See #9 in the fiche. You need four, if you are replacing all of them. That may-not be necessary, but you need a disassembly to discover their true state. Fortunately, given the design of the downdraft carbs, you can easily pop-off the CV caps (those shiny round things below the side scoops) and determine their condition. An advisement, one of the screws on each of the CV diaphragm metal caps is a security screw. A Vise Grip with a pair of straight jaws will loosen the screw's torque, you just have-to search a bit for where you can grip the screw head. An alternative is to use a Dremel to cut a slot across the screw head, and them a tight-fitting slot screwdriver to loosen it.

Do not use a hand impact tool on a carburetor! The zinc alloy bodies are not strong enough to withstand such tools. Some guys do use 'em. Like the Russian roulette player said, "so-far, so-good!" The straight-jaw Vise Grips will loosen any VMax carb screw your screwdriver cannot seem to unfasten. If you really want to get the correct tool, purchase the JIS screwdriver sized to the screw you need loosened. The JIS standard is different from a phillips screwdriver, though in most cases, a phillps will do the job.

1998 Yamaha V-MAX 1200 (VMX12K) Carburetor | Ron Ayers
Diaphragm Assy part #9


Retail Price: $160.99

Your Price: $128.49

VMax carb complete.png

Rebuilding the carburetors is a greater task than I will relate here. Because of ethanol in gas, the small pilot jets that work to control idle and low-speed operation tend to plug-up. In a 'totally-blocked' condition, all the Sea Foam, or gas additive is not going to open-up the hardened deposits in the pilot jets. The carburetors need to be removed, split into two pairs of two carburetors, and the float bowls removed. Then the jet block removed, and finally you can access the pilot jet (fiche, #42) and the main bleed pipe (fiche, #44). These small brass screw-in jets need to be accessed, removed and cleaned, as-well as the carburetor body.

See gasket #35, which lies below #32 jet block assembly? That will usually tear into pieces from trying to remove the jet block, which is held by 3 screws. Two are on the jet block body. One (fiche #32) screws into the main nozzle (fiche #34). If you're lucky, and you use patience and a small metal pick, you may be able to remove the jet block assembly and preserve the gasket. Me, if I was going to be disassembling the carburetors and wanted to do things properly, I'd just count upon replacing that jet block assembly gasket. (times four). A warning: when you remove the CV carburetor CV caps to see what kind of shape your CV diaphragms are in, do not lose that tiny O-ring (fiche #10)

O-Ring part #10



It's easy to overlook, and while it often sticks to the carb body once you remove the CV cap, it's also known to run and hide from the unsuspecting home mechanic.

Download this and save it, you will be referring to it frequently as you deal with the lazarus-resurrection of your '98 muscle bike.

VMX12- Service-Manual.pdf (

I would print out a copy and put it into a loose-leaf binder, and for the pages you need for getting down & dirty, slip 'em into those clear plastic sleeves with binder holes, so you don't get things dirty.

This is just to serve as an introduction to your VMax time. There is much to learn, Grasshopper. The more you know, the better you are able to service your bike. In the case of the carburetors, it will take you a lot longer the first time, and you're bound to have some 'moments.' Take your time. Look at the diagrams, look at your workspace, you need room and a clean place to do this. I have a large fiberglass tray I work in, to keep parts from flying-away into crevices and unknown places in the shop.

OEM is the best way to go for things like carburetor parts. dannymax has a reputation for using OEM. Me, I'm a cheap guy, sometimes I use aftermarket parts. The K&L carb kits for O-rings and gaskets (it also includes the float valve and float valve seat) are less $ than OEM. K&L is a supplier to the Japanese manufacturers. I think if you try to order one of the ebay sets which contain all parts for all four carburetors, you will be disappointed with what you get. Numerous people have tried the no-name kits, which appear very-impressive for their quantity of shiny parts, but after seeing many complaints on the poor quality, stay-away from these.

As to second gear, the engagement dogs wear, and the holes they go into do too. Assuming that's the issue, replacement of the gears is needed, that's "split the cases, engine out of the frame" time. You can actually operate the bike by skipping second gear, just shift from 1st to third. Many members do it, instead of making the out of the frame repair. Once in awhile, you will select second gear, especially on a downshift, and when it jumps-out of gear, with some throttle, you're reminded that it needs to be fixed.

Early bikes had a shift drum/shift segment 'star' which has pins in it, held in-place by that 'star,' and when the shift segment star fails, you lose gears, maybe 3rd and 4th. By 'lose,' I mean you cannot select those gears anymore. Fortunately, the replacement of the star segment is not a big deal, it can be done with the engine in the frame, but you want to be sure that you account for all the pieces which are now loose in the bike engine. Yamaha sells an improved star segment. Assuming I was keeping a bike, and I had to split the cases to fix second gear, I would also replace the entire shift drum, and the shift forks. That's just P.M. as an accident/tip-over where the bike falls onto the left side can bend a shift fork. Do it once do it right.

1998 Yamaha V-MAX 1200 (VMX12K) Shift Cam Fork | Ron Ayers

VMax shift drum.png

There is a lot to learn. However, you probably have seen that there is a lot of knowledge shared here, and if you want to have services provided, you can enlist the labor of members who have businesses devoted to fixing these bikes. If you're just doing a "only what's broken" repair, the cost can be less-than you doing a "I wanna ride this for years without removing the engine from the frame again" mindset. What you spend is up to you. If you aren't feeling the ability to tear-into a set of VMax carburetors is something you are willing to approach, you will find dannymax's abilities to set-right a dirty, broken set of carburetors is well-worth the $ investment. There are others here who also do this work, and more. dannymax specializes in carburetors, Sean Morley (Derby KS) [email protected] can repair that transmission, he can have the gears undercut to make shifting easier and help to prevent the gear dogs rounding-off, and if you want a large-bore engine of anywhere from 1300cc to 1500cc + he can build it; power-adders, what is your choice: NOS, supercharged, turbocharged, all it takes is money, baby! He does paint and chroming services too. CaptainKyle in TN is another mechanic who fixes bikes, and he also has a reputation for quality paint [email protected]

I enjoy seeing people fix their problems, and relating their fixes posted here. In nearly-all cases, you will find the attitude and rudeness some websites suffer-from rarely happens here. The technical orientation to fix issues is one of the site's strengths. If you find that you benefitted from what you found on-here, please make a membership payment to keep the site operational. It's far-cheaper than shop rate at your local Yamaha shop, some of-whom don't want to work on older motorcycles like a Generation 1 VMax.

Use the 'advanced search' for topics you are interested in researching. I can tell you now, there is no problem you have, that has not been discussed and fixed here, before your arrival.

(17) New Vmax Owner members please read! | Yamaha Star V-Max VMAX Motorcycle Discussion Forum (
This thread will answer many questions.
Last edited:
A guy with tools and basic know how can do both ,with a learning curve of course. I, after pulling the rest of my hair out, set the float levels with the rack split in half for access to the float bowls. Usually they check out well on the bike after. A good cleaning of course. Brass parts I stick with factory stuff. Sync and adjustments most can handle. Or, if you want them right, and minimum aggravation, box them up, and send them out to Dannymax. A trans apart should have 2nd gear dogs undercut. Sean can get that done for ya. For me, a good running Vmax is worth the effort & cost. A shift segment upgrade made my 89 shift a lot better, but doubt if it is your trans issue.
I can buy your bike if price is right. Send me PM with price and your zip code.
Hey, thanks for answering my same question, although mine is 5th gear missing and no.2 carb is sticking. Wacked it with a screwdriver and it quit but I know it will stick again. I've done my dirt bikes carb in my teens so now its college level vmax time. I currently have 4 into 2's and stock air box . My a/f screws won't stall engine when turned all the way in to seat. They are currently set at 1 3/4 to 2. Spark plug on 2 was wet, hence stuck float. I just purchased the Drag Star black ceramic 4 into 1 so $650 is out of my wallets capacity right now. I also ordered new segment, star and pins thinking this is my 5th gear issue.
My Question is this, if I purchase OEM carb kit what jet sizes should I be installing with 4 into 1 headers and an air box conversion filter? Do I need to purchase slide needles?
Also, what kind of exhaust do I have currently installed? (For Sale, soon) Thanks for your opinion !


  • IMG_20211029_180013892.jpg
    99 KB · Views: 11
  • IMG_20211031_175716023_HDR.jpg
    162.3 KB · Views: 13
  • IMG_20211031_175740510_HDR.jpg
    318.5 KB · Views: 14
  • IMG_20211031_175800625_HDR.jpg
    283 KB · Views: 16
  • IMG_20211031_181416031.jpg
    193.4 KB · Views: 16
  • IMG_20211031_181436631.jpg
    193.3 KB · Views: 15
  • IMG_20211020_091037557.jpg
    168.3 KB · Views: 13
  • IMG_20211020_091256772.jpg
    151.2 KB · Views: 12
Those are Cobra pipes. They are good looking pipes but the absolute WORST pipes you could ever put on your bike. They cause more problems than you can shake a stick at.

Until you get rid of those Cobra's and get a decent exhaust system on the bike, you're pretty much wasting your time doing anything to the rest of the bike as far as tuning. I wouldn't even bother with the carbs at all until those pipes are gone.
Thanks for the much needed advice, that's why I purchased the Drag Star 4 into 1, will get back after install.

That is going to require a stage 7 jet kit, I'm pretty sure. Maybe @Fire-medic can weigh in as I think he runs that exhaust.

That's a good thing really as you can get it, go through your carbs and exhaust all in one go and come out the other side with a bike you wont freaking believe.
Cobras 4/4's are a system for appearance's sake, not enhanced performance above OEM sake. They cost you 10-15% HP so instead of being in the 110 RWHP range as a stock exhaust, you're dipping-down to maybe 95 RWHP. Also, the throttle response with the Cobras and the VBoost response is very-disappointing. Put it this way, returning to a OEM exhaust and jetting and then tuning the air bleed screws behind the blank-off caps pressed into the holes for the air bleed screws below the CV diaphragm caps, will:

  • return your 'lost' horsepower
  • eliminate that 'soggy' throttle response
  • make your VBoost function as it was designed to function
  • be such a different animal, overall, you will wonder why you waited so-long to change (perhaps, "I didn't know any-better!")
Wear ear plugs with the Drag Star system, your ears need it for protection. You don't want to go through your older years partially-deaf! I'm not kidding!
He said he ordered a drag star so the Cobra pipe discussion in irrelevant you do not need a stage 7 with it unless you are looking for maximum horsepower. Do not do a stage one either ! Depending on your elevation you can most likely drop down to a 147.5 main and maybe shim your needles and you will be fine.
Thanks Fire-medic, just tried to cancel order. Wish me luck, truth is I'm on disability and have no business spending a grand on pipes, then carbs. New in the beginning that it needed to be stock @58 but it pulls amazingly well. Only can imagine what Parminio described, maybe screaming. If I get the cancel from seller or have to return I will, then buy a stock muffler and save $ for carbs if they need it. Thanks again for common sense advice. P.S. I have tinnitus.
I would also like to say thanks to Sean Morley for incredible video's, fixed my steering and added air to forks, different bike until no.2 float stuck, but no worries banged it with screwdriver. No seriously carbs are coming I know that much. And everybody's opinion is welcomed and appreciated as well.
Kyle, yes, I saw he had Cobras, and was in the process of buying the better system, not Cobras! Apparently buyer's remorse may have set-in, and a desire to install a OEM system has taken-hold.

I agree that going to a 147.5 Mikuni main jet will make a + difference in the bike's operation especially for someone at sea level. Removing the CV caps to shim the slide needles can help to fine-tune the mix, use thin washers. Contact Sean Morley for ordering the shims. [email protected]

Latest posts