Gen 1 blowback thru carb

[Ryce]

Hello; I am a new (to me) 2000 Max owner. My bike suddenly started running on the 2 left side cylinders. Pulling the air box off , I started doing the shotgun approach to a clogged jet. I then started the bike and now it pops from the exhaust and blows fuel out of one of the carbs. Mostly from the air-bleed holes. I really don't want to pull the carbs apart. So I am asking if there is something else that might cause this. I have spark, I don't think it is intermittent. Any thought or feedback ill be appreciated. Thank You for your time.

Ryce

 

[Fire-medic]

If you've been reading (76) New Vmax Owner FAQs....new members please read! | Yamaha Star V-Max VMAX Motorcycle Discussion Forum (vmaxforum.net) , you know these bikes are sensitive to plugging the pilot jets. That happens when sediment from the gas tank rusting clogs them. A dirty fuel filter can cause the problem, too. You can buy a generic 1/4" filter at your local auto parts store, take yours to compare, or 'advanced search' on here for exact vendors and parts #'s to look-for. There is also the rebuildable, anodized aluminum gas filter available online or maybe your local bike shop, though online is cheaper, probably.

Unfortunately, the ethanol/gas used almost everywhere domestically, also causes issues.

Does your bike only run all the time on the left cyl's, and not at-all on the right cyl's? Or, is it something that happens at idle & off-idle, and as you rev the bike, the right cyl's begin to operate?

Consider adding two things to your on-screen info: where you are, and what year you have. Access that in the upper right-hand where your screen name is. That helps us to understand issues for a particular year, assuming you don't have a swapped engine from another year. We can see what engine you have, from the engine VIN. That will show the year and the country for which the engine was made, in a cross-reference.

Some references: VMX12- Service-Manual.pdf (vmoa.net) Download this and familiarize yourself with it. Note that the beginning has 'Supplements' for different years of the bike, which is a confusing thing until you see the divisions. Updates and info on service for modified running changes during production are shown here.


Air bleed screw below CV diaphragm covers may have a metal cap over it if it hasn't been removed

Part # air bleed screw. See all the parts which need to come-out of that small passageway

Where the fine-tip of the air bleed screw (just-barely) protrudes into the venturi

The K&L rebuild kit # for the VMax carbs. The needle valve and its seat control the gas flow through the carb, one gasket is for the enrichener valve on the side of the carb body; the other gasket is for the jet block, which is held by screws, removing the jet block usually causes this gasket to tear, necessitating a new gasket. The various O-rings are often capable of being re-used, but if you've got things apart, might as-well replace them. Save the old pieces if they are intact. There is a fat, small O-ring under the CV carb cap, at the bottom, it has a nasty habit of running-away upon disassembly. Often it sticks inside the depression/relief for it, and if you renove the carb CV covers be sure to rescue each of these, and stick 'em into a baggie or an old pill container for replacement.

Drain screws for the float bowls. You don't need to completely-remove these, but you do-need a well-fitting screwdriver to loosen them. Once loosened, gas from the float bowl pees-out the rubber hose sticking out of the chrome bracket with the 'caution' sign.' Collect the gas into a container, one at a time, and see if sediment or water comes-out. Water in gas floats on-top of the gas, and it appears to-be a 'lens' of a different viscosity. A #2 phillips not-worn will usually do it, though technically, the 'phillips' screws are JIS Standard, which takes a slightly-different shape to fit perfectly. One of the CV cap's screws is a security screw, you can get the correct screwdriver from a common supplier like Harbor Freight, they come in a set. Or, you can dremel a slot across one of the phillips slots to turn it into a slotted screw. Third is to use a straight-jaw Vise-Grips to clamp onto the screw head to loosen it. The small O-ring under the CV carb cap is below the casting at the 6 o'clock position, once the CV cap is removed.

This is where you find the Yamaha crimp brass band you can solder to increase the continuity of the volts transmitted through the wire harness. Yes you need to remove some wrapped insulation to expose it, be sure to securely re-insulate it.

float bowl adjustment info

The pilot jet which often clogs with sediment or rust due to contaminated fuel and or a rusty gas tank.

A thin SS wire used to poke through hardened deposits in the lumen (opening) of the pilot jet.

 

[Ryce]

I appreciate that info. I made some assumptions (yea I know about them) I bought the bike a few months ago and the tank was out to extend the fuel capacity. So I assume that it is clean. I had the carbs out to adjust the V-Boost. The servo motor was toast. I tested that motor and it used 800 ma and locked up pegging my amp meter. I replacement the motor and it draws 100 ma. And works correctly now. I turned the carbs upside and drained some gas out. My next assumption is the fuel pump puts out enough volume to fill the float bowls. Anyway. In other CV carbs that I been around, I never had that type of blowback with a lean pilot jet situation. Regarding your electrical advice. I noticed the wires coming from the switch was warm. Essentially all of the current that is used by the bike goes through the switch. I added a relay to reroute most of the current around the switch with a relay. I now show full battery voltage that is shown on my volt meter mounted on the handle bars and at the ignition box . I think my biggest confusion; is why a lean (clogged pilot jet) would cause that much blow back. I have always been told a lean mixture burns slower. Apparently a lot slower to burn through the valve overlap. I hope that is correct or I may have a bigger problem then I want to mess with. Thanks

 

[Ryce]

One more question, if I may; Is there a "best way" to remove the jet block? I removed the 2 screws holding it on. However it is resistant to coming off, as if I missed a hidden screw. I don't want to distort or damage anything.. Thanks a lot again.

Ryce

 

[dannymax]

No hidden screw...it's probably sticking on the gasket.

 

[Dansmaxresto]

Make sure you take out the main nozzle ( I believe it’s called). It’s the bigger screw head on top of the jet block.

 

[02GF74]

As he says. The large brass slotted. screw. At the top of the picture, just below one of the steel jet block screws. If I recall correctly, there is a copper washer under.
It holds the needle guide in place. The guide has a small tang on the side to locate it in the carb body and you may need to poke it with a finger from the other side as it can drop out when the big screw is undone.

 

[Fire-medic]

Make sure you take out the main nozzle ( I believe it’s called). It’s the bigger screw head on top of the jet block.

The smaller brass with a hole is the main jet for fuel delivery, of course.

The two screws removed (and that big brass one, the needle jet screw-#28)? Just give it a tap or two on the side, and it should break-free from the gasket. Much of the time, the gasket will tear at its narrow end when it's removed, so if you have the replacement gasket on-hand, you're ready to go after your cleaning regimen. Do not lose those rubber plugs!