Baffling carb issues....

[vmax2extreme]

I am posting this for one of my local vmax riders here in MD:

He has a 1990 vmax that in stop-and-go traffic when the engine temperature rises, it begins running very badly and has poor off-the-line throttle response (lots of sputtering and spitting to get moving). It is not over-heating, and the cooling fan is working. But when this happens, the float (fuel) level in one or more of the carburetors drops significantly, which I believe is causing the running problems. Once I get moving again, the problem goes away. I don't know what could be causing the low fuel levels, but I think that the heat is causing the fuel to boil in the bowls. I have tried everything I can think of except replacing the fuel pump.

Any suggestions to relay to him would greatly be appreciated.

Thanks,

Mike

 

[maleko89]

I would check plugs to verify leanness. Then, check float level. Make sure fuel/air filters are clean and then try the peashooter and if necessary teh shotgun. It sounds like you are way lean at idle but once you get moving you are okay.

 

[headknocker]

just curious; how do u know that the fuel level is low in those carbs?

 

[Rollie]

I am posting this for one of my local vmax riders here in MD:

He has a 1990 vmax that in stop-and-go traffic when the engine temperature rises, it begins running very badly and has poor off-the-line throttle response (lots of sputtering and spitting to get moving). It is not over-heating, and the cooling fan is working. But when this happens, the float (fuel) level in one or more of the carburetors drops significantly, which I believe is causing the running problems. Once I get moving again, the problem goes away. I don't know what could be causing the low fuel levels, but I think that the heat is causing the fuel to boil in the bowls. I have tried everything I can think of except replacing the fuel pump.

Any suggestions to relay to him would greatly be appreciated.

Thanks,






Is the bike stock ? Stage 7 ? Jet kit / upgraded exhaust ? :ummm:

 

[vmax2extreme]

Is the bike stock ? Stage 7 ? Jet kit / upgraded exhaust ? :ummm:

Relaying info now for response.

 

[Rhoy Carter]

Also check the charging system, that was my problem with the same symptions

 

[vmax2extreme]

His responses:

This bike is pure stock. Nothing in the carbs or exhaust. I know the fuel is low in the bowls because I've measured the level using a U-shaped tube attached to the drains.


I used to know what the peashooter and shotgun procedures were, but figured once I had cleaned the carbs several times as part of the effort to solve this problem, that would be sufficient. I have replaced the floats and float valves and the carbs are synched to perfection. At this point I need to find someone who has experienced (and fixed) this before. Also, I may need to try a known good fuel pump to see if the problem is some sort of vapor lock. It seems like that could be the issue.
I definitely have charging problems. Years ago I ran many checks and found that I wasn't seeing the right voltage. My recollection is that I saw DECREASING voltage as I revved the engine and never saw any voltage near the expected 13.5 -14.5 or so. Mine was something like 13.2 at idle and dropped to 12.9 at higher revs. I replaced the voltage regulator and that did nothing. The AC voltage measurements were all good. Regarding charging, I would really like to redo those diagnostics in the presence of another expert AND a VMax that produces the correct readings. Any ideas?

...but I have to wonder: how does a weak charging system cause low fuel levels in the float bowls? Is it because it essentially weakens the fuel pump, causing low pressure in the lines to the carbs which in turn allows the fuel to boil (aka vapor lock)?

 

[naughtyG]

I would most definitely try swapping the fuel pump with one known to work, just to eliminate it from the equation.

I've also had weird things happen here in hot traffic, so it could also always be electrical..

 

[MoPure]

How low are the wet levels? What do they measure? I just wonder if he's measuring from the right spot. I know I wasn't the first time I did it.

 

[BLKMAX]

Also check the charging system, that was my problem with the same symptions

+1 on that.

 

[jfeagins]

TWO THINGS.

The small rubber diaphrams in the pump BOTH need to be in place for the pump to create sufficient pressure to the carbs.

And a bad charging system and/or marginal battery voltage can/WILL cause significant ignition problems with the CDI box, including stalling at idle when hot, misfiring at slower engine speeds, and errant spark jumping, etc... Some of which might seem like carb issues when happening.

I've had all these conditions. Fixed the pump myself. Soldered wiring connectors, improved ground connections at the R/R and installed the larger battery. My problems were solved.

ps. knock on wood.

 

[atVMAX99]

His responses:

This bike is pure stock. Nothing in the carbs or exhaust. I know the fuel is low in the bowls because I've measured the level using a U-shaped tube attached to the drains.


I used to know what the peashooter and shotgun procedures were, but figured once I had cleaned the carbs several times as part of the effort to solve this problem, that would be sufficient. I have replaced the floats and float valves and the carbs are synched to perfection. At this point I need to find someone who has experienced (and fixed) this before. Also, I may need to try a known good fuel pump to see if the problem is some sort of vapor lock. It seems like that could be the issue.
I definitely have charging problems. Years ago I ran many checks and found that I wasn't seeing the right voltage. My recollection is that I saw DECREASING voltage as I revved the engine and never saw any voltage near the expected 13.5 -14.5 or so. Mine was something like 13.2 at idle and dropped to 12.9 at higher revs. I replaced the voltage regulator and that did nothing. The AC voltage measurements were all good. Regarding charging, I would really like to redo those diagnostics in the presence of another expert AND a VMax that produces the correct readings. Any ideas?

...but I have to wonder: how does a weak charging system cause low fuel levels in the float bowls? Is it because it essentially weakens the fuel pump, causing low pressure in the lines to the carbs which in turn allows the fuel to boil (aka vapor lock)?

I realize this post is over 1 year old but did this problem ever get solved? This is exactly what's happening to mine now and I'm poking around here to get some ideas.
Mine also is pure stock and is a 99, it last was ran in the Spring for about 40 miles where I got a fresh tank of gas and it ran fine then although since it was a cool day the temp guage never went above the dot even sitting at stops. I was planning to take it for a several hundred mile ride this Sat with my bro however when it was idling in the driveway and the temp rose to kick on the fan the idle got erratic and kept stalling and was hard re-starting. I took it to a gas station anyway to get a fresh tank and it ran great going there however when I pulled up at the pump and the temp guage was above the dot the erratic running was there and kept stalling. Luckily after I filled it, I got it running again before the battery gave out and I got it home where again it kept doing this, the temp of the day was low 90's and humid.
I'm WELL aware of the charging woes of these bikes so of course when messing with it in the driveway I have my Fluke meter monitoring the electrical system while running. When it's "behaving" I get 13.95 but when the idle starts faultering it starts going into the low 13's and when the fan kicks on it heads into the high 12's until the bike dies. I did the imfamous crimp fix and I'm under the impression that 97 and better Vmaxes got a R/R upgrade, of course it doesn't compare to the R1 one that some people upgrade to but this bike didn't suffer from this before and I'm the original owner. I pulled the plugs and didn't see anything to make me suspicious of them although I will replace them to rule them out. I have no problem accepting a low system voltage will effect the bike's running as the ignitors as well as the fuel pump could starve for power with a crappy charging system. The battery is 2 years old and the bike always has a Battery Tender on it.
My buddy has an 86 Vmax and we constantly battled the electrical issues with his bike but what won the day for him was corrosion at the stator plug and his bike did this as well until the plug was replaced. I have yet to verify mine as of this writing because I'm not sure what path I want to persue yet especially since the 13.95 is very acceptable and the idle starts to stumble BEFORE the fan comes on dragging it down more. You have me curious with the fuel pump issue although I don't understand why the fuel pump would work fine until the engine temps go above the dot?

So once again, did you guys ever solve it?

 

[SpecOps13]

I have an 89 and a 94. Both have Odyssey batteries and will hold 12.9 when left overnight. I've installed bypass switches to turn the fans on at lights on hot days. Have you flushed the cooling system and refilled with the proper coolant and mixture? Sounds like the carbs may be vapor locking due to the added heat... Just thoughts.

 

[atVMAX99]

I have an 89 and a 94. Both have Odyssey batteries and will hold 12.9 when left overnight. I've installed bypass switches to turn the fans on at lights on hot days. Have you flushed the cooling system and refilled with the proper coolant and mixture? Sounds like the carbs may be vapor locking due to the added heat... Just thoughts.

The coolant was replaced about 4 yrs ago when I had to do the water pump seal. Do you know if vapor lock is a common ailment for Vmax and if so is there a correctable solution?

Thanks for the reply!

 

[SpecOps13]

4 years is a long time for coolant. Fan Switch will keep it cool if you religiously use it and turn it off when you're moving again. It could run overspeed if on the highway and burn up... I run mine whenever the temp goes past the middle of the heat range. Remember, all 4 carbs are somewhat enclosed by the hot engine and covers. They are prone to heat sensitivity for sure...

 

[atVMAX99]

4 years is a long time for coolant. Fan Switch will keep it cool if you religiously use it and turn it off when you're moving again. It could run overspeed if on the highway and burn up... I run mine whenever the temp goes past the middle of the heat range. Remember, all 4 carbs are somewhat enclosed by the hot engine and covers. They are prone to heat sensitivity for sure...

Did you add a bypass switch to ur bike because it acts like mine and the original poster's or did you do it out of general purpose and if you left the bike stock it would be able to handle the higher temps and maintain idle?

 

[grimmie]

Mine did the same thing you're describing a few years ago. It ended up being plug wires with mine. I replaced the wires and the problem disappeared.

 

[SpecOps13]

atVMAX99: My 89 had all kinds of weird occurrences before the fan switch was added. I did it as one of the last steps to fixing a "Possessed Bike". Even had problems of the fuel pump running continuously. With and without ill effects. Fan switch fixed a lot of bugs that drove me nuts... Cost about $25.00 and has a waterproof switch. The 94 also has an indicator light to show that the fan is on...

 

[atVMAX99]

Mine did the same thing you're describing a few years ago. It ended up being plug wires with mine. I replaced the wires and the problem disappeared.

Grimmie, I'm leaning towards an ignition issue at the moment either plugs and or wires. Unfortunately today was the first chance I had to try to score a new set of plugs and the place I went to was out of stock of the NGK's these bikes take and they didn't sell another equal brand, they did expect a shipment late this afternoon or tomorrow.
On the wires, I assume you purchased several feet of a decent igniton wire and cut 4 pieces to the lengths you needed?

 

[atVMAX99]

atVMAX99: My 89 had all kinds of weird occurrences before the fan switch was added. I did it as one of the last steps to fixing a "Possessed Bike". Even had problems of the fuel pump running continuously. With and without ill effects. Fan switch fixed a lot of bugs that drove me nuts... Cost about $25.00 and has a waterproof switch. The 94 also has an indicator light to show that the fan is on...

SpecOps13, I totally agree that the stock configuration of triggering the fan is way too late and if you're stuck in stop n go traffic on a hot day the fan runs constantly trying desparetly to bring down the temp rather then coming on sooner and not allowing the bike to get to "core meltdown stage" before coming on.
However I know on my bike, at least going by the voltage readings I get with this fan on, the battery would be done if I forced the fan on sooner then normal operation thanks to the Vmax possesing the electrical system of a riding mower! If I was more willing to do Yamaha's job for them by increasing the size of the charging wire, grounding the R/R better then it is and giving it a R/R with the amperage capabilty like the 50 amp R1 rather then the 20 amp they threw on Vmax, I would force the fan on sooner like you do.