WOT Throttle - carb woes. High elevation?

Well, the bike has seemed to run fine for quite some time. But today I did a little 70 mile hop from the bike's primary location (5700ft) to where I am now (6700ft). I noticed along the way that I can't go WOT - the bike stumbles like it's only running on 2 or 3 cylinders the minute I whack the throttle open. I can only go up to 3/4 throttle but the minute I go past that - regardless of RPM or gear, it flubs. I'm guessing at the point that the jet needle is fully out of the main jet, she floods.

So I get it to flub and kill the engine at the flub point, pull into the driveway, yank 2 plugs (will look at the others tomorrow). #1 looks carbon black. #2 was more of the grey/brown. Hmmm... I would have expected all 4 to be the same color, because at the point I killed the engine, I was at WOT. So I don't expect carb synch or pilot jet mixture issues to be into play, here.

The wife will arrive tomorrow sometime with my tools and the carb synch, so I'll have to see what I can figure out. Almost seems to me like:
1. PO who drilled out the mufflers caused the bike to run richer
2. I bought the bike out of Nevada - not sure if it the jets are all stock or if they are richer (as Nevada is even lower elevation) - but current jets seem too rich for my elevation...

Several references I have seen suggest that the main jet should be reduced by 3% for every 1000 feet above sea level (not counting changes to stock configurations). Anyone else have to rejet for 5000+ ft elevation? Someone remind me what stock pilot and main jets should be?

Anyone have any general suggestions?

You do not know what mains are in it now?152.5 mk is stock.You'll definately need to go smaller than that.

VMOA member in Colorado rides in 5K-12K above sea level and here's what he's doing.

4 main jets in the size of '145' (3G2-14231-29-00)
4 pilot fuel jets in the size of '42.5' (4G0-14142-42-A0)
4 pilot air jets number 1 (PAJ1) in the size of '95' (3G2-14231-19-00)
4 pilot air jets number 2 (PAJ2) in the size of '160'" (3G2-14231-32-
00)

He basically floods it at idle and then chokes it as the rpms increase. Personally, I would leave the PFJ's alone. Put the 145 main jets in and see where you're at. Set your mixture screws like you would normally and test things out. Make sure your floats are all 17 mm too.

Thanks for the advice, guys. Remember, I also have drilled mufflers. In another thread, it was stated that drilled mufflers richen the mix.

So....

I am stock configuration (0) with:
drilled mufflers + 1
stock jets (most likely - will check as soon as I can) + 1
>5000ft elevation + 1

I have 3 items, then, that contribute to an overly rich mixture. Mark recommends 145 mains. I think maybe I need to go even a tad smaller - or - maybe 145s with a K&N?

X, K&N only makes a difference if you shim or remove your air box "Y". The air box is the restriction so you could run w/o an air filter and it wouldn't change air flow at all.

Hi Mark,
Those jetting specs are mine. The theory behind them is this,,, I'm not flooding it at idle. I run the same fuel to air ratio with the larger jetting but this gives me more 'volume' and capacity. What that does is give me a smoother transition into the midrange (needle). No coughing when blipping the throttle or transitioning to midrange like a lot of guys get. I decreased the main jetting just for the altitudes I run at. At sea level, I'd go to a 150 or 152 main. The 160 PAJ2 works in conjuction with PAj1 and the pilot system to run at correct mixture in the midrange without having to run an overly large main jet to overcome the lean midrange settings that come with a stock bike. I have a very small airbox modification also. My Vmax runs very crisp with quick throttle response at even small throttle openings. Then I 'wack it open' at low engine speeds, about 1500 rpm, it just pulls with no hiccups whatsoever. After my initial jetting, when I first reported the findings with this setup, I changed to the DynoJet springs. I did this because after I made the small airbox mod, I found that my throttle response suffered just a little bit due to less suction available to pull my slides open. The lighter DynoJet springs solved that. This thing has never been more resonsive. Makes the stock setup seem sluggish. I'm still running my stock exhaust. I get about 44-47 mpg our here in Colorado. Just thought you might like to know.
Have a good one,
Vinnie

Vinnie, thanks for the explanation.

So you put the bigger PFJ to tune transition to needle? Did you have to turn your mixture screws in at all or did the increase in PAJ1 take care of that for you? You increase your PFJ two sizes...same with PAJ1. Did you try decreasing PAJ2 the same amount to 165's?

I'm wondering if shimming your stock needles a tad would take care of it the same way. I'm reluctant to change PFJ's since they're so damn expensive. lol

Hi Mark,
With the larger pilot fuel jetting in place and the also larger air jetting with it, I only have my idle mixture screws out about 1.75-2 turns out. To get the same fuel volume before I had to have them out about 2.75-3 turns. I thought that was at the upper end of their adjustment range and wanted things to run more 'in the middle' of the adjustments. I did try stuff such as shimming the needles but that really lost the crisp performance. Providing more volume down low allowed me to keep the needles where they are tuned best to the slides. My best performance yet (including gas mileage) was with the needle left stock with no additional shims, and using more of the idle circuit capacity. I was thinking that maybe some people are shimming the needle for better transition from low to midrange, when if fact they may have a slightly limited idle circuit that would benefit from more volume. That's my reason for keeping the larger volume idle circuit and leaving the needle without shims. The change in the mains was, like I said before, just for me at my altitudes. For guys at lower levels, they probably want just a little more like a 150 to a 152 with stock exhaust. I used to read that a lot of mains jets are actually a little too big also. I heard the factories do it sometimes to get a little more gas in there when on the road to overcome the lean condition they have to use at idle for emissions purposed. Don't know if it's true but I've read if before and it kind of makes sense.

Vinnie

Well.....

I'm still on my "trip" so I haven't had time to tear into the carbs. But here is more of what is going on:

Regardless of RPM, air filter installd or uninstalled, or gear, if I roll on the throttle, from 3/4 to full, the bike ceases to pull. It sputters, coughs, etc. I just became aware of this condition this week. I've made no changes to the bike since then except one thing: I ran sea foam through it while running.

Bike is stock except for drilled muffs. I also did a carb synch last night, which did not help. V-Boost sounds and appears to be working properly.

If I do a plug chop at the point the engine runs like crap, two cyls (plugs) on the left of the bike are dark and the right hand cyls (plugs) are white.

I'm thinking the sea foam screwed something up, as the bike ran fine before that, even at high elevations.

Looks like it's time to yank the carbs and look for weird stuff, obstructions, etc. Maybe the sea foam loosened some crud...

Nonetheless, I plan to install smaller jets.

Also, my '85 airbox boots are having a hard time sealing the areas around the carb intakes. Heat, time, and exposure have changed the shape of the rubber and it's crapped out. Should I just install individual filters or bother with trying to get another air box?

X, you can get the velcity stacks/boots separately. It takes a little bit to remove and install but not too bad. It's part # 42 on the fiche: 1FK-14453-00-00

Hi X,
I'm at 6000 ft ( in Nevada) and have only minor mods to the carbs,air box and exhaust. One of the first things I did to my bike after I bought it used was to change the fuel filter. It was somewhat clogged at 4000 miles:ummm:I often ride the Sierra Nevada passes up to and over 10,000 ft with no problems pulling to redline.
Good luck,


Lew

Did some more testing. Changed spark plugs. Made no difference.

I got thinking about how the sea foam works and how I used it. I just removed the rubber vacuum port caps and injected while the bike was running. The sea foam does not even go through the carbs. Yet now I have this problem.

So, I thought spark plugs would fix the problem but they don't. Did another plug chop during the sputtering and 1, 2, and 3 look good and #4 is black. What the hell.

Is it possible that I have some kind of spark problem instead? I really don't see how the plugs should be different color at 3/4-full throttle. If it were a stuck float in #4, wouldn't the carb overflow and dump all over the floor?

If it were a coil problem, wouldn't two cylinders be affected?

:bang head: (starting to have nightmares of XS11 carbs....)

X, refresh my memory...did you test plug wires and coils? If you measure resistance from plug boots to ground what do you get? Are you getting 12 volts to red/white wire going into igniter? What's the resistance of your p/u coils when it's sputtering? Have you tested for spark by removing plugs? Easiest way is to get an inductive light and while bike is running touch the plug wires.

I discovered that my carbs have 152.5 for all 4 mains, 170s for PAJ2, 90s for PAJ1. Couldn't see the markings on the pilots. Looks like I could stand to go down quite a bit on the mains.

Sounds like stock carbs so more than likely 37.5 PFJ's. Only way to see what they are is to remove from jet block since numbering is on the side of the jet.

maleko89 said:

X, K&N only makes a difference if you shim or remove your air box "Y". The air box is the restriction so you could run w/o an air filter and it wouldn't change air flow at all.

Click to expand...

I am currently running my max with the "y" removed and the mixture screws opened to 3 1/2 turns with the Dale Walker hole shot slip on cans and it runs ok but, I was considering replaceing the "y" and turning the screws back to 3 turns( Dale told me that if it runs good then I could leave it but sometimes after a long ride it dosen`t want to start right back up again any ideas ????
I don`t have that much experience with V-4`s. I`m not at high elevation but I need some advice on this.

vmax626 said:

I am currently running my max with the "y" removed and the mixture screws opened to 3 1/2 turns with the Dale Walker hole shot slip on cans and it runs ok but, I was considering replaceing the "y" and turning the screws back to 3 turns( Dale told me that if it runs good then I could leave it but sometimes after a long ride it dosen`t want to start right back up again any ideas ????
I don`t have that much experience with V-4`s. I`m not at high elevation but I need some advice on this.

Click to expand...

I'm not at a high elev either, around 440ft here. Just for shits and giggles, one lazy afternoon, I removed the Y and went for a ride back when I was running trapps. The bike was noticeably weak.

I put everything back together and things were just fine. My A/F is about 2-3/4 out.

With slipons you don't really need to rejet. they are restricted by the stock headpipes, so they offer a very slight increase in flow. If anything drop down to a 147.5 main. I did this and my mileage went up a little and the bike was much more crisp.

I think you'll get positive results by putting the Y back on.

vmax626 said:

I am currently running my max with the "y" removed and the mixture screws opened to 3 1/2 turns with the Dale Walker hole shot slip on cans and it runs ok but, I was considering replaceing the "y" and turning the screws back to 3 turns( Dale told me that if it runs good then I could leave it but sometimes after a long ride it doesn`t want to start right back up again any ideas ????
I don`t have that much experience with V-4`s. I`m not at high elevation but I need some advice on this.

Click to expand...

If by "doesn't want to start right back up" you mean that the motor has a hard time turning over, then that is a charging/battery issue not a carb problem.

I realized that in this thread, I never posted the solution to this problem. The solution is here:
http://www.vmaxforum.net/showthread.php?t=4572

In short, I replaced the 2 rear coils/leads, which fixed the problem.

Since then, I have gone down in main jet size as well, since the bike's elevation is at least 5700.