Stalling Vmax - carbs or fuel pump?

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pjmac5

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I know there are many threads related to this subject as I spent days reading them. I decided to start a new thread as I want to get some feedback specific to this situation.

So I recently performed Shotgun, changed clip on needles from 2nd groove to 3rd groove. I also changed spark plugs and fuel filter. After this, the bike seemed to be running well so decided to ride her to work.

In the morning she starts fine, warms up for about 5 minutes and I am off. Initially, I can feel some hesitation at anything over 4000 RPM's but I keep riding. I am about 10 minutes down the freeway and she starts to sputter and then stalls. She will not restart immediately. After sitting for a few minutes, she fires right up. 3-4 minutes later, she stalls again. I get her off the freeway and into a parking lot. She will fire right up after sitting a few minutes and stall after 5 minutes of running even while just sitting and idling.

Well I get her on my trailer and instead of going home; I decide to take her to a mom and pop mechanic shop with a good reputation. I need new tires anyway so I grab the tire from home and figure the shop can put the tires on and I will spend $100 to have then assist with the diagnosis.

So I ask them to check a few things:

Regulator – Mechanic said OK
Fuel Tank Vent – Mechanic said OK
Fuel Tank Sensor – Mechanic said OK

Mechanic then checks gas flow to Carburetor. He calls me and says that the left side Carburetors are flooding and stalling the bike. He thinks rebuilding all the Carbs will solve the problem ($$$). This makes some sense to me because they were both running rich which is why I performed the Shotgun and changed clips. Although she ran rich and crappy, she was not stalling. Also, The Mechanic said that he connected the bike to a bench tank so it would gravity feed fuel and when he did that she never stalled. I said that if she was stalling as a result of flooding, then she should have stalled during a gravity feed of which he agreed with that statement. I told him to change the tires, and change the oil and I will think about how I want to proceed.

Questions:

Why is she stalling? Fuel Pump? Or is it the flooding but gravity feed works.

Two Carbs running rich, mechanic said flooding and I have already performed a Shotgun but never really tuned them or synced them. Opinions on complete rebuild of the Carbs or possibly an easier solution?

I would greatly appreciate any and all opinions on this.

Thanks to all!
 
I have been reading additional carburetor info. Based on my understanding NOW, changing from the 2nd groove to the 3rd groove on the needle would in fact make the bike run richer at the low end?

Is that correct? Does anyone have thoughts on the groove setting (1st, 2nd, 3rd, etc)
 
From what you have stated, I would look at fuel delivery, relay/electronics, Pump, filter, fuel lines, etc....................Tom.
 
I have been reading additional carburetor info. Based on my understanding NOW, changing from the 2nd groove to the 3rd groove on the needle would in fact make the bike run richer at the low end?

Is that correct? Does anyone have thoughts on the groove setting (1st, 2nd, 3rd, etc)

Raising the needle relative to the ground will richen the mixture. Lowering the needle closer to the ground will male it leaner.
 
+2 to all the above, I'd start with a new filter then check the fuel delivery at the tee. So, if they are flooding, is gas coming out the vents? Float level is? What do the plugs look like?
Steve-o
 
I have been reading additional carburetor info. Based on my understanding NOW, changing from the 2nd groove to the 3rd groove on the needle would in fact make the bike run richer at the low end?

Is that correct? Does anyone have thoughts on the groove setting (1st, 2nd, 3rd,
etc)

It depends on what rpm you mean by low end. Idle or just off idle I'd say no. This is more of a mid range circuit and would run richer on 3rd clip from the blunt end of the needle. It'd be checked at about 4k rpm.
 
You asked for opinions on the carb rebuild.

In my opinion - gravity feed is much lower pressure than the fuel pump. So, the supposed flooding problem is likely a little less of an issue and why the bike continues to run = Fuel pump not the problem.

So I would check wet bowl levels. It's easy to do with great instructions found here on the board.
My first inclination would be the float needles aren't seating, and you should see a higher bowl level on the left side.

If you haven't tried Seafoam in the tank, that would be my first recommendation. Get the bike to run for a few minutes so that the Seafoam will be in the carb bowls. Let it cool down so you can clean the spark plugs or even put a brand new set in for testing purposes.

Go for a ride close to home and when/if it starts to sputter, take it home and pull the plugs as soon as you can to inspect them. Check for any signs of fouling or being wet, and this too will verify flooding and you can even narrow it down to a particular cylinder.

A rebuild might be a good call, but it's a lot of money, and you want to be sure. If you're sure you need a rebuild, I'd recommend you contact Sean Morley (Morley's Muscle). I've read he offers a rebuild service at a fair price.
 
Thank you for the info. so far. Unfortunately, the bike is still at the shop. I am going to go into the shop Tuesday so I can get better idea of the level of flooding.

Mechanic said the bike runs on reserve.

Good point on the Gravity feed versus fuel pump. So just because she doesn't stall using a gravity feed tank, doesn't mean she isn't flooding out on the fuel pump.

I know the left side plugs were fouled pretty bad, Mechanic pulled them. I changed the plugs just prior to the stalling problem so the fouled plugs had less then 15 miles on them. When I pulled the old plugs, none were fouled but all were wet.

I also put Sea Foam in the tank at that time, but did likely put in way too much

I think for me, I want to determine if the flooding is in fact causing it to stall. If that is the case, then the course of action becomes more clear, I have to suck it up and rebuild these carbs or pay someone to do it.

The bike has been running rich since I bought it but never stalling. The only changes were:

Changed the Needle setting (Sounds like in the wrong direction)
New Plugs
New Fuel Filter
Added T back to the top of Air box (Again probably the wrong move)
Added Sea Foam (Too much)

So based on the needle setting change and restricting the Air flow (adding the T), I can see that I might have made the bike worse. Can the flooding be a result of these actions or just a coincidence? I should know a little more Tuesday.
 
I am going to say its an electrical problem and has nothing to do with the fuel. Carbs and problems with them dont typically vary over a short amount of time, so if a needle valve isnt seating, or if there is something else going on with the carb, its going to be quite evident from the second you start the bike and should remain relatively constant for hours on end.

Electronics, like an ignition coil, DO work just fine till they get hot, then breakdown after they reach a certain temperature.....let them cool off and they're good to go again until they get hot enough to breakdown again.

If your carbs were flooding, your exhaust would just absolutely reek of fuel and you'd be pumping out A LOT of bluish/whitish smoke that smells like straight gasoline.

If you feel that the carbs were flooding, you could disconnect the fuel line, pinch it off, or remove power to the pump and try running the bike. If overflowing is the only problem, the bike should run normally for about a minute.

ALSO, if your carbs were flooding, with the engine off, key on, you'd be able to hear the fuel pump running constantly. If it doesnt stop, that would be a clear indicator of the carbs overflowing, however I doubt this is your issue.

Good luck!
 
I ended up towing my VMAX home and keeping my fingers crossed that I will have this problem licked. I attacked this problem on several fronts:

1. Replaced the R/R

2. Cleaned Tank Vent

3. Pulled Carb rack. Main jets were DJ170. Dropped them to DJ160. The tip of the float needles were brittle and breaking down so I replaced them. Float were set rich so I adjusted them and cleaned the carbs again. Carbs have DJ Stage 1 needles which are pretty short so I moved the clip from the 3rd groove to the 1st groove from blunt end. Needle is about the same length as an OEM needle now.

4. I bought UNI individual filters and DJ breather assembly...WHY? I don't know but this forum makes me want things for my VMAX. Haven't installed them yet but this weekend.

5. Bought a Motion Pro Sync so I can sync the carbs once I get it all back together.

Haven't completed all of this so I do not know if I fixed her but by Saturday, I should know.
 
What type of exhaust is on this bike?
Good move buying the sync tool. The breather set up isn't a bad idea either.
Steve

It has a Supertrapp. I currently have 7 discs with a closed end cap. If I can, I want to drop to 6 discs. We will see, when I get her running.
 
I'd stick with the stock air box and K&N or stock filter.
Those individual filters will just cause it to run worse without aftermarket headers and air restrictors.
You might even have better luck with some Stock needles, Sean Morley
(one2dmax) can get you those if you don't have them.

Also any where from 6-8 discs on a Stock jetted Vmax works fine.
7 discs just adds a little more noise than 6 discs.

Going back down to DJ160's should help since they are equivalent to the Mikuni 150 mains.
You should also check ALL the jets and make sure they are the stock sizes.
 
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So I think I figured this. Put Airbox back on and fired this bike up so I can Sync the carbs. Noticed the fuel light is on but I am about certain she has at least 2+ gallons. After 10 minutes she stalls. SH!!!!!!!!!!!!T. Well I throw on the reserve switch and she fires right up. I but it back on the tank and she runs for quite a while. As soon as I hear hesitation, I flip the reserve switch and she stays running.

Of course the mechanic said he did this? I guess not.

So I have heard the Fuel Tank Sensor as the likely problem. What other possibilities are there?
 
I got this completely figured out. Ran her for an hour without any problems. Finished the Sync this morning which was way off. I can start to fuss over the details now, but she seems to be running very good (knock on wood). Thanks again for the replies to this post as well as the many people who have documented their work for all the rookies. I am not sure it is possible to buy a used VMAX without a forum like this.
 

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