Drilled out stock Exhaust carb issues

[toytime]

Hello all. I am new to the Vmax and have a problem that is stumping me.

I bought a 2005 with 7k miles, but the previous owner had removed the plates on the rear of the stock exhaust pipes (ground off the rivets), and drilled the holes out to about 1/2 inch - all five holes. Sounds pretty good (louder than I want), but pops when letting off throttle, and has a stumble/sputtering at ~3500 - 5k RPM....pulling choke helps this. Acceleration, top end and highway speeds seem good, but mid range around town.... sputtering/popping. (embarrassing)

Since pulling choke helps the sputter - is this the air screws? or pilot air jet sizing? The caps on the air screws were removed, so they had been adjusted (messed with). They were out 2 7/8 turns. I tried to adjust, but noticed the 2 screws in the carbs for the front cylinders - do nothing. I can turn them all the way in and the engine does not change idle or stall. So - seems like air/idle circuit.... but I tried all the tricks on this forum - pea shooter, PA1 and 2 and air screw shotgun cleaning. Nothing works.

Is the 3500 - 5k rpm sputter due to the inability of adjusting the air/idle? Or could the drilled out stock exhaust be the root of my problem causing a lack of vacuum ? But why does pulling the choke seem to help...running too lean...due to the air/idle issue?

I haven't pulled the carbs off yet, so don't know if main was changed, but this won't affect the air screw/idle all the way in issue? Needle is stock, and the bike does get descent highway MPG....30-35 going 75-80MPH.

Nice bike - but having this much trouble is really disappointing... any ideas?

 

[toytime]

Note - bike does seem to idle fine..... but don't understand how 2 air screws can be turned all the way in....with no affect.

 

[scuff]

http://vmax.lvlhead.com/tips/shotgun.htm try this should help, drilling out the stock exhaust is probably not your prob

 

[toytime]

Tried the 'shotgun' method - didn't help. Also tried the carb cleaner /pea shooter video on Youtube - nothing.

Is there a way to 'snake' air and fuel passages in these carbs? I would think Gumout or Seafoam and air gun would clear them.

 

[scuff]

wouldn't want to get too aggressive blowing compressor air or copious amounts of carb cleaner/seafoam down your jets you could ruin your carb internals and make your problem worse, IMO if you have done the shotgun and peashooter it may be time for a carb rebuild or you could try the shotgun a few more times I know some ppl on here have stated it took 2 or 3 shotguns to clear the issue

 

[sdt354]

Note - bike does seem to idle fine..... but don't understand how 2 air screws can be turned all the way in....with no affect.

The carbs need to be in sync before adjusting the A/F screws. That may be why you don't hear a difference when turning them. The shotgun procedure is regular
maintenance on a Vmax as well as a means to check sync.

 

[toytime]

Got a hold of a Cartune kit and synced the carbs....still have a carb that the air screw has no effect. Appears the cylinder is not getting gas in idle.... exhaust is cool until choke is set a little.

I have put seafoam in gas and have been putting on some miles.... still no idle screw effect. Tried shotgun and peashooter again... nothing.

I also still have the initial 3500-5k rpm issue when driving. sputters until the choke is pulled and then runs great.

 

[scuff]

i would contact DannyMax his banner is on the top of the page

 

[sdt354]

It's very possible you have a vacuum leak. All the rubbers should be inspected for cracks. Worst case, a tear down is in order. Danny is an excellent choice.

 

[D-Max2012]

Toytime,
I've been dealing with this exact same problem since I got my 91, 2 summers ago.

Not only have I've tried multiple times with Seafoam, and Peashooter, but synced each time after pulling the carbs. I broke down each carb into parts, putting them into an UltraSonic cleaner (TWICE).. They came out way cleaner than any other cleaning method, but the problem remains.

The PO drilled out the stock plates also.. Why he did it? I don't know. I purchased some plates from a guy here on this forum and re-riveted them back on.. Still, The problem remains. IMO, sounds better.

The PO put some higher end needles in there but didn't change the muffler, so I put a set of stocks in there I got from Sean.. Problem still remains.

I put the main jets back to stock configuration (150's and 152.5's as per the manual), still the same results. Tried 150's all around, then tried 152.5 all around.. No difference what so ever.

A/F screws all set to 2 3/4 turns out. I've tried multiple settings. It seems like mine at 2 3/4 out, affects how well the bike idles and transitions from high RPM to low. With other settings, the engine would stall out if I dropped RPM too quickly or had poor response getting to 3.5k.

I did a compression test, all 4 falls within specs as per the manual.

I coated my fuel tank to make sure there were no Foreign Matter (FM) getting to my carbs, (BTW, carbs looks great inside - spotless, no FM anywhere).

Pulled the Fuel pump, cleaned and checked all seals, diaphragms, and operation.. Pump works strong. It's a loud sob when you have it in the house :biglaugh:

There was a mixture test on this forum about seeing if you're running rich or lean.
It was pretty basic.. You take some duct tape and cover 1/2 of each of the intakes on the air box. If you find that the bike responds better, then you were running too rich. Needless to say, do this at running temp.

In my case, the duct tape showed that I was running too rich because the bike took off like a bat out of hell when I put the tape in place. Please Note that this does not seem to help that stumble around 3.5K to 4.5K.. Just raw power getting there, had improved greatly. Beyond that 4.5k area, the bike pulls like a SOB.

I've been trying to get that stumble out and I'm feeling that there is something that is allowing a bad mixture as the needles start pull out of the needle housings, around that range. I'm guessing that there is an air / fuel mix problem, since there is already a problem getting too 3.5K - 4.5K, without the use of the tape on the airbox.

So my thoughts are. If I have to back down the amount of air with tape, then I'm letting in too much air without it.. Now the question is, where is this extra air coming from?

I've changed out carb boots and intake couplings, (I thought I found the problem when I found two of my boots had serious cracks in them and one had a complete split in it). That was not the issue.. I tested for air leaks, after changing everything out, with starter fluid and propane gas test.. NO change in RPM at all.

Now, I did notice there is a small hole at front of the airbox on the bottom, with a fitting you can see from with the airbox in your hand. I could not find where this fitting goes into. There was no hose connected to it when I got the bike. I doubt that this could cause the air mixture issue but who knows?

So, as of right now, I'm running with the tape and dealing with the stumble - starting at 3.5k ending at 4.5k.

I want to remedy this once and for all. It's frustrating as hell. :bang head:
If I find anything more or that can be done, I'll let you know.

 

[Traumahawk]

Well to limit the amount of air coming into the carbs.....you can change paj2. ...which is under the diaphragm covers. Is that still the stock jetting size...which is 170?

 

[D-Max2012]

Mine is still stock.. Mikuni 170's

 

[Traumahawk]

Toytime,
I've been dealing with this exact same problem since I got my 91, 2 summers ago.

Not only have I've tried multiple times with Seafoam, and Peashooter, but synced each time after pulling the carbs. I broke down each carb into parts, putting them into an UltraSonic cleaner (TWICE).. They came out way cleaner than any other cleaning method, but the problem remains.

The PO drilled out the stock plates also.. Why he did it? I don't know. I purchased some plates from a guy here on this forum and re-riveted them back on.. Still, The problem remains. IMO, sounds better.

The PO put some higher end needles in there but didn't change the muffler, so I put a set of stocks in there I got from Sean.. Problem still remains.

I put the main jets back to stock configuration (150's and 152.5's as per the manual), still the same results. Tried 150's all around, then tried 152.5 all around.. No difference what so ever.

A/F screws all set to 2 3/4 turns out. I've tried multiple settings. It seems like mine at 2 3/4 out, affects how well the bike idles and transitions from high RPM to low. With other settings, the engine would stall out if I dropped RPM too quickly or had poor response getting to 3.5k.

I did a compression test, all 4 falls within specs as per the manual.

I coated my fuel tank to make sure there were no Foreign Matter (FM) getting to my carbs, (BTW, carbs looks great inside - spotless, no FM anywhere).

Pulled the Fuel pump, cleaned and checked all seals, diaphragms, and operation.. Pump works strong. It's a loud sob when you have it in the house :biglaugh:

There was a mixture test on this forum about seeing if you're running rich or lean.
It was pretty basic.. You take some duct tape and cover 1/2 of each of the intakes on the air box. If you find that the bike responds better, then you were running too rich. Needless to say, do this at running temp.

In my case, the duct tape showed that I was running too rich because the bike took off like a bat out of hell when I put the tape in place. Please Note that this does not seem to help that stumble around 3.5K to 4.5K.. Just raw power getting there, had improved greatly. Beyond that 4.5k area, the bike pulls like a SOB.

I've been trying to get that stumble out and I'm feeling that there is something that is allowing a bad mixture as the needles start pull out of the needle housings, around that range. I'm guessing that there is an air / fuel mix problem, since there is already a problem getting too 3.5K - 4.5K, without the use of the tape on the airbox.

So my thoughts are. If I have to back down the amount of air with tape, then I'm letting in too much air without it.. Now the question is, where is this extra air coming from?

I've changed out carb boots and intake couplings, (I thought I found the problem when I found two of my boots had serious cracks in them and one had a complete split in it). That was not the issue.. I tested for air leaks, after changing everything out, with starter fluid and propane gas test.. NO change in RPM at all.

Now, I did notice there is a small hole at front of the airbox on the bottom, with a fitting you can see from with the airbox in your hand. I could not find where this fitting goes into. There was no hose connected to it when I got the bike. I doubt that this could cause the air mixture issue but who knows?

So, as of right now, I'm running with the tape and dealing with the stumble - starting at 3.5k ending at 4.5k.

I want to remedy this once and for all. It's frustrating as hell. :bang head:
If I find anything more or that can be done, I'll let you know.

After reading your post....I find that interesting.....even in stock form....I had mine at 4 turns out....and never had those issues.

If the fitting is at the front of the airbox, it doesnt go anywhere....it is a drain.

 

[scuff]

I have stage one needles in mine and had a stumble at the same RPM's had to move my needles up 2 1/2 clips before it stopped, do you have stock needles ? maybe you could shim them ? might help just sayin...

 

[D-Max2012]

I had mine at 4 turns out....and never had those issues.

What mains are you running?
The farthest I've had my A/F screws out was 3 3/4. It seemed that the more I turned them out, the worse the bike would react, so I put them at 2 3/4 to 3 turns out..
No matter what setting I had them set at, the bike still stumbled around 3.5k to 4.5k.

 

[Traumahawk]

What mains are you running?
The farthest I've had my A/F screws out was 3 3/4. It seemed that the more I turned them out, the worse the bike would react, so I put them at 2 3/4 to 3 turns out..
No matter what setting I had them set at, the bike still stumbled around 3.5k to 4.5k.

This was when the bike was stock.....so the 152.5's. I have a question.....when you changed the needles....etc, and you fit the doughnut back into the needle, and you slip it back into the slide....did you lightly twist the needle, to make the little tit on the slide fit back into the slide? If not....it will artificially raise the needle....and make you too rich.

 

[toytime]

D-Max2012,
When your bike stumbles at the 3500-5k....does pushing the choke 'full' help? Mine clears right up....idles up of course, but no more sputter/stumble with the choke on full.

Per the stock needles... to shim them, the shaft/top then hits the big plastic cap in the slide.... can this be cut off with a Dremel/grinder?

Where can 'stock like' needles be obtained - but with the clip slots? I hear that the stage 1's can cause too much gas/rich effect.... plus kill gas mileage.

Changing PAJ2 to limit air (like tape addition)... I assume take size down from 170? down to... 165? Suggestions? Where are these found... JetsRus? elsewhere?

 

[Traumahawk]

D-Max2012,
When your bike stumbles at the 3500-5k....does pushing the choke 'full' help? Mine clears right up....idles up of course, but no more sputter/stumble with the choke on full.

Per the stock needles... to shim them, the shaft/top then hits the big plastic cap in the slide.... can this be cut off with a Dremel/grinder?

Where can 'stock like' needles be obtained - but with the clip slots? I hear that the stage 1's can cause too much gas/rich effect.... plus kill gas mileage.

Changing PAJ2 to limit air (like tape addition)... I assume take size down from 170? down to... 165? Suggestions? Where are these found... JetsRus? elsewhere?

First of all....you your needles are hitting the plastic cap, there are OTHER issues...IE shim too big...etc. Normal shimming is only .020-.030. If I remember correctly past .038.....you hit the cap. DO NOT TRIM THE TOP OF YOUR NEEDLES. The only times that I know of shimming a stock needle would be if your running a kerker 4-1.

The only "stock needles" with slots in them....are canadian. Ive used stage 1 needles before....but ONLY in the first clip from the blunt end.

I think that you did a shotgun...correct? Did you use an air compressor with about 100 psi like it says on lvlheads page?

http://vmax.lvlhead.com/tips/shotgun.htm

 

[Traumahawk]

D-Max2012,
When your bike stumbles at the 3500-5k....does pushing the choke 'full' help? Mine clears right up....idles up of course, but no more sputter/stumble with the choke on full.

Per the stock needles... to shim them, the shaft/top then hits the big plastic cap in the slide.... can this be cut off with a Dremel/grinder?

Where can 'stock like' needles be obtained - but with the clip slots? I hear that the stage 1's can cause too much gas/rich effect.... plus kill gas mileage.

Changing PAJ2 to limit air (like tape addition)... I assume take size down from 170? down to... 165? Suggestions? Where are these found... JetsRus? elsewhere?

Also.....where are you putting the shim? From the pointy end.....it should be dough nut...shim...E-Clip....washer...spring....plastic screw. Also to help seat the needle....there is a small tit on the doughnut. When you put the needle back in the slide...lightly twist the needle....to help seat the tit into the slide. If its not seated...the needle will be elevated too much.

EDIT....I forgot to put in the washer into the list

 

[Dragmaxster]

My first question would be did either one one you guys take the pilot jet out of the jetblock? When you turn that a/f screw and nothing happens IT IS CLOGGED.
There is almost nothing you can spray or run through there to completely unclog it.
I have used the smallest guitar string you can find to get them unclogged and i have a jet tool.
It is the smallest passage on the entire bike and the most problematic.