Need Help with Low Speed Issue

fozfoz · Nov 29, 2007

Hi all

First post here

I have thoroughly read all posts pertaining to idle/low speed issues and carb issues and I still have a low speed/idle problem.

Conditions: I have owned the bike from new (1994). It is completely stock. I do not ride much (about 1000 miles/year). Recently I let
the bike sit for a year without starting it. The bike was running fine before this period of inactivity.

Symptoms: When I started the bike after the year of inactivity it would only run with the choke on and would bog down and die if any
throttle was applied. I researched this site and others and have performed the following procedures.

Checked fuel tank and drained fuel. Fuel was in good shape. Tank was not rusted. Drained carbs and no debris or particulate matter
was noted. Fuel filter looks fine and fuel pump appears to be working properly. Replaced fuel and added seafoam.

Checked spark. All seemed to be working adequately. Checked ohms on spark plug wires ( all running around 23-24k). Plugs had very few miles on them. All plugs looked good with the exception of #2 being wet when pulled. #2 did not have any buildup. It was clean just like the other plugs, but wet with fuel when pulled.

Performed shotgun. Diaphragms all looked fine. After using this procedure there was a marked improvement in performance. Bike
would actually idle without choke and I could actually ride the bike. However it was very sluggish and hesitant off idle to about 2 to
3 k. Above the 2-3k range it ran normally through the upper rpm range including vboost. After this procedure I ran 3 tanks of
seafoam with no further improvement.

Performed peashooter with no further performance improvements.

Pulled carbs off bike. Tore down carbs including the jet block assembly and all the associated jets (including the removal of PAJ1). Cleaned all with carb cleaner
blown through with the red straw provided with the carb cleaner. I must say, the carbs were cleaner than I imagined for 13 year old
carbs that had sat unused for a year. However there was some (slight - see pic below) residue buildup on the bottom of the bowls around the
gasket material. Other than that bit of residue there was no visible problems. Note: I simply tore down and cleaned then
reassembled the carbs. I did not replace any carb parts. The results of this teardown was no obvious performance improvement
(may have made it a tad worse).

Replaced all carb and vboost boots. No noticeable improvement.

I also just noticed today that cylinders 3 and 4 heat up substantially faster than cylinders 1 and 2.

Additionally, currently it won't quite idle without dying when the choke is off. (see example video here - choke is slightly applied during the first 10 secs of video, then turned completely off)

I am at a quandary as what procedure to attempt next.

Any input would be appreciated.

Thanks
Foz

hubeerjw · Nov 29, 2007

The very first thing I would do is to get new plugs. I had a very similar problem with an older Honda Magna, and when I pulled the plug and cranked it over, there was a nice blue spark, and was scratching my head. I got new plugs, put them in and everything was fine.

davidon · Nov 29, 2007

Did you take out pilot fuel jets in the jet block and spray the jets themselves with carb cleaner?

-Lee- · Nov 29, 2007

Have you tried checking the carburetor boots? I mean the rubber tubes that the carb bottoms fit into. If it is stock like you say and these are 13+ years old there is a good chance that they are cracked and dry-rotted.

There are a few ways that you can check them.

1. Remove the carburetors and then remove the boots. Bend and flex them carefully to see if you can see some cracks. This is not always effective since even the slightest crack can let in enough extra air to cause the engine to run badly.

There is a 2nd way that I think involves spraying starter fluid (??? Help me here guys) on the boots with the engine running. I have never tried this. Supposedly if the engine surges when you do this then you have crack that are letting in extra air. Somone set me straight on this!

My recommendation would simply get a new set of those boots. They are not very expensive and with a new set you can at least eliminate that as the potential problem.

The Yamaha part number to order them is:
1FK-13597-00-00
Between $10 and $15 each.

I hope that this helps.

fozfoz · Nov 29, 2007

hubeerjw: I meant to replace the plugs earlier but kept forgetting to do it. It is a cheap thing to try hopefully will get some today. Although, does it make sense that the plugs seem to work fine at higher speeds?

davidon: I did remove the jets inside the float jet block and cleaned them as good as possible with carb cleaner. However I did not replace any of the jets.

Lee: as I mentioned in the original post

Replaced all carb and vboost boots. No noticeable improvement.

Thanks for the input

Foz

-Lee- · Nov 29, 2007

DOH!!!:bang head:

Note to self: Make sure you understand what you are reading before you post.

Sorry man!

shawn kloker · Nov 29, 2007

fozfoz said:
Hi all

First post here

I have thoroughly read all posts pertaining to idle/low speed issues and carb issues and I still have a low speed/idle problem.

Conditions: I have owned the bike from new (1994). It is completely stock. I do not ride much (about 1000 miles/year). Recently I let
the bike sit for a year without starting it. The bike was running fine before this period of inactivity.

Symptoms: When I started the bike after the year of inactivity it would only run with the choke on and would bog down and die if any
throttle was applied. I researched this site and others and have performed the following procedures.

Checked fuel tank and drained fuel. Fuel was in good shape. Tank was not rusted. Drained carbs and no debris or particulate matter
was noted. Fuel filter looks fine and fuel pump appears to be working properly. Replaced fuel and added seafoam.

Checked spark. All seemed to be working adequately. Checked ohms on spark plug wires ( all running around 23-24k). Plugs had very few miles on them. All plugs looked good with the exception of #2 being wet when pulled. #2 did not have any buildup. It was clean just like the other plugs, but wet with fuel when pulled.

Performed shotgun. Diaphragms all looked fine. After using this procedure there was a marked improvement in performance. Bike
would actually idle without choke and I could actually ride the bike. However it was very sluggish and hesitant off idle to about 2 to
3 k. Above the 2-3k range it ran normally through the upper rpm range including vboost. After this procedure I ran 3 tanks of
seafoam with no further improvement.

Performed peashooter with no further performance improvements.

Pulled carbs off bike. Tore down carbs including the jet block assembly and all the associated jets (including the removal of PAJ1). Cleaned all with carb cleaner
blown through with the red straw provided with the carb cleaner. I must say, the carbs were cleaner than I imagined for 13 year old
carbs that had sat unused for a year. However there was some (slight - see pic below) residue buildup on the bottom of the bowls around the
gasket material. Other than that bit of residue there was no visible problems. Note: I simply tore down and cleaned then
reassembled the carbs. I did not replace any carb parts. The results of this teardown was no obvious performance improvement
(may have made it a tad worse).

Replaced all carb and vboost boots. No noticeable improvement.

I also just noticed today that cylinders 3 and 4 heat up substantially faster than cylinders 1 and 2.

Additionally, currently it won't quite idle without dying when the choke is off. (see example video here - choke is slightly applied during the first 10 secs of video, then turned completely off)

I am at a quandary as what procedure to attempt next.

Any input would be appreciated.

Thanks
Foz

So all of the idle mixture screws are free and you syncronized the carbs after putting everything back together?

fozfoz · Nov 29, 2007

Shawn:

The carbs have never been synced on this bike. :doh:

I guess I am going to have to get a carbtune or some such device.

Would the carbs being out of sync cause a low speed issue (lack of power/poor idling at low rpm) but not cause a noticeable problem at higher rpm's? Remember the bike was running fine before the inactive period and the only thing that seems to help it was the shotgun method done without taking the carbs off the bike.

During the shotgun procedure I did remove all the set screws. They are currently set at the recommended 2.5 turns and I did record the original factory settings which varied from 2.125 to 2.75 turns.

Thanks for your help
Foz

davidon · Nov 29, 2007

When you cleaned pilot fuel jets did you squirt cleaner (with red straw) through top of pilot jet and see it coming out bottom of jet??. Also blow out the air jets (PAJ1, PAJ2) the same way

davidon · Nov 29, 2007

Whoops looks like you did that..must be way out of sync then

Buster Hymen · Nov 29, 2007

fozfoz said:
Shawn:

The carbs have never been synced on this bike. :doh:

I guess I am going to have to get a carbtune or some such device.

Would the carbs being out of sync cause a low speed issue (lack of power/poor idling at low rpm) but not cause a noticeable problem at higher rpm's? Remember the bike was running fine before the inactive period and the only thing that seems to help it was the shotgun method done without taking the carbs off the bike.

During the shotgun procedure I did remove all the set screws. They are currently set at the recommended 2.5 turns and I did record the original factory settings which varied from 2.125 to 2.75 turns.

Thanks for your help
Foz

When you strip the carbs to clean them, you should always sync the carbs. Carbs that are way out of whack (sync wise) can cause a lot of different running issues. There is probably someone on this forum in your area that can lend your carb sync. Eventually though, you should buy one as it is part of the maintenance.

shawn kloker · Nov 29, 2007

I prefer to use compressed air with a rubber tipped airgun through all the jets and passages right after the carb cleaner while it is still wet.

DO NOT DO THIS WITH THE DIAPHRAMS AND COASTING ENRICHENERS IN! Could blow them.

Vmax carbs need to be synchronized quit often.Specially after removing the carbs and unracking them.

Any one with one of these bikes should get a syncronizer and learn how to use it.The sync screws are delicately balanced between springs and it kind of free floats on the tension.

This should be checked every few weeks of riding season in my opinion.Just flooring it too hard(against the stops) can knock it out.

The reason it runs better in the higher rpms is that once the vboost starts to open 1&2 cylinders and 3&4 cylinders start to share the load(gas and air charge),2 carbs feeding one cylinder.Its easier to run this way rich or lean than in the 1 carb per cylinder-vboost closed.

My guess is that your one cylinder is way rich unless it was #2 then the rest would be way lean.

fozfoz · Nov 30, 2007

So the consensus is the next step is to sync the carbs?

Tried new plugs yesterday with no improvement.

I have a hard time imagining it is out of sync enough to cause all the symptoms. However, I guess that could explain the uneven cylinder temperatures?

Once I get the carbs synced, if I still have issues, would the next step be a carb rebuild?

Thanks for the input.

Foz

shawn kloker · Nov 30, 2007

fozfoz said:
So the consensus is the next step is to sync the carbs?

Tried new plugs yesterday with no improvement.

I have a hard time imagining it is out of sync enough to cause all the symptoms. However, I guess that could explain the uneven cylinder temperatures?

Once I get the carbs synced, if I still have issues, would the next step be a carb rebuild?

Thanks for the input.

Foz

Synchronizing the carbs makes the 4 cylinders work together instead of having 1,2 or 3 of the cylinders carrying all of the load. The cylinder that is hotter is working harder.

An engine that is out of sync is losing a lot of the available power.

4gasem · Nov 30, 2007

I would perform the shotgun even though you were just in there and then run Seafoam in the fuel and sync them...

Check out the VMF links above for more carb info as well as the shooting the shot gun procedure.

Oh and ride it more...:whistlin::biglaugh:

Every couple of tankfuls with 4 ounces of Seafoam isn't a bad idea...

G-Luck.

MONTREALMAX · Sep 23, 2008

Hello foz did you ever get her back together and running correctly?

Great post by the way love the video you included almost brought a tear to my eye knowing i was not alone having these low speed issues

carb sync works wonders on this machine buy the sync tool worth every penney

fozfoz · Sep 23, 2008

Hi All

Sorry for not updating my progress.

Carb synch was not the issue.

I had to do a partial rebuild of the carbs.

I did get a carbtune II and it does work very well.

Thanks for all the input on this topic.

jaikrishnan · May 17, 2014

Hello everybody, greetings from dubai , UAE. thanks for sharing your experiences on this forum so that others can gain a lot from that. can you tell me where to find the peashooter video?

Traumahawk · May 17, 2014

Here is the video.....and also sending you a link to how to do the shotgun.

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

https://www.youtube.com/watch?v=xItRzty9_hA

Need Help with Low Speed Issue

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