Work in Progress....forever

Get your questions answered here! Also be courteous and answer any you may know. Its a give and take kinda thing, we think you'll enjoy!
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tyler440
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Work in Progress....forever

Post by tyler440 »

Why wont your vmax run? Good Question, maybe because it isnt just right or maybe because it hates you... with enough time im am going to to ATTEMPT to make a step by step flowchart of everything that is neccessary to make your sled fly like it should... all of this things have been listed ALL OVER the forum already i just thought i might me nice to put them all together in a huge write up so a person could start at the begining and work down through everything until his sled runs... ideally this would be better as a webpage but, this is easier to edit and pick up and put down whenever i have a chance

the thread will be locked however so dont bother trying to chime in and slow my flow haha
My airbox is held on by one screw, not because Im lazy but because it is less weight!

Any questions or comments about this site itself can be directed to me at tylerochs@hotmail.com
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tyler440
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Location: Clarion, PA
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Re: Work in Progress....forever

Post by tyler440 »

Alright where do i start...

A guess for a lack of a better place i will start by saying every gas powered internal combustion engine requires 3 things to start

1) Compression
2) Fuel/ Air Mixture
3) Spark

Here is where it hits the fan....

1) Compression- Here is how i go about measuring compression.
The vintage vmax garage has a compression tester EXACTLY like this: http://www.carid.com/images/actron/hand ... cp7821.jpg
It simply gets pushed into the spark plug hole and as you pull the recoil the needle moves up and holds the highest reading...

TOOLS: There are several, if not hundreds, of differnet compression tester designs but they all do the same thing. One thing you have to watch out for is they will not all read the same or at least take the same amount of pulls to get to the true reading. One such as this: http://www.northerntool.com/images/prod ... 507_lg.jpg can be screwed into the spark plug hole and allows for 1 person operation. However the longer tube will result in a lower compression reading, because the air in the cylinder is filling more volume in the tube. Some versions with a hose may have the check valve at the end of the hose opposite the gauge and in these models it will only require more pulling to reach the highest reading. The particular model I linked to has the valve near the guage and will ALWAYS read lower than the one we have at vintagevmax. (not that, that's a problem, just be aware)

we also have a leak down tester, exactly like this one: http://www.harborfreight.com/media/cata ... e_2899.jpg but we have honeslty never used it! haha (as of yet)

HOW TO CHECK FOR COMPRESSION:
One very simple way to check for compression, especially on the trail is to take a spark plug (or both) out and press you thumb over the hole while someone else pulls the rope. You will want to make sure the key if off for this, for 2 reasons. 1 being, a non-grounded (spark plug) coil is bad when you pull the rope, and 2 when that plug wire tries to find ground through you hand your will not like how it feels. I have yet to see a man that can keep the compressed air inside of the cylinder with just a thumb and a loud PSST or POP should be heard. If you can keep your thumb over the spark plug hole, you might as well call the hook, you have lost compression. (been there)

The above is the "redneck" way of doing things but for those of you who have no compression tester, no access to one, or are in the middle of the woods it will get you by, barely.

The following is the CORRECT way of testing compression....
To check compression, I first start by taking BOTH spark plugs out and pressing the compression tester into a spark plug hole. Have a someone pull the rope with the throttle WIDE OPEN for as many pulls as it takes to get the needle to quit moving higher, usually around 5 good pulls. Then read the gauge (we'll say it measures 130psi) then clear the gauge and check the other side the same way. Now the manual says that the pressures should be within 10 percent of each other. Therefore of the pressure in the first cylinder is 130 then as long as the second cylinder is within 13psi you are within limit. AKA 117-143psi. If it is not within the limits then you need to take the motor apart and rebuild it. As I stated before all gauges are going to read slightly different but for reference my 84 engine, using the gauge we have, reads 130 in the right and like 125 in the left.

Readings will also be higher if the motor is warm (providing it runs). One last thing, oil is very important to piston rings sealing. If the motor has been sitting for 20 years it may be pretty dry in there and (among many other things, covered later) i suggest putting some thin oil (marvel mystery oil) down the plug holes and turning the motor over SLOWLY a couple of times before allowing it to soak in for several hours or days.
My airbox is held on by one screw, not because Im lazy but because it is less weight!

Any questions or comments about this site itself can be directed to me at tylerochs@hotmail.com
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tyler440
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Re: Work in Progress....forever

Post by tyler440 »

#2 Air/ Fuel mixture.

From what i have seen with these sleds if everything is together right the sled will run great (well duh) If my sled takes more than 2 pulls to start, there is usually a problem. Stock jetting should be close enough to get your sled to fire up.

If the motor does not fire in the first couple of pulls then you most likely have a carb issue. You can first take the spark plugs out and see if they have fuel on them. If they are wet, then you are likely getting too much gas. If they are dry then not enough. That of course is the easy part.

Wet Plugs: The engine has too much gas. Possibly your chokes are stuck open, or maybe you just pulled the sled off the trailer and with all of the bouncing around the carbs leaked into the motor. At this point i turn the key off, leave the plugs out and pull the rope about 10-15 times (maybe more) to try to get some fresh air in the motor to balance out the gas. Often you can turn the gas off and even start the motor with the gas off. It will run for longer than you would think on just the fuel in the float bowls. If it starts to bog, quick turn the gas on.

Another reason you may have gas and not run is because you dont have spark. At this point call a friend, and have him pull the rope while you have a spark plug connected to the wire and the threaded part touching the bare metal of the head. You should see a nice bright blue spark. If not make sure the key is on. If the key is on, make sure your tether and/or kill switch are functioning properly.

Dry Plugs: Your carbs need cleaned. If you do a search here you should find some threads on how to clean them. Take your time and check everything on them. Make sure everything is absolutely spotless so that you can rule that out
My airbox is held on by one screw, not because Im lazy but because it is less weight!

Any questions or comments about this site itself can be directed to me at tylerochs@hotmail.com
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tyler440
Posts: 692
Joined: Tue Jan 24, 2006 12:47 am
Location: Clarion, PA
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Re: Work in Progress....forever

Post by tyler440 »

#3 Spark

AAAAAAAAAA the dreaded spark issue... You can chase these for a while and that is probably why half of the people find their way to this website.

The first thing to do when you don't have spark is buy some brand new spark plugs. Basically anytime you try to troubleshoot any thing in this world it is a process of ruling different parts out. Although i hear of people get junk spark plugs out of the box, i have never personally seen it. New spark plugs will rule them out. Stick the new plugs on the wires and hold them to bare metal. (ground, the silver parts on the head) If you see nice blue spark, then chances are your problem is solved.

If you do not see blue spark, dont fret. If you have any kind of spark chances are it will run, just possibly sub par.

If you see no spark at all then the fun begins! :roll:

Generally no spark conditions are caused by a loose or dirty connection. The service manual goes thru a 100 different things to check before they finally resort to the dreaded "inspect harness.." solution. If you plan on keeping the sled for any amount of time i highly suggest getting a service manual, the newer the better. But i DO NOT suggest a chilton. Get the yamaha manual. In my opinion Chiltons are like choose your own adventure books that have you skipping forwards and backwards and pulling your hair out. (i cant afford any more hair loss)

More on this later...
My airbox is held on by one screw, not because Im lazy but because it is less weight!

Any questions or comments about this site itself can be directed to me at tylerochs@hotmail.com
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