Fuel Filter/ carb issue

[He Man]

1999 Monster 900

My friends bike has been riding well until now. Its having a major fueling issue. I can get the bike to start up, no problems, but after some riding (say 20 mins), it will cut out and behave like its out of gas. After this, any subsequent attempt to start her will get her to fire up for a few cycles of the piston and immediately cut out even if i try to give it some gas after i get the engine to fire upI suspected a clogged fuel filter and replaced it (it was all sorts of rust nasty) and it ran great for a while, then went back to having that problem, but its not as severe.

Any tips? the tank is venting properly.

I am thinking that there could be something logdged inside the vaccum pump or carbs and just needs to be completely cleaned out.

[Howie]

When the bike stalls open the float bowl drains and see how much comes out.  Three likely possibilities; vacuum fuel shut off, fuel pump or the fuel hose that runs by the bottom of the cylinder collapses when warm.  I assume you checked for good spark and flooding.

[koko64]

+1. My bike had similar symptoms.
Be ready to clean the tank, carbs, tap and pump (or replace it). I went through a few filters when my tank shed a layer of scale. The bike had been sitting when I purchased it. I ended up with a Mikuni rectangular pump from Cal Cycleworks. I also changed to a clear plastic filter to keep an eye on things. I can look at how the fuel is flowing and what crud is accumulating.

[He Man]

okay here goes the whole check list

1) Riding the bike cold it runs great. After about 20 minutes the left side of the bike has gotten EXTREMELY hot. About as hot as a 4v radiator fan blowing hot air right into it, possibly worst.

2) Bike ceases to run after above mentioned.

3) Bike will turn over great, you can hear and feel the bike starting up, it just wont keep the idling. but it will start up. It will only hold over for about 3 cycles of the piston before going dead.

4) Check for spark? yes, nice big fat red spark on both pistons.

5) Fuel filter? was originally orange, but replaced it with a Napa equivalent. I blew through both filters, old filter was very clogged.

6) After replacing the fuel filter, bike was much more resonsive, but after 20 minutes the same issue, when ridding at 6am, bike is great, on the way home in traffic, it dies again. Refuses to start. The bike actually starts on first try every time. Its a very good motor.

7) emptied the fuel tank, inspected interior, no signs of rust.

removed the line between carbs and vaccum pump and cycled the bike, there was more than enough gas coming through it with just the starter motor running the engine. But it seemed kind of weak, not a strong pulse or anything just kinda dribbling out.

9) opened up the vaccum pump, looks fine, but i wouldnt know what a damaged one looks like.

thats all i have. Cleaned the carbs too. bike gave 1000 no problem miles until now

[ducpainter]

Spark should be crisp and blue

[He Man]

Spark should be crisp and blue

it was crisp, but red. what does that mean?

[ducpainter]

it was crisp, but red. what does that mean?

Not positive, but you may have an electrical issue...not fuel.

Check the spark when things cool off.

[He Man]

will check again in the morning, but the color was read when the bike was sitting for over an 3 hours already.

[ducpainter]

will check again in the morning, but the color was read when the bike was sitting for over an 3 hours already.

Would it run with that spark?

[He Man]

yes, it will idle just fine i hauled the bike about 3 blocks from my house and rode it the remaining 3 blocks into my garage and it rev'ed up without issue and developed full power on the butt dyno.

[ducpainter]

then I guess that isn't the problem.

I've never seen a red spark from an internal combustion engine coil.

I've seen blue ones...they're good...and yellow ones...not good.

[koko64]

Sometimes ignition faults are revealed when a coil or module reaches a higher temp and they may work fine until they reach that temp. A cracked coil winding is an example.

Is the weather hot where you are?  The heat on the left side, would you call it excessive?

[He Man]

to answer howies question before, there was adequete fuel in the bowls. not as much as i expected.

the heat on the left side is BEYOND excessive. Ive ridden 4vs in traffic and it sucked hardcore. this one was worst. it was actually scorchingly painful. the weathe risnt hot, this all happend in the lower 70F

[koko64]

That level of heat and on one side is a worry. No more riding until the area is inspected. Do you think the heat is coming from the alternator cover or cylinder/head area?

A thought would be to check how many volts are getting to the battery. If spark is only off the battery then that would explain weak color. I hope nothing is binding or grinding under that cover. The support beating can go, taking out the alternatoe and if you leave it, possibly the bottom end.

Just being over cautious.

Another thing for the checklist, is the oil level in the sight window dropping when the motor is started?. Just checking.

[Howie]

The color of the spark indicates temperature.  It should be blue and jump at least 1/4''.  Red is not good.  Extremely lean, as in low float bowl level will cause a notable increase in engine temperature, but, as koko states, so can an internal engine problem.  Easy shade tree check?  Pull the spark plugs and turn the engine over mechanically when cold.  Run the engine until it stalls.  Pull the plugs and rotate the engine again. 

Oh, have you looked at the spark plugs?