4/6 Running Problems

[mswyka]

We picked up an excellent 4/6 this past winter - the winter with no snow.  She came in with a few nits that we patched up and for as often as I attempted to start the sled over the course of the year she started right up and hummed pleasantly.  About a month ago I was in the machine shed to start a few sleds and she didn't want to start and when she did she only ran on the prime and then died out.  This week we brought the carbs into the shop and replaced all the jets.  Put the carbs back in and she runs the same way.  Starts fine when primed and will run fine until the prime runs out.  Everything in me points either to sticking fuel needles or some clog in the fuel delivery system.  The thing that confuses me about this is the fact that when the carbs came off, the bowls were full of fuel.  So, I am interested in suggestions from other 4/6 owners who may have had similar experiences.

Mark

[jimvw57]

sounds like a blocked passageway inside the carbs. time for a good long soak.  also check for a crankcase leak or a carb boot leak.

[mswyka]

Thanks Jim.  I also like the way you hinted at crank seals by saying crankcase leak. 

[mswyka]

OK, spent some more time with the sled this afternoon.  Confirmed that fuel pump is pumping fuel.  Pulled carbs again.  They look reasonably clean (reasonably meaning that they look cleaner than most of our carbs) and I was able to blow carb cleaner through each of the jets.  Back on the sled it behaves the same way - it will run if primed or if the enricheners are opened.  More fuel added when she dies and it will pick back up again so I am discounting electrical issues and am guessing that it is back to the carbs.  I will swap in the 36s off the other invader and see what she says.

[jimvw57]

I would guess that if it runs when you add MORE gas, then it is probably getting too much air in there from someplace. Not only a leaking crank seal, but maybe a crankcase leak along where the case splits. I have seen this happen if the wrong sealant is used and the motor gets flooded.

[Interceptor398]

With any old machine like these you need to assume all the seals are of the same age unless you know for sure otherwise.  If the machine is to run like new you will need new seals and gaskets.  Never over look the primer, they leak air into the fuel system.

[Checkmarks]

Mark,

I have had a pilot jet passage plugged that caused me a day to find the problem.  It is a little tiny pin prick of a passage.  One grain of sand and they are plugged.  Spraying carb cleaner through did not get mine out.  My motor did have new seals and good boots.  Be cautious not to smoke one of those pistons.  Swapping carbs with known good running carbs is a great choice testing for other Notorious leaks. 

Found now two 4/6 sleds.  One of the sleds had single plug cylinders (darn).

[mswyka]

Good afternoon and Merry Christmas.

Since the last post the engine has been out, received new crank seals and everything put back together nicely.  Crank seals were due to be replaced, but were not cracked or broken and no obvious blow by.  Engine still ran the same.  I then convinced myself that it must be that the fuel degraded over the summer and it needed fresh fuel.  So, the old fuel came out and fresh fuel went in.  Still runs the same.

To recap -

Prime the engine and it will start and act like it is running properly for 30 seconds or so and then it dies.  Re-prime and it will start again.  Alternatively, if I open the enrichener when it starts to die it will come back.  It will stay running with the enrichener open. 

The carbs have been out, all the jets replaced, and carb cleaner blown through each of the ports.

Still not sure what I am doing wrong.  Earlier this year it would start and run just fine.  It was only toward the end of summer that it started behaving this way.

[gixxer6]

Is fuel getting to the carbs?  If not, check the fuel pump.  If you have fuel in the carbs, there is probably a clogged passage. 

[Checkmarks]

Mark,

I am with Gix here.  If there is fuel in the carburetors, then you have the pilot passage plugged.  When a sled idles it only draws fuel through the pilot passage that is metered by the pilot jet.

A fresh air leak is also something to look for specifically around the rubber boots the carburetors plug into.

Recap:  plugged pilot system, no fuel in the fuel bowl, or a air leak (piston melter). 

Merry Christmas.  For my Christmas I got to change the seals in my 4/6 motor.  I should have taken a pictures for the lot of you.  Jim would have just one more nail in the 'change your seals' plank.

[jimvw57]

fought a similar issue for quite awhile when  first got my 4/6 going. Ended up being a coil problem. Only running on one plug per cylinder...

When it doesn't make sense, start at the begining, fuel, compression, spark... 

[Checkmarks]

Mark,

You say it will stay running with the enrichener (choke) on.  Stop playing around and pull the carburetors.  Use a thin steel wire like on you find for tying trash bags closed.  Strip the plastic off.  Take that and push it through the pilot passage.  Of course remove the pilot jet.

Now you said you replaced the jets.  Did you replace the pilot jet?  Tell the truth. 

[mswyka]

Thank you for the advice and suggestions.

OK, carbs are coming off again today.  I will let you know what I find.

Mark, yes, the pilot jets were changed.  New OEM pilot, main and power jets.  New "O" ring on the needle jet thing.  Everything inspected upon re-assembly and re-installation of the engine into the sled.

By the way, we had a white Christmas but not enough to run yet.

[Interceptor398]

Is the primer hooked up and have you watched for air bubbles in the gas lines?  Is the gas line in the tank good and the end sitting on the bottom of the tank?

[mswyka]

Thanks for the suggestion.  I will double check.

Carbs came out, were cleaned out, sprayed out, blown out and then re-installed.  Ran the same.  If I can keep it up around 3,500 she will stay running. 

For now back outside to plug off the primers.