340 invader bog

[78invader2]

Hi guys,  my 78 invader 340 tends to bog when you hit the throttle. I cleaned the carbs and put all new jets in it. The air box is hooked up as well. It almost seems like it is running too rich. When it is cold it has no problem idling, but if it is warmed up it will slowly die if left idling. Its almost impossible to start if this happens, but choking it seems to make it worse. I know its getting fuel in the carbs. The plugs look normal though. Also, there is a nipple on the bottom of one of the carb bowls that is capped off, is this suppose to go anywhere? Thanks for the help!!

[mswyka]

Our experience with our 79 340 sounds similar.  It would take some milking of the throttle to get it going and if left to idle it would die off fairly quickly.  In our case we found two problems.  The first problem that we found was that we had pinched the fuel tank vent line between the tank and the bulk head frame.  The second problem that we found was that the moats in the needle jets were filled with oily sludgy gunk.  Once we fixed those two issues she runs great.

[78invader2]

Exactly what mine is doing. Where is the vent line located? like where does it come off of the tank at?

[mswyka]

There may be one or two vents.  They are small and located at the front of the tank on the top at either the left or right or both.  There is normally a 1/8" fuel hose attached that is doubled up on itself and held in place with a cable tie.  When we put our tank in, the hose ended up being squeezed between the frame and the front of the tank.

[78invader2]

okay ill have to take a look. Does your 340 have the econo jets on it?

[Checkmarks]

If you are rich at idle it can most definitely cause the symptoms you describe. 

Sounds like the idle mixture screw is out too far.  1/4 turns at a time to find the correct idle mixture. 

Then somebody may have changed the pilot jets to a different size (couldn't read the numbers on the jet).

The base setting is just that 1 1/2 turn out is a best guess.  Fine tune adjustments make it correct for your machine.

Three turns out is maximum LIGHTLY seated screwed down complete is the entire range for this adjustment.  If you need to get leaner such as your case you need the next jet lower if a seated idle mixture screw does not correct the air/fuel mixture.

When it is cold outside it idles correctly.  This is because a motor requires a richer mixture when the motor is cold (hence the choke).  When the motor is warmed up, better shut off the choke.  More specifically the choke cable had better close the enriching portal letting in the additional fuel.  Is the choke cable adjusted properly?  Do the plungers inside the carburetors close off the additional fuel passage?  Are these plungers seating properly?

[mswyka]

okay ill have to take a look. Does your 340 have the econo jets on it?

No, our 340 has the non-econojet 32 mm carbs - 32/139

[mswyka]

I would add too that we also recently had a problem with a perfectly good sled that would not idle even though the carbs were cleaned multiple times and the jets were new.  I think the problem ended up being a problem with the jets.  Don't rule out changing the pilot jets - again.

Attached is photo of the needle jet looking down into the moat.  Take a fine wire like a torch tip cleaning tool and make sure that there is no sludge or gunk in the moat.  Blow through the pilot passage to be sure that it is clean and flowing freely.   With the slides closed, air flow through this passage is critical to keep the fuel atomized so that the engine can idle.

[78invader2]

Okay, I put the screws back the way the guy before me had them. The smaller screw was 2 turns out on one and 1 on the other carb. The big screws were out 3 turns on one and 3.5 on the other. Im not sure what factory settings are for them.

[Gilson435]

Okay, I put the screws back the way the guy before me had them. The smaller screw was 2 turns out on one and 1 on the other carb. The big screws were out 3 turns on one and 3.5 on the other. Im not sure what factory settings are for them.

The air screw(smaller) is 1.5-2 turns out from seated and the idle screw(big) is 3 turns out from spring coil bind then adjust to achieve 3,000rpm idle speed. This info is from the Kawi assembly & prep manual.

[78invader2]

Sounds good, and how do I make sure the choke cable is set correctly and not allowing extra fuel in?

[Checkmarks]

Adjusting the big screw "throttle idle screw" can cause havoc.  You must balance the carburetors MUST.  Then this dilemma does not have effect on the idle (not entirely true).

Choke cable can be difficult.  When the sled is running, pull up each cable to see if it enriches the motor.  Should be some slop in the system of cable.  A spring is on the inside when you use the 12mm wrench to pull out the choke cable.  When you actuate the choke does the plunger move up and down?  How does the neoprene sealing look?

When you had your carburetors off cleaning them did you look thru the pilot jet hole?  All a moot point if you cannot see thru the jet.

Mswyks (Mark), you make a very good point.  Just because the pilot jet is new does not mean it was a Mikuni new jet.  Darn Chinese will sell anything to us cheap.

Just focus on idle FIRST.  Bog this bog that later. (suspect carbs out of balance).

[78invader2]

Okay, thanks. I ordered the genuine mikuni jets from Dennis Kirk, but they could be chinese crap. I ordered 170s for the mains and 25s for the pilot jets. Should I put the throttle idle screws back to the stock setting or leave them where the PO had them?

[Checkmarks]

Dennis and mikuni jets and they should be good to go. 

Once you play with the throttle screws you must balance the carburetors.  Thought I mentioned "must" once before. 

When you are in balance, how does it idle (3000rpm)?  If you are low or high (rpm) then set it to the proper rpm.  Now balance again.  Until you have the right rpm and balance carburetors you are not winning a up hill battle. 

Now that you are in balance and the proper rpm, you can set the throttle pull on the top of the carburetors.  When you move the throttle, both throttle valves had better go up at the same time.  With this adjust-ability set you are in business.

If you want to adjust the rpm of idle and just turn screws, even if the right screws are turned you have to balance the carburetors.  Balance carburetors when you have more than one carb.  K makes it easy with the enriching primer ports that are already plumed into the throat of these carburetors.  Need more tutoring? (I may need to say my language is not in design to belittling or condescending just more to the point of which screws to turn)

Your PO was lost or your sled would start and run like a champ. Do you have a proper idle yet? 

[Interceptor398]

The choke is set correct when you can move the cable at the carb about 1/16 of an inch before all the slack is used.  That is to make sure the fitting in the carb is completely seated with the choke off.