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WHnoob

K341 Running Rough/Starving for Fuel

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WHnoob

I received this 1974 C-160 8-Speed last spring from my father-in-law, and it worked well enough to mow the lawn last season until the hi-low fork broke in the transmission.  Over the winter I replaced the transmission and rebuilt the fuel pump using the full kit from Then and Now Automotive and got to move a little snow with it.  But now it is acting up and preventing my lawn from getting mowed.  The main problem is that it starts starving for fuel after 5~10 minutes of running.  Otherwise it seems to run a little rough and the governor hunts at full throttle.

 

So far I've done the following:

1. Washed out fuel tank and replaced the shutoff valve with screen and rubber bushing.  Hoses were replaced and inline filter added at the same time the pump was rebuilt. Confirmed fuel flow at pump inlet.  No improvement.

2. Disassembled and cleaned the carburetor.  It was already pretty clean, though the throttle shaft has noticeable side play.  Ultimately replaced the float valve, valve seat, and seals.

3. Removed inline fuel filter to see if it was adding too much resistance.

4. Gravity-fed fuel from another tank.  But I couldn't drive it around to get it hot with this setup so I'm not sure if this fixed the starvation.  Only observed it still hunting.

4. Replaced points and condenser.  Spark plug was replaced ~25 hours ago last spring.  Noticed the coil currently installed is supposed to use an external resistor.  It measures ~1.4 Ohm primary, 12 kOhm secondary.  Observed bright sparks at the points with the cover off (due to excessive primary current, presumably).

 

At this point I suspect the fuel starvation is caused by the fuel pump, even though it was just rebuilt.  When cold at least It moves fuel when the engine cranks, but it is not exactly "spurting".  More of a dribble.  Once hot it seems to have trouble.  Last night when it shut down I again confirmed strong fuel flow at the pump inlet, but only vapor/bubbles coming out the outlet.  But I can't really think of a way the fuel pump would fail without leaking, unless maybe the replacement check valve springs are too strong, or the cam lobe is worn.  This engine also has the original Nelson muffler (innards are shot, based on the rattling it makes) that runs across the front of the engine a couple inches from the fuel hoses.  So I'm also wondering if it may also be related to vapor lock.

 

Anyway, my wife and I are getting tired of the long grass so I just ordered a bunch of parts from eBay to fix it once and for all - plastic fuel pump, new carburetor, new "Gravely" style muffler, ignition coil, spark plug wire.  Also a vacuum powered fuel pump in case it is cam lobe wear (don't worry - I have other plans for this if it is not needed).  I will try to post updates as progress is made.

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slammer302

Does adjusting the high speed needle on the carb help any?

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WHnoob

It might have helped with some of the hunting/rough running, but made no difference when it was starving for fuel.

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rmaynard

I have found that the kits from Then and Now are hit and miss. I have rebuilt several within the last two years and only 1 out of 3 have worked for more than a couple of hours if at all. First thing to check on the fuel pump is the check valve. That's the two little fiber discs on the inside. if you blow air (low pressure) into the inlet side, you should get air coming out of the outlet side. But air blown into the outlet side should not exit the inlet. 

 

With the price of new pumps so reasonable, I wouldn't put much time or energy into repairing the metal one.

NAPA auto parts as well as other sources have the pumps. Lots of guys are using a small electric pump.

 

Here is a mechanical one from Amazon.com

 

 

Edited by rmaynard

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WHnoob

I think I chucked the original check valves already :-(.  The only reason it needed a rebuild was probably just that the bottom casting was warped so the diaphragm wouldn't seal.  Even the replacement diaphragm didn't seal until I pounded the housing flat-ish again.

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953 nut
6 hours ago, WHnoob said:

throttle shaft has noticeable side play.

The extra air being pulled in at the worn throttle shaft pivot could be the problem. While the engine is running put a drop or two of 90 Gear Lube on the shaft to form a temporary seal and see if it helps. @Ed Kennell did a post the other day on fixing this problem.

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squonk

You may have a worn cam lobe that drives that pump. (I did) I would install an electric. (I did) 

Edited by squonk

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WHnoob

Great news!  The K341 is now running like a champ!  I reached the conclusion that the fuel starvation was caused by vapor lock and the otherwise rough running was mostly due to the ignition coil.  Here's what I did today, with media:

 

1. Replaced the rebuilt metal fuel pump with plastic one from eBay.  The fuel flow is much stronger, but it still started stalling after ~10 minutes of mowing.  When I detached the pump output hose to check flow it was under pressure, and it was bubbling like the fuel was boiling in/around the pump.

Original pump - wimpy flow:

oldpump.mp4

 

New pump: strong flow:

newpump.mp4

 

Boiling/bubbles:

fuelboil.mp4

 

2. Replaced original Nelson muffler with "Gravely" style pointed out the right side of the tractor instead of crossing the front of the engine.  This seemed to clear up the stalling issue.  It's still loud as hell - sounds about the same as the Nelson even with its detached innards.

P_20160430_125844.jpg

 

 

3. Replaced ignition coil and spark plug wire.  New coil measured 3.3 Ohms primary, 9.8 kOhms secondary.  Spark tester showed strong, consistent spark.  I forgot to test the old coil beforehand, but I recall the tester not being as bright/consistent when I did a couple weeks ago.

spark.mp4

 

I have a replacement carburetor also but did not install it yet - didn't want to change too many variables at once.  However I did notice a lot of governor hunting at mid-throttle while sitting.  So I put a few drops of oil around the throttle shaft and the hunting stopped completely.  So the throttle shaft wear is definitely still an issue, but not as noticeable at full throttle.  While it was sitting I also changed the transmission oil - yuck!

P_20160430_132629.jpg

 

So finally I got out and finished mowing the lawn, which was getting pretty long and still had over-wintered leaves in some spots.  As proof, here are some short clips of me tearing through the high grass and leaves:

mowing_1.mp4

mowing_2.mp4

revup.mp4

 

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