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View Full Version : Sputtering, running rich up high in the mountains


CBone
07-26-2011, 12:28 PM
Ran some trails Sunday that were pretty high up with the nose of the truck pointed downhill for quite awhile. The truck really began to sputter as I descended and even stalled out a few times. Fuel filter, fuel pump all replaced in the last year, carb recently rebuilt by Jim C., HAC valve functioning properly--or so I thought. Any suggestions, thoughts? Thanks

BreckBJ44
07-26-2011, 07:45 PM
HAC shouldn't help you here in denver or higher as it is completely open at around 4000 to 4500 feet above sea... I only left mine on since I drove my old 60 to california often and wanted those extra air inlets to close when I hit the desert. Adjusting the carb in High heat over a hot engine sucks!

Only thing that comes to mind is crap in the fuel system that may stick the needle valve open and flood the carb... Happened to me so that is where my mind goes first.

Good luck!

RicardoJM
07-27-2011, 09:21 AM
Wowzers, considering the rebuilt carb and tune up/maintenance aspects, it is odd that you would have had issues. From your post, it would seem you only had issues when descending and at a steep angle - correct?

When it did stall, did it start right back up? Did you take a look at where the fuel level was on the sight glass?

CBone
07-27-2011, 10:43 AM
Kraig, thanks for the insights. Ricardo, the truck started to run rich and sputter only on the descents. It stalled 3-4 times, started right back up on all but one, where it took a few cranks to get it going. Always produced a nice dark cloud of exhaust. I did not pop the hood and look under when it was stalled with the nose pointed downhill, but I did stop twice when it was back on level ground and check the carb and fuel filter. The level of petrol in the fuel filter and the carb window were "normal". Maybe to Kraig's suggestion, just some bad gas?

subzali
07-27-2011, 11:01 AM
how do your plugs look? Maybe you're running slightly rich anyways down here, and it just got worse at altitude.

RicardoJM
07-27-2011, 11:18 AM
While it doesn't apply to your situation, on the F engine side covers the PCV valve port is near the front of the engine (on your 2F it is near the rear of the engine) and when on a steep decent oil could make it to the PCV and get sucked into the intake altering the air fuel mixture and causing the engine to smoke.

I suppose it could be bad gas, but if that were the case the gas would not be good on level ground as well as at an incline.

The dark cloud upon restart would seem to indicate that something (oil or excess fuel) is making its way into the combustion chamber. Prior to stall when the engine was sputtering, did you notice if the exhaust was smoking?

CBone
07-27-2011, 12:54 PM
Will definitely check the plugs this weekend. No black smoke, no sputtering until I spent about 30 minutes with the nose pointed downhill. In fact, it started right up after our lunch stop, and then it sputtered the entire way down.

Air Randy
07-29-2011, 01:53 PM
It sounds like your float level is a little high and that is why it's only running rich when you are pointed steeply down hill and slopping extra fuel into the motor.

subzali
08-08-2011, 04:15 PM
It sounds like your float level is a little high and that is why it's only running rich when you are pointed steeply down hill and slopping extra fuel into the motor.

I was thinking about this - wouldn't a high float level cause that to happen on an uphill? If on a downhill the fuel would "lean" up against the front of the carb, which would reduce its chances of "spilling over" into the venturis. In addition, I thought Aisan carbs were pretty resistant to "spilling over" - don't know enough about them to explain why, but I know I've seen it explained somewhere before.

BTW Carlton - any progress?

subzali
08-08-2011, 04:28 PM
I've never experienced this before, but:
http://forum.ih8mud.com/40-55-series-tech/501702-weird-experienced-before.html#post6784143

Here's an interesting post, that talks about the relative positions of various pieces of the carb:
http://forum.ih8mud.com/40-55-series-tech/442276-secondary-venturi-pouring-gas-into-second-barrel.html#post6164344

So I guess Aisans can overfill the bowl and flood, which could presumably be replicated by a steep incline, though again I don't know why it would be doing it on a downhill, it seems like it would be an uphill thing.