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I have been told these are the correction jets for high altitude. In town here is almost 7,000'. The truck will see that and higher most of the time (up to around 10,000').

When I swap out jets, will I need to re-adjust/sync the carbs? Will this give me a bit of a power boost. Truck did seem to accelerate a bit better at the lower altitude where I bought her. I know it's not going to be a race car, but every little bit helps. I'm more concerned about the further loss of power when I head up further into the mountains.

If 125 jets are for high altitude then my truck certainly needs different jets. Would 120's be better for just above sea level and good up to 3000'?

While you can, it is not wise to run 125's below 4000' as overheating due to lean mixture can cause piston and or head damage.
The standard jets for sea level to 5000' are 140's.

How do I know what jets are in the carb now?

Cheers,
Morris

Pull the jet cover and read the number stamped on the end of the jets

No, but it is always wise to double check adjustments.

Whoa! 140's huh? Guess I need to swap those out! Thanks Jim.
Bruce

I run my three 710M's regularly at altitudes from 9,000 ft. to over 13,000 ft. and I am running standard (non- high alt.) jets. They run the same at the top of the passes as they do down in the valleys. I'm not sure I believe that the high altitude jets are even needed!

Well my experience running 125's tells me that they do indeed work better at high altitude. My truck ran really great on the drive back from Arizona, through Neveda, Idaho but...
Once I dropped into the low lands of the Puget Sound area the lower altitude really affected the engine. More hesitation, less power, longer warm up. Just seat of the pants observations, your truck may be different.

I figure they make them for a reason. Ordered a set today, we'll see how it goes.

The float level makes a BIG difference in how much/little fuel gets through the jets. If you float level is too high you MIGHT get by with 120's at sea level; if you float level is too low it might run OK at altitude with 140's. But if the float level is off you will probably always have some issues and problems. Best bet is to get the float level spot-on and stable (good needle valves, floats not sunk, float pivots OK, etc.) and then get the right jets. Makes a world of difference!

Jim M.
712W and 710M

Well we balanced the carbs and checked the float level before I drove the 1100 miles home. I can't imagine that it would have now changed but certainly worth a check. I am torn as to whether swap the main jets or not. The EFI system is coming soon!

Installed the 125's today. Truck seems to idle better (smoother). Also seemed to warm up faster as well. Wish I could tell you about power from the test drive, but another project (parking brake) forced my hand.