Loss of power as day warms up

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Nov 16, 2004
I've noticed over the past few months....commuting to-from work

Early in morning (dark o'clock, still cool) I can push to 73, 75 mph as max.
and can (as best as an ol 60 can) just zoom right on up to speed....

Evening of same day (much warmer) I'm lucky if i can get over 65,67 mph
and 'enterence ramp' on hiway is no where near long enough,,,,end up entering hiway at 45 if I'm lucky....mile or so later I might finally get to 65, almost can't keep limit of 70....

Question: Most likely cause ?
- carb, lean? rich ? Float adjust needed ?
. . . sub question: as carbs age, do they get lean from gunk build up
. . . or , abrasive gas, wear out to running rich?
- timing (no ping or rattleing, run mid-grade)
- compression ( haven't tested, afraid of what I may learn)

Rig is over 441,xxx miles (I'm orig owner), engine never opened; valve adjust 150,xxx miles ago; timing checked back then too.
Spark plugs every year (current ones are 3 months old); plug wires 2 or 3 yr ago....of course air cleaner & fuel filters are clean / recently replaced....
Starts right up every morning, stops clean (no dieselling)

I've done the 'spritz' with carb cleaner searching for manifold / vac hose leaks....none found

Thanks in advance
Is that a true speed or are you running larger tires. Its a drop in power either way I know.
Check and see if the HAI valve is working properly. This is a valve inside the air cleaner that opens the trap door that brings air into the cleaner from the big tube that leads from the front grill behind the headlight. When the air is cool, it takes air from a tube that points down the side of the engine for air that is pre-heated by the engine or exhaust. There is a round vacuum diaphram on the metal air intake tube facing the front of the engine.


part #34 controls part 40 in the picture.
1. Thanks for y'all input

2. 'true' speed as measured by GPS unit, and I can 'sense' the lack of 'enthusiam' when the air is warm...

3. The 'trap' door system has been defeated (years ago), trap door stays shut (not sucking hot air from over ex manifold)

I'll pull the plugs & look-see; may answer one of my questions (carburation); carb running lean - in warm air even leaner effect or
carb running rich... in cold air good, in warm air not good...
Ramblings from the top of my head.

You running a cat? Maybe effected by warmer temps.

I think your suppose to adjust the valves every 10-15,xxx miles. So those are well over due. Have you ever re-built your carb?

Maybe moving to Cananda is an option?;p

You making it to Tellico this year?? you'll be missed if your not.
How about this one....

Maybe your brakes are heating up causing drag.

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