Power Loss ?

[Large]

I have a 1999 IS stock exhaust rebuilt carbs with 38 slow jets. I have power loss in 90+ degree weather is this normal ?

[sandy]

A most talented mechanic on this board, told me that 38 jets are way too large for Valks. His exhaust gas analyzer shows that idle mixture is too rich at 1/8 turn open. IMHO; These bikes run best completely stock. I've had 3 Valks and love my current stock '97 Tourer.

[98valk]

A most talented mechanic on this board, told me that 38 jets are way too large for Valks. His exhaust gas analyzer shows that idle mixture is too rich at 1/8 turn open. IMHO; These bikes run best completely stock. I've had 3 Valks and love my current stock '97 Tourer.

I've been yelled at for stating same, no need for 38s unless air box mods are done.  Pilot jets are good up to four turns open. need more than that, then next size PJ.

[Bagger John - #3785]

I've run #38s in 4 of 5 of mine. Additionally, adjustable jet needles. This with stock airbox and stock exhaust.

1 1/2 turns out on the pilot screws and the needle clips in the 2nd notch from the top.

Plugs are inspected annually for coloration and condition. Unless there's something wrong with an individual carburetor or the bike has an overly dirty air cleaner element, none are any darker than they were when the stock carb components were installed.

Power is definitely not "down" at any temperature. I've ridden them in 30 degree weather and in 100 degree weather with equal results, other than a freezing or sweaty driver.

To the OP:

Have you verified adequate fuel flow, and have you inspected the plugs for rich/lean indication?

[98valk]

I've run #38s in 4 of 5 of mine. Additionally, adjustable jet needles. This with stock airbox and stock exhaust.

1 1/2 turns out on the pilot screws and the needle clips in the 2nd notch from the top.

Plugs are inspected annually for coloration and condition. Unless there's something wrong with an individual carburetor or the bike has an overly dirty air cleaner element, none are any darker than they were when the stock carb components were installed.

Power is definitely not "down" at any temperature. I've ridden them in 30 degree weather and in 100 degree weather with equal results, other than a freezing or sweaty driver.

To the OP:

Have you verified adequate fuel flow, and have you inspected the plugs for rich/lean indication?

plugs cannot be read with unleaded gasoline.
 put a gas analyzer on them and u will see your rich and losing power.

[nogrey]

On a bit of a different vein, I’m going to throw this out there because I’ve only seen it with one of my bikes. Every summer, when the temps got in the 90’s and I’d take my 01 Interstate out. If I were climbing a long hill or the like at highway speeds, if I’d throttle up (as if to pass) she’d start to act like she was vapor-locked or like maybe the fuel tank vent was plugged. Oddly, if I’d switch it to reserve (even if the tank was full) it seemed to remedy the issue. This happened several times over the course of that summer and the next. I finally replaced my petcock with a Pingle hi-flo and never experienced the problem again.
May not be your problem at all, just throwing it out there as it was an odd-duck problem.
I’m no carb expert, but I ran 38’s in my ‘97 red/white for a couple of years. The only effect it had on my bike was to use more fuel. I switched back to 35’s and never looked back.
That’s just my experience. Stock ‘97 with stock air filter and pipes.

[Large]

Thanks for the responses my IS only has 17,000 miles thinking about adjusting the valves. I do tend to stay in the upper rpm range. Only losses power on long steep grades in 90+ temps. Idle mix set at 1 5/8's turns out one shim on the needles, desmoged ,new red eye gaskets last year, and vacuum lines, plugs look good not running hot or blueing the header pipes do have the ect mod (no knob)

[Bighead]

Your valves will be in spec.

[98valk]

Thanks for the responses my IS only has 17,000 miles thinking about adjusting the valves. I do tend to stay in the upper rpm range. Only losses power on long steep grades in 90+ temps. Idle mix set at 1 5/8's turns out one shim on the needles, desmoged ,new red eye gaskets last year, and vacuum lines, plugs look good not running hot or blueing the header pipes do have the ect mod (no knob)

manual states at 12k miles adjust the valves. do it to have a base standard then re-check at 24k, and you will know for your bike and riding style if 12k is a good interval or you can go longer.

[nogrey]

Thanks for the responses my IS only has 17,000 miles thinking about adjusting the valves. I do tend to stay in the upper rpm range. Only losses power on long steep grades in 90+ temps. Idle mix set at 1 5/8's turns out one shim on the needles, desmoged ,new red eye gaskets last year, and vacuum lines, plugs look good not running hot or blueing the header pipes do have the ect mod (no knob)

That’s interesting. The only bike I’ve had this happen on was my ‘01 interstate. The Pingle hi flow petcock was the issue. It won’t be your valves. If it runs fine until this issue pops up, it’s not going to be valves. It’s most likely fuel delivery. You could try just removing your petcock and checking the screen.

[Ricky-D]

Thanks for the responses my IS only has 17,000 miles thinking about adjusting the valves. I do tend to stay in the upper rpm range. Only losses power on long steep grades in 90+ temps. Idle mix set at 1 5/8's turns out one shim on the needles, desmoged ,new red eye gaskets last year, and vacuum lines, plugs look good not running hot or blueing the header pipes do have the ect mod (no knob)

That’s interesting. The only bike I’ve had this happen on was my ‘01 interstate. The Pingle hi flow petcock was the issue. It won’t be your valves. If it runs fine until this issue pops up, it’s not going to be valves. It’s most likely fuel delivery. You could try just removing your petcock and checking the screen.

I agree completely that it is not the valves.
I also want to add that seeing the carburetors have been modified with needles and jets, it seems that a lot of the problem is self inflicted. I mean, any kind of a baseline has been lost since it's not stock, and most all comments over the years regarding these kind of "adjustments" is that there has been a loss of performance.
So now it's just on a steady decline.
My suggestion would be to get it back to stock and regain all that lost power.

***

[signart]

Petcock failure? Tried switching to reserve? Open tank lid? Inline filter added? K&N filter?
Not your 38's!

[Large]

Until this problem has been running great has new stock style air filter, rebuilt petcock last year as a preventive maint and timing belts. Carbs had been cleaned by a local honda dealer lol. When I took them apart they were dirty and had clogged slow jets So I put in new jets, idle mix seals and gaskets. I also had a harsh ride bottomed out on small bumps so I took the forks apart to change the fluid to 15W after the same dealer had rebuild the forks and I found only about 12oz off fluid in each fork about half of the recommend amount. I was gave the bike by my father he had all the dealer work done before I received it. It will not go to a dealer again. I have a friend that has a carb sync kit going to check and see if that is the problem. 

[Paladin528]

The higher the outside air temperature gets the less dense the air becomes.  if the air is humid this makes it worse.

At that temperature your bike thinks its 8000 feet in the air as far a density goes (rough calculation) performance will suffer