Dyno Run

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Ran the ST on the dyno tonight....she's running way rich. Air filter looks fine, but I'll replace it anyway. What are the stock main jet sizes? Anything else to look for? She's a 92 with 50k miles.
 

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according to the graph, you're at the 10:1 limit of its air/fuel measurement range, or lower, which is very, very rich. I would think at those ratios your plugs would be very black, check them out and see. The ST is claimed to have about 100 factory hp, so the 83hp reading would be consistent with a very rich AF mixture.

However, its possible that neither the HP nor the AF readings are trustworthy. If someone else wanted to run their ST on it for comparison that would be interesting to see. I'd do the plug check as a first sanity check, and if they look normal you may be wasting your time going any further with the carbs. But, I could be wrong.
 
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The highest rear wheel HP I've seen on a ST1100 is 95HP. That bike had a modified air box and a "Factory" brand jet kit. The average is upper 80's to low 90's for RWHP.

You've not stated what kind of ST1100 you have, so OEM jetting will vary pending on, ABS, CA emissions, or 49 State bike.

Your A/F ratio is off the chart. I doubt it's accurate, but close. Putting a sniffer up one muffler(which they probably did) on a dyno run, will get you in the ballpark.

There is a possibility of the carbs being out of tune, sticky float, etc. However, the very first place you'll need to go, is the ignition system. Only takes about an hour to replace the plugs and do all the required resistance checks to make sure your getting full fire in the hole... Please verify that your getting full ignition power before you dig into the carbs.
 
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Seafoam ?? Might be worth a try. Run a full tank with 10 oz. of Seafoam , then refill tank and then do another pull. That may put an end to the Seafoam questions.
 
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The highest rear wheel HP I've seen on a ST1100 is 95HP. That bike had a modified air box and a "Factory" brand jet kit. The average is upper 80's to low 90's for RWHP.
yeah, I wondered about that. the Honda claimed 100HP is most likely crank HP, not RWHP, but I wasn't sure how they spec'd that. 100 crank would equate to about 85 rear wheel
 
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Any manufacturers claims for BHP will be at the crank and not the back wheel.
So yes DWalby you are not far off what would be expected after being driven through the gearbox, sideways through the diff and so on.
And remember that the 100 is in perfect operating conditions on a brand new engine.
Upt'North.
 

CruSTy

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I'd do the plug check as a first sanity check, and if they look normal you may be wasting your time going any further with the carbs.
++1 Verify the rich mixture with a plug check before you spend time and money on carb work. You have a 25 year old vehicle and unless you are the original owner who knows what could have been done if anything to fatten the mixture. Worn needle jets, shimmed needles, float levels are just a few of the possibilities.
 
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yeah, I wondered about that. the Honda claimed 100HP is most likely crank HP, not RWHP, but I wasn't sure how they spec'd that. 100 crank would equate to about 85 rear wheel
That is a rated 100hp AT the rear wheel from Honda. As I'm sure you already know, a few owners(3) have dyno proved that at minimal elevation some 5-7yrs. back with 97,95 and 96hp respectively;). IIRC, one on east coast somewhere, one in Nebraska and not sure of location of other.
 

ST Gui

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Brant said:
That is a rated 100hp AT the rear wheel from Honda.
That's somewhat surprising. I have no knowledge one way or the other. Well other than most manufacturing HP/torque specs are from the crank and not the rear wheel.

In any event it's all Power to the Axle Right On! And it's enough from either bike that anybody would leave me at the light and I'm OK with that. :D
 
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Thanks for the replies....I forgot to mention that it was a portable dyno in a trailer and it was in the 90's outside...so I bet that is part of it. I have been busy rebuilding the kid's dirtbikes, to look much more into this, but I have ordered a new filter, plugs and wires since I have no idea how old they are. I bet a good tune up will go a long way......

Thanks again all!
 
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Thanks for the replies....I forgot to mention that it was a portable dyno in a trailer and it was in the 90's outside...so I bet that is part of it.
good point, that's about a 7% change in air density compared to standard sea level atmosphere conditions just in temperature alone, and you didn't factor in altitude either.
 
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Took another look at your graph today. Don't know if I believe the A/F ratio. for the three runs, it's all over the place. Not even close for the three runs, BUT the three H.P. traces match.

Does that make sense ? Why isn't there a difference in the H.P. traces, if the A/F ratios are so different ?
 

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Took another look at your graph today. Don't know if I believe the A/F ratio. for the three runs, it's all over the place. Not even close for the three runs, BUT the three H.P. traces match.

Does that make sense ? Why isn't there a difference in the H.P. traces, if the A/F ratios are so different ?
I agree, those portable dyno's aren't real accurate somethimes. No regular calibration on them so take them with a grain of salt.

Here's a question for the original poster. What's the gas mileage like. If it's real low then I'd worry about changes.

First thing I'd do would be change the air filter then look at carb needles and jets. Needle and jet changes are a norm for crazies "looking for more power" over the years on any bike. Usually just messes up the gas mileage...
 

ST Gui

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Needle and jet changes are a norm for crazies "looking for more power" over the years on any bike. Usually just messes up the gas mileage...
+1. I went through that phase when I modded my 750-4's air intake. Four K&Ns and the bike ran very lean. Raised the needles changed the needles got bigger high-speed jets.

Had no idea what I was doing and most of the people I queried didn't really know much more than me. I didn't know any real tuners. I did increase performance noticeably by reading the plugs for top end performance.

Overall the bike felt better but other than the fuller rotation of the speedo-needle it may have all been a placebo affect. Replacing the tank with a 7gal. version offset my 'mileage' tuning.
 

lomita

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+1. I went through that phase when I modded my 750-4's air intake. Four K&Ns and the bike ran very lean. Raised the needles changed the needles got bigger high-speed jets.

Had no idea what I was doing and most of the people I queried didn't really know much more than me. I didn't know any real tuners. I did increase performance noticeably by reading the plugs for top end performance.

Overall the bike felt better but other than the fuller rotation of the speedo-needle it may have all been a placebo affect. Replacing the tank with a 7gal. version offset my 'mileage' tuning.
Yeah, speed kills. Course every once in a while hit a gold vein, bike runs great. Then mileage is a big part in any machine, all controlled by the wrist or the ankle. I get 25 miles a gallon around town at sea level with spirited driving. And yes, I love the thrill of victory, of obtaining mastery over the mechanical objective. It was no easy climb to the summit, but not everyone is cut out to deviate off the beaten path. Someday, I will actually get out on the road and see what my highway mileage is like. In the meantime, my heart glows with a certain flame that is warming, I have emergency war time power.
 
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lomita

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Nice crisp socal morning. Jetted down to the beach.

Confirmed 75, 2nd gear. Discovered that a week ago and said to myself, no way. But WAY!

Today, closed the throttle well before redline at 100, 3d gear.

Must be the Yoda stretching.

Came rolling back in at 8 a.m.. Son told me my pipes were rattling the windows as I drove up the driveway past his bedroom. The horror of it all. : )

Warms my heart.
 
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