Just found this, might be of interest to some. It may also have been posted before but I hadn't seen it before.
ST1100 Fuel intake modifications.
- Thread starter Upt' North
- Start date
Uncle Phil
Site Supporter
Interesting read but at the end it did not seem that it made a lot difference other than to his 'butt' dynamo and his ears. 
As we say out in the hills where I'm from - 'Looks like too much sugar for a nickel'.
I've always been interested in what (if any) difference in performance would be if someone converted the ST1100 to simple fuel injection.
But as I've said before, the best and cheapest performance mod I could make to my ST1100s is for me to lose some weight!
As we say out in the hills where I'm from - 'Looks like too much sugar for a nickel'.
I've always been interested in what (if any) difference in performance would be if someone converted the ST1100 to simple fuel injection.
But as I've said before, the best and cheapest performance mod I could make to my ST1100s is for me to lose some weight!
Slydynbye
Will ride for Pie
I think there was a recent post where the user was undoing that mod because of poor running. YMMV
ST1100Y
Site Supporter
Yeah, kinda the young boys on mopeds with cleaned out silencers, if it's loud it must be mega fast...Interesting read but at the end it did not seem that it made a lot difference other than to his 'butt' dynamo and his ears.
Any OEM setup presents the the best compromise for working during all situations ever encountered...
cold, warm, hot, wet, dry, at sea level or high altitude, low, mid, high RPM, good/bad fuel, uphill/downhill... it'll work... mount it, hit the button, go ride...
The author says "
Your fuel mileage will decrease slightly
(3-5 mpg) "
I guess I have a different view on the word slightly. To me, that is a substantial loss..
Your fuel mileage will decrease slightly
(3-5 mpg) "
I guess I have a different view on the word slightly. To me, that is a substantial loss..
Just wondering here. Given that the 1100 has a low pressure fuel pump, is it capable of providing enough fuel volume during go-fast acceleration with this mod?
Problem with sites like those are they have ZERO quantitative objective data from before and after mods: NO dyno charts with AFR. Much less performance data before and after such as 1/4-mile times or radar-measured top-speeds. Butt dyno impressions as presented may possible, but clouded by psychosomatic effects. Perhaps double-blind butt-dyno testing... then you'd need to have identical bikes to start for back-to-back comparison.
Issue with getting more power isn't amount of petrol. You can always add more, but that doesn't increase power. Max BMEP in cylinders theoretically occurs at 12.5:1 AFR while in-field testing shows it's closer to 13.5:1 on NA engines. Factory mixtures are always richer than this to provide safety margin in case you get bad petrol out in boonies on super-hot day and end up with detonation/knocking (pre-ignition is something completely different). Usual factory mixtures set my manufacturers is in 11.0:1 AFR range under WOT. Anyone have dyno-chart of stock ST1100 with AFR? Typically reducing petrol is common way to increase power, remember that '60s hot-rod saying?
I did all mods possible on my Ninja 250 from cummulative racers' knowledge over past 35-yrs. Here's factory dyno (with airbox snorkel removed), stock power+1.5hp, super, super rich mixtures like most carby bikes (target is dashed line 13.5:1 AFR).
I went with all mods allowed under Superstock rules (everything external to engine that makes difference):
- snorkel removal
- K&N air-filtre (caused tonne of extra ring & cylinder wear over 5-yrs)
- full Tyga exhaust with high-mounted race-muffler
No racer has been successful at using pod-filtres due to incompatibility with CV carbs. Causes tonne of mid-range stumbling due to unstable non-laminar air-flow in that range. Dyno-testing shows they provide zero improvements, so no racers uses them. Took my bike to sponsor's dyno for final tuning. He immediately installed one size smaller main-jets before putting on dyno, since he too was 250 racer 20-yrs ago. After couple runs we got major improvement in power, but mid-ranbge lean spot 6-7.5K seen in original chart got worse to 14:1 range. My sponsor agreement doesn't allow me to share final chart, so this is intermediate table. We got +11% more power from snorkel-removal and leaning out WOT mixtures from 10:1 to 11:1
To repair mid-range lean mixtures, we went with DynoJet Stg2 needles. These have thinner mid-section to increase mid-range petrol, yet much, much thicker tip to reduce high-end fuel. Needle-clip set to lowest/leanest position.
Then he went down an additional size on main-jets. Final result was similar to this, mine's pretty much exact overlay of this:
Final results of dyno-tuning:
DYNO-TUNING IS A MUST!!! There wasn't any gains to be had on N250 by opening up airbox with additional holes. On larger ST engine, it may be possible. But I would do ONE hole at time and do dyno run to measure actual gains. Then stop and go back when gains diminish. AFR is mystery and dyno-tuning is required to optimise mixtures for max gains. FactoryPro kit came with smaller main jets for reason, they've done their dyno-testing and came up with common sizes for increasing power on ST1100. Factory jets still too large for +10% increase in flow, with would be maximum you'd get out of ST with these kinds of mods. To increase speed on street-driven ST, you'd want to focus more on increasing mid-range torque than peak high-end HP. My 1st mod would be high-lift cams to take advantage of factory rich AFR and increase torque. Something that'd require objective feedback data from dyno to really do.
Major reason many report improved performance with larger jets is because they have old clogged & dirty carbs. So 1st "mod" before anything else is complete carb disassembly and restoration to get OEM factory-clean as baseline. Then do dyno-run in bone-stock configuration to get starting-point before any mods. Resultant AFR curve will point to specific areas to improve performance.
Issue with getting more power isn't amount of petrol. You can always add more, but that doesn't increase power. Max BMEP in cylinders theoretically occurs at 12.5:1 AFR while in-field testing shows it's closer to 13.5:1 on NA engines. Factory mixtures are always richer than this to provide safety margin in case you get bad petrol out in boonies on super-hot day and end up with detonation/knocking (pre-ignition is something completely different). Usual factory mixtures set my manufacturers is in 11.0:1 AFR range under WOT. Anyone have dyno-chart of stock ST1100 with AFR? Typically reducing petrol is common way to increase power, remember that '60s hot-rod saying?
I did all mods possible on my Ninja 250 from cummulative racers' knowledge over past 35-yrs. Here's factory dyno (with airbox snorkel removed), stock power+1.5hp, super, super rich mixtures like most carby bikes (target is dashed line 13.5:1 AFR).
I went with all mods allowed under Superstock rules (everything external to engine that makes difference):
- snorkel removal
- K&N air-filtre (caused tonne of extra ring & cylinder wear over 5-yrs)
- full Tyga exhaust with high-mounted race-muffler
No racer has been successful at using pod-filtres due to incompatibility with CV carbs. Causes tonne of mid-range stumbling due to unstable non-laminar air-flow in that range. Dyno-testing shows they provide zero improvements, so no racers uses them. Took my bike to sponsor's dyno for final tuning. He immediately installed one size smaller main-jets before putting on dyno, since he too was 250 racer 20-yrs ago. After couple runs we got major improvement in power, but mid-ranbge lean spot 6-7.5K seen in original chart got worse to 14:1 range. My sponsor agreement doesn't allow me to share final chart, so this is intermediate table. We got +11% more power from snorkel-removal and leaning out WOT mixtures from 10:1 to 11:1
To repair mid-range lean mixtures, we went with DynoJet Stg2 needles. These have thinner mid-section to increase mid-range petrol, yet much, much thicker tip to reduce high-end fuel. Needle-clip set to lowest/leanest position.
Then he went down an additional size on main-jets. Final result was similar to this, mine's pretty much exact overlay of this:
Final results of dyno-tuning:
- downsized main-jets 2 sizes
- reduced high-end fuel even more with Dynojet Stg2 needle, AFR in 12:1 range, still too rich for max-power
- +21% gain in HP in top 25% of rev-range. Was 1.1s/lap faster around Laguna Seca. Nothing noticeable on streets since mid-range torque more important and only got +10% increase in mid-range areas.
DYNO-TUNING IS A MUST!!! There wasn't any gains to be had on N250 by opening up airbox with additional holes. On larger ST engine, it may be possible. But I would do ONE hole at time and do dyno run to measure actual gains. Then stop and go back when gains diminish. AFR is mystery and dyno-tuning is required to optimise mixtures for max gains. FactoryPro kit came with smaller main jets for reason, they've done their dyno-testing and came up with common sizes for increasing power on ST1100. Factory jets still too large for +10% increase in flow, with would be maximum you'd get out of ST with these kinds of mods. To increase speed on street-driven ST, you'd want to focus more on increasing mid-range torque than peak high-end HP. My 1st mod would be high-lift cams to take advantage of factory rich AFR and increase torque. Something that'd require objective feedback data from dyno to really do.
Major reason many report improved performance with larger jets is because they have old clogged & dirty carbs. So 1st "mod" before anything else is complete carb disassembly and restoration to get OEM factory-clean as baseline. Then do dyno-run in bone-stock configuration to get starting-point before any mods. Resultant AFR curve will point to specific areas to improve performance.
Last edited:
John OoSTerhuis
Life Is Good!
I remember seeing this page/report back in the last century/millennium. And debating it on the ST1100 LiSTserve. You juST can’t “hot rod” an ST1100. Adam F has some ideas on jets, but that’s about it. Leave it be, IMHO.
John
John
Walleye
Site Supporter
I believe the camshafts are the limiting factor along with valve diameter.