Still no increase in power.

[GiGs]

wrapped the carb boots in electrical tap

ya, I suggest NOT doing that...the engine heats the boots up quite a lot (ask me how I know ).

Point is, if they are gone...replacement is THE only fix (and no silicon doesn't work either...ask me how I know - none got into the engine).

I also use my bike very hard (granted I don't track it so consider it a street comparison in a way I guess) and my SS headers still look like they just came out of the box.

Do you have the stock sprockets by any chance ? My suggestion would be to put the stock sprockets back on, check EVERYTHING, and re-start the jetting process.


I'd hate to see the engine go BOOM

check your PM's...

[JMcDonald]

Yeah, I figured I'd take the tape off next time I took it all apart. I couldn't see any cracks, and I couldn't find any leaks creating a vacuum in the boots, but I figured I'd at least temporarily eliminate them as a problem with the tape.

[ztrack157]

I have any boots you may need if you need them.

[JMcDonald]

I don't think I do, but I will keep that in mind! Thanks .

[DaBlue1]

Getting a little off the current subject. Are you still running with the Zero Gravity Sport Touring windscreen? I read somewhere that the stock windscreen was about 51 degrees. The ST windscreen would be taller than this and causing a little more wind resistance. No?

[JMcDonald]

I am not at the moment, but after installing it I noticed no difference in how it ran up top. I think this is because it was still only about as high as the top of my helmet.

[JMcDonald]

I was thinking this morning about my header color, and realized there could be another factor.

If the left cylinder's spark is firing late (retarded ignition timing), it would result in higher EGTs from a greater fraction of the mixture burning as it leaves the exhaust valves, which would also cause the heating issue. Additionally, if that cylinder had retarded timing, it would indeed reduce power.

Is there any way ignition timing can be mechanically adjusted? Or, would it be plausible that a damaged coil would cause this to occur?


However, that none of the airflow mods seem to have increased top-end power (though while noticably increasing performance everywhere below about 10k), I am really wondering about some carb issue affecting fueling or even flow at the top end. If the slides aren't opening all the way, this would reduce airflow, which might mask an otherwise lean condition because then maximum main jet flow wouldn't be needed because there isn't the airflow to match it.

After syncing the carbs and lubing the wheel bearings, my next step is probably replacing the carbs and then possibly the rest of the ignition system (coil, wires, and plugs).

[GiGs]

my next step is probably replacing the carbs and then possibly the rest of the ignition system (coil, wires, and plugs)

duuuuuude no, check your PM's - I have a feeling that once you get everything correct (whether it is or isn't now i'm not sure) you still won't be happy in regards to power

I'll try my best to help as i'm sure others here will but in the end it might come down to : buy a 600....otherwise I think your going to go on a very expensive journey with a goal that's never achievable regardless of however many $$$ you spend.

[JMcDonald]

I am not trying to make my bike into a 600, 650, 500, or whatever. I don't have any expectations beyond (or even necessarily equal to) what anyone else has when they mod their 250s, but as Almost40 said, there is a clearly a problem with my bike, and that's all I'm trying to solve.

The more I run through the technical principles of slide-carb operation, the more I am beginning to wonder about the slide(s) not opening all the way. I say this because, despite mods which should have significantly increased the maximum airflow capabilities of the engine by a good fraction (and thus fuel requirements and thus power output), total airflow doesn't seem to have increased much, or I'd be making more power up top. Not only would a slide's failure to open reduce airflow potential, but in doing so would limit the affects of changes in jet sizes (as I've experienced) as the needles would never fully move out of the way of the main jets anyways.

But, that is my current hypothesis. There are only a few people left who seem to even care, but I figured I'd get that out for posterity's sake :P .

This weekend, I might remove the filter and make a video of what the slides are doing when revving the engine hard, as observation would obviously be the best way to determine the validity of this hypothesis.

[HKr1]

^CV carbs do suck!

[JMcDonald]

I found several threads on various forums of people discovering their slides werent openig all the way. Their symptoms seem consistent: the engine runs great up to a certain point, after which it seems to just stop trying, and mods otherwise known to increase airflow dont do anything. However, the causes, if ever discovered in those threads, seem to vary from simply binding slides, to slightly pinched diaphragms, to slightly leaking diaphragms, etc. Hopefully I can at least determine if this is the problem this weekend.
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[Shiloh]

Are you using 6th gear and top speed attended to judge power generated? If so and you are running 16/41 gears, try 4 or 5 gear runs, 6 gear is way high , 125mph at 12,300 actual, 135-140 indicated, which would require far more power that this bike will produce. Very likely, your bike as geared, will have a lower top speed in sixth, than it does in fourth.

[JMcDonald]

Yup, 4th gear!
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[JMcDonald]

Which side of the needle hole is the vacuum port supposed to be on? If think if I had ever got the slides' orientation reversed, then there might be less vacuum at that location, and thus the slides would rise less for a given amount of airflow.

[Flashmonkey]

Hey J...have you pulled the plugs to check for any signs of a lean or rich condition? If you're as off sync as almost40 thinks you are then you might see it in the plugs.

[kkim]

Originally Posted by JMcDonald

Which side of the needle hole is the vacuum port supposed to be on? If think if I had ever got the slides' orientation reversed, then there might be less vacuum at that location, and thus the slides would rise less for a given amount of airflow.

slides can only go into the carbs one way. if you had them backwards, they wouldn't have gone back into the carbs.

[JMcDonald]

Here is a pic I took this weekend, before switching from the 110s to the 108s.

Kkim, you're back! Thanks, that's good to know. I take it there is no base ignition timing to be adjusted?

Here is the tear in the diaphragm, and the left and right plugs, respectively. And the last two pics will be what the left plug looked like a month or two ago when I first started feeling like I was having some additional problem. It is with 110 and 112 mains. The one with the glove is with the 110s, and the closer one is with the 112s. In the pic with both plugs together, it is hard to tell but the left one looked very close to how it did in the pic with the single plug with 112 mains (hover over the pic for the name), if not a little more tan.

I wanted to clarify that both pics with single plugs are the LEFT side (the side currently in question), before I had the sportisi exhaust but when I had my custom dual exhaust I built. The one with both plugs is showing that the right cylinder did indeed seem to be running richer than the leff. Of course, that is after a couple hundred miles of just riding around with the setup, so the condition was produced from a combination of all RPM and load ranges.

[GiGs]

I think that tear shouldn't affect anything...maybe just (i'd be very careful with it as they are quite expensive to replace).

EDIT: Just realized which picture was which.....

Plugs looks on the lean side at 110, 112 looks a bit rich but both could be correct with some fine tuning...

108's would be to lean period.

You could also run a little bit richer to get some more power @ WOT, i.e 112 main.


Oh and if you want to test if the slides are working properly, with the carb assembled (either on or off the bike) and the air filter off, put your finger inside and slide the slides up and down. They should go all the way to the top and both feel the same with a sort of suction feel...

[JMcDonald]

Over the weekend when I disassembled the carbs, indeed one of the tests I did was to lift and drop each slide. I could tell no real difference in how quickly they dropped. HOWEVER, I did notice what seemed to be either a reduction in vacuum resistance as the slide reaches the top ~5/16" of its throw, OR a slight snag at this location. I say this because while the right cyinder (no tear) would slide smoothly all the way up, on the left side there was a noticable change in pressure required to move it, and my finger would hit the top of the carb with a more noticable "tap," as if it had accelerated at the last second. This would be due to me either subconsciously applying more force to get past some snag, or the slide moving easier at the end of its range.

I did think it looked lean with the 110 mains (at least, on the left cylinder, which seemed to be the problem in the first place), but kkim assured me it was acceptable. Also, there was a noticable reduction in power when switching to the 112s last weekend. I had the 110s in when making all the runs that changed the header color, and Almost40 seemed to think the right cylinder even looked too rich based on header color. If the right cylider is running correctly, then I'd probably stick with the 110s for both if the left ever gets some Act-Rite.

[GiGs]

I did notice what seemed to be either a reduction in vacuum resistance as the slide reaches the top ~5/16" of its throw, OR a slight snag at this location

I had the same thing, made sure the spring was straight, turned it around, re-seated it, problem solved...have to lower the top pieces slowly and evenly.

I said lean side...acceptable yes, with some fine tuning should be able to correct that (needle clip and mixture).

Note that there may be a noticeable reduction in power if you simply just switch main jets....needle clip and mixture need to also be adjusted suitably

Get the set up perfect with 110's...ride around for a week and see how it is. Switch to 112's, re do the jetting (don't just simply throw bigger main jets in), ride around for a week and see how it is.

IMHO don't worry about which set up gives you the highest top speed unless you ride around at top speed everywhere, all day, everyday....

If your still not happy then, 2 options : buy an A/F gauge OR take it to a dyno to be tuned.....

[JMcDonald]

Originally Posted by GiGs

I had the same thing, made sure the spring was straight, turned it around, re-seated it, problem solved...have to lower the top pieces slowly and evenly.

So you have had the problem of a slide not opening all the way?

[GiGs]

Just 1 slide, the left, yes...(I never rode it like that on the street though) but like I said...I did correct it

[JMcDonald]

Dang, and I've been sitting here thinking I was the only one to ever have such a problem with these carbs :P . Well, that is good to know it is a plausible cause to my problem! But, I won't know for sure til I can test this weekend. What would be great is if I could get the camera mounted solidly enough in front of the carbs, I could actually just run back and forth down the street so I can get some potentially more accurate data than simply revving it in the garage.

[Ken08Ninja]

To get a good reading on the plugs you need to install new ones, run the bike wide open for a stretch and shut the motor off. You can't read the plugs if you have any idiling or coasting.

How long are you going to mess with this? Save yourself the headache and have someone dyno tune the bike. It seems you are in over your head.

[Racer x]

One thing to remember about shutting off the bike.Either on the dyno or while riding . DO NOT drift with the engine off.
The engine oil pump feeds the transmission. If you shut off the engine while the rear wheel is spinning .You cut the oil supply to the trans and the input shaft will weld itself to the fifth gear sprocket . So always stop before turning off the engine.

ask me how I know.

[JMcDonald]

It's really, really not just a jetting issue. Dyno tuning wouldn't help fix my actual problem, especially with just a sniffer in the tailpipe. It is very obvious each cylinder is running differently, and the why could neither be determined on a dyno, or with standard tuning practices.

Ah, heh, thanks RacerX.

[Racer x]

How about a dyno and an experienced motorcycle mechanic? At the shop I use (RnR Cycles-Sterling Virginia) The owner of the shop uses the dyno for normal diagnostics. I have seen them fix some wacky stuff. And found things I did not know about.Just from there experience.

[JMcDonald]

Oh, I'm sure In experienced motorcycle mechanic might be able to figure out the problem, or at least have the time and equipment to readily do so. I just mean, sitting it on the dyno and doing a few runs with a tailpipe sniffer to determine AF won't help figure out why the cylinders are running differently. And, they clearly are, which is obviously then more than just a simple jetting issue.

But, I'll report back this weekend with whatever I find when testing slide function. If that turns out to not be the case (slides consistently open all the way), or I can't reliably determine (both slides barely open under revving and / or can't get camera stable enough for road testing) this is the cause, I will start thinking about taking it in.

[JMcDonald]

Havent tested slide function yet, but just reporting the observation that on the same stretch of road last night I was able to get up into the mid-90s starting runs in 4th, 5th, or 6th. Obviously it was a bit slower getting there starting at like 7.5k in 6th, but I was still able to reach top speed (about 95ish) at even 9k in 6th gear. That I am making the same amount of power at 9k as at 12k definitely shows the top end is not what it should be. Will report back with test findings.
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[HKr1]

Originally Posted by JMcDonald

I take it there is no base ignition timing to be adjusted?

.

Theres only 1 pickup coil. I guess you could slot the holes, to advance or retard it a bit? The timing should be the same for both cylinders, maybe you have a weak left coil/wire??
Did your old plugs look like they were wearing the same? other than color...

[Racer x]

The Brt ignition is the best way to change timing. Have you done a compression test?

[JMcDonald]

The plugs, physically, looked to be in the same condition. I didn't measure specifically but I don't remember the timing marks on the ground straps being markedly different. No compression test yet, which I definitely need to do.

And for timing I was just wanting to make sure some user-adjustable base timing hadn't been set correctly (not enough advance), as I've had that happen before resulting in poorer performance than normal.

[JMcDonald]

Hmm as far as i can tell, the slides are opening equally and fully. It was easy to see with just the side panels and air filter removed. Is it normal for a mist to come out of the intake sides of the carbs at WOT?
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[Racer x]

Originally Posted by JMcDonald

Hmm as far as i can tell, the slides are opening equally and fully. It was easy to see with just the side panels and air filter removed. Is it normal for a mist to come out of the intake sides of the carbs at WOT?
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It may be normal.I think that is the idea behind velocity stacks.They catch that mist. But you may also have a leaking intake valves.This in not that uncommon.A compression test will tell you if the pressure is low .But there are a couple other tests to determine why.

[JMcDonald]

Yeah some things came up this weekend so I didn't have as much time as I thought I would to mess with it. Maybe next week when it isn't in the teens every day I'll run it by my local bike shop and have him do a compression test to see how it looks. Though, the midrange is still quite nice (like I said, it will just about reach top speed at barely past 9k rpm in my tallest gear).

Now, all this said, I'm getting horrible gas mileage because it still overall runs and sounds way better than stock, so it isn't like I'm not enjoying it like crazy. I just like to tinker, and there is obviously something wrong (looking at the headers and comparing power at 9k and 12k on other modified graphs).

I'll have the compression checked, sync the carbs, and see if I can't have the ignition system checked. If timing is somehow retarded on that side, it would cause the apparently higher EGTs.

[Racer x]

Are you still running a 16/41 that is 9000 rpm at 104 mph It will not go faster than that.

[JMcDonald]

It was at around 9300 or so at 95mph (about 104 on the speedo). My top speed is ~95mph actual, whether I am at about 12100 in 4th or 9300 in 6th. From this data I deduced that, if I am making the same power at 9k as I am at 12k, my top end is not what it should be. On most graphs of modified bikes, there is at least a notable power difference difference between those RPMs. The Are P, Sportisi, and even Wayan's dyno are showing about a 4-6hp difference (at least 15-20%) between those two RPMs with their basic exhaust sytems. If I am making about 24-25hp at ~9k rpm (which is about what seems to be required to hit 94-95, actual), I should at least be making several more higher up, no?


Also, it would hold that same top speed in 6th whether I went to WOT or kept it at about 2/3 throttle. Between these two throttle positions I could hear more noise from the intake (I could hear because there is so little wind noise behind my ST windscreen), but it did not make any more power with the increased throttle. I don't remember if I tried playing with the throttle in 4th or 5th gear at this top speed, as I was just in 6th gear traveling somewhere.

[mrlmd]

How much longer will this go on? Why can't you accept that with the balance of HP, torque, gearing, wind resistance, etc, you just run out of power and will not get any faster than 95mph or 104 or whatever you are measuring, despite all your tinkering, meddling, adjusting, and obsessive compulsion to insist it can be better? How much faster do you expect or want out of this bike? And you wonder why you're getting "horrible gas mileage"?
You may have actually increased your HP slightly, but because of gearing and wind resistance, that doesn't necessarily translate into a significantly higher top speed.
You are at the limit of your knowledge and ability, probably at the bike's limits, maybe you know a little too much. If you want to get this solved, then get some professional help with a good race engine mechanic and a dyno to measure what's going on. You will fuss with this forever and I don't think you will ever solve this to your satisfaction and are possibly screwing up the bike and it's resale value pushing it to it's limits, as well as wasting a lot of time and energy and money and gas. You want to go faster - get a bigger bike with higher displacement - it's very simple. Just MHO and some friendly advice.

[JMcDonald]

It is hard to accept comments as friendly when they are based on wild assumptions about my attitude, but thanks I suppose . I don't know why people keep attacking me with this "get a faster bike" dismissal. I don't hear anyone throwing this at the hundreds of other people that mod their ninjettes. The "horrible gas mileage" was from simply enjoying peppiness of the bike more. But "horrible" really just refers to like 40mpg rather than the ~45 I've been getting since I got the bike.


Most everyone seems to be able to get at LEAST several HP more than stock at the top end. RacerX, with his extensive land speed and engine performance experience, seems to think a 30hp bike should be able to get to at least around 104 or so (actual). He (and most everyone else who has modded or dynoed their bike) also seems to expect more power at 12k than at 9k. That I am not even close to either of these tells me both I am not making anywhere near 30hp, and my top-end is not what it should be (and am in fact making more like 25hp based on so many other tests and anecdotes). Especially with the apparent differences in cylinder efficiency, something has to be wrong.

And if nothing else, if something is wrong I'd definitely want to repair it, especially if it is something that could on its own cause conditions (like a lean condition in one cylinder) that might be inherently more harmful than any basic mods I've done.

Just because I am not thrilled from the moment I bolted the parts on does not instantly mean I will be forever dissatisfied with the bike. I mean, I've provided plenty of evidence why I think the bike isn't running as it should be, all of which has been at some point backed up by respected members of this community, but I'm still treated so antagonistically. I really don't get it.

[Racer x]

Please don't think I am doing anything but trying to help. I think you would go 104 mph acctual with a 15/43 .that is about 12000 rpm. As you increase the ratio the rpm drops and the engine makes less power.that is why you are only getting 95 in 6th and the same speed in 4th.

How long a distance are you using to get the top speed rating.I can get to 90 in a 1/4 mile. But over 100 takes a lot longer. I have a full mile and it takes every bit to get up to speed. There may be something wrong with your bike . But that is how long it takes my bike to get over 100 mph.

To really check I. Guess a drag strip and the plug chop method will tell you a lot . You really should try to keep this type of thing off the street