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Mystery power loss puzzle

3K views 40 replies 16 participants last post by  duc96cr 
#1 ·
Okay so just for fun the 1993 in the shop was run on the dyno today as the first bike since setting the dyno back up. All systems go and runs went without a hitch.
Except... the bike only made about 25rwhp. Double checked the settings because I must have hooked something up wrong , swapped the ignition pickup to the rear cylinder to test for a bad ignition. Both runs look fine just no one is home. A little background on the bike is in order, it was a cheap bike that everyone loves to find and yes it had all the trademark issues.

Compression and leakdown tests were done and both were good.
full tune done and the valves probably had not been done in a looonnng time.
carbs sync'ed and the fuel screws set on a gas tester (1 screw was falling out)
air filter plugs etc all good. not running on one at any point, sounds fine just weak.
I was shocked as the bike sounded much better than it looked and was shaping up to be another good bike finding a good home, by ear it sounds normal and good.
Air fuel on the dyno showed a little rich down low rpm but gets better as the rpms climb, certainly not bad enough to cause a 2/3 loss of power.

Well that's how my day ended tomorrow I see if my finding is correct but for now what do you think?
975043
 
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#2 ·
seems like the carbs are suspect. things are working as you say but no power. wrong jetting or reduced jet sizing due to coating of ? on the bores of the jets.... I would look into the carbs.

Fred
 
#4 ·
I think you will notice something NOT moving.

well you would if the video would have loaded, anyway good guess as with the filter out you can see that neither slide budged, i force fed air into the right carb and the slide moves but the left is dead as can be.

Going in
975053
tomorrow.
 
#6 ·
i've had a few recently that have been sitting for some time where the needles have been stuck in the needle jets with fuel residue. i think it's the yellow die they put in our unleaded. a friend who used to work at the refineries said that the raw die is so concentrated in the drums it's black. in the carbs it's dark green.

years ago when we were doing bimota we had an sb6 dyno rather low that the owner was pissing and moaning about. turned out he'd adjusted all the free play out of the rear brake. not sure why it didn't just melt it though.
 
#8 ·
Well I made no progress on it today as I need the okay to do more work on the bike,costs and all. I assume I will be back on it next week but I have the 94 that needs a cylinder fixed and its fresh carbs installed first.



975077


The 94 needs dyno time and for me to re-install the horizontal top end and make sure tyhe oil consumption problem is gone. then I will have time to re-visit the carbs on the 1993.

Brad the slides will lift if you manually move them or blow air in the hoses well on the right side the air will move it on the left it igf not budging. I am going to guess a pinched or holed diaphragm.
jimc2
exhaust is clear and seems to flow well at 8000rpm on the dyno buy who knows if the carbs dont fix it that is one step before I touch the motor.
 

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#37 ·
Well I made no progress on it today as I need the okay to do more work on the bike,costs and all. I assume I will be back on it next week but I have the 94 that needs a cylinder fixed and its fresh carbs installed first.



View attachment 975077

The 94 needs dyno time and for me to re-install the horizontal top end and make sure tyhe oil consumption problem is gone. then I will have time to re-visit the carbs on the 1993.

Brad the slides will lift if you manually move them or blow air in the hoses well on the right side the air will move it on the left it igf not budging. I am going to guess a pinched or holed diaphragm.
jimc2
exhaust is clear and seems to flow well at 8000rpm on the dyno buy who knows if the carbs dont fix it that is one step before I touch the motor.
Jumping into the middle of the thread jack...

Another method of testing CV carbs, is (with them removed from the bike) to attach the suction hose of a vacuum cleaner to the manifold side of the carb. With the vacuum on full suck, operating the butterfly (throttle) should cause the carb slide to raise.
I wrapped the nozzle of my vacuum so it could be jammed into the front of the carbs with a good seal.
 
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#10 ·
As usual it is not the fault of Ducati, Mikuni or the rubber tree plant that gave us the diaphragm. More likely the fact the carbs were cleaner than the rest of the bike and there are other hints to the prior owner/mechanic like the cases holding 2 extra quarts of oil, 7 chrome studs and one updated stud that seems to be slightly further exposed than the rest. A 8mm bolt holding the sidestand bracket to the case because they could not get the rest of the broken steel bolt out of the case. I could go on....
 
#12 ·
Stages of bike ownership

first owner= love and care
second = love and some care
third = love
fourth =cool bike for cheap, abuse and no care
fifth =look a running motorcycle
sixth = look a non-running project bike
My customers = Hey look how cheap I got this bike for, followed by its going to cost how much to fix it? lol
 
#14 ·
Where to start

Who ever hacked this bike should really take up a new hobby, I should not complain as this is all billable hours to fix screw ups.
Today's chores was to tackle the carbs first as I already knew the slides were not opening. BUT THAT'S NOT ALL....
If you have a bad gasket, don't change it just add some goo.
If you are missing a o-ring or two don't worry leave them out.neither o-ring in the diaphragm chamber.
shims on the needle? mix it up, put one on top and the other side put it on the bottom.
Pilot jets? well it is a 1993 so it might be a 37.5 but then some like a 40. so to get there use a 37.5 in one carb and a 42.5 in the other.
at least the needle jets are fine.

That's not even mentioning the broken off bolt in the tank latch and in the engine cases from the side stand.

975363


well at least it survived the dyno runs without a problem and the gains were worth the effort. I was only surprised at how decent the fueling was with both slides fully closed at 7,000rpm


975364
 

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#17 ·
Where to start

Who ever hacked this bike should really take up a new hobby, I should not complain as this is all billable hours to fix screw ups.
Today's chores was to tackle the carbs first as I already knew the slides were not opening. BUT THAT'S NOT ALL....
If you have a bad gasket, don't change it just add some goo.
If you are missing a o-ring or two don't worry leave them out.neither o-ring in the diaphragm chamber.
shims on the needle? mix it up, put one on top and the other side put it on the bottom.
Pilot jets? well it is a 1993 so it might be a 37.5 but then some like a 40. so to get there use a 37.5 in one carb and a 42.5 in the other.
at least the needle jets are fine.
.... wuhl hell fire ..... partz iz parts, right? ....

.... damned fussy ass I-talyun thing ... if'n it wuz a HARLEY it wooda run jist fine !! .....

.... whuts this werld comin' to .... everthing iz jist goin tuh hell in a hand basket I tell ya whut !!




(some people's children! they go out and buy a junior mechanic's tool set at Harbor Freight and suddenly they're master technicians. makes me wonder what else you're in store for!!!!)

.... wuddya mean I caint put 30wt in the forks? .... hell I put it in the brakes too !!! .... it's all jist oil ... !!!

:rolleyes:
 
#18 ·
I'm starting to wonder if the previous owner of my 900 is the same person that did this one. Mine also had a mis-matched longer head stud - he proudly explained that he changed it, taking a stud from a salvage monster motor. Why would anyone go through the trouble and then only change one.... I should've walked away then but I was already there with a rented van...

He couldn't explain why the engine would cut out when you turn on the choke, even though he "cleaned the carbs". I found out that he had mixed up the choke jet and the screw that holds the jet block to the carb body. Sure they have the same thread size, but one would think the lack of a hole could be a bit of a tip which is which. Of course all this work done without replacing a single o-ring or gasket. Cheaper that way, just like the self tapping screw from home depot used to hold on the oil cooler.

Anyway, I'm guessing the electrical system will not look much better on that bike. Watch out for the old "twist and tape" trick.
 
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#20 ·
All I can say is----Other peoples children----it would be hard to fuck them up that bad without trying lol
 
#21 ·
What at least is heartening is the number of people who are starting to bring them back from the brink. Some of these are costly due to needing so much work but the upside is if you do re-do everything you know what you have when done.
 
#22 ·
I to see the same thing with BMW's that I work on --if they are ridden and maintained it's a hell of a lot less expensive to keep them in nice running condition then it is to try to resurrect one that was abused before it was parked in the corner for way too many years. The most expensive motorcycle you will ever purchase is the one you got for a fraction of the price that it is really worth---This is especially true for those that cannot diagnose & repair the bike themselves
 
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#23 ·
the first half of this year i had a real run of been sitting for years resurrections - f1, st2, 900ss, mts1000. for varying reasons they all ended up around $5k - pretty much the value of all except the f1. my estimates going in were probably in the 2k range. just a mess when every single thing you touch is a problem. it's very unsatisfying work, and even though i lose money the customers are pissed off with the price.
 
#24 ·
I here ya! It seemed like every time I went way out of my way to do an extra good job, and even charged far less than I should have (sometimes below cost) it almost never went appreciated. For that matter sometimes they'd even bitch about something, even though I spent 2x the billable labor that I actually invoiced them for. It got to where I became uninterested in doing anyone "beyond expected" work.
 
#25 ·
I know what you mean. I had a reputation for working on old bikes , many times where there wasn’t a dealer or good parts source. I enjoyed bringing them back to life. I didn’t charge anywhere near the going rate . I did more than I was asked, fixing small items I found wrong as I went. People who don’t work on them have no idea what it takes to get a bike that’s been in storage back on the road.
 
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#26 ·
I am done with giving 50% of billable time away, yes I still give away far too much but these days i make it clear that if they want/need me to help then they need to pay what it truly costs to do the work. when I was deciding if I was going to keep doing bike work everyone said you CAN'T quit, yet I should not be paid? This is always a balancing act for any shop and it is hard no matter the business. As I told a recent customer who is spending more on his bike than it is worth.

I can work on your bike as it needs and you can pay for the work done
Or
I can do half the work for half the money
or
I can do the work for half as good for half the money.

Odly enough he wanted good quality work and all of it as well.
 
#27 ·
I'm the same way mate --when working on BMW's I charge book flat rate--If the bike has any accessories that must be fiddled with in any way thats extra $$$, If I run into seized fastners etc thats extra $$ as well, computer diagnostics again extra billable hours I give away nothing nor will I---I am still $40.00 an hour less then the 2 dealerships near me--so even with giving nothing away the customer still saves a bit with me on a per hour basis. I charge 15% over BMW retail on parts because I have to pay 15% over BMW cost on parts that way I keep my % margin profit on parts---I do not and will not allow customers to bring or supply their own parts because of liability laws in Florida. I make absolutely no exceptions to this policy--If the customer does not like my policy they can go elsewhere or do it themselves. This may sound harsh but I have no problem telling people that want to gripe where the door is and escorting them out --But remember what BMW really stands for----BMW= Bitch, Moan, & Whine
 
#29 ·
bavarian money waster. fuck their flat rate bullshit. the day i decided i wasn't going to work on them anymore was a very happy one. i wouldn't piss on one of those pieces of shit if it was on fire. any of them.

almost got to giving away guzzi, aprilia and mv too. i have stopped working on diavels. i don't have to, don't want to, so i'm not going to. simples. might have to go back on it if i run out of other shit to work on, but i still probably lose as much work as i take on due to the wait.

imo no where near enough customers get told to stop their whining or to fuck off.
 
#30 ·
... imo no where near enough customers get told to stop their whining or to fuck off....
Man that's the truth! A big part of why I quit building custom hand made audio gear (for about eight/ten or so years, starting in 2007) was after about five or six years my gear became too well known. Up to that point my customers were touring/recording pros ... very select clientele ... guitar players/bass players/Hammond players that played professionally for a living. They fully understood that custom hand made gear took a while to make, refunds were out of the question, as were returns. But once word got around about what I made, I started getting orders from the mainstream consumers. That was a major pain in the ass. Those people are so goddamed SPOILED. Free shipping, no questions asked returns, full refunds 4 weeks into the project because they didn't like a 6 week turnaround. Holy shit. I put up with it for a few years, mainly because I felt like I had a gun to my head. They'd talk major shit on forums if things didn't go just like buying from Amazon (or any other monster sized on line retailer). So I felt as though I had to deal with those morons to protect my reputation. After roughly a total of ten years, having built roughly 500 units by then, I just shut down my website and refused any further orders.

I just couldn't see myself chained to the workbench for the rest of my life, dealing with the bitching/complaining "children". I had enough, and just shut it all down. Every year or so I take on a project for a touring or recording pro as long as it pays right, but beyond that, the consumers can all just eat shit and jump off a bridge.
 
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