Hello all!
I just finished getting everything put together on a 2002 M750 (injected) after a rebuild.
Currently I'm trying to get the crank position sensor shimmed correctly. I've been told I should get it as close as possible without it actually touching.
When I get the crank shim as close as possible I can start it fine and it idles nicely, but when I give it some throttle it backfires up out of the intake.
I can tell its the intake, because I have the airfilter/box completely off and the intakes exposed... I can see the spark from behind the throttle plate.
I was very careful about the timing belts so I'm confident its not that - anyone have any ideas on how to stop this from happening?
Thanks
-Jordan
You are probably either running lean or have a vacuum leak causing a lean condition.
do the injected bikes fire at both TDC'ish positions like the carby's? or only on the compression stroke? (the answer to this question may be related to this thread, hence me asking here)
Quote from: howie on November 01, 2012, 06:40:09 PM
You are probably either running lean or have a vacuum leak causing a lean condition.
Would running with no air cleaning make me run lean?
Quote from: motoxmann on November 01, 2012, 06:49:26 PM
do the injected bikes fire at both TDC'ish positions like the carby's? or only on the compression stroke? (the answer to this question may be related to this thread, hence me asking here)
Theres only 1 crank position sensor so I assume it sparks both cylinders, and since I would assume they fire out of phase I think the answer to you question is yes.
thats not what I mean.
car engines only spark at TDC on the compression stroke, meaning every other revolution. but the carb monsters fire at tdc on the compression stroke and at the end of the exhaust stroke, meaning every revolution. I was asking if the injected monsters spark every revolution like the carb monsters, or if they spark every other revolution like a standard car engine.
Quote from: motoxmann on November 01, 2012, 08:34:42 PM
thats not what I mean.
car engines only spark at TDC on the compression stroke, meaning every other revolution. but the carb monsters fire at tdc on the compression stroke and at the end of the exhaust stroke, meaning every revolution. I was asking if the injected monsters spark every revolution like the carb monsters, or if they spark every other revolution like a standard car engine.
I'd have to take the alternator cover off (again :() to figure that out... why do you ask?
Also: how would a lean cause backfiring through the intake? It seems like, if the intake valve is closed, then exhaust/combustion shouldn't be able to make it up into the intake manifold.
For vacuums leak: the net effect of this is that the engine would run lean, right? another way of asking the same thing: vacuum leak is a cause of lean mixture?
I can't see any reason for there to be a vacuum leak - I plugged up the emissions ports on the intakes and the o-rings are brand new. Everything is torqued to spec. I don't see any other places for a vacuum leak to occur.
I appreciate the advice!!!
To the best of my knowledge they have a wasted spark.. ie they fire on every 360 degree cycle NOT 720 degrees like a car.
Quote from: wiggy_nz on November 01, 2012, 11:52:40 PM
To the best of my knowledge they have a wasted spark.. ie they fire on every 360 degree cycle NOT 720 degrees like a car.
Many cars are wasted spark. injected motors can also be bank injected: where both injectors fire at the same time at a nearly unrelated to piston/cam position... it isn't as efficient as say the super cool direct injection currently creeping in, but it is easier to do.
Injected ducatis get timing from the jack shaft which drives the belts, so it's possible they don't have wasted spark. I believe they only fire once per cycle but I do not recall actually testing for that.
Quote from: chris on November 02, 2012, 05:34:15 AM
Injected ducatis get timing from the jack shaft which drives the belts, so it's possible they don't have wasted spark. I believe they only fire once per cycle but I do not recall actually testing for that.
You are correct.
The injected models do not use a wasted spark.
huh, ok, good to know.
my only guess then is that one or both timing belts is off a tooth or two. I know you said you're pretty certain they are on correctly, but in every engine I encountered backfiring through the intake it was due to either the spark plug wires being on incorrectly or the timing belt(s) being on incorrectly.
and if you said it idles decently, then I'm sure the spark plug wires are correct, which only leaves cam timing (timing belts). it typically occurs when the intake cam is advanced 1 or two teeth, which allows still-burning exhaust to go up the intake at a point when there is load and retarded ignition.
I would triple check the timing belts, and their tension. a loose belt can even cause the valve to flutter around that point. if the valve adjustment is too far out of whack, that could also cause it I'm sure.
I'm not too experienced specifically with monster engines yet, so I'm learning some things here too, but the above is my common experience with other various engines in general
Running with no air cleaner will make the bike run lean if it is tuned to run an air cleaner. A vacuum leak will create a lean condition at low throttle, such as cruise. You can have a vacuum leak where the carbs mount to the manifolds and where the manifolds mount to the heads. Easy, cheap stuff first. And, yes, recheck valve timing. Did you do anything with the valves and valve seats during the rebuild? If so, think about a cylinder leakage, or, at least, a compression test.
As far as I can tell the belts are exactly right. When I installed them I put bolts through the holes in the back of the case to lock the timing gears at TDC.
I put the engine at TDC and took some pictures...
Here is the main timing gear - There is a smaller dimple at the top of the pulley... don't know what thats for but the larger one lines up perfect.
(http://i28.photobucket.com/albums/c235/FurrorNos/timing_tdc.jpg)
Here is the Mark on the alternator - the window was dirty so I highlighted where the tick mark and indicator arrow are. There is also a "dot" just outside the view through the little window, but I think its the timing mark for use with a timing light.
(http://i28.photobucket.com/albums/c235/FurrorNos/alt_TDC.jpg)
Here is the horizontal cylinder... there was no "mark" for me to work off, but the screw hole in the back still lines up with the mark
(http://i28.photobucket.com/albums/c235/FurrorNos/hor_tdc.jpg)
Vertical cylinder:
(http://i28.photobucket.com/albums/c235/FurrorNos/vert_tdc.jpg)
Here is me pinching the belt - I used a 5mm allen key when I snugged it up. I used a 6mm on the vertical cylinder.
http://youtu.be/IqnAOe6Uhpw (http://youtu.be/IqnAOe6Uhpw)
And here is the engine running. After it started I gave it some gas then held the throttle steady. Backfires start at ~15s.
http://youtu.be/0a1BxEpDaE0 (http://youtu.be/0a1BxEpDaE0)
Could lack of air cleaner really cause this much backfiring?
I really appreciate the advice!!!
-Jordan
timing is out , believe me i have been down this road before on jap bikes
either the belts are out a tooth or the spark is at the wrong time
2 things you have to do
check the belts are right meaning with a degree wheel
2nd is using a timing light to check the actual spark timing
i would go with the timing light first since its easier and you are playing with the sensor
but i would also like to degree the cams to make sure they are right since you its a fresh build
rechecking valve clearances
its the only way you are going to fix it
If I advance the belt by 1 tooth do I risk bending a valve?
The valves were re-seated during the rebuild, but I don't know why that would effect timing as long as the valve clearances are correct (which they are - I rechecked them today and they're spot-on).
It won't, but a leaking intake valve will cause backfire through the intake. So will an intake valve that does not fully close.
the belts look good.
I don't recall the flywheel having a tick mark like that. the only timing marks on the flywheel should be blunt obvious circles. you said there's on of these slightly off to the side out of view not quite lined up?...
it's possible that the ignition timing is out, but there isn't a whole lot of adjustment on ignition timing, probably not enough to cause popping out the intake. but maybe its possible? either way you def need to check/adjust ignition timing. did you make sure to set the gap properly and to spec between the pickup sensors and flywheel trigger "lump"?
my guess due to the above info, and general causes for this, is still cam timing. while your belts are definitely on correctly, are you absolutely sure the camshaft driveshaft gear and it's drive gear on the crank were lined up properly? if that is off 1 tooth it could definitely cause what you're experiencing. and it would explain why the mark on the flywheel in the view window doesnt line up properly even though belt gears all show good.
motoxmann is talking about a carb bike, which is completely different to an injected. the flywheel should have the single line marks. i usually set the rotation sensor gap to 0.5 to 0.7mm. i dno't know if having it at almost nothing will effect the way it runs, but it shouldn't. ignition timing is not adjustable.
i would confirm that when all the marks line up the engine is at tdc horizontal firing. if the timing gears are off (how far disassembled was the engine?) than that will only show up comparing timing marks to actual piston position.
if the cam timing is right now and you advance the cams 1 tooth (40 degrees) it should bend the inlet valves.
my mistake, I thought it was a carbed M750, should've re-read first post before posting again haha
Quote from: brad black on November 03, 2012, 03:22:58 AM
if the cam timing is right now and you advance the cams 1 tooth (40 degrees) it should bend the inlet valves.
Should as in it
will bend them?
Marks on the timing gear were lined up, but there is some damage on the timing gear that could be the culprit. Its probably from when I installed the alternator - I used an allen key to lock the gears while I tightened the nut. It also could have happened just now when I removed the alternator.
Just ordered a new timing gear set on eBay - hopefully this fixes it. Another week waiting for parts.
And then I'll probably be right back where I was yesterday. :(
(http://i28.photobucket.com/albums/c235/FurrorNos/tim_g2.jpg)
ouch, at least you caught the damage this soon before it started wreaking havok on other stuff.
I went through this same type of thing in late spring, did a full rebuild of my engine as well, bike was down for 6 weeks may-june. that was tough
After looking at the wear on the timing gears some more, I've decided that most (all?) of the damage is from just today when I took the alternator nut off.
My theory on why the horizontal cylinder is backfiring is: worn camshaft and/or rockers.
I got the bike for $700 with 80k miles and a broken vertical belt/bent valves. It was the same price to get a whole (lightly used) vertical head on eBay than to buy a new valve, so the vertical head has far fewer miles on it.
The horizontal head appeared fine, albeit in dire need of a valve job.
I had a hard time doing the valve job, however, because the intake lobe was so worn that I couldn't slide a new opener shim on normally; I had take the rocker shaft out, line up the rockers with the shim, and slide the rocker shaft through the assembly.
Thus, my theory is that the bike had horizontal timing problems before I even got it on account of 80k wear on the camshaft/rockers.
From the manual it looks like offset woodruff keys are available to tweak the timing, and it looks like adjustable pulleys may also be available.
EDIT: Turns out the timing is adjustable on this bike after all!
Quote from: Jordan1234 on November 03, 2012, 01:25:51 PM
The horizontal head appeared fine, albeit in dire need of a valve job.
I had a hard time doing the valve job, however, because the intake lobe was so worn that I couldn't slide a new opener shim on normally; I had take the rocker shaft out, line up the rockers with the shim, and slide the rocker shaft through the assembly.
WTF did I just read?
um, dude? there's your problem right there. sounds to me like you forced the rocker onto a shim that was way too thick, and now your rockers are probably bent, causing the valve lash to be all sorts of out of wack, making the valve hang open slightly almost at all times
I think I stated that wrong -
With everything assembled the clearance on the intake opener shim is in spec.
The problem was that with the rocker arms and rockers installed, the lobe next to the intake opener lobe prevented me from sliding the rocker over on top of the shim.
Using an opener shim thin enough to allow the rocker to slide over into position left me with .2mm of opener clearance.
Quote from: Jordan1234 on November 03, 2012, 04:35:08 PM
I think I stated that wrong -
*sigh!*
Quote from: Jordan1234 on November 03, 2012, 04:35:08 PMWith everything assembled the clearance on the intake opener shim is in spec.
The problem was that with the rocker arms and rockers installed, the lobe next to the intake opener lobe prevented me from sliding the rocker over on top of the shim.
thats normal, mine is the same way, and has nearly zero wear on all valvetrain parts. you usually need to remove the belt and rotate the cam a bit to get the rocker to slide over
should as in i don't know because i've never actually tried it because i don't want to bend my valves, but from my measurements of lift and clearance it should. if i say it will and it doesn't then i'll get some petty prick telling me i was wrong. and i'm somewhat over that.
so to sum up i'll say, imo, it's a really bad idea to advance the cams one tooth.
I've personally seen the results of one tooth off.
I'd listen to Brad.
I was a tooth off after a valve adjust and it's immediately obvious after starting that something is wrong. I never took it apart to see if there was any damage and it still runs strong so I'm 'assuming' nothing is bent. YMMV, but there is no way I'd set it up a tooth off intentionally.
Day before yesterday I misread someones response and tried it one tooth off -
The valve was obviously hitting the piston. I took the head off (the horizontal head is easy) and the valve is not bent, amazingly. i used a sharpie and some lapping compound to check the valve seating and it looks good.
I'm pretty sure my problem is that the factory timing is no longer sufficient for whatever reason - lobe wear I guess.
My manual is for a carbureted M750 - it says intakes should open 11deg before TDC and close at 70deg after BDC, exhaust opens 50deg before TDC and closes 30deg after TDC.
Are those numbers the same for the injected M750s?
Quote from: Jordan1234 on November 04, 2012, 02:51:06 PM
My manual is for a carbureted M750 - it says intakes should open 11deg before TDC and close at 70deg after BDC, exhaust opens 50deg before TDC and closes 30deg after TDC.
something about that sounds horribly wrong, even assuming you meant ex opens 50deg before BDC.
is this true? the carbed 750's have 261deg duration intakes and 260deg duration exhausts? I would think they'd barely idle with overlaps and durations like that
From the 750 carby manual
Data measured with 1 mm clearance
and timing belts tensioned with
service tool no. 051.2.001. 1A at
11.5.
Intake valve opens at:
110 before TDC
Intake valve closes at:
70° after BDC
Exhaust valve opens at:
50o before BDC TDC is probably a typo on Jordan's part.
Exhaust valve closes at:
30° after TDC
Valve lift
Data measured with 0 mm
clearance.
Intake:
9.3S mm/0.368 in.
Exhaust:
8.SO mm/0.334 in.
750IE uses the same cams so lift will be the same and so should the timing. You need to be anal about clearance and belt tension for degreeing. In your case, not so much. Yes, a worn intake lobe can cause your symptom. The wear would be obvious to the eye.
interesting. I guess that does explain why they only pull around 8-9in/hg vacuum at idle
Ok! It took me just 7 months to get back to this project.
I have a degree wheel on the crank, and a micrometer on the intake valve.
I've got the crank at TDC...
The main timing gear indicates TDC: http://i28.photobucket.com/albums/c235/FurrorNos/vlcsnap-2013-06-08-16h12m43s133_zpsaea713d2.jpg (http://i28.photobucket.com/albums/c235/FurrorNos/vlcsnap-2013-06-08-16h12m43s133_zpsaea713d2.jpg)
The windows on the other side shows TDC: http://s28.photobucket.com/user/FurrorNos/media/vlcsnap-2013-06-08-16h12m57s227_zps02f3167b.jpg.html (http://s28.photobucket.com/user/FurrorNos/media/vlcsnap-2013-06-08-16h12m57s227_zps02f3167b.jpg.html)
But it seems like TDC for the horizontal cylinder is like Crankshaft TDC+360deg. Is that right?
In other words:
- The intake valve is 1mm open at Crankshaft TDC + 350deg
- The intake is 1mm from being closed at 70deg after BDC, which is like crankshaft TDC + 610deg (360+180+70)
Also, when I set it such that the intake is 1mm from closed at 70deg after BDC, the intake is 1mm open at 4deg before TDC. Its more important that the intake is closed at the right time than open at the right time, right? I assume the deviation from spec (10deg before TDC open, 70deg after BDC closed) is due to lobe wear.
Thanks!!
-Jordan
Wow I just talked this through with my dad and realized its a very dumb question. Of course the intake valve opens 360degrees after spark. :-[