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Discussion Starter #1 (Edited)
Ok, posted this in the Super Sport section a week ago, no response there so back up for another shot.

I cannot get my 93 900SS rebuilt engine to run above Idle, any movement off the throttle stops causes a bit of a sputter with a bit of a back-fire then bike dies.

What I did:
I rebuilt engine after my cases split at the track, before I tore motor down it ran perfect. Prior to cases splitting engine was a 966 with Carillo rods, knife-edge crank, balanced by Guy Martin, heads also ported by Guy, Ducati performance aluminum flywheel, Cams degree's by me to 107 degree lob centers. Had shorty manifolds and single FCR flats, engine Dyno'd at 106HP two years ago.

This time out I rebuilt engine as a 944 due to cost more than anything else, my flat slides, (singles) were drained, fuel line capped and put away in a sealed plastic bin, coils, all electrical, plug wires ect disconnected at the engine only, rest left assembled on the bike.

With new cases in hand I swapped over my entire engine internals, set crank pre-load and tranny end float to perfection. I checked crank run out and it was near null. New pistons fitted, ring gap check perfect, checked/set squish and finished build. Heads while off were never touched other than lapping them into the new cylinders as I had done a valve job on them less than a year ago. My timing marks all set by putting FWD Cyl at TDC by using my piston stop and degree wheel. Once I found TDC I checked all timing marks on flywheel, belts, ect. Air gap was also set. check all this twice.

So far I have double checked all timing marks, pulled off flywheel checked that my crank/cam pulley gears dots, line up. no problems.

I pulled off my FCR flatslides, twice, opened them up, floats work perfect, no crud etc, pulled out all jets, cleaned with carb cleaner and blew out all passages with high pres air, put everything back together, same problem. Throttle adjusted perfect, opens both carbs fully no binding and they spring back to closed, Yes petcock is open.

I Ohm checked my pick-ups, coils, plug wires and stator wires, all check good, I checked for spark while cranking engine, both Cyl check good. I swapped out spark plugs, no change.

I swapped out the coils, two ignition boxes, and plug wires no change

I swapped out my alternator rotor and stator, no change.

My fuel pump runs fine, filter is new, pet-cock is open, I ran supply line into a gas can and pump gives a nice steady stream of fuel.

I completely drained tank and put in new gas, same problem

Pulled off exhaust thinking a dead rodent may have found it's way in was blocking airflow, no such luck

I have a spare set of FCR's but have not tried them yet and I have not changed out my pick-ups on the flywheel, they did Ohm check good though.

Since old engine ran perfect even with a split case and all I did was swap parts over, bike (in theory) should fire and run without an issue.....right?!?!?

Really dumbfounded here, open to any ideas, :think: maybe I tire pres is off....I'm to that point!!
 

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I melted a crankcase vent timing gear on my fatboy, it wouldn't run above 2 grand, took a week to find. Not your issue? This one closer, same bike. The Edelbrock carb (lectron) quit working one day as I got off the freeway, it wouldn't take throttle but spit & sputtered, barely running by actuating the choke on and off to get home. I reinstalled the stock carb, it ran good, sent it to Edelbrock for a rebuild, came back with a new slide and vent tubing. Worked great no explanation.
 

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This is kind of a crazy idea because of the little backfire you describe, but could your clutch be hanging up somehow causing the motor to stall?

Just grasping at straws...
 

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I don't know, but it sounds like a timing problem to me.
 

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You mentioned it back fires when you open the throttle, is that a backfire at the exhaust pipes or out of the intakes? When it idles, will it run for a long time before touching the throttle? What do the plugs look like?

A backfire out of the pipes is an indication of too much fuel (too rich), out the intakes is not enough fuel (too lean).

Another thought, when you rebuilt it, is there a key on the fly wheel? Is it a square key or does it have an off-set (step)? If it has an offset and it's in backwards, it'll change the timing.
 

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Did you change the carb jetting to suit 944 vs. 966? There's no choke on the FCR's, so rule that out. Checked the float needle seats? I once had a small shard of fuel line stick a float needle open; caused a similar symptom... easy to diagnose if fuel is running out float bowl overflow.

Did you clean the carbs with carb cleaner? Carb cleaner will eat the $h!t out of the rubber seals in those FCR's.
 

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If you have fuel and spark it has to be some sort of either timing issue or electrical. Stranger things have happened than having a perfectly good part fail while it is being removed from a bike only to be put back on days later and it does not work anymore.

Really hard to diag with out it to look at but triple check your timing and how you set it, and start wiggling all your electrical connections and see if you can get something to act up. Maybe you pinched or damaged the pickups or pick up wiring or possibly the timing is not correct and the flywheel is off in some way???

not likely but it could be the ignition boxes, those can be a bit temperamental.

Good luck.

p.s. check the gap on the pickups!!
 

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Sounds like a lean condition and possibly spark advance.

How long do you let it run? Does it have time to get to running temp and still do it just as bad? Does it improve somewhat if you have given it a chance to get to running temp?

One thing to try since you have cleaned out all the jets (even though there may be some debris in the carb passages left - storage can do weird things) is put your hand over the carb, partially blocking the carb acting like a choke which will draw in more fuel. If this allows a higher RPM there is a blockage in the carbs. I’m not familiar with the carbs so I don’t know if they have a choke you can use to accomplish the same thing.

Also +1 on the vacuum leaks.
 

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Discussion Starter #10
Thanks for all the input guys, haven't had a chance to work on the bike the past few days...soon as I find anything I will post it here...

Thanks again
 

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Dood I have felt your pain. When you swapped cases, did you take the ignition pickup wires out of their little plastic connectors so that you could run them thru the hole in the new cases and then put them back into the connectors? Don't ask me how I know this but I went thru the exact same thing when mine split itself in half. Checked all the stuff you did probably 47 times. bought another module and pickups and still had problem. The pickup wires are polarity sensitive. If one set of wires is backward you will get the symptoms you describe. Pull one pair out and swap positions and try motor. Stir and repeat till combo is found. When I get to shop I will look at wire color and positions and let you know. Hope this helps.
Roy
 

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Discussion Starter #12
Dood I have felt your pain. When you swapped cases, did you take the ignition pickup wires out of their little plastic connectors so that you could run them thru the hole in the new cases and then put them back into the connectors? Don't ask me how I know this but I went thru the exact same thing when mine split itself in half. Checked all the stuff you did probably 47 times. bought another module and pickups and still had problem. The pickup wires are polarity sensitive. If one set of wires is backward you will get the symptoms you describe. Pull one pair out and swap positions and try motor. Stir and repeat till combo is found. When I get to shop I will look at wire color and positions and let you know. Hope this helps.
Roy
Ding...Ding....Ding..... We have a winner!
DUCZILLA...... Dude I owe you a beer! If you ever get to GA look me up! Swapped wires around inside the plugs and Wala....problem solved, I miss marked them when I took engine apart, since it ran I figured they had to be right.......

BTW engine sounds great!

Thanks all
 
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