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Discussion Starter #1
Another FCR thread! Hooray!

I have FCR39s on a 1992 900ss that has unknown head polishing and/or porting and possibly other engine work. I do not know the details.

Since I purchased the bike, I have had a lot of surging and stumbling with maintenance throttle at small throttle openings and a very rough bog followed by abrupt acceleration going over the transition from 1/2 throttle -> WOT. I've been gradually leaning the carbs out until the bike is now behaving relatively nicely. It seems to still be rich.

Now that I can actually enjoy riding the bike, I can't get past 7k at WOT - the bike stutters and stops accelerating. I've gone up to 170 mains with the same result while going backwards on smoothness across transitions.

Any suggestions (besides dyno it)? Here's where I'm at:

Mains: 155
Main air jet: 200
Needles: EMT, 2nd position
Slow air screw: 2 turns out
Fuel/mixture screw: ¾ turns out
Slow/pilot jet: 55

Thanks!
 

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I can't get past 7k at WOT - the bike stutters and stops accelerating. Any suggestions.
Before you started your jetting changes did you first change out both the in-tank fuel pick up screen and fuel filter Pogolo?

Found out for myself that all the jetting changes in the world on a set of FCR's will not cure a high RPM fuel starvation stumble caused by a clogged fuel pick up screen and dirty fuel filter.
 

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Read the plugs or hook up a wide band O2 sensor controller and logger. Both require some expertise but there is unlimited documentation for both. Before you do that, make sure compression is adequate and ignition timing correct. Test fuel flow volume.
 

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It is always difficult/impossible to jet by internet but you might get close.

Lets start with some more information on the bike and i can throw some more numbers at you to try .

1. split singles or a bank of carbs
2. pod filters or airbox
3. flat top pistons or high compression
4. ported or not
5. stock ignition or aftermarket
6. bike tuned recently (valves adjusted carbs sync checked)

I do see you are unsure if the heads are ported but that does matter in that a well ported head will use less fuel ie: smaller jets, what makes you think they were ported? It would be rare to have ported heads on a otherwise stock motor, do not confuse stock head work which was hand done in that era. Hi comp/big bore can be discerned by looking for a raised piston dome this will also effect jetting slightly.

keep in mind these carbs have accelerator pumps as well that will dump a ton of fuel as well if you wack the throttle open, depending on the rpm you decide to go WFO will make this not noticeable or possibly cause a bog.
 

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Ducvet's questions are going to help give a more thorough diagnosis.

Generally though, it seems like fuel starvation. If you have already replaced the filters, there are three more points to check.

1. Is the fuel petcock all the way open?
2. Have you verified the fuel lines are not kinked under the tank from poor routing when closing it?
3. Have you serviced the carbs and verified float height is correct, fresh float needles and smooth operation?

I had an issue that *felt* like fueling but was a bad coil. It felt almost like an electronic rev limiter that would "bounce" the engine at about 7000 rpm. Turns out I had a bad aftermarket coil from a reputable brand. I went back to the OEM coils and wires and the problem went away.

Caveat: I am a total amateur to this stuff.
 
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Discussion Starter #9
Thanks for the replies! My best attempt at answers:

1. split singles or a bank of carbs: They're connected
2. pod filters or airbox: Airbox with the top cut off.
3. flat top pistons or high compression: No idea.
4. ported or not: That's what I was told.
5. stock ignition or aftermarket: Aftermarket Ignitech igniters + the CA Cycleworks coils
6. bike tuned recently (valves adjusted carbs sync checked): Yes. About 800 miles ago.

1. Is the fuel petcock all the way open? Theoretically, yes.
2. Have you verified the fuel lines are not kinked under the tank from poor routing when closing it? Yes.
3. Have you serviced the carbs and verified float height is correct, fresh float needles and smooth operation? Recently had a knowledgeable person go through the floats, etc.
 

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Discussion Starter #10
Ducvet's questions are going to help give a more thorough diagnosis.
I had an issue that *felt* like fueling but was a bad coil. It felt almost like an electronic rev limiter that would "bounce" the engine at about 7000 rpm.
Caveat: I am a total amateur to this stuff.
^^ That sounds a lot like what I'm feeling. It's very much like a soft rev limiter. Though the pinging I heard at one point would seem to point more to inadequate fuel delivery. I do have the old igniters and coils...
 

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Resolution:

Ended up finding a mechanic with a rolling road here in Austin (Moto Lab & Machine - Austin Motorcycle Repair, Service & Maintenance. 512.450.2311 Texas). Turned out to be a two-fold problem: 1. One bad (stock) pick-up, 2. One or more igniters (I had replaced stock with "Ignitech"). The engine was not able to get to full advance.

On the dyno it runs a bit rich at WOT, but makes 70hp to the rear wheel + 52ft/lb of torque.

Thanks for the help!
 

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Resolution:

Ended up finding a mechanic with a rolling road here in Austin (Moto Lab & Machine - Austin Motorcycle Repair, Service & Maintenance. 512.450.2311 Texas). Turned out to be a two-fold problem: 1. One bad (stock) pick-up, 2. One or more igniters (I had replaced stock with "Ignitech"). The engine was not able to get to full advance.

On the dyno it runs a bit rich at WOT, but makes 70hp to the rear wheel + 52ft/lb of torque.

Thanks for the help!
Don't ya just hate it when there's TWO problems in the system to find. One set of symptoms often tends to mask or confuse the other set. Glad it's all sorted.
 

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Resolution:

Ended up finding a mechanic with a rolling road here in Austin (Moto Lab & Machine - Austin Motorcycle Repair, Service & Maintenance. 512.450.2311 Texas). Turned out to be a two-fold problem: 1. One bad (stock) pick-up, 2. One or more igniters (I had replaced stock with "Ignitech"). The engine was not able to get to full advance.

On the dyno it runs a bit rich at WOT, but makes 70hp to the rear wheel + 52ft/lb of torque.

Thanks for the help!
Are you stating that the OEM igniter(s) were bad or that the Ignitech was bad?
 

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Another ignition problem that was blamed on carburetion, this is very common to do even by pro's.

Earlier he stated he had a Ignitec unit on the bike so I assume he returned to the oem boxes. I wonder if the unit is just needing setup was the dyno operator or you able to connect to the ignitec and check parameters? I would make sure the rev limiter was just not set too low as it is adjustable, any part can go bad so it is possible for the ignitech to fail but before I tossed it I would try and find out why it is not working. Did you install it or did it come on the bike?

Most of the time I have a bad pickup the bike drops a cylinder completely as opposed to just running poorly on two. Either way congratulations on getting the bike running again now go and make up for lost time.
 

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Discussion Starter #19
... I wonder if the unit is just needing setup was the dyno operator or you able to connect to the ignitec and check parameters? I would make sure the rev limiter was just not set too low as it is adjustable, any part can go bad so it is possible for the ignitech to fail but before I tossed it I would try and find out why it is not working. Did you install it or did it come on the bike?
We (honestly) replaced the igniters wholesale for no good reason. I don't think there's any way to test the igniters nor adjust them - though I'm eager to learn. My carbed '92 does not have a rev limiter. The symptom was that the motor was not able to advance timing fully. I can hear a difference at idle and it sounds different all over. I'm just thrilled to have a free-revving bike to enjoy!
 

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The Ignitech (Procom) igniters were bad. Putting the OEM igniters back in solved part of the problem.
I do not think the procom units are made by ignitec, personally the only unit I have seen aftermarket that has been okay so far is the ignitech like this model below.

SPARKER TCIP4 - IgniTech P?elou?

I have had far more problems with aftermarket CDI units than the oem kokosan boxes, I just had a customer have a failure on her track bike of a ducati performance box that I know made it less than 2000 miles IIRC these were made by Pederzini (SP). Another customer bought 2 boxes new off ebay and the bike would not run over 7000rpms, I think these boxes are being labeled for the Ducati but are a universal made for some other bike.

If yours looked like
then I am not sure I would trust them from my experience.

I don't think there's any way to test the igniters nor adjust them - though I'm eager to learn
True you simply swap in a known good one and see if it runs. Honestly I see far more people swap inferior components just because they are new and often find out new is not always better.
I'm just thrilled to have a free-revving bike to enjoy!
No there should be no rev limiter on the carby Ducati's so it is up to you to not over rev too much. Know that you are likely done by 7500-8000rpm so after that you are going slower and wearing things out for no good reason. Now go have some fun!!
 
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