clean and tune your carbs might work

 

Thanks. Jets and needles are soaking right now. Will finish cleaning the carbs by today and put it back together. Hopefully this followed by a sync will resolve the issue. I will report back with an update once it's running again.

Edit: carbs cleaned, I have yet to sync them as I need to order or make a tool. I test rode after cleaning and the stutter remains.

 

It sounds like you have a damaged slide diaphragm. They have to seal perfectly. A pinhole in the diaphragm or damage to the sealing flange (not uncommon, because an improperly seated diaphragm will get pinched by the cover) will cause this problem. The normal amount of vacuum doesn't lift the slide all the way, but when the main jet takes over the engine accelerates enough to create enough vacuum to lift the slide up, giving you that jolt.

As simple as everybody says carburetors are, we've seen a never ending succession of people who haven't been able to get them right, even after multiple tries. They ARE simple, but they are very precise instruments and require a methodical, careful approach.

 

It sounds like you have a damaged slide diaphragm. They have to seal perfectly. A pinhole in the diaphragm or damage to the sealing flange (not uncommon, because an improperly seated diaphragm will get pinched by the cover) will cause this problem. The normal amount of vacuum doesn't lift the slide all the way, but when the main jet takes over the engine accelerates enough to create enough vacuum to lift the slide up, giving you that jolt.

edit:fixed quote

The diaphrams showed no signs of damage or tears, I thoroughly inspected them. The rubber lips of the diaphrams seated right into the grooves and I gently pressed them in with a gloved finger to ensure a good fit.

 

Do the slides move up and down smoothly by hand?

 

I did not play with them much, but they seemed to slide back into place easily enough.

 

Update: I made a manometer and synced up the carbs. They seemed to be pretty consistently synced through the whole rev range. I made sure they were synced at the rpms I'm having trouble at. However, no difference in the way the bike rides was made. So far I've tried spark plugs and carbs. What's next to look at, ignition?

 

Another update. I looked into my coils, but everything seems normal.

Primary on both sides 3.4-3.5ohms
Secondary 14.80 k ohms
Cap resistance was 4.70 k ohms, all within spec. The primary is a bit high, but the manual says 2.3-3.5 for primary.

At this point, I am considering Ducatimans carb cleaning service. Always open to more advice (please help me).

 

Just wanted to ask to get this out of the way.....your carb internals are stock? As in main jets and needles...no jet kit funny business?

130 Keihin main, N36N needles for sure...you can attest you've seen them?

 

While I did not take pictures of the inside of the carbs, a google image search of each part you gave did seem to be what was installed in my carbs. The previous owner also stated all stock carb internals FWIW. Again, the bike was running fine before adjusting my valves and then installing new intakes.

Edit: to add, my carb internals all looked identical as all the pictures in the wiki. I did not go so far as to read the engravings on the jets and whatnot.

 

Not to promote a service in particular, but i had this exact same problem. Bike would accelerate just fine, hit 6000 and bog down, cross 7000 and surge power again. Cleaned carb so many times, I can remove the darn thing in 3 minutes now.
I had Ducatiman service it for me and got it back looking brand new. We also tweaked the setup for my altitude (I live at 6,000' and regularly ride higher in the mountains). Problem solved.
Sometimes you have to have a pro help you out. There are several here on the forum who will take good care of you.
From personal experience, I can tell you that Ducatiman does good work.

 

All 4 CYL engines suffer from this malady, it is caused by the resonance of the exhaust pulses. At certain frequencies they conspire to block the exit of the exhaust or scavenge it so forcefully as to nearly delete the power pulse.

Note not flow or restriction, resonance

Carefull turning of the exhaust can reduce this tendency but not eliminate it. Any monkeying around with the stock exhaust or cams or to some extent the intake mixture, can upset the carefully designed in/ut system from the factory.

I have given you'll the best solutions that exist in the How too section, I tire of re chewing this cabbage.

But for the FOG MOD airbox tune stock is always best

FOG

 

Hmm..... Problem started after you bent the intake valves. How did you happen to bend them?. When you rebuilt the head what were the valve guides like? Valve seats?
I would be starting there. You may have bad guides, seals, and/or seats causing a leaning/ starvation of fuel. Hope you get it sorted.

 

To answer you and O_E_M as to why the valves were replaced, when I jumped the timing I tried forcing the crank to turn, causing the intake valves to meet the pistons. At this point, I realized I did not want to risk breaking anything else so I took the top end to a local shop.

There, it was cleaned, inspected, intake valves were determined bent and replaced, and new valve seals were installed as per shop reccomendation (they suggested this simply based on my mileage). I was told everything else was good to go. Given back the top end, I reassembled with new gaskets and my issue began.

O_E_M, the 6.5k explosion is one I remember and long to get back. The other day I was on the highway in 5th and the bike got stuck at 6900rpms. Wouldn't gain any speed, was just hanging at 6900 with WOT. This is really starting to bother me.

I will do a compression test as my next task. Thank you both for giving me more places to look.

Edit: I ordered a carbset from Ducatiman, and while the carbs look and perform great, I can confirm that my issue does not lie in the carbs. There was no difference in the hesitation after switching to Ducatiman's set.

 

Ding ding ding!
All this started after a botched valve adustment.
OP replaced intake valves... okay...? Why?
Not to read too hard into it but...

I want to see compression test numbers.
I’m wondering if was running lean and there might be a burnt EXHAUST valve or MAYBE the lash is still out.

Any one want to chant with me.... compression test, compression test


O_E_M

And btw op, Under “normal” operating conditions you should feel a surge in third gear about 6.5k rpm.
No better way to explain, it’s a feel.
It’ll also get you in trouble with the “po-leece” for exceeding the speed limit. Haha

45 mph in 3rd.... roll hard on trottle... roll in and WOT... if it picks up around 6500 RPM with a “**** it went from 6500 to 11+” then its fine.
It’s pretty simple to hear/feel when the engine picks up and peaks up.
No one needs a tach if they are in tune with an engine.

O_E_M

 

And btw op, Under “normal” operating conditions you should feel a surge in third gear about 6.5k rpm.
No better way to explain, it’s a feel.
It’ll also get you in trouble with the “po-leece” for exceeding the speed limit. Haha



O_E_M

when the bike transforms from some old ladys daily driver to a screaming demon from hell.. i love it