No WOT power, jet kit, airbox questions

[Abflyboy]

Hey guys, new member here,

I am in the process of resurrecting a 1990 Kat 600 from a poor previous life. The bike sat for over four years before I got it. A couple of car mechanics messed with it for about a year and never got it running.

I took the carbs off and thoroughly cleaned them and WOW! the bike fired right up. Imagine that. (found all four pilot jets plugged solid and float levels all over the place)

Ran good enough to get oil hot for a change and valve adjustment. Compression is good by the book and the engine doesn't make any unusual noises. Synched carbs. I installed new plugs and since it was a Cali bike, purchased a Dynojet jet kit.

Prior to installing the jet kit, I noted no power at WOT and wouldn't pull beyond 7,000 RPM. No performance mods done to the bike. Yet. I installed the DJ needles and 106 jets. Problem seemed a little worse. Thinking that going richer won't hurt to try, I installed the 110 jets. Problem was WAY worse. Put 106 jets back in. Have played around with idle mixture and it likes 2-1/2 turns out.

My question is, will the air filter inlet restrict air enough to cause rich fuel mixture at WOT? Should I modify the stock airbox or go right to the K&N pod filters? Why is there a velocity stack (sort of) in the stock air filter that looks more like a restriction? Can I cut it out or is the airbox "tuned"?

Thank you in advance and sorry for the long winded story.

[The CyberPoet]

(A) The stage 1 jetkit shouldn't be paired with the pods. The stock filter (if in reasonable condition -- might not be after 4 years of sitting) should flow sufficient air to work with the stage 1 kit reasonably fine at all settings.

(B) If you didn't treat the tank for rust right off the back, your problem probably lies in more rust that was sucked into the carbs after you ripped them apart and cleaned them. See my "How To Deal Gas Tank Rust in your Motorcycle" for more help with this.

(C) If you did treat the rust issue (or weren't running off the tank, but a known-good fuel source), then the problem almost assuredly lies in the vacuum levels (bout a 90% chance) or in the DynoJet diaphram spring if one came with the kit (being too stiff). Replace the carb sync nipple covers and closely inspect all your hoses for cracking/leaks. Spraying around the hoses with starter spray or WD40 while the engine is idling should let you know where the leak is, if one is present.

Maybe someone else has another answer as well...

Cheers,
=-= The CyberPoet

[Abflyboy]

The inside of the tank is pristine and I replaced all the vacuum lines and stock air filter. As for further troubleshooting, I removed the air filter and went for a ride. Bike runs great with no air filter in stock air box.

I noted in my dynojet kit that stage 1 jetting with no mods is a 106 main jet and stage 3 with pod filters is 130. Is there really that much restriction in the stock air filter?

I am looking at a D&D full exhaust to go with my K&N pod filters. Any thoughts?

Thanks

[The CyberPoet]

I noted in my dynojet kit that stage 1 jetting with no mods is a 106 main jet and stage 3 with pod filters is 130. Is there really that much restriction in the stock air filter?

There really is that much of an easier time for the engine to build sufficient vacuum with the airbox and OEM filter in place. The pods greatly drop the vacuum levels at idle, so the jetting has to be that much larger to draw sufficient fuel with the low vacuum levels at idle.

As for the rest, I have no comments right now (very tired, and sitting in a den that smells strongly of the bug bombs we set off last night although we aired out all day today).

Cheers,
=-= The CyberPoet

[Abflyboy]

Thanks Cyber,

I have been swamped lately and finally got around to doing some cool stuff to my Kat.

I installed a V&H SS2R complete system and K&N filter pods. I jetted per the dynojet instructions and also contacted V&H tech for added input. They recommended using the dynojet specs and bumping the idle mix screws out to 3 turns. Runs AWESOME.