Jetting Issuses

[tweeleft]

Hey Gang
I have a 79 sf, I just installed a mac 4 to1 exhaust. Ordered a jet kit for it and it still runs about the same as without it.
147.5 jets in 1-4 150 jets in 2-3
needles richer by one notch
drilled slide
as per directions @3000 feet
Kit also can with 152.5 and 155 jets
Feels like it's starving from idle to mid range, craps out at wot, then takes off.
Plugs are all black suted up after a test ride. Found air box drilled out and tried
it with tape over the holes still not much of a difference. Do I need to raise the needles more? Also my tach likes to do a dance around 3-4000 until I get on it.
Stock jets were 137.5 Help I love this bike

Jerry

[tweeleft]

Directions also had me turn scres out to 4 turns

[TADracer]

If you are using Mikuni jets you are way rich, IMHO. I now run Keihin carbs from a ZRX 1200 but before that switch I had the same type of setup (at sea level, though). I ran 142.5 on the mains and 42.5 on the pilot jets (with real Mikuni jets). If you are using a jet kit then you cannot rely on the jet numbers being in relation to the Mikuni jets that were originally in the carbs. Jet makers use different methods to arrive at their flow numbers. For instance, Mikuni numbers equal the CC's of fuel passed through the jet at a certain pressure in one minute.

As far as drilling the slides, if the hole is too big it will kill your mid range. I take it your jet kit had the correct drill size so if the hole is just slightly larger than the original hole then the slide will react quicker leading to more of a rich condition faster.

[11Rider]

Along those lines, it seems like four turns out on the screws is excessive too.

[XS1100carbon]

jetting issuses

TADracer,could you start a thread,about those klein carbs,how they work for you and what you had to do to set them up?What size and model?Hows the fit?I have a set available to me,just wondering if I should go with them.

[natemoen]

What kind is "kit" did/are you using. When you say drilled slides, what do you mean?

I would alao agree and say that you are waaaay to rich, and your black sooty plugs agree. I haven't ever heard of anyone needing jets that much larger than stock, even the guys with big bores and lots of other mods don't need to be that large. My setup is pretty much the same as yours and I am only using 140 mains. I would suggest going back down to stock and working up from there, and put your needle back in the center, most find it best there anyways.

[natemoen]

TADracer,could you start a thread,about those klein carbs,how they work for you and what you had to do to set them up?What size and model?Hows the fit?I have a set available to me,just wondering if I should go with them.

There is a couple threads about them. Search Keihin and zrx and you will see them.

[TopCatGr58]

From what I have read in the past, and his statement of Drilled Slides, that's SOP for installing a Dyna-Jet kit, and their sizing is different than OEM Mikuni's. Also there are 2 stages, and IF he went with the Stage 3...which is really for a more modded type engine, big bore kit, hot cams, etc., then like folks have stated, he's too rich, most likely overall! It picks up performance power in the upper rpm range because it's moving more air and can run a little better there.

The slide needles should be put back at OEM middle position. Yep, 4 turns out on the Pilot screws is a bit much, try the 1.5 to start. Also, it's the 79 carbs, make sure you have the Pilot Jet TOWER caps in place, not open to the carb bowl fuel supply, since the pilots get their supply THRU the Main and the shared tunnel between the jet towers, so pilot jet tower needs capped!

Air filter clean? Uncover the drilled air box holes. Make sure nothing is obstructing the SNORKEL tube...critters or nests, spider webs, etc.!

You're at 3k elevation, thinner air, so you don't need as much fuel also. I don't recall if the Dyno-jet kits provide the PILOT Jets, or just the Mains, the sizes you were talking about were all MAINs. Does it have OEM/Mikuni pilot jets, and are they the correct style...the BS style vs the VM style, both will fit into the carb, but the VM one is known to cause excessive richness in the same size jet!!! Here's a diagram to help differentiate the styles:



As a last guess, you've got the fuel lines connected to only the lower carb T's, and the upper T's are VENTED to the airbox nipples?! And what are your floats set at??

T.C.

[tweeleft]

Thanx for the info. I'll be working on it today and let you know

[cywelchjr]

Also, it's the 79 carbs, make sure you have the Pilot Jet TOWER caps in place, not open to the carb bowl fuel supply, since the pilots get their supply THRU the Main and the shared tunnel between the jet towers, so pilot jet tower needs capped!

To add to this, it's not the idle that will be messed up if those caps are not in place, it's the mid and high range, cause the main jets get bypassed without those caps.

[natemoen]

I asked about the slides because dynojet has not made kits for the early model carbs for quite some time. Not saying the are totally unavailable but near impossible to find. If one were to use the kit for the late model carbs, well now you are screwed. Or maybe he has late model carbs on his 79. All things that need clarification.

[tweeleft]

Still looking at it. clean all electrical connections. Here's another question I'm getting a 1/2 volt drop at the tci box compared to the battery and at the starter relay's blue/redand red/blue. Could the relay be bad? Emailed company I got the "Kit" from but haven't heard back yet. Haven't touchd carbs yet probably tomorrow

[tweeleft]

Well I leaned the needles and she runs better at mid range and wot, still stumbles off Idle. Going to do a sycn and idle adjustment hopig that cures it