Carb help

[Blowout]

Thanks. Wasn't sure if needle manufacturer mattered or not. It is in 3rd groove from flat end. The previous po had oem filter on it with 185 main and 135 pilot. I will move the clip down this evening.

[davej]

It will run great for you when you move it. In fact it will run better than it ever did with the old jetting. The old jetting was way off even with the oem filter. My guess is that if you look at the old jet is is not a Mikuni jet and the kit that was used was a dynojet kit A Mikuni jet will have a symbol on it that looks like a square inside a square. Dyno brand jets are numbered different than Mikuni. If it was a 185 dynojet main it would be a size between a 172.5 and a 175 Mikuni. That would be very rich for a 1600. If it was a 185 Mikuni main jet it would have been blowwing black smoke out of the exhaust every time you took off from a light or goosed the throttle

[SKWEARpeg]

I've got a 2000 RSS with a stock carb. I have Freedom Performance 4" duals, a ported intake, a Barons BAK and no AIS. It runs great and gets 40-42 mpg at 75-80 mph. I'm running a stock pilot, 167.5 main with the needle on the fourth clip and a washer underneath. My RS pulls smoothly from idle all the way through to 4500rpm. I have great throttle response without having to grab big throttle to get out of a flat spot. Occasionally I get a cough through the carb when not fully warmed up, but other than that, no issues once it's up to operating temp. Going up a grade wide open in 3rd through 5th gear it pulls away slightly from a friends 2016 HD Dyna Street Bob with a 103 and a 2 into 1 exhaust!

I don't like the Dynojet kits because the numbers on the jets they send are not similar/equal to Mikuni jets so you have to go off that chart in the tech section to find the equivalent jet size. I fiddle farted around with mine for 8 years...the previous owner used the Dynojet kit, it always ran rich, it popped and backfired! I could never get it to run right until I bought the jet kit from Shane at SS Custom cycles...he specializes in Road Stars and is very helpful. His kit only comes with Mikuni jets so the numbers make more sense.

Give the Mikuni 37.5 Pilot a try. Your experience with bikes would make you a great source for input as to whether or not you think it works better. I'm running about 2 3/8 turns out from lightly seated with a both my Hack and my Springer with the Two into One, and it works good. The Hack seriously needs a two into one pipe, but before hanging the car on it, it ran much better with the 37.5. The aggravating lean cough, pretty much became nonexistent.

[hotrod460]

just ordered my 37.5, and gonna put the 170 back in, after ive dialed in the 37.5, i do have a 167.5 as well to try, she runs good when warmed up but hard to keep running when cold on idle

[SKWEARpeg]

just ordered my 37.5, and gonna put the 170 back in, after ive dialed in the 37.5, i do have a 167.5 as well to try, she runs good when warmed up but hard to keep running when cold on idle

Resist the temptation to push the enricher all the way in, until the bike is at operating temp. I usually push mine about halfway in, after the rich stumble starts 5 t0 10 seconds after you start the bike. Make sure the idle is set properly to between 850 and 950 rpms on a hot motor, as well. With the pipes you have on the Bobber, the Mikuni 170, should be ok.

[hotrod460]

thats just how i do it, apart from when i push it in half way she stumbles and will die eventually,

[hotrod460]

as soon as theres a little heat in the manifold she'll run ok, say about a minute at 6deg C

[Jim Simmons]

So I just went pumpless with my 04 RS, readjusted my float back to 4mm above the lip, and I'm getting this dying every 20 seconds thing. It just sputters out. So if I sit for a second, it starts up, I can go a bit then it dies. Is it possible the carb is fuel starved? I have ordered the Grizzly jet, it's just not in yet. My pilot is 37.5, main is 165, pipes are Cobra two into ones, Ignition is Dyna 3000. Airbox is stock. It sounds like I should have talked to Shane at S&S for a jet kit. And installed the BAK and a ported intake before going through all the trouble of rejetting etc... It was running well with a 35 pilot, 165 main and 1 turn on the PMS. the needle is a Barron's and the clip is on the fourth ring, with one washer underneath. The Cobra guys recommend a 175 main with their pipes and a 37.5 pilot. But they are assuming a BAK probably. Any ideas? I'm gonna bet it's the float valve I'm still waiting for.

[Duke]

Make sure the fuel tank is venting good.

[Spydr]

Did you vent your gas cap?

[RRS_07RdStar]

Mikuni and Dynojet pilot jet size comparison

So what parts are different? None of the jets that come with that kit are the correct size for your bike. But that is what Dynojet corp thinks is right for the bike and they are wrong. That is one of the problems with the dyno jet kit. Their jetting recommendations are wrong for your bike. You can use the needle from that kit but order some mikuni jets. You should order a 167.5 Mikuni main jet and a mikuni 37.5 pilot jet. The dynojet 37.5 that comes in that kit is not the same as a Mikuni 37.5 the Dynojet 37.5 is the same fuel flow as the OEM 35 Mikuni pilot jet.

I know this is an old topic, but I wanted to point out something that I just discovered and thought it is useful knowledge about Mikuni and DJ pilot jets.
Background behind this is I'm selling my Roadstar and I removed my V&H Bigshots (replaced with stock stage1 exhaust) and went back to a stock airbox with a OEM filter. All I had was DJ jets but I didn't want to mess around with trying to re-tune it again. So Davej was nice enough to provide me with the stock main and pilot jets, and stock single slot needle. I put the stock parts back in, but I couldn't remember what the PMS turns out for stock motor was, so I started by searching the forum and came up with this thread. Reading through I found the stock PMS is 3.5 turns out. So I tried that and found the bike hesitates off idle, which seems to be typical for stock according to what I read here. It seems from the info here, that you really don't want to turn the PMS out much more than 3.5 turns, so my thinking is to use the DJ #37, assuming it would deliver more fuel that the Mikuni #35. I saw Davej comment above, that the DJ# 37 was about the same fuel flow as Mikuni #35 pilot.

So I decided to actually measure the flow to compare the 2 jets. The attached pictures clearly show the emulsion end is much larger diameter on the DJ compared to the Mikuni. I was going to measure the orifice, but that won't tell the whole story. I have a couple of pictures of the setup I used, a 60cc syringe, open on the top. I used some clear plastic tubing that fits the end of the syringe and over the large end of the jet. I did 2 separate test to verify the validity using gasoline. The first test I filled the syringe to about 44cc and waited until level got to 40cc and started stop watch, and end test when level got to 20cc. The second test I didn't want to wait so long, so I filled the syringe to about 44 and started stop watch at 42cc and ended test at 38cc. Below is the results:

DynoJet37, 20cc in 130.53 seconds. Mikuni35, 20cc in 315.41 seconds
DynoJet37, 4cc in 132.94 seconds. Mikuni35, 4cc in 169.69 seconds

So clearly the DJ37 flows more than the Mikuni 35. I'm sure the 37 Mikuni probably flows a lot more than the DJ37. But for my particular situation, I just want to add a little more fuel to the pilot circuit instead of trying to back out the PMS more and worry about loosing screw with not having enough spring tension. I'm hoping I can set the PMS out between 2-3 turns out with the DJ37 and eliminate the lean off idle hesitation.

Davej, what's your opinion on this, or anyone else's for that mater?

[davej]

The info that I quote that the dj 37.5 pilot flows the same amount of fuel as the mikuni 35 pilot jet come right from Dyno jet tech support on a phone call that I made to them inquiring about it.

[RRS_07RdStar]

The info that I quote that the dj 37.5 pilot flows the same amount of fuel as the mikuni 35 pilot jet come right from Dyno jet tech support on a phone call that I made to them inquiring about it

It's hard to argue actual flows at same given head pressure from my test. Only difference in the bike is the fuel is pulled through in inches of mercury of vacuum instead of head pressure. I wasn't trying to be negative or prove you wrong, I just thought you may have assumed that from the way the main jets sizing compares. My real point was to question if using the DJ (assuming my DJ37 flows more)) seems like a way to possibly eliminate the stock idle leaness? The needle already has both washers and the plastic spacer under the E-clip. Sorry if I came off the wrong way.

[davej]

Install the dj pilot and see if it helps. If not install a Mikuni 37.5 pilot. I'd be curious to know. As Said I would never put out that type of info based on my assumption, It was from research and talking to DJ tech support to obtain that info. I guess the only assumption on my part was assuming that the tech support guy knew what he was talking about. lol

[davej]

Also there should only be 1 washer Under the clip. Putting 2 under the clip only richens the fuel mixture at cruising speed by about a 1/2 groove on an adjustable needle. In the stock configuration the cruising speed AFR does not need to be richened at all. The 2nd washer should be placed on top of the clip for the little spring to set on.

[brianmac]

If nobody already said it, while you're in there pull out all the air Jets and make sure they are correct also. If there were dynojet jets in there, the PO could have put in a hypercharger at some point, and at one point they've required a different air jet up to the top of the carb, if I remember correctly. Don't leave any Stones unturned

[Jmcdonner]

Newbie question...though reading many of the articles I think I have a good idea where to start. Putchased 2005 Midnight Silverado 1700 tgat had been sitting a while....a number of years. Set up has tge Kuryakin Pro Hypercharger with Hard Krome Bug Staights. Pullrd tge carb to clean it up and Looks like carb was never jetted by original owner. Ordera rebuild kit, Baron adjustable needle, and jets. Seems like I should start with 167.5 , 40, and needle on 2nd clip. Agree. Live in Northern Virginia.

[davej]

If you have a 1700 start with a 172.5 mikuni main jet and a 40 mikuni pilot jet. Clip in the 4the groove on a barons needle. PMS 2 1/2 turns out. with the Hypercharger you may have to go to a 175 main jet but I would start with a 172.5.

[Jmcdonner]

Thanks!

[Jmcdonner]

Anyone know the size of the pilot air jet on a 1700?

[davej]

Doc, that is wrong. the one under the diaphragm cover is a 2.0

Pilot Jet, Air (2.0)

#239-14172-20-00

Retail Price: $5.49

The one in the mouth of the carb is a 100

Jet,Pilot Air (#100)

1HX-14231-20-00

Retail Price: $6.49

[Doc_V]

Well cut off my pinky and call me Betty... I've been running a 1.0 for years, in both my 1600 and 1700, based on the recommendation of another RSC member; who shall remain nameless. But it's right there in the on line factory parts catalogs: 2.0 https://www.yamahasportsplaza.com/oe...2a4/carburetor

Thanks for the heads up Dave. Looks like I need to order a new one.

[davej]

Doc,If I remember correctly the 1.0 was the jet that comes with a HC kit.

Edit: I just looked at your profile and it says you have a hypercharger. If you do then the 1.0 is the correct one for your bike. If you get rid of the HC then you will need to swap back to the 2.0

[Doc_V]

The older I get, the more I forget... I'm like Homer Simpson, if I learn something new, it pushes out something old. ...So I went back and did some more digging; the Hypercharger comes with a 1.3 air bleed. As you probably know, if you do a full on re-jet, sticking with the 1.3 air bleed can make proper tuning difficult. Switching back to the stock 2.0 essentially treats the HC as typical BAK and makes things easier. And yes, at one time, based on a recommendation, I did have a 1.0; I was looking at those old records late last night when I posted. But after checking further, I did switch to the 2.0 back in 2016, when I got my 1700. So that much is good. Thanks again for pointing that out.