fuel shutoff, replumbing, & individual filters

[Mike Hart]

Rick, I'm glad to hear the DJ kit worked for you, maybe the big bore kit had something to do with that. I figure those kits got to work for some people, otherwise they'd never sell any

Question - do you know the stock pilot air jet size? The service manual left out that info, and I haven't looked (next time I change mains I'll inspect).

How did the taper compare on the needles?

Here is a chart of how Mikuni and DJ jets compare for VMax, so the range of sizes is not of direct interest to us, but the basic info is very interesting.

I'm guessing your DJ 138 mains are roughly equivalent to 130 Mikunis based on that chart. The DJ190 pilot air would be between 177.5 and 180 Mikuni.

I'm assuming your larger combustion chambers require more fuel and air than stock.

The white plugs spook me out - can't be a good thing.

[TopCatGr58]

Jet Prices

Hey there Mike,
After you turned me down for your old jets,(now I see why), I went shopping as well. DK has them for $9.99, and they state that they are a set of 4 in their description, even though the order refers to the item as "EACH", but I'm hoping that means "Each SET". I ordered the 117.5's and 45 Pilots, and they should be in in a few days, will let you and the list know for sure. Rob Reilcorp has them for ~$3.25 each plus a few bucks shipping.

[Mike Hart]

T.C., don't be surprised if you have to go bigger on the mains. Keep us 'posted'

I put in 122.5's today (four sizes up so far), will ride tomorrow and find out if I'm there yet.

Rick, while I had the carbs off, I removed a pilot air jet to check the size, the stocker is 170.

Ken D, Wayne, JCarlton - in this thread woodstoc brings up the fact that the Emgo cones also have a shoulder inside, but read to see that in the Emgo case, it doesn't appear to interfere. From what you guys reported, the shoulder your filters had must have actually interfered, according to the way your bikes ran so poorly.

[Mike Hart]

yet another test ride report on jetting

I'm stumped - I put in 122.5 mains yesterday (so now I'm four sizes up on mains, one size on pilots) and the dang plugs are still white! Rode 100 miles on rural roads, not super-aggressive on the throttle (just one run to redline in 3d), but not namby-pamby either, got 42mpg - would much rather have seen 38 with plug color!

Double-(triple)checked:
plugs - BP6ES, gapped at .75mm
sprayed flammable stuff at carb boots, no leaks there
plugs do turn black if idle w/ choke on when cold

Guess I just need to keep throwing bigger jets at it. Before I do that, I'll take up the Moto-Guzzi shop's offer of a free sniff of the exhaust gasses to give me some real data to work from.

[woodstoc]

I checked the EMGO's like you suggested Mike and they are clear. There appears to be enought space on the angled shoulder that it shouldn't be an issue.

Keep climbing on the jets. My next try will be the 137.5 on 80SG carbs with a 42.5 pilot! Those EMGO's make it a snap to pull out the carbs. I love it compared to struggling with the stock box.

[ratbyk]

The search continues.
Mike, Iam now running:
Mains-137.5
Pilot-45
Air jet(in mouth of air horn)-210
Needles-5GZ6( in second slot from bottom)
Float height-1 3/16
When I ended up with this configerstion after playing with the shouldered cones I was a bit rich with a 1 inch float height but it ran well. I raised the floats to 1 1/8. It ran even better but was still just a bit rich. I raised the floats to 1 3/16. BINGO! The bike ran perfectly. It had instant throttle response at any RPM. It felt alive,like REALLY ALIVE! and would rev seamlessly all the way to 8500. The pugs have a perfect tan colour. I am as close to perfect as I can get.
I am running the stock rubber ram tubes but no air box at present. Just a fine mesh stainless screen over the end of the ram tubes.Not much dust around the NW at this time. Insurance runs out in Nov. I expect to take it off the road at that time for some more rejuvination work. Will put the stock air box in at that time.
Ratbyk as turns 25 years old in Nov. so will attempt to get Vintage or Collector plates at that time. Big reduction in insurance rates with these plates. It is supposed to be original for Vintage plates so will need the air box in place to pass that inspection.
Anyway, I am very pleased with the way it performs now. Compression is; 180-175-175-180. This bike is alive and well, living in Sooke. Last Wed/Thurs when I rerun the BI2K route in reverse it just sang over the whole run.
Ken/Sooke
78E Ratbyk

[Mike Hart]

Originally posted by woodstoc
I checked the EMGO's like you suggested Mike and they are clear. There appears to be enought space on the angled shoulder that it shouldn't be an issue.

Keep climbing on the jets. My next try will be the 137.5 on 80SG carbs with a 42.5 pilot! Those EMGO's make it a snap to pull out the carbs. I love it compared to struggling with the stock box.

Great, glad to have confirmation on that air passage clearance. Man, I really want to get this right, I hated that stock airbox!

[Mike Hart]

Originally posted by ratbyk
BINGO! The bike ran perfectly. It had instant throttle response at any RPM. It felt alive,like REALLY ALIVE! and would rev seamlessly all the way to 8500. The pugs have a perfect tan colour. I am as close to perfect as I can get.

well dang can it feel any better than that?!?! Way to go Ken. It'll probably run crappy w/ stock airbox/filter (leave the filter out??) for inspection, but come spring you'll have it hummin' I bet

[nashville_bill]

Maybe you can help be understand why, after twenty some years, the original configuration of the air box and filter is suddenly no good. Isn't this the same way the original bikes were tested and raved about? Looking inside the air box, it looks like the Yamaha engineers spent a lot of time on that design. Wouldn't it have been much easier, and cheaper, for Yamaha to just put four little air filters on the bike?

I remember, in the seventies, that kids turned the covers of the General Motor's air cleaners upside down to make more horsepower. It made geat throaty sounds when you nailed the throttle but did little to make the car go faster and probably made for a lean mixtue.

[Mike Hart]

Bill, it's not that the orig design is no good, it works fine.

My reasons for switching: when replumbing my fuel hoses, it was such a major pain to get the carbs out (XJ airbox moves even less than the XS airbox) that I decided to change that too. I like the look and sound of the individual filters too. Also, there is no aftermarket air filter for the XJ, they are paper, not cleanable, and danged expensive. There is also a tad bit of hp to gain as well. I've spent approximately the cost of one air filter to do these changes. Well, 2 air filters, if you count the fuel delivery mods.

Others may have other reasons, those are mine.

Yamaha certainly wouldn't have wanted that noisy Bwaahhhh from the carbs when you twist the throttle

[woodstoc]

I agree with Mike. My main reason to go with the cones are ease of getting the carbs off. I have had them off no less than 20 times in the past couple of weeks and it was such a pain to get them out with the stock airbox. I was also tearing up the rubber on the stock box doing this. I can have my carbs off the bike and on the bench in two minutes now.

[TopCatGr58]

Re-Jetting Update

Hey there Mike, and the list,

First, the DK jets were the correct ones, they were the same as the set I got from my local performance shop. Secondly, the Pilot Jets are also the correct ones, however, now after tearing into my carbs again, I re-discovered that those were the ones that I was NOT able to remove the first time around, buggered up the slot heads, essentially they are corrosion-welded in place, was only able to get one out, but after inspection, just put it back in.

Happier note, I was able to drill holes into the Pilot Jet screw caps on the top throat of the carbs, screwed in a sheet metal screw into them, then used a plier to remove same plugs without damaging the screws. Then was able to apply liquid wrench to them, and after filing/grinding down the sides of a slot screwdriver head, was able to loosen the screws for removal, cleaning and re-insertion. They were only 1.5 turns out factory "stock" set. Almost didn't see the little rubber o-ring/washers but eventually did and got them back in in proper order....phew!! I set them at 3 turns out since I wasn't able to use the larger 45 jets(still 42.5), and this adjustment was per the performance shop's recommendations.

My floats are also set at about 20.5 to 21.00 mm height, just an FYI. Got the main jets in no problem. Found a damaged leaking petcock during the process...right side, but at least I know my float valves work on #'s 3 and 4! Repaired that with another homemade rubber gasket, slightly thicker material this time, works fine.

Also, sorry to say, I found that I had placed a hose on the intake port of #2 that went to the old Octopus valve, but had forgotten to cap it off.....surprised that the bike ran as good as it did with that vacuum leak, and that was the same intake that my vacuum advance ran off of as well!!!!!! It is now properly capped!!

Bike idles fine, has same strong run and pull thru 8.5k plus, no stumble off idle or thru rpm range. And....I now have a light tan color on the tip of the insulators on all four plugs, so at 117.5, I can stop messing with my carbs......aside from a possible true vacuum synch possibly to be done at the NC rally in a couple of weeks.

Hope this info helps someone with their tuning fun. Re-cap of engine info, runnng Round can style Indy foam filters; old 4-1 black ceramic coat pipes; have 1179 big bore kit, otherwise stock cams and carbs.

[ratbyk]

Petcock Watch

Goody on Super Rat.
Suggest that you keep an eye on the repaired petcock.
If rubber you used in the repair is neoprene you will be OK.
If not it will degrade very quickly, start to swell and could block off the fuel flow. Just a thought on this on going saga known as XS.
Ken/Sooke
78E Ratbyk

[TopCatGr58]

Re: Petcock Watch

Originally posted by ratbyk
Goody on Super Rat.
Suggest that you keep an eye on the repaired petcock.
If rubber you used in the repair is neoprene you will be OK.
If not it will degrade very quickly, start to swell and could block off the fuel flow. Just a thought on this on going saga known as XS.
Ken/Sooke
78E Ratbyk

Ken, Funny you should mention that, I actually use Latex household gloves often when doing my mechanic work, due to I'm also a surgical asst. and can't have cuts and such on my hands for sterile technique/proper scrub preparation,etc.

When I found the petcock leak, was frantically trying to put the fuel lines back on, and gas poured all over my hands, and the latex gloves kinda melted and tore quit easily. The gasket material was from large Neoprene washers at local hardware store, cut it out with scissors and hole punch, the prior one was a tad too thin, and it had just torn between holes, no more seal!! But thanks for the info, for others benefit as well.

[Mike Hart]

TC, you have plug color, awesome! I am jealous. Tomorrow I'm hoping to get to the EGA, to sniff out some numbers...