carb nomad performance?

[madcow]

i always hear on here of people fitting a tfi on their nomads, but it seems that this is for fuel injected bikes only (please correct me if im wrong). i am running debaffled and was wondering if i added some better air filters would this upset the carb? , would i have to tune or rejet the carb? im a little confused on this and would love someone to put me right. cheers mc.

[ringadingh]

It may change the carb enough to require an adjustment, but you wouldn't know until you tried riding it and taking a spark plug reading. Then by reading the plug color you could determine if any changes are neccessary.
Sometimes just a adjustment may be all thats required, and other times changing jets, or a needle may be needed. This is a trial and error type of change that depends on a few factors theat change with each bike and location. Temp,barometric pressure, elevation etc, have a lot to do with the finetuning of a carbed motor.

[macmac]

A TFI/ Cobra/ PC III and other fuel moduals are just for electronic injection. These work in different ways to re-jet a injected bike.

None if these will do you any good what so ever with a carbed bike.

I haver have had a carbed Nomad, so I can't be very telling as to what you can do to gain power, but you can gain power.

The first thing I would do is put some kind of lesser baffels back in the ?stock set up?? That will increase back pressure some, as no baffels looses that feature.

On a carbed bike are the pipes crossed so engine beats pass thru both sides or not? I don't know, but if the exhaust has a cross over pipe and you took it off, put it back on.

What you are looking for is moving the most possible air you can thru the system, and matching fuel to that air.

I will assume the carb is a CV (constant velocity) type. If this is correct there is a black rubber diafram under the top cover on the carb. The slider then has a long brass needle, that is adjustable by some means.

Some needles have a clip and slots to raise the main needle, while others have a pointed screw coming from the side of the slide under a ledge on the main needle.

The higer you raise the needle the more fuel can flow. That is for middle and upper rpm, with out adding other parts.

Then there should be a pilot screw somewhere behind the throttle plates. I called these idle mix screws like they are known on cars in the USA. These cover idle and low rpm fuel, and stop working in low mid range rpm.

Also you have a carb float in each carb there is. I think you have just one carb, so one float. These work like a float in the toliet tank, and can be adjusted in tiny increments for more or less fuel in the float bowl.

There is a book spec for the setting, but you can bend the rules a little bit for more fuel , which makes a higher fuel level, so engine vacuum can get that fuel somewhat easier.

The trick is knowing the bike, knowing it so well you can tell what is better over all and what isn't.

The next trick is knowing which adjustments to make when.

You always start with low rpm and work one adjustment for max bennies before moving on.

So with a free flow air filter, the first thing you do is see about adding MORE fuel with that pilot screw.

Then if you can get a good strong and proper idel and the low end has romp, the next thing to mess about with might be the main needle, rasing in 1 notch, and trying that out for a healthy mid range.

That might not happen so very easy, as these things are sensitive. it is likely you will create and find flat spots, and depending on where they are in the usable power band, certain other adjustments should happen.

And then it can be determined that you need a set of bigger jets in drill sizes. DO Not go about drilling any jets you have in the carb ever! Your drills are not nearly of the quality needed to do this job and neither are mine!

Any time this task is under taken you must record where you started so you can go back.

Jets come in 2 types. press in with O rings and screw in with sometimes shimmed gaskets, so they can be screwed in just so far.

Some side draft carbs have a main adjustable jet as well, but I doubt the carb you have does.

Another thing you might try is hunt down a Type 6 SU carb off a Jensen Heally, Maybe some old Austin Heally, or a Jag XKE with a 1 and 3/4er's inch bore, and see if it can be adapated to the bike.

Getting back to stock parts, I don't know who offers a jet kit, but someone must.

The problems with jet kits is unless you do what some one else did exactly you are on your own.

I did my 1981 Yammi Triple 850 @ 826 real cc's. It has 3 carbs, and I matched each one to any other.

Jets for that bike cost 18 dollars each for 9 jets! I didn't buy any jets.

I raised the float level, and these carbs have the pointed screw to raise the main needle, but the screw didn't go high enough, so in sterling silver I use for making things I made up shims, and installed one in each carb. That wasn't enough, so I made 3 more shimes and installed these on the other shims, each time measuring, and letting the screw back down, and test riding.

That didn't get me where I needed to be either, so I made a 3rd set of shims, which worked, but I had to raise the screw so the needle was almost fully up as well.

Lots and lots of trails and testings is what happens when you enter the unknown.

I did that in 2000 the 2nd year of messing with my junk yard find bike. If IO messed up with no notes getting back to basics would have been hard to do.

I have better than 30 years of carb work under my belt, too, and still I know there can be trouble lurking. I just know how to get out of it.

If you want I can help. You will need air, and to read up on carbs.

You will need to find out what jet sets you can buy, what the numbers are on the jets you have now. Find out who else did what you want to do.

It is very possible you need more than one jet set, and or will find you need many differnt jets over all.

In the past I had to get 4 different jet sets to run one Honda 750 made in the late 70's set up for track racing. Lot and lots of tiny details.

[zoom45]

I'm carbed and debaffled but no other mods. No adjustments needed so far.
Zoom45

[madcow]

thanks so much guys, you have all been of great help. looks like i will make up a new filter set up, then see how it all goes. if it still needs work i will drop it off at my mechanics, he is a big ducatti and guzzi nut so the nomad should be the least of his problems. many thanks, mc.

[macmac]

I was writting as if you wanted to get more power. I always assume anyone wanting free flow items wants more power.

I think you will find a flat spot in useable rpm ranges.. A flat spot iof you don't know what I mean is where you trottle up and at first the bike moves about right, then it starves for fuel and slows, not doing what you demanded. After the slowing the bike sort of catches itself and goes faster, but not like it should.

[madcow]

bugger, yeah i would like a bit more power. i like the factory filter set up but want to get better fuel economy first and more power as a secondary request. i might buy all the bits, and send her to the mechanics for the carb to be rejetted/tuned to the new set up, that way i know she will be right.

[macmac]

Better economy might happen by making air more, and more free flowing, but you will need to add fuel which seems nuts. I haven't worked on a carbed Nomad so I don't know if that is pissible, because i don't know if carbed nads are as leaned out as injected nads are.

So for me it a maybe.

other things you can do are to run full syn oils in the engine and the rear gear box. Slippery stuff that is, so less friction.

This will seem right off the wall. Get forward engine crash bar covers on the bike and leave them on for better MPG's. i couldn't belive that myself, but I found out I got better MPGs with 2 big sails into the wind. Must be added to the windscreen it makes a bubble you ride in.

A taller rear tire will add in nice fat parts of miles. I just found tha the Dunlop Sport Sp 5000 symetrical tire will fit a 1500... It is taller than, but is more grabby than any mc tire, so when I put mine on it ate apx 2 MPG's. That isn't as bad as it sounds I guess since the trade off is traction and so I still get 40 to 44 MPGs.

As stock I got 34/37, so I am ahead of the game.

Pump the tires up to 42/42 psi for a stiffer ride and better made miles. (Chances are you knew that)

Will your tech work with you? Many won't and will install stuff, and leave it at that and not set the stuff up right.. It is a tad to far for me to swim.

[madcow]

i will shout a set of floaties to help with the swim..... yes i have a great bike tech, but i thought it would be better to do some research here first to give a grounding of what can and cant be done he will definetly work with me as he loves to do somthing different, and loves my nomad. you have definrtly given me a lot to chew on there mac, as soon as she comes back from the paint shop i will try and put it all to good use. thanks again, madcow...

[macmac]

Don't let me scare you off either. A bike with one carb, is a lot easier than a bike with as many carbs as there are cylinders.

More over I have high doubts you are going for the Racing Nomad track bike

With freeer moving air and a stage 1 carb kit you get more power. Whether or not you will get better miles for it I can't say.

All systems are never perfect. There is always some range that the mix is wrong. The ideal mix is 14 parts air to 1 part fuel, but this never happens consistantly.

The injected bikes are much leaner and i suspect something like 18 maybe 19 to one.. as stock. I can't test that as I haven't the tooling on hand, but maybe someone with tooling will come shoot me down and tell me the facts.

The tye carbs we have catch up, so there is a minimal lag time even if no one can feel it.

The injected bikes respond faster since there is a electronic signal. but if the signal doesn't demand more fuel, or of the demand comes up short in fuel we get ping.

I have no idea if carbed Nomads ping ...... ever.

[madcow]

the carb nomad will ping very lightly, but only if its over 100deg at full throttle and using standard petrol, so its not a big issue as in the warmer months i just use premium unleaded and all is fine. i agree on the carbs, my last bike was an xj900. i was pleased never to have to tune that sucker. it should be relatively easy to tune a bike with just one .

[macmac]

If you got PING, you should strive to add more fuel one way or another. Compression of 9:1 isn't in the realm of hi test gas... The reason 'we' do is because the mix is too lean.

So I suspect at this point the carbed bikes are also a bit too lean.

Have you discovered the pilot jet screw? It might well be hidden, perhaps capped over so you can't see it and or find it.

That is step number 1.

Step 2 is with great care to turn it all the way in, but when it stops you stop on the instant. There is a pointed end on this screw inside, and that point is delicate!!!

Before you do the turning in, you mark the screw with a pin point dob of paint, and make another dob on the carb body.

This way you can count parts of a turn IN, and then put the scrrew right back where it was turning it OUT. Record the parts of turns on paper.

Then you fire up the engine and go for a ride of no less than 8 miles round trip to home, so the engine is at full warm.

With the engine still running you turn the screw very slowy OUT, for more fuel, and listen hard for any improved RPM. Go past the improved RPM to where the RPM drops a beat, showing Too Rich.

Rev the engine here to clear it, at apx 1,700 RPM, not very hard revving.

Then turn the screw IN to LEAN, and find best RPM again. Then turn the screw back OUT towards rich a little bit but not so far as the first time. Not to where the engine drops a beat, but a point mid way to that.

Reset the black idle knob (Do carbed bikes have a black air Idle knob?)

You will not have the best rpm at idle, and this will cross over into lower RPM modes above idle to mid range rpm.

If you can find the screw you should be able to do this with out much trouble. Record these steps and the screw points I mentioned so you can go back.

Where novice shade tree techs mess up is making all sorts of adjustments at once, and usually messing with linkage on multiple carbs and they can't go back.

You have one carb so you can't really mess up that bad.

If you can do these 2 steps and try the bike you should find improved power in the lower RPM range. If you do and tell me we can move on.

[madcow]

thanks mac, that sounds very easy. the bike is in the shop being painted at the moment but i will give this a shot when i get her back. thanks again, mc.

[macmac]

Painted?? painted before mechanical work??? AYyyyyyyyyyyyeeeee

Remember Skin heals Paint don't! Take great pains to not mess up the paint.. That means new cloth fender covers, and rags lots and lots of nice clean rags..