Using pilot screw depth measurement to tune

A short time ago, RickOMatic posted some info on setting the pilot jets by measuring their depth - the distance from the top of the screw to the top of the hole in which they go ...

The numbers given for the XJ500 Maxim were:
Carbs 1 & 4 @ 11/32 deep
Carbs 2 & 3 @ 9/32 deep.

I tried using this and found that I couldn't even get the screws to 11/32.

Perhaps there are different carbs on these bikes with different depths?

My caliper has a "probe" that goes out the end to make it useable as a depth gauge. I put it out to the appropriate amount (using the digital values) and set the screw to the correct length and put it in. Even with the pilot screw tightened all the way down on carb #1, I couldn't get it to the stated .343 in depth.

I had thought that Rick had saved me from buying a color tune, but not it doesn't appear so. Any thoughts, comments or suggestions?

 

Re: Using pilo screw depth measurement to tune

I'm sorry I should have jumped on that one sooner but you are correct; I think there's a difference between the 900s Mikunis and the 550s besides just the massive bore. (Maybe the idle screw pitch?) I know Rick's post said "550" but I do believe he was basing it on his vast experience with the 900.
I'm not sure about the "leaner on the outside" thing, that's usually only the 1100s (maybe it's a 900 thing too) and other "big" motors.

I've got Secas or I'd tell you where my screws are (all 8 of 'em) as a reference; but with the different cams the settings have to be different Seca-to-Max.

Did you make a note of where you found them?

Try 2-1/2 turns to 3 turns (turn=360*) out if you didn't, as a starting place.

Buy a ColorTune or you WILL be buying the equivalent $$$ amount in spark plugs eventually.

 

Does someone out there with a 550 Maxim have the ability to precisely measure the depth? It would be a big help to me right now.

 

I don't know fitz if you'd buy the equivelent of a colortune in plugs. unless you changed them every year for 4-5 years. I never even heard of a colortune before finding this site and still don't own one. Yes it has probably taken me far longer ot get things dialed in with having to read the plugs alot more. But with patience it can be done. Oh and I haven't fouled a plug at all since I have owned the bike I did put a new set in when I first bought it about 1200 miles ago. I would still like to try one out just to see where I am but haven't yet.

Tumbleweed, The problem with taking the value from another bike is there are no two engines exactly the same. You will have to tune your motor to your conditions and the condition of your motor. Yes it could probably get you close quicker b ut it is not the cure all set it there and your good. As stated start at 2 1/2 out and tune your motor from there.

 

At something like $10 per set of plugs, if you are burning them rich, flooding them out, you will pay for the colortune in about 6 sets of plugs, not counting fuel costs, etc. If you are running lean ... I don't know how long it takes to burn holes in pistons and such, but clearly, that damage is significantly more than a colortune.

Carbs being what they are, I think that the measurement should be fairly consistent across the board for the same carbs on the same bikes, so if you get the depth measurement of a bike that has been precisely tuned, getting within a short distance of the measurement should be pretty much on the mark, even allowing for variances among bikes.

 

are the carbs machined at the top of the hole? if not your just measuring to a casting, put those calipers on some other parts of the body and see how accurate the castings are

 

Machined? I don't know. Are they normally? I would think that stock carbs would all have the same measurements, particularly if casted in a factory system?

 

I think I would measure from the bottom of the mixture screw well to the top of the tower and see if there are any changes. Base your adjustments on that measurement.

MN

 

Oh if that were only true we'd never have to sync the carbs/motor EVER.

But in the real world there are slight differences even between cylinders especially on ikes of our age. You'd have to be running really rich to foul out the plugs fast enough to need 5-6 sets before you got done tuning. Maybe I just got lucky hehe.. I do see the point of having the colortune but in using the colortune you are going to adjust the screws that you are trying to set to the same measurement. You will be most likely turning them a slight bit different for every cylinder.

 

Alright already HERE:

My '83 550 (Seca) has been running OK. I need to do a full sync and re-tune the mixtures; I have the rack off right now and set up for float height measuring; I haven't touched the idle screws yet and the bike WAS running:

#1: .208" #2: .220" #3: .224" #4: .218" measured using the "probe" end of my digital caliper the same way you were, from the top of the idle screw well to the screw itself.

I haven't run the screws in and back out yet to test how many "turns" that works out to. Not touching them right now.

 

Thanks Fitz, I wasn't meaning to put anything on you specifically. If a couple of people with Maxims did it and the numbers were pretty close, then that would suggest a functional measurement that would be useable if not as perfect as a colortune. That is really what I was going for. I don't know if the carbs/mixtures are any different between the Seca and tne Maxim.

 

The thread pitch is much more precise than you'll measure with a dial caliper.

Problem is every carb is different. If they could all be made the same there wouldn't be an adjustment screw.

 

Precisely. This is exactly why nobody can "publish" a list of pilot screw settings that will work for every XJ or every 550 or even every 550 Max.

Not only is every carb slightly different, so is every MOTOR.

If you just want to use them as a starting reference, fine; but don't for a minute think you can simply set the screws to a "pre-determined" depth and call it done.

The factory didn't even do that; they used a sophisticated piece of technology (EGA) to set them and then plugged the holes so us mere mortals wouldn't mess with 'em.

Little did they know...

 

It's interesting that recently the forum is hung up on how many turns to set the screws. As Carl says every carb is different as is every cylinder and spark plug etc. as Fitz is pointing out. The depth or # of turns gives you a great starting point then tune from there.

Just my 2 cents.

I have been wondering why Yamaha capped them and said don't mess with them. I understand the EPA rules etc but it stands to reason that over time the engine changes and would need retuning. Maybe they didn't think they would be on the road so many years later.

 

I think they assumed that, and also assumed that you would be taking the bike to a dealer. The book doesn't JUST say "don't touch them" it says to take it to a Yamaha dealer if you feel they need attention.

The DEALERS were given the EGA specs.

 

Because the EPA told them to. You leave it exposed and it becomes an adjustment and Yamaha is responsible for the results.

The earlier bike that were meant to be adjustable often had "stops" on the screw to keep the average nimrod from getting into too much trouble.

You can bet the day is quickly coming when it will be a crime to touch them without the proper equipment and EPA certification. The shops in Nevada just over the border from California do a brisk business in California bikes because the regs in California prevent local shops from making motorcycles run well.

 

The pilot screws on my 550 Mikunis are M6 x 0.5mm which works out to about twenty thousandths of travel per revolution.

I don't know what the pitch is on the coarse screws, but obviously, it's even more than that per rev.

 

There actually are "average" nimrods?

How do you describe the others?

 

Nimrods are also available in below average and above average.

 

That's the funniest thing I've heard within the last week. LMHO.

dave

 

Dear Gawd,please let me fit into the above average category!!!

 

Danno, I wouldn't be so quick to jump here... I'm not sure which way the scale goes.

I mean would you rather be a below average nimrod, or an above average nimrod? :lol: Haha!! It's unclear to me which end of the grading scale is actually desired here!!

In other words, which is worse... being an a-hole or a complete unmitigated a-hole? :lol:

 

Average, above average, below average ...

A nimrod of any grade is still a nimrod ...

Uh, Danno? ...

 

Nimrod, a Mesopotanian monarch who built the city of Babylon, definitely above average, that one.

 

Are you serious? There actually was a real guy named Nimrod? And he built Babylon?

Excellent! :lol:

 

Also a town, ship, race horse .....


http://en.wikipedia.org/wiki/Nimrod_(disambiguation)