Airhead parts - the dark secrets revealed

silly question, but does it Brake better?

Not a silly question, Jason. Haven't actually been for a ride yet. It's 4C and raining and I don't want to try it badly enough to suit up for that. Theoretically it ought to work, though.

The larger total piston area of the 4-pot caliper will provide greater resultant force at the pads with lighter, more progressive action at the lever - ie: greater lever travel.

This part bears up in practice: The stock GS has a hard, "wooden" feel to the front brake lever. The stocker hits the "pressure point" and stops dead. In comparison, with the 4-pot caliper the lever feels softer and the "pressure point" is felt through a broader range of lever travel. This is because the larger 4-pot caliper requires the m/c to move more fluid to drive it through it's braking stroke.

Creating hydraulic pressure is all about piston area ratios. The greater the difference in area between slave (caliper) and master cylinder, the greater the resultant preasure. Applied pressure is multiplied by the ratio of the areas of the master and slave cylinders.

Braking force is the product of that created pressure times the area of the caliper's pistons. (divided in half if caliper pistons oppose one another).

I hope I helped it make sense. It's easier to "see it" in your head than it is to articulate.

Lornce-- so as not to hijack this thread-- see latest posts in Brakes thread:

http://advrider.com/forums/showthread.php?p=4367167#post4367167

...O.K., where's the best place to by em, huh?
FEGV-S3802?

Whoever said radiator hose wouldn't work was right. Despite assurances it was the same as the carb-to-cylinder hose, mine started to fade at about 2K miles. It'll work as an emergency fix, but should be replaced ASAP with the real deal. I replaced mine last night. Put this in the "roadside repairs" category.

udpated it. Thx for the feedback. i was wondering about that one myself.

I should have given it a bit more of a test before posting. I was excited.

On a related note, tighten the clamps on the new rubber after a short ride and overnight rest. Otherwise, you will have an air leak and one pipe will glow all the way to work while the bike acts funny. I found this out at about 5 this morning.:huh

The replacement diaphram for a Stromberg Carb. on 68-69 Triumphs (I think) are almost perfect replacements for stock diaphrams. Almost perfect because they are slightly beefier and will alter your throttle response. If you keep your ride in perfect tune and are ultra-sensitive (or a racer) you will notice a difference.

Moss Motors in Riverside, CA and the Web has the parts for about $15/pair.

I will have to do some more research for the part number.

Dave

Keep us posted and I'll add it to the first page. Thanks.

The carbs in question are the CD150 and CD175 for the 32mm and 40mm Bings.

From Moss Motors, the part numbers are 365-320 and 366-040. Tthey are $20.10 each for the CD150 and $3.95 for the CD175.

(as the owner of a 1976 R75/6 I am most distressed by this)

Aren't they the same ones used by the Mercedes-Benz carbs? What did you mean earlier by a different throttle response by using beefier diaphragms? Beefier = better or not?

I sourced the CD150 diaphrams from a place called: www.classicautospares.us

Their price was $5.00 each plus shipping.

As for response, a beefier diaphram will respond slightly slower to vacuum changes. If you are a racer, or die-hard originalist, that might be an issue. I would guess that durability would win out over barely perceptable changes in throttle response.

But that is, of course, a personal issue. "Better" is a loaded term.

I do not know if Mercedes used Stromberg CD150/175 carbs or not.

Keep the rubber side down

Dave

I replaced mine with MB ones 2 months ago and experienced slower response and lean mixtures. When I replaced them with the original ones, the performance improved a lot. So much so that I had to adjust my mixture settings as it was too rich. Wonder if the new diaphargms had anything to do with the mixtures?

Absolutely!

The diaphram picks up the slide and the needle (in response to intake vacuum) which changes the size of the fuel orifice because the needle is tapered. For the same amount of intake vacuum, a stiff and heavy diaphram will not move as far as a thinner, lighter one.

The trick (for me) is to find an affordable substitute for the stock diaphram that will not change the carb's behaviour too much.

Some people also replace the stock spring in the carb for the stromberg. If you do that, you also have to move the needle setting to the lowest groove because the spring is beefier.

Everytime to change things in a carb you are going to get performance changes. The %#*^ things are rather sensitive.

Cheers

Dave

If the slide moves slower you get a richer mixture in transition only .

There is a choice of at least six springs for the SU CV Carbs, and the selection of the correct one is one of the secrets to tuning SU Carbs.

Okay, before this thread goes completely down the toilet: Would you girls mind discussing carb theory somewhere else?

This is meant to be a compact and concise listing of useful alternate parts to keep airhead boxers rolling down the road. Not pages of inane dialogue arguing the minutea of carb function.

We've got lots of threads already devoted to that.

Thanks,
Lornce

I posted this info on Flying Avantis 2-up thread and thought it oughta go here for general consumption...

From a tech article in the UK BM Club magazine about a R100RT starter failing in France last year.

Pics showing a BM Valeo and Peugeot starter motors together and they are identical, both showing the D6RA model number clearly on the label. The Valeo D6RA was fitted to Peugeot 200 and 300 series cars along with their Renault and Citroen relatives.

If any of these autos were imported into States in the early/mid 90's, then there should be a ready supply at the local breakers/parts store of a much cheaper alternative.

Charlie

Most of the french autos stopped coming to America in the eighties.
In any case this info might help when availability is the problem, but it is going to beat $179 shipped new.

I was told that this part number has been discontinued, does anyone have any idea on the replacement part number?

Also, where is a good place to order Sealed Power rings from? My web-fu only led me to one online source, who told me the number was discontinued.

Do the Hastings rings work equally well for Nikasil 1000cc airheads?

Thanks for any info.

I've gotten fuel filler hose from an industrial hose supply - probably for semis or heavy equipment. But I made the mistake of getting the reinforced style molded around a wire spring. It still works, but the spring deforms it and... it's hard to describe. If you can, get the stuff that doesn't have the metal inside.