SU HIF Carburetor

[GreasyRag53]

Running rich, fouling plugs. Spits & backfires.
No casting marks but is an SU HIF carburetor
Took carb off & apart, cleaned it up, left most settings the same, added damper oil to the top of the carb.
Now I can get the bike started and running....kind of.

I pull the throttle and...BANG! POP! wants to die real bad.. but I made it home.

Anyways, Ive taken the carb apart again, now that Ive made it home.
Cleaned it all up, blew it with air, etc..
It has a Grose Jet (needle) valve in the float bowl. Not like your standard needle and seat type float.
Is anyone familiar with this type? Know how to set the float height in this type of float set-up?

Ive got the damper part of the carb lifting and dropping in a more fluid motion now, it wasnt so much before. Probably a lack of damper oil..

Any helps appreciated. Thanks.

[kitabel]

What size?
What needle?
What kind of fluid is in the damper?

[boxtriker]

No damper oil just finger wet the damper with a spot of oil on it should sort it out if you have not upset any thing else. they never seam to run right with oil in them on a bike.

[Cotten]

GreasyRag53!

I know nothing of the carb,
but be quite gentle with the Grose Jet floatvalve!
Do not suck upon it, or shake it.

....Cotten
PS: Have you bubble-tested the manifold?

[steve_wood]

As Cotten suggests, you may have an intake manifold leak. You may also have an exhaust system leak that is causing the backfires.

[rrhawg]

I also don't run oil in them. The slide seems to need cleaning on a regular basis and I've just sprayed them down with WD40 when I put them back together.
Rich

[1950Panhead]

Well, doc, the last thing I remember I started to swerve ...

[kitabel]

The oil in the damper is not an option - it's how the carburetor was designed.
It serves 2 functions:
1. prevents the slide from chattering up and down at idle
2. slows slide movement when the throttle is opened too quickly to improve response without enriching mixture.
I've seen everything from sewing machine oil, ATF, Marvel Mystery, 10W30 etc. used; IIRC S.U. suggests 20 weight. I use the lightest motor oil that gives good response (if it's too heavy, the slide doesn't pick up).

PS: The main jet is a (more or less) fixed size. If you don't know what needle you have, the entire mixture range is hidden.

[Cotten]

Folks,

The "Grose Jet" floatvalve is a 'jet' in name only.
Here is one for a Linkert:

GROSEJET.jpg (43.4 KiB) Viewed 1388 times

...Cotten

[Huck]

The level control valve is fancy but works the same as any other.
I use 10w40 in mine per the SU eliminator instructions, the slide must be free to move so it needs lightly lubed. The spring dictates the rate of movement. There are a variety of spring rates available. Different weight oil as a method to tune wouldn’t be day to day repeatable. With the carb upside down a straight edge should just miss the center of the float, if I remember correctly. (google lots of info on SU) If you run the level too high on an eliminator gas will run out the primer piston, if you don’t have a primer it could go to the throat, not sure as I don’t have that style to play with. Shut the petcock off and start the bike. See if it behaves before it runs out of gas. I’m thinking you’re on the right track, the level is too high & flooding the motor. SU’s are notorious for washing down cylinders! Always shut the petcock off when parked.

[Bosheff]

I will assume the HIF is/was intended for use on a Brit auto. I don't know much about them. The Rivera SU was/is based on the HS series SU which may or may not be the same as HIF you describe. On the Rivera units you don't need the damper, just pull it outta the cap and go. The needle is spring loaded and is tapered and rides in a pick-up tube (jet). The older Rivera SU carbs had a needle and seat, but sometime in the 80's were replaced with a gross jet, which is nothing more than a glass ball loosely captured in a brass cage, which does the same thing as the old conventional needle and seat. As far as adjusting the float, pull the bottom off the carb, and lay a straight edge across the base at the center of the float where it pivots. At that point the the float should just touch the straight edge. The SU's biggest enemy is loss of vacuum (it is a demand carb which works off engine vacuum), and dirt in the bowl (bottom cover), or in the piston chamber. These carbs don't work well on a tired engine as vacuum is essential for their correct operation. They are really pretty simple to operate and maintain. You can't run to many fuel filters with these units, and a high quality air filter is a must....bosheff

[Cotten]

...The older Rivera SU carbs had a needle and seat, but sometime in the 80's were replaced with a gross jet, which is nothing more than a glass ball loosely captured in a brass cage, which does the same thing as the old conventional needle and seat.

Bosheff!

Yes, it is just another valve.

But it is a glass ball above a metal ball that does the actual seal.

The benefits are anybody's guess, but I got a couple!

....Cotten

[Huck]

HIF means integral float, meaning the float chamber is made into the body of the carb. The old SU’s had a little pot hung on the side, that being the fuel bowl.
Also they have to have the dampener spring to operate. A heavier spring results in a richer mixture from off idle, lighter spring would be leaner, they’re color coded.

[Bosheff]

I guess I'm talkin bout a different part than you when we're talkin bout the dampner. I think you're talkin bout the spring in the chamber, while I'm talkin bout the brass do-dad that hags from the plastic cap on top of the chamber....bosheff

[Limey_Dave]

H1F Type

http://www.sucarb.co.uk/ProductCategory ... rentId=178" onclick="window.open(this.href);return false;

HS Type

http://www.sucarb.co.uk/ProductCategory ... arentId=76" onclick="window.open(this.href);return false;