• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

tuning carb timing

Share this page

T

TomFromStLouis

Jedi Trainee
Country flag
Offline
I met a guy the other night who races his BMW 2002. He seemed to know a thing or two about carburetor adjustment, at least more than me. This is not a difficult achievement. All I have done to tweak my idle is turn the little screw at each one back and forth until the car sounded right.

His first recommendation was to replace the SUs with Webers, Webers being superior and not as finicky. Perhaps, but that is the kind of originality I choose to keep. He went on to describe what sounded like some easy to use adjustment aids that attach to the carbs and visually tell you when each matches the other in flow. This sounded more like the kind of gizmo I could use, but his description is several days old and beer was involved, so I need you guys to tell what you recommend along these lines.

If simply turning the screws until things sound right is all I ever need to know, please say so. But if dialing these things in a bit better is possible, please link to a product that is easy to use.
 
Hi Tom, why not take the car over to Keith's for "Washup-Tuneup" and you'll get all the help you'll need. Keith has the tools also.
 
:nonod:, Keep the S.U.s. Simplest carbs. for your engine. You could get a Uni-Syn , a gizmo that reads the vaccum, but using a length of flexible tubing can serve as well or better. Simply put, you place one end at the carb. throat, the other end at your ear, and adjust the carbs. until the pitch is even. There IS more to do, and surely more info. will follow from others. Unless you got plenty o bucks and want to spend them, stay back from the Webbers! Invest in a manual, READ and UNDERSTAND it. Save that buddy for hoisting a few beers! :cheers: --O'elrey
 
TomFromStLouis said:
I met a guy the other night who races his BMW 2002. He seemed to know a thing or two about carburetor adjustment, at least more than me. This is not a difficult achievement. All I have done to tweak my idle is turn the little screw at each one back and forth until the car sounded right.

His first recommendation was to replace the SUs with Webers, Webers being superior and not as finicky.

:savewave:
Nope the SU is one of the simplest and most reliable carburetors available ,after all it has only one major moving part.

Perhaps, but that is the kind of originality I choose to keep.

He went on to describe what sounded like some easy to use adjustment aids that attach to the carbs and visually tell you when each matches the other in flow. This sounded more like the kind of gizmo I could use, but his description is several days old and beer was involved, so I need you guys to tell what you recommend along these lines.

Well SU produces a little tuning kit with wire indicators which you simply attache to the carb pistons. The alignment of the wires tells you when the pistons are both in sync. It is very simple and not costly at all. You can get one from most LBC suppliers

Additionally, there is more expensive tool calle a " Uni-Sync ' that is actually an air flow meter. This tool is also available from our LBC suppliers and it measures and shows when the air flow through both cabrbs is the same..


If simply turning the screws until things sound right is all I ever need to know, please say so.

But if dialing these things in a bit better is possible, please link to a product that is easy to use.

Yep! ! Sure is Your call--Keoke- :smile:
Click to expand...
 
:thankyousign:

---------------------------Keoke-- :lol:
 
You do want a uni-syn, plus the SU tool kit that has the "pointers" that go in the top of the pistons to make sure you have them set the same at idle. Since you don't know much about these carbs, I will urge you to read the workshop manual on carb adjustment and then you will see what I am referring to.
 
I read the title of this, and thought, geez, what have I missed all these years?
What is a tuning carb, and how does one set the timing on it?

Been one of those weeks.
 
You do want a uni-syn, plus the SU tool kit that has the "pointers" that go in the top of the pistons to make sure you have them set the same at idle.

Well Bill, you can actually use either tool. The SU tool with the "Pointers' can be set so the pointers match with the engine off, then when you start it and it idles any unbalance will be shown.--Fwiw--Keoke
 
I wouldn't trust a BMW owner that said Webers were less finicky than SUs!

I consider the SUs to be the simplest fuel metering device of the 20th Century (there were some 19th Century devices that were simpler__the unleaded fuel just overflowed back to the reservoir). However, I consider the SU to have three (3) moving parts; the damper piston, the butterfly, and the float.

The Uni-Syn can be difficult to get into position on the Healey, and the air filters must be removed to use it. You're better off just using the pointers, and developing your skill with them.

First check, is to see where the jet tubes are sitting in relation to each other (2 or 3 carbs). Take the three (3) screws out of each dashpot cover, lift out the piston, and visually check the jet heights. DO NOT mix up the pistons/covers with the other carbs__put them back exactly as they were removed.

A good rule of thumb, is to lower the jets two (2) full turns, and start your tuning from there. You'll find plenty of write-ups online about all the steps to take from start to finish.

Note: when tuning "carbs" the carbs are the last thing you touch. Make certain the valves, points/ignition and timing are spot-on before taking a screwdriver to the carbs. The engine should also be stinking hot.
 
What is it they say, 90% of carburetor problems are timing?
As stated above the Unison requires the air cleaners to be off. A lot of work. And cut hands. The wire thing Keoke mentioned is great and it allows you to raise the pistons the 1/8 inch needed to adjust the richness by seeing the amount of lift where the pins at the bottom of the dash pots are a guess.
I'm not sure what the stethoscope thing Roger showed does for the carbs. It is used when there is a ping or noise somewhere in the engine. A two foot piece of 1/4 inch tube works fine. You can do a fair job with the air cleaners on it you block the return (black) hose on the rear air cleaner (old wine cork or duct tape works well). A wine cork also works well to block the vacuum advance tubing at the rear carb.
Moss and others sell an SU carb book which is great for rebuilds and tuning but over the top for the casual maintenance tuning. There is a tuning supplement that is about 8 pages with great pictures. I gave one to Roger (Asumhly) and a few others 5 or 6 years ago. Contact me and I might be able to Email you a copy or sent it via snail mail. I don't want to do a million copies so if someone wants to walk me through a way to post it, I will be happy to do so. I doubt it is copyrighted. Now if the more computer literate, Roger will do it????? Do you remember it, Roger?
 
You pull the pointy thing and transducer off the hose and use it like you piece of old fuel hose, only it works better.
 
Legal Bill said:
....Since you don't know much about these carbs, I will urge you to read the workshop manual on carb adjustment and then you will see what I am referring to.
Click to expand...

Somehow it never occurs to me to check the manuals for this sort of thing. They are out there, you guys are right here. ;-)

Thanks for all the tips. I never seriously thought of abandoning my SUs. I just wanted to give you an easy target.
 
:savewave: Good timing on carb tuning! Thanx for the question. You're spooking a lot of info. out of the woodwork. --elrey
 
TomFromStLouis said:
Legal Bill said:
....Since you don't know much about these carbs, I will urge you to read the workshop manual on carb adjustment and then you will see what I am referring to.
Click to expand...

Somehow it never occurs to me to check the manuals for this sort of thing. They are out there, you guys are right here. ;-)

Thanks for all the tips. I never seriously thought of abandoning my SUs. I just wanted to give you an easy target. [/quotIt really is too many steps for people on here to try to list from memory. If you have a bell crank linkage in place, you should really start with that to make sure all the little rods are set at the right distance. Plus, check the teflon or felt bushings to make sure they are not worn. Basically, it is good to make sure everything on the car side of your right foot is in good condition before you start tuning. Everything on your side of the sole of your right foot is a different problem beyond my expertise.
Click to expand...
 
Back
Top