Tuning SU H6 Carbs

[af3683]

I'm taking a shot at adjusting my SU H6 carbs. I have a copy of the original TR3 manual as well as various instructions I obtained from the web. My problem is that I find the manual a bit confusing and instructions found on the web often use language that differs from the manual. For example:


Web: Loosen "throttle linkage" nuts
Manual: Refers to "throttle spindle connecting rod"

Web: Back out "throttle stop screws"
Manual: Refers to "slow running stop screws" and "throttle adjusting screw on each carb"


Web: Back our fast idle screw(s)
Manual: Refers to "adjustable screw which abuts lever"

Can anyone tell me if these terms are the same. I actually may only need to adjust my idle a bit, but I'm not even certain which screw is the idle adjusting screw. Thanks.

Art

 

[Geo Hahn]

I'll try. My usual sequence is to adjust valves, adjust points gap, set timing, (start engine) sync carbs, (engine now warm) adjust mixture.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Web: Loosen "throttle linkage" nuts
Manual: Refers to "throttle spindle connecting rod"[/QUOTE]

These are the nuts and bolts that tighten the accordian-like clamps that connect the shafts of the 2 carbs. You want them loose so the carbs can be adjusted independently (sync'ed).

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Web: Back out "throttle stop screws"
Manual: Refers to "slow running stop screws" and "throttle adjusting screw on each carb"[/QUOTE]

These are the set screws that hold the carbs partially open. I don't know that you want to back them off completely, they are the screws you will adjust to get the same air flow in the carbs front and rear.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Web: Back our fast idle screw(s)
Manual: Refers to "adjustable screw which abuts lever"[/QUOTE]

Similar to the above-mentioned set-screws, but this one rests on a cam that operates as part of the choke mechanism. This one should be backed off completely so it does not interfere with the sync'ing.

The problem with using 2 sources of information is that rather that making things clearer they can give you too much information and (in this case) be hard to reconcile.

Almost any manual will have an exploded view of a carb that will identify the parts to be adjusted/loosened (such as the idle adjusting screw). Even the Moss catalog illustration may prove helpful:

https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29127

The couplers you loosen are item 66. The idle adjustments (3 incl 'choke') are items 17.

 

[af3683]

George, thank you very much for your informative reply. I may try to pick up a Haynes manual which may be more helpful than the original TR3 service manual.

Regarding loosening the throttle linkage nuts and bolts, I assume that you only need to loosen 1 of the 2 sets ? Also, I noticed that #71 of the Moss diagram shows a "throttle disc" which I either can't see or don't seem to have. Not sure why. Thanks again.

Art

 

[TexasKnucklehead]

In order to see the throttle disc, you must remove the air cleaner #162, lift up the piston #5 and look inside the body of the carb. The disc (or butterfly) is what the linkage and/or screws open/close to increase/decrease engine RPM.

 

[martx-5]

Can anyone tell me if these terms are the same. I actually may only need to adjust my idle a bit, but I'm not even certain which screw is the idle adjusting screw. Thanks.

Art

All those terms appear to be the same. If you just need to adjust the idle, there are three adjustment screws involved. One is the "fast idle screw", which is the one that is moved when the chokes are pulled. There is a cam that that moves and hits that screw. That's for adjusting the high idle when the choke is in use. The other two are for adjusting the idle on each carb. They have to be adjusted separately (yet together), which is why the you have to loosen the coupler shaft between the carbs. The "yet together part refers to the fact that you have to go back and forth between each carb, using a Uni-Syn type tool of even a section of heater hose to listen (tuning by ear) to get each carb pulling the same at the proper idle rpm.

 

[rlich8]

Not sure what your symptoms are, but:

I know you probably know this but it's best to make sure everything else is in order before you touch carbs. Adjust valves, set timing, make sure vac advance is working, then leave the carbs for dead last.

Many people think ignition problems are "carb" problems when they are not.