Carter BB1

[broker-len]

this is a updraft with the main meetering adjustment under the bowl   have rebuilt it a few times     new bowl gasket   checked the float    tried a few needle and seats        car runs and idles ruff       the idle screw make no difference       i in adjustment    runs the same if it is all the way in    running it on a 32 PA plymouth      what do you think ?

[robert b]

on some bb1s i have found that the idle hole drilling down near the float vent hole is some times cross drilled into the vent hole allowing to much air into the idle system and gives similar results to what you have described , all so a flat spot on throtleing under load . just a thought bob

[F&J]

13 minutes ago, robert b said:

allowing to much air into the idle system and gives similar results to what you have described , all so a flat spot on throtleing under load

Yes a lean idle mix can allow a flat spot at very light acceleration, but not too far off the idle speed.

 

There is an old Mechanic's term of "90% of carb issues are electrical".  Meaning make darn sure the ignition parts and all settings are perfect before climbing into the carb. The ignition system & settings can sometimes cause the same symptoms as carb issues.

 

An oldtimer I know with 30 pre 1932 cars, has several known good updrafts to start old barn finds.  He says he just clamps them to the intake if bolt holes don't line up.  Then after he dials in the rest of the engine really nice, then he puts the correct one back on, and if there is now a running issue...it IS that carb, and can be nothing else.

[Mark Shaw]

If your BB1 has a hole in the surface of the mounting flange, make sure the gasket does not cover it.  Note the flange gaskets with holes and slots shown in the pdf below.

 

Carter BB1 Carburetor Instructions and Parts List.pdf

Edited June 2, 2017 by Mark Shaw (see edit history)

[broker-len]

thanks every 0ne-------for some reason   I am getting a situation where the idle screw makes on difference    will idle with it all the way in  may be one of the jets is bad,,,,  am rebuilding one of the brass bowl carbs   that came standared     am going to try it      if still the same going to look at coil

[Mark Shaw]

This might also help...

[PFitz]

12 hours ago, broker-len said:

thanks every 0ne-------for some reason   I am getting a situation where the idle screw makes on difference    will idle with it all the way in  may be one of the jets is bad,,,,  am rebuilding one of the brass bowl carbs   that came standared     am going to try it      if still the same going to look at coil

 

Typically, when the idle needle screw loses all affect on engine speed, there is a leak supplying excess fuel from somewhere. Running rough is another indication of that.

 

If the float level is too high it can cause the same problems. Happens often when someone added an electric fuel pump without checking fuel pressure specs. If the electric pump has a higher output pressure than the original mechanical pump, or vacuum tank it raises the float level. Every increase in fuel pressure can raise a float level about 1/32 inch per pound of pressure increase.  Some updraft carbs are very sensitive to float level changes at low idle speeds.

 

Can also happen when a novice "rebuilds" updraft carbs with just a gasket kit thinking that's all that is needed. If there are submerged brass fuel valves, they need to be replaced with new, or have the valve seats lapped so that they seal as designed.  Years of alcohol gas can erode the sealing surfaces of brass valves/jets leaving then unable to seal properly.   Same happens to the brass seats for the check valves in fuel pumps. The surface erodes and looks "textured" like it was sand blasted. That rough surfaces does not allowing the check valves to seal well enough, thus lowering pump output pressure.  

 

Any submerged springs controlling those valves can be erodes, too, thus weakening and not allowing the valve/jet to seal sufficiently.

 

Some early diecast (potmetal) carbs can develop cracks internally and "bleed" fuel through the thin walls separating fuel passageways, thus bypassing the jets/restrictions that control fuel flow. With age, potmetal can become porous, too.  Most reputable carb rebuilders will not work on diecast carbs from the 20's and early 30's for that reason.

 

Paul

[broker-len]

thank you all so much----------good advise      I guess I can replace all the jets or get it professionally rebuilt      but just don't want to spend the money when it is not the original carb and I do have one         will try the brass bowl as soon as I have the time

Edited June 4, 2017 by broker-len
/ (see edit history)

[carbking]

The most common cause of the idle adjustment (mixture) screw having no effect is a defective engine valve. This causes the tuner to adjust the throttle positioner screw in further than normal opening the throttle butterfly further than normal. If the throttle butterfly is open beyond its range, it effectively removes the idle circuit from the carburetor.

 

Second most common cause would be the adjustment in the above paragraph.

 

A third, although rare, cause is installing the throttle butterfly upside down.

 

When the throttle butterfly is open beyond its normal operating range, the dynamic area between the throttle butterfly and the throttle body is increased, thus lowering the velocity of idle air to the point where there is insufficient negative pressure in the idle pickup point to allow the idle circuit to function. Result: the idle will not change if the mixture screw is completely seated, or removed and placed in the pocket of the tuner.

 

First approach - compression test.

 

All of the above assuming that BOTH sections of the idle tube were removed and passages cleaned when the carb was rebuilt. Failure to remove the hidden lower idle tube and cleaning the passage below will also cause problems.

 

Jon.

Edited June 4, 2017 by carbking (see edit history)

[F&J]

23 hours ago, broker-len said:

thanks every 0ne-------for some reason   I am getting a situation where the idle screw makes on difference    will idle with it all the way in  may be one of the jets is bad,,,,  am rebuilding one of the brass bowl carbs   that came standared     am going to try it      if still the same going to look at coil

 

 

Can I say something without causing issues?  You are all over the place...timing,..wondering about a bad jet, if not... a coil. 

 

>>, all over the place, is nothing more than either refusal to take diagnosis advice, or not hearing it said...like nobody here ever mentioned one point to test.

 

One thing that bugs me, is a shop that just keeps throwing stuff at a problem, as their way of diagnosis.

 

 

[broker-len]

Sir-----thanks for your response       this motor was rebuilt  checked valve settings,   checked compression     60 in all holes   checked timing and points  condenser is newer,,,, checked for vacuum leak     the plug wires are older     but does not explain my problem          the plugs are black     and the idle screw does not seem to affect anything       was told low coil out put could cause this kind of problem       I have rebuild the BB1  a few times    with a new bowl gasket        I am not a professional but not a novice either        since the BB1 is not original for car and I have a brass bowl      will try that before I start putting money in a BB1 professional rebuild       if I still have issues will try a different coil        after that will make a planter out of  the car

[broker-len]

thank you carb king---did not take butterfly off      have had this carb for ever      I think I used to drive with it before it was rebuilt with better success -----I will check  it

[hchris]

57 minutes ago, broker-len said:

Sir-----thanks for your response       this motor was rebuilt  checked valve settings,   checked compression     60 in all holes   checked timing and points  condenser is newer,,,, checked for vacuum leak     the plug wires are older     but does not explain my problem          the plugs are black     and the idle screw does not seem to affect anything       was told low coil out put could cause this kind of problem       I have rebuild the BB1  a few times    with a new bowl gasket        I am not a professional but not a novice either        since the BB1 is not original for car and I have a brass bowl      will try that before I start putting money in a BB1 professional rebuild       if I still have issues will try a different coil        after that will make a planter out of  the car

 

"the plugs are black" - not sure what the cause is, but certainly too rich.

[trini]

I have a similar problem with the BB1. The idle screw makes no difference. Old screw, new screw, same thing. The mounting gasket  has 4 cut outs on the inside perimeter so there is no way to make a mistake in installing. I idle the engine using the  jet underneath the bowl . My engine is also rebuilt.  At the moment I am doing a ground up rebuild. so tuning will take a holiday.  (1928 dodge senior)