Rebuilt my carbs - need help with troubleshooting!

[Stevehose]

Ok I have rebuilt my carbs, a project that when finished also included a new starter motor (because it was relatively easy to get to), all new hoses (even the little ones from carbs to block etc., as well as heater hoses as some were crunchy and easy to get to with the the manifolds off, cleaned and resprayed the engine block, stripped and sprayed the radiator overflow tank, resprayed the power steering resevoir cover, yanked the radiator and flushed and resprayed that, took the fan off and cleaned and repaired a crack in it, and polished the aluminum head a bit. Some carb project!

Anyway here are my issues:

First off the rebuild kits come with the incorrect idle screws and choke plungers so I had to reuse those - I had to patch holes in the plunger diaphrams.....so i dont know if those parts are a factor in my problems.

The engine is difficult to start when cold and backfires through #1 carb. Once it starts it revs well but will not idle without stalling until it warms up. Not sure my accell pumps are working but they have new skirt gasket on them. I set the idle screws to about 1/2 a turn in after they start to move the throttle butterflies and the mixture screws are at 1 3/4 turns out. I left the choke adjustments/linkages alone from before the rebuild (except for the plunger adjustment), should I redo those from scratch or twist the choke covers counter clockwise (they are set at the notch now)? Should I increase the idle screws to help cold idle? Can anyone walk me through the choke setting procedure procedure better than the manuals do? How far shut should the chokes be on a cold engine with ambient air temp of 95 degrees? The rear choke is a beeotch to get to!

Once warm, the car will idle but every minute or so the car surges rpm for a few seconds then drops back again.

I guess to get me going in the right direction, what should my checklist be to:

a) solve the cold start issue
b) solve the surge issue (could this be a float setting or vacuum leak??)

Sorry for the rambling post and I appreciate any input. I hope these don't have to come back off but something tells me they might unless these are typical rebuild tweak items. At least my new starter works, it's getting a workout! Thanks.

 

[61porsche]

Carbs Continued

Idle screws- as long as the originals weren't deformed you should be fine.The originals are better design. Did you change the O rings? Use the listen/rubber hose test to check.

Choke Diaphrams- You'll need to find replacements. Perhaps Mesa can help.

Backfire on front carb- mixture wrong. Assuming there's not fuel dripping from the venturi which means the float needs adjustment- Use the screw you refer to as Idle which is the throttle plate screw and turn in another 1/4 ( More air/ fuel) or so until the engine smooths out. Or you have too much advance and the vacumn connection is manifold vs. ported... it adds 12 degrees advance if manifold. If you have a vacumn guage you can see when the best vacumn comes in from the screw adjustment. It's probably what's causing the surge too- lean, in one or more cylinders. Beacuse the secondary plates are not closed completely, the screws won't be exactly the same from carb to carb.

Hard to start- the choke flaps should still nearly close regardless- find a drill size close to the dimension in the manual and adjust the linkage/ plate. Looks about 1/4". Equal and operating the same is what your looking for.

Starting choke running should be 1500-1700 rpm. Since the choke circuit introduces more fuel it's probably what is keeping the engine from idling.(Wants to die) There's a screw almost hidden until you turn the throttle- in the choke housing low- check the manual. I set mine on the low side since it's alway hot here. If the idle is 1200 or so one carb is working and the other not so much. Check the manual.

Linkages- the most critical ones are the plastic linkages- you must mike them. ( Cheap digital caliper) They above all else control balance. But let's not go there just yet.

Choke housing setting- turn to the other page of the manual- US cars are set further than the first mark to the second.( More emissions, more choke) Compare both so they're equal. I've seen them turned as much as to about 11 o'clock at the wiring point for the idle valves, etc. ( N. Ca. car)

Regardless, chokes help start, running is different. If you can get the backfiring to stop and the engine warm...... screw both idle screws home. The engine can idle at 600 or 700 from the throttle plates being set correctly and balanced. Rubber tube, stethescope, air meter..... the both should have the same sound or hiss level and the smoothest idle. Get this right and the rest gets easy. The idle screws just raise the idle/ mixture a small amount. Say, back up to 850-900. As balance gets close you're moving things in very small increments. FYI- weber sells the horn adapters and air meters... Alamo Motorsports in San Antonio has them if you prefer or you can make a homemade manometer if you want. If you're idling at 1100 or so you're no longer in the idle circuit only and into the primary. Keep tuning at the lower rpm till you get it right.

Linkages- the ones discussed already are critical. The car will idle too high or stumble... bad juju. The rest- what you're looking for is that they all work the same and the plate linkage movement is equal.

Squirters- as long as they squirt you're fine... a dribble won't do. With the new gas vs leaded.. a little less is good as flow/ engineers/ racers now set them at 1/2 the volume. You don't want to flood at startup... but you want a little more gas when you press hard on the throttle for the transition. If you're really serious- you can fashion a measuring vial from a cutdown kids eyedropper and a piece of wire .. one to three ccs ( 1/3 tsp.) or buy a Porsche one for $40. For larger engines- yeah... more squirt=less hesitation or stumble.

Since it's all nice and clean now check/ grease/ oil all the linkages to make sure you're wide open throttle. The assembly gets slack after so many years/ miles. Could just be the cheapest HP you ever found- free.



Call the cell...or blackberry.

 

[Tony_V]

Have you checked for leaks between the carburetor and manifold.
Forgot to tighten all the screws below the carburetor.

 

[Stevehose]

Tony - yes I made sure of the tightening and did so gradually in a pattern, there was no warping at all before doing so and the carb bases and manifolds met perfectly flush before gaskets installed.

Jerry - Thanks for your usual in-depth answers, I got the rebuild kits from Mesa and will call them about getting the proper choke plungers. I did not replace the mixture screw o-rings because there were none to do so with. Cleaning and greasing the linkages was omitted from my list of ancillary work so they are nice and smooth. I will go through your other suggestions, you very well may get a call sometime from area code 504!

Thanks and will report back in a few days.

 

[Stevehose]

I replaced the o-rings on the idle mixture screws, the front carb responds to turning (although not until 4 or so turns out), and the back carb mixture screw does nothing. No leaks (I sprayed them to check) and no change in idle. Suggestions?

I turned the choke housings a little counter clockwise as you suggested to close the choke plates and it started right up, I also screwed in the throttle plate screws to achieve idle. No more surging. I also had the advance and retard hoses mixed up at the distributor and corrected that.

My rear carb accelerator pump was not working so I took it apart to inspect it and when I replaced it something took a chunk out of the skirt seal (twice) and now I am screwed - is there a source for these seals? There is nothing in the orafice that looks like it could catch it but something is doing so.

I was making progress until the accel pump tragedy, any ideas on the above issues? Thanks.

Idle screws- as long as the originals weren't deformed you should be fine.The originals are better design. Did you change the O rings? Use the listen/rubber hose test to check.

 

[61porsche]

Carbs Continued

Old school tricks-

On top of the carbs, next to the air jets is a tiny drilled hole. It's actually the air for the idle mix. Closing it ( I use an eraser from a pencil or metal foil tape) will cause the idle to go up (lean or small leak) or down (rich). You most likely need on the front carb to back off slightly on the throttle plate- 1/16, 1/8 turn, then screw back in the idle screws.

The opposite is true for the back carb from what you describe ( Turn the plate screw in 1/4) or the float is really low. For grins make sure you have 12v at the idle valves and they're slightly more than hand tight as the tapered tip is the seal against the body.

Ok, now more on the back carb. Remember the secondaries aren't closed? There's the small spring loaded screw and lever way down at the throttle plate below the choke. You can check the secondary adjustment by quickly lifting the lever and the idle will do something or not. If correct, it shouldn't do much. One more even easier trick- hold your hand over the secondary very breifly.

What you're doing is trying to see if the mixture is just right or needs to be changed. ( Or if you're really old school- SU's where they had the lift pins to check settings ( Jags, Tr, etc.)

I don't understand completely about the accelerator pump. It broke? A chunk of the seal? The bottom is plastic, the top/ seal is stamped on so it's not repairable. It only comes up through the top after you move the arm. You can run without it temporarily, but they're available. The two most important things about the pump is the check valve/ steel ball cap at the bottom of the bore that lets fuel in but not out. Clean it good so it moves freely. The pump- what happens is what you're describing-- new gas with alcohol and deposits- the bore gets gummed up and the pump travel is less.( dribble) Clean and working the cap should come up above the bore.( good squirt). Just one carb? You'll have to clean/ hone the bore if things are sticking bad from deposits or take out the broken plastic. I can send you one from my spare carbs if you can't find them. Let me know. A picture of the broken part might help in diagnosis. Was the bowl pretty clean or lots of white deposits?

Sounds like you're getting closer though. Easy with the carb cleaner; listen with the hose for leaks.