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Mon Sep 29, 2014 7:34 am

Received my new carbs from ACN with there set up option. For a 2007 engine Scat 110 cam and 043 heade. Install carbs, when got to tuning 1&2 cylinders mixture screws 1 turn out. 3&4 cylinders mixtures screws 1/2 turns out. 50 idle jets all around. Speed screws 1/2 in after contact. Engine rpm 700rpm. 3/4 cylinders appear to rich. Go down to 45?. Can a engine run with different jets sizes? Fuel pressure 3#. Main jet 155, main air 200. Air bi-pass screws closed. 28 vents. Thanks , George

Mon Sep 29, 2014 7:43 am

All jets should be same... You have adjusting/sync issues...

On side that is to lean screw in idle speed screw a tiny bit (maybe 1/8 turn) and make it richer, on side that is rich screw out idle speed jet same amount (1/8 turn) and make it leaner continue process till you get both side running equal and idle speed is where you want... A little faster idle like around 850 is ok... Each change of idle speed screw also requires changing mixture screw to compensate.... What you want is both side "about" the same...Do you have snail sync tool or manometer...

Check by load test, pull one spark plug wire at at time and note how much miss engine has and put wire back in, do this on all four cylinders, "miss" should be same on any cylinder if you have carbs correct...

Dale

Mon Sep 29, 2014 8:02 am

Thanks Dale. Did not know that when speed screw is moved, mixture screw needs to be adjusted. Yes have a snail Sysc tool reads #4 on both sides. Will do load test this Wednesday. Will give results thanks George

Mon Sep 29, 2014 8:22 am

Having a problem similar to this.

@ Dale I just noticed I was not getting as much power so I did the pug test you mentioned here. #2 had no effect on how the engine was running. Changing the idle mixture screw did nothing either. So what you're saying here is that the speed screw needs adjusted when the idle mixture screw is adjusted. Is there a "turn speed screw x amount for each x turn of the idle mixture screw" best practices or just go by ear and snail?

Mon Sep 29, 2014 8:52 am

Clean idle jet before doing anything else...

Then tune to "lean best idle procedure"...

http://www.piercemanifolds.com/category_s/313.htm
http://www.piercemanifolds.com/category_s/312.htm
http://www.piercemanifolds.com/category_s/311.htm

Dale

Mon Sep 29, 2014 9:07 am

azbob wrote: Having a problem similar to this.

@ Dale I just noticed I was not getting as much power so I did the pug test you mentioned here. #2 had no effect on how the engine was running. Changing the idle mixture screw did nothing either. So what you're saying here is that the speed screw needs adjusted when the idle mixture screw is adjusted. Is there a "turn speed screw x amount for each x turn of the idle mixture screw" best practices or just go by ear and snail?

Set all four idle mix screws 1 - 1.5 turns off seat
Remove linkage from one carb.
Set both idle speed screws 1/2 turn in from just touching.
Set all four air By-pass screws (the ones with lock nuts) to just seated

Check with sync tool. If the idle is too high (probable) adjust idle speed of high carb to match low carb (back out speed screw)
Check idle speed and set to about 800 +/- 50
Set each barrel to Lean Best Idle by turning idle mixture screw in 1/8 turn at a time until max RPM is reached.
recheck sync
reset idle speed to 800 +/- 50
recheck/reset lean best idle on each barrel
recheck sync
reset idle speed to 700 - 850 (what you like)
recheck/reset lean best idle on each barrel

Shut the engine down and check each idle mixture screw. They should all be very close to the same. If you have on screw at 1 1/2 turns out and the others at 3/4 turn out, something is wrong. Start over.

Check the idle speed screws. They should be very close to the same on each carb. If one is 1 turn in from just touching and the other is 1/8 turn in or not touching at all, something is wrong. Start over.

This is not rocket science. Carbs are simple, stupid devices. They respond to a pressure differential between the intake of the choke and the manifold. A weber system is just 4 single barrel carbs. One per cylinder (like a lawn mower). :-)

If the engine is mechanically sound, the ignition good (and timing correct), and the carbs are clean they will adjust right in with no issues. The idle settings for the carbs will be almost identical right to left and between cylinders.

Until you reach this point you cannot draw any conclusions about jet sizes etc.

For a single cylinder miss, run the mixture screw in to the seat (gently) and note how far open it is. Do the same on a cylinder that is not missing. Are the settings close? (Within 1/8-1/4 turn). If they are you don't have a carb problem. Look elsewhere. If the settings are wildly different you either have a mechanical, ignition, or vacuum problem on that cylinder or a wrong sized or clogged jet on that barrel.

Once you have everything happy, reconnect the linkage. Make sure the idle does not change and that both carbs open the same (and both have wide open throttle). Go for a 30-45 minute drive to get everything fully warmed up and do the lean best idle adjustment one last time. Then back the idle mix screws out 1/8 turn to make the idle mixture just a taste richer. This will help cold start and idle quality on all those short hops where the engine never gets to fully warmed up.

For the OP:
I agree 700 RPM is too low. Try setting the idle speed at 800-850 and go through the idle speed/mixture setting cycle a few times. Check your settings and see where the idle mixture screws are. If one side is 1/2 turn out and the other is 1 turn out you haven't got them right yet or you have a problem with one side of the engine. (low compression, vacuum leak, tight valves, weak spark, etc.)

Mon Sep 29, 2014 2:16 pm

leen best idle can be diferen at different times of the year.summer may not run fer poop in winter.or not so good till engine is hot.but a winter adjustment may work fine for both/4 seasons. but location can determan that. I get both snow and sauna hear, I like the winter setting all year round.starts&idles good year round. your idle timing also can affect things too.

Thu Oct 02, 2014 5:17 pm

George here. Sorry for not responding on Wednesday it rain all day. Thursday went thru all which Dale and RHough recommend. Here is the facts. Cleaned all 4 idle jets and used force air thru idle circuit. Speed screws 1/2 in after touching arm. Mixture screws 1 1/2 out after light contact with seat. New svda distributor at 7.5 degrees btdc static. Start engine ran very slow 725 rpm per tech. But not smooth. Used snail brought rpm to what was recommended 800 +- 25. Adjust mixture screws all four to 1 turn out. Ran fast to 950rpm.back down speed screws to 800rpm. Used snail again brought both carbs down so they are like this cylinder 1&3 at#3 on snail. 2&4 at 3.4 on snail. Now speed screws are 1 1/2 in after contact. Am I opening throttle plates where the progressive circuit is comming in? Red line says only 1/2 turn in. Mixture screws are at 1 turn out. Took bus out for a drive ran silky smooth. Ran up to 55 mph for 30 minutes '71 bus stock gearing. Head temp on #3 275 degrees oil temp 180 degrees on a 70 degree day. Can home readjust mixture screws no really changs. Plugs are still new. Need to drive more. Thanks :?

Thu Oct 02, 2014 7:05 pm

storm wrote: Red line says only 1/2 turn in.

Ignore that.
The idle speed screws should be adjusted so both sides are running the same strength.

There is some variance in far the carbs can close, and this does not matter.

Redline sells a lot of carbs but they don't know much about them.

Thu Oct 02, 2014 9:45 pm

Also, sometimes you just get a bad carb. It can be a burr or piece of machining left in a passage way. A component may have warped or not been machined square, so it is leaking internally. Sometimes you end up with the raw end of the deal. Not saying that this is the case here yet, but follow the instructions that were mentioned previously, but once you have eliminated any engine issues (Vacuum leak, compression, timing etc) and you still can't get it to run right. Don't be afraid to change the jetting in just one barrel.

Fri Oct 03, 2014 5:40 am

modok wrote:
Ignore that.
The idle speed screws should be adjusted so both sides are running the same strength.

There is some variance in far the carbs can close, and this does not matter.

Redline sells a lot of carbs but they don't know much about them.

This is one of those rare times I don't agree with you. Past experience has taught me that opening the throttle plates too much will create a huge flat spot as you have negated any effect the throttle plates can have on the transition ports. Better to open the Air Bypass Screws or drill a small (very small. ie .060") hole in the throttle plates.

Fri Oct 03, 2014 6:48 am

George here, even thou the engine appears to run and perform well, I feel that 1-1/2 turn in on both speed screws is to much. Redline says 1/2 in. The engine runs fine for now. I put a gas analizer in the exhaust pipe. Running high on the hydrocarbons. This test confirms that I am running a little rich. So, I am to record what settings I have now and try the way the Weber book says and Redline. If it doesn't work I will go back were it was and balance the carb thru the air bleed screws. Cylinders 3/2 are 3.4 on the snail gauge were 1/4 are 3 on the snail. It could be I need a smaller idle jet #45 or if I can fine one 47.5 jet. Thanks for all you thoughts on this subject. I makes for interesting reading. Thanks.

Fri Oct 03, 2014 7:40 pm

Dougy Dee wrote: modok wrote:
Ignore that.
The idle speed screws should be adjusted so both sides are running the same strength.

There is some variance in far the carbs can close, and this does not matter.

Redline sells a lot of carbs but they don't know much about them.

This is one of those rare times I don't agree with you. Past experience has taught me that opening the throttle plates too much will create a huge flat spot as you have negated any effect the throttle plates can have on the transition ports. Better to open the Air Bypass Screws or drill a small (very small. ie .060") hole in the throttle plates.

I was maybe not clear enough. what I mean is that "counting from closed" is wrong, because they may not close equally. Throttle plates can be worn or not centered, can hang up on gunk deposits.
NOS italian carbs this is maybe OK procedure, but with old or cheap carbs it may just cause confusion.
I assemble the carbs with the throttle plates set halfway through first transfer port and tune from there, keeping both sides equal. this way I am aware of the position. :D

AS for our boss here, maybe they are open too far, but IMO you may have to take them off and look at the position to varify before changing the bypass screws. If done beforehand you would already know, but that's not in redline's instructions

Get the idle jet figured out first! A size too big and it may be too rich at idle, because having half the first transfer port half open is within acceptable range.

Fri Oct 03, 2014 7:51 pm

my immediate thought of a 3-4 snail gauge and 800 RPM is too much idle timing.

Should be 5-6 on the snail. Around 8 BTDC at idle, hose off or on should not change the idle timing. If it does change timing at idle with the hose off/on, the idle speed screws are in too far (and you are well into progression, which is a no-no). Idle vacuum should be ZERO. This is when using the bypass screws helps, but that's normally only needed on center mount applications, OR at a significant elevation.

Sat Oct 04, 2014 8:26 am

Since I purchase these carbs from John AC.net, I've asked him now what to do. As with the instructions above I try the ignition timing with vacuum hose on and hose off. I do have a gauge to measure vacuum which I will T in. will get back to John and others that have given me info. Thanks George

Sat Oct 04, 2014 8:50 am

john@aircooled.net wrote: my immediate thought of a 3-4 snail gauge and 800 RPM is too much idle timing.

Should be 5-6 on the snail. Around 8 BTDC at idle, hose off or on should not change the idle timing. If it does change timing at idle with the hose off/on, the idle speed screws are in too far (and you are well into progression, which is a no-no). Idle vacuum should be ZERO. This is when using the bypass screws helps, but that's normally only needed on center mount applications, OR at a significant elevation.

My car runs about 3 - 3.25 on the snail too. The Pextronix SVDA is set at 30° BTDC @ 3000 RPM and the idle timing is whatever it is. I think it ends up between 5 and 10 BTDC. My carbs seem to adjust/respond correctly so I haven't been concerned about the actual snail reading.

Sat Oct 04, 2014 9:44 am

Note my 5-6 on the snail guide is correct for GERMAN snail gauges. I have no idea what the Chinese ones read. If the # is low either the engine has too much timing, or look for possible vacuum leaks (bypassing the gauge). It's common to have a leak between the stack and filter base, for example.

Sat Oct 04, 2014 10:54 am

Ok George here, got my timing light back. Start engine let it warm up. Would like to take it for a drive but it 32 degrees rain/snow mix. To get real warm up. I have in the heated garage with a exit for the exhaust. Now reset advance to 8degrees btdc. No change in idle speed. Readjusted idle mixture screws speed went up to 950 rpm. Readjusted speed down to 825rpm. Speed screws are 3/4in after contact. No vacuum change at idle with hose on or off. #4 on snail. Mix screws 1 turn out. Total advance (no load) at3000 rpm 28 degrees. Runs smooth at this rpm 825 Svda distrubutor is new with points.

Sat Oct 04, 2014 11:45 am

:) Since we are working with a man made production item things will happen for the good or bad reasons.

Opinions are nice to consider over as testing mode.

I hook up my Tach/timing light.
Back off mixture screws two full turns from bottom.
Turn idle screw til it touches the throttle plate plus 1/4 turn.
Disconnect #1/2 side linkage.
Static set dist to 7.5 degrees (009)
Fire up engine to warm up.
Verify timing.
I have never used a snail but have (two) unisyns...round and oval.
Will check bubble on #3/4 to a specific line and adjust to meet on #1/2 side.
THis should tell me that there is a even flow of air to both cyls (hopefully)
Will now turn in mixture on #3 till engine hesitates and then back off 1/4 turn.
Repeat on other cyls.
Recheck bubbles and mix screws...if okay hook up linkage and adjust for positive response by blipping the throttle and then a test drive.
Worked many yrs for me.
(Retired VW mechanic/business owner) :wink:

Sat Oct 04, 2014 12:47 pm

E-mailed, John from AC.net. what found now that the timing was set when the motor was running. Speeds screws down to 3/4th turn in from contact was 11/2 before. Mix screws 1 1/4 from seat. All is well running smooth. The sun is out and the pavement is dry. Going to take the bus for a drive. Thanks all and John