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Carb 308: Creeping Idle

Discussion in 'Technical Q&A' started by thecarreaper, Jul 10, 2004.

  1. thecarreaper

    thecarreaper F1 World Champ
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    i have noticed that my 308 when cold will idle around 1000 rpm. However, as the car gets warm , the idle is creeping to almost 2000 rpms, running dead rich. i have stock 55 idle jets and 135 mains. a new set of # 60 ilde jets came in yesterday from Pierce Manifolds. i could have gotten the jets cheaper elsewhere, but i have called them and spoken to thier techs and they were extemely helpful. the previous owner of my car had the carbs completely redone. now it time to tune.

    anyone else here have a creepng idle problem ? i am hoping by adjusting the mixture and idle screws and syncing the carbs, that i can finally drive the car farther in heavy traffic!!! my choke is disconnected, not that i need it, but its almost like it is working in reverse. no vaccum leaks have been found as of yet. i will post an update and pics when possible. next i will be getting rid of the dual single points distributers!!! comments welcome. michael
     
  2. Birdman

    Birdman F1 Veteran

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    Hi Michael,
    Mine did the same thing, except that someone removed the "cold idle" device from my car, so that means that my experience and yours may not be caused by the same thing. In general, without the cold idle device, the car wants to idle slower when cold, so the option is to adjust it so it idles when cold (so it idles too fast when warm) or adjust it so it idles when warm, in which case, it will likely stall when cold!

    It seems that the idle speed on a 308 is a bit touchy. Does your car still have the dual points (idle and run) or has one set been removed? My car only has one set and that means that the idle speed is a little twitchy because as the car warms up and the idle goes up, the spark advances a little and that tends to increase it a little more, so you get a situation that doesn't like to be stable.

    I found that once I had my carbs really synched well, I could get it to idle very smoothly at a low enough RPM (around 800) that it wouldn't "run away". The downside is that without a cold idle device, my car will barely idle until I warm it up for a minute or two. (It idles, but it's so slow that it sounds like its going to die at any minute).

    I will say that the synch of the carbs and having the right idle jets makes a world of difference. Before I got my jets/synch right, my car was a nightmare at idle. It popped, it idled too fast, just awful. Now the thing just sits there idling perfectly like it's fuel injected. Honestly, the jets and synch worked more of a miracle than I expected.

    I can't remember, what is the reason you are trying the .60 jets?

    Birdman
     
  3. don_xvi

    don_xvi F1 Rookie

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    Try this: Will the idle speed come back to where you want it if you cut the ignition while it's at high idle, then turn it back on before the engine comes to rest? Mine does. I know I have idle mixture problems, just gotta get to it! I've also wondered if this is a potential symptom of the throttle shaft bearings leaking air in.
     
  4. Mike328

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    Good thought, but not an issue for Michael - Pierce Manifolds replaced the throttle shaft bearings with sealed bearings... So, assuming they did the job right, we could eliminate this as a possibility.

    Michael, I seem to recall a generally low idle when the car was first started, which would get to around 1100 rpm indicated when warm. This whole thing may get exaggerated for you due to the altitude change. With the jets you have, you should not be running rich because of the jets, but perhaps because of the tuning. I'd recommend starting fresh with a complete sync via the air balance screws, throttle speed screws, and idle mixture screws.

    Also--60 idles you may find too rich; most folks at sea level run stock idle jets without any issue (although hans, IIRC, runs 57 idles).


    --Mike
     
  5. thecarreaper

    thecarreaper F1 World Champ
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    thanks for all the replies, for the record, my car has dual dizzys with single points, no cats , no air pump, no emissions stuff ( just the fuel vapor recovery) and a K&N fitler and a Ansa. my thoughts are that the idle is too high allowing the plates to draw fuel from the primary fuel circuit. the car back fires through the exhaust at shutoff, inducating rich condition. i need to turn the idle down to 900 -1000rpm and let the car run off of the # 60 idle jets. the 55's seem to be too lean for most folks at sea level, at least from what i found posted in the archives. i would rather be rich and work towards lean, than be lean and burn a piston.
    pierce manifolds said at 1500 rpm the car is ignoring the fuel from the idle jet, its getting tons of fuel from the main jets and its designed to be that way under load, ie accelerating. not sitting in neutral idleing. car reaks of fuel at the tail pipes when hot at 1500 -2000 rpm. by turning the speed down and going to the #60 jets i hope i can get the mixture and the idle in a " happy medium"!!!! i may be all wrong, but this is my train of thought so far....... will update in the morning........ hope to have the car running better tomorrow......... 4 new tires come in monday.
     
  6. thecarreaper

    thecarreaper F1 World Champ
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    notes, drivers side forward carb is spitting thru both barrels, others are fine. idle speed screw is doing nothing as it is. all the mixture screws were WAY WAY out. installed # 60 idle jets in carb that was spitting, spitting stopped and idle improved, car smells really rich. shut off car, and am installing all the # 60 idle jets. my tops for the main jet / emulsion tubes say " 200" on them. have not pulled one out yet. going to screw all the mix screws all the way in and back out 4 turns and see what happens. then i will mess with the idle speed and carb sync. the sync cant be to far off, judging from the way it ran before. most of the lines and hoses look serviceable, the coolant hose against the drivers side firewall looks old ( must remove wheel and wheel well to see well). will replace asap. will update later today!
    i am going to the search feature to look for bulk coolant hose sources ( Napa???), may do all of them at once if i have to drain the car again.
     
  7. Birdman

    Birdman F1 Veteran

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    Not necessarily. Backfiring at shutoff when the idle is high can happen when things are perfect. The engine is not designed to be shut off when running at that RPM. Getting the idle speed right will eliminate it. You can prove this to yourself easily. Start the car. When it's idling high, use the clutch with the car in gear to slow the engine a bit just as you shut the car off. It won't backfire.

    I highly doubt it. At 1500 RPM the car is getting most of its fuel from the progression holes, which are fed from the idle jets, but which are unaffected by the idle mixture screws. I strongly suggest that you get a book on Webers and investigate the way the carbs work. It will make them much less mysterious. The main jets don't do much until about 3,000 RPM is my understanding.

    It sounds like you are getting there. If you have spitting through the carbs you are running LEAN at idle, no matter what you think the exhaust smells like. You are smelling fuel most likely because of the fuel spitting out the top of the carbs and unburned fuel coming out the exhaust because of incomplete combustion--due to the lean condition. I'm going to bet you that those .60 jets help a LOT. Keep us posted.

    Birdman
     
  8. thecarreaper

    thecarreaper F1 World Champ
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    thanks Birdman, i have 3 weber books, been reading up on things, you are correct of course. i am sad to say i belive the carb hatw as earlier doing all the spitting and had the idle mixture screws, may have a float problem. i can get the other 3 carbs close but this one wants LOTS of fuel.

    example. turned all the idle screws all the way in, then out 4 turns. way rich, wont idle at 1000rpm. went in 2 turns, will idle at 1000rpm, oil / water temps all ok. cooling fans working ok.

    But, the carb that was spitting , though it is now running better with the #60's, wants the mixture screws about 6 turns out. i kept turning the screws out until the idle stpooed going up, and then back in until i noticed a change in rpm. i need to eat, then back at the carbs i will go. i still have a long way to go before a test drive. when i can get the idle "better" i will put the meter on it and see what the readings are. i would be happy for a steady 1500 so i can check the sync!!
     
  9. Birdman

    Birdman F1 Veteran

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    The jets are only part of the idle equation. Gotta synch the carbs for it to idle worth a damn. Go through my procedure in the other thread. The actual idle snych is actually the last part of the procedure. You have to get the linkage synched first, then the idle. You could have a float issue, but since Pierce Manifolds just did those carbs for Mike, I kinda doubt it. (Sheesh, I need to get a life. Not only do I know the previous owner of you car, but I know what service procedures were performed on it. WAY too much time on FChat!)

    Birdman
     
  10. Mike328

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    Reaper, the 200 number you see is the size of the air corrector jets, which are positioned on top of the emulsion tubes, which are in turn on top of the main jets. I believe 220 may in fact be stock.

    Note that going smaller on the air corrector jets, because they limit AIR and NOT fuel, will have a different effect of going smaller on other jets. Smaller on the air corrector jets will reduce airflow at high RPMs with the otherwise same amount of fuel, which will result in an increase in fuel to air ratio, which is enrichening the mixture on the top end a bit. The carb experts can chime in here: this may not mean more power though, because you're not adding more gas--you're limiting the amount of air, etc. I wouldn't mess with these unless you think the car should have more power at, say, 6000 RPM and up. Keep in mind the power/torque curves for these cars peaks somewhere around there, too.

    Reaper, I got a bit untraditional with the way I synced the carbs using the air balance screws. Unlike most other folks carbs, which will have been tuned according to the manuals that you have, with one of the screws all the way in and the other screw out to obtain barrel to barrel sync of an individual carb, I used these screws to actually fine-tune the idle speed. It worked well, and I was confident in my logic.

    That said, your idle is probably too high because these air balance ("depression balance") screws are open way wide, flowing WAY too much air at idle and just really giving lots of good air for combustion at idle. Try closing them all the way and re-evaluating from there... There is no sense in trying to keep any aspect of my 5000ft sync job at sea level; my recommendation is to just close everything and start from scratch.

    Also note that the throttle linkages are critical; I adjusted them really, really precisely to ensure that EACH butterfly opened at literally PRECISELY the exact same time. If these were off, one bank would get more combustion than the other, causing off-idle roughness. These linkages are tricky and will take some experience.


    Good luck getting these synced--it CAN be done :).

    --Mike
     
  11. thecarreaper

    thecarreaper F1 World Champ
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    thanks to all for the input. (hee hee) before i read the post i had gone ahead and set everything to " 0 " :). the air mixture screws can indeed be used to fine tune the idle. the car seems to like the #60 jets , i even drove it around the block last night. still has some popping through the tailpipes, may be rich / mis balanced still. i will work on it today and concentrate on the linkage adjustments with the Syncrometer. the 2 threaded turnbuckles for the carbs make a HUGE difference. and as Birdman stated in his Carb Tutorial they are Very sensitive. i think i can get the rest of the bugs worked out today.
    new tires came in !! i had a friend source 4 tires, 205/7014, H speed rated for $39.00 each . there is nowhere to go over 100mph around here ( too many cops) and i doubt i will have the 14's on for very long anyway, i want to put the 16's on . but those wheels need tires too! the car is driveable so it must be " close" thanks for the help, threads like this are great for all of us !
     
  12. thecarreaper

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    ok any folks out here that can expalin how one carb can have 3 kg/h of flow and all the others are strong and have 7kg/h at 1000rpm? the forward right hand carb wont " wake up" with the linkage. tomorrow i am going to take all the damn linkage apart and set it all to zero again. i got rid of the backfire, but i am undecided as to whether or noy the car likes the number 60 idles or not. so close, but so far away.
     
  13. bill308

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    #13 bill308, Jul 14, 2004
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    Michael,

    Your flow numbers suggest your balance is way out. You should be in the area of 3.5-4 kg/h air flow for all barrels at 1000 rpm.

    Front and rear banks are balanced by the push rods. Carbs within a bank (i.e. 1-2 to 3-4; and 5-6 to 7-8) are balanced by carburator synchronizing screws on the linkage between the carbs in a bank. Please see screw B in the attached drawing from the WSM. Adjustment of the balance screw between the 5-6 and 7-8 carbs should allow you to awaken the right front carb. My guess is that once this carb is working, you will have to back off on the other carbs and your flow rates will approach acceptable values.
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  14. Mike328

    Mike328 F1 Rookie
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    Reaper, don't mean to mention something you're already aware of, but: the throttle linkgage stuff is really, really tricky. More than just the linkages, which you fine tune to open at the EXACT same time with no slack, there are also tricky adjustment screws surrounded by springs which control the front/rear AND left/right carb syncs... Those have to be set up as well... Two additional adjustments. You're focusing on those as well, right?

    Also, expect that the rear left carb might be a bit tricky, as there is an additional vacuum hose attached to that (for the brake booster, IIRC?).

    Bill308, I concur.
     
  15. thecarreaper

    thecarreaper F1 World Champ
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    thank you Bill and Mike, i am not going to touch the car today, i need a break , since its been like 120 with the heat index here!! its really funny how they work against each other, yet the linkage is what makes them work together. i will start all over, and this time i will hook up another tach as i feel the ferrari tach is very inaccurate. thanks for the help!!!!
     
  16. Birdman

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    Michael,
    You shouldn't be synching the linkages at 1000 RPM. That is idle territory. You need to pull both idle screws all the way out of contact with the throttle assembly, and jack the idle up to at least 1500-2000 RPM using the throttle cable adjuster. This high enough that the air bypass stuff won't make any difference. NOW, adjust the front pair of carbs to each other. Do not worry about the actual flow NUMBER, just make them the same. Next do it for the rear pair. Next, use the "turnbuckle" assembly between the front and rear pairs to adjust the pairs to each other. You should be getting somewhere in the neighborhood of 7-10 kg/hr flow at this higher idle setting. This isn't an exact number. Just make them all the same! At this point, the linkages are in synch, now you need to get the idles in synch.

    Next, back off the throttle adjuster so the idle comes down. At this point, if you adjust it all the way out, the engine should stall, because the throttle stop screws (i.e. idle adjusters) are all the way out. You will have to diddle with these until it will stay running with complete SLACK in the throttle cable. Now you want to adjust the throttle stop screws without any influence from the throttle cable. Set the two throttle stop screws (one for each bank) so that the flow from front to rear is the same AND you get about the right idle speed. At this point, you should be getting about 3.5-4 kg/hr flow.

    The thing is that a throttle stop screw will completely throw off the adjustment of the linkage, so you have to separate the two procedures (linkage adjustment and idle adjustment) and do them separately.

    At idle is where you will need to adjust the air bypass also. Typically, the rear left carb, left throat, requires a tad more air bypass than the rest because there is a vacuum line on there. (I have never been able to understand WHY it should if there is no leak in the vacuum line, but it does need it).

    Good luck!

    Birdman
     
  17. thecarreaper

    thecarreaper F1 World Champ
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    thanks for the post and the PM help, will update when possible!!! :) michael
     
  18. thecarreaper

    thecarreaper F1 World Champ
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    thanks to all that helped, ( Birdman , MikeP ect) carbs are synced, car is driveable.
    however, it will NOT idle at 900-1000rpm , i keep hearing " something" around 3000 rpm like one of the banks are out of time, the car dies at stop signs with the idle turned down. no vaccum leaks found, carb float level seems ok. anyone here with Ansa or Tubi exhaust care to comment on a resonance or " warrble " sound ???? exhaust " pops" when you let off the throttle, like a car with headers and short pipes. in 5th gear , going up a large over pass, car will STILL pull if you floor it, no hesitation or poping, makes me wonder if the timing is ok and i am hearing the exhaust resonance in the car. neighbors tell me car is loud, and sounds sweet! ( i have cool neighbors, and i dont make lots of noise early / late) :)
    maybe this needs a new thread!!! and i still like carb cars!
     
  19. Mike328

    Mike328 F1 Rookie
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    Mike, the car ALWAYS had light popping on overrun, even before the ANSA. Nothing loud, just a light burble; I quickly became accustomed to it. My old motorcycle did the same thing... It's character. If it's a backfire and not a burble, then that's a problem of course.

    One thing I remember at the test drive at the dealer (F of Central Florida) was that it would pop as the RPMs dropped between upshifts...

    --Mike
     
  20. thecarreaper

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    thanks so much for all the help and insight with the car, sorry if i seem like an idiot with these simple things, but i had never sat in, seen or heard a carb ferrari until i sat in " mine" when it was delivered from your home. its been a lot to learn in a short time!!! i detest points, but i will check the timing this weekend, and leave it alone if its ok, i really want to tackle the gearbox / shift linkage issue.
    i really like the " character" the car has, it sounds evil -mean above 3000rpm!!! the popping in the Ansa seems to add to it, i just want to make sure its not a timing issue. the car pulls so well in every gear i think it may be just me bieng paranoid. still i must determine why i cant get it to idle at 900. that would get rid of the backfire when its shut off.
    the cars idle still creeps, ie it gets higher as the car warms up, back to square one, there must be a vaccum leak somewhere! :)
     
  21. judge4re

    judge4re F1 World Champ

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    Wait, you didn't hear the 365 run at Roebling?
     
  22. thecarreaper

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    very funny Judge, good point! i should have specified "carb 308" your 365 sounds different ( better!) than a carb 308. one day i hope to have 12 cylinders to play with!! :)
     
  23. thecarreaper

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    ok , i removed all the vaccum lines and started the car stone cold. both intake gaskets are leaking, that solves my creeping idle, and the wierd things the carbs were doing. last time i checked the intake gaskets , i had driven the car a few hours earlier, so they must have had some seal left from the heat and expansion. glad i learned a lot from the carb sync , since it appears all the carbs have to come off to replace the defective gaskets. going to remove the rest of the emissions crap and put it aside, in case the next owner wants it. thanks for all the help, i will post a pic thread about " 308 intake removal " for fun later. thanks for all the help! michael
     
  24. don_xvi

    don_xvi F1 Rookie

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    Be more selective than my car's PO and don't take off the PCV system! That thing's really a piece of work! I'm also a fan of evaporative emissions systems, but I've read that you like that smell of raw fuel when you park the car...
     
  25. thecarreaper

    thecarreaper F1 World Champ
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    lol , no the pcv and the fuel evap are staying, i carefully removed the last bits of the air pump bits and the billion miles of vaccum lines that went nowhere. everything i take off the car is bagged, tagged and put away. i hope i can redo the a/c so it will work with 134a, a very good friend has warned me that his shop will not put 134a in any car with any copper parts in the a/c system. he says the copper cannot take the pressure of the 134a. engine compartment is as original , except for the cats and air pump crap ( have the air pump ect) . i really want to get rid of the points while its running well!!! intake gaskets and belts / tensioners are next.
     

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