Hi Everyone, A new puzzle for you all. My '77 308 GTB has been idling poorly, hesitating, and generally running badly under 3500 RPM since I got it. In particular, any kind of driving where the throttle is closed or very close to closed, it runs rough and hesitates. When you get out on the highway, it's fine. I was at an event at KTR motorsports last weekend here in MA. They have a carb expert there who drove my car and thought that there were two issues: 1. idle jets were plugged 2. carbs were not opening at the same rate (the butterfly valves were not all in the same place as they open). I'm assuming this is the carb sync. Last year I had the carbs "synced" at Boston Sports Car in an attempt to fix this. This did not fix or even slightly improve the running condition of the car. They didn't rebuild the carbs, just claimed that they synced them. Still runs like ****. The guy from KTR suggested as a first attempt to run a couple bottles of Techron fuel system cleaner through it. He said it was the only "snake oil" that was worth a damn and it often would help quite a bit. If that didn't work, then: a. clean the idle jets. b. have the butterfly valves adjusted to work together so that they uncover some kind of "holes" in the carb at the same time as they open. I got a quote to do the work and he quoted me 4 hours. Sounded perfectly reasonable to me. My wife said "NO WAY!" (Seems she is still a little upset about all the money I spent on the car last year. We are building a garage this summer and I have been put on a limited Ferrari budget!) So unless I can figure this out myself, the car will be runnin' like crapola all summer! So, I got the techron and I'll start treatment. Here's my question or two... 1. What is involved in cleaning the idle jets? Anyone have advice and even better, a few pics? 2. What are the "holes" he is talking about? He showed me on a carb that he had on the bench...there are small holes in the "throat" of the carb that are uncovered in sequence as the butterfly opens. What are they and what do they do? 3. Is adjusting the butterflies with respect to each other considered "syncing" or is this done with the other millions of adjustment screws? Yes, I am a complete carb idiot. I know basically how they work (venturi, tube into the gas, floats with a needle valve, low pressire in venture sucks gas into the airstream and atomizes, etc.) but the intricasies of these complicated Webers seems like a black art!! Any carb experts want to give me a carb 101 for the benefit of the rest of the FChat tech dudes too? Thanks in advance... Birdman
Jonathan, any idea when the last time the carbs were rebuilt? If it were me, I would rebuild them then sync them up.
Hi Dave, I was thinking that, but I would prefer to rebuild in the winter when I won't be inclined to rush the job to drive the car. I'm hoping I can get the car running better for the summer then study up and tackle a rebuild with a bit more knowledge and time! I'm not at all afraid of getting the carbs apart, cleaning them and rebuilding them. What I am afraid of is adjusting them so the car runs when I'm done!! Birdman
if you are handy enough with the tools to build your own cars, may i suggest you pull the spark plugs out and read them indiviually and 1 bank versus the other. this should give you a good indication of too much or not enough fuel, or it could be a ignition issue, but i doubt it given the info at hand.
If you want to clean the idle jets. They are on the side of each carb. 8 total. One of the left of the carb up near the top and one on the right. Flathead screw driver. 55s are stock on my 78' for idle jets. Remove them, clean them with carb cleaner and blow them out. Mine were clean when I rebuilt my carbs but they could be clogged up. Here is a pic. They are the two on the right in there housing.
Jonathan To your questions: 1. Pull the idle jets out, blow through them. Do not insert any kind of pointed instrument. 2. The holes are progression holes and determine the off idle performance of the car. 3. Sync'ing is designed to balance air flow across the carbs so they draw even amounts of air. When you sync the carbs you include mixture setting. Usually done at idle and 500 rpm above idle when variations in flow are most noticeable. It is not hard. It is time consuming. You will need an SK or similar synchrometer to measure air flow. The procedure is well documented in a myriad of books on Webers, including Haynes ($20-ish) and Pierce's tuning manual ($12.50). If you do not have these, I would suggest you buy. The SK is also available from Pierce ($30 - 40). While you are at it, buy new top cover gaskets. You are likely to want to check the float heights. When the previous shop "sync'd" the carbs, why did it still run poorly and how did they explain this? Good luck. Philip
Jonathan, Ah carbs... So FREAKIN cool yet so much FREAKIN work! I've been through the whole carb thing. My gut guess is that your progression holes are not being uncovered at the same rate/time as all the other carbs, and lean conditions (or rich conditions!) are occuring, possibly in some barrels but not the other, etc. Here is some required F-Chat Reading: 308 carb rebuild complete - by Pierce Manifolds http://ferrarichat.com/forum/showthread.php?t=6526 308 Throttle cables/linkage by carbs - fine tuning? http://ferrarichat.com/forum/showthread.php?t=7932 Carbs synced! http://ferrarichat.com/forum/showthread.php?t=7362 Does your carb 308 experience hesitation or stumbling in the corners? http://ferrarichat.com/forum/showthread.php?t=7218 Carb sync update - problems: air leak, high air flow rate http://ferrarichat.com/forum/showthread.php?t=7249 Final word on 78 308 carb float heights? http://ferrarichat.com/forum/showthread.php?t=6723 Need help - carb sync - can't get an idle http://ferrarichat.com/forum/showthread.php?t=7062 And finally, the "Big Mama" thread on Carbs and Progression Holes: Advanced 308 carb sync question -- throttle plates and progression holes http://ferrarichat.com/forum/showthread.php?t=6973 And, if you're going to work on the carbs, don't forget these quintessential resources: 1. (Braden, Pat). Weber Carburetors. ISBN 0-89586-377-4. Amazon.com Price: $13.27 (+ shipping) 2. (Haynes Techbook). Weber Carburetor Manual. ISBN 1-56392-157-X Amazon.com Price: $13.97 (+ shipping) 3. (Pierce Manifolds). Weber Carburetors Tuning Manual. Part #95.0000.54PM. Piere Manifolds Price: $20.00 (+ shipping) 4. Synchrometer Type SK 1 with adapter, to sync Weber DCNF 40s found on Ferrari 308s (see attached photo) EuroPartsDirect.com Price: $39.29 (+ shipping) You CAN learn to do this stuff... Lots of reading... Lots of research. We're all here to help!
Mike, Holy crap! That's going to keep me busy, thanks for the references and the tools/books sources! 308GTS, thanks for the pic! I guess I'm going to have to learn about these damned things! Jonathan
Jon, I would try cleaning the idle jets first before messing with the syncronization of the carbs. Does the idle float at all? That's a typical sign of being off sync. If your carbs don't leak, and they don't spit, you can hold off on rebuilding them for now. Now that I think about it, it probably is your idle jets being clogged from what you said in the description. I'd pull them and clean them and then put a gumout additive in your fuel for a tank or two. These cars are similar to older (japanese) motorcycles with the 4 carb set up wich I have experience with. Usually on these bikes if you let it sit for three months or so, the jets will gum up so fast, the bike won't start, or clog either the high end or low end jets. I've seen both, and in your case it seems like your idle jets are clogged. I also remember you saying that when you shut your car off, it backfires. I would clean the jets. Clean the jets, and drive that sum' *****! It could just be one idle jet that is clogged. It doesn't take much since one carb will affect 2 cylinders. You may be able to tell which carb it is by pulling your plugs and reading them. Or just pull all the jets out and clean them. Jim
Mike, Do you have a direct link or a P/N for that syncrometer? Can't find it on their site. Also, has anyone ever considered getting the butterfly valves working together by actually physically measuring their relative positions with respect to each other with the throttle opened a tad? This would open the butterfly valves just a smidge, and I would think that you could use a tiny ruler dropped down the throat of the carb to actually measure the deflection and get them all pretty close that way, then use the syncrometer to adjust the air bypass valves for the right flow matching. Mike, all those threads at least brought me up to speed on what you call all this crap, even if I don't completely understand it. I'm getting there. Thanks. Jonathan
Jim, Good ideas. I'm going to pull the idle jets, soak them overnight in carb cleaner and blow them out, then put them back in. I'll run some carb cleaner through the engine as well and see where it stands before I do anything else. After my total rebuild of the rear suspension that took all winter and made virtually no difference in the way the car rides, I have started adopting an "if it ain't broke, don't fix it" mentality! (Except with timing belts, I'm still replacing them before they break!) I have no inclination to rebuild the carbs (especially right at the start of the driving season) if I can address this specific problem. I got to drive another carb 308 this weekend that is in a perfect state of tune, and except for the low RPM weirdness that my car is exhibiting, it's running about the same as the other one. Mine has a smoother transmission though! (No second gear issues when cold). Jonathan
Jon, You should be able to see if their clogged as soon as you remove them. If you can, try to blow air through them. I'm not big into replacing everything either. Do the critical maintenance first, and drive that mutha ******! If you need to let the car sit, put a gumout additive in the gas, and run the car for a while. It had worked in my bikes, and cars. I've never had a problem when I started doing this.
Jonathan, after you clean the jets, and get a little better aquainted with the carbs. Let me know when you are ready to sync them up, and you can borrow my STE's, if you don't need to purchase.
Chech here for a flow meter, it is the very last item on the page: http://www.superformance.co.uk/parts/dino3/carb2k3.htm Have fun.
Or here: http://www.webercarbsdirect.com/tuning_aids Just do an internet search on: "STE Synchrometer" (the model you need is SK-1, no additional adapter required)
Jonathan Each two barrel has one throttle shaft therefore, unless the plates have been staked incorrectly, the throttle plates will open evenly on each carb. Don't stick anything down into the venturis. The sync'ing process is designed to match the air flow across the 2 venturis of a single carb, using the air balance screws, repeating for all 4 carbs; then, with 1 matched to 2; 3 matched to 4 etc, you match the 1/2 to the 3/4 carb using the adjustment mechanism between the carbs on a single bank. Repeat for 5/6 and 7/8. Finally match 1 - 4 against 5 - 8 using the throttle stops. Now raise the idle to 1200 - 1300 rpm. You'll be into the progression stage. I usually do this by adjusting the throttle cable adjuster at the top of the front bank cam cover. Check balance again. Next, go and drive it to get it really hot (10 miles). Now it is time to check the idle mixture screws. Choose a cylinder. Turn mix screw one out half a turn, motor get faster or slower? Faster, come out another 1/4 turn. As soon as it gets slower, turn it in 1/4 turn. Electric tach helps a lot at this time. Move to next. When done, re-check the air balance and tweak as necessary. By the way, none of this is worthwhile if the float heights are not set correctly (common), or if the jets are not clean (common) or if the throttle shaft bearings are worn (rare). As I said, it is not hard, just time consuming. One caution. Whenever you strip down a set of carbs, always check the fuel flow BEFORE you start the car. Turn the ignition on, listen for the fuel pump. Watch the venturis. If a float sticks or is not set correctly or a needle valve gets stuck, raw fuel can pump into the engine. This gets expensive fast. When done, you'll come inside the house smelling strongly of gasoline, your children will wrinkle their noses at you, your wife will object that a "small job" has taken 4 or 5 hours on the weekend but you'll have the pleasure of knowing you've done it right. Have fun. Philip
Thanks guys. I have a business trip coming up but after that I'll delve into this!! Dave, thanks for the offer on the loaner syncrometer. I might take you up on that! (The wife will give me big brownie points for not buying yet another tool for the Fcar.) Best, Jonathan
Hi Guys, I'm back from my trip and I had a chance to pull the airbox off today and get at the idle jets. I pulled them all and they are FINE! Nonetheless, I'm soaking them overnight in carb cleaner anyway, and replacing the o-rings on them when I re-install. I did notice that the adjustment between the front and rear carb banks seemed off a bit. When I pulled on the throttle cable, the front butterflies would start to move a bit before the rear. I adjusted that with the linkage that connects the front and rear banks so that they start to pull at exactly the same time. That will be my starting point to sync them. Once I get the thing back together, I'll start looking at the sync. Gotta get me one of those cool sync-o-meters. One more question. When I start the car without the airbox to do the sync, will anything change dramatically in terms of mixture, idle speed, etc. once I replace the air box? Thanks. Birdman
One more thing...can someone comfirm that this is the meter I need? I'm going to order it ASAP! Thanks! http://www.webercarbsdirect.com/inc/pdetail?v=1&pid=794 Birdman
It's difficult to adjust the front-to-rear linkage at idle, as the idle speed screws will screw you up (bad pun), and it's difficult to take into account slack in the mechanism. Try this: Bring the car up to a fast idle - say 1500rpm or so. I do this by inserting a folded matchbook cover into the cold fast idle mechanism. Don't do it by advancing the idle speed screws! And, don't do it by tugging on the linkage on just one bank. You need to advance the throttle linkage BEFORE the bellcrank mechanism. Check the air flow in the 2 banks using a syncrometer. Equalize by adjusting the linkage. At fast idle, other airflow adjustments (such as air bleed screws) have a much less effect.
OK, my cool flow meter showed up yesterday. Such a simple but elegantly designed instrument. As soon as a few other parts arrive so I can start the engine (see 3/4" fuel hose thread), I can sync these babies. I think I'm ready. Thanks for all the advice! I'll let you know how it goes. Birdman
