Guys, I just went through adjusting the carbs, but my front bank of carbs doesn't idle as smooth as the rear bank. Everything is in-synch, but I'm thinking maybe the front bank timing may be off. The symptoms that I have while driving is excessive popping at 2500rpm and during excelleration, and it's all coming from the front bank. The idle jets are 60's. With 55's the carbs popped at idle. That is now gone. My main jets are 130's, air 200, emulsion f38 I believe. I went through the carb tuturial that's why I'm thinking I have a timing issue. Does anyone else have suggestions? Thanks in advance, Jim
Jim Where's the popping coming from - out the chokes (lean/less advance) or through the ex pipe (rich/more advance)? From your description, I am assuming it is popping through the carbs, indicating it is either going lean or timing is retarded on that bank. Do you have twin distribs and does the popping only occur at 2500 or over a broader range? If you are sure on your carb settings, that the jets are all matched and clear (BTW, my guess is you mean F36 emulsions) and the carbs are pulling equal amounts of air flow at idle and off idle (1200) then I'd look at the distributor weights and springs to check the advance curves. Unfortunately, this means pulling the distribs and having them calibrated. HTH Philip
Philip, Yes I mean popping through the carbs. Also, when I advance the throttle fuel mist sprays out of the top of the carbs on the front bank. Jim
Thats very unusual and indicates something is very far off. I'd check ignition timing and cam timing. By the way nothing to do with your current problem but changing your idle jets to get rid of popping at idle is not the correct course. The idle jets aren't really idle jets, the correct term is slow running jet. The idle mixture screw is for the purpose of controlling the idle mixture. The slow running jet provides fuel for idle and the progression ports that supply fuel for lower throttle openings for a smooth transition to the main circut. The progression circut in reality does most of the work at low and cruising speeds. That is an area of weakness on 308's built for the US so you may have done the car a favor. With the lower density fuel we have in Kalifornia I often make that change anyway, but in the future if you want to change fuel mixture for idle use the mixture screw. Make sure that when you are doing the ignition timing on the 5/8 bank you are using the 5/8 timing marks. In fact turn the motor to PM5/8 on the flywheel, find out whether it is firing on 5 or 8 and remove the distributor cap and ck to see that the rotor is pointing the right direction. Something is a long way off .
I forgot to mention, yes I have twin distributors. Well, I had the belts done by a dealer when I bought the car, so I'm going to say that the cam timing is good for now. I've put 4k miles on the car since then. I've noticed that there are timing marks on the front distributor and that they're not aligned, so I may do a slight adjustment of the distributor to see if the front bank idles normally when I line those marks up. I figure it couldn't hurt to do that before I start to tear things apart. What do you think? Also, do you think maybe the carbs could be at fault? Thanks, Jim
I don' t think you should just be moving things to see what happens. There only three things that are required to make a motor run, Fire, Fuel, and Compression. Always go back to the basics. For fire you have to find out if you have spark at the right time, and for compression you have to find out if the cam timing is correct. It would help if we knew when the trouble started. But I think you should TDC the motor and have a look to see if the cam marks are close. then TDC #5 and have a look at the distributor rotor position. The only time I have seen the symptom you describe as fuel mist coming from an entire bank of carbs one of the two was way off, like a distributor in 180 degrees off, or a cam way out of time. Also just to make sure we are all talking about the same thing, when you say front bank are you talking about the bank closest to the cabin?
Yes, I'm talking about the bank closest to the cabin. The reason I started messing with the carbs is because the car would pop at idle off and on, and the idle didn't drop between shifts like it should. The engine was real strong up until about 5k then the car would run out of breath. Sometimes if I accelerated hard and ran it up to 5k, at 5k it would pop pretty bad. This did not happen all the time though.
I looked at some diagrams, and basically your saying that if a cam is off, then the intake valves are slightly open during the compression cycle causing the fuel to spray back through the carbs. I have a question, what causes normal popping through the carbs on a car that has perfect cam timing?
As far as cam timing goes, yes but that is an over simplification. Popping through the carbs can be caused by many things but lean mixtures are a common one. Lets start at the begining a little, as I said earlier, it only takes three things to make a motor run, fire, fuel, and compression. On a motor with points for ignition, carbs for fuel delivery, and soild lifters, that is really, truely properly tuned in the first place the one thing that is most constant and needs the least attention, is the least prone to wear and degradation, are the carbs. That has been true since otto cycle engines were invented. That is why I never take in a job to adjust carbs. They may have been badly adjusted the last time. But if the motor ran well, and got bad, if it's not from debris in the carbs, it's problem is probably not the carbs. Personally I believe to make your car run proper you should start at the begining, do a valve adjustment, check the cam timing, test the compression, service the distributors (prob the single biggest problem area on 308's), time the motor and then adjust the carbs. If you notice adjusting the carbs is the last thing on my list. It is the last thing done in any tune up, and you are doing it first. That course of action has led many good mechanics down a road of real frustration. Don't do it, the best it will get you is a so so running car and there is no point in having a so so running Ferrari.
great thread, my rear bank, closest to the trunk is spraying fuel out of the carbs and will turn the header pipes red if allowed to run. will only run with lots of fuel. seems timing of the points on that bank is bad. i am ordering all new Crane systems for both dizzies and checking cam timing and valve clearance. i met someone who has done this recently, and they offered to help. my carbs and gaskets are fine. car did this " all of a sudden". has to be in the crappy points dizzies. will update if i can help.
Three points: - first, Micheal, if your rear bank is exhibiting the symptoms you describe, sounds like you are not getting any advance. You'll get really high EGT from retarded timing. - Second Jim, when you started the thread, you were (IIRC) describing a problem localized to one bank, one rev range (2500 or so). The most probable cause for this is, I believe, sticking distributor weights, or the weights over or under advancing versus the other bank. Given it was popping up through the carbs, it struck me that you are not getting enough advance. Now if I am reading correctly it is a bigger issue with lack of power above 5000 rpm. This can also be caused by the distribs not advancing. - Third, you can get popping out one bank if you get it a bit out of sync with the other (i.e., the throttle linkage is pulling differentially on one bank or the other), but, from memory, you'll experience this just off idle (1200 - 1300) on up before it tends to disappear (as the airflow differential becomes less apparent at larger throttle openings). Jim, again, I'd start with the distributor on the front bank and have the advance curve checked. HTH Philip
Yeah, I'm thinking I could have two problems. Well the reason I'm messing the carbs and not the distributors, is that they were serviced when all of the other work was done. A valve adjustment had been done a short time (miles wise) before that, and so I didn't want to mess with it. I do think they're could be an advance problem, but I also think something (hopefully ignition timing) is making the fuel spray out of the carbs. With the car idling I notice the airflow on the carbs isn't smooth like rear bank. It has a slight waver to it on the flow meter, and the rear bank has almost no waver at all. It's real smooth. Philip, and Rifeldriver, thanks for helping me on this. Philip, do you have any relatives that were in the air force, or were you in the air force? Jim
i totally agree, i have never messed with ferrari points. my plan is for my friends and i to install new points in both distributers tomorrow morning and see how it runs. one of them has 2 ferrari's and 6 cars collector cars, he and a few others have made offers on the car so it may be gone before i get to do the Crane upgrade!!!!!!
Jim, My dad was in the RAF and a POW in WWII in (East) Germany. I am just a regular business type. Michael, Remember, the advance is controlled by the (centrifugal force acting on the) distributor weights, rather than the points per-se. Good luck to both Philip
Guys, I drove my car back to the shop that did the timing belts. It turns out that the cam timing on the front bank is off by a notch. Thanks for the advice Rifledriver.
I guess this verifies the theory that the timing can be off by one "notch" on the timing belt and not do any damage. Glad it is all worked out. Those guys that did your belt are damned lucky they didn't mess it up more than a notch. That would've been pretty expensive to fix on their dime! Birdman
Cam timing can be a long way off (more than one tooth) and still not do damage if it happens in just the right way with the right cam. On 308's this is quite common on the 5/8 bank as at top dead center on 1/4 where the cam timing is done the 5/8 cams don't want to stay in place by themselves. This is compounded by the fact that most people want to simply look in that direction and not use a mirror to see the marks from the correct perspective. At Ferrari school Ken McKay (The former national service instructor) used to hammer home "if you have a problem that effects an entire bank, check the cam timing". He was correct, it was done wrong on many,many cars, and just because it didn't just get done this time doesn't mean it was done correctly last time. I have serviced lots of Ferrari's where the cam timing was incorrectly done at a prior service. These days if I don't find a cause almost immediatly for a running problem I go back to the basics, Fire, Fuel, Compression. You would truely be surprised how often it is cam timing. I am glad you found it and hope everything else goes smooth.
Thanks, As for who's fault it is, the place that did the belts is saying that the timing slipped. I'm saying bull, but this is a whole other story. Thanks again for the help.
Well, I just called the shop, and they said that the car is running great. I'm anxious to see how this thing runs. I thought it had a good amount of power with the timing being off. I wonder what it drives like now.........
If it makes you feel any better just about 5 minutes ago I found a 308 QV in my shop that doesn't sound any good (owner wasn't complaining about poor running, he just wanted to get a smog check) and it has both 5/8 cams way off, judging by the external marks they both must be at least 2 teeth too advanced. I'll be surprised if it didn't have a piston/valve interface on the intakes. According to the owner the belts were replaced at a dealer about a year ago. And no, cams don't just slip a tooth, for all my misgivings about belt drive cams that is not one of their shortcomings.
The external marks on QV, especially 5-8 are quite vague. You can bend the tag to make it look like anything you desire, so unless you've got the covers off, it's probably guess work. The 5-8 bank externals are marked deliberately off centre a bit to help with the angle you view them from, where as the 1-4's are marked at 90 deg straight up in line with the pistons. If both 5-8 cams are 2 teeth or more off, it couldn't pull the skin off a rice pudding...so what does it go like?? HC's will be out the window too....1000ppm or more probably. For a quick check, if you pull the dist cap off, with 5-8 on PM (NOT 1-4), the rotor on the inlet cam will point perfectly at either 5 or 8 post, depending on which stroke you've got it on, but even that's a crude guide...it's a covers off job to verify properly.
