| Author | Message | ||
| Andrew A. Illes (Andyilles)
Junior Member Username: Andyilles Post Number: 95 Registered: 10-2002 |
Mark... the last "boost" I got was a procto. Ok, so I need a life. | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 545 Registered: 5-2002 |
Andrew, thanks...it was a lot of work. I'm building a new one now with an intercooler built in and a bigger blower.....remember, boost is your friend  | ||
| Andrew A. Illes (Andyilles)
Junior Member Username: Andyilles Post Number: 94 Registered: 10-2002 |
Mark.. that's just an AMAZING job you did building (never mind figuring out) that plenum... hats off!!! | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 537 Registered: 5-2002 |
If the timing is right, then it is probably a mixture problem. 2 jet carbs, like webers, are notorious for mixture problems at the transition between the jets, between about 1/3 and 1/2 the rpm band . The problem will be worse on a carb that has worn throttle shafts. There just never seems to be a pair of jets that work well all the time. All carbs also have trouble with accelerations (corners or otherwise) changing the mixture because even if the float is working right, the acceleration makes the surface of the fuel not level and effectively changes the float height setting. So�..I�m a big fan of dynos, I would make an appointment to get it dyno tuned. As it sits, there is almost certainly a huge dip in the power curve at about the 1/3 rpm point. I like to do jetting with the accelerator pump disabled, set that after the jets are right. The when you know it�s jetted right, roll it off the dyno and try the corner again. I think you�ll find it�s fixed. Also note the air temp, pressure and humidity, because when any of them change significantly, the problem will probably be back. I know a couple guys who have spring, summer, fall jets they put in to help minimize the problem. You should be able to get it sorted out, but there is a reason factories stopped using them 25 years ago..... Good luck with it. | ||
| Andrew A. Illes (Andyilles)
Junior Member Username: Andyilles Post Number: 84 Registered: 10-2002 |
Mike.. Neither of our theories holds water. I just went out and pulled the top off one of my spare 40 DCNFs. To counter your theory that there is surely enough fuel in the bowl to get you through a curve, I doubt there's an ounce in a full bowl (the float is HUGE!!). On the other hand, to counter my own theory, the float sits perpendicular to the car's centerline, so cornering loads alone seemingly couldn't cause it to bind, as I had opined. Plus, the float pivot is at the exact full level and centered on the float when the bowl is full.. it's also on the left side, while you guys are describing problems in right turns only, so forget centrifugal force. JRV.. I agree, but timing, advance, etc. would seemingly not be affected by cornering, where these guys are having the problem. So guys.. having stared at that carb through 2 really decent single-malt scotches, I'm left with a far out possibility. Noting that the barrels are also perpendicular to the car's center line, I can conceive that a poorly connected/grounded fuel pump - i.e., needs more alternator output to keep pressure up (ergo, only on the street, not track)- combined with low float settings, also combined with centrifugal force possibly forcing the resultingly lesser available fuel to one barrel or the other. On the other hand, that should produce the same result in either a R or L turn. Know what? To hell with it.. think I'll go have another scotch!!! | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 388 Registered: 10-2002 |
Agreed, the problem does detract greatly from the overall experience. Andy, your thoughts below seem to be sound, but the idea is to keep the float bowls filled, right? And there's a fair amount of volume of fuel there... With the levels set correctly, I can't see how temporary shutoff of fuel would cause hesitation (on one or more cylinders)--there SHOULD be enough fuel in the bowls to "Weather the storm" of the corner, right? We're only talking 4 seconds or so... And even then, if you FLOOR the car through the turn, there is no problem--it's as if when you're on the main jet circuit the problem goes away, suggesting that there may be some problem with the idle jets (which I believe you're running off of at low to mid throttle, low RPM, like you do when you're turning...). | ||
| Bob Briley (Bob_briley)
New member Username: Bob_briley Post Number: 4 Registered: 5-2003 |
I also have this problem and was told it is related to the carbs. The problem happens in sharp right hand and long cloverleaf merge lanes. The cloverleafs take longer for the engine to recover. Could this be related to the orientation of the floats relative to the car? This problem really detracts from the overall experience. | ||
| Andrew A. Illes (Andyilles)
Junior Member Username: Andyilles Post Number: 76 Registered: 10-2002 |
My thoughts... All float systems (whether Weber or Rochester) are designed to do one thing.. keep a sufficient level of fuel available. On the track, you're flat out with a fairly high constant demand, so the float needle tends to be open most of the time, whereas in street driving, it tends to open and close a lot more. The float is attached to a pivot arm, the other end of which actuates the float needle, which opens or closes the inlet orfice. In a corner, the float pivot can "bind" from centrifugal force, and it can bind anywhere between open and shut. In street driving it's more likely to be able to bind in the shut position because of the lower fuel demand, while on the track, it will more likely be open if it binds. Obviously, if it binds when shut, you're gonna get fuel starvation. The only "fix" I can think of is to polish both the float arm and the "bracket" on the float cover through which the pin passes to reduce any binding tendency. Thin teflon washers too maybe?? | ||
| billy bob (Fatbillybob)
Member Username: Fatbillybob Post Number: 283 Registered: 8-2002 |
""I wouldn't necessarily describe it as "missing" so much as "hesitation". For me, it happens only at a constant, light-to-medium throttle through corners--most notably, making a right-hand 90-deg. turn at an intersection."" This is a known 308 carb problem due to float levels and happens stock oem setting. You can increase the levels a bit to compensate. This is not much or a problem to most street giys but the racers have had this problem since day one. | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 381 Registered: 10-2002 |
It doesn't happen at the track, because at the track, you're applying a lot more throttle in a turn, which will cover up the situation. I think we've narrowed down the scenario to non-track, street driving, low speed/low and constant throttle through turns. This is what seems to cause the hesitation. I had it, and then it was *fixed* for a while--then it started slowly coming back. If I had to guess, I would say it's related somehow to the age of some of the carb components, and that a complete teardown and rebuild might help out? None of the reviews I've read of the carb 308s (I've got a bunch!) from the 1970s ever mentioned this problem. (Oil starvation and subsequent oil pressure reduction is an entirely different issue.) The float heights seem to be the most obvious thing--for sure. But they ALL check out fine! So far, I count me, Todd, James, Bob, and Andy all having the same problem. There's gotta be a solution here! It happens regardless of fuel tank level... New fuel pump... And medium to heavy throttle will always cover it up. I believe, during the light-throttle street cornering we're talking about, that we're running on the IDLE jets only--e.g. 3000 rpm, light throttle. It really seems as if the engine is encountering a lean condition during the turn. During the turn, if the fuel in the float bowls is forced against the sides of the float bowls, would this affect the flow of fuel through the idle jets? Would the engine sucking & venturi effect in the carbs be somehow minimized? | ||
| Andy Falsetta (Tuttebenne)
Junior Member Username: Tuttebenne Post Number: 162 Registered: 3-2003 |
My '77 GTB s/n 23153 does the same thing. It happens at part throttle on the street but not on the track. If it was caused by float height I would expect the same (or worse) result at full throttle on the track. | ||
| david handa (Davehanda)
Member Username: Davehanda Post Number: 913 Registered: 5-2001 |
Randolph, I hear ya man; Carlo is never hurting for business. He is perpetually backed up with cars. I have been on the list for many months as well. We had trouble finding a steering rack, but once found, we was able to finally work me into the schedule. Lot's of cool cars parked in there, 512TR, 550 Maranello, 328's, 308's, Mondials, Lambo Countach, etc. | ||
| RANDOLPH MADAMBA (Pogibm)
New member Username: Pogibm Post Number: 44 Registered: 8-2002 |
Dave i've been on the waiting list since March to have my Mondial fixed. | ||
| david handa (Davehanda)
Member Username: Davehanda Post Number: 909 Registered: 5-2001 |
Hey Todd, Please don't take up too much of Carlo's time, he's supposed to be working on my 328... :-) | ||
| Bob Campen (Bob308gts)
Member Username: Bob308gts Post Number: 631 Registered: 9-2001 |
Last year after rebuilding the carbs on my 308, setup included checking and setting timing, curve is same on both banks with 34 advance at 3500 rpm. I too have the same stutter in a corner. Have 60 idle and 140 mains I'm going to try. | ||
| Todd Lozier (Tklozier)
New member Username: Tklozier Post Number: 4 Registered: 5-2003 |
Great information here. Thank you all. Yes, it is more of a hesitation than a missfire. I'm going to experiment a little and call Carlos Durante, the previous owners mechanic. I'll post any conclusion I come up with. Todd | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1688 Registered: 11-2002 |
>>there are shops that can check the distributor advance and reset as needed << The advance operation can be checked with a timing light in about 15 minutes in your own driveway. The olny part that even needs to be touched is the timing hole cover. You open the hole, hook up the 3 wires of the timing light and check away. It's so simple I'm confounded why people will try so hard to avoid "checking timing" & operation. | ||
| James P. Smith (Tigermilk)
Junior Member Username: Tigermilk Post Number: 153 Registered: 7-2001 |
Mine ('78 #25975) will do that on tight turns, usually at lower speeds (0-25 or so). Was even pulling a hard left into the gate at work last week and it stalled right in the middle of the turn. The car was in neutral at the time so no throttle applied. One stall in 2+ years. | ||
| Philip Airey (Pma1010)
Member Username: Pma1010 Post Number: 268 Registered: 7-2002 |
Todd I have 21819 - Yellow gtb of June 1977 -- so we are close in build date. First, no, it isn't completely normal - although Bill Pound tells me some fuel starvation is somewhat normal at the track. Second, JRV and the other guys know their stuff, but the fact that it happens on a turn sure sounds more like float heights to me. When were they last rebuilt/checked? If it were me, I'd start there. Third, there are shops that can check the distributor advance and reset as needed - Continental in Hinsdale being one. HTH Philip | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1687 Registered: 11-2002 |
>> how would inconsistent distributor advances between the distributors cause the stuttering in the corners? << To produce power under load timing advance operation is critical, as well as both banks working in perfect concert with each other. If the timing doesn't jump towards more advance (especially under part throttle then quick loading) the engine will lack the power it needs to deal with the new quickly loaded situation, and as such it will stumble and hesitate until it can catch up to the new demands being placed on it. Perfect dwell and advance operation is "Critical" to the way an engine behaves. With no load and marginal advance operation it may go unnoticed, but when a load is thrown on the engine it can't produce torque without correct advanced timing of both banks. | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 379 Registered: 10-2002 |
Todd, I've had the exact same problem for about a year now. A few others have also had it--check the archives. (When I get back home, I'll try to post a few things that I've been able to learn). I wouldn't necessarily describe it as "missing" so much as "hesitation". For me, it happens only at a constant, light-to-medium throttle through corners--most notably, making a right-hand 90-deg. turn at an intersection. We thought we had fixed the problem by richening up the idle jets and accelerator pump jets, and the problem did go away--but now is back. I'm pretty much at a loss at this point. John (John A. I believe) had a similar problem (archives), on and off, and made some progress by completely rebuilding his carbs... You'll notice (perhaps), that the problem only occurs with light to medium, constant throttle throught the corner. If you really push it, your problem might disappear. Still, very annoying for driving in traffic for it to "almost" die like that. For some reason, I'm thinking it might be elevation-related, since both John and I (if I recall) are at some 5000ft+; at what elevation do you drive (I assume there in WA)? I would also recommend trying what JRV has suggested (knows his stuff). JRV, how would inconsistent distributor advances between the distributors cause the stuttering in the corners? | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1683 Registered: 11-2002 |
Have the Distributor Advance Mechanisms checked for proper operation of the advance curves and perfect conformity to each other before suspecting the carbs imo. | ||
| Todd Lozier (Tklozier)
New member Username: Tklozier Post Number: 3 Registered: 5-2003 |
My first ferrari, hopefully not my last. Just got the car about 5 weeks ago #21719. The missing on hard corners must have something to do with the float level in the Webers? I can't imagine that this is normal, any thoughts before I dive into it. Otherwise, the car is a blast and this forum is such an education! |