| Author | Message | ||
| DJParks (Djparks)
Junior Member Username: Djparks Post Number: 90 Registered: 2-2003 |
Thanks Hans. When I tie up some of the other things I'm doing to this car I'll come back to it when I'm ready to take it on the road. Too mant directions at once. DJ | ||
| Hans E. Hansen (4re_gt4)
Member Username: 4re_gt4 Post Number: 993 Registered: 4-2002 |
My '75 GT4 had some popping up thru the carbs when I got it. It would also occasionally occur at a constant light throttle cruise. Sounded sort of like a twig snapping, or a spark. The guys at Pierce Manifolds explained that this is a lean condition in the IDLE circuit, and is common with independant runner manifold/carbs. I upped the idle jets to 60 from 55, and all was well. The only problem is that I neglected to readjust the idle mixture screws, and it idled very rich. I recently screwed them in to about 2 turns out each - each cylinder would just fire at 1 1/2 turns. With this adjustment I've reacquired a little popping when stone cold (no choke), but quickly goes away. | ||
| DJParks (Djparks)
Junior Member Username: Djparks Post Number: 89 Registered: 2-2003 |
Great reference thread Steve. Just what I needed. I do the 20 second fuel pressure build then let the engine crank with out touching the throttle for about 5 -10 seconds to get some oil pressure up then pump twice and it fires right off and stays lit. After a few seconds it starts the popping (lightly). After reading your comments I won't worry too much about it but I will check the jets for reference and comparison with you carb guys out there. Thanks again, DJ | ||
| Russ Turner (Snj5)
New member Username: Snj5 Post Number: 40 Registered: 2-2003 |
Steve - GREAT summary thread. Perfect answer. Many thanks. Russ | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1546 Registered: 1-2001 |
Russ T. -- some previous discussion on using/not using the DCNF carb start valves (a.k.a. choke): http://www.ferrarichat.com/discus/messages/112/184538.html | ||
| Russ Turner (Snj5)
New member Username: Snj5 Post Number: 39 Registered: 2-2003 |
From DJ: "the chokes on the 308 are disconnected and everybody I've talked to said they are more trouble than they are worth" Could some carb'ed 308 owners comment on this, please? Is it worth the effort of setting up the 40dcnf enrichment circuit if currently no cable linkage? Any suggestions for warm-up proceedures? Many thanks Russ | ||
| DJParks (Djparks)
Junior Member Username: Djparks Post Number: 88 Registered: 2-2003 |
An AirSync is one thing I need to pick up for these down draft carbs. The one I was using for my side draft DCOE's finally gave up after 30 years. One thing to consider is there is no intake air heat or intake manifold heat on these cars which makes them pretty cold blooded from what I have seen. My 240 is the same way but will settle down when I use the enrichment circuit. (No chokes on DCOE's). I notice the chokes on the 308 are disconnected and everybody I've talked to said they are more trouble than they are worth so maybe I'll have to settle for a 'warm up routine'. DJ | ||
| Steve (Steve)
Member Username: Steve Post Number: 334 Registered: 2-2001 |
DJ all of my carbs were running at about 4-4 1/2 turns on the idle mixture screws. I have 1 carb.which is the rear (cockpit side) left unit that pops during startup. I can't do any C0 tuning because these tubes ars shot. I am using a air meter (sync) gage that I use to set the air bleeder screws.Seems these carbs run lean on start up and once they get warm they run good. Thanks for the info , keep us posted. | ||
| DJParks (Djparks)
Junior Member Username: Djparks Post Number: 87 Registered: 2-2003 |
Hi Steve, A note I forgot to mention, The popping was occuring on the two rear carbs more than the front. Here are the number of turns for each; L/F 5.8-5.5 R/F 4.75-5.5 L/R 4.0-5.4 R/R 3.75-5.1 Notice the low numbers on the aft carbs. Starting to make sense. I haven't really had a chance to tinker with these carbs because I have been concentrating on other parts of the car. It's been on jacks nearly all of the time since X-mas while I went through everything underneath. I'm almost ready to drop it down and start driving it some more and checking the tune. I can't do any vacuum numbers because the V-stacks aren't bolted down yet. My brother has a four gas anylizer so I can get ballpark figure on the fuel/air mix once I get the car on the road. I'll still have to dial in each carb though. Just not quite there yet. DJ | ||
| Steve (Steve)
Member Username: Steve Post Number: 333 Registered: 2-2001 |
DJ please do me a favor here and see how many turns your idle mixture screws are.I'm looking for a reference for my 77. Also have you checked your Vacuum to see what kind of numbers you're getting? Just asking if you have the time. Thanks | ||
| DJParks (Djparks)
Junior Member Username: Djparks Post Number: 80 Registered: 2-2003 |
Thanks for the input everybody, I've pretty much entertained the same speculations. KERMIT,I understand the importance of throttle plate positioning after learning how to rebuild the 3 DCOE 40's on my 240 last winter. Dave Handa also recommended Carb Connection to me and I will put that on my to do list. I have a feeling they are booked big time being the spring rush and all.I may look them up right after the cruizing season is over and get a jump on the punch list I'll have at the end of the summer. JOHN, I was told by a previous owner that the carbs had been rebuilt when he had the car so the type and size of the jets are an unknown at this time. Being that they are accessable at the moment I should pop them out and record them for a base line. Again, Thanks for the help, DJ | ||
| John_Miles (John_miles)
New member Username: John_miles Post Number: 46 Registered: 7-2001 |
This is similar to what I've always seen with my '76... light, occasional popping primarily when cold. In my case, the symptom went away almost entirely when I had the carbs rebuilt. What jets (main, idle, and AC) are you running now? There are supposedly "idle air corrector" jets but I'm not even sure where they are. The usual air-corrector jets -- the ones at the top of each emulsion tube -- won't have any effect at idle. | ||
| Matt Morgan (Kermit)
Junior Member Username: Kermit Post Number: 114 Registered: 8-2001 |
DJ, It could easily be the throttle plate position being too a bit far open at an idle . This causes it to go into the intermediate circut ( the ports are just above the throttle plate). I would heartedly recomend Alex @ Carb Connection in Kirkland. Very professional, as well as knowledgeable. IMO | ||
| "The Don" (Mlemus)
Advanced Member Username: Mlemus Post Number: 3255 Registered: 8-2002 |
DJ, If it is a little, "chirp" it's normal | ||
| DJParks (Djparks)
Junior Member Username: Djparks Post Number: 77 Registered: 2-2003 |
When cold and the throttle is slightly cracked it will make a light popping sound through the carb throats, random and intermittant, one to three a second. The sound isn't very loud but it is noticable. I also see a small amount of vapor above the carb when it occurs. It will stop doing it for a few seconds then start doing it again. Also,a plug will misfire during this event on occasion. A previous owner mentioned the air correction jets may be to blame. I think after a good shake down cruise this spring I'll know better. Thanks again, DJ | ||
| '75 308 GT4 (Peter)
Advanced Member Username: Peter Post Number: 2603 Registered: 12-2000 |
How often is intermitant and how loud is the backfire? I get on the rare occasion a pop/spit when cracking the throttle stationary and on highway acceleration. Its an indicator of a lean condition, but in my case, I haven't investigated fully as I said, it happens seldomly and I'm not concerned/bothered by it (it only occurs when the planets have been misaligned...  ). The dyno test can reveal what's up. | ||
| DJParks (Djparks)
Junior Member Username: Djparks Post Number: 76 Registered: 2-2003 |
After starting my '78 308 (cold) it backfires lightly through the carbs intermittantly and usually happens just when I crack the throttle (off idle). It also occurs when the engine is warmed up but less frequently. When the backfire occurs through one of the carbs there is a also corresponding stutter in the exhaust. Is this a 'leanout' condition or is it something more serious related to the valve train etc...? One note; When the car is under hard acceleration it goes like a bat out of hell, One light stutter then it goes hard and smooth. Haven't had a chance to dial the carbs in this winter yet so I thought I would ask for opinions on which direction I should go with these. Another F*chatter here recommends Carb Connection (Kirkland) for complete dial in and DYNO for top tune, good idea but what to do in the mean time? All information is much appreciated, I have a back ground in things mechanical but there are many gaps I must admit. Thanks, DJ |