| Author |
Message |
Paul (Pcelenta)
Member
Username: Pcelenta
Post Number: 412
Registered: 7-2002
| | Posted on Friday, October 31, 2003 - 7:25 pm: | |
mike, I left the jetting alone...I will tell you this, the last time the carbs were adjusted/tuned was by a former mechanic of mine (no longer use him after he screwed me on a small block chevy rebuild) who did not believe in balancing/setting the carbs at idle..his rationale being that you don't drive at idle...this weekend I plan on giving his method a shot. |
john asselta (Cavallo_nero)
New member
Username: Cavallo_nero
Post Number: 14
Registered: 10-2003
| | Posted on Friday, October 31, 2003 - 4:25 pm: | |
Hi Mike
nice chattin with ya again. (ferrarilist). thank you for digging into finding my article - i appreciate that. but still, i have some new stuff on the carb rebuild that i would like to add. i went thru the rebuild process again a year after i wrote the article and have more stuff to offer. and Mike, the fuel starvation around heavy cornering was not eliminated, although going to concave float design allowed for more fuel in the bowls and reduced the fuel starvation around corners. |
john asselta (Cavallo_nero)
New member
Username: Cavallo_nero
Post Number: 13
Registered: 10-2003
| | Posted on Friday, October 31, 2003 - 4:19 pm: | |
I used a trick the britts use on their cars, advance it til it pings, then back off til it doesnt. more advance over stock due to altitude compensation.
john
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Philip Airey (Pma1010)
Member
Username: Pma1010
Post Number: 498
Registered: 7-2002
| | Posted on Friday, October 31, 2003 - 4:00 pm: | |
John
Sounds like a lot of advance. On what basis did you override stock? Dyno or other?
Philip |
Mike Procopio (Pupz308)
Member
Username: Pupz308
Post Number: 620
Registered: 10-2002
| | Posted on Friday, October 31, 2003 - 3:14 pm: | |
John,
Were you able to eliminate all fuel starvation / hesitation / cutoff around corners with your carb rebuild?
By the way, here is John's excellent rebuild article... The full thing (the one on FerrariList is not complete):
http://www.fca-se.org/carbs/
--Mike
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john asselta (Cavallo_nero)
New member
Username: Cavallo_nero
Post Number: 12
Registered: 10-2003
| | Posted on Friday, October 31, 2003 - 2:31 pm: | |
here is a link to the procedure on ferrarilist. but it is not all there - hmmm. maybe i can post the whole procedure here, but i do not know where to put it.
http://www.ferrarilist.com/index.php?query=docs&action=showdoc&docid=17
as far as total timing i have dialed in, using my electromotive unit, 18 degrees initial, plus 21 degrees at 3000, plus another 10 degrees to 8000. this gives 39 degrees total at 3000 rpm. and a total of 49 degrees at 8000 rpm. and 44 degrees at 5500 rpm.
here are a few good tips in rebuilding: use GENUINE weber parts (the gasket matching is better and the parts line up better than aftermarket). insulate the fuel line against heat. i cleaned out all the lead freeze plugs (casting plugs)with an exacto blade and filled the void with seal all. there are no more leaks in the carbs to date from doing this, and the response is very crisp. completely disconnect the chokes and make sure the choke covers seal against the carb bodies.
john
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Sean F (Agracer)
Member
Username: Agracer
Post Number: 427
Registered: 2-2003
| | Posted on Friday, October 31, 2003 - 12:27 pm: | |
John,
Can you post a link to your write up? I looked at the FerrariClubAmerica site but did not see it anywhere.
Thanks |
Hans E. Hansen (4re_gt4)
Intermediate Member
Username: 4re_gt4
Post Number: 1775
Registered: 4-2002
| | Posted on Friday, October 31, 2003 - 11:54 am: | |
John: What is the total advance you're using at 5000 rpm? There is a flywheel mark at 34deg for that purpose. Are you at 38-40 deg? |
john asselta (Cavallo_nero)
New member
Username: Cavallo_nero
Post Number: 10
Registered: 10-2003
| | Posted on Friday, October 31, 2003 - 10:35 am: | |
I live at 7800 feet above sea level, and the best advice i can give to rejet the carbs is to make sure everything on the car is OK and the way you want it, (ignition system, exhaust etc.). then go to the dyno and see where you stand at the entire rpm range. bring a bunch of main and air correction jets with you so you can experiment while there. i dialed my 308 in very well that way, and it pulls strong throughout the rpm band all the way to 7800 rpm. i wrote a carb rebuild procedure that is up on FCA web site if you want to check out some tricks and mods, or email me for some rebuild tips. (i need to update that procedure with some other mods i found). for now, bump up the timing by at least 5 or so degrees.
john
78 308 GTS Euro Nero/Crema |
Mike Florio (Mike_in_nevada)
Junior Member
Username: Mike_in_nevada
Post Number: 51
Registered: 6-2003
| | Posted on Friday, October 31, 2003 - 10:19 am: | |
Road & Track reviewed the Dino 308 GT4 in the September, 1974 issue - I have it here right here on my desk. Paul Frere says "In fact the engine will accelelerate in 5th from 1000-1100 rpm (25 mph) and soar right up to its maximum speed of 152 mph without flat spots or cam effects being felt."
In the September, 1975 issue R&T published a comparison between the GT4, Maseratti Merak and the Lamborghini Urraco. TRhe Dino was the winner "by a wide margin."
I'd be interested in the jetting changes Mike Procopio made for 5000 ft, since I and my GT4 now live at that altitude. Any possibility you could post them, Mike?
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Mike Procopio (Pupz308)
Member
Username: Pupz308
Post Number: 619
Registered: 10-2002
| | Posted on Friday, October 31, 2003 - 9:53 am: | |
Ack! I was thinking of rebuilding the carbs to help ALLEVIATE this problem!
I wish there was some way all of us could go back to 1978 and drive a bunch of these cars new from the factory to see if it happened back then as well...
Paul, did you change your jetting at all?
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Paul (Pcelenta)
Member
Username: Pcelenta
Post Number: 411
Registered: 7-2002
| | Posted on Friday, October 31, 2003 - 6:16 am: | |
what is with the 3500 rpm transition? I just rebuilt my carbs and now I have problems in that range....it's driving me crazy..never had the problem before. I did change the fuel pump to a holley red with a regulator set to 4 psi and suspect that the flow rate is too low...I am running 7 mm fuel line...thinking about bumping it up to 8 or 9 mm.
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David A. Ward (Davidgt4)
New member
Username: Davidgt4
Post Number: 14
Registered: 5-2003
| | Posted on Friday, October 31, 2003 - 1:49 am: | |
Very helpful guys.
More work to do! |
Hans E. Hansen (4re_gt4)
Intermediate Member
Username: 4re_gt4
Post Number: 1768
Registered: 4-2002
| | Posted on Thursday, October 30, 2003 - 11:10 pm: | |
Absolutely no noises on 'over-run' here either. Runs just like a FI car. I'm running 60 idle (slightly larger than stock), 135 (? - they're stock) mains, and 195 (smaller than stock) A/C. Runs perfectly (except - see below) thru any transition areas - ie. say 3500, feed in more throttle. No problems at all.
The only problem I have is extended running at city speeds and low rpm. After such running, when I nail the pedal, I get a HUGE cloud of smoke. Too rich thru some aspect of it's tuning, and it needs some frequent "cleaning out". Usually redline in 2nd, then 3rd, and all is well again. Idles w/o smelling rich, tho. |
Philip Airey (Pma1010)
Member
Username: Pma1010
Post Number: 495
Registered: 7-2002
| | Posted on Thursday, October 30, 2003 - 10:09 pm: | |
John, Mike
I also have the Electromotive ignition. I think the waste spark might have something to do with it. However, I had an ANSA and it didn't do it, so....
Put on the Tubi (77, no cats) and burble burble on the road and flames at the track on the big double de-clutch downshifts. |
Mike Procopio (Pupz308)
Member
Username: Pupz308
Post Number: 616
Registered: 10-2002
| | Posted on Thursday, October 30, 2003 - 8:12 pm: | |
Surely there must be some explanation? I thought it was related to either a lack of backpressure in the exhaust system (though my car did this with stock exhaust & cat config as well), and/or carb setup...
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dave handa (Davehanda)
Intermediate Member
Username: Davehanda
Post Number: 2208
Registered: 5-2001
| | Posted on Thursday, October 30, 2003 - 7:13 pm: | |
Funny, I had a 78 308 GTS with stock exhaust, cat test pipes, K&N air filter, carbs rejetted with 140 mains (up from 125's) and good state of tune, and never had this popping, spitting, over run thing you guys all talk about....I have seen and heard this on other cars, but never experienced it myself....Hmmmm. |
Mike Procopio (Pupz308)
Member
Username: Pupz308
Post Number: 615
Registered: 10-2002
| | Posted on Thursday, October 30, 2003 - 6:17 pm: | |
David,
Mine (78 308--very similar setup as yours) pulls strong 2500 to 7700 when floored, not a single "blemish" along the way. Stock carbs with the correct jetting adjusted for 5000ft altitude, original ignition.
I, too, get popping on the overrun with my ANSA. No backfires though--just spatting, spitting, gurgling, and booming.
John Miles, you also have an Electromotive electronic ignition setup though, right? Wouldn't this affect the popping on overrun effect somewhat? Does its "waste spark" nature have an effect? |
John_Miles (John_miles)
Junior Member
Username: John_miles
Post Number: 107
Registered: 7-2001
| | Posted on Thursday, October 30, 2003 - 5:08 pm: | |
Actually, I get almost no popping/banging with my Tubi. I would suggest checking for intake leak s(both vacuum and throttle-shaft seal areas) and exhaust leaks.
Opening up the idle mixture screws a bit also seems to discourage exhaust popping on these cars.
Hans is right: it should basically feel as smooth and strong as a fuel-injected car. If it doesn't, there's something wrong. |
Philip Airey (Pma1010)
Member
Username: Pma1010
Post Number: 492
Registered: 7-2002
| | Posted on Thursday, October 30, 2003 - 4:45 pm: | |
David
I'd first check the jetting. The issues you highlight are right at the points of transition between the various jets. They can have an issue around 3500 - 4k with the transition from idle jet to main, sort of a stumble or hestitation. Between 4000 and 6000 they are on the main jet and above 5800 or so they are also relying on the air corrector jets. Compare the jets to the WSM for your carb body numbers (i.e, 3X series, 4X series, 6X series of the DCNFs - according to MY - have some variation in jetting). The jets are easy enough to pull.
FYI, a rebuild of the carbs usually involves setting float heights, putting in new gaskets and pump diaphragms and setting (idle) mixture and sync'ing the carbs.
The Tubi will make it pop and bang on the over run (mine does), all part of the charm. |
Hans E. Hansen (4re_gt4)
Intermediate Member
Username: 4re_gt4
Post Number: 1764
Registered: 4-2002
| | Posted on Thursday, October 30, 2003 - 3:25 pm: | |
Sorry, not a lot of help here, except to say that if running right, it should pull smoothly at any throttle setting and any rpm above 2500 or so. Dumping the throttle suddenly wide open at 1500-2000 will probably produce a large bog, but otherwise it should run like a modern FI car.
If the dual point system is working correctly, it should have no effect on driveability. The microswitch on the throttle linkage will disconnect the second set of points just off idle. The only reason for removing them is that it simplifies life a bit when you're doing a tune-up. But no performance/driveability issues with the second points. Many here are still using points and reporting no problems at hi rpm.
Life is simplified even more if you get rid of the points altogether and substitute optical triggers, such as used with the Crane XR700 system.
You said that distributors were rebuilt. I hope that they properly set up the advance curves, as you can easily have a mismatch between the two.
Sounds like you probably have some carb issues. Again, hope they were assembled correctly, and someone didn't screw around too much trying to "improve" things by rejetting, etc. I'd be suspicious if the jets are very far from stock. Lastly, a check of the syncronization and idle mixtures should be done, preferably by you, and not a mechanic. Mechanics will sometimes do "It's close enough", and not get the precision required. |
Sean F (Agracer)
Member
Username: Agracer
Post Number: 425
Registered: 2-2003
| | Posted on Thursday, October 30, 2003 - 2:23 pm: | |
Do a search for 308 Carb Rebuild and Rejet.
Don M from KC redid his carbs and their a a lot of good info. in that thread on timing, setting the carbs, etc.
Or better yet, search for 308 weber (using the AND) and you'll get a bunch of posts.
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David A. Ward (Davidgt4)
New member
Username: Davidgt4
Post Number: 13
Registered: 5-2003
| | Posted on Thursday, October 30, 2003 - 2:07 pm: | |
308GT4 finally on the road and running after a lot of work since buying it earlier this year. It's a series 1 from late '74. Will post some pics to the GT4 thread as soon as I can get the camera/computer/human interface working...
First Ferrari and first "classic carburettor" engine for some time so advice as follows please:
-Presumably the engine if set up properly should run smoothly and evenly from low revs to redline with no jerks and misses?
-It's still got the standard twin distributor set up - the first attempt at setup (after a professional carb and distributor rebuild) ran very rich and not at all cleanly above 5000rpm. But it felt good around town and started and idled well.
-Someone else had a go at it... they advised (and did) removing the "second" set of points from each distributor as part of their tuning process. Thoughts on this? I understand these were there for emission reasons. Now it starts and idles OK but is rather jerky and reluctant at 2-3000rpm, runs well from 4-6000rpm but stutters badly 6000 onwards. It has a Tubi on and I get a lot of popping and banging when coming off a hard throttle. This is new after the retune and not necessarily unpleasant - sounds very racerish but may get wearing!
Sorry for the detail..I can expect better can't I if the setup is spot on?
I've looked at some of the threads on alternative ignition setups - is this inevitable?
Thanks for your thoughts |