| Author |
Message |
Hans E. Hansen (4re_gt4)
New member
Username: 4re_gt4
Post Number: 18
Registered: 4-2002
| | Posted on Wednesday, May 08, 2002 - 7:05 pm: | |
Don't bother with Ebay for the Haynes book. It's still in print, and I recently got one from a local parts store for $13.00 |
Bill Sebestyen (Bill308)
Junior Member
Username: Bill308
Post Number: 219
Registered: 5-2001
| | Posted on Wednesday, May 08, 2002 - 6:04 pm: | |
Andrew,
Backfiring through the carbs, is normal after startup on a 308. After warm up, the back firing should stop. This is commonly caused by a slightly lean mixture when cold, that becomes acceptable and probably desirable when warm.
Backfiring from the exhaust is a different animal imho. Backfiring could be caused by an overly rich mixture, faulty carb balance, a malfunctioning emission system, incorrect ignition timing, bad plug wires, and other factors.
I think you're going to have to go through a systematic process of elimination.
Did you ask the shop what they adjusted?
Check the ignition timing of both banks with respect to initial advance at idle, total advance, and smoothness of advance with respect to rpm.
Check that all emissions systems are properly hooked up, if fitted, and functioning properly, especially the air injection system.
Ensure that the cam timing is correct. Marks on the cam and cam bearing caps must align properly, with the engine set at TDC, on the compression stroke, for the number one cylinder.
If all this checks out, now you can begin adjusting the carbs. To perform this properly, you need at least one air flow meter. The best one I've used is a Synchrometer model BK available from Superformance in the UK for 23.5 BP (about $35).
http://www.superformance.co.uk/download/Special%20Offer%20Vacuum%20Gauge.PDF
You will likely need to balance your carbs and the Synchrometer is an essential tool. Better yet, get a matched pair, so you always have a "control or reference meter" to match, while you move the second meter from barrel to barrel.
The basic steps are:
1. Get the engine good and hot.
2. Set and maintain idle at 900-1100 rpm
3. Adjust the balance at idle.
4. Adjust the balance, at the linkage, at part throttle, or about 1600 rpm.
5. Adjust the mixtures for each barrel at idle 900-1100 rpm.
6. Set the idle speed to 900-1100 rpm.
A reasonable manual for DCNF's is the Haynes, "Weber Carburators Owners Workshop Manual", that is sometimes available on ebay. This manual has photos and step-by-step instructions for rebuilding your carbs.
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andrew amsden (Ajax308)
New member
Username: Ajax308
Post Number: 8
Registered: 9-2001
| | Posted on Wednesday, May 08, 2002 - 4:45 pm: | |
Thanks! Back fires are coming through the exhaust, i'm pretty sure. What does that tell me?
I really appreciate your feedback and help!! I've worked on carbs on other cars (xke's) is there something like a workshop manual that could help me through?
Thanks
andy |
Terry Springer (Tspringer)
Junior Member
Username: Tspringer
Post Number: 58
Registered: 4-2002
| | Posted on Tuesday, May 07, 2002 - 8:30 pm: | |
I dont know him personally, but he is doing the pre-purchase inspection on a 308GTB I am looking to purchase that is in Scottsdale. He comes highly recommended.
Dwayne Samuel at SST Racing 623-776-1994
He has apparently worked on Ferraris for over 30 years including many race cars. Based in Phoenix. The guys from Italian Design say he is great and does all of their engine work. When I spoke with him he seemed to know what he was talking about.
I agree the car is running lean, that would hit all the symptoms you describe. Should be fine after someone who knows sets it up correctly.
By any chance do you know a guy named Ashley Key? I am looking at buying a Dino Blue '77 GTB from him. |
Bill Sebestyen (Bill308)
Junior Member
Username: Bill308
Post Number: 218
Registered: 5-2001
| | Posted on Tuesday, May 07, 2002 - 7:14 pm: | |
I concur with Greg. Does this shop know its way around DCNF's? You might want to ask them exactly what they did.
Is the back firing coming from the exhaust or back through the carbs?
If the ignition timing is correct and they didn't touch valve lash and cam timing, I think you need to rebalance the carbs, then set the mixtures.
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Greg Rodgers (Joechristmas)
Member
Username: Joechristmas
Post Number: 284
Registered: 3-2001
| | Posted on Tuesday, May 07, 2002 - 6:22 pm: | |
It sounds like since they tuned your carbs to pass emissions that they leaned them out. The car is probably not firing on all 8 cylinders. Is it a loud backfire every 5 secs. or so, or is it small popping? Did they only mess with the carbs. Your head gasket should be fine. The car didn't over heat did it? I would pull a plug wire at a time with the engine running to see which cylinders aren't firing. I don't think that you need a compression test at this point as the car was running just fine before the adjustments. |
andrew amsden (Ajax308)
New member
Username: Ajax308
Post Number: 7
Registered: 9-2001
| | Posted on Tuesday, May 07, 2002 - 5:51 pm: | |
You guys have heard the tune before. I live in Phoenix and there is not a decent mechanic that won't screw me, if you own a ferrari in Phoenix you better work on it yourself. I got my car back from a simple emissions adjustment (carbs) and the car is now losing power once I get to a decent running temp. It's been backfiring overall is running pretty crappy. Before I dropped it off it had been running fine. Where should I start, Would a compression test and vacum test be the first step, does anyone know a mechanic in Phoenix that really is honest? I rebuilt the carbs 2000 miles ago, Had a major tuneup and top engine rebuilt 3000 miles ago but they were done buy Southwest European (FBI busted them in December!) My points and dist cap are great, even made a new harness for plugs..Does it sound like a head gasket or ? |
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