| Author |
Message |
david schirmer (David)
| | Posted on Monday, January 28, 2002 - 11:27 am: | |
Tony Palladino is a good guy. Works on some pretty hot cars.
http://www.modena-motors.com |
Mitchell Minh Le (Yelcab1)
| | Posted on Sunday, January 27, 2002 - 11:16 pm: | |
Well
I am going to start from scratch because I do not trust the work that was done before me, and I find it most difficult troubleshooting in the middle of a bunch of unknowns.
So, I am going to pull the belts, the camshafts, and the distributors. I will bring the distributors to have them tested for advance. Can anyone recommend a place for this? I live in the Bay Area so there is ... Los Gatos Ferrari, but are there other trust worthy shops?
Second, I am rebuilding all four carburetors again. This time, I hope to do a thorough job and not the half-ass job that was done before I got the car.
I will check the valve adjustments, and compression before I fire her up again. Any other thoughts?
Mitchell |
stacy o'blenes (Stacy)
| | Posted on Sunday, January 27, 2002 - 12:00 pm: | |
Mitchell,
I am trying to figure out a similar problem on my carbureted 78 GTB. I was wondering how the plugs look under the carb you think is rich. Are they wet fouled? I also had a problem with popping misfiring and backfiring. The car also tends to idle a little high when warm (1500rpm). I changed to a breakerless ignition (new coils, wires) which fixed things for a while but the problem came back. The two plugs under the rear left carb were wet fouled, the rest were fine. I changed the plugs and they were immediately getting wet again. Like you I wondered about bad float level or needle valve. I checked these and they were OK. There doesn't seem to be a problem with the choke.
If I figure anything out I will let you know. I did come across this website that talks about fuel dripping from the accelerator pump jets like you mentioned. They say this can be due to a bad accelerator pump membrane. Here is the address.
http://www.themaseraticlub.com/tech.html#Tuning those
The only other thing I can think of is that I might have an oil control problem in those two cylinders (bad valve seals or rings) but the car didn't burn that much oil. It also seems like quite a coincidence that those two cylinders would go bad and the rest are fine.
Any way, good luck and please keep us posted.
Stacy |
Steve Magnusson (91tr)
| | Posted on Sunday, January 27, 2002 - 11:33 am: | |
Mitchell -- IMO fluctuating between 800 RPM and 2000 RPM idle (if a "carb"-related problem) can only be caused by a massive intake tract air "leak" (not some subtle mixture/adjustment wackiness). If carb-related, either some or all of your linkages (throttle plates) are not always closing correctly, or you have a large intermittent vacuum leak somewhere, or the cold idle cam mechanism is wacky...something along those lines. Are you sure it's not an ignition timing problem -- i.e., one of your distributor's advance mechanisms sticking with a lot of advance? |
magoo (Magoo)
| | Posted on Sunday, January 27, 2002 - 12:27 am: | |
Even though you checked the floats you probably still have varnish in the jets,valves, somewhere. |
magoo (Magoo)
| | Posted on Sunday, January 27, 2002 - 12:24 am: | |
Mitchell, You probably have dirt or varnish under the needle valve or valves in the carbs. First I would try and use Techron Fuel system cleaner. Use 2 bottles for high concentration, run engine for at least 15 to 20 mins. and shut down and let sit for overnight. Then try again. It just may fix the problem because that is great stuff. Start with the small potential problems and work to the larger ones. |
Mitchell Minh Le (Yelcab1)
| | Posted on Saturday, January 26, 2002 - 11:42 pm: | |
OK,
I am a little frustrated.
I spent all morning tuning the carbs while the engine is hot, matching the airflows, getting the mixture just right, and setting the idle at 800 rpm.
I took it out for a short drive and as soon as it warms up, it idles at 2000 rpm and runs a little rich, popping alot and back fires when I shut it off.
Tomorrow, I am going to turn the idle down by 1/4 turn, drive it until it's hot, park it in front of the garage and immediately tune the mixture idle screws until the run right, and then stop.
Any other idea??? |
Mitchell Minh Le (Yelcab1)
| | Posted on Saturday, January 26, 2002 - 3:11 pm: | |
You are right, 2000RPM is too high. I drove it last night when it was doing that and the exhaust was glowing red. So, I pulled the top off the forward carbs and check the valve and floats. They are all fine. So I put them back.
I adjusted the carbs again after letting the engine warm up to operating temp. This time I adjust the idle to 800RPM. Adjusted all the mixture screws to get the best RMP with a real tachometer.
Checked all the linkages to see if any thing binds. Got one return spring that seems to have hooked into the wrong place but it was still working alright.
The carbs are still popping, and since it is raining out, I can not take a long drive to test it. So, I will wait for a couple of days.
If it idles high again while I am driving, I am out of ideas.
Mitchell |
'75 308 GT4 (Peter)
| | Posted on Friday, January 25, 2002 - 9:04 pm: | |
The manual states to wait 20~30 sec. while the fuel pump primes the carbs, before starting the engine. I only press the throttle lightly once (or sometimes twice, depends how I "feel" it when it turns over and it doesn't catch) to start the engine running. |
Mitchell Minh Le (Yelcab1)
| | Posted on Friday, January 25, 2002 - 7:14 pm: | |
Peter, I only let it sit for a few seconds, push the pedal 5 times, and start the car. Is there a prefered method? |
'75 308 GT4 (Peter)
| | Posted on Friday, January 25, 2002 - 6:53 pm: | |
Your guess is probably right. The floats could have leaks, therefore will never rise and close the needle valves (fuel then just keeps pouring in and out and over. This could also be giving your that smell we talked about earlier).
When you first start the car, how long do you let it sit with the pump priming the bowls before turning the engine over? |
Richelson (Richelson)
| | Posted on Friday, January 25, 2002 - 9:57 am: | |
I think that 2000 rpm is a little high on the idle. I would set it about 900-1000 rpm. Carb cars will always idle low without the choke when cold. Mine idles at about 500 rpm when cold. After I let it sit for a while and restart it will idle lower too. This is the nature of the carb cars. About the leak, I would look into that. |
Mitchell Minh Le (Yelcab1)
| | Posted on Friday, January 25, 2002 - 9:18 am: | |
I have a difficult (for me) problem to troublshoot and need some ideas. Here is what's going on.
My 75 GT4 idles low when cold with no choke.
After driving for about 10 blocks, it idles at 2000 RPM after that
After stopping for 10 minutes, starts fine, idles low at 500 RPM, then starts to idle high at 2000 RPM soon after that.
When I adjusted the carbs last weekend, I notice that there were some gas dripping into the venturis from over the accelerator pump jets whenever the car was idling high. I do not know where that is coming from. The rear bank runs well, spark plugs are just perfect. The forward bank (where I notice the carbs with dripping gas) runs rich with black deposits on all plugs.
My guesses are:
1. The forward carbs floats / needle valves are worn out leading to flooding in the bowl with some excess fuel dripping over the accelerator pump jets into the venturi.
I will pull off the tops of the 2 forward carburetors and check them. Any other ideas? That seems a long shot. |
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