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Discussion Starter #1
I have not been messing with m

I have not been messing with my 308 for the past couple of months because im trying to finish a HUGE project on my 911S. Full race suspension, exhaust, lightweight body panels and interior blaaaaaa blaaaaa blaaaaaaa

However, Im now compelled to finally finish the 308. Its all back together and runs/drives pretty well.. except for one issue.

It has a maddening and pronounced stutter at certain times. It does not do it in first or second gear at all, only in 3d, 4th and 5th. When I shift into 3d and revs drop back, if I give it full throttle it goes WaaaWaaaaWaaaaWaaaa in rythmic stutters. It feels almost like its not getting steady fuel or spark. Very rapid hesitation. Once revs build back to 5k or more it tends to smooth out and pull hard. Its bad under full throttle. If when I shift to 3d I only give it slight throttle until the revs build and then slowing increase to full throttle, its fine. If I shift to 3d and floor it, its WWHHHAaaaaa WHHhaaaaa Whhaaaaa Whaaaaaa waaaaaaa waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa Maddening!

Im running a Millermon distributor. When installing it, I really thought the mechanical advance appeared to be advancing very little and the "spring" effect seems very weak. Im now wondering if something is indeed not right with the advance? It seems that under hard acceleration in the lower gear, the centrifugal force exerted on the mechanical advance is plenty to ensure it does advance properly, but in the higher gears where it is not advancing as quickly, perhaps the timing is not keeping up with the fuel? I just got a timing light with an advance tester, but have not tried it out. I worry that testing timing and advance without the engine being under load would not reveal the problem outlined above.

I have thought about this being a fuel issue, but if its the carbs how come it runs like a bat out of hell in 1st and 2nd gear. Accerations is really strong in the lower gear all the way to the rev limiter at 7k. Its only the higher gears where the problem is noticed.

I thought that perhaps its related to fuel percolating or vapor lock? In the lower gears the engine is revving faster and thus burning fuel faster, keeping fresh and cool fuel flowing through the lines and bowls. In the higher gear the fuel is moving slower and thus could get hotter? This seems a real stretch.

I keep coming back to the distributor and an advance mechanism problem. Ben Millermon has always been great to deal with.... when you can find him. He is not exactly easy to reach and getting any parts or supplies is always extremely slow.

Ideas? Im planning on spending time on it this weekend. I am signed up for a track day at Road Atlanta on the 23d. Despite working on it all I can, the 911 just isnt going to be ready
If I can get the 308 running sweet, ill put in some super blue fluid, perhaps put some track brake pads in and drive it on the track! Either that or Ill sell it. There is a local Gentleman who is very interested, but I dont want to sell it until Ive had a chance to drive it some with it really running perfectly.

Thanks!

Terry
 
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Discussion Starter #2
Terry,

checking the timing


Terry,

checking the timing without a load will have no effect on readings or how the distrib performs.

Timing advance mech checking is certianly a good place to start and definately something that will need to be ruled in or out. Plus it's easy!

Regards, JRV
 
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Discussion Starter #3
JRV,

If there is some bindi


JRV,

If there is some binding or interference with the centrifugal advance, I was thinking that in lower gears and thus rapidly increasing revs the advance mechanism is turning fast enough to sorta spring past the problem. As slowly increasing revs, it would not have as much momentum and thus is snagging? Theory only here..... Then again I am probably totally in left field.

I am going to start with checking the timing and advance curve. Ill post those results.

Given what I have posted so far.... what would be your initial guess ?

Terry
 
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Discussion Starter #4
Terry,

the torque requirme


Terry,

the torque requirments (power requirements) in the higher gears are so great that problems are greatly magnified.

Checking timing is easy, quick, striaght forward and if it's perfect we can scratch it off the list and move on to other possibilities.

Regards, JRV
 
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Discussion Starter #5
Finally had time to do a quick

Finally had time to do a quick check on timing and advance. I had no other choice but to get my wife to help with the throttle.... so results are only preliminary until I can get some competent help. She doesnt quite understand what "hold that rpm" means. She actually asked me "which pedal" when I told her to press in the throttle.

Anyhow... I have idle set at a pretty consistent 850rpm and timing at 6 degrees before TDC. I am getting advance of about 16 degrees by 1500rpm. Advance progresses slowly to around 20 degrees total at 2800rpm and reaches a maximum of perhaps 34 degrees by 3800 rpm. The wifes inability to hold a steady rpm or apparently to understand english frustrated attempts at more accurate readings!

I am going to test again when I have my father come over to help. I need 3 hands.

I was expecting to see advance of about 35 degrees total and to see full advance around 2500 rpm.

What should I be seeing?

thanks,

Terry
 
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Discussion Starter #6
Hi Terry,

>She actually


Hi Terry,

>She actually asked me "which pedal" when I told her to press in the throttle. <<

that's a good thing, means she'll never be sneaking your Ferraris out when you're not around..{
}


If I'm following along correctly those numbers look correct. you could add a couple degrees on the bottom (idle) to add a couple on the top end.

A couple degrees is not going to cause the problem you are describing. It certianly can get more difficult from here.

The rest of the checks and tuning is best done with the air cleaner off.

Once certian it's not timing advance and all plugs are fine and engine is in fact running on 8 cylnders a check items list would go something like this:

1- No intake vacum leaks

2- Fuel Pump Pressure

3- Accelerator Pumps are fine as noted by observing Acc.Pump Nozzle Spray quanities.

4- Throttle Linkages actuate all 4 carbs at exact same time, and that full throttle is actually achieved.

5- Float Levels are correct

6- All 8 idle circuits are clean and functioning correctly

It's hard for me to pick a most likely from the above list after timing. Truly it could be one of the above or a combination of more than one that causes an engine to fall off in the mid range.

Once you pull the air cleaner housing you might be able to check the timing yourself by carefully pulling the throttle cable. Although the relative positions do make one man timing checks a PITB.

HTH's

Regards, JRV
 
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Discussion Starter #7
#2 seems unlikely since the pr

#2 seems unlikely since the problem disappears at higher rpms, even under hard throttle.

I could easily see #3 or #6 being the problem. The carbs sat for 6 months with no fuel in them while I was doing all sorts of stuff. I'll start at the top and figure it out.

Thanks!
 
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