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Discussion Starter · #1 ·
I picked up my Daytona today f

I picked up my Daytona today from the mechanic. I took it to him for a general tune up. Check timing, adjust carbs, change oil, flush and change coolant, check/clean plugs.... He knows this car very well and rebuilt the engine in it about 15K miles ago.

I took it to him to begin with due to the car running poorly. Upon hard throttle application, in 3d, 4th or 5th gear from a constant cruise, the car would stumble badly and act as if it was being flooded or such before eventually catching and then pulling strong to redline.

The car also has a tendancy to foul its plugs. I have fought this running condition before along with the plug fouling. Once before my mechanic tackled this and the car ran great... but now were back to the same thing.

I will try and describe better the exact nature of the symptoms. The car fires and idles fine. It pulls away from a stop fine, but sudden hard throttle application will induce a stutter. The car under hard throttle will bobble, stutter and act as if its being choked down. Then as it slowly builds revs for a moment it will eventually clear its throat and roar off. But it also fouls plugs. Not the same plugs consistently... but apparently most of them. When the plugs get fouled it will run on 10 or 11 cylinders.

My mechanic says compression tests out good... around 175-180psi and within a 5% variance. I may also test the compression myself over the weekend.

I called him on cell as I was driving home and discussed that the car was still behaving as before I brought it to him. He is going to come out monday and pick the car up, take it back to the shop and tackled it again.

Any ideas on the problem?

As I said, this engine has about 15K miles on it since rebuild. When it was rebuilt, it was balanced and blueprinted, the heads were ported and polished, larger stainless steel valves were installed, factory competition pistons and custom liners were used. It has hot cams, dual MSD ignition boxes. The timing checks out great.

I have not dealved into the car myself due to time constraints. I am building a Porsche RSR vintage racecar and its currently scattered all over the garage, basement and parts of the house. So it has been my top priority relative to my free time.

The issue seems carb related. I would guess something is up with accelerator pumps, main jets or something else that is causing it to dump far too much fuel upon initial throttle application. The car is not burning oil and it does not smoke beyond a very small puff at startup sometimes.

So.... what do you guys think???





Terry
 
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Discussion Starter · #2 ·
I have a similar issue with my

I have a similar issue with my GT4, I have been advised that it may be the timing advance curve (distributor being warn out) or springs gone soft.
Might be worth checking?
Cheers
Nick
 
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Discussion Starter · #3 ·
The timing was just adjusted a

The timing was just adjusted and advance checked. The distributors are properly synched and reaching full advance correctly at 6k rpm. They are only very slightly out of synch at idle. The mechanic just checked this.

I had thought this could be the problem as well, but apparently it is not.

I am thinking carb related. Somehow under acceleration it is dumping way too much fuel down the chokes. How or why? No clue.



Terry
 
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Discussion Starter · #4 ·
Terry,

I wrote a post on th


Terry,

I wrote a post on this subject quite some time ago entitled "What's wrong with my BB"...or something like that. The symptom you descibe is typically caused by a sticking/jammed accel pump discharge valve (in the body of the carb)....and/or a loose accel pump nozzle check valve (at the point of fuel discharge).

Based on your description, I'd place my money on the pump discharge valve....as if it were to stick open, you'd siphon fuel via the pump circuit under all throttle positions....

Carb rebuilds....or just pulling and cleaning this specific jets on the car will solve the problem.

Regards,
David
 
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Discussion Starter · #5 ·
David,

That makes sense and


David,

That makes sense and it sounds very likely. I am really hoping it is just a carb issue and there are no major engine problems!!!

Would you mind if I share you opinion on other boards where I have posted on this problem?




Terry
 
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Discussion Starter · #6 ·
Terry,

No problem sharing t


Terry,

No problem sharing this information with the other board...
Although the BB carbs are different in design than what's on your Daytona (super cool car!), the Weber internals are very similar...

Regards,
David
 
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Discussion Starter · #7 ·
check fuel pressure.
Webers d


check fuel pressure.
Webers don't run well with more than 3.0 psi.

the problems you describe are symptoms of excessive pressure.
 
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Discussion Starter · #8 ·
Sort of simple test, wear saft

Sort of simple test, wear saftey glass's.

With the Air Box Off and the return line attached with an extra hose of course, start the engine and simply let it idle (after the normal blipping to build a little heat) then with a flashlight look down into each carb throat, slowly, both sides and look for "ANY" drips into any Cylinder. After 1 or 2 go rounds with a couple blips, if you see NO DRIPS at idle, shut off the enginge & by hand check all the discharge tubes. There's more but let's not get to fat ahead of the game.
 
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