help with carb tuning

worksalot · #1 (**permalink**) 02-09-2002, 08:50 PM

today i spent most of the day rearranging my holley 670 street avenger...here is the problem the car runs great when you accelerate but when you drive along noramlly(city driving)about 1200-2200 rpm the car seems to sputter and choke alot.i replaced the 670 with a holley 600 dual line vac secondary carb from my wifes 65 mustang and it ran like a top through the whole rpm range.the 670 does great "WAO" but does not have what i would call drivability.any ideas??
any help would be appreciated i truly love to enjoy my cobra but this is starting to suck.
thanks john b

JT · #2 (**permalink**) 02-09-2002, 09:47 PM

Did you check (I mean recheck and recheck) the float levels?
Good filters, no ca-ca clogging a jet?
If the 600 worked well, can you use it-can the 670 work on the Mustang?
Are you certain you have a carb problem, not an ignition or other problem?
Carbuerator problems-my life story.
Best of luck with this.

worksalot · #3 (**permalink**) 02-10-2002, 06:01 AM

JT i checked the fuel levels several times.I am pretty certain the problem lies with the 670 carb because the 600 worked flawlessly.I don't think the 670 will work on my wifes mustang because her 302 is not as built up as mine in the cobra.i even went as far as changing out the primary mettering block and float bowl with accelrator pump thinking it might be the problem but alas no help.i just can't imagine that the 70 more cfm would cause the 670 to be to big.the engine is a roller 302 with twisted wedge heads,b303 cam,roller rockers and an edelbrock performer rpm intake with a new proflow air cleaner.
still looking for help
john

CHRIS POTTER · #4 (**permalink**) 02-10-2002, 06:05 AM

Just a shot in the dark. Did you check the power valve? $5.00 part, happened twice on my Cobra, problems similar to your description. Look for the simple stuff first. Good luck!

Roscoe · #5 (**permalink**) 02-10-2002, 09:50 AM

Worksalot,

I am going through the same problem. I recently re-plumbed the gas line (braided Stainless) and relocated my filter and pressure regulator down to the chassis and out of site.

Now my Cobra has been running like a top until now. I have a 650 Speed Demon that was tuned to perfection.

I took it out for the first time since the re-plumbing and I am getting a low speed stumble, sputter, backfiring out of the pipes. Over 2500 rpm it runs like a rocket.

Could not figure it out. Re-tuned the carb. Vacuum gauge says it's right on the money. Floats are fine. I installed a new set of plugs. I disassembled my MSD dist and checked for loosening. Timing is perfect. SO WHAT IS IT?

I had to stop working on it yesterday and will not be able to address it until during the week but I now believe it has to be dirt in the line from the new hose I made. This is the hose that comes out of the filter and runs to the carb. A piece of foreign material must have gotten into the accelerator pump or jets or whatever.

I am going to take off the front float bowl and totally clean and blow it out and then take it for a test run. I am certain that this is the problem.

Roscoe

Roscoe · #6 (**permalink**) 02-15-2002, 01:19 PM

Worksalot,
Just to give you an update, I took off both float bowls and metering blocks and sprayed them down with carb cleaner. Then blew out all the orfices, changed the accelerator pumps and the little diaphrams that go with them, took out the idle mixture screws, etc. I took off the fuel lines that run from the final filter to the carb and blew them out.

I took it out today and it runs fantastically well. Like a new car! Very responsive, no stumble or pipe backfireing. Looks like that was the problem.
Roscoe

CobraEd · #7 (**permalink**) 02-15-2002, 01:25 PM

Rosco, sometimes when you fool around with the fuel line, you dislodge tiny pieces of rubber that flake off the inside of the hose. These get lodged in the float valve and cause flooding at certain speeds. That might be what you experienced.

By the way, you're not allowed to say "Orifice" on Club Cobra!!!

Ed

Roscoe · #8 (**permalink**) 02-15-2002, 01:38 PM

Ed,
Read my earlier post on the thread. I re-plumbed the line and relocated it so I had to make a new stainless braided run from the chassis up the back of the engine to the rear of the carb. Apparently this was the culprit and I got all those pieces of debris in the bowls.

And that's the or·i·fi·cial version!!

Roscoe

worksalot · #9 (**permalink**) 02-15-2002, 05:38 PM

thanks forthe info Roscoe.
I have been messing around with the accel pump linkage and i think it is getting better i should know tomarrow.i'll keep you posted
john b