another stumbling into secondaries question?

[D111]

my recent cobra purchase has a Rouch 342 motor with a 770 carb 3000 miles , it idols and runs very good until a hard push into secondaries then it stumbles, when it clears its throat it runs like a bear after that. I changed the plugs no difference.

I've searched the threads and it seems like this question has been asked quite a bit but I haven't found much feedback on the resolutions.

Thanks
Dennis

[blykins]

Stumbling is usually the result of a lean condition.

Which carb do you have? Depending on what you're running, there will be different answers.

[D111]

Originally Posted by blykins

Which carb do you have? .

holley 770

[blykins]

Street Avenger?

[bret a ewing]

Vacuum or mechanical?

[Sailfish]

D111,
I have the same engine/carb setup as you (342 Roush/770 Holley) and experienced the same condition you described. I tried many different fixes to the carb, and managed to find a combination that eliminated the worst of it. However, the condition still remained. I contacted Holley and they ultimately replaced the carb at no charge. Holley was decent enough to indicate they had a batch of carbs that experienced the problem. Anyway, after receiving the new carb I bolted it on and the condition was resolved. I would encourage you to contact Holley to see if your carb was one of the problem children.

[STEVE-O]

Have you tried anything related to changing the power valve?

[D111]

it's a vacuum secondary 770

Actual model number is 80770 -- 1

thank you sailfish for the info, my production date seems to be mid-2005 for the carburetor.I will call tomorrow to verify.do you remember when yours was manufactured?

before i came home and read these posts
I called Holley tech support the guy seemed very confident that it needed a stronger secondary spring he recommended that I purchase a 20 - 13 kit. and go one spring stronger

just a footnote when I went into the garage to check the production date of the carburetor it smelled horribly like gas for some reason my gas cap Was over flowing quite a bit onto the paint and onto the floor for some reason. I did fill it up before putting it away last weekend but it did not seem like the gas attendant overfilled it at all??

[mreid]

Not to side track this too much, but that was one of the things I hated about NJ, you can't pump your own gas. Many times they would rather have me do it than screw up and get gas on the paint or worse.

Back on topic. Does your car have a fuel return line to the tank? Is it an electric or mechanical fuel pump?

[D111]

Originally Posted by mreid

Back on topic. Does your car have a fuel return line to the tank? Is it an electric or mechanical fuel pump?

not sure about fuel return line, it has a electric fuel pump.

excuse me for not knowing much about the car, I've only had it barely a month and it's my first cobra .

[jhv48]

I believe you have a Holley Street AVenger carb. Thus, vacuum secondaries, and electric choke.

My Roush came with the same carb, and after futzing with it for a year, I called ProSystems and had them make a double pumper for me. All hesitation and stumbling problems disappeared immediately, and throttle response was vastly improved.

Just keep that in mind, these light cars do not like vacuum secondary carbs very much. And, you are right, it is a momentary lean condition that is causing the stumble. There are only a couple of adjustments you can make to the secondaries, raising the float level, opening sooner and faster or trying a larger secondary jet. You can try a weaker spring, larger main jet or more agressive secondary cam. But, ultimately, you will probably end up selling it and adding a mechanical secondary carb. Not sure why Roush supplies these carbs, but they all seem to have driveability problems right out of the box.

Have fun.

[bret a ewing]

Originally Posted by jhv48

I believe you have a Holley Street AVenger carb. Thus, vacuum secondaries, and electric choke.

My Roush came with the same carb, and after futzing with it for a year, I called ProSystems and had them make a double pumper for me. All hesitation and stumbling problems disappeared immediately, and throttle response was vastly improved.

Just keep that in mind, these light cars do not like vacuum secondary carbs very much. And, you are right, it is a momentary lean condition that is causing the stumble. There are only a couple of adjustments you can make to the secondaries, raising the float level, opening sooner and faster or trying a larger secondary jet. You can try a weaker spring, larger main jet or more agressive secondary cam. But, ultimately, you will probably end up selling it and adding a mechanical secondary carb. Not sure why Roush supplies these carbs, but they all seem to have driveability problems right out of the box.

Have fun.

Yep..........

[mreid]

I agree with Jim that a double pumper on one of these cars is the best solution if you don't have EFI!

Without knowing your set up, it is possible to occasionally have fuel pushed through the fill neck after a recent fill up. Usually this happens with an electric pump, return line, and poor tank vent. Do you have a manual switch for the fuel pump? If so, turn it off just before shutting off the ignition and that should address the problem. You really should map out the fuel line plumbing so you know just what you have. That will make it much easier to troubleshoot in the future. Good luck!

[Sailfish]

D111
I purchased my car new in late August 2007. However, the car was built prior to that (it sat on the dealer floor for a while). My carb. was built around the same time frame as yours.

Some of the "fixes" I tried included changing the secondary spring (installed a weaker spring). I also changed to a larger main jet and a more aggressive secondary cam. In total, all these changes made a big difference, but still didn't completely resolve the issue.

Check with Roush again to validate your carb. is, or is not, one of the affected problem children. I remember they asked me what color paint was on the carb. Turns out they put a drop of paint on the carb. and the color I had was part of a larger group that had known issues ( I don't recall the specific color).

At any rate, the new carb. they supplied was perfect from the get-go. No issues and no problems. Couldn't be happier.

[D111]

Originally Posted by Sailfish

D111

Check with Roush again to validate your carb. is, or is not, one of the affected problem children. I remember they asked me what color paint was on the carb. Turns out they put a drop of paint on the carb. and the color I had was part of a larger group that had known issues ( I don't recall the specific color).

Sailfish,was it Roush that actually replaced the carburetor or Holley?
I haven't yet contacted Roush with the problem.

I called Holley again with the production date they said I would have to send the carburetor in to be evaluated they would either rebuild it or replace it with a brand-new one.

[D111]

Originally Posted by jhv48

it for a year, I called ProSystems and had them make a double pumper for me. All hesitation and stumbling problems disappeared immediately, and throttle response was vastly improved.

Have fun.

Jim
they look like a serious carburetor, may I ask what you paid for yours?

thanks
Dennis

[DAVID GAGNARD]

I've tried to tune a number of Street Avenger carbs,all vac. sec. carbs with the same problem as yours on a number of vehicles including heavy 4x4's to lightweight cars..doing on the little "tricks" helped,but never completely got them right.....
I'd suggest a 650 Holley double pumper for your engine combo, you will not be disappointed.........

For some reason, the vac. sec. Street Avenger carbs I've seen never did run right no matter how much tuning was done on them...
Just my 2 cents on the subject....

David

[jwd]

Originally Posted by D111

it's a vacuum secondary 770
I called Holley tech support the guy seemed very confident that it needed a stronger secondary spring he recommended that I purchase a 20 - 13 kit. and go one spring stronger

He's exactly right. The process for getting the correct spring is to keep going lighter until it stumbles, then go back one spring heavier.

I've tuned dozens of SA Holleys and have never had a problem. For the money, they are the best thing out there. Double pumpers are fine if you're racing but on the street, they suk because that's not what they're designed for. There's a good reason Roush uses the SA.

[jhv48]

Originally Posted by D111

Jim
they look like a serious carburetor, may I ask what you paid for yours?

thanks
Dennis

Dennis,
I think I paid around $670 for the ProSystems carb. My car is purely a street
Car. I went from the 770 street avenger to an 850 ProSystems HP double pumper. What a difference! Instant throttle response! No crapping out on hard cornering! No stumble on throttle tip in! And, my mileage hasn't changed. It's still crappy, but I didn't buy this car for the fuel economy. Patrick at ProSystems knows his stuff. But first, call Roush and see if your carb is on the recall list. Who knows? It's worth a shot before spending any more $$ on your carb.

[Sailfish]

D111
It was Roush I contacted to get the carb. issue resolved (sorry if I indicated Holley). They had me file a Warranty Claim report and then they took it from there. As a side note, I was told that Holley supplied the carb. to Roush and then Roush modified it to suit their needs. I have no way of validating this. Roush was very good at resolving the issue and even followed up with me to ensure it was all ok. Overall, I'm very pleased. Oh yes, the issue cropped up almost immediately after I took possession of the car. I changed the carb. at approx. 4000 miles. I now have over 12000 miles on the car and it couldn't run better.