Cold engine=fine performance. Hot=bad performance - Team Camaro Tech
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post #1 of 23 (permalink) Old Apr 25th, 01, 02:22 PM Thread Starter
 
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Hi all,

I have a bit of a situation here. My car has a 350 with a 4160 Holley on it. When the engine is cold and freshly started it runs great. I can tromp on the gas pedal and the tires light up (no, that isn't the problem, heh). But after a while running and getting hot, it starts to get really sluggish. Eventually after reching normal operating temperature, it will stall when I plant my foot on the gas. I have tried everything from various discharge nozzles to various jets sizes but to no avail. I am beginning to think that the heat itself is the problem. The carb sits right on top of the manifold and it gets hot to the touch. The fuel in it even forces itself out of the squiters in small "pops" when it is this hot. I have managed to get the cold air induction working again, which may help cool things down. Still, I am curious if a spacer between the carb and the manifold will help me with this problem or if I should continue to lean out the mixture. The thing is though, like I say, it just runs great when it is cold, and I don't want to make is so lean that it has to warm up before I drive it. Is this sluggish/stall symptom often associated with a hot carb/fuel?


Any help and advice would be greatly appreciated.
Thanks in advance,
BW

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post #2 of 23 (permalink) Old Apr 25th, 01, 03:05 PM
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You need to inform of the actual temps you are reading..ie. what are you defining as HOT...
What is the thermostat ratting??
What type of radiator??
What type of fan..electric..flex? or clutch?
IS there a fan shroud???
What are the details of the motor...like compression, cam and gearing...
Are you running a trannie cooler, if automatic???? If not, and this is Hi-performance situation..you could cause exceesive heating in the radiator exchange from the trannie..
Going too lean can also cause HEAT...
What jets are you using??
A spacer can help with heat isolation..BUT be carefull to get a spacer with 4 holes..since an open spacer can move the torque up in the power-band..
Is the water/panty-freeze ratio correct in the radiator???
CHEERS
Chris

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post #3 of 23 (permalink) Old Apr 25th, 01, 03:50 PM
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Also describe how your fuel lines are routed, how the fuel is delivered the carb (e.g., electric or mechanical), and where your fuel filters are located.
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post #4 of 23 (permalink) Old Apr 25th, 01, 05:35 PM Thread Starter
 
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Well, the engine is fine. It is where it should be temperature wise. I am referring to the heat that is being transferred to the carb from the engine; The fuel line routing is the same as it was with the q-jet, which had no problems, the rad is ok, coolant... That is all normal. Basically, I know it is in the carb because it ran fine with the q-jet, and nothing else has changed except for the carb swap. Also, I have read that the spacer with 4 holes is better on a dual plane manifold, and then I have also heard that it doesn't matter. Now I see you say an open one is better. I am a bit confused now about spacers, heh.

If I can keep the carb cool, I will likely have a better chance at getting the right jet/squirter combo. I hope a good spacer and the fixed cold-air intake will help with this.

Oh, forgot to mention, I have the whole Holley jet kit, from 64 to 99, and also have 4 different discharge nozzles (25,31,37,40) and I have tried many combinations but still face the same problem when the carb gets hot.

Thanks for the replies, and any further aid would be vastly appreciated.

L8ER,
BW

[This message has been edited by BreathWeapon (edited 04-25-2001).]
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post #5 of 23 (permalink) Old Apr 25th, 01, 10:24 PM
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Well..if the Q-Jet worked before..eah
Does the 4160 have thick gaskets to the manifold???? this may be a heat source.
Sounds like the spacer will be the ticket or possibly your only chance to enjoy the car..
If you are using a dual plane manifold then you would want to retain the dual plane effect with the spacer, so get a spacer with a divider in the middle... If you have an open-plane manifold then it would be good to use a spacer that is open ...actually using a divided spacer with a open-plane mainifold wouldn't be bad either..since majority of the area and volume is shared anyway..
I love the 4150's and Q-Jets equally..and have performance modified Q-Jets for some time...if the Q-Jet is properly modified and set-up it can really be Bad-to-the-Bone!!
What was the casting number for the Q-Jet you were using?? The # should be on the side of the body on the linkage side..and start with 70----- or 170----- ......
Another thing...DO NOT use PCV and feed it into the base of the carb... not only is this anti-performance by diluting the intake charge BUT it can raise the temp of the carb base as well....
Make sure fuel lines are as far away as possible from any headers or exhaust routing..
Also make sure you have a source of FRESH outside air to get to the carb...
CHEERS
Chris

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post #6 of 23 (permalink) Old Apr 26th, 01, 02:36 AM
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Also make sure your floats are set correctly. Mine out of the box were too high causing a rich condition when hot. A cold motor will tolerate richness ( same condition as having a choke on ). Check your fuel pressure too. Holleys will leak past the needle valves if the pressure is over about 8 pounds.
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post #7 of 23 (permalink) Old Apr 26th, 01, 10:33 AM Thread Starter
 
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Great, thanks for the tips gents! I went and got a 1/2 inch spacer with the 4 holes. I WOULD be putting it on right now, but I forgot to get longer bolts while I was out (DOH!). I was also told that when cold, the float level might be fine, but after heating up, the fuel may expand a bit anyway, so I should lower the floats by a hair to make up for this. I will let you know what the results are.... once I get back from the hardware store with some bolts, heh.

L8ER,
BW
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post #8 of 23 (permalink) Old Apr 26th, 01, 12:19 PM
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Breathweapon:
I don't know what kind of exhaust you are using but that may be where your problem is. Don't believe me? If you are running stock exhaust manifolds, your heat riser valve may be going out. I had this problem about 10 years ago. The spring steel in on the valve was worn, so the valve would stay closed, even when the engine was warm. Thus, great cold performance, and it would lose all power once warmed up. It's an easy fix.

Or maybe you have headers, in which this is all mute.

Good luck!

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Granada Gold, deluxe interior (black), 4spd. all stock
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post #9 of 23 (permalink) Old Apr 30th, 01, 01:47 PM Thread Starter
 
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Well, I got the spacer on, and the carb is cool all the time. Still crummy response though I think the carb may just be too big for the engine. I mean, it is a 350 with very few mods, and the carb is a 750 cfm. I think I will just put up with it for the next couple of months until the 400 is finished.

Anyway, thanks for the help!
BW
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post #10 of 23 (permalink) Old May 1st, 01, 03:17 PM
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How about something simple like a misadjusted or sticking choke? I have always heard that you should look for the obvious, simple stuff first. Does this carb have an electric or manual choke?
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post #11 of 23 (permalink) Old May 1st, 01, 09:29 PM Thread Starter
 
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It was electric, but it has been removed. Trust me, I have done the whole 9 yards to this thing, and realistically I think it is just a bit too big for this engine combo.
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post #12 of 23 (permalink) Old May 2nd, 01, 04:56 AM
 
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Well If it is too big it wouldnt run properly at any temp. I am assuming you checked the filters and that the hard line is no where near any exhaust system, also I have had this problem before and Once I ripped it apart and gave it a good rebuild and cleaning it ran great. If it ran ok with the quadrabog, what was the cfm of the old compared to the new? Were ANY lines moved or "adjusted"? check your vacuum lines, One time I had a small crack in the vacuum line and as we all know things Expand when heated. The crack sealed itself cold and opened when hot.. Produced a similar scenario to yours.

Hope these Suggestions help!

-MM-
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post #13 of 23 (permalink) Old May 2nd, 01, 04:58 AM
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I had this exact experience and it turned out I had a vacuum leak. When the car is cold, the engine runs at fast idle and so could overcome this leak. But once the choke came off, it ran horrible. It would die alot on acceleration and when it did run, it was sluggish when warmed up. But cold, it had tons of power. Check the vacuum lead from the distributor to your carb and make sure your new carb is getting the proper vacuum to the distributor. The new carb may be sending too much/too little vacuum to the distributor. Look anywhere else you may feel a leak could come from - spacer, spacer gaskets, PCV hose and connections, anything that you messed with when putting the new carb on.
I guess my thought is that if the Q-Jet worked ok with the current fuel delivery set up and current spacer, there is something wrong with the new carb itself.

[This message has been edited by denverRS/SS (edited 05-02-2001).]
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post #14 of 23 (permalink) Old May 2nd, 01, 06:42 AM
 
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I have had the same problem too. I drove to the race track it was awesome. I did the burnout, staged....then when I planted my foot it fell on its face. After talking to some serious racer guys, I replaced the squirters in the carb. It was like a whole new car. I can spin tires on demand-hot or cold. I went up several numbers. It is a bigger hole so when you give it gas the accelerator pump can pump it all faster. I also replaced the spring (vac secondary holley) with the yellow spring so that it will open much faster. That helped a lot. Good luck shredding the tires while hot too.
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post #15 of 23 (permalink) Old May 2nd, 01, 01:30 PM Thread Starter
 
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Yeah, see the Q-jet was small, like in the 500's. The Holley is 750 cfm, which is considerable larger. At any rate, the carb is brand new, and I am sure it is okay. The engine is just not up to par I think. I mean, it is a '79 engine, and is just getting a bit old. I can still drive the car the way it is, so I am not too worried at the moment. The 400 should be ready in a couple of months, so I will live with it.

Thanks for the help though, much appreciated.

BW
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