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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Brave man not milk bull... only stupid man

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

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.

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).]

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

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.

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

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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67 RS Convertible, 327/210hp
Granada Gold, deluxe interior (black), 4spd. all stock

Well, I got the spacer on, and the carb is cool all the time. Still crummy response though http://www.camaros.net/forum/frown.gif 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

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?

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.

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-

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).]

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.

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

Breathweapon,

I had this problem with a 355 and 700 DP. Gobs of power when the engine was cold, but became mediocre when warmed up. It turned out that it was running too rich - I had to go down like 6 sizes on the primary and 4 on the secondary. Then it ran fine.

Your engine will love a very rich mixture when cold but will fall on it's face when hot. What do your plugs look like? If they are black you are way too rich. You need a light tan color on the insulator. IMHO Holleys are often way too rich out of the box.

ps. The 750 cfm 4160 I have on my 383 came with 72's in the primary. I'm running 67's now and converted to a 4150 so I could lean out the secondary (72's now on the secondary from 76's)

[This message has been edited by Eric68 (edited 05-02-2001).]

I tried 67 jets the first jet swap, and the same story, but that was before the spacer. Right now I have 70's in it, and along with the spacer, is an improvement. I am also at about 3600 feet, so I think I will try to jet down gradually and monitor the results. Wish me luck, and thanks for the tips. I have the whole jet kit, so that is nice, just a matter of taking the time to do the swaps over and over and over....

Thanks again,
BW

3600 ft means you would want to jet down 2 sizes for altitude alone. Holley recommends 1 jet size for every 2000 ft. I still think you are too rich. What color are your plugs!?!?!

I appreciate the help alright, but there is obviously a reason for the #70 jets in my carb: STOCK JETS=#72... 3600 feet (roughly 4000 feet)= 2 jet sizes down, therefore #70's. See my logic? Same as yours. I will continue to jet down and see what happens. This should be a good learner for others who experience the same thing, if I ever get it figured out, hehe.

L8R,
BW

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Brave man not milk bull... only stupid man

BW,

I was not trying to be pushy on the jets/plug thing - hope I did not come across that way. Just trying to make the point that you don't have to guess on the jets size, you can read the plugs and know if you're rich/lean for sure without ever changing a jet. BTW I keep a couple new plugs around just to have one to stick in when I do a jet change to get a good clean read. You've helped quite a few guys here - just trying to return the favor. Good luck.

Eric

[This message has been edited by Eric68 (edited 05-04-2001).]

Hi..
This whole non-sense about moving jet sizes down based on altitiude from your stock jet is false...
You are assuming that the stock jet sizes would be perfect if a sea-level...
Basically you have NO reference to work from..so you have to start from scratch...
You need to start jetting only the primaries first and not get on the motor..or else testing goes out the window..
CHEERS
Chris

check the gaskets(metering block)i tried those "bunna" gaskets and they worked for awhile but then leaked and it would run like crap. also check the secondary diaphram,is the spring still in there? if not it'll open too soon, i have actualy seen people do this thinking it was going to go alot faster. what color are your plugs? maybe its the distrbuter,control moduel. when they get hot sometimes they crap out,or even the coil. just some sugestions,the 750 being a vacuum carb should self adjust itself for the engine. try throwing it on a buddies car to see if its even the carb. hope you get it fixed soon!!!

Hmm... just noticed something here. The car hesistates when I start it hot, kinda like a weak strter would do. I think I might have the timing a bit too advanced (+8 right now). I may back it off a bit. The vac advance works well too BTW.

As for the jets, I still have the 70's in there. I just need to find the time to try jetting down some more. Initially I thought I was running too lean, but I think it is still too rich now. I will post as to what transpires.

thanks again for the tips,
BW