[1970fastcat]

A little history on it first. As most know, I haven't had my car on the road long (just broke 300 miles today), only 5 months. Been tweaking on it and working on getting it just right. When the engine gets hot it has issues idling in gear, seems to be even worse in the 90° heat now. I had to turn the idle up to about 1600 just to get it to idle at 900 in gear, which is odd since I have a 3800 rpm converter (it won't even move at idle). I thought it may have been the carb getting hot, so I made a wood spacer this morning, no change. I can tell the carb is cooler than before, but it ran even worse today once hot. Going down the road it seems to run fine, but when I come to a light I have to hold my foot on the gas a little to keep it running sometimes. When the engine is cool, it runs fine, maybe 100 rpm change when I put it in gear.

I also realized that the engine gets pretty warm in this heat too. It got up to about 225° on me in a 20 minute trip, but only climbed at lights. When moving it would slowly drop temp, but go right back up at the next light. I believe I am going to get the Cleveland bypass block off plate and try a Windsor thermostat. I believe that will take care of it. I dont think it is a fan issue because when I got to my destination I let the fans run for maybe 2 minutes and it cooled it back down to under 200°. I think the thermostat "hat" isn't sealing against the bypass plate well.

At any rate, could the 2 be tied together? Or is there an issue with my carb that needs to be addressed? Holley DP by the way.

 

[390XR7]

What type of fuel pump are you running?I had the same problem with my cat ,was running a Holley pump.changed it over to a street/strip Carter and it's been great since.

Terry

 

[cougarshaman]

Fix the heat issue and see what happens. Drive it without the hood tomorrow in the heat and see what happens, if you don't feel like fixing it.
200+F is too hot for a Clevo running a street tune.


The two could and probably are tied together. Fix the heat issue first.

 

[towcat]

Sounds like a vacuum leak at the carb., maybe the throttle shaft is worn. My 2cts

 

[1970fastcat]

The hood was off Andy, still procrastinating on body work before I put it back on. No time for driving today anyway, working on smoking some Memphis style spare ribs for todays festivities, so have to monitor the smoker.

I think my fuel line may be a little close to the exhaust. I will run it to the other side of the frame rail and see if that make a differance. Plus the block off plate and a new thermostat.

The fuel pump is fine, it is a Mallory electric pump, and holds dead on 5 psi.

Carb is good too, as far as I can tell. I just went through it recently and everything was good and tight, thought I do want to upgrade to a Quick Fuel 850.

I will tinker with it in the days to come and report back, thanks guys.

 

[doctordesoto]

i think towcat hit a home run---the other culprit could be the vac advance hooked to manifold vac instead of ported vac---i had a 57 bird with the wrong pcv valve--it was designed to flow the opposite way---causing a 3/8 dia vac leak @ idle
doctordesoto

 

[cougarshaman]

running hot without a hood is major.

I'm doing holiday food duties too, so I'll put my subconcious on it and hit the pork and whiskey this afternoon.

 

[1970fastcat]

I am not running anything off of vacuum, all ports are either capped or plugged. I was also thinking maybe a smaller water pump pulley to speed the water flow up.

 

[1970fastcat]

Well the idling issue is still there.

I re-routed my fuel line away from any heat. Had to wait on some AN couplers to finish it (good thing Summit is next day shipping from me). It was within a half inch of the muffler, not sure how I didn't notice that before. I ran it on the other side of the frame rail/subframe connector and got it away from everything.

Also changed the thermostat to a Windsor type and blocked the bypass. I didn't run it long enough to really tell if it was going to overheat, but didn't get over 190° sitting in the driveway idling.

Either way, I am starting to think towcat and the doc are right. It is slow to return to idle sometimes, but runs just fine going down the road. It runs fine when I am getting it warmed up, and even at normal temp, until I get out of the neighborhood. I guess I am in the market for a new carb, just wish I could afford the one I really want.

 

[towcat]

Still sounds like a vac. leak around the carb, spray some starting fluid around the base, and the throttle shaft on both sides, a little at a time and see if the engine speeds up at some point, if it does, you have found a leak. Keep us informed with what you find, it might help others. PS starting fluid is very combustible.

 

[1970fastcat]

I should have added that the fuel line felt much cooler after moving it. I will try to pick up some carb cleaner tomorrow and play around with it (need to clean the turbo inlet on my truck anyway). I just hate doing that on a nicely painted engine. In fact, I may not even bother with it. I checked the throttle shafts earlier and they do have to play in them.

I could either buy a new baseplate for 150, or just buy the carb I want and not throw the money away on it. Anyone have a good reccomendation on one of the Holley "builders" out there, or should I just stick with Holley? Looks like I need to list a couple of my coins on ebay to fund a new carb now.

 

[towcat]

Everyone has their opinion on Carb's, I like Holley because I understand them and they have a good tech people(at least the ones I have spoken to). Just don't over carb. your engine. Small is sometimes better

 

[Smith Brother]

Amen to DON'T oversize. I have seen too many try a 750, and then find a 600 does a better job. IMO

Dale in Indy

 

[1970fastcat]

According to the CFM calculator on summits website, I can get away with between a 900 and 950 cfm carb for racing. I was thinking 850 since it will be 99% street. I am intrigued buy the Proform 850 race carb. Mostly because it has billet components and upgraded features over a Holley HP. Just not sure if they are any good. They are over 100 bucks less than the Quick Fuel counterpart, which is enticing, but still expensive. http://www.summitracing.com/parts/PRO-67201/

 

[Art]

I have a Proform 750 race carburetor on my racer, no problems!

 

[clanceman427]

Mike have you pulled a plug or two to see if you're rich or lean/get a feel for how the plugs are? Have you verified the float levels? Is it a 4 corner idle carb? Maybe secondaries are open slightly at idle. Obvious things yes and if u already checked them, sorry, but I always seem to see these as the root of problems and they are easy to overlook I'M GUilty myself of it. Fine cold/warming up then problems when hot sound like a rich condition/issue to me.
Kevin

 

[1970fastcat]

The float levels have been checked, rechecked, and checked again. It isn't a 4 corner, just a standard 4777. The secondaries are only opened enough that they don't bind up when closed. The plugs do tell me that it is running rich, but I have adjusted everything multiple times so that it is just right, and it still shows a little black on the plugs. I think it is just time for a new carb. This thing always seemed to blacken the plugs when I ran it way back in the day too, and I have no idea how old or much use it actually has. I got it from a friend for freeeeeeee, so, I am not too concerned about replacing it. I just didn't want to part with any of my valuable coins just yet. Oh well, maybe I can get away with selling just one.

 

[Art]

At what RPM is your advance "full in"?
Or what is the timing at idle?

Sometimes when the bowl screws are tightened too much the main body will warp. When this happens fuel will be drawn from the pump passage (between the metering plate and main body) into the power valve vacuum chamber and be burned in the engine. Rich idle and hesitation.

 

[1970fastcat]

Total advance is 36° at around 3000 rpm, 12° at 1000 rpm idle. I was running it at 16° idle and 34-36 total, then pulled it down to 12° with 30° total to see if that would help anything, but all I did was loose power and the idle thing stayed the same.

I have adjusted the idle mixture screws several times. Always out until it idles its highest, then turn them back in 1/4 turn. Currently they are only out one full turn. I am not getting any hesitation, but it does feel like it is loading up. When it goes into gear after hot, it wants to sputter out, but as soon as I hit the throttle is goes like hell. I almost forgot, I have the power valve blocked off at the moment because I have such low vacuum at idle. It didn't seem to effect the way it ran going down the road though, no flat spot and no hesitations.

 

[Art]

I adjust idle backwards to you, run the idle up approx. 1500rpm, run the screws in until the idle drops off, then back out 1/4-1/2 turn, lower the idle and repeat.
Sounds like a classic case of "big cam Vs. tight converter".
You may can tune the air bleeds for a little better idle, the outboard air bleeds control idle. When the engine is idling if you partially cover the air bleeds with your fingers and the RPM's go up, the air bleeds may be too big. When you partially cover them and the idle gets more ragged and dies they MAY be too small. Proform (probably others) carbs come with replaceable, tunable air bleeds.
With the engine idling, make sure there is no gas dripping from the "mixers" onto the throttle blades.

Was any backyard porting done on the heads? Incorrect porting can kill velocity and low speed performance.