Slant running poor on HOT days.

[cudajim]

My 225 stock slant six runs and idles really well and strong most of the time except when it's really hot outside (over 90 degrees F). When it is hot it idles rough and sometimes it will stall but otherwise runs great. The carb has been rebuilt and has a new float too. I'm also running an orange box for ignition and it's in a 67 Notchback Barracuda. Any ideas to fix this would be appreciated.

 

[RustyRatRod]

Probably a fuel percolation issue. You need to either insulate or isolate the fuel line from heat. It would also not hurt to install a heat shield under the carburetor.

 

[cudajim]

Probably a fuel percolation issue. You need to either insulate or isolate the fuel line from heat. It would also not hurt to install a heat shield under the carburetor.

I should probably clarify, it runs poor on hot days mostly when the engine is cold and warming up.

 

[Woods74]

Whens the last time you tuned that carb?

Here, look at this, the basics are there:

http://www.forabodiesonly.com/mopar/showthread.php?t=73834

 

[Abodybomber]

Probably a fuel percolation issue. You need to either insulate or isolate the fuel line from heat. It would also not hurt to install a heat shield under the carburetor.

Yep,my 72 did the same. Following this idea,problem solved.

 

[nm9stheham]

I should probably clarify, it runs poor on hot days mostly when the engine is cold and warming up.

Heat percolation does not seem to be the issue if the engine is having problesm when warming up....??? Another possibililty: It may be choking too rich in the warmer weather. Does it have the 'heatwell' type of choke control (not electric)? (This is where the small rod to the choke plate goes to a metal 'lump' bolted to the manifold. ) If so, remove the 2 bolts and pull the choke spring assy out of the heat well and see if it has a small nut on the side with a round plate with several small marks, with L (Lean) at one end and R (Rich) at the other end of the marks. Loosen the nut and move the pointer so it is closer to L to lean out your choke for summer operation, and tighten the nut and re-intstall. Reverse in late fall to enrich the choke.

I just leaned out my '62's choke for summer and it idles much better for the summer weather.

 

[cudajim]

I'll check it out this weekend with a vacumn gauge.

 

[TrailBeast]

Easy test.
What does the exhaust residue in the pipe look like?
Bet it's black.
(Running rich to start with, hot days, choke part way on, and not coming off fast enough.)

 

[nm9stheham]

But check the exhaust pipe color a few mintues after starting; if checked after a long drive, it will show the rich/lean situation of the cruise conditions, not the start-up condition.

 

[TrailBeast]

But check the exhaust pipe color a few mintues after starting; if checked after a long drive, it will show the rich/lean situation of the cruise conditions, not the start-up condition.

Couldn't hurt, but I'm bettin it's rich all the time anyway.

 

[nm9stheham]

^^^ I would not be shocked either!

 

[BillGrissom]

Probably something with the choke. Test the "vacuum choke pull-off" at the top of the carb. If you don't have a hand vacuum pump to test it, pull the hose, push it in, cover the vacuum tube w/ your finger and see if it stays in. Its job is to pop the choke open slightly the second the engine fires.

If not working, you have to keep adjusting the choke between summer and winter, like I used to do with my 69 slant in my dumF kid days. I didn't know what the choke pull-off was or how to test it. I was so gomer then that I thought the Holley 1920 was complicated. Of course we didn't have the internet like today where all info is a few clicks away.

 

[cudajim]

Yea, I'll take another look at the choke too. Last time I checked though it was working just fine as was the vacumn pull-off.

 

[Ben Drinkin]

Any clue where one would find an under-carb heat shield for a /6 1barrel? a quicksearch for p/n 5214 558 didn't get me far..

 

[RustyRatRod]

Make one.

 

[Ben Drinkin]

3/16th alum plate and a couple gaskets? Is it that simple??

 

[RustyRatRod]

Yeah I guess you could go that thick. It will insulate like a big dawg.

 

[Ben Drinkin]

Thanks RRR. That just happens to be what I have.

 

[pishta]

You can make it out of delrin or other high heat plastic or get a real thick gasket like the TQ's run. The AL heats up pretty good itself. Choke adjustment is free.

 

[cudajim]

Ok so here's an update. I finally had time to pop the hood and take a look at the carb. Turns out there was a split in one of the large vacumn ports I had blocked off. I replaced it with a new one and lo & behold it ran much better! In fact it ran so good It felt like a new motor. I did richen up the idle screw just a tad but everything else was ok. Thank you all for your responses.