misfire when hot

Gentleman, and I quote,............. " There is no way a powervalve diaphram can rupture due to a engine backfire ". If the carb has been built after 1992 it should qualify for this statement. Please go to Holley.com and read the correct information and hopefully stop spreading false myth's. Best of luck to all, TR

 

Saddly my carb has the number E1** making it an 81.

 

To the O/P, if you are clearly seeing boiling fuel in the clear filter, I would concentrate my efforts on eliminating the sourse of heat from the fuel system including the pump if mechanical all the way up to and including the float bowls. Remember, you have stated your mis fire is only under load and hot, TR

 

This fuel boiling started all of a sudden ?

Id bet you got some junk stuck in a secondary fuel supply someplace.
Todays fuel is not old fuel system friendly

 

OK, easy repair then to replace the P/V, and convert to blow-out protected. I do see that you are in the U.K., making things a little more difficult to procure parts, I wish you the very best of luck, TR

 

I am thinking fuel, as all the ing system has been changed apart from the rotor arm and dizzy cap.
The fuel pump is in the boot so heat there is not a problem. So you would suggest a thicker spacer and other heat proofing measures for the carb.

 

This car is only running a single fuel line no return. So relatively low pressure Holley red pump in the boot.

 

Easy test for older Holley carbs to test P/V. At idle turn your idle mixture screws all the way IN. { easy with those too LOL }, If your engine dies, the P/V is NOT blown, CHEERS!! TR

Mr Gasket has a simple kit to convert to P/V protected, 720-1511G, all of $6.99 U.S. at Jeggs.com.

I hope this info helps, TR

 

No, not a thicker spacer, but one that covers the underside of the fuel bowls. If you keep spacing the carb upwards and you have a dual plane intake, you will really hurt the performance and efficiency. Look close at my post number 25, the spacer on the left is about 13 inches long to give you a idea, you can make one from say .080" aluminum plate. Be sure to leave room or a small slot for the acclerator pump arm and the secondary opening linkage and you will be fine, TR

 

Thanks for that I will try the idle screws tomorrow. Making sure I count the number of turns in of course.

 

My 60 Chevy was running poor when it got hot as well. I added some heat shield to my fuel line, and I have not had a problem yet -but we still have more Summer to come.

http://www.jegs.com/i/Thermo+Tec/893/17062/10002/-1

Kelvin

 

1 and 1/2 turns out from lightly seated is the starting point. From there final tune them with a vacuum gauge if you have one. Be sure EVERYTHING else from a tune aspect is complete, as the idle mixture screws are last in line to be set. TR

 

You wouldnt be confusing a ping for a misfire would you?

 

That is also something worth a look.

 

This is most definitely a misfire I have not tried it but I bet that if I kept the throttle to the floor when it was doing this it would die.

 

That is why asked the question above. My first thought was power valve as well, ***uming it's a Holley. It sounds like it's going lean...be careful, you could burn a valve. Replace it and let us know...

 

The carb is a motorcraft 2150, but I will get a service kit and power valve from somewhere. As mentioned in one of the posts the Holley power valves are the same.

 

Did the engine run good for more then 1000 miles?You say all of a sudden.
Those engines sometimes the timing chains would jump time.The timing could be off causing it to run hot.

 

What about the secondary spring did you change it...............

 

I had an annoying miss that was very hard to figure out, turned out to be a crack in distributor cap you couldn't hardly see. When car was running at night I lifted hood and the spark was clearly visible thru a very thin crack......maybe?

 

Get your self a spark tester. When it acts up put it on a plug wire at the plug and see how strong the spark is. It should be able to jump 1/2 -3/4 inch [13-19mm].

 

Hay,
I have ordered a dizzy cap, rotor arm and carb service kit.
If the timing chain jumps that would mean the valve timing was out relative to the crank and that would mean bent vales wouldn't it?
Sorry carcrayjohn I do not know which spring you mean.
Fletch

 

If the thing runs fine cold, runs fine on light throttle, and only acts up at operating temp with heavy throttle under load there is nothing mechanically wrong. No need to look for a zebra when you see horse tracks or search for rocking horse ****. A simple compression test would eliminate that and a good practice to do first anyway.

Try this,
Rig up something to the choke ARM that you can work from the cabin. It can be piece of string. Take it for a ride.
When it starts acting up close the choke partially and see if it straightens out.
You will be changing the air fuel ratio by limiting air to keep up with fuel being supplied. What should be happening is the carb increase its fuel because you are increasing air via your foot.

 

I had a 302 that was overheating and when hot it would run bad.
If you have a temp gauge don,t want it over 200 degs.
You raditor maybe not good enought,may need and electric fan with should.
When cold and runs strong i,d say timeing is ok.
Hot is not good.If you are moving at 35mph you shouldn,t be overheating,thats rad problem.

 

Does your ignition have an external control mod or internal? The external control mods were known to go bad and act up when they got hot. If it is the large unit on the fender you can wrap it in a cold wet rag when it starts to act up for a back yard test.

Once when I was in mexico one of the fellas had an '84 Ford truck qwith a 400m. The control mod took a dump in the middle of the night about 150 miles from home. I grabbed a hankerchief off the dash and soaked it in a mud puddle and wrapped the control mod. It would run fine until the wrag would get dry or hot then we would have to soak it again.

Anyway sounds like the control mod. They were the weak link in the ignition.

 

Hi,
Yes I should have done a compression test but I got lazy and a bit disheartened with the car and just did a vac test reasonably stable needle at 19 psi vac. But I will do a comp test. Does anyone know the correct main jet size for this engine set up. It is a 302 with open headers and a 2150 carb. I will try the carb string thing, that 31vicky suggests but are you implying a carb issue? I do not think it is mechanical as I get no smoke on start up or when on throttle. The dizzy timing could be out but I will have to wait until I can take out the rad to static time the engine.

 

I have tried a second ign module with the same results, though for some strange reason car will not run at all with the ballast resistor in line

 

That is because it takes 12V to run your distributer.

Jets will not make it miss when hot. I would not only run a compression test but also a leak down test and do them both hot and cold. Just for comparison's sake.

 

Yes will do a drop test as well.

 

The rad is the one out of the rover and is bigger than the ford so I dont think it is getting too hot. Does not usually get far into the green on the gauge.