help me understand why

[69chargerdad]

Hi were back again with yet another issue. When we initially cold start the engine it will run poorly and backfire until it reaches 180 degrees or so. What could cause this? When the engine warms up everything seems to be running properly. We are running a freshly rebuilt 440 with moderate hyd cam. the comp cam specs out at .525 of lift and 237 duration at .5 lift which is reasonably low duration. The ignition is mp electronic conversion kit and initial timing was set at 14 degrees. We are also running a new 750 demon with vacuum secondaries. When the engine warms up everything runs smoothly however it runs so poorly upon start up it will die if I am to put it into drive. Also the engine starts almost immediately but when we try to get the r's up a little and smooth out the idle it nearly dies. Any help would be greatly appreciated.

The current temperature here is 40 to 50 degrees and we have an electric choke

thanks Marcus

[golden73]

My engine did the same thing.

I am not positive this is the reason why, but I will take a stab at it anyway. Your engine is made up of many different types of metals, some will expand faster than others. But after the engine is at operating temperature, all the metals have expanded to give all the correct clearances, and tolerances. Therefore; the engine would run smoothely.

Again, I am not positive that is the reason. But that is what I believe it is.

[dodge freak]

I run a holley hp 750 with no choke, my engine will idle not smooth but idle without dieing even after 20-30 seconds when I first start it. When I step on the gas it runs fine so its not the metal doesn't fit right. If you know the intake gasket has no leaks and sometimes the only way is to do it yourself with a very good gasket like fel-pro printoseal and a little  bit of high-tack the aerosol type around the ports, I use something  like that but its made for airplanes but high- tack by permatex is what most places have . Then I would jet up 1 or 2 jet sizes and see if gets better. It may or may not, might be a weak spark at the spark plugs or even both. Might even be a bad valve in the head but that is not to likely. You could do a leak down test  to make sure. 440 is a big motor the carb might be jetted for a 350 so I would jet up the carb first if you know the intake manifold has no leaks.

[dodge freak]

Oh the piston rings might be leaking bad when cold also that leak down test will show it just do it hot and cold. Man its hard to firgure out without being there ,sorry

[deputycrawford]

Try looking for a vacum leak. Sounds like a common symptom of the carb base. Use a small propane torch that is not lit. Turn it on with the engine running and run the torch all over the carb base and intake area. You might be surprized there is a leak there that clears up when the engine is at full temp. The engine will rev up where you find the leak. Don't ask me how I know.....LOL

[Chryco Psycho]

the engine is running too lean with the choke , the choke should be adjustable to make it richer when cold 

[is_it_EVER_done?]

I agree with Chryco. Also coupled with the lean condition, your plugs are probably about one step too cold, but if your happy with fully warmed operation, just adjust your choke to stay on longer.

[Plumcrazy]

the engine is running too lean with the choke , the choke should be adjustable to make it richer when cold 

  Richen the choke.

[TylerCharger69]

I dunno,  but it sure sounds like a choke issue to me....I went with a manual choke cable on mine, and it works great!!   Sounds to me like the choke isn't engaging enough during start-up and the first few minutes afterward......That's where I'd start.....

[dodge freak]

my carb. does not have a choke so I did not think of that. Yes if it runs fine when hot I agree maybe its opening up to fast.

[TylerCharger69]

no choke at all?...well....im going to take an educated guess and assume that's where the problem lies.  Some prefer an electric choke, some prefer the stock choke that gathers heat from the intake....and I prefer a cable choke.   My own personal theory is.....the less electrical bs  to deal with...the better....Hell....I even tore out my heater and a/c completely  just to do away with excess wiring  and power robbing components....lol  (I'm not saying that's what you should do...lol)   They are just preferences, but  if you want factory appearance...go with the heat transfer choke assembly!!!

[dodge freak]

Dear TylerCharge ,I was not the one who posted the problem. I reply to it earlier and said maybe he should jet the carb, up 1 or 2 jet sizes. I forgot that carb. came with a choke and it might be opening to soon. Maybe its both he says it runs fine when it is hot but if he went up 1 jet size it might run even better or maybe not. My hp carb. came with no choke and has a different type  of idle feed circuit in the metering block. It idles ok   rough but ok until it warms up in 3-5 min. I don't have a demon carb. so maybe I should have not said anything but I have been working with holley carbs. for 25 years so I though I would reply. Sorry if I confused anybody.

[TylerCharger69]

lol....no problem...i should of realized it wasn't you who originally posted...it was easy to get confused though...lol....my bad

[deputycrawford]

I guess my post could have been way off. My Mighty Demon carg has no choke and starts fine even when its 40 degrees out. No lean pop, hesitation or anything. I hope its just a choke adjustment. When I first started my rebuilt 383 I had an Edelbrock carb on it and didn't have it tight enough. It caused the same problem. It went away when it warmed up. Just thought I'd give my two cents.

[TylerCharger69]

Well....in my opinion....in this forum...everybodys 2 cents helps!!!

[69chargerdad]

     



  I  adjusted the choke  richen it up a bit   starts and runs great  thanks guys           ken

[Chryco Psycho]

Great !