| auxiliary fuel pump/idle screws/choke slop [message #265274] |
Sun, 02 November 2014 04:55  |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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I finally got my 455 to run better and start easier cold (yesterday 35 degrees) and basically had many trials and errors on the way. I decided to drop my timing to 8-10 degrees TDC and start over on the idle screws. I barely seated the screws and went 2.5 turns. I also leaned out the carburetor 2.5 hash marks from the original setting. My plugs were getting slightly fouled out. After that I could see that the carburetor was still getting a bit wet on the upper gasket. My float is fine. My vapor canister is still not hooked up. My pooping noise in the carburetor is gone. Too much fuel pressure. They say a plugged canister/vapor line can increase the pump pressure a few pounds. Anyway, I decided to try something and I unplugged the connection for the auxiliary fuel pump and see if the coach ran better and it did. No more super saturated upper gasket on the carburetor. I did as Dick Paterson said and slowly turned my idle screws until my vacuum increased and steady out without dropping. I went 1 full turn each. I know my methods are not conventional but I have my coach running normal at 18 inches of steady vacuum and choke basically fully engaged when warm, 8-10 degrees TDC at idle and my RPMS are at 625 or so. I have yet to check my advanced timing as I throttle the engine. I know the concept of that at least till I get to the 16-20 degree mark. I might redo my plugs from .45 to .40. Still need to inspect the plugs. So in order to get my carburetor to function good I had to decrease my fuel pressure (float was tested for 1/2 hr on pump at 4lbs pressure from rebuild guy)and I had to open my idle screws 1 full turn past 2.5 and lean out the gas/air mixture. After all that it started fairly easily at 35 degrees outside on a cold start. I hope to replace two mufflers next Spring. I have one off right now. Oil has been changed and hoping for the best. Thanks to all for the input.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: auxiliary fuel pump/idle screws/choke slop [message #265313 is a reply to message #265274] |
Sun, 02 November 2014 17:53  |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Senior Member |
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Good to hear.
Not sure If someone mentioned checking the carb float...if the Qjet floats get scratched they will soak up fuel and lose boyancy.
Q Jets dont like a lot of fuel pressure even when working right.
76 Glenbrook
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| Re: auxiliary fuel pump/idle screws/choke slop [message #265398 is a reply to message #265274] |
Mon, 03 November 2014 20:57 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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The idle mixture screws are in the circuit during a very narrow rpm range. The best procedure is to back them way out and then slowly turn them in until you notice an idle roughness or a decrease in engine rpm. At that point, turn them out at least 1 turn. Unless you are worried about emissions, set them for the best idle quality. Above idle, they do nothing and have no effect on overall engine performance. They will not affect cold startup at all untill the choke starts to come off. At thet point it is all about idle quality and smoothness. You will find that if you open them up past the point where idle gets unstable, you can open them multiple turns without affecting how smooth it runs. Some spitting in the carb throat is normal
Bob de Kruyff
78 Eleganza
Chandler, AZ
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