New member with a question!

[mhoneycutt85]

Hey everyone,

First off, I wanted to say how happy I am that I have found a forum where I can talk to other 67-72 truck lovers. Now, I have a few questions about my 70 c-10. I have been working on this truck for a few years now and have just gotten it out of the shop where I had a friend finish putting in a motor for me. My question pertains to ignition timing. My truck has a 454 HO that has a mild cam and an Edelbrock 750 cfm carb. I am having the hardest time setting the ignition time in this truck. I have a timing light and have tried to set it multiple places between 4 and 8 but I am still experiencing carb spitting. Every time I advance the time on the truck it begins to fire back through the carb. I live far away because of school now and it is not really an option for me to take this issue back up with my friend. Unfortunately, I am not sure about any of the specs on the cam, but I do know that I cant get any type of even sound from the exhaust. The idle sounds best around 8 degrees BTDC. I have also leaned back the carb and slowly adjusted the screws to help even out. I am concerned there is something wrong with the valves but am hoping there is something I am missing. Any help would be great. Thanks again for the read and assistance in advance!

Mike

[60ratrod]

first off are you checking the timing with the vacuum advance disconnected? backfires through the carb is usually in my experience the timing is too retarded or you are possibly too lean. but i would bring the motor back to tdc(compression stroke with both valves closed) and see where the rotor is facing on the distributor. once you have verified that you are sitting at #1 on the distributor at tdc next i would check the firing order. i'm not a bbc guy so i don't know the firing order. once you have verified all of this i would then look into checking for vacuum leaks at the base of the carb, around the perimeter of the intake, and around any vacuum hoses and vacuum fittings screwed directly into the intake with either some starting fluid or carb cleaner, or with a vacuum gauge connected to full manifold vacuum. you are going to be looking for changes in rpm with the carb cleaner/starting fluid, and fluctuations with the needle on the vacuum gauge. and i would reset the idle screws back to the factory setting before going any further. once you get it to run without any backfires or anything like that then i would look into tuning the carb. you should also download/print off the edelbrock owner's manual. it has tables, charts and guides to help with tuning the carb, as well as trouble shooting tips. here's the links for the owner's manual and vacuum gauge reference:

http://www.edelbrock.com/automotive_...ers_manual.pdf

http://www.classictruckshop.com/club...ts/vac/uum.htm

[mhoneycutt85]

Thanks so much for the reply. I am going to take a look at the information you sent over to me and have another go at it. Thanks again.