OK...I learned a bunch, so I thought I would put it out there for guys going through the same thing.

I have an 86 F350 crew cab dually. I put a 750 cfm Edelbrock carb on that I was impressed with. Then after the reading I did here, I put a set of Edelbrock roller timing gears in and started the debate of setting them to straight up as opposed to 4 degrees retarded, or advancing them 4 degrees (see "Straight up or Advanced").

I did install them 4 degrees advanced, and it immediately was backfiring through the carb pretty bad. I tore into it before I did any damage (that same day) and set them to straight up. I still had a problem with backfiring through the carb though. I mistook this for an ignition problem and replaced the module, disconnected the MSD, replaced the cap-n-rotor/plugs/wires, and finally the whole distribotor, and nothing worked.

I finally figured out it was a carb problem, and found out that advancing the cam timing creates a lean running condition, and that Edelbrock makes the 1411 (750cfm) as lean as it can be out of the box. This is what was causing the backfiring through the carb. I tried advancing the timing as far as I could, but had to remove the distributor back a tooth to get it to advance to about 30 degrees. This helped. I then started installing richer metering rods until the backfire went away.

So to make a long story short, if you are thinking of installing roller timing gears, install them straight up, and be ready to deal with a severe lean condition. Advance the ignition timing as far as you can using the hot start method, and in the case of Edelbrock carbs, be ready to install richer metering rods, or in Holleys, I think you have to change the jets (don't know much about Holleys).

Performance is now fantastic, and I am not smelling any fumes, so I think I am running the carb about right. I haven't had a chance to pull the plugs and look at them yet, but I will.

I hope this helps. I learned a ton about my truck, and performance in general, but am now very happy with how my truck is running.

Good luck

 

If advancing the cam timing creates a lean condition (not enough gas), can I assume that you didn't see a gain in economy?

I want to do the straight up in my EFI 460, but I'm not convinced yet it's all good.

 

Good report.

How much richer did you end up going with on the carb? Did you just do the rods or did you end up having to also change out the jets?

As I remember from the Edelbrock web site they recommend rod or jet changes but, in most cases it is both the rod and jet that they say needs changing to move the enrcihment one way or the other.

Thanks,

Mark

 

I changed the rods only, from .077 x .044 (stock, and the leanest rods they make for the 1411, or the 750 cfm) to .070 x .037. I am following the local speed shop advice, and changing the rods I believe does the same thing as changing the jets in other carbs. The Edelbrock media says to change the metering rods to either make the mixture richer, or leaner, depending on altitude and other factors.

I tried two rod changes in between and each got better, but this seems to be the best. The exhaust is not smelling of fumes, and it runs great.

About economy, I haven't gotten a chance to check it yet, but this is a crew cab dually and only got between 6 and 7 mpg anyway, so fuel mileage isn't too much of a factor for me since I am towing a heavy trailer. Since I had to run so much richer, I doubt if I will see any improvement. I did this for the power, not the economy.

I do see a noticeable improvement in the low end and the smoothness of the power bad. I also notice the engine much smoother at and above 3000 rpm.

With the fuel mixture issues, I would really suggest that you research this on an EFI engine, as I am not sure what a straight up timing set would do to the sensors, computer etc.

I hope all this helps.

 

I'd love to know the answer on the straight up timing for the late EFI'S. It sounds like a good mod if possible with the computer programming.

 

Dan,

I have read a lot of your posts about the straight up or advance of the cam timing. If I am not mistaken, I have read somewhere in one of your other posts that you are in California. If I am correct, I was wondering if you have had a smog test yet with this setup? I have a 87 crewcab with stock 460 and am looking at doing pretty much the same as what you have done so far. I am just curious what kind of trouble I'll have when it comes time for the good ole smog inspection.

Thanks,

Ron

 

Hey Dan: I just pulled the 460 out of my 85 dually today. Set me straight here. Timing gears, center holes and straight up, Edelbrock 750, performer cam and manifold? You did have to run distributor one gear retarded even with the new carb rods? I should be ready for reassemble in about one week (machine time).
Thanks
MT

 

Man I'm glad I found this post. I saw it before a while ago, but couldn't seem to locate it. I put new timing gears on my truck, straight up, and ran it for a while with some adjustment to my old 600 cfm Holley. Couple weeks ago, I bought a 750 cfm Holley and threw her on, and I have some issues. I wonder if they also come lean new out of the box?? I have checked much, even pulled my covers off to double check my timing gear and chain setup, but I am good to go. And to think I put in a new dissy and ignition mod over the last few weeks. Maybe chasing my tail? My question is, assuming everything is in order, except maybe the carb needing adjustment, where should I start? I am much the freshman novice, have none experience with carbs except fine tuning the other Holley. Could somebody make some reccomendations please? Jets? Was your carb backfiring alot George? Just once in a while? New Holleys come with power valve blowout protection, but can I drive her for short trips till my stuff gets in? PLease advise, thanks too, Blair

 

[updated:LAST EDITED ON 16-Dec-02 AT 06:58 PM (EST)]If your carb is backfiring after installing the Holley, you need to change Jets.
The 750 Edelbrock, model 1411 (what I have) comes as lean as they can get it. Stock it will run good, but the straight up timing will lean it out, causing backfiring through the carb. It will most likely pop during lean running conditions, like at freeway speeds with the engine warmed up, not under acceleration, as the acceleration will richen up the mixture. You will notice it get worse in cool damp weather.

I would worry about the power valve, unless they are protected like you said. I don't know much about Holley's or how to work on them, but I would assume that they come pretty lean, especially if they are trying to meet emmissions.

I went with the Edelbrock because I am after low end torque, not a high end racer, and I wanted an easy carb to work on. Holley's are better for High end, and are more difficult to work on.

Let me know if all is OK. Took me a while to figure this out, and I learned a ton!

Good luck

 

All right. Finally got her fired up and I have a question or two. As of right now, I have adjusted nothing except the idle mixture screws and they are at two full turns out. The truck was idling, but a little rough. I cut her off, jumped out and advanced the dissy a little to try and get her a little closer before I brought out the timing light. I restarted her, and right away got a backfire through the carb. I again shut her down, backed the dissy half-way to where I had started from. Restarted truck, and another backfire through the carb. I have done nothing else. It seems as though I will not be able to correctly set the timing without a backfire issue. What do you guys think? Should I be looking into a jet kit? I have done almost everything like Dan has, checked and rechecked, but I haven't enough experience to proceed comfortably. I don't want to mess up my new carb or anything else from the backfiring. If it was super lean, would the carb backfire at idle if I where to try and advance the timing, or is it something else? I must assume from everyone's input, between running straight up, (stock motor), new carb (leaned out), I must need to richen up the carb. How many turns can I go with the idle mix screws before any trouble? Would there be any trouble by having them out a good bit? Will adjusting these bring any relief or is that not enough? Please adivse, many thanks, Blair

 

Tried to run her again. She started and idled rough. I again shut her off and was moving the dissy a little. She seemed just to want to crank. I put the dissy back where I had it, then tried to start, cranked and cranked, she started and then backfired through the exhaust this time. I don't think I'll do anything else until I hear from someone. Please advise. Thanks, Blair