gas mileage and hot start problems

[TexasRed]

Well, since I got the engine built and in the truck, I've been trying to keep a log of gas, repairs, and other stuff I do to the truck.

My engine: 383 with 9.5:1 or so compression
Isky 264 megacam single pattern .450 lift
vortec heads
long tube headers
Quadrajet built by a reputable shop
700r4 transmission
2.73 rearend (I believe, since it's factory I think)
Airtex electric fuel pump
Holley bypass regulator
AP605
Accel distributor with Jeg's coil and BW module
Edelbrock performer intake

With mostly highway driving, I got like 9mpg. I had a summit racing carb that I was getting around 10 mpg in city. Maybe because I had the vac advance set to manifold and now have it to ported? I figure the gas mileage should be significantly better but maybe a rear end change to say 3.23 or 3.42 would be the best idea?

The other problem I had was that if I let the truck sit for more than 5 to 10 minutes, the engine turns over fine, it just won't fire unless I hold the throttle down some. I thought it was because the fuel was getting hot and vapourizing and the throttle opening allowed fresh air. Then it stumbles for about 20 seconds and then acts normal. I have a one inch plastic spacer under the carb with the 3/16 gasket and then I also have the fuel line going into the carb wrapped with that heat wrap stuff from summit. I also have a bypass regulator so the fuel SHOULD be going back to the tank to cool off. The carburetor seems pretty cool when I shut the motor off when the motor's hot.

I checked plug #1 and it seems ok. There's a little bit of carbon on the insulator along with some tan deposits and there's some carbon on the strap. Doesn't look too bad. But could the pickup coil in the distributor be causing my problems? I doubt the ignition coil is getting too hot, but it could be. I'm thinking of replacing it with a DUI distributor that they curve to my application. It may clear up the exhaust smelling fairly hydrocarbon-y.

Tomorrow I plan to make sure the distributor hold down is clean and make sure the initial timing is 12 degrees and then lock 'er down. Put the can to manifold, reset the idle mixture (2 turns?) and idle speed. I may replace the thermal fan clutch, since I didn't do that when I built the motor as it was fairly newish. I may run a new distributor wire to make sure it's getting a full 12 volts and all the amps it can get. Would a bad alternator cause this? It's an old autozone rebuild for some years ago, maybe it's giving weird voltage out?

Thanks for any thoughts or help.

[Irish_Alley]

im getting 11 with 4.10 and 38s with a sm465. to me a 700r4 and 2.73 is useless do you even reach overdrive with that. I would go with at least 3.42 maybe even 3.73. check your choke make sure its working or open (about the hot start problem) I doubt its anything electrical since it does work you just have to mess with the gas

[TexasRed]

Seem to reach overdrive around 45-50 I think. Seems fairly smooth. I'll check the choke operation but it seemed to open the other day.

[Irish_Alley]

Is your tq converter locking up.

[TexasRed]

Seems to, it's felt like it a few times. I could try driving it in 3rd and seeing if that changes things a bit.

[TexasRed]

Update, I may have found someone to change my rear ratio and possibly put in a limited slip. Question though, my axles are 27 spline right? I can't seem to find rear gear and pinion setup for that but is the 30 spline compatible? I looked at richmond gear's site and it seems they say so??

[Irish_Alley]

I think blazin had a post about this or someone did. Search for it also what rear do you have

[TexasRed]

My rear is pretty stock. Should be the GM 8.5 10 bolt. It looks like randy's gears and richmond list them as the same. I could call randy's but I may do that when I'm ready to start the process of swapping. I need to find out if my coworker is willing to take on the work, cost, etc.

[Irish_Alley]

Yeah I think blaz also had the 10 bolt and if I can remember right the front is one spline count while the rear is another 27 seams right for the rear

[Lt.Del]

i agree w/ Irish in that the hot start problem may not be ignition if you say messing w/ the carb does something.  However, if you aren't sure, simply check for spark when it won't start hot.  That'll narrow down the field as to possible problems.

[TexasRed]

Well as another update of sorts, it seems that maybe I didn't have the bypass regulator setup to low of enough pressure. It may have just been deadheading the pump since the psi never rose enough to trigger the return system. Let it sit for about 15 minutes and she fired right up, a very slight stumble, but nothing really.