Rebuilt 350 - Abysmal Fuel Econ

[Nalanthi]

I like that zip tie idea. I have a whole pack from HF, so I might as well tidy up a bit although I really need to get new wires anyway.

It's gonna be a week or two - tight budget the first part of July.

So long as engine stops overeating (TBD this week), I'll tackle a bit at a time. I honestly did not know that the heater core was vital to operations.

Here's to hoping that a regap, and most importantly routing the return line will make it daily drivable. Next weekend will be 'gear ratio assessment weekend'.

 

[MadOgre]

So it was over heating ? Carburetors don't like to much heat. You also need to try and keep your fuel lines as cool as possible. so away from the headers but not to close to the block either. Make sure your exhaust is not to close to the frame rail where your fuel lines run from the tank.

 

[MadOgre]

OH I ALWAYS spend the couple extra dollars and use the fail safe thermostats. I cooked a motor once by starting it and walking away. The damn thermostat never opened and when I came back my engine was cooked.

 

[Driver4r]

Nope, But I'm going to make a set for my R30, first saw them on Roadkill.

The Rotsun.

 

[Nalanthi]

Ogre,

It actually isn't overheating.
I only overheated it once back when I was piecing everything together and realized that the JY sold me a fan blade/clutch from a serpantine setup.

She sits around 200 normally.

One thing that I find slightly alarming is that upon regapping my plugs, #s 2, 4, and 5 were showing signs of oil on the plugs. I haven't had a chance to recheck compression, but after the initial startup/drive when this was first built... compression appeared to be fine in all cylinders. I wonder if the rings didn't seal up completely on those yet, considering <100 miles on this build.
Edit: Checked oil again - still no fuel in oil, so that's good.

 

[MadOgre]

Ogre,

It actually isn't overheating.
I only overheated it once back when I was piecing everything together and realized that the JY sold me a fan blade/clutch from a serpantine setup.

She sits around 200 normally.

One thing that I find slightly alarming is that upon regapping my plugs, #s 2, 4, and 5 were showing signs of oil on the plugs. I haven't had a chance to recheck compression, but after the initial startup/drive when this was first built... compression appeared to be fine in all cylinders. I wonder if the rings didn't seal up completely on those yet, considering <100 miles on this build.
Edit: Checked oil again - still no fuel in oil, so that's good.

Ok Good.

If you were not getting good spark it would be expected that they would be fouling.

100 m ? That's not much mileage on a new motor. I hope your not letting it idle ? Did you break it in properly ?

 

[Irishman999]

IM all about timing lights and doing stuff right but a friend of mine showed me a cool trick for setting your timing. I wont do it to anything with TBI but give it a shot. Just retard the timing until the engine slows down and the carb sounds like sucking through a straw, then just advance it a smidge.

Pull the top of that carb off and check the float adjustment, try bending the tabs up a little bit. Also go get some Lucas oils break in additive for your break in, I swear that stuff is the ****.

Im at a loss of words here, Im getting nearly three times your mileage out of a truck with a big block and a 3.73 rear end. Back when I was daily driving my 85 I was running the same carb as you on a 305 and somehow managed 17 MPG on a trip from Springerville Arizona to Tuscon, it always averaged around 15 though. I cant help but feel like there is a bigger problem not related to the engine, if its not running like complete **** I would start checking stuff like brake shoes dragging or hung up calipers. Does the truck roll freely?

 

[Nalanthi]

Ogre, I went through the usual break-in procedure, then varied driving.

Irishman, It's not running like complete **** - granted that it's a near stock early 70s 350 (which are generally ****** and underpowered anyway). It won't peel out, but it'll get up and go. It will also roll when taken out of gear without any hangups or sounds. Back when I first got it, I tore into the hubs to check everything and it was all greased up and looked fine to me. We're both at a loss for words, because I got that K5 I mentioned earlier tuned and running like a champ. I will agree that it may not be the engine on this point, but with no leaks or anything else immediately suspect...

As stated earlier, I have not yet had a chance to check the gear ratio, but it shouldn't be too high to run 31s.

I'm going to recheck drag/roll again now that you mention it. I understand that this can be a detriment - but could it be a major detriment?
Maybe this 'other' reason is probably the same reason that the original inline 6 sucked as well with 6MPG...

 

[Irishman999]

Ogre, I went through the usual break-in procedure, then varied driving.

Irishman, It's not running like complete **** - granted that it's a near stock early 70s 350 (which are generally ****** and underpowered anyway). It won't peel out, but it'll get up and go. It will also roll when taken out of gear without any hangups or sounds. Back when I first got it, I tore into the hubs to check everything and it was all greased up and looked fine to me. We're both at a loss for words, because I got that K5 I mentioned earlier tuned and running like a champ. I will agree that it may not be the engine on this point, but with no leaks or anything else immediately suspect...

As stated earlier, I have not yet had a chance to check the gear ratio, but it shouldn't be too high to run 31s.

I'm going to recheck drag/roll again now that you mention it. I understand that this can be a detriment - but could it be a major detriment?
Maybe this 'other' reason is probably the same reason that the original inline 6 sucked as well with 6MPG...

Its always some dumb **** that leads to the moment of figuring something out you dont want to tell your friends about. Case in point here, the big block I put together had a bad ticking sometimes knocking sound. It kept me up at night knowing I screwed up somewhere and my engine was on its way out because I am a *******. Turned out to be a loose bolt on the crank pulley with a washer rattling around on the shoulder. Pulled the bolt out and the noise is completely gone.

I hope you have a moment like that.

 

[Nalanthi]

That's what a fat chick and a moped have in common: both fun to ride until your friends find out.

I need to check the rear drums, as I haven't pulled 'em yet and I know damn well that my e-brake is gone. It never worked since I brought the truck home.

Facepalm scenarios - I live for those.

 

[rich weyand]

Any mileage numbers since hooking up the fuel vent line?

I forget: Did you check the float levels in the carb?

This one has me scratching my head. The fuel is going SOMEWHERE!

My most recent facepalm was due to the distributor rotating retarded because it was not bolted down tightly. And I don't think it was me. I think the last time the garage did some heavy work for me, they had it just snug enough that they could adjust it by putting some effort into it, and then neglected the final step of tightening it down. Performance gradually went to hell, and it took me a while to find it, because I KNEW the timing was OK, and so didn't check it.

 

[MadOgre]

Well I guess one other thing is that these fuel tanks are notorious for rusting a leak.

But definitely need to address those heater hoses.

 

[MadOgre]

Are those 202 heads by any chance ?

 

[Nalanthi]

I haven't gassed up yet to see if hooking up the return line helped matters.
The floats are fine - I didn't even bother with 'em. Short story: When building that K5, I was retarded and put the carb on right out of the box which gave way to a flooding condition. Upon popping the top, I noticed that one of the floats was way high - came that way from the factory. After bending and measuring, everything was fine.

Therefore, I can verify a good float level, having been there already with this unit.

The dist. is good n snug. I did yet a THIRD time check/vac check and everything looked fine.


I think Irishman is going somewhere with his thoughts on it... as I think (and stated) - why would I have been getting ****** econ on the old inline - and why on two different carbs on a freshly rebuilt engine that isn't giving the vac gauge symptoms of having internal problems? I'm sitting here questioning my build and am starting to think - maybe that's not the case. Maybe my build is fine and my own doubts are keeping me from thinking outside of the proverbial box.

I wonder - what if? Since I never yanked the rear drums (something I really should have done when I picked this truck up back in March) - what if? It doesn't feel/sound like dragging, and the truck rolls on its own. I wonder if there could be enough dragging to let it roll, but kill that much fuel?

It sure doesn't smell like it's burning rich and I know that I'm not leaking fuel from the tank or any of the hoses.

This SOB has become the biggest challenge I've worked on yet - not going to let her beat me tho.

 

[Irishman999]

You should really check those floats anyways.

My brain is telling me that not having a return line might have over pressurized the carb and bent the tab on your float. Now that you have a return line just double check the floats and if that does not solve the problem start looking into the drum brakes.