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70 El Camino aka FRANKENSTEIN
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738 Posts
Discussion Starter · #1 ·
Ok so I have been working on this issue for sometime now. I have tried many different things to help with the issue but i still havnt fully figured it out yet.

Here is the whole set up:

71 C20
700r4
4.11 rear gears 30" tires
GM goodwrench 350 (16"hg of vacuum at idle)
MSD pro billet dist (timming is 18* initial and I dont remember the total Ill have to check if anyone wants that)
MSD street fire ign box
Summit full lentgh headers
K&N air filter
Edelbrock fuel pump (running 5psi)
Edelbrock 500cfm carb manual choke (choke is wide open and not in use)
Edelbrock performer intake

Here is a little history on my issues...

It had a th350 that burned up on me and instead of rebuilding the th350 I slapped in a 700r4 that I had laying in the garage. Once that was fitted and the truck driving again the weather started to get very hot (102* and up). The truck developed fuel boil in the carb. I cured that by insulating the hood and fuel line and I also installed a 1" phelonic 4 hole spacer. Hot start issue and fuel boil is now completly gone.

The truck has always smoked on start up its partly oil burning I know that. I smell very strong fuel odor every start up. I have tried all kinds of combos on the carb to lean it out or richen it up and the leaner I go the better it gets. But Im unsure of going to lean because Im already very lean...

Currently set at...
0.083 primary jets
0.086 secondary jets
065x052 rods
blue springs 3"hg
floats are set at 7/16 (upside down) and 1" hanging (right side up)

Its currently running at 12% lean primaries and 12% lean secondaries softest step up springs with the smallest plunger squirt. I have no lean spots or lean surges in the throttle at any point. I even stole my sisters 600cfm eddy carb and the truck was VERY rich.

With the th350 I was getting 9mpg city and 10-11highway. Now with the 700r4 Im getting 12mpg city and 10mpg highway!

I should be getting far better milage right now and I cant figure out why.
 

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Registered
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1,684 Posts
Is this the GM 290 hp Crate motor? If so one problem is the compression is too low (8.0-8.5) for the cam installed. If you go on line and pull up the specs on that motor the cam was ran in an early model 350 ci with 11.0 compression. Another thing the head ports are small and the engine don't breath all that good. Good luck!
 

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70 El Camino aka FRANKENSTEIN
Joined
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738 Posts
Discussion Starter · #5 ·
I was messing with the mixture screws just the other day but got side tracked and never finished I'll check that and tune with my vac gauge.

No its not the 290hp engine it's the 195hp this engine...
GM Performance 10067353 - Chevrolet Performance 350 C.I.D. Base 195 HP Engine Assemblies - Mobile SummitRacing.com

It was in the truck when I bought it. I pulled it apart to check it all out and it was incredibly clean. A friend of mine and I believe there's under 20,000miles on the engine. All I did was regasket and paint it I didn't change anything.
 

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70 El Camino aka FRANKENSTEIN
Joined
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738 Posts
Discussion Starter · #6 ·
Ok so I messed with the mixture screws and it's running better and the smoking seems to have gone down a bit but time will tell. I was able to get much higher vacuum at idle went from 16"hg to 22"hg. Needles to say that was very much needed.

I noticed that when I hit the throttle gas doesn't just come out of the booster nozzle but around it where it's pressed into the booster so I'm thinking I need new boosters.

I've read that lowering the floats from 7/16ths to 3/8ths or even a hair lower can help out with the fuel consumption.

I did not find any vacuum leaks either.
 

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WFO
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5,030 Posts
I noticed that when I hit the throttle gas doesn't just come out of the booster nozzle but around it where it's pressed into the booster so I'm thinking I need new boosters.
Check to see if the cluster screws only need tightening. If they're already tight or it still leaks after retightening, replace the gasket under the cluster.

Click on image for details:

 

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70 El Camino aka FRANKENSTEIN
Joined
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738 Posts
Discussion Starter · #8 ·
Well the valve covers do have the crapy baffling but i have semi improved on that I have a breather on the valve cover then rubber hose to the in line pcv then to the carb. Really cuts back on the oil in the line. Yes there is a breaher on the other side :)

I left the heat crossover wide open but I might pull the intake to completely block it off. That would help with the heat quite a bit.

I really rather not spend money to improve the engine any further unless it's my only option to cure this issue. As for a cam swap Im sure it would run far better but again I rather not spend money like that if I don't have to. Plus the time I have to work wih and this being the only truck. It would mean I take time off to do the work.

I'm sure I can get those heads I know many ppl with engines laying around and there's a bunch of junk yards around me. Swapping heads wouldn't take long at all.

I have no issue with running 91 if needed. Tho the prices these days staying at 87 would be nice.



I removed the carb tore it apart checked everything and all is well. There was a bit of dirt in the carb. I changed the fuel filters. I have 2 filters in line. The first is a paper filter right of the sending unit the next is a screen filter right before the pump.
 
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