My "New" 350

[ThatOneBlue67]

Finally got her in (even though it's only been two weeks since I originally bought it). But it seemed like an eternity. I had my dad actually mount the motor for me as I had to work that day (and weld up the exhaust as I'm not too good with that). (This is all a learning experience for me so I won't lie and say I did this ALL on my own.)

Most everything else on it I took care of myself (truthfully), and then the Rochester Q Jet started leaking. The truck ended up broke down for the night at a grocery store parking lot. I wanted it on the road as soon as possible though, so I gave pops 400 bucks and told him to stick a Holley on it (while I had to go to school, dang it I miss all the fun!). It'll be a good investment seeing as how even my dad, whom I always assumed to be a genius with mechanics, doesn't know a thing about carburetors. But I'm keeping the Q Jet handy 'cus it probably just needs to be cleaned (the float is suck, that I do know).

So now the used 1976 350 has a Holley Street Avenger.

And so the results? Man she's fast! No doubt a step up from the 250 I6. And the exhaust cuts off under the cab so it's as loud as a fog horn. So awesome! Still needs some tuning as the carburetor tends to hesitate, any ideas?

Other than that she purrs like a kitten. I'm trying to stay out of trouble, as constantly advised by many, but I can't help but celebrate the fact that I can burn out on a straight away.

All in all, it's a very decent engine considering the price I paid, $200.The carburetor was about 400 bucks, but indeed a very worthwhile investment.... now if only to pay off insurance and union dues....

QUESTION: Why is my carb hesitating and what can Ido to fix it? AND about every half second I feel a rumble coming through the accelerator. The "powerfulness" of the rumble increases with throttle opening (if that makes any sense).

I'll have pictures up tomorrow after work hopefully.

P.S. As I suspected, the gas mileage is already going down hill. Oh well.

[Boog]

Well good for you! New carbs are high but sure makes an engine run good. I rebuilt an old quad for mine and looks like it may be alright. At least you have driven yours. Yeah, 4 barrel carbs and short loud exhausts are hard on gas mileage for some reason... Rumblings under the gas pedal? A vibration of some sort like maybe the exhaust pipes or hangers or something loose would be my guess.

[67ChevyRedneck]

$400??? Holy smokes! I paid $230 for my edelbrock 650cfm brand new!


There should be adjustor screws somewhere on the carb (I'm not familiar with hollys). Start the truck. Let it warm up. Turn the screws until the truck dies, then turn them about 1/4 turn back to where it runs good and that should get it pretty close.

[ThatOneBlue67]

Yeah I've been fooling around with the mixture and idle screws. The instructions said that it should have ran fine with the preset specs. but it didn't wanna hold idle.

I more worried about the rumbling. Maybe I'll take a secondlook at theexhaust hangers.... it was a trip trying to get those to work...

[JAKES 68GMC]

When I put the Holley 2bbl. on my truck, I had to mess the the carb mixture and float for a long time before I got it adjusted right and it ran good. But it's too bad I wasted the money on the 2bbl, now that I want a 350 which i will probably have to buy a 4bbl for. Oh well, you learn by making mistakes.

Glad the 350 runs good for you. Congrats on getting it in.

[ThatOneBlue67]

Hmm... the float height? I'm not even THINKING of diving into that one. That carburetor is just way to confusing looking. But that may explain the hesitation... I have two fuel lines running to it. Shouldn't be a problem with getting gas to it... so it very possibly could be the float.

As for the weird rumble, apparently I never tightened down the transmission bolts that go down to the crossmember. So I'm looking at doing that today as well as checking my exhaust hangers.

Oh! And I think I'll go take a picture or two and show you my exhaust setup.

[JAKES 68GMC]

Oh it's not too hard. Just put a wrench on the nut for the float adjustment, and a screwdriver for the screw adjustment oh the float, and lower the float down. As for the carb mixtures, just play with the screws until it runs best. Be stubborn and don't follow the instructions.

[ThatOneBlue67]

Shoot that seems like the key idea on these old trucks... prove the directions wrong. So I can just access the float with a wrench eh? I thought I had to tear the whole thing apart and bend those "metal twinges". If twinge is even a real word.....

[crm318]

you should also check to see if your vacuum advance is stuck on the distributor. just a thought.

[ThatOneBlue67]

lol Funny you mention that... my dad said the same thing. Anyway I can test this out? Maybe just suck..... or blow...... and see if anything happens with the cap off?

[Myself]

You never said what size yur Street Avenger was. Maybe too big for the engine?? They all say ready to run out of the box, that doesn't mean properly tuned to your engine. I also had some idle trouble and hesitation with my Street Avenger carb. After setting the timing, checking the advance, and hooking up a vacuum guage, I ended up cracking open the secondaries a wee bit. That changed everything. She runs like a S.O.B. now!! My buddy had this same problem on his 429 Thunder Jet in his '70 Cougar. We also got it to run great by cracking open the secondaries a bit. Sometimes you can't get enough air flow at idle and when you turn the idle up too much you uncover too much of the idle transfer slot. Cracking the secondaries a little usually cures this. If you've ever bought a used Holley from an old racer and found holes drilled in the butterflies, this was the same problem they were trying to overcome. By the way on the Street Avenger carb the secondary adj. screw is on the p. side rear of the carb facing downward toward the intake. Might have to unbolt the carb to adjust it.

[JAKES 68GMC]

Originally Posted by Myself

By the way on the Street Avenger carb the secondary adj. screw is on the p. side rear of the carb facing downward toward the intake. Might have to unbolt the carb to adjust it.

Yeah that could be. Probably the Street Avenger's are different than the old school Holley carbs.

[ThatOneBlue67]

Crack the secondaries while the engine is running?

Oh I get it! So have the secondaries always cracked open a tad? Hmmm... I suppose it's worth a try!

[ThatOneBlue67]

In just one week, I went

From this:



To this:

[Boog]

Aw yeah. Headers and straight out the packs. That'll make some rumble...

[Palf70Step]

Yeah...Rumblings!!!

You did good in a week. It looks like a whole different motor.

[ThatOneBlue67]

Boy do they rumble! It's not so much that they're oud but that pitch just amplifies inside the cab and makes your ears wanna bleed. I think I'll bring them just a tad farther back and out the side (under the steps).

She's not much for top speed but has great acceleration. And as for that hesitation, I found out that Holleys tend to have too lean of jets (for GM anyway). So I plan to have those replaced sometime during the winter. Even still though.... GREAT engine. I'm really happy with it.

[JAKES 68GMC]

Man thats a pretty engine. Are those Cherry Bomb glasspacks? How do you like them? They must sound good.

[ThatOneBlue67]

"The sign" said they were cherry bombs, and I assume they are glasspacks. The inside is greyish and has a lot of circular dips. Craters. I dunno how to explain it..

They sound great except that one of the headers has an exhaust leak so I hear mainly that. The cherrybombs were cheap $30.00 ones at Chief's auto parts. They sound pretty good though. It's mainly temporary but I've already decided that I don't want flowmasters. Too expensive and I prefer to stay classic.