My Jetstar currently has a 455 from a 1975 Vintage vehicle along with an edlebrock 650 Carb. It seems to be lacking. When I start it up it is very cold blooded and a good hesitation for the first 10 min or so of driving (keep in mind this car sat unused and not started for the past 5 years) after the 10 min mark of driving it the Hesitation is completely gone. I step on the gas.. It goes.

My friend is recommending putting on a 750 Carb on the engine and says it will run lots better. The plugs and wires, Cap rotor were all put on new shortly before it was parked.

Any other ideas?

I am also looking at rebuilding the engine as well. I have 2 choices for this. I can rebuild the current one in the car or I have been offered a 455 that was removed from a 68 Toronodo. Which Would be a better engine to use and any recommendations for good performance.

Thanks
Jeff

 

The 455 beast is just cold natured, Mine does the same thing and I got a 750 Edelbrock on it. It's gonna be the same with just about every old carbureted motor. Check the distributor cap for corrosion since it sat for so long. Other than that just running the motor might clear things up a little. A couple of upgrades to consider is an aluminum intake and headers.

 

Jeff, have you rebuilt the Edelbrock carburetor? If not, you might consider it. Your choke might not be set properly.

Also, if the 455 in your car came out of a 1975 Oldsmobile then it has J heads on it. J heads aren't bad for a street driven car but are definitely the worst big block head available. You might consider finding heads from a different 455 to put on your engine. C heads and G heads are good heads that are easy to find.

BTW, I disagree 100%. My 455 starts everytime I crank it, and doesn't have any hesitation. If the choke is set properly then you shouldn't have any problems.

 

I have had someone recommend putting roughly 8oz of laquer thinner in a full tank of gas as well.. any experience with doing that?

 

Start with a bigger carb and checking fuel pressure. Then plugs, wires, and Distributor advance.
Timing is next.

 

Yes check the timing, my 403 was bad about that until I timed it properly. Well actually the hesitation never fully went away until I timed it. And the choke, If it is tuned right it shouldn't do that.

 

I say ditto to J's comment of larger carb. The symptoms are all carb related and it is too damned small for a 455. BUILD A Q-JET!!!

AND GET THE 455 FROM THE TORONADO!!!!!!!!!!!!!!!!
More compression, bigger cam, LARGE VALVES included with it!
Jim

 

And if the choke doesn't work right on the Q-Jet will it fix his cold start problems? I think not.

Fix the one you have, it's a choke problem.

 

I agree. It's best to start at square one.

Despite this, J is correct. You'r engine could use some more carburetion; however, the 650 cfm Edelbrock you have on it now won't hurt it. Afterall, there were plenty of 455s available with the 2 barrle carburetors in the late 60s.

If you tune/rebuild the carburetor I'm sure you can fix your hesitation and hard start issue. Once you have it running good then you can decide if you want to upgrade to a Q-jet/larger aftermarket carb.

 

A 1975 with J heads a 650 would be ok. Sounds like the choke needs to be adjusted. If your going to rebuild it, and want more power. On a build you need to start with higher compression piston, a lot of head work bigger valves or different head. But if you use the 68 engine you could rebuild it pretty much stock or at least use the 68 head on the 75 engine. When you build it up you will need a 750cfm carb.

 

Point made, I got ahead of myself.
Yes on the choke, get your hands dirty on this one first. You need to learn how to adjust this, sometime.
If you still desire more power later, the q-jet will be a step up. You will need to learn to adjust this unit also.
The Toro engine will be another step above what you have now.
You can make either engine work just fine with the Edelbrock carb, but it will always be down on power (20 HP) as compared to the q-jet. The q-jet is 20 horsepower down from a Holley 850.
The Holley will cost you mileage.
Jim

 

I'd like to see a dyno sheet reflecting the same. Apples to apples, same air/fuel to same air/fuel, I find it hard to believe any carb is worth 20hp, especially a Q-jet.

 

my 2 qjets on 2 1976 455s behave quite differently. The Toronado starts and runs cold perfectly, as designed. 2 - 3 pumps, turn the key, starts, idles high, end of story. The Custom Cruiser stalls. Restarts, idles fine, but it always stalls and always restarts, idles high, and is ok.

They both run awesome hot.

But the wagon stalls.

Both have had major tune up (plugs, cap, rotor, wires, qjet overhaul, all by same mechanic)

I just let the wagon warm up for a minute and then all is well until next time.

Annoying but wtfe.

 

Q-jets are good carburetors if they are set properly. The good thing about an Edelbrock or Holley is that you can buy it and bolt it on right out of the box and drive it.

 

I find it hard to to believe that YOU are into fuel metering and can not understand why a 735-750 carb will make 20 hp more than a 600.
Especially a QUADRAJET.

I do not know injection, but you should know this one.
These are the basics.
Sorry dude-my opinion.
Jim

 

Make sure the advance curve in the distributor is working OK (no rust under the rotor). Proper jetting and metering rods will help responsiveness, as will the correct choke setting.

 

I believe I said "apples to apples". Didn't I? Read it again.

 

My '71 455 Olds 98 runs like the devil when it's cold, takes right off as soon as I crank it w/ the choke still on. It won't burn the tires w/ the choke on as it won't go to WOT, but as soon as it goes off, I stomp it, and as soon as the secondaries kick in, the tires start to burn. Not cold blooded at all.

 

Then please be specific on your test parameters, and not use only metaphors.
If you want to do a test cfm/cfm test, That's another story.
We ran a q-jet within a tenth of a 750 holley DP 20 years ago, although neither were running the fuel bowls empty (the BIG q-jet issue). 12.80 sec car.
The Holley had more top end, the q-jet had more on the launch (for our car with a little 350).
The Holley made more power, but I seriously doubt it would have got the mileage the q-jet did.
Not even near an "apples to apples" test.
Hard to do-
The q-jet has it's issues (complex, small fuel inlet), but it's superior metering (for a carburetor) and small primary boosters, has advantages.
This guy just needs to get his paws dirty.
Jim

 

Actually, you'd probably be best off putting a bakelite fuel bowl Thermoquad on it. That way the guy with the red beard would know that you had it blue printed and mapped.

 

I Have discovered that my carburetor does not have the choke plate on it.
Therefore making it hard for me to start. and would also cause it to be a bugger to idle when it's cold

I didn't notice the choke assembly on the side of the carb either?

Any suggestions?

 

I am sure someone on this board has a choke for a Holley available.
Jim

 

Unless you have something radical,you don't need anything more than a 750cfm carb on a 455. They don't spin that high,so there isn't any real need for something larger.

 

Brian, I have to disagree. A friend had a 750 Edelbrock carb on his 455. Ran out of adjustments. Stuck the 750 off my car on and it improved. Borrowed an 850 from a friend and that went faster yet. These were all done at the track.

 

Question: What size (cfm) is the Q-jet that comes on the 455? F/ example, the '71 455, which is the one I have. Thanks in advance.

 

Sounds like you're declaring that "rpm alone" determins the amount of fuel required. I feel that there are many more factors involved, and that the "NUMBER" amount of rpm, since so many configurations rev at different rpm f/ so many different reasons, is irrelevant.

 

Not exactly.One of the common misconceptions is that ALL larger engines need a huge carb,& that is not always the case.There does seem to be a pattern that a dual-plane inductions require more cfm than a single-plane.
I guess what I was getting at is that your average stock or mild 455 does not need some huge carb to wake it up.Some tuning to the factory Q-jet or a Holley 750 should be adequate.If your car,with the average weight of a Cutlass,is running 12:50's or slower,you should be fine like this.
I also know that there are plenty of stories about certain carbs,both factory Q-jets,as well as aftermarkets,flowing 800cfm or better,when they are not even close.The only Q-jet that I have ever seem actually flow 800cfm,without altering it,was a mid-80's Chevy truck/Van carb.The stuff like Edelbrock's 800 & such do not flow that.If you actually looked at the anotomy of it,it can't.I did so much as to call them personally on it,& got silence.Don't get me wrong,they have some great carbs,& they are nice & reliable,but just don't buy something based on the cfm numbers,hoping to make a chunk more power.

Did I clear that up or make more mud?

 

The Q-jet available on Olds engines was 750 cfm. There were also 800 cfm Q-jets available; however, I don't think they were available on any Oldsmobile engines.

Brian, were these Q-jets the ones that were rated from the factory at 800 cfm? I'm wondering if the factory rating system for Q-jets was sort of like the factory HP numbers? One always has to be suspicious.

 

The ratings could be like the HP numbers,guessed or inflated.One of the common beliefs is that the 500 Caddys have an 800cfm carb.No they don't.Just test one.

 

So Crzyjef, did you find a choke for your carburetor or did you get the Q-jet off of the Toronado?