1986 Chevy 350 Rochester problem

[jddenham]

I have a 1986 Suburban with 350 and factory Rochester 4-barrell that was recently rebuilt by the previous owner.

The truck runs and drives great but starting it is a major PITA.

You have to either pour a little gas in the carb, which makes it fire right up, or pump it vigorously 20 or more times and it will finally start.

The previous owner says that this is common with the Rochester carbs, that the bowls drain out and there's no gas to prime the engine. He also mentioned a fix of JB welding something in the carb.

I find it hard to believe that in 1986, a salesman at a Chevy dealer would have to explain the cold starting procedure to a prospective buyer. I'm sure the problem didn't exist when new.

Any ideas?

Also thinking of a new intake manifold and carb(Edelbrock). Maybe get a little performance and no more carb problem.

 

[SpinnerBait_Nut]

Re: 1986 Chevy 350 Rochester problem

The choke is not working.
When cold, remove breather and work the gas by hand a couple times and notice if choke butterfly closes.

 

[Gary H NC]

Re: 1986 Chevy 350 Rochester problem

The Rochester carbs were known for the plugs in the bottom of the bowl leaking.If it is you should see or smell gas on the intake after the truck sets a day or two.The most likely problem is what SBN suggested.Check it cold and see if the choke is working if it is then i would pull the carb off and check it over.

 

[Caveman Charlie]

Re: 1986 Chevy 350 Rochester problem

The previous owner is fill you full of s**t. Either the choke is not working or, the carb needs to be rebuilt because there is a internal leak somewhere. This would also kill your gas mileage. Unfortunately, although great carbs when new they are a pain to rebuild.

How much money do you want to spend????

If the truck sets more then a few days it is possible for it to start hard because the gas evaporates out of the carb.

 

[SpinnerBait_Nut]

Re: 1986 Chevy 350 Rochester problem

As CC says, the quadjets were good when they were right and bad when they were bad, no in between with them.
A throw away item IMO.

 

[oops!]

Re: 1986 Chevy 350 Rochester problem

im not a mechanic, but ive replaced a carb or two.

my guys say the carb needs to be set up properly on a bench before they work right.

also one time i went thru 4 rebuilt carbs directally outta the box before i got one that worked right.

if its a off the shelf type of rebiuld....you might have the same prob. but the guys are right.. fuels draining outta the bowls....your outta gas every time you fire!

good luck....
oops

 

[jimr]

Re: 1986 Chevy 350 Rochester problem

throw that quadrajunk away and slap a edelbrock on it and be done with it.

 

[Silvertip]

Re: 1986 Chevy 350 Rochester problem

There is no need to junk a Quadrajet and the previous owner doesn't obviously understand the carb. While it is true the bowl plugs may leak and there were some issues with porous castings, your issue is different than that. If you have to pour gas into the carb, fuel leakage is not the problem. If that was the issue and you pour gas in on top of what would already have drained down the manifold you would never get it started. The Q-jet is also not "difficult" to rebuild but the average person attempting it doesn't understand it, has no idea how to adjust it and it wouldn't matter if it were a Rochester 1bbl because amatuers don't understand them either. There are specific adjustments for the choke, choke primary and secondary pull-off, fast and intermediate idle, air valve, accelerator pump, float level, and mixture. As with any engine work, a service manual is worth it's weight in time saved. Hit the library and check out a shop manual. Everything you need to know is there.

 

[Benny1963]

Re: 1986 Chevy 350 Rochester problem

I AGREE most people dont understand the quad i dont throw them away ..
some of the older quads were great carbs .but for the most if you dont understand them its easier to get a edelbrock /carter or whatever /
i personaly will run a holley 600 over a edelbrock / due to parts cost and avalibiltiy /but they do lack in the fuel cons dept .to each there own /use the specs on the rebuild kit /check the casting and weigh the float /and check throttle shaft play if you have idle issues /
good luck bennyb

 

[dolluper]

Re: 1986 Chevy 350 Rochester problem

Need an on-line manual for the quad google 'the old car project 'they have manuals there

 

[Caveman Charlie]

Re: 1986 Chevy 350 Rochester problem

I don't remember the site But there was someplace on the internet selling rebuilt q-jets for about 300 dollars. Personally I've heard bad things about edelbrock carbs. Weren't they basically just a thermo quad? I like Holley the best but, they are not a spread bore carb like a q- jet and would require a different manifold.

Again, how much do you want to spend??? And what do you use the truck for?

This problem might be a good excuse to get a different aftermarket manifold and carb. And, as long as your doing that you might as well get new heads, camshaft, headers and dual exhaust at the same time. First, though,we need to talk about gearing. Then build up the tranny, then work on the engine. Of course some nice rims and a custom paint job would be cool.

 

[ICEMAN]

Re: 1986 Chevy 350 Rochester problem

I recall years ago, when I was in the auto industry, there was a fuel filter in the intake of the carburetor, which had a spring loaded check valve in the filter. It was not uncommon to get a replacement filter and it not have the check valve in it. You could easily remove the valve and put it in the new filter element. However, if the tech was not familiar with this he may miss it in the swap. This check valve would stop the fuel from draining back down the line if the vehicle sat for a while. allowing for quicker and easier starts. Could this carburetor require the check valvle in the filter and it is missing?

 

[Benny1963]

Re: 1986 Chevy 350 Rochester problem

the line on the quad is high on the bowl they are tempermental when it comes to the choke and starting procedure.the edelbrocks look like carter to
me mabe afb ,but they were great carbs wish i had and afb with good throttle shft
bennyb

 

[newbie4life]

Re: 1986 Chevy 350 Rochester problem

There is no need to junk a Quadrajet and the previous owner doesn't obviously understand the carb. While it is true the bowl plugs may leak and there were some issues with porous castings, your issue is different than that. If you have to pour gas into the carb, fuel leakage is not the problem. If that was the issue and you pour gas in on top of what would already have drained down the manifold you would never get it started. The Q-jet is also not "difficult" to rebuild but the average person attempting it doesn't understand it, has no idea how to adjust it and it wouldn't matter if it were a Rochester 1bbl because amatuers don't understand them either. There are specific adjustments for the choke, choke primary and secondary pull-off, fast and intermediate idle, air valve, accelerator pump, float level, and mixture. As with any engine work, a service manual is worth it's weight in time saved. Hit the library and check out a shop manual. Everything you need to know is there.

I concur 110%. After having a Quadrajet on my 83 350, I had some issues with it. Had it rebuilt twice, and still didn't do any good. So, I installed an Edelbrock (you know, the ones that have had problems? ) and I've never had an issue... until recently. It wouldnt' idle correctly, so I took it to the local OLD GUY mechanic (that remembers what carburetors were for) for a tune up. Turns out, it was a vacuum line, and not the carb after all. $3 and I'm on my way.

He commented about the Edelbrock -- and wondered why I didn't keep my Quadrajet. I told him my issues, and he asked if when it was rebuilt, they changed some part, or fixed some orfice or something. Usually (according to him), there's a part on the carb that is overlooked when it's rebuilt. It doesn't take a big part to screw up a simple job. I wish I could remember what it was he said -- I can ask in the next day or two. I was just too excited to get outta there for $3.

 

[Kenneth Brown]

Re: 1986 Chevy 350 Rochester problem

The carbs are commonly referred to as quadrajunks for a reason and that reason is that they aren't simple to work on. My dad was a carb guy and could do just about anything with them. Unfortunely they did require his full attention and I couldn't pick up on his skills. When I got into racing stock cars we were restricted to a 2 or 4 barrell Rochester. There were 500 cfm variations of the 2 bbl and they were easy as can be to modify and tune. I ran one for a year and loved it. The next year I decided to go to the 4 bbl. Trouble non-stop, flat spots, float sticking, bog off the corner, running short of fuel at the end of the straight, you name it I had it. I had my dad tinker with it for awhile and he finally told me it had been rigged too much and I needed to start over. I went to Autozone (even though I hate the big box auto parts stores) and bought another one. It was junk too. Returned it (thats the good part about big box) for number 2. Number 2 was great! I adjusted the secondary door after my heat race as it was a little tight and all was good. The car easily picked up 5-6 mph. When their good their great. Many like the Holleys because a caveman can work on them. What you gain in ease though you lose in power. A properly set up qjet will out power a same size Holley all day.

 

[dolluper]

Re: 1986 Chevy 350 Rochester problem

Fixed many ,the rebuilt ones alot of time had the M/rods not located right,It's about the most important thing on them,plus pump and float levels set correctly....The 70's ones with the lean drop adjustment were the sweetized ones in my opinion Never ever had one I couldn.t fix ...mostly easy adjustments to get them rockin even replaced throttle shalfs ,I like the Qjets

 

[Caveman Charlie]

Re: 1986 Chevy 350 Rochester problem

The carbs are commonly referred to as quadrajunks for a reason and that reason is that they aren't simple to work on. My dad was a carb guy and could do just about anything with them. Unfortunely they did require his full attention and I couldn't pick up on his skills. When I got into racing stock cars we were restricted to a 2 or 4 barrell Rochester. There were 500 cfm variations of the 2 bbl and they were easy as can be to modify and tune. I ran one for a year and loved it. The next year I decided to go to the 4 bbl. Trouble non-stop, flat spots, float sticking, bog off the corner, running short of fuel at the end of the straight, you name it I had it. I had my dad tinker with it for awhile and he finally told me it had been rigged too much and I needed to start over. I went to Autozone (even though I hate the big box auto parts stores) and bought another one. It was junk too. Returned it (thats the good part about big box) for number 2. Number 2 was great! I adjusted the secondary door after my heat race as it was a little tight and all was good. The car easily picked up 5-6 mph. When their good their great. Many like the Holleys because a caveman can work on them. What you gain in ease though you lose in power. A properly set up qjet will out power a same size Holley all day.

Yes, that purty much sums it up. The 4 barrel q jets were a metering rod style where you had to get the rods just right. Plus, they hang off the cover so it was hard to take them apart and put them back together easily. When they work right they are great. I still say find that site, or the proper mechanic, and spend 300 dollars rebuilding them and you will be happy.

As I recall one of the q jets problems was that they would wear out where the main throttle plate shaft would move. So it ended up being a small vacuum leak. A small leak but! in a important spot. A lot of guys rebuilding them really just take them apart clean and replaced the gaskets. To do it right you have to measure the clearances of all the parts and replace any that were worn. In the case of the throttle shaft rod you needed to over bore it and add a bushing. Very few kids mechanic theses days would know how to do simple skills like that.

 

[dolluper]

Re: 1986 Chevy 350 Rochester problem

Here's the non direct link
5ttp://www.tocmp.com/manuals/Carbs/Rochester/QJet/index.htm
Change the 5 to an h.....after you paste it ,this page is real slow if your using dail up

 

[MikDee]

Re: 1986 Chevy 350 Rochester problem

I've had Q-jets on many cars, & boats over the years, never really had much of a problem with them, if set up right. My choice of carbs are the Carter/Edelbrock clone, these are simpler, easier to work on, and give great results. Holleys I've never had luck with Waddaya expect from a Ford product?,,,lol

 

[HyperFox]

Re: 1986 Chevy 350 Rochester problem

Id take a carbed truck over a EFI one any day of the week, and twice on Sundays.

Only because I was raised on carbs. I know how to set them up with a service manual. I can rebuild one over two days.

Now this EFI stuff.. Thats a whole different matter... Wasnt so bad with TBI like on the old chevy's but these days its like you need a degree in computer science just to work on the things..

Except my caravan... Flick the keys on and off 3 times, the problem shows up on the dash then open wallet..