1986 Chevy 350 Rochester problem

[SuperNova]

Re: 1986 Chevy 350 Rochester problem

The biggest problem with the Quadrajet--besides morons fooling with them-- was the "main well" welch plugs would leak. Not bowl plugs (it doesn't have any) or anything else. It sounds to me like one of three things- 1. Choke valve not closing properly (easy to check visually- it's the tin plate over the front 2 barrels and it should be closed cold) 2.- Accelerator pump not moving enough fuel (have to pump 20 times) but this should produce a hesitation on hard acceleration as well as the hard starting. 3.- The welch plugs (or something else) is leaking and causing the bowl to drain. To verify this do the following: Don't touch the throttle at all. Crank the engine over for about 15 seconds, do this twice but wait 30 seconds between to allow the starter to cool a little. Now press the accelerator pedal to the floor ONCE. Now crank the engine again--if it fires right up or at least tries real hard (it may take two pumps of the pedal to get it to start sometimes) then the bowl is draining. The correct fix for the welch plugs is to spread epoxy over them to seal them permanently. They are on the underside of the carb and will require it's removal. Switching to an Edelbrock (Carter AFB) is a very good and viable option if you have the cash and Holley also make a spread-bore type replacement carb that isn't half-bad. Both will require fuel line modifications at minimum.
--
Stan

 

[Lakester]

Re: 1986 Chevy 350 Rochester problem

hello jd'ham:

enjoyed seeing ur boat projects. u do get them cleaned up.

i also enjoyed seeing the pix of snake river. i used to live in pullman and had gone down the 'snake hiway' to louiston, id many times. and swam in the river there, too at the park. well, it may have all changed as that was in the 50's. my dad liked to stop at the texaco on the snake hiway side of town. i remember the big star on the texaco sign there.

i had a Q-jet on a 454. i was doing the engine. i sent it to The Carb Shop in cal and they did a rebuild of it for me. $95. not sure what it would cost these days... seems there is some confusion over who is who as to the carb shop. i googles the carb shop and there are 2.

the one i used is in ontario ca

http://www.customcarbs.com/

i am sure both could be helpful.

good luck

regards,

lakester

 

[Gary H NC]

Re: 1986 Chevy 350 Rochester problem

Look up flyingfish carbs on the net.I have bought a few from them.Best prices you can get and they sell marine carbs. I also just put one from them on my neighbors TransAm.It ran great out of the box.Very little adjustment was needed.Lifetime warranty too...

 

[jddenham]

Re: 1986 Chevy 350 Rochester problem

Thanks for all the input!

How do I find my carb model number? I assume it is stamped on the carb body somewhere?

To answer some of the questions;

It is a third vehicle for towing the boat, camping, and for the wife to haul kids around once in a while. It doesn't need to be high performance by any means, but she's not enthralled by the starting procedure.

I had a high performance 350 before but it was set-up as pre-emmisions. I'd rather leave this smog equipt and fix the std carb. If I end up replacing it I might go edlebrock performer intake with carb and strip the emissions stuff.

We are in backwoods Idaho, so no smog police.

There is a choke idiot light on the dash and it lights up at starting. The choke butterfly is also closed on the carb. When I get it to fire up after 15-20 pumps, it will start to idle fast and then falter off and die. If I give it gas it just dies. I have to just start it, let it die, pump it twice, start it, let it die, pump it twice etc.

After letting it die 3-4 times it will stay running and warm up fine.

I am going to read the carb manual and then pull the carb and look for anything obvious, as well as inspect the welch plugs as SuperNova suggested.

 

[Caveman Charlie]

Re: 1986 Chevy 350 Rochester problem

THERES A CHOKE IDIOT LIGHT ON THE DASH? And people say Fords are weird.

You may have a combination of problems. The carb loosing fuel and another leak in the fuel line.



This truck has a mechanical fuel pump right?

Check closely for gas leaks near the truck. Some times when fuel pumps go out they leak a little gas out a weep hole on the bottom of the pump onto the ground. When this happens the pump looses it's prime and then you have to crank it a lot to get it pumping again.

Fuel pumps used to be cheap and there easy to change. If I were you I would give it a try. All you are doing in pumping the gas pedal is removing your frustrations. If there is no gas to the carburetor because the fuel pump is bad and lost it's prime then the engine won't start.

How long does it set between starts?

 

[Caveman Charlie]

Re: 1986 Chevy 350 Rochester problem

How long does it set between starts?

 

[jddenham]

Re: 1986 Chevy 350 Rochester problem

Sitting overnight gives it problems.

I drove it to work today, let it sit for 8 hours and started it. It fired right up after two pumps, but then faltered and died. A couple more pumps and it started again fine.

Looks as if gas is leaking out somehow. I will pull the carb and check it over sometime soon.

FWIW - the truck drives fine when warm and has normal power under full throttle.

 

[Kenneth Brown]

Re: 1986 Chevy 350 Rochester problem

Look for a number beginning 140 or 141, it'll end up being about 9-13 numbers long.

While its cold pull the air cleaner and look into the top of the carb. Grab the linkage and go to full twice just like your sitting in the seat. Do you see any fuel spray inside? If yes then the choke needs adjusting. If no (which is my vote) then turn the motor over several times, maybe 10 seconds or so. Now do the pump test again. Do this several times till you see how long it takes to get fuel to the carb. If after 4 times or so it still doesn't spray when you work the linkage I'd lean to a faulty accelarator pump in the carb. Its fairly simple to replace although I don't know if you can get just the pump instead of the whole kit. Look on top of ths carb towards the bottom left of it, see the little 1/4" rod sticking up with an arm mashing on top? Thats the acc pump. As has been said it appears to be that you have several problems but we'll work through them just give it time.

 

[dolluper]

Re: 1986 Chevy 350 Rochester problem

The JB weld fix part is probably your problem...float bowl maybe??

 

[Benny1963]

Re: 1986 Chevy 350 Rochester problem

there right about the welch plugs and also the fuel pump may be and issue if its leaking past diafram i have several that are on running motors
if you want to pay shipping i will send you one of mine and you can send me yours i havs 15 or 20 of them 10 of them are tuned very well just need to know a little abut your motor to send you one that will woek with your motor
i will swap you for free to help you out
pm me , bennyb

 

[Benny1963]

Re: 1986 Chevy 350 Rochester problem

kenneth browns quote sucks everyone on her is trying to help
ive been building carbs for 20yrs as well as lots of motors big and small block
from 200hp to 775 hp you seem to think you are the god of carbs
man you shouldnt dog anyone trying to help i fix motors and carbs that are worked on by book certifyed techs all the time, people like you are to full of your self seem to think you know everything and thats why you never will
BENNYB

 

[Kenneth Brown]

Re: 1986 Chevy 350 Rochester problem

kenneth browns quote sucks everyone on her is trying to help
ive been building carbs for 20yrs as well as lots of motors big and small block
from 200hp to 775 hp you seem to think you are the god of carbs
man you shouldnt dog anyone trying to help i fix motors and carbs that are worked on by book certifyed techs all the time, people like you are to full of your self seem to think you know everything and thats why you never will
BENNYB

The quote is called sarcasm Benny. Look at my avatar- Proud rider of the short bus. The short bus is the one that the mentally challenged (read retarded) have to ride. Its all a joke man, lighten up.

I haven't been building carbs for 20 years. I'm not the god of carbs. My dad however is, theres not much he can't do with one. I can build a good motor though. Built several 302 small block fords that were pushing a true 350 hp on motor only, no nox, no blower, just motor. Built a 351 cleaveland that would redline at about 7800 AND would be right at home pulling a 24 foot camper trailer. When I raced stock cars built several sbc's that were tough. First race motor I built for my first race car in my first season got me 2nd in the season, only missed first by 23 points. Built several motors for IMCA modifieds- 355, 377,383,406 and one 427. NEVER had a motor blow up. At which point did I dog anyone out? All I've offered has been my advice, no critisism of anyones response. Till now I guess. You say you fix carbs and motors that are fixed by "book certifyed techs" , does this mean you work on them after others have failed or that you might possibly be ASE certified? Kinda confusing there buddy. I'm so much not full of myself. You are correct on one point here- I never will know everything. None of us will. Some will know more than others but nobody is gonna know it all.

It appears that we might have gotten off on the wrong foot here with a misunderstanding. If your halfway as knowledgeable as you claim I'm sure that I'll learn alot from you. If we're lucky you may learn something from me. As Rodney King said- Can't we all just get along?

 

[Benny1963]

Re: 1986 Chevy 350 Rochester problem

perhaps your right kenneth my certs expired long ago i only build motors for myself now didnt know that the saying you posted was permanent. till i looked at some of your post .my apologies if i was ruff on your statment .
i try to learn everything i can from anyone i can .sorry we got off on wrong foot . i dont know jack ---- about outboards but am learning
7000 plus is outstanding on any smallblock .sorry for the slander ,
my fault .sounds like your father has been a mech for quite a while
will read further before i open my mouth.
your post on the quad were right on by the way


knowing is knowing you know nothing
apologies to kenneth
happy new year bennyb

 

[Kenneth Brown]

Re: 1986 Chevy 350 Rochester problem

Can't ya feel the love everybody!!!!!
Thanks Benny, I knew that we were gonna be alright.

All of the responses so far have been correct IMO. I suggested checking the acc pump first as it was the easiest (and possibly cheapest) to do. Looking back again in the post it says that it runs fine after it is warmed up, no problem at all. That kinda knocks the acc pump out. A weak acc pump would still have problems after the truck is worn.
Lets look at the other responses. Next simplist is to check for the fuel filter diaphram. Pull the filter out and on one end it should have a small rubber piece stuck into it. If its not there fuel can run back down the line causing the fuel bowl to be dry.
The welch plugs can be leaking. This is where the JB weld comes in. This is an area where I would reccomend someone that knows what the're doing fix it, its a little toox scary for me.
Fuel pumps do tend to wear out and sometimes they also will siphon fuel from the carb since its higher than the tank.

I'm kinda wanting to see this problem fixed and the results. I'll be honest here though too. My wife NEVER drives my truck. Its an 89 F250 turned F350 that lives on our farm and has a very hard life. It really is held together by wire and tape. Since she doesn't drive it I can let the simple problems I know how to deal with not get fixed. Might be an option in your case too. Naw, fix the truck....
Note that I'm not a mechanic. I used to be in a former life. I've done alot of stuff that I'm not so I know a little about most everything. My opinions are just that.

Heck of an offer by Benny BTW.

 

[Caveman Charlie]

Re: 1986 Chevy 350 Rochester problem

Theres a fuel filter diaphragm that works like a check valve? I didn't know that .I thought the fuel pump diaphragm was just responsible for the fuel pressure staying up and not bleeding back to the tank. Glad I learned that. Might come in handy some day. um... but, how could the fuel get past the pump back to the tank unless the pump was bad too?

 

[Kenneth Brown]

Re: 1986 Chevy 350 Rochester problem

Thats true Charlie. I was reccomending the FF second becasue it takes 2 wrenches, 3 bucks, and 5 minutes to replace. On the plus side it will never hurt to have a cleaner filter on it. I try to do the simplest things first, along with the cheapest. theres a saying- KISS Keep It Simple ST####. I learned that thats the best policy by far.

 

[petryshyn]

Re: 1986 Chevy 350 Rochester problem

Hi
Don't pitch that rochester!! Its the simplest carb around...

-First off, is the choke valve closing for sure?
-Is it possible you are mistaking the choke valve for the secondary air valve?
-If you pump it once when cold, does the choke valve close completely?
-If you pump it once slowly when cold, then crank, does it fire up and then
die?

If you answer these questions accurately, I'll tell you your problem....

Good luck

 

[jddenham]

Re: 1986 Chevy 350 Rochester problem

Hi
Don't pitch that rochester!! Its the simplest carb around...

-First off, is the choke valve closing for sure?

YES

-Is it possible you are mistaking the choke valve for the secondary air valve?

NO

-If you pump it once when cold, does the choke valve close completely?

YES

-If you pump it once slowly when cold, then crank, does it fire up and then
die?

NO

If you answer these questions accurately, I'll tell you your problem....

Good luck

The motor won't fire until after cranking for 10 to 20 seconds.

 

[schematic]

Re: 1986 Chevy 350 Rochester problem

I will help you but you must not answer these question from memory. Please go and retry these tests again with a cold engine. When you do, also check the choke valve when it closes. Is it tight against the housing when you attempt to open it by hand or is there a slight amount of freeplay in the valve?

Don't crank the engine more than 5 seconds, as I have another test we'll perform pending your results...

 

[JCF350]

Re: 1986 Chevy 350 Rochester problem

The motor won't fire until after cranking for 10 to 20 seconds.

How's about low vacuum when cold?? Check it when cold and then when hot at cranking speeds and at idle.