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Re: Twin Rochester trouble
chevyfiftynine #1377678 Sat Sep 19 2020 10:27 PM
Joined: Feb 2004
Posts: 21,203
H
Boltergeist
Jon- - - - -here's a little music for your entertainment. It's very appropriate to this discussion.

https://www.youtube.com/watch?v=vwuoFt0c1VM

Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Twin Rochester trouble
chevyfiftynine #1377679 Sat Sep 19 2020 10:43 PM
Joined: Sep 2001
Posts: 30,561
ace skiver


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: Twin Rochester trouble
chevyfiftynine #1377714 Sun Sep 20 2020 01:21 AM
Joined: Dec 2017
Posts: 824
D
Shop Shark
You are too cool Jon! Thanks for posting. I agree, a dual set up is not optimal, triples would be better but a lot of cars and trucks simply don’t have the room to fit a triple so duals. I ran early carter YFs for many years and loved them. But truth be told, the holly Weber 5200s ran a little better. If I was going to go back to a dual or triple single set up, I would definitely look at the carter W-1s.


Right now though, my 20 something son has me convinced to start looking at maybe working out a dual fuel injection set up. It’s intriguing. I have never messed with F.I. before but when a friend installed dual four style F.I. setup on his tunnel ram, and how that car now starts and drives, I was sold on at least trying to investigate the possibility.


Mike
Re: Twin Rochester trouble
carbking #1377897 Mon Sep 21 2020 04:24 PM
Joined: Mar 2005
Posts: 1,439
C
Shop Shark
Originally Posted by carbking
If the throttle throws are perpendicular to the engine, the procedure is a bit more complicate, but certainly within the ability of any enthusiast with a few tools. The idea is to fabricate two brackets, one for the front of the front carburetor and the rear of the rear carburetor to hold a rotating rod. Make the necessary fittings to hook the rod to the carburetor throws, and adjust.
Jon.


Chevyfiftynine,

Read the above paragraph very carefully as I believe it strikes right to the heart of your difficulties. What is NOT said is that the linkage provided by the repop manifold vendors is an exercise in futility as return spring pressure is not equal, it puts excessive stress on the throttle shafts, and it won't stay in the same place for long. Using that information the solution I came up has resulted in the dual Rochesters on my Fenton intake not requiring adjustment or tinkering in over a decade. I also made one for Paul Schmehl (Stovebolt IT guy) seen in the second picture on his Offenhauser intake with dual Rochester carbs. I wonder how long he has gone without adjustment...


Regarding the Racer Brown article I cut up, modified, and flow tested several heads to investigate individual improvements...my flow bench guy said that opening the intake runner up to the size of the intake rings was a serious velocity killer and not beneficial in any way. Likely other mods masked this defiency.

Attached Files
Curt.jpg (190.62 KB, 158 downloads)
Paul.JPG (240.77 KB, 157 downloads)

1952 1300 Canadian 1/2 ton restomod

Photobucket

You Tube

Re: Twin Rochester trouble
chevyfiftynine #1377909 Mon Sep 21 2020 06:38 PM
Joined: Jan 2020
Posts: 533
D
Shop Shark
This seems to be a constant occurring and fretful subject regarding two carburetors on a 235/261. If one insists on making water run uphill and helping politicians be honest then your task is pretty much futile. Your dealing with a subject that is impossible. Unless extensive modifications have been made to both the top end and bottom end of the engine you are trying to make a mule into a triple crown winner. Pages and pages on The Stovebolt have been dedicated to this issue. It will NOT work! A good running model B or Holly is as good as it will ever get. You are trying to make a very good farm truck into a Ferrari. The 235 will most definitely finish the twenty four hours of LeMans but about 20 + hours later. I have had two double Rochester's on both Offenhauser/Fenton type intakes. I think it added about 3 to 6 horsepower and about 24 hours of work each week. Too much money spent on linkage, jets and experts. You can put a 68 Pontiac DOC and get better performance if you want H.P. from a six cylinder. Doc.

Last edited by Doc.Hall; Mon Sep 21 2020 06:40 PM. Reason: misspelling

Currently making 1954 3100 better than new
Re: Twin Rochester trouble
chevyfiftynine #1377916 Mon Sep 21 2020 07:02 PM
Joined: Sep 2001
Posts: 30,561
ace skiver
This 1959/1959/60 261 has been running reliably with two 235 carburetors for over two decades. [1954advance-design.com]

It has "off-the-shelf" dress-up and intake/carburetor parts.

The 1960 261 in my Suburban has a single 2-barrel GMC AA1 carburetor with adjustable jets.
It has very nice power/acceleration (at all speeds) and good gas mileage (except when I cruise between 65-75 mph).

I am proud to be a "shade tree" mechanic.


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: Twin Rochester trouble
chevyfiftynine #1377974 Tue Sep 22 2020 12:38 AM
Joined: Dec 2008
Posts: 1,490
P
Shop Shark
EFI using a TB works, but the manifolds are not great.
Individual port injectors and a throttle valve has the siamese intake ports obstacle.

Re: Twin Rochester trouble
chevyfiftynine #1378053 Tue Sep 22 2020 02:10 PM
Joined: Feb 2000
Posts: 4,192
J
Shop Shark
I strongly disagree with the above statements about dual or triple carbs not working. They do work when done right. I did not gain a lot of HP, what I did gain was a big gain in fuel mileage at highway speeds, better drive-ability, better starting, less fuel smell after driving, and it looks really cool. I have a bone stock 250, and it runs better then it ever has, and I drove it with a stock intake for years trying to get fuel mileage out of it. With dual W-1 Carters, I went from 14 to 21 miles per gallon at 65 miles per hour. It gets even better at slower speeds. Did I gain more power? Some, but that wasn't the reason for the I went this way. I have a cylinder head flow bench, so if I wanted more power, I would hog out a head and run the engine at high rpm, thats not what I'm after. To top it all off I made the intake from scraps of steel left over from a project at work! I also added a picture of the triple Rochester Corvair setup I ran for awhile. I originally made the intake for dual Rochester Mono-jets, so the mounting holes and port openings are much bigger. You can see the spacers under the carburetors that adapt the Carters to the bigger openings.

Attached Files
IMG_1033.jpg (34.45 KB, 77 downloads)
IMG_0141.jpg (36.8 KB, 78 downloads)
engine pictures 013.jpg (46.17 KB, 75 downloads)
Last edited by Joe H; Tue Sep 22 2020 02:12 PM.
Re: Twin Rochester trouble
chevyfiftynine #1378067 Tue Sep 22 2020 03:07 PM
Joined: Jan 2020
Posts: 533
D
Shop Shark
That is a nice looking job but you are using it on a very different engine. The 235 head and intake has a poor circulation (swerle), if air was a rope it would look like a knot coming into the combustion chamber. Both the 230 and 250 were developed to remedy intake/exhaust problems. I agree that two Rochester's can be used, even a blind chicken can catch a worm every once in awhile. Most of us out there will agree that one Model B is enough to take care of. I can't remember the brand name carburator a buddy of mine ran in his roundy roundy 51 Chevy 235 automatic but he won his fair share. I'm thinking it was an Autolight. Anyway Yahoo, for the guy that has two model B's on a 235 if I'm reading it correctly. A 261 is adaptable due to the larger intake pull, it kinda straightens out the knots. It's to bad that we don't have the old dirt tracks around here anymore, remarkable innovations were accomplished by equally remarkable men. I'm talking the 50's and 60's here. Joe H,I have a 250 on a frame that I use to check carbs, don't do much carb work anymore your rig would be just right for my 34. Doc

Last edited by Doc.Hall; Tue Sep 22 2020 03:10 PM. Reason: additional info

Currently making 1954 3100 better than new
Re: Twin Rochester trouble
chevyfiftynine #1378203 Wed Sep 23 2020 01:57 PM
Joined: Dec 2017
Posts: 824
D
Shop Shark
Curt, if I may be so bold to ask, during your investigation, what did you find were the better improvements to make to the 235/261 head?


Mike
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