The Stovebolt Page Forums Home | FAQ | Forum | Swap Meet | Gallery | Tech Tips | Events | Features | Search | Hoo-Ya Shop
Helping out ...


EVENTS

Check in for status!

Jump over to the Events Forum, to post events -- new ones or the ones we have been enjoying for some time.
Look to see what's been cancelled or postponed.

Encourage one another!

Stovebolt Site Search
 
Old Truck Calendars
Months of truck photos!
Nothing like an old truck calendar

Stovebolt Calendars

Check for details!


Who's Online Now
14 members (55_2nd_Series, dphipps, dirtball, 4 invisible), 170 guests, and 3 robots.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums50
Topics121,048
Posts970,425
Members43,831
Most Online1,229
Jan 21st, 2020
Image Posting Policy
Previous Thread
Next Thread
Print Thread
Page 1 of 2 1 2
twin carb problems
#1375954 Fri Sep 04 2020 09:13 PM
Joined: Apr 2010
Posts: 17
C
New Guy
Hi Forum, I have a '58 Apache 235 which has been fitted with twin Rochesters and an Offenhauser manifold. Since I've had it it has always run too rich with sooty plugs. I've tried carb kits, new jets and eventually two new carbs. I've read many times it should only have one carb, so is it possible to ever get it running properly with the dual set-up? Can one carb be decommissioned so it only runs on one? The second problem is that the Offenhauser linkage which operates both carbs won't shut down properly when idling so it always runs too fast. I suspect the accelerator rod isn't able to pull down the mechanism for both carbs. Fit a stronger spring and the throttle pedal can't be depressed. This twin set-up is so common that surely it must be able to be adjusted properly. Anybody got any ideas? Thanks.

Re: twin carb problems
chevyfiftynine #1375966 Fri Sep 04 2020 10:20 PM
Joined: Feb 2000
Posts: 4,178
J
Shop Shark
I ran two Mono-jets on a 250, everything was set right on the money, even the linkage was set with indicators so I knew they were even. I got about 5 miles per gallon with that set-up. It was so bad I could almost see the fuel gauge moving as I drove. The problem I had and what you have, is the air velocity through the carburetors. The carburetor bores are to big for the amount of air required to run the engine. You need two carburetors off a 216, both identically set and metered. The bores are smaller so the air speed is quicker which makes the signals closer to what the carburetor is calibrated for.
A lot of guys are running twin Pinto carburetor, a progressive two barrel with each half having very small bores. I will bet yours runs pretty good at full throttle, peak rpm, and even half decent just driving, both due to air velocity being higher.

So, to cure your problem, you need smaller carburetors, nothing else you can do. If you block one, you will lean out the far cylinders. If you run progressive linkage, same thing, the farthest away cylinders will run lean till the second carburetor is opened. No amount of jetting will lean it out.

I run dual Carter W-1's from a 216 on my 250, It took quite a bit of tuning to get it right, but it was worth the trouble to me. It runs much better then even the stock set-up the engine came with.

Joe

Re: twin carb problems
chevyfiftynine #1375967 Fri Sep 04 2020 10:29 PM
Joined: Mar 2010
Posts: 130
B
Curmudgeon
This website is full of examples and information on this subject. Here is one that some others have posted:
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=84514

With time and money, certain dual carbs can be made to run well on your engine. There may not be that much improvement in performance. It's usually more for aesthetics. It's a personal choice. I like low maintenance, "runs well" and minimum aggravation. For me it's a working stock intake and a Carter YF 2100S carburetor with a new ethanol resistant rebuild kit.

Last edited by buoymaker; Fri Sep 04 2020 10:41 PM.
Re: twin carb problems
chevyfiftynine #1375971 Fri Sep 04 2020 11:02 PM
Joined: Feb 2004
Posts: 21,052
H
Boltergeist
Find a set of matched Carter W-O carbs for a CJ-2 Jeep, the flathead 4 cylinder used in WW II. There are usually several of them available on Ebay. Stay FAR away from the new offshore-made substitutes that are advertised as replacements. Rebuild them to be as close to identical as you can. They will only be slightly overcarbureted on a 235, not massively too much.
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 carb problems
chevyfiftynine #1375978 Sat Sep 05 2020 12:17 AM
Joined: Dec 2008
Posts: 1,485
P
Shop Shark
Which Rochesters (bolt pattern 2-11/16" or 2-15/16", or throttle disc diameter)?
What # manifold?
Your rich condition is probably your power valve open at part throttle due to reduced engine vacuum.

Re: twin carb problems
chevyfiftynine #1375997 Sat Sep 05 2020 05:28 AM
Joined: Apr 2005
Posts: 2,612
C
Shop Shark
If you don't have a Uni-Syn tool then get one. Under fifty bucks and is the only way for the home enthusiast to set multi carbs. I don't know what base size or bolt pattern the Holley 1904 carb for a 144ci Falcon has but it would be another one to check out and is available from Rock Auto. Two of these would not be completely out of range for what you need. I do know over carbed (or over cammed) engines run like crap.


Evan
Re: twin carb problems
chevyfiftynine #1376006 Sat Sep 05 2020 01:07 PM
Joined: Feb 2000
Posts: 4,178
J
Shop Shark
I have found the Uni-sync tools doesn't work for setting my carburetors. At idle, the amount of air each carb is pulling is not enough to activate the float ball in the uni-sync tool. If I close the tool down enough to activate to ball, the calibration is off in the carb due to high restriction.

My tool of choice is dial indicator on the throttle lever. I set both for the same ( X-amount of ) opening, then adjust both for proper idle rpm. It's not hard to get them the same once you are close, just keep adjusting while watching a tachometer, you will see the rpm raise with even the slightest adjustment.

Re: twin carb problems
chevyfiftynine #1376035 Sat Sep 05 2020 06:38 PM
Joined: Mar 2010
Posts: 9,446
5
Master Gabster
Or, you you can just go buy you a nice trailer. Everyone needs a trailer anyway. I need a trailer.

Re: twin carb problems
chevyfiftynine #1376062 Sat Sep 05 2020 11:17 PM
Joined: Apr 2005
Posts: 2,612
C
Shop Shark
When all the other shops stopped working on Corvairs we specialized in them. It bought me two houses and a four time shop upgrade. Enough prelude, if a 140 cubic inch engine works with a Uni-Syn then a 235 should. The way ours worked was the tool completely covered one carb to measure how the OTHER carb was being tuned. The 4 carb 145hp Corvair engines were a bit more involved but doable.


Evan
Re: twin carb problems
chevyfiftynine #1376121 Sun Sep 06 2020 12:12 PM
Joined: Feb 2000
Posts: 4,178
J
Shop Shark
I'am not sure my gauge works right, it has to be almost complete shut for the float ball to raise. It may have been banged around before I got ahold of it. It did work on my Corvair carburetors at one time.

Page 1 of 2 1 2

Moderated by  KCMongo 

Link Copied to Clipboard
Home | FAQ | Forum | Swap Meet | Gallery | Tech Tips | Events | Features | Search | Hoo-Ya Shop
Powered by UBB.threads™ PHP Forum Software 7.7.4