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| | | | Joined: Apr 2016 Posts: 22 'Bolter | | 'Bolter Joined: Apr 2016 Posts: 22 | Having an issue with a stumble of idle, lean condition feels like. It bogs down then takes of. Does drilling the idle circuit help with this ? It's on a offenhauser intake. Both carbs rebuild, Acc pump working as it should | | | | | Joined: Jan 2013 Posts: 1,384 Shop Shark | | Shop Shark Joined: Jan 2013 Posts: 1,384 | Sounds like the carbs are too big.
If you go from one carb to 2 without changing bore or stroke, you need to use a step smaller carbs (in CFM) or you just give the engine too much air. | | | | | Joined: Feb 2000 Posts: 5,209 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,209 | I think Jim is right on this one, the air is moving so slow when both throttles open, it can't pull any fuel in with it. Try opening the idle mixture screw some more. If you can get it to idle really rich, you might over come the off idle lean. If it does work, then you are going to have to figure a way around the rich idle. My dual mono-jet carbs were way to big for the 250, one was plenty, it ran rich all the time. Full throttle felt really good, as did normal driving, problem was you could almost see the fuel gauge moving.
I now run dual W-1 Carters, a much smaller carburetor. Fuel mileage went way up along with all the problems of the Mono-jets.
What type of linkage are you running? Maybe you could go with a progressive type with the back carb slightly behind the front with a slightly quicker opening ratio. At highway speed both would be open the same or close to it, but off idle one would lag behind to off set the airflow of both opening at once. | | | | | Joined: Feb 2004 Posts: 29,782 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,782 | Buy a good fire insurance policy.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Jan 2013 Posts: 1,384 Shop Shark | | Shop Shark Joined: Jan 2013 Posts: 1,384 | Here's an easy way to size your carbs; find out the CFM rating of the original stock carb. Take 2/3 of that number and find 2 carbs with that rating. (if the stock is 300 cfm so get 2 200 cfm carbs = 400cfm.)
With headers and 2" pipes the engine will breath well and the carbs will function properly.
I used an Offenhauser manifold on a 235 speciffically because they offer manifolds with either small mounting base or large mounting base, that way I bought the small base and could put 2 W-1's (much better than Rochesters, sorry)that were sized for the 216 and they worked fine.
Last edited by Jim Sears; 09/28/2016 6:01 PM.
| | | | | Joined: Apr 2016 Posts: 22 'Bolter | | 'Bolter Joined: Apr 2016 Posts: 22 | Thank you for the replies. It's a stock 235, Fenton headers. The linkage looks like the kit you buy with the offenhauser intake. I will try and play with some more. | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Easiest way is to install 1(one) carb on the engine.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Nov 2002 Posts: 2,766 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,766 |
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Apr 2016 Posts: 22 'Bolter | | 'Bolter Joined: Apr 2016 Posts: 22 | Thank you Jon, I looked at that. I found a lot by searching and tried couple of things. I ended modifying the carbs. It's getting better, ran out of time. I will do more tomorrow. The reason I messed with the carbs is that if I do damage them then I will try and get 2 216 carbs or zenith carbs. I'm trying to use what came with the truck. I bought it like this. I don't think it ever ran correctly. I found couple issues so little by little I'm getting there. | | | | | Joined: Apr 2005 Posts: 7,440 Bolter | | Bolter Joined: Apr 2005 Posts: 7,440 | Silenpro slow and steady wins the race. Sounds like your on your way to making it right. Can't beat that.
Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
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| | | | | Joined: Apr 2016 Posts: 22 'Bolter | | 'Bolter Joined: Apr 2016 Posts: 22 | This is true Martin. I almost have it bog free. It was my idle / throttle that was off. So one carb had diff vacuum then the other. Set the linkage so that both are equal and started again with a vacuum gauge. It's so much better. Then I picked up edelbrock uni-syn. Tomorrow is another day
Last edited by Silenpro; 10/02/2016 2:28 AM.
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