moran75 Posted January 18, 2019 Share Posted January 18, 2019 Hi all My car has a slight hesitation under initial acceleration. Apart from that it runs very well. Vacuum advance working as it should by the way. With engine warm and running (in Park) and accelerator pump worked by hand there is no fuel shooting from accelerator pump jets. When engine off, fuel does shoot out of the pump jets- any clues as to what is wrong with carb? Or is all this a red herring? Thanks in advance Kevin Link to comment Share on other sites More sharing options...
Jim Cannon Posted January 19, 2019 Share Posted January 19, 2019 Red herring. When engine is running and you open the throttle the air pulls the enrichment fuel off of the accelerator jets faster than you can see it. I would look for a vacuum leak somewhere. For example, clean or replace the PCV valve. Check all vacuum hoses to PCV and to brake booster. Check that carb mount bolts are snug, that carb gasket is good. Do you have the stainless steel plate under the base of the carb? My engine hesitated once warmed up and it was because I did not have this plate. 1 Link to comment Share on other sites More sharing options...
moran75 Posted January 19, 2019 Author Share Posted January 19, 2019 Yes , I have the plate. I’ll get checking the bolts and hoses many thanks kev Link to comment Share on other sites More sharing options...
telriv Posted January 19, 2019 Share Posted January 19, 2019 Bad or WRONG accelerator pump 1 Link to comment Share on other sites More sharing options...
Jim Cannon Posted January 19, 2019 Share Posted January 19, 2019 5 hours ago, telriv said: Bad or WRONG accelerator pump This could also be a problem. How long has it been since the carb was rebuilt? Do you know? The leather piston on the accelerator pumps do wear out. They also dry up if the car sits for extended periods of time, and not seal well. And does the engine stumble on acceleration out on the road if you really stomp on the gas pedal, instead of a gentle press down? There are little check balls and things in the carb that can get a bit of dirt or other crud on them to make them leak. When they do, you don't get a good initial spray of gas for the first part of the stroke. So stumble with small gas pedal movement, but no stumble when you really press down. Or the piston could leak a bit on initial press, then seal and pump beyond that. I was really just answering the question about "why can I see a spray when the engine's not running, but don't see it when it's running". 1 Link to comment Share on other sites More sharing options...
moran75 Posted January 19, 2019 Author Share Posted January 19, 2019 1 hour ago, Jim Cannon said: This could also be a problem. How long has it been since the carb was rebuilt? Do you know? The leather piston on the accelerator pumps do wear out. They also dry up if the car sits for extended periods of time, and not seal well. And does the engine stumble on acceleration out on the road if you really stomp on the gas pedal, instead of a gentle press down? There are little check balls and things in the carb that can get a bit of dirt or other crud on them to make them leak. When they do, you don't get a good initial spray of gas for the first part of the stroke. So stumble with small gas pedal movement, but no stumble when you really press down. Or the piston could leak a bit on initial press, then seal and pump beyond that. I was really just answering the question about "why can I see a spray when the engine's not running, but don't see it when it's running". Interesting stuff....I got the carb rebuilt straightaway when I bought the car about 18 months ago...the kit was bought from rock auto.com and to be honest I don’t even know what was in the kit...I just forwarded on. Ive noticed the hesitation on slight acceleration, like pulling away from lights ...I’m not much of a stomper but my wife is! I’ll ask her! I don’t think I’ll be taking itbout for a week or so but will put it through its paces ASAP and let you know... many thanks for her info kev Link to comment Share on other sites More sharing options...
RivNut Posted January 20, 2019 Share Posted January 20, 2019 (edited) Get a kit that's unique to your carb, not a Zip kit that's a one kit fits all. The best place to get one like this would be from Jon Hargrove, "The Carb King" on this forum Visit his website and look under the passenger car kits link. http://www.thecarburetorshop.com/ One thing that you might want to check before installing a kit is to make sure that someone prior to you hasn't replaced the carb with one from a different vehicle. I looked at what numbers are listed for a 65 Buick w/ AFB carb. There are two different numbers listed for the '65 with a 401, and each carb requires a different kit. It gets really nitty gritty when you get down to it. The 425 engine has its own listing. Edited January 20, 2019 by RivNut (see edit history) 1 Link to comment Share on other sites More sharing options...
demon452 Posted January 20, 2019 Share Posted January 20, 2019 I second the acclerator pump is the issue. As stated "wrong or bad". Make sure the housing section it slides in is as smooth as possible. If not you will damage a new 1 if replaced or it will not operate correctly. 1 Link to comment Share on other sites More sharing options...
moran75 Posted January 20, 2019 Author Share Posted January 20, 2019 Many thanks all. BTW Carb is a carter Number 3921S which i believe is original to the car. I’ll investigate in more detail next time I get her out bearing in mind all your comments and will get back to you with how it turns out . Cheers kev Link to comment Share on other sites More sharing options...
Zimm63 Posted January 21, 2019 Share Posted January 21, 2019 If you can't get it right, send it to Tom Telesco. I know AFBs are supposed to be simple and easy to rebuild, but mine kept giving me trouble. Tom set it right. Link to comment Share on other sites More sharing options...
telriv Posted January 21, 2019 Share Posted January 21, 2019 3921-S is the correct number. Thank you Zimm 63 for the plug. Tom T. Link to comment Share on other sites More sharing options...
RivNut Posted January 21, 2019 Share Posted January 21, 2019 Tom, Any reference to a 4453? I see it listed as a Carter AFB for a 65 401. Ed Link to comment Share on other sites More sharing options...
demon452 Posted January 21, 2019 Share Posted January 21, 2019 4453 carb is a 65 "400" package I believe. Not a 401 nailhead. Link to comment Share on other sites More sharing options...
RivNut Posted January 21, 2019 Share Posted January 21, 2019 A 65 "400" is the exact same engine as the 401. GM put the 400 cubic inch limit on intermediate bodied cars in 65. Rather than retool, Buick did some creative math using the same bore and stroke to come up with 400 rather than 401 cubic inches and the requirements were met. The "400" was coupled to an ST300 transmission rather than the ST400 as were the full sized models.. There is probably a difference in the linkage on the two different carb numbers. Link to comment Share on other sites More sharing options...
moran75 Posted February 28, 2019 Author Share Posted February 28, 2019 On 1/19/2019 at 9:19 PM, Jim Cannon said: This could also be a problem. How long has it been since the carb was rebuilt? Do you know? The leather piston on the accelerator pumps do wear out. They also dry up if the car sits for extended periods of time, and not seal well. And does the engine stumble on acceleration out on the road if you really stomp on the gas pedal, instead of a gentle press down? There are little check balls and things in the carb that can get a bit of dirt or other crud on them to make them leak. When they do, you don't get a good initial spray of gas for the first part of the stroke. So stumble with small gas pedal movement, but no stumble when you really press down. Or the piston could leak a bit on initial press, then seal and pump beyond that. I was really just answering the question about "why can I see a spray when the engine's not running, but don't see it when it's running". update . . the vacuum hose coming from the PCV valve def needed replacing ... however as prompted by the responses to my post its very clear that my accelerator pump isn't working, maybe the inlet valve is also dirty/broken so fuel is leaking back into the bowl? Anyway , I've ordered the correct complete kit from Mike's Carb's..many thanks all! Kev Link to comment Share on other sites More sharing options...
moran75 Posted March 14, 2019 Author Share Posted March 14, 2019 On 1/21/2019 at 3:26 PM, RivNut said: Tom, Any reference to a 4453? I see it listed as a Carter AFB for a 65 401. Ed Link to comment Share on other sites More sharing options...
moran75 Posted March 14, 2019 Author Share Posted March 14, 2019 All sorted...new pump and inlet valve fitted..had bit of an issue (see other post!) with floats but all good now. thanks all for your help kev Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now