ChrisM

Hello,
I have a '73 delta 88 with a 350 and the 2 barrel Rochester carb. I have recently rebuilt the entire engine, replaced the stock distributor and coil with MSD, and have had the carb gone through with new gaskets, etc. Note, that no machine work was done to the carb.
My question is that occasionally the car will stutter,hesitate, and have zero power at first acceleration. Once it is moving it runs great, but will again stutter and hesitate when starting from a stop. I recently had the mechanic that has done all of the work and rebuilding on this car set the timing and adjust the carb, but the car still does this. He says that he thinks I need a new carb, but I don't have a lot of extra money lying around right now, so I'm not ready to just start throwing parts at the problem. Any suggestions on things I can check/adjust to fix the problem or at least determine for sure that I do need a new carb? I am thinking things in the areas of fuel mixture, or vacuum problems, but any ideas are welcome...

Any help would be GREATLY appreciated.
Chris

mjc79

sounds like the accelerator pump is bad.

Olds64

There is no reason a rebuild kit shouldn't fix a carburetor issue, unless you have a carburetor that is physically broken (ie. cracked fuel bowl, air horn, or throttle plate).

I agree with Mike. It sounds like an accelerator pump problem.

joe_padavano

First of all, does "...had the carb gone through with new gaskets, etc." mean it was rebuilt? Was the accelerator pump adjusted properly? Is the engine properly tuned? Is the idle mixture set correctly? Don't blindly throw a new carb at the car until you are sure it needs it. Most mechanics today are simply parts replacers. Now, I may be cynical, but most shops also make a profit on parts that they sell.

Oldsguy

My exact thoughts yesterday but I restrained from saying so, didn't want to sound negative, but since you brought it up....

Cutlass69S

Giving the assumption you had a creditable mechanic kit the carburetor, the accelerator pump is probably ok. (Just my opinion) There are a couple of areas to check/adjust. First off, since you rebuilt the engine, it is drawing fuel differently than before you rebuilt the engine. You need to determine if it is too rich or too lean. Typically if it coughs through the carb, it's too lean, if it bogs and black smoke out the tail pipe, it's too rich. Once you determine rich or lean, there are several ways to go. Too rich? Check the position of the accelerator pump rod, make sure it isn't or hasn't been bent or straightened (to straight will give more travel/larger fuel shot). Re-jet the carb. Pretty easy, just buy a couple of smaller jets and pull the top off the carb, remove the float and they'll be in the bottom of the bowl. Too lean? Just the opposite of too rich, check accelerator pump rod, give it more travel, larger jets in the bowl, etc. gl, Mark

ChrisM

Yes the carb was rebuilt. The engine is properly tuned. The mechanic did set the idle mixture, so I am assuming they are set correctly.

I am going to look at the accelerator pump next as it seems that everyone is in agreement that this could likely be the cause. I am very new to even touching the carb, so any advice/direction on where the pump is and how I might go about inspecting and adjusting, would be appreciated.

Also, I should mention that the car did do this from time to time before the rebuild, so I am thinking that maybe there was a problem with the accelerator pump then as well.

Also, I forgot to mention last post that the car runs terribe(meaning rough idle, no response to the accelerator) until I get on the pedal a few times and rev it up. I am guessing that there is some sort of water or fuel moisture build-up that need to be cleared out of the carb each time I start. After I "clear it out" it runs beautifully except when it hesitates on acceleration occasionally. The "clear out" doesn't seem normal, so I thought I'd mention it since it also seems carb related and may help in diagnosing my hesitation problem.

Cutlass69S,
I don't have any black smoke, so I don't think it is too rich, but could possibly be too lean, I guess.

Thanks for you help so far everybody. I would be lost without this forum.
Chris

Olds64

If you paid the mechanic to do a tune up and rebuild the carburetor it sounds like he didn't do it properly. Ask him specifically what he did. He should have set the dwell, timing, idle speed, and idle mixture screws during the tune up. In addition, he should have completely disassembled the carburetor and set the accelerator pump, choke, etc. while rebuilding it. IMHO, there is no reason your car should be running poorly if all this was already done and done correctly.

Cutlass69S

Does it only hesitate when it's cold or all the time? If it hesitates when it's cold mostly, ritchen up the choke, loosen the three screws on the thermal cover and rotate about one noch clockwise. If it hesitates all the time, your back to getting more air than fuel, i.e. accelerator pump or jets.

ChrisM

It hesitates both when cold and hot. I really need to just get into the accelerator pump and see if that straightens the problem out.

I agree, but now I'm just tired of having someone else figure out the problems and then have another one pop up. I just need to get in there myself so I know what is and is not being fixed.
The mechanic didn't set the dwell because I don't have points, but he did set the timing, idle speed, and idle mixture. I don't think he did anything with the accelerator pump, and I know he didn't set the choke because the choke needs to be replaced and is currently not working.

I am going to see if I can straighten out the accelerator pump problem, but if I can't get it to work I will probably just take the whole carb to a carb guy I know and have him look at it.

Please let me know if you all have suggestions or instructions on how to replace/repair/adjust the accelerator pump. I was looking on line and apparently there are cams that can be changed out and there may be a set screw that I can adjust to give more or less "squirt" on acceleration. Any help here? I think the set screw would be the first place to try, but I'm really not sure where it is and how I should approach adjusting it.
I guess another option is that I need to replace the accelerator pump diaphram? How do I know if this need replacing?

Thanks everyone, I feel like I am at least on the right track. And, I feel better to be attacking this myself. I really need to get to know the carb, as I feel like a lot of my car problems in the past have been due to carb issues.

Thanks,
Chris

Olds64

If you are going to replace the accelerator pump diaphragm then you should go ahead and buy a carburetor rebuild kit. They are less than $20 at the local auto parts store. This will have a new diaphragm in it and will include basic instructions on how to disassemble the carb and do on-the-bench settings.

marcocutty82

I too have the same problem with my 2 barrel carburetor. If someone can post some pictures as to how to adjust it, It will be greatly appreciated. Thanks in advanced.

Oldsmobomb

The diagnostics for an accelerator pump are pretty simple. With the engine off and the air cleaner off - take a good look down the throat of the primaries of the carb, with the choke valve (or plate) open for a good look. Use a flash light or other light source if things are too dark to see well.

With your hand, open the throttle linkage on the side of the carb pretty deliberately. You don't have to slam it open, but don't dawdle or tease it open. You should see a good solid double stream of gas spurt from the accelerator pump discharge nozzles into the primaries of the carb. If you see no gas, or the stream fizzles out very quickly, you either have a bad accelerator pump piston / pump cup seal, or you may have plugged discharge passages.

Earlier posts are correct that a linkage connection controls the volume and duration of the supplemental fuel "shot" - but this basic test will give you an overall good/bad diagnoses of the accelerator pump. Try this procedure at least twice just to make sure you are, or are not, getting a good solid shot of gas into the primary carb openings when you open the throttle.

(side note: I had a Holley 2-bbl that sat idle for awhile, and those passages became completely plugged with oxidation/crud (bad gas). A new accel pump did NOT fix the problem. I had to perform an 'angioplasty' on that carb - but that's another story.)

Aron Nance

A LONG time ago (about 1955) I had a '50 98 Hard Top DeLuxe (sure wish I still had that one, extremely rare), did the same thing yours is doing. I was very young and just learned to live with it, having no mechanicial ability (basically, still don't). BUT. At the time, the "in" thing to do was name your car, and "block/paint" that name on the rear fenders. Guess what I named her: HESITATION! Small world, absolutely no help to you today, just thought it might help put things in perspective.

joe_padavano

As noted above, first verify that you are getting some discharge from the pump shooter inside the carb. Assuming the pump is working, adjustment is simply bending the rod that runs between the pump arm and the throttle arm.

Here is a link to the 2GC manual:

http://www.oldcarmanualproject.com/m...ual/index.html

rocketraider

Is the EGR valve still in place and operable? If it is, disconnect its vacuum line and plug it and see how the car behaves.

Olds64

You inserted an inflatable balloon into the carburetor passages and forced out the crud? That is AWSOME!