NTXOlds

HELP REQUESTED:
I have a '68 Cutlass with the 350 2bbl carb. The car sat for five years, and while I got it running, I was having a lot of issues with the carb as you might expect. Since I needed to drive the car a pretty good distance for today's appointment to get the TH350 installed, I had a shop close to my house rebuild the carb last week. They thoroughly cleaned the carb, replaced the fuel filter and all of the carb gaskets. It does run better for sure, but the carb is still behaving strange from time to time.

When I picked up the Cutlass from the shop, the temperature outside was in the 60s and the car was fully warmed up having just returned from the shop taking it for a test drive. The idle was fine, but it almost died every time I gave it just a little throttle after a stop light or waiting to turn. Giving it more throttle pushed through the hesitation and fueling from partial to WOT seemed fine. I parked it for a few minutes when I got home and tried to restart it, and it did not want to start. I had to hold the pedal to the floor to get it to warm start again, just as it was before the rebuild. One thing to note is that the engine was quite hot, and I discovered that the fan clutch was probably bad. I lost about a pint of radiator fluid from the overflow tube when I parked it. The idiot light never came on, but I am not sure I can trust the sending unit.

I changed the fan clutch the next day which really helped maintain the temperature. I test drove it following the new fan clutch, new alternator and fan belt. It started immediately when cold. I drove it around the neighborhood until the car was fully warmed up again so that I could check to see if the choke was sticking. After it was warmed up, I checked the carb, and the choke was maybe 30 degrees from vertical with maybe a 1/4" or 3/8" gap at idle. The car drove beautifully the whole time with no throttle hesitation whatsoever. I shut it off for a minute before trying a warm restart, and it started up fine this time.

Last evening, I drove the car to the transmission shop about 20 minutes away in stop and go traffic, and the hesitation was very noticeable again. It never died on me, but I had to be pretty deliberate in how I accelerated. It drove best if I gave it just a little throttle after letting off the brake and then giving it a lot more throttle after a second or two. If I gave it a lot of throttle off idle, it would bog down and almost die for a second before accelerating.

My guess is that they did not replace the accelerator pump. I think that this would explain the hesitation, but I don't think that it would explain the hard starting when warm. Perhaps the engine was heat soaked due to the bad fan clutch?

Thoughts?

Cutlass Fan

Take it bake to the shop that rebuilt the carb and explain your problem. They should be able to fix it, and on their dime. The choke should have been fully open after your drive around the neighborhood.
late timing will also cause hesitation on acceleration.

edzolz

Sounds like the accelerator pump stroke is too short, OR they used an older style pump, OR the float is not adjusted properly, for sure it is not getting enough fuel when the peddle is depressed to accelerate.

NTXOlds

Thanks. I will definitely take it back as soon as the transmission is replaced.

I might try watching the choke while letting the engine tun after starting from cold. Perhaps it simply needs an adjustment, or perhaps the thermostatic spring is not working correctly. Either way, I want to be able to have a better idea of what the problem might be before taking it back to them.

NTXOlds

Thanks. I would have expected all of these to have been corrected in a proper rebuild, so once I confirm that the choke is working correctly, I will take it back to them to have the check these items.

RetroRanger

Ideally the shop willbe able to straighten it out foryou. Unfortunately unless the shop has the csm or good carb knowledge thats probably not the case. If its an average shop they may occasionally get a carb in for rebuild, and shops today are always under the get it done and out the door time constraints that rarely allow the mechanic to spend the time to get it 100%. They drove the car they must have felt the hesistation, unfortunetly it would take additional time to rectify it, or just pass it off as eh old carb hesitation.

you seem interested enough, and its to your benefit if you get a csm and rebuild or reset the carb yourself. I set my qjet up up following the csm specs exactly, it works just like you remember these cars did when they were new. At any speed, under anycondition, i mash it and the engine roars. I took my buddy who has a holley on his car for a ride, and he kept asking it doesnt hesitate or bog at all?

NTXOlds

You are spot on, I think. A lot of these shops may know how to do a basic carb rebuild but might not really know how to set it up correctly. I am not expecting perfection, but if I can make an adjustment or two enough to keep it from being at risk of dying upon acceleration, it should be good enough to get a few more things done before pulling and rebuilding the engine anyway.

dragline

Do you see 2 good streams of fuel from the accelerator pump nozzles when you move the throttle? If the pump cup isn't designed for ethanol fuel it may already be bad.

NTXOlds

Thanks, Dragline. I checked that the other day when the engine was warm but had sat for a few minutes. It looked fine, but I am not sure I would know what bad looked like.

I may check it a few more times to see if it is consistent, though.

oldoldss

I've had the same 'almost-stall from a stop' problem with my 1971 with a 2-bbl/350. What seemed to eliminate it was adjusting the linkage for more accelerator pump than the specs call for.

I bought the car from a dealer, but was able to track down the original owner a few years later. The original owner gave me a detailed history of the car. One of the things he mentioned was that from the day it was new, it often had a hesitation when he pulled away from a stop. The dealer tried many things to eliminate the hesitation, even replacing the carburetor and distributor under warranty. Nothing they did ever completely eliminated the problem -- but it must not have been too bad because he kept the car another 21 years! (This also explains why my carburetor number comes back as a service replacement and my distributor is not stamped with any part number.) Even in the 1971-72 era dealers couldn't always figure it out.

acavagnaro

I recently rebuilt my '69 Rochester 2GC with great success. It ran and idled fine prior to the rebuild but the choke wasn't functioning properly and it made cold starting difficult. The CSM for your model year will have very detailed rebuild instructions with several pages of necessary adjustments which need to be made after the rebuild to dial everything in. Sounds to me like this step was likely skipped after your rebuild. Very easy to simply replace gaskets but it takes a little more time and effort to properly dial everything in.
I purchased the rebuild kit from Mike's (https://www.carburetor-parts.com) and it came with a printout of the tuning details. Interestingly, these sheets looked to be a black and white copy of the info from the CSM. The kit comes with a new rubber cup that goes on the accelerator pump assy. It also includes a new garter spring that may, or may not, be used for your particular year. It's possible they skipped replacing these as well.

NTXOlds

Thank you, guys. This is all very helpful.

NTXOlds

Well, I finally picked up the Cutlass after almost a month at the transmission shop getting a TH350 installed in place of the Jetaway.

Besides having an extra gear which made the car much more fun to drive, the car drove perfectly with great throttle response almost all the way home. After I tested out the downshift and gave the engine almost WOT, at the next stop light the engine bogged down with partial throttle. It kept this up at every stop for the rest of the way home.

Does this give anyone more insight into what I should look into first?

edzolz

Sounds to me like the float is not set correctly. Maybe the carb is draining the float bowl when you accelerate at WOT. Maybe the fuel pump is weak? Check your fuel pressure.

NTXOlds

That makes a lot of sense. Thanks!