Power hesitation in full throttle position
I brought my carter carburetor back to the guy who sold it to me as it was dripping gas. After two tries, he stopped the dripping. However, now I have what I would describe as a "power hesitation" in 3rd and 4th gears when I am pushing hard on the gas pedal to accelerate into traffic. For example, when I enter the freeway and push it hard in 1st and 2nd gear, there appears to be no problem. When I continue to 3rd I begin to feel a hesitation which get worse in 4th gear. It does not happen on street shifting even if I "goose" it good. The hesitation only occurs when I push it hard to enter the freeway. Also, if I am driving along at 55 in 4th gear and floor it, the engine hesitates like it is not getting gas. It feels like it gets gas and then doesnt get gas and I kind of "bunce along." If I lift off on the accelerator and keep it in 4th gear I have no problem. The gas flow seems to be steady and there is not hesitation. My carb man has had the carb out of the car four times this Spring with no good effects. He has had me do many things to no avail. (For example, advance the timing to almost 10 BTDC, put new spark plugs in, check the dwell, run the car w/o the vaccuum advance on, to name a few). I should mention that I had a paint job last Fall which left my car with alot of white dust that was in the breather hose in the gas tank. I cleaned the gas tank out with a rag, but a new sender in and cleaned the gas tank filter, and blew the gas line to the fuel pump out with an air compressor. My carb man found no evidence of this powder in the carb when he went through it. I have not changed the AC external filter into the carb which I might do next. I have had alot of advise including the secondary jets which my carb man says are working. Any other suggestions would be great. Thanks, Rick. By the way, this is a 64 corvette engine (327/300) in a 67 vette.
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Re: Power hesitation in full throttle position
Richard,
Sounds like a fuel problem to me, there is a filter sock inside the tank on the sender pick up that could be clogged so you may want to start there. I assume you have allready replaced the fuel filter so the next check would be fuel pump pressure. -
Re: Power hesitation in full throttle position
Change the fuel filter before you do anything else. In fact, that's the first thing you should have done.
Tim - read his original post. He already cleaned the tank and the in-tank filter sock, but he hasn't touched the inline GF-90 filter.
BTW, the sock in the fuel tank should be replaced rather than "cleaned". IIRC it's rated at 80 microns, it's cheap, and it should be replaced, apriori, any time the sending unit is removed for a fuel tank inspection, which probably averages once every 20-30 years. The GF-90 is a 10 micron filter.
DukeComment
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Re: Power hesitation in full throttle position
Tim/Duke: I did replace the sock in the fuel tank when I restored the car the previous winter (2/11). I took the whole unit out this winter (12) and inspected it and it was very clean. I only replaced the gasket and metal lock mechanism on the outside of the tank (still have the original AC sender). I have not replaced the GF-90 as I believe my carb man said not to but I will do that next. The black ones are hard to find outside of ZIPs. I believe they are $45. My local car parts stores do not carry AC parts but I will keep trying before I order it from ZIPs. Thanks for your responses. RickComment
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Re: Power hesitation in full throttle position
If you can find an inexpensive generic replacment for the GF-90, buy one. Remove the old filter, drain it and blow thorugh both. If the currently installed filter has significantly more resistance, it may be the culprit.
In any event, install the inexpensive generic, and see if the problem resolves.
I have reservations about many "reproduction" parts. In some cases they may look OE, but from a functional standpoint, don't meet OE specs.
DukeComment
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Re: Power hesitation in full throttle position
Also, check the inlet filter screen (if installed). This is found just inside the large inlet fitting. Sometimes people get carried away with thread tape on the fittings and some finds itself caught in the inlet screen. This is also possible if you use a section of fuel hose and take it off and on a few times. The sharp edge of the brass hose fitting may cut loose some of the hose inside (spoken from experience). These screens should be used as a final defense against hanging up a float needle and seat. They are readily available and inexpensive.
Additionally, check with your carb man about what dimension he used for the float level. I, and others, have been lowering the float levels as a means to reduce the percolation problems with the ethanol tainted fuel. I have found that the former maintenance manual recommendation of using a 5/16" drill is probably about the maximum one should go in lowering the level. Anything more than that can be too much under conditions you note. I prefer 9/32", but I am now running non-ethanol exclusively so much of my former problems with hot soak percolation are gone - even here in Florida.
Stu FoxComment
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Re: Power hesitation in full throttle position
Stu: I did not think about the filter inside the carb. Again, I assumed my carb man took care of it when he rebuilt my carb. I have had it out of the car three times this Spring alone and one time we took it out in his parking lot. But, I will check it out as I took off the inline filter (AC GF90) to bring it to my local parts stores to no avail. I cannot believe no one has this filter (NAPA, OReilly, and AutoZone). I ended up ordering an inexpensive one on Amazon.com for $15 plus shipping but that means 3-5 days with no car to run. Anyway, thanks for the FB. By the way, I run deoxygenated 91 octane only in my vette so hopefully the float level is not an issue for me. I also had a 90 degree turn in my fuel line where the pump to filter line goes in and the filter was slightly crimped at the receiving bolt (unbeknownst to me). I plan to straighten the line out so there is more of an arch that an angle. Maybe this severe bend and the crimp prevented gas from flowing as it should into the carb. I really appreciate the NCRS tech help you guys have given me especially considering what it costs to get this help from the "other" professionals. THANK YOU!Comment
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Re: Power hesitation in full throttle position
Richard;
In case you are not able to resolve your problem and decide to re-post about it, please provide as much information about your set up as possible. As you say; you have a 64 engine in a 67, i.e. which engine specifically, what carburetor model, what intake manifold, are you using the correct base gasket configuration for your manifold/carburetor combination (w/ or w/o phenolic spacer and SS plate), are you using a heat riser valve and is it operational, what kind of fuel line/filter combination are you using, etc. etc.??
One reason your carb man may have asked you to try disconnecting your vacuum advance is that your symptoms sound a lot like a possible "tipping" vacuum advance plate. What VAC can are you using? For that matter, did any of the things you tried make it at all better?
Just a few thoughts. Keep at it and let us know how you rae doing.
Stu FoxComment
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