When the car is warm, and the gas pedal is fully depressed RPMs climb to 4000 then immediately fall to 2500 then climb back to max 6000–all without changing pressure on the gas pedal. We have replaced the ignitor and distributor recently. If the RPMs were shown on a graph with time, the line would be jagged instead of a constant slope. This car has a ton of vacuum hoses. We don’t know where to look next; can you help? Thanks.
Cars of this vintage should NEVER be run at full throttle unless you are taking them on their “Final Drive”…Yes, your carburetor is HOPELESSLY complex and NOBODY alive today knows how to fix them and very few ever did know how to fix them…That’s why they bought fuel-injected Rabbits, which ANYBODY can fix…
In YOUR case, changing the fuel filter and pressure-testing the fuel pump is about all any human can do…If that fails, you can cut and plug all those vacuum hoses, remove the carb, and install one off a Pinto or a Vega…
If you are driving a 26 year old Honda Civic at full throttle, that right there could be the source of your problems.
If this car has an automatic transmission, it sounds like it might be trying to drop into a lower gear based on input based on the throttle position.
The problem is probably with the power valve in the carburator or the power valve vacuum control solenoid. Unless you have expierience working on these carburators and the vacuum control solenoids, it’s best that you it have checked by someone who does.
Tester
Hey Tester, if you offered to do mail-order rebuilds on these carbs, you could retire in a year a rich man…People would send them to you from all over the world…
I had an 82 that did that so I kept the full throttle operation to a minimum and relied on the engine torque in higher gears. I was driving on California hills at the time which is tough driving and it was OK. That hill from Camarillo to Thousand Oaks on 101 is a great test drive.
Does the engine speed go down or is it just the tachometer reading being in error?
This is not an automatic transmission going stupid is it?
The carburetors are not difficult to rebuild at all. The only trick is to mark all of the vacuum hoses and all of the air bleeds, emulsion tubes, and whatnot so they go back into the right spot.
Hey, it’s the other person working on this car, here. (My name’s Pete, but I’m posting under Linda’s account because I’m lazy )
The transmission’s a standard, so it’s not anything to do with automatic kickdown nonsense. As far as I can tell, the problem is brought on by a lack of vacuum (although I don’t have a vacuum gauge to tell whether it happens at a specific point). The car accelerates like it should briefly when I push the pedal down hard, then bogs down. Oddly, if I run it at, say, three-quarters throttle, it goes for a few seconds like it should, then starts to slowly bog down there, as well.
It’s almost like the carb is running out of fuel in the bowl, but as far as I can tell through the little inspection window, it’s not. I am wondering if it could be a vacuum problem inside the bowl - I’m not particularly carb-smart in the first place, but I do know that they require a very delicate balance of pressure and Bernoulli magic to work. There’s a vacuum-operated diaphragm that’s supposed to vent the top of the bowl into the charcoal canister when the car’s off, and into the carb throat when it’s running; there’s a solenoid that’s supposed to hold vacuum in the diaphragm when the car’s running at full throttle or close to it. My current theory is that it’s either a problem with that solenoid/vent setup (I disconnected it from the charcoal canister and the car feels a tiny bit happier, although that could be placebo) or I’m misreading the fuel level in the bowl and it’s actually running dry when I ask for a bunch of fuel. Today I’m going to try tweaking the float adjustment screw, hope I don’t overflow the darn thing, and see if I can’t wedge that vent open somehow to bypass the charcoal canister entirely. At this point, I’m okay with the evaporative emissions of an ounce or so of gasoline.
Other stuff I’ve done: replaced both fuel filters and the fuel line on the output of the fuel pump, run it without the air cleaner apparatus, replaced the PCV valve and hose (which did liven up the car, although it’s still got issues), hosed out the top end of the carb with carb cleaner, and checked the power valve, accelerator pump, and secondary diaphragm according to the service manual (all seem to operate OK).
Thanks to everyone who’s posted with ideas. Pleasedodgevan, yeah, the engine speed itself drops; the tach is accurate as far as I can tell. I’ll take the advice to buy an injected Rabbit under advisement; a friend in high school had one of those a few years back, and I don’t know, man.
Maybe a clogged catalytic converter. The easiest way to test this is with a vacuum gauge. The more difficult method is to unbolt the header pipe and run it down the street to see what happens.
I’d be a bit antsy (real antsy) about an injected Rabbit if the reference is to a 70s/mid 80s version. With CIS injection you’re opening up a real can of worms that may cause you to appreciate the Honda carburetor.