New member from Portland, OR - '86 Tercel Wagon DLX

[scrapz253]

very clean. are you testing diaphragm s as you replace hoses? find any vacuum leaks yet?

[dlb]

I would just check the tire calculator to make sure your speedo stays in spec. The Corolla might have a different stock tire size. Check it out here:

http://www.1010tires.com/Tools/Tire-Size-Calculator

yup yup. stock tire size on the 4wd corolla is 185/70r13 so i will be going with either 195/55r15 or 185/60r15. the all seasons i have on the stock alloys are still good for a while so i won't bother with it for a while yet.

[Petros]

I have driven cross country is 5 or 6 different Tercel4wd, and not one of them had a very accurate speedo (even if the odometer was pretty close), they have been off by up to 5 mph over and sometimes even under by 3 mph (in an auto trans DLX) based on my GPS speed (which should be pretty accurate). Not once have I seen it be right on accurate. Interestingly on my daily driver '84 T4wd, it is EXACTLY accurate, as near as I can eye ball the needle, it is right on correct speed. I have 14" alloy wheels with Michelin P185/65x14 tires. Not quite the same rolling dia as the factory tires, but it seems to have compensated for the speedo error.

[irowiki]

The wagon I bought from you is reading about 3mph fast, is that a tire thing?

[GotToyota?]

Tires play a factor as well as other things. But the tire size affects overall diameter which alters the speedo.

[Petros]

I do not know if tires size will affect it much, it has stock size tires on it, you would have to put tires larger on it to make it read better. Most I have measured, all of which were manual trans, were reading 3 to 4 miles under, which means you would need smaller tires to read better. They too all hand factory size tires on them. Some were further off than others, which does not make any sense. More likely difference in the speedo perhaps?

But we switched your speedo before you drove home, so the old speedo was under as well (actually that was the first one that read under actual speed, all of the others were manual trans and showing higher than actual speed).

different tires might help.

[GotToyota?]

So turns out I still have some hesitation when I give it throttle, but it's random.

The only thing I haven't done yet is replace the cap and rotor but they're on their way to me.

Can a bad cap/rotor cause hesitation? If not then I know I gotta check my timing.

Funny enough, I called a shop about a carb rebuild and the guy said I'd be better off getting a whole new car.

[irowiki]

You can rebuild it yourself! Bonus if you find one from a junked tercel and rebuild then swap.

[GotToyota?]

That is assuming that I do need a new carb. It honestly could be timing or a cap/rotor. I'll know when they arrive in a few days.

[Petros]

usually cap and rotor, and poor timing will cause rough running or be down on power. it does not result in hesitation. If you have hesition a new cap and rotor will not help. It might need a new cap and rotor, and it will improve how it runs if the old ones are bad, but it will not stop hesitation.

Hesitation occurs when there is not enough fuel in the air stream during rapid throttle actuation (when you stomp on it). The main jets supply fuel at a certain ratio to the air stream going down the carb during steady state operation. When you stomp on the pedal you get a sudden blase of air into the manifold and the main jets can not keep up with it for several seconds, causing a lean or weak mixture momentarily, causing a hesitation. A vacuum leak causes the mixture to be overly lean in the first place and will exacerbate the commendatory lean mixture during throttle transit operation.

to avoid this momentary weak or lean mixture during rapid acceleration there is an accelerator pump that squirts extra fuel down the barrel. So either you still have an overly lean mixture caused by a vacuum leak, or the accelerator pump is not putting out sufficient fuel. this can be inspected by simply looking down the carb primary barrel with a flash light and rapidly open the throttle, if you get a strong stream of fuel squirting down the barrel, you likely do not need a carb rebuild.

Have you done this test yet?

If you get a dribble, or nothing, or an intermittent squirt, than it needs a new accelerator pump, and likely a carb rebuild. Or at least pull the top off the carb and clean it out, and install a new accelerator pump.

[GotToyota?]

I have not done that test yet.

I'll check it tomorrow and come up with my results.

[GotToyota?]

Is the accelerator pump hard to replace?

[Petros]

not too bad, you have to remove the top off the carb (you do not have to remove the carb from the engine, but that is easy and only takes a few minutes). the top comes off with a number of philips scews, several vac lines and the fuel supply line has to be pulled off, and several tiny clips have to be removed to disconnect some linkage (careful not to loose them!). the top lifts off and you can swap out the accelerator pump. while the top is off you can inspect the bowl and float chamber, and clean it out if necessary.

[GotToyota?]

Is it worth it to just do a rebuild kit at that point?

[dlb]

it is definitely easier to replace just the accelerator pump rather than rebuild the whole carb. as peter mentioned, the pump can be replaced with the carb still on the manifold.

when i put a weber on my first terc, i had a hesitation that would primarily occur at the first moment of acceleration. it was most noticeable when i stomped on the throttle. it wasn't hard, like BOG, WAAAAAAAA. (great description, hey?) it was just that when i stepped on the throttle more, the car would hesitate for a split second before accelerating. when i finally hooked up the vac advance hoses correctly, it went away.

i believe scrapz253 described a similar problem which was also solved by getting the vac advance system hooked up properly, so i suggest looking at that. put a clean hose on the ports of the vac advance unit on the bottom of the distributor and suck on it. if you can suck air through, the diaphragms are broken and need to be replaced. they're pretty cheap, a bunch of us just got some from rockauto (via irowiki, mad props!) for $10 plus shipping or something like that. until you can replace them, disconnect and plug the hoses.

i will also note that there are two diaphragms in the unit and one can be broken while the other is not. the lower diaphragm has one port and is straight forward to check. the upper diaphragm has two ports, though: the main one goes to manifold vacuum while the other one with a smaller hole goes to the HAC. when testing this diaphragm, you must plug the HAC port while you suck on the main port, otherwise you will suck air through the HAC port.

check the accelerator pump and vac advance unit and let us know what you find. and the mechanic who said

Funny enough, I called a shop about a carb rebuild and the guy said I'd be better off getting a whole new car.

is typical of most mechanics. carbs are rarely used now so most new guys have very little, if any, experience with them. you are better off to learn and do it yourself. since it is your car, you will likely take more care to do the job right than they would.

that being said, i still think you should exhaust all the other possibilities before rebuilding the carb.