New Carb Install Adjustment...TURTCEL

[TURTCEL]

So I just replaced my new carb that was leaking at the throttle shaft with my warranty carb from Guaranteed Carbs, I also replaced the EGR valve and cleaned the EGR pipe out. After everything was back together and all the vacuum lines were confirmed to be all correct I fired it up. **Just a note...it is 3 degrees outside too**. The car ran nice and smooth right off the get go but when I kicked the throttle quickly it felt very boggy, if I throttle up smoothly it is ok. After the Terc warmed up for a bit the idle would not drop below 1200 rpm's and the idle was unsteady (feels like an up and down surge).

I also have a new vacuum advance that I have not put in yet. I reused the carb base gasket which was only 2 weeks old and looked fine. I also checked for vacuum leaks and found none. I live at 4000 ft above sea level as well. The carb comes from Florida at a much lower elevation...could the carb be set incorrectly for where I live and be causing these symptoms? I will have to double check for vacuum leaks because it almost seems that the symptoms are deriving from a possible leak somewhere that I haven't detected yet. I also adjusted the throttle cable slightly but it still releases completely and has a little slack at full release so the higher idle doesn't seem to be coming from that adjustment.

Anyone have any thoughts?

Peace

[Petros]

it is acting like a vac leak, sometimes an internal problem in the carb can cause that too. List member Tercel4wdrules has had that happen, but I never have it happen to me. Every time I had the rpm cycling it was becasue of a vac leak, I just had to hunt it down and fix it.

It also sounds like you need to adjust your cold idle speed adjustment, it might be dropping the rpms too fast as it warms up. And one issue with the carb, they never did handle very cold nor very hot good, but they can be tolerated. Once warmed up and running normal it should run fine however. Go through all the extralegal adjustments in the FSM and double check everything is set properly, it should not take too long. Do it systematically, do not change more than one thing at a time until you find and fix the problem.

reusing the gasket should not be a problem, as long as it was not damaged. I reuse gaskets all the time.

Good luck

[TURTCEL]

Thanks Petros. I will do some more investigating tomorrow when it warms up to the mid 20's...it has dropped to -3 outside so no interst in freezing to figure it out. I will go through the FSM and do the sdjustments in order.

I also talked with my Dad who is a mechanic and he told me that I should pull the hose off the EGR valve when it does the surging and see if it goes away. He said that if the rpm's are staying too high then the vacuum in the intake could be causing the EGR valve to partially open causing a vacuum leak. He also told me that since I adjusted the throttle cable that I should start the car and then disconnect the cable to see if the rpm's lower...says that even if I think it is adjusted properly it might not be and disconnecting it would let me know if the rpm's lower that the cable it too tight.

Guaranteed Carbs presets and checks all their carbs just like National but the shop I go has used them before and likes their quality but usually has to ajust the mixture to accomdate the elevation difference. If I can't pin point anything myself I will run it to the shop and have the guys do a once over and adjust it for me. I will be doing my dizzy rebuild this week for the vacuum advance replacement but will wait till I get this problem figured out first.'

Since I know my vacuum advance is bad and that it causes a vacuum leak should I undo the lines going to the dizzy and plug them off while I am looking for the surging issue? My thoughts are that the dizzy could potentially be the vacuum leak causing the runnabilty problem. Has anyonw experienced this before?

Peace

[Petros]

YES! if you know the vac advance is leaking, cap off the lines! It is just another vac leak. The adjust the carb on the bench, I would be surprised if they could get it right all of the time without running it on an engine. Might work close enough most of the time, but not at your elevation. Also, use the FSM to verify your high altitude compensator (HAC) is working correctly, at your elevation that will be engaged all the time.

[TURTCEL]

Awesome response time Petros, thanks again for the advice. I know my vacuum advance is bad but don't know for sure if it is leaking but since the diaphrams inside are bad I imagine that it is causing an internal leak.

I believe DLB is the one who told me about the internal vacuum advance leak. I plug all 3 lines going to the advance correct?

**A note on the carb...Guaranteed Carbs says they do a flow bench test and then a running engine test but how could they have engines that could accomodate all the carbs they rebuild? My thoughts are like yours...they do the best they can but fine tuning is most likely a necessary thing.**

If the HAC is having issues can I get one new anywhere still or will I be looking for a parts car piece?

Peace

[Petros]

cap all the lines to the vac advance, if the diaphragm is leaking, than any and all lines will see it as a vac leak.

Yes, right, they have an engine just sitting there for every type of carb they rebuild, ready to install the carb and actually start and run it. even if they could, which I doubt, that is not the same as actually driving it in a car. And what about your altitude? not likely.

i do not know if you can buy the HAC new anymore, but it was common to all carbed toyotas at the time, easy find in a wrecking yard.

[TURTCEL]

So a useful piece of info worth knowing for those with a leaky carb throttle shaft. All throttle shafts will leak a little because it is a bushing and not a seal, the shaft must be able to move so a little air will always pass through this area. But some will leak worse than others and improper mixture can also cause more of a leak. This may be common knowledge but sometimes it is helpful to have as many tips posted as possible.

To help compensate and reduce the vacuum leak at the throttle shaft just slightly richen the mixture screw (turn left to richen and right to lean out). Do not over do the richness, this can cause runnability issues and poor economy.

I personally had a pretty gnarly throttle shaft leak. After talking with Jeff at Guaranteed Carbs and learning about the mixture change affect on the vacuum leak I decided to try it. I noticed there to be more responsiveness and no hesitation during acceleration. There are two systems that inject small amounts of air into the carb during acceleration to lean the mixture. The HAC system (FSM; EC40)(not all models have this) and the EBCV (FSM; EC33). Combined with a throttle shaft vacuum leak there can be a headache of runnability diagnosis time if you are unaware of how these systems work.***Bad O2 Sensor can also be a factor so don't rule that out*** Check components is these quick adjustments do not show improvement, you could have a different problem.

If the Terc's carb is stock from the factory you will have to drill out the carb's mixture screw plug in order to access the screw. The mixture is preset from the factory and then plugged off. Be careful that you do not drill too deep and damage the mixture screw. Refer to the FSM sections FU-28--FU30 for mixture screw plug removal and adjustment. Most rebuilt carbs will have this ploug remved for the consumer since adjusting to specific areas is almost inevitable these days, mostly because of old worn out components, high mileage cars, and crappy gas. Be sure to have all 3 new carb mounting gaskets ready to go before starting this job. It is possible to reuse gaskets some times but for the price just grab new ones to assure no leaks. Do not use any sealer on these gaskets...can cause improper sealing and can soften the gasket making the risk of it cutting during tightening down more of a risk.

Just thought this was good info to share.

Peace

[TURTCEL]

So I have been driving the Terc now for a few days since I installed and adjusted my new carburetor. The car is running fine but I decided to pull a spark plug today just to see what it looked like as far as mixture adjustments went. The plug has a very light brown coloring on the insulator which tells me that it is adjusted properly.

These are new plugs but I did however read the postings about the MK3 runability issue and saw the postings of the spark plug pics. Mine looks very similar to the normal plug but lighter. Does this mean it is slightly lean or will the plug darken as it wears?

I figure that I could richen it just a little and see how it runs and if I am not happy with the results I can set the mixture back. I am also looking to have the most efficient economy possible so I don't want to richen it too much.

A side note ***I only run 91 octane non-ethanol fuel***, it is available where I live so I buy it exclusively when in town.

Peace