Weber Backfiring... Vacuum issue?

How-to's and repair secrets for your 4WD can be found here. Have a question? Ask it in here!
Post Reply
Posts: 1
Joined: Tue May 26, 2020 4:37 pm
My tercel:: 1984 Toyota Tercel SR5
Location: Portland, OR

Weber Backfiring... Vacuum issue?

Post by Manderson » Sun May 31, 2020 1:57 am

Greetings everyone. New to the forum, and new to ownership of a 84' Tercel 4wd Wagon here in the Portland Oregon area. I recently purchased a 84 Tercel SR5 Wagon. Very clean, ran alright but could pull hills and bogged down under acceleration. I decided to go for it and began the process of bringing it back to life. The carb was extremely fowled up, so I invested in Weber 32/36 kit from Redline. I also replaced all the Vac lines that remained (I left everything just incase I went back to stock). I set up the idle jet at 2 turn out and speed at 1 turn in following the Redline instructions and posts on this forum. It idled fine, but backfires out the carb when the throttle is fully engaged.

I went to the next step of checking the timing, only to discover that TDC does not line up with the mark on the Crank pulley. I verified by removing the #1 spark plug. When at TDC, the timing mark on the pulley is around 9 o'clock. After double and triple checking TDC, I made a new mark for reference with a paint pen. I double checked the dizzy position and everything checked out. I could not get timing to advance passed +5 with vacuum advance disconnected.

I decided to double check the pulley position and Timing belt condition. Belt needs replaced (on order, going to knock out the water pump as well). I also discovered the EGR valve was plugged up with carbon, but the diaphragm still functions and will be cleaning out the carbon tomorrow. TVSV seems to function as it should per the FSM.

Once I nail down the above repairs, I am curious as to proper vacuum set up with a Weber while maintaining the EGR. I have found alot of topics on this, but unfortunately they either reference pictures that are no longer there, or links that are "not found". Can someone help me out with the proper vac set up for a weber? Prior to tearing into the timing, I had the lower port on the dizzy vacuum advance connected to the gas filter on the manifold. Weber advance port was plugged, and EGR port was connected to Port P on the modulator (EGR connected or not made no difference to backfire and bogging down up a hill).

Anyway, looking for some help before I get to scattered with this. All the info on this forum has been helpful thus far, but as I mentioned the pics and links provided in many topics are no longer good. I'd appreciate a fresh update!

Thank you very much!

User avatar
Highest Ranking Member
Posts: 11394
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Weber Backfiring... Vacuum issue?

Post by Petros » Tue Jun 02, 2020 5:50 pm

back firing comes from either being too rich, or timing is off.

in the weber thread on this forum many share what jets they are usning in the weber, despite what weber might tell you, it is not likely the higher speed jets are teh right ones for our engine. most will buy a jet kit, and start with those recommended in the thread, and you can experiment up and down from there. fortunately on the weber the jets are easy to access and chance out.

you might want to see if your harmonic balancer is good, if the timing mark is off that much is usually an indication that the rubber bond between the front pulley and the hub has broken down. you will need to replace the front pulley/harmonic balancer. it is not good to run without the harmonic balancer, it reduces the stress on the crankshaft.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

User avatar
Highest Ranking Member
Posts: 6636
Joined: Mon Jul 06, 2009 9:03 pm
My tercel:: none currently, 7 previous
Location: bc, canada

Re: Weber Backfiring... Vacuum issue?

Post by dlb » Wed Jun 03, 2020 12:04 am

Did you see this thread on the EGR setup for a Weber? All the pics seemed to work fine for me.


With the poor running symptoms you mentioned and the timing not being able to get past 5* BTDC, it sounds like the distributor is one tooth off. I would advance it one tooth and see what you get.

While you are at it, make sure that the rotor in the distributor has some spring-loaded play: you should be able to easily turn the rotor one direction (sorry, I haven't had a Tercel in years so I can't remember which direction it is) and when you let go it should snap back. If it is hard to turn and/or doesn't snap back, the advance mechanism inside the distributor is gummed up with dirty old grease and needs to be cleaned out and re-greased. This takes an hour or two and there are some tiny parts in there but it's not hard to do. I found that very problem with a few of the t4's I fixed up over the years, and it was the cause of inconsistent timing and poor running.

Post Reply