Thanks guys, weber swap complete...but....

[justajester]

hey yall, thanks to everyone that answered all my questions about the weber swap. this forum has been a great help with my brat. I completed the operation and she's running much better than she was. I'm considering making an instructional video showing the whole process just for future people here that have a question. I'll probably get that posted up here in a few days. So with all that said I am having a slight issue of backfiring when the engine is reved to high too fast. Turning up the idle seemed to help a little, retarding the timing made it worse, adjusting the idle mixture seemed to have a little effect but not much. I also noticed under load while driving the brat seems to lug down past 40mph, it gets a lot louder, and makes a sound I'm not sure how to describe but, it sounds a little like a Harley, just gets really loud and kind of a thumping sound. it remind me a lot of my Harley that was running drag pipes. I really think there is something wrong with the way the distributor is working. I noticed that before I adjusted the distributor, the previous owner had it advanced as far as it would go. with it being that advanced, there is absolutely no pinging. I suspect the vacuum advance is broken and maybe the previous owner turned it all the way up to compensate. Or....i'm not sure....anyone have any guesses? would the timing cause he backfire and lugging under load? I should also mention the engine diesels sometimes...

[mr sarcastic]

Definately sounds like timing. Do you have a vacuum pump to help you bleed brakes? If so, connect it to the vacuum advance and see if it holds vacuum.

[justajester]

I don't have a vacuum pump but I think I can get one. Where can you get a new vacuum advance if it is broken? I've been thinking the vacuum advance is a likely culprit but I can't find a replacement one.

[BratRod]

I don't have a vacuum pump but I think I can get one. Where can you get a new vacuum advance if it is broken? I've been thinking the vacuum advance is a likely culprit but I can't find a replacement one.

Finding one new will be tough, as I spent a considerable amount of time looking and I could only find ones on distributors for sale. There is a place that rebuilds them... I dont recall the name, but it is highly recommended by other members.

 

As for my personal solution. I ordered one for an 82' civic, swapped the springs, and compensated for the difference in throw on the arm, and it runs beautifully.

[justajester]

Not sure how you usethe civic vacuum advance but it seems to be 40-60 bucks to buy one depending where you get it. A completely rebuilt cardone distributoris 125 from rockauto. Considering isn't a ton more I'm almost inclined to just buy a new distributor. Is there a likelyhood that there are other Distributor problems causing these issues such as mechanical advance or other worn parts. Does it seem reasonable and worthwhile to just go ahead and get a new Distributor?

[ferox]

Yes, getting a reman distributor is a worthy investment if you don't know the history of yours or how old it is.

 

The rebuilder BratRod is referring to is the Philbin Group.  That would probably net you about the best stock reman disty, second only to NOS.  I am guessing that it would cost more like $250 + core though.  I am running a Cardone reman Hitachi that I bought at Schuck's (now O'reilys) in 2005 (70K miles) and it's still going strong.

[justajester]

Well, I might be crazy here but I replaced the fuel filter today(which was not in good shape) and the car doesn't seem to back fire hardly at all and the acceleration seems a lot better. Could a fuel filter have that much effect on a car? I think I'm gonna drive her a few days before I put money into a distributor...she might be ok...once again thanks guys!

[peterelliott05]

That would be awesome if you made a video!

[jonas]

Well, I might be crazy here but I replaced the fuel filter today(which was not in good shape) and the car doesn't seem to back fire hardly at all and the acceleration seems a lot better. Could a fuel filter have that much effect on a car? I think I'm gonna drive her a few days before I put money into a distributor...she might be ok...once again thanks guys!

Yes. With the Weber you will find you will have some dieseling that will require some fine tuning of the disty/carb. Get that hammered out first before getting a new disty. Once that is done you will probably find your backfire prob will disappear as well. Mine is well tuned but it will still diesel but very rarely, usually when hot out.

[djellum]

1 question.  is it a backfire (out the carb) or afterfire (out the exhaust).  Just checking since you dont say specifically and many people use the term backfire for both.  if its an afterfire what did you do about the ASV system?  it was a system that pumps air into your exhaust from the airbox.  after the weber swap theres no airbox and if you didnt close up the ASV system (or it just is leaky) its basically a bit exhaust leak.

 

couple of easy things to check.

 

1) is the tank vent tube open to atmosphere?  if you plugged it and dont have a vented gas cap you could have fueling problems.

 

2) is your distributor hooked to ported vacuum or manifold vacuum.  it should be on ported vacuum from the carb, and our cars dont have the same manual advance as other cars so they cant be swapped between like a chevy.  easy way to tell is to put your finger or tongue on the hose to the distributor and rev the engine.  if the vacuum increases with rpm its ported, if it gets less its manifold.  also some older cars had a dual advance can distributor.  check an make sure you dont need the other line or if you have 2 of them that they didnt get crossed up.

 

3) id make sure to replace all the fuel system filters.  in the carb, by the tank, and if you have the one in front on the firewall, replace it as well.  a can of seafoam probably wouldnt hurt as well.

 

id recommend a fuel pressure gauge.  you can install one inline by the carb for about $20 and then you always know what kind of pressure your getting and whether its stable or not.  webers are sensetive to pressure so you really should at least take a reading so you know what your pumps producing.

[justajester]

        And I'm back... @djellum , it is and afterfire in the exhaust. I ran the car around town for a while to give it a really good test and it still makes a series of backfires in quick succession when you rev it to 3500+ rpms and left off the throttle/shift. It still diesels sometimes too. I tried adjusting the timing a few degrees at a time then revving the engine all the way retarded and advanced, the timing seems to make little to no difference on the backfiring. It seems to me like the engine wants to keep going like it has a bunch of gas in it but the when the throttle closes and cuts off the air it makes it rich and blamo! I need to pull the spark plug later to check for rich/lean/etc(I want to give it a good drive to get some decent color on the spark plugs first(only driven it 5 miles so far)...I did change the fuel filter at the fire wall and will try to get a fuel gauge now that I have some money but, it doesn't seem like a fuel pressure issue to me...maybe there is something I'm not thinking of however.

        I forgot to mention earlier a few things. The weber is bone stock from the factory, I haven't changed the jets. I live at 6500 ft. elevation on the mountain. Is it possible the jetting could be causeing backfires and dieseling? Could the elevation have it running that rich?

 

P.S. I'm editing the weber swap video and will be posting it soon.

[ferox]

You should check to see what jets you have.  It's important to verify that because the car will run sub-optimal at best if the jets are off.  Every engine is different, so you have to figure out the jetting within a certain range for each engine, especially at 6,500 ft.  That's high enough that the carb is going to be more sensitive to jetting.  

 

As I have mentioned in earlier posts, Weber seems to be shipping factory kits with idle jets that are too large, so they run rich.  The ideal jetting regime is posted in several threads in the archive to compare with whichever factory jetting you received.  It means taking the top of the carb off, but it's important.  The idle jets are easily accessible from the exterior of the carb though.

[djellum]

timing is a general culprit of backfires out of the carb.  I doubt it has anything to do with the after fire, though if you have drivability issues it may be related to that.  I don't know what engine you have but I am betting you have an EA81 since you mentioned the brat (distributor in the front passenger side of the motor).  if so then your timing should be 7-8 degrees and no more.  EA82's will run up to 20, but I haven't heard of the EA81's upping it too much.  for at least the baseline tune you should make sure its at 7 degrees.

 

most engines allow some extra fuel to reach the exhaust and get burned off in the catalytic converter.  the after fire is generally when you add some air to the equation, you get air, fuel, heat, and boom.  you will always have a little fuel in there at some point and you can't control the heat either.  stop the air that is getting into the mix and you will stop the problem.  first thing to check is the ASV's.  there is a system that has tubes entering the exhaust right where the exhaust manifold enters the head.  trace it back to a squareish valve behind the motor (could be 1 or 2 of them).  pull the rubber hose off if it and plug that hole on the valve itself.  the rubber hoses just go to the air box, don't worry about them. its common for that system to leak and allow air into the exhaust.  also check for leaks in the ASV's metal tubes and normal exhaust leaks as well.

 

if your just talking little popping noises then you can tune them out, but they aren't terribly destructive.  its just air and fuel mixing in the exhaust not inside the engine.  Id fix the drivability issues first.  if its a big boom id check into it though.

 

theres multiple values that matter for your fuel supply, psi is one, but flow is another.  at idle you may be able to flow enough gas, but once your engine needs more then dirty filters or weak pumps could get behind and cause problems.  you really need to change the rear filter (its the main filter for the car).  its on a shelf by the rear tire.  id also check the fuel pressure and flow if you can.  you can't really say what the carb is doing without knowing what your feeding it.

 

also just give a check on your cap/rotor/plugs and such. 

 

a decent check is to slowly turn down the fuel mix screw on the carb till it bottoms out (gently, don't force it).  if the car still runs you have an issue.  

 

how many turns out are you on the mix screw?