SCCAIT7

Hello everyone - I am helping a friend bring back a 1st gen that has been sitting for many years after his father passed away. It was a project of theirs and he is hoping we can make it run again. I am having some issues that I simply can't get figured out.

I just rebuilt the carb and now the car will start and idle ok - However when you try to give it gas it just breaks up and backfires very heavily.

Someone has done a hack job removing the rats nest - So the distributor does not have a vacume advance - However it seems like it should not be backfiring ... My question is ... Where can I get vacume from? Can I go to any location on the carb plate?

Any other ideas why it would be backfiring so bad?

I really would like to make this thing run for him so he can enjoy the dream he and his Father had ...

jdi_knght

If the rat's nest removal doesn't look like it was done well/properly, take a peek at the pdf tutorial at http://maz_tutorials.ten15.net/ .

It should also show the locations of the vacuum line to the distributor which I believe was 2nd vacuum line from the front unless I'm remembering incorrectly. Then again I seem to recall a thread where there was a pile of debate as to which vacuum nipple to run to the dist, so who knows :p I'd start by browsing through that tutorial first either way though so you can hopefully finish up / fix anything from the rats nest removal that wasn't done correctly.

Good luck!


Edit: BTW check the timing in case it's been set to make up for the lack of vacuum advance in which case you'll prob want to change it if reconnecting the vacuum. Timing might also cause the backfiring you mentioned? Not sure, hopefully someone else has some suggestions.

Romulan_7

Are the cap/rotor/wires/plugs all good?

mazdaverx713b

iTrader: (91)

start by replacing all needed components such as the plugs (NGK), wires, cap rotor, fuel filter, air filter, oil and filter, coolant, and the actual gas itself. next check the timing and compression for good measure. once all thats done if its still running poorly, i would remove the carb once again, remove th air horn, and check the float adjustment and thoroughly re-clean the float bowles and make sure the jets are COMPLETELY clean. no spec of dirt can be left behind. makr sure you replaced the accelerator pump, the needles and seats, and replaced all gaskets as required.

once the engine is running smoothly, change the fuel fulter again for good measure, as the 7 is picky towards a clean filter. also, look into replacing the trans and diff oil, brakes all around, bushings and worn suspension components, and if your're really into it, replace all the door, window, and hatch seals.

DivinDriver

iTrader: (15)

Nope... some are simple vacuum sources, others are ported/controlled. Section 1a of the FSM gives a pretty good idea of which do what.

mazdaverx713b

iTrader: (91)

i would just reinstall the rats nest at this point...

blackdeath647

iTrader: (2)

just go back through the rats nest removal manual and check for things they missed. although it almost sounds like a timing problem

Kentetsu

Is there any chance that you got the jets switched around between primary/secondary when you put the carb back together?

Lots of good troubleshooting info at www.sterlingmetalworks.com
Or you can post carb questions at www.sterlingmetalworks.com/bymc

j9fd3s

iTrader: (3)

just off the top, old fuel will do this. also if you have insufficient fuel delivery, or a weak spark it will also do this.

SCCAIT7

OK. I have changed the plugs. Replaced the wires. Checked compression. I am getting an unbelievable backfire when I am attempting to start it. I mean this thing sounds like a damn cannon!

Here is what I have done since I felt it was a timing issue. I have popped the side plate on the transmission bellhousing and rotated the engine around so that flat piece of the flywheel is verticle in the viewing area. Then I placed the distributor in so that the arrow on the rotor button is pointing to the front of the car. BTW - When I align the flywheel the timing mark on the front pully is at the right point also ... I just can't figure out why its A.) having such a hard time starting B.) once it does start it spits suptters and BACK FIRES!!!

Suggestions? Have I done something wrong?

BTW - This is a 1980.

SCCAIT7

Fuel tank has been drained ... cleaned and refilled. The spark seems to be good ... I am going to throw ANOTHER set of new NGK plugs in it - However at $45 dollars a set I am starting to think that is not the problem ... They do not appear to be fouling very badly ... just a black color - Not allot of build up.

arran

Fuel pump?

SCCAIT7

Fuel pump has been replaced!

Kentetsu

Is there any chance that you got the jets switched around between primary/secondary when you put the carb back together?

Also, see what level the fuel is at in the float bowls just in case you've got a float hung up or something.

SCCAIT7

When I take one of these things apart I put a sheet of white kraft paper under the work area and draw circles and label EVERYTHING! I guess its possible the jets are swapped - but I am 99% they are right.

Float levels are at the half way mark in the sight glasses.

DivinDriver

iTrader: (15)

The huge afterburn (a "backfire" is technically firing backward thru the intake) makes me think you are only igniting one rotor, and the other is dumping unburned air and fuel in to the exhaust, where it goes off when met by the next pulse from the operative rotor.

Is the backfiring constant, rythmic, or irregular? Does it seem to synchronize with engine RPM?

Have you done a compression check? Even the ghetto "whoosh" test?

You mentioned that this is an 80 with a removed ratsnest; is the exhaust still stock (thermal reactor/heat exchanger)? What other changes have been made - - is the ACV still in place, or is it blocked off?

Some good detailed photos of the engine with the air cleaner off would help us all a lot.

t_g_farrell

iTrader: (1)

Sounds like timing still to me. Sometimes the front pulley can get put on 90 or 180 degrees out of whack. So saying the pulley marks line up isn't always accurate. You need to look at the eshaft to tell.

Kentetsu

Sorry, I wasn't trying to insult your intelligence or anything, but sometimes things like that happen even to the best of us.


I also agree that it sounds like an ignition issue, but I didn't want to go down that road because in your original post you said that you rebuilt the carb and now you're having issues. Were these issues present before you rebuilt the carb, or did they only appear afterwards?

Was anything else changed or altered besides the carb?

DivinDriver

iTrader: (15)

If he's still got the stock '80 front pulley, it's indexed with a rivet & hole... if you try to put it together wrong, it doesnt fit flush. If you persist, it would run wildly out-of-round.

t_g_farrell

iTrader: (1)

Maybe leading and trailing reversed on the cap or the plugs?

Good point about the 80 pulley, I know FBs can have that issue thats why I mentioned it.

SCCAIT7

Kentetsu - Not at all. Its a good question. Thanks -

The engine would not run well before I rebuilt the carb. I was hoping the rebuilt carb would change that - However I am seeing now that there might have been another problem.

You guys are talking about the front pully - Can you help me understand that a little more? The front pulley has not been off. What I was attempting to say about that was ... I took the side plate off the transmission under the intake and rotated the engine over till that flat spot on the flywheel came into view. At that point I went to the front of the engine and the timing mark lined up. Then I put the dizzy in with the arrow on the rotor button pointing to the front of the car.

The gunshot of a backfire seems to be random. When you do get it started and try to rev it up it just spits and sputters - The only other way I know how to describe it is...when we were all children we watched cartoons where the car would go down the road and pop and spit.

Compression seems to be ok - Just from the whooosh test. Having someone turn the engine over on the starter - I cannot keep my finger in the spark plug hold because the compression pushes it out.

SCCAIT7

Also also also also -

whoever did the rats nest removal didn't take the air pump off. So its still there... along with that thingy under the carb on the intake -

DivinDriver

iTrader: (15)

Random's actually good - - means it's not a blown apex or something that happens on every rotation.

Regarding the front pulley; on FB's, the part of the pulley that carries the timing marks can go on in 4 different positions; many people have gotten it on rotated, and ended up with timing that is some multiple of 90 degrees off. On SA's (78-80), the stock pulley has a raised rivet that engages a hole, so it's very difficult to get it on wrong. So you should be fine, with regard to that, unless the pulley was changed out sometime in the past & replaced with a wrong-year part.

The thingy under the carb on the intake, is the ACV (air control valve). Without a ratsnest, I'm not sure how it would affect operation. It controls the flow of air injection into the exhaust heat exchanger and thermal reactor, for smog purposes. Generally, part of a ratsnest removal & header install includes removing it and replacing it with a blocking plate, as well as another line at the rear of the intake.

If you've still got the stock exhaust, it's probably best to keep the air pump and ACV in place, or else the exhaust components might overheat and fail.