You say engine is 287....is that an overbored 283 you are referring to??
Chevrolet never made an actual 287 engine is why i ask.

if it is an overbored 283, the 487X heads are a terrible choice....if the 283 has flat top pistons your compression ratio with the 487X heads is only about 7:1

As far as your backfire...maybe one of the air bleeds or fuel metering orifices is gummed up in the carb. today's pump gas is not very stable beyond 3-4 month time.

 

Sorry about that, had a bit to drink earlier. It’s a 283 and based off of what I read I figured it would not have much compression and that’s why it’s pretty underwhelming. It originally had a 350 in it that eventually needed rebuilt, with those heads on it and I suppose. the 283 block was lying around and and they slapped it together and dropped it in to get it mobile.

I was Thinking it may be the carb and went ahead and picked up a kit for it today in case I rip any of the gaskets tomorrow. Im very familiar with bike carbs but Never really worked on a carbed car. I’ve seen a few post talking about them but What exactly are the air bleeds

 

Could be lack of fuel, could be timing in that could be cam, ignition or both. Or could be an intake valve not seating or a miss-wiring at the distributor cap.

12 inches of idle vacuum isn’t much, this leans toward a pretty big cam, way out of time, major vacuum leak as in wasn't there before hooking up the vacuum brakes and now post connection here ya are?

Bogie

 

Yeah I’m hoping it’s not the booster. I’m going to try it afterwhile. The only thing is about the cam or timing is it wasn’t doing it before, and it only does it sometimes now. And only around 1/4 throttle. Also like Eric nova said, the block and head choice is not exactly ideal probably with very low compression so I’m wondering if that could cause the vacuum to be so low

 

Sounds like a lean sneeze. I would go thru the carb and verify timing

 

Might be a broken exhaust rocker arm or pushrod.

 

As far as I know the only difference between now and then is that the brake booster is now hooked up

Perhaps the brake booster is bad. Remove brake booster vacuum line, and plug; see if the problem goes away.

 

I hope not as a just replaced it but i suppose it’s possible. I’ll try it later and see what happens

 

Do the low cost and inexpensive experiments first. In this case isolate the vacuum booster and test the result.

The 487 head is a 76cc low compression head the X version simply has larger intake ports and bigger intake and exhaust valves. Compression ratio with these heads on 383 would be horribly low unless dome pistons were employed to bring it up. Whether low compression alone would lead to back fires isn't too probable as very low compression engines were the norm till WW-2.

Heavy backfire through the carb is classically a mixture ratio or timing problem. Here the old saying that “most carburetor problems are electrical” would tend to lead you to the ignition before attacking the carburetor.

Unless this engine is using a big cam the low but steady vacuum is signaling a large and common to all cylinders vacuum leak or late timing which could be cam and or ignition timing. Given this wasn’t a plague previously it’s in this case more likely ignition than cam timing.

What I’m pointing out is a method of thinking through the problem and starting from simple low cost tests and working toward the more complicated thus more expensive to investigate. I’d recommend keeping a note book as this can get complicated if early investigation doesn’t expose anything obvious so it’s important to keep track of tests and their results.

It would be helpful to have an idea of the cam, my initial take away of the heads against the small displacement engine was this was built by someone that didn’t understand the engineering and was using parts based on their reputation moreso than application. This gets a lot of people into trouble. Obviously using an large and open chamber head meant for a 350 SMOG era engine on a much smaller pre SMOG engine would take considerable compensation which would appear as a dome on the piston crown to recover compression ratio that being simply the math of all volumes found within the (cylinder swept volume and its piston crown, gaskets and clearances, and the chamber volume) divided by the volumes of the (piston crown, gaskets and clearances, and chamber volume).

Here a big cam with lots of lift and using domed pistons could create a situation where a piston kissed and bent a valve so now it doesn’t seat well and allows combustion past itself into the ink ake with the resulting stream of flame out of the carb. But this is more difficult analysis and obviously a pretty expensive repair if there. But a simple compression test could give some insight if a cylinder was showing abnormally low compression. Another test that requires an air compressor in the “leak down” test which requires an air compressor to apply pressure into the cylinder(s) being tested, here a valve not sealing would produce a leak that you can hear let alone see on a gauge.

So this is mostly a matter of looking for possibilities and testing for them as I said, start with the low hanging fruit of simple and cheap to do then work toward the more complex and expensive in an orderly manner.

Bogie

 

I didn’t get much of a chance to mess with it today but I did pull off the distributor cap and there was hard white corrosion? On what I assume are the points. I cleaned them all off with some fine grit sand paper and went ahead and pulled the plugs and am going to do a compression test in the morning, install new plugs and then recheck the ignition timing. If that does nothing I’m going to pull the vacuum booster hose and see what happens. If still no affect I’m going to pull the carb again and make sure everything’s good in it.

I really appreciate the help. I’m a bike mechanic and have no issues with carbs and ignition systems on them, as well as newer efi vehicles. But I know nothing about distributors or car carbs. Or American vehicles for that matter😂😂. So I’ve had to learn a fair amount on it.

one thing I’d really like to do is check the valve lash but I have no idea if it has solid or hydraulic lifters. I’ve heard people talk about adjusting while it’s running is insane to me as I’m used to checking jap vehicles with a feeler gauge and never heard of that. I’d also like to check how degreed the cam is but I know nothing about the cam that’s in it.

as far as I can tell the 350 needed to be rebuilt and he had the 283 laying around and put the heads and cam from the 350 on the 283 and threw it in just to get it driving. I really just need to get this thing running halfway decent so I can drive it some till I get around to rebuilding the 350

 

Except for dirt bikes my exposure to Japanese bikes is pretty limited. For two wheels on the street I‘m strictly an old Harley guy, though my wife gave me Heritage for my 60th birthday but that’s creeping on to 25 years ago. I gave my old hard tail to my son about 10 years ago as my body reached a point where it just can’t take that beating any more.

Bogie

 

I’ve actually been looking into getting a Harley soon. I had never rode one until recently, my pap had just got a sweet softail custom before he got sick that we were going to make into a trike for him. Dad got it and I got the car, pap told me since I was little he was going to fix it up for me and give it to me when I turned 16. Unfortunately that never happened as he was in a wheelchair and a number of other reasons. Anyway I got the soft tail running and driving and it’s actually a sweet ride.

I grew up riding jap dirtbikes and four wheelers so when I started transferring to the street I continued on with them but damn the Harley just feels so much cooler underneath you. And yeah I’d imagine the hard tail would be pretty rough on you, the roads around here are way too rough

 

My 1st bike was a Hodaka Combat Wombat LOL

 

Man I bet that thing was cool. It’s too bad they aren’t around anymore

 

You might want to just go ahead and replace the points and set the dwell.

 

At least service the points

 

I drove it today and the backfire is gone. I cleaned the points, replaced the plugs and adjusted the accelerator pump. Not sure which was the issue but it’s gone now.

 

So I have a 47 Chevy with a 69 camero subframe under it. I recently inherited it and from what I was told by a 3rd party it’s supposed to have 283 in it. The heads are 487x, it has an hei distributor and as far as I can tell an Edelbrock 1406. 350 turbo trans. No idea about cams or any internals. Although he said he thought he heard pap say the heads had had some work done to them and it had a cam of some sort in it.

I cleaned the carb and did a basic tuneup last winter and got it running well enough to drive at his funeral. However the wiring was far beyond repair and the brakes barely worked as well as the steering feeling terrible.
So I rewired the entire car with a new fuse box, replaced all brake components including hoses and bent/flared my own lines. Rebuilt the steering column and a few front end parts. As well as a ton of other random things in and around the car.

And for the first time in 30-40 years the key actually works, as well as all lights and the brakes and steering feel nice and tight now.

anyway, almost a year later I’ve finally got everything done and the car ready to drive and now it’s backfiring out of the carb at about 1/4ish. And not a small pop, but a huge flame/bang and it almost dies. If I can get past 1/4 throttle without it doing it it runs fine, although a little underwelming. As far as I know the only difference between now and then is that the brake booster is now hooked up.

So far what I’ve checked is, initial timing was set at 8, moved to 12 which helped idle quite a bit made no difference on the backfire, vacuum and mechanical advance are working I don’t have the proper light to test . Vacuum gauge holds pretty steady at 12. Cleaned the contacts in the distributor. Accelerator pump seems to working fine.
Tomorrow I’m gonna go ahead and put new plugs in it and if still no effect I’m going to pull the carb back off.

anyone have any ideas? Anything to try as I’d love to get this thing driving this weekend

It’s too lean, try 1/4 turn out on the idle screws.

 

So I have a 47 Chevy with a 69 camero subframe under it. I recently inherited it and from what I was told by a 3rd party it’s supposed to have 283 in it. The heads are 487x, it has an hei distributor and as far as I can tell an Edelbrock 1406. 350 turbo trans. No idea about cams or any internals. Although he said he thought he heard pap say the heads had had some work done to them and it had a cam of some sort in it.

I cleaned the carb and did a basic tuneup last winter and got it running well enough to drive at his funeral. However the wiring was far beyond repair and the brakes barely worked as well as the steering feeling terrible.
So I rewired the entire car with a new fuse box, replaced all brake components including hoses and bent/flared my own lines. Rebuilt the steering column and a few front end parts. As well as a ton of other random things in and around the car.

And for the first time in 30-40 years the key actually works, as well as all lights and the brakes and steering feel nice and tight now.

anyway, almost a year later I’ve finally got everything done and the car ready to drive and now it’s backfiring out of the carb at about 1/4ish. And not a small pop, but a huge flame/bang and it almost dies. If I can get past 1/4 throttle without it doing it it runs fine, although a little underwelming. As far as I know the only difference between now and then is that the brake booster is now hooked up.

So far what I’ve checked is, initial timing was set at 8, moved to 12 which helped idle quite a bit made no difference on the backfire, vacuum and mechanical advance are working I don’t have the proper light to test . Vacuum gauge holds pretty steady at 12. Cleaned the contacts in the distributor. Accelerator pump seems to working fine.
Tomorrow I’m gonna go ahead and put new plugs in it and if still no effect I’m going to pull the carb back off.

anyone have any ideas? Anything to try as I’d love to get this thing driving this weekend

Do a compression test on it.

 

Hello 47, it sounds to me like a timing chain issue and valve adjustment perhaps. I also had something simular years ago and my floats in the carb were set too high. When this gets corrected, enjoy it, sounds like a cool ride.

 

Thank you. I got it running right. Ish😂 it runs fine now but with the 283 and the head, cam combo it’s super low compression and fairly unimpressive. Still it’s awesome to drive and Im loving it. Now that I’m that I’ve got it driveable I’m going to put seatbelts and heat in it and I can start working on the body

 

I'm a little concerned about these heads on a stock bore 283 SBC. The stock bore isn't large enough to clear the bigger 2.02" valves these heads have unless someone relieved the top of the cylinder bores. Usually a 283 is limited to the smaller 1.94" intake valves, unless it is bored out, or relieved.
I'd go along with the suggestion of doing a compression test, if the large valve is bumping the cylinder walls there could be a bent valve.

 

Interesting. Compression test showed between 110-120 on every cylinder. I’m assuming due to the large cc heads with the flattop 283.

 

Compression test showed between 110-120 on every cylinder. I’m assuming due to the large cc heads with the flattop 283.

combo it’s super low compression and fairly unimpressive.

I think you answered your own question

Eric covered the CR many posts back

if it is an overbored 283, the 487X heads are a terrible choice....if the 283 has flat top pistons your compression ratio with the 487X heads is only about 7:1

 

Yes sir. I got the backfire to stop though. After cleaning the contacts in the distributor and adjusting the accelerator pump. Not sure which one actually fixed it

 

Even with low compression cylinder heads, that's not very impressive compression. Good that it's close cylinder to cylinder, but seems a bit low still. Likely why it's not got a lot of performance.

 

Yeah I thought so too. But was happy they were all close at least. She’ll work for now till I get around to rebuilding the 350