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DRLA 45 backfiring out of carb and exhaust (SOLVED)
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Matthew
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PostPosted: Thu May 13, 2021 4:18 am    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Like others have said I think you have a couple of things going on.
Sounds like:
Plugged idle jets
No ignition advance

That original distributor that you swapped in - if it’s correct for a 30 pict-1 is a vacuum only unit. It does not advance at all without a vacuum signal.
If you could stick with a plain old German mechanical distributor and blue coil with good quality OG style wires (all known to be in good working order) that would go a long way towards sorting this out. You can try the fancy modern stuff once you get the engine sorted.
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PostPosted: Thu May 13, 2021 9:11 am    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

I don't think I have a good mechanical distributor around is the problem. I wouldnt mind an 010 for this build but those seem to be treated like solid gold now. The price is too high cuz everyone wants them and the hoarders have em all stashed away, lol. I wish the swap meets were still going on. I was thinking I might go straight to a CB black box setup with a 40hp big cap distributor.

I'm thinking the distibutor is working ok enough for testing now. New starter should be here today so I can continue working toward fixing this.
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PostPosted: Thu May 13, 2021 9:17 am    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Evan,

I have an 009 with electronic module and MSD coil I could send you if you want it. It requires a ballast resistor which I will send as well.

Just let me know...you can have it or use it to test and send back
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PostPosted: Thu May 13, 2021 3:52 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

evanfrucht wrote:


I'm thinking the distibutor is working ok enough for testing now. New starter should be here today so I can continue working toward fixing this.


Don’t expect it to rev clean or be responsive off idle without any ignition advance. It should idle smooth at around 10* btdc but that’s about all you can test with no advance. You can move it up to about 24 degrees manually once you have it running to test the revs but it won’t settle down the same idle speed.
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PostPosted: Thu May 13, 2021 5:50 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Matthew wrote:
evanfrucht wrote:


I'm thinking the distibutor is working ok enough for testing now. New starter should be here today so I can continue working toward fixing this.


Don’t expect it to rev clean or be responsive off idle without any ignition advance. It should idle smooth at around 10* btdc but that’s about all you can test with no advance. You can move it up to about 24 degrees manually once you have it running to test the revs but it won’t settle down the same idle speed.

Well holy shit I just re-read your previous comment and you are right, I was not aware of that. This 1967 only distributor is VACCUM ADVANCE ONLY, not mechanically advanced at all... not an SVDA, but rather a SVSA. Thanks for clearing that up and bringing that to my attention! That's one of my issues right there....

BUT, I still got a carb thing going on...

Need to figure out why the idle increases when I spray cleaner into the 1/2 side (and why the 3/4 side does the opposite, when I spray the exact same amount into that carb the engine wants to immediately bog down and die) Big mystery there, lol. I don't have a vaccum leak at the manifold as far as I can tell. So something else is causing only that side of the engine to run lean.
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PostPosted: Thu May 13, 2021 6:18 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

txoval wrote:
Evan,

I have an 009 with electronic module and MSD coil I could send you if you want it. It requires a ballast resistor which I will send as well.

Just let me know...you can have it or use it to test and send back

Thank you! That would help me out a lot especially if it's a known working setup. I may have to take you up on that.
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PostPosted: Thu May 13, 2021 6:45 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

evanfrucht wrote:

BUT, I still got a carb thing going on...

Need to figure out why the idle increases when I spray cleaner into the 1/2 side (and why the 3/4 side does the opposite, when I spray the exact same amount into that carb the engine wants to immediately bog down and die) Big mystery there, lol.


Consider the carb cleaner to be fuel. The side that causes the engine to speed up is lean and the extra fuel you are providing is making that side more happy. The side that slows down when you spray carb cleaner is running well, the extra fuel from the carb cleaner is causing that side to be overly rich, hence the slow down.

Now, just to find out why that side is lean....
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PostPosted: Thu May 13, 2021 6:49 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Evan, just let me know on the distributor/coil. I can send it your way tomorrow if you want
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PostPosted: Thu May 13, 2021 6:53 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

evanfrucht wrote:
Matthew wrote:
evanfrucht wrote:


I'm thinking the distibutor is working ok enough for testing now. New starter should be here today so I can continue working toward fixing this.


Don’t expect it to rev clean or be responsive off idle without any ignition advance. It should idle smooth at around 10* btdc but that’s about all you can test with no advance. You can move it up to about 24 degrees manually once you have it running to test the revs but it won’t settle down the same idle speed.

Well holy shit I just re-read your previous comment and you are right, I was not aware of that. This 1967 only distributor is VACCUM ADVANCE ONLY, not mechanically advanced at all... not an SVDA, but rather a SVSA. Thanks for clearing that up and bringing that to my attention! That's one of my issues right there....


I said this on page 1. I said to set it up just to find out if it was your old distributor.

Pruneman99 wrote:
10-20 degrees of scatter is way too much.

You can use the SVA distributor as a test. Just set it up to about 7.5-10 degrees BTDC and don't hook up the advance. It should idle smooth.

If you need to rev it, and hold revs, like to continue break-in, just advance the timing by hand and a light.


It will let you confirm the distributor you are running now is the culprit.
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PostPosted: Thu May 13, 2021 7:22 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Clean the idle jets and idle circuit passages on the lean side. I blow them out with compressed air and verify the jets are clear in bright light.
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PostPosted: Thu May 13, 2021 8:32 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Since you didn't get a chance to adjust the idle mixture, don't really know how far it is off.
You did mention it was synchronized with a snail, you might recall how far you had to adjust the idle speed screws VS bench set. If they were very close then it must be a fuel thing. If they were far off then it's a difference of air

All that is SURE, if I have skimmed it right, is the idle mixture is uneven with the mix screws all the same, and that may not be a big deal at all, depending on how far it's off.

If the #1 cylinder is running lean because of a vac leak.....but snail says it's the same as the others......then that cylinder will be idleing stronger than the other cylinders ONCE you supply it with enough fuel to run.
How could you do that?
Slightly unscrewing the idle jet, or putting in a bigger idle jet, and/or unscrewing the mixture screw to six turns.

Choking or spraying fuel in #1 has told you it is lean, but that isn't a stable enough condition to really see how strong it is firing, or low lean it is, or why.
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PostPosted: Thu May 13, 2021 8:52 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

modok wrote:
Since you didn't get a chance to adjust the idle mixture, don't really know how far it is off.
You did mention it was synchronized with a snail, you might recall how far you had to adjust the idle speed screws VS bench set. If they were very close then it must be a fuel thing. If they were far off then it's a difference of air

All that is SURE, if I have skimmed it right, is the idle mixture is uneven with the mix screws all the same, and that may not be a big deal at all, depending on how far it's off.

If the #1 cylinder is running lean because of a vac leak.....but snail says it's the same as the others......then that cylinder will be idleing stronger than the other cylinders ONCE you supply it with enough fuel to run.
How could you do that?
Slightly unscrewing the idle jet, or putting in a bigger idle jet, and/or unscrewing the mixture screw to six turns.

Choking or spraying fuel in #1 has told you it is lean, but that isn't a stable enough condition to really see how strong it is firing, or low lean it is, or why.

Thanks. I follow your logic.

At this point I'm still trying to figure out why both sides respond completely differently to the exact same fuel squirt test. One side literally will die with the tiniest little squirt of fuel. Other side idle will speed up with a tiny squirt? Everything else aside... that doesn't seem right.

And yes I Snailed them and they are all pretty much equal. Except I get a lower reading on number 3 for whatever reason but that seems to be the "good side" or the side that is a
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PostPosted: Thu May 13, 2021 8:54 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Pruneman99 wrote:
evanfrucht wrote:
Matthew wrote:
evanfrucht wrote:


I'm thinking the distibutor is working ok enough for testing now. New starter should be here today so I can continue working toward fixing this.


Don’t expect it to rev clean or be responsive off idle without any ignition advance. It should idle smooth at around 10* btdc but that’s about all you can test with no advance. You can move it up to about 24 degrees manually once you have it running to test the revs but it won’t settle down the same idle speed.

Well holy shit I just re-read your previous comment and you are right, I was not aware of that. This 1967 only distributor is VACCUM ADVANCE ONLY, not mechanically advanced at all... not an SVDA, but rather a SVSA. Thanks for clearing that up and bringing that to my attention! That's one of my issues right there....


I said this on page 1. I said to set it up just to find out if it was your old distributor.

Pruneman99 wrote:
10-20 degrees of scatter is way too much.

You can use the SVA distributor as a test. Just set it up to about 7.5-10 degrees BTDC and don't hook up the advance. It should idle smooth.

If you need to rev it, and hold revs, like to continue break-in, just advance the timing by hand and a light.


It will let you confirm the distributor you are running now is the culprit.


Yes you did, in my scrambling confusion I seemed to have missed it. Much thanks.
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PostPosted: Thu May 13, 2021 8:55 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

j-dub wrote:
evanfrucht wrote:

BUT, I still got a carb thing going on...

Need to figure out why the idle increases when I spray cleaner into the 1/2 side (and why the 3/4 side does the opposite, when I spray the exact same amount into that carb the engine wants to immediately bog down and die) Big mystery there, lol.


Consider the carb cleaner to be fuel. The side that causes the engine to speed up is lean and the extra fuel you are providing is making that side more happy. The side that slows down when you spray carb cleaner is running well, the extra fuel from the carb cleaner is causing that side to be overly rich, hence the slow down.

Now, just to find out why that side is lean....

Yep I figured as much. That's where I'm at now. Why is one side telling me it's lean Question Question Question that's what I'm trying to figure out... back at it tmrw...
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PostPosted: Thu May 13, 2021 8:59 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

It means one side is lean, other side is rich.
The quesion is why.
is it a difference in the fuel circuits.... (maybe?)
the air supply (snail says no)
Or vac leak of SOME form

Did you pressure or vac test the heads or intake manifolds after your welding? Or fill them with solvent and see if it leaks?

Crazy things can happen. the manifold leaking from one side to the other internally COULD happen, in fact it surely has happened.

One time, and nobody guessed it, it was the manifold was too big to bolt on the head, it hung up on an edge, I don't think you would be fooled with something as silly as that, but this confusing situation is very similar to the that confusing situation, if you know what I mean.

If those carbs were absolutely blueprinted, then the problem is below them......
But could be blueprinting carburetors might not be what you consider a fun time.
In the industry we usually "Vac test" the heads to make sure they seal.

What if I told you... all you need is some kind of plate to go where the carb bolts on, connected to one of those hand held vac...brake bleeding thingy, back off the rockers, you might make it happen pretty easy. Just to "eliminate that variable", as they say.

If it tests good, the carb is already off.......
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PostPosted: Fri May 14, 2021 6:50 am    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

This may seem dumb.
But have you verified the jet sizes?
I mean by measuring the orifices'. They can be different from one another. Think idle jets on the 1-2 side smaller than indicated on the stamping.

Keep in mind, Dell jet sizes are an indication of flow. Not the orifices' diameter.
If that makes sense.
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PostPosted: Mon May 17, 2021 12:28 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Alright well it's still doing it. Kinda just randomly backfiring at pooping in the low to mid rpms.

I haven't verified jet sizes but I got them from samba member Mcdragracer and he told me checks them.

Its still acting like its lean on side or maybe a vaccum leak.

I installed brand new throttle shaft bearings, has anyone ever had an intake leak from those?
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PostPosted: Mon May 17, 2021 12:30 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

modok wrote:
It means one side is lean, other side is rich.
The quesion is why.
is it a difference in the fuel circuits.... (maybe?)
the air supply (snail says no)
Or vac leak of SOME form

Did you pressure or vac test the heads or intake manifolds after your welding? Or fill them with solvent and see if it leaks?

Crazy things can happen. the manifold leaking from one side to the other internally COULD happen, in fact it surely has happened.

One time, and nobody guessed it, it was the manifold was too big to bolt on the head, it hung up on an edge, I don't think you would be fooled with something as silly as that, but this confusing situation is very similar to the that confusing situation, if you know what I mean.

If those carbs were absolutely blueprinted, then the problem is below them......
But could be blueprinting carburetors might not be what you consider a fun time.
In the industry we usually "Vac test" the heads to make sure they seal.

What if I told you... all you need is some kind of plate to go where the carb bolts on, connected to one of those hand held vac...brake bleeding thingy, back off the rockers, you might make it happen pretty easy. Just to "eliminate that variable", as they say.

If it tests good, the carb is already off.......

What do you mean by manifold leaking internally?

I did not pressure test the heads but I lapped the valves and they appeared to be sealing I also did a solvent test after.
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PostPosted: Mon May 17, 2021 2:45 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Ok so I put some larger idle jets I had in. These are probably too big, when I measure them it seems they have been drilled out to roughly a 72-75.

BUT they seem to have made the issue much better and oddly enough just changing the idle jets have made it so both carbs will respond very similarly when I spray carb cleaner into them (both want to die out/lower rpms)

I'm still getting a good amount of backfiring inside the header or something (popping) but no more puffs of smoke coughing from carb.

What does that tell you?
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PostPosted: Mon May 17, 2021 4:37 pm    Post subject: Re: New engine build backfiring out both carbs and exhaust. HELP! Reply with quote

Solvent testing is fine with me, just saying... 8 out of 10 monkeys would fill up both sides at the same time.
You would not know if it leaks from one port to the other. In the head or manifold
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