Backfire from carbs, poor performance

[Thepspack]

I've been beating my head against the wall for 2 weeks now trying to figure this out.  About 4 months ago I broke a piston in my 521, figured i'd get the original engine rebuilt instead of making things complicated with a swap of some kind.  I scored an awesome deal on a dogleg and a set of SU's on a 220 intake so I figured while I was at it I'd put that stuff on it too. Long story short the engine is done.  It's a L16 with a A87 peanut ported to 1.5" to match the intake, everything else about the engine is stock.  While the engine was being machined i sent the carbs out to Ztherapy so they're nice and new too,  

 

The problem I'm having is that I can't get this thing to run right.  I watched the ZT video, installed my carbs and set them up for the start up, after realizing the oil pump drive shaft was 180 degrees out it fired right up and idled perfectly.  I set the timing at 18 advanced, (thats where it seems happy) synced the carbs and everything was good.  However when I took it out for it's first drive, I noticed that as the RPM's would approach 3k it would start to cut out, not like loosing spark but like starving for gas, it just feels like it looses steam.  If I tried to slowly coax it past 3k it would fall on its face and backfire out the carbs.  If I floor it, it bogs and reluctantly revs out.  I'm not pushing it really high though as it's a fresh motor.  

 

So it seems to me like a lean condition.  I turned the mixture nuts out to the point where it barely runs, no real change just shittier performance and slightly less backfiring.  Checked the floats, they look good.  I installed a fuel pressure gauge to check the fuel pump, 3.5 pds steady.  Has a new fuel filter, and all new fuel lines with no kinks.  Checked for vacuum leaks with carb cleaner, found none.  Checked valve adjustment, spot on.  Checked valve timing, I think it's right, I'll post a pic below.  The distributor was the one on the engine before, it's a points style with pertronics, vacuum advance moves and it appears to advance properly when it watch the timing marks as I rev it.  When I back the timing down to 10 degrees it idles a little more rough and still backfires badly.  

 

I called ZT and talked to Steve he was very helpful, he said it sounds very lean and was surprised because the needles he installed (M66) work great in SSS l16's.  He sent me a set of M43's (slightly richer).  I installed them with no real change.  I called Steve back and he told me that I'll most likely have to make a set of needles that work with my set up. He shipped me a grab bag of needle sets to experiment with.  After some research on needle modification I ordered an O2 sensor and I'm awaiting its arrival.   

 

I just want to make sure I'm not missing something before devote a ton of time into modifying needles.  With all the research I've done on the forum I haven't found a case where someones vehicle was practically undrivable because of symptoms similar to mine.  Help me Ratsun it's killing me having a fresh truck that I can't drive.

 

Shot of the piston with a little chunk missing.

 

 

 

Heres a shot of the cam timing.

 

 

A few of  the engine after I got it back.

 

 

 

 

Engine installed 

 

 

 

The day I drove it home.

 

 

I was so proud of it that I threw it in a car show for shits and giggles.

 

[wayno]

I would go back to the start, turn the engine to TDC, remove the valve cover and check to make sure the cam lobes are at 10am and 2pm, remove the dist. cap and make sure that the rotor is pointed at the post/wire that goes to #1 spark plug, make sure all the valves have play.

If the photo of the cam timing was at TDC, then the lobe in the background looks wrong.

[flatcat19]

That's a sexy motor. 

 

I hope you get it figured out. 

 

To me, the pic of the cam gear looks like you're a tooth off. 

[Thepspack]

I had the engine at TDC #1 when I took that photo.  The valves for #1 where at 10 and 2 with a little play in the rockers.  The distributor was pointing at #1.  I think the lobe you see in the photo is on cylinder 3.

[Thepspack]

That's a sexy motor. 

 

I hope you get it figured out. 

 

To me, the pic of the cam gear looks like you're a tooth off. 

Thanks!  I did a lot of searching for posts about the cam timing.  I was unable to find an answer that made me feel confident about if the timing was correct or not, so I figured I'd post a photo and see what people think.  

[wayno]

10am & 2pm, see how that lobe in the background in this photo is not pointed up like yours.

TDC

I set my cam timing by eye now, I have been off a tooth in the past, but it did not backfire out the carb, it just didn't have power.

Back firing out the carb or exhaust has always been tight valves for me, to get home when on the road I have always pulled the problem plug wire if an intake, if it was a tight exhaust valve I just drive it home and fix it.

[Sealik]

The cam is advanced too far....

 

 

 

Should look something like this at TDC

 

[datsunaholic]

The cam off by that little isn't why it's backfiring at high rpms and bogging under heavy throttle. . I think its starving for fuel.  You may have sufficient pressure but insufficient volume.  The cam being off is why you need so much advance, though. 

[datzenmike]

Yes cam too advanced. It should be on the #1 sprocket hole for L16 or what ever gives the same as Sealik's picture.

 

Worse is the 18 degrees advance. L engines are closer to 12 degrees.

 

Try both these simple adjustments.

[dr.feltersnatch]

it sounds to me like you have multiple issues. it also sounds like you may have a small blockage on your fuel delivery causing it to go lean. i would pull the dome and slide CAREFULLY out and remove the fuel line from the fuel bowl and blow air back through the jet to be sure there isnt a small piece of debris in there. it doesnt take much to block it off. how did you set the needle? how much oil did you put in them? what oil?

[Thepspack]

Thanks for the help everyone!

 

Yes cam too advanced. It should be on the #1 sprocket hole for L16 or what ever gives the same as Sealik's picture.

 

Worse is the 18 degrees advance. L engines are closer to 12 degrees.

 

Try both these simple adjustments.

I've watched Mklotz's video on reclocking the cam sprocket.  The idea is dicking around with sprocket till it looks just like Sealik's picture?  Seems simple.  If the cam is too advanced, that may be why it seems so happy with the timing way advanced at idle.

 

it sounds to me like you have multiple issues. it also sounds like you may have a small blockage on your fuel delivery causing it to go lean. i would pull the dome and slide CAREFULLY out and remove the fuel line from the fuel bowl and blow air back through the jet to be sure there isnt a small piece of debris in there. it doesnt take much to block it off. how did you set the needle? how much oil did you put in them? what oil?

When set the new needles I used the technique in the ZT video.  Screwed the nozzles all the way in, lightly set the needle in the slide, and gently push the slide in while holding the nozzles in place till the slide bottoms out.  Then tighten the needle.  I filled the slides with oil just to the threads.  A tiny bit would spill out as push the damper thingys in.  On both needles that i've tried I used ATF as recommended by ZT.  I've also tried 20 WT fork oil to slow the slide down a little and enrichin the mixture upon acceleration.  

[ggzilla]

The Hitachi carbs have an oil dipstick. Don't fill it to the top!

 

[dr.feltersnatch]

I only run 3cc of atf in mine. Thats like a tbsp or so. Not much oil is needed. some people count the drops as so little is needed.

[ggzilla]

Multiple causes make sense:

* excess spark advance gives smoothness but limits RPMs

* excess damper oil causes problems with throttle transitions. Steady RPM would probably be OK

* idling problem

[Thepspack]

The Hitachi carbs have an oil dipstick. Don't fill it to the top!

 

Shit! I never saw those marks I'll fix that too.  Thanks!

[wayno]

I just pulled the valve cover off the LZ23 to look at my lobes at TDC, yours looks close, the L16 engine is supposed to be in #1 dowel hole and timed on the #1 gear mark.

I also fill my damper to the top of the SU, and start the engine, it seems to self level as it is not at the top anymore after running for just a little while, I have never had an issue in 20 years of doing it this way, it doesn't mean I am doing it correctly, but I have had no issues doing it that way.

You said your idle was rough, was it a very high idle that you turned down?

Check your PCV valve, pull the hose off it that goes to the case vent, does it sound like a very slow leak, or does it sound like a big leak while running?

If you put your finger on the end of it and stop the leak, does the idle change?

[datzenmike]

 

 

I've watched Mklotz's video on reclocking the cam sprocket.  The idea is dicking around with sprocket till it looks just like Sealik's picture?  Seems simple.  If the cam is too advanced, that may be why it seems so happy with the timing way advanced at idle.

 

 

 

An advanced cam closes the intake early and favors low speed running above high RPMs.

 

At idle the closed throttle does not allow the cylinder to fill completely with air. Maybe a half a cup volume. When compressed and fired there is just enough power made to keep the engine turning. Any engine with week cylinder filling needs more ignition advance because it takes longer for the flame to jump between widely placed molecules. Yes, I have no doubt that it loves being at 18 degrees but since the late 60s all distributor advance has been ported from the carb giving zero advance at idle and vacuum advance above where the engine likes it.

[Thepspack]

I just pulled the valve cover off the LZ23 to look at my lobes at TDC, yours looks close, the L16 engine is supposed to be in #1 dowel hole and timed on the #1 gear mark.

I also fill my damper to the top of the SU, and start the engine, it seems to self level as it is not at the top anymore after running for just a little while, I have never had an issue in 20 years of doing it this way, it doesn't mean I am doing it correctly, but I have had no issues doing it that way.

You said your idle was rough, was it a very high idle that you turned down?

Check your PCV valve, pull the hose off it that goes to the case vent, does it sound like a very slow leak, or does it sound like a big leak while running?

If you put your finger on the end of it and stop the leak, does the idle change?

It idles great as long as I keep the timing around 18-20 degrees advanced.  If I set it to 10 or 12 degrees it's not very happy, I have to crank the idle up and the exhaust manifold gets pretty damn hot.  I'll check the PCV when I get it back together.  

[flatcat19]

It idles great as long as I keep the timing around 18-20 degrees advanced.  If I set it to 10 or 12 degrees it's not very happy, I have to crank the idle up and the exhaust manifold gets pretty damn hot.  I'll check the PCV when I get it back together.  

 

 

An advanced cam closes the intake early and favors low speed running above high RPMs.

 

At idle the closed throttle does not allow the cylinder to fill completely with air. Maybe a half a cup volume. When compressed and fired there is just enough power made to keep the engine turning. Any engine with week cylinder filling needs more ignition advance because it takes longer for the flame to jump between widely placed molecules. Yes, I have no doubt that it loves being at 18 degrees but since the late 60s all distributor advance has been ported from the carb giving zero advance at idle and vacuum advance above where the engine likes it.

 

PS; PT

 

Clock our cam gear on a different hole to better line up the marks. 

[wayno]

It idles great as long as I keep the timing around 18-20 degrees advanced.  If I set it to 10 or 12 degrees it's not very happy, I have to crank the idle up and the exhaust manifold gets pretty damn hot.  I'll check the PCV when I get it back together.  

If the PCV valve goes bad(the guts come out), the engine revs higher than normal while you would think it would be idling, you would be trying to slow the engine down, not trying to speed it up, and when it happened to me, the hose going to the engine case hid the issue, when I removed the hose going from the engine case to the PVC valve, I realized what the issue was right away, BIG vacuum leak.

You need to get the cam timed correctly first.

[datzenmike]

 

It idles great as long as I keep the timing around 18-20 degrees advanced.  If I set it to 10 or 12 degrees it's not very happy, I have to crank the idle up and the exhaust manifold gets pretty damn hot.  I'll check the PCV when I get it back together.  

Lets assume that your timing is correct and you have to run 18 degrees. This would indicate to me that you have very low compression or very little air and fuel to compress. Generally the more the cylinder is filled or the higher the compression the less advance is needed.

 

Get or borrow a vacuum gauge and connect to the intake. At idle you should have about 15 inches of mercury. (more is better) Good vacuum will show that the intakes are shutting and sealing properly and the cam is close to stock. Low vacuum might be a  gasket leak or some source of air getting in. This would lean out the mixture requiring more advance and backfiring out the carbs.

 

As wayno said about the PCV valve just remove hose and temporarily seal it and try.

 

But first set the cam back one hole or run on #1. 

[Thepspack]

I made a cam chain tool last night after some 4th of july libations, think I did a pretty good job considering.  I'm going to pull my truck into the garage and attempt to fix the cam timing.  I'll report back the results.  

[Thepspack]

Ok, so I put the cam on the #1 hole, still don't look quite right.  I think it's because of my timing pointer, in the photo it looks bent.  If I set to time to it, that could be throwing everything off.  I backed the sprocket one more tooth but that puts it to far back.  It looks like if I bend the pointer to where it should be that would rotate everything a few degrees counter clockwise and everything would look right.  

 

 

Sprocket on #1

 

 

 

[datzenmike]

Yup to the bend. If the chain is good and set on #1 then assume it's all good. This is where the factory set it.

 

Try a vacuum gauge at proper idle speed.

[Thepspack]

Got the truck back together.  Fired right up, set to timing to 10 degrees advanced and it seems pretty happy.  Threw a vacuum gauge on it and it's reading 17-18 pds steady.  Backfiring issue still persists.  

 

 

Straightened pointer

 

 

 

Cam timing with straighter pointer

 

 

 

When I first tried to get this thing running i realized the distributor was 180 out.  I dropped the oil pump and corrected it but it still looks like it's wrong, maybe a tooth off there as well?  My timing gun says 10 degrees advance but the plate looks like a lot more.