Light white smoke and backfire at high RPM or under load

[Grit dog]

@iflyfisher
Sounds like it’s advancing ok?
My light has an advance knob so you can set that and read zero on the crankshaft. At high rpm’s should see idk 35-40deg advance.
I’m no timing expert so fwiw.
Sounds like the motor is solid and just needs a little more tinkerin.
and one of the coolest models. First year K20 in an awesome color!

 

[DoubleDingo]

Yeah old engine, no cats to trap stuff. The 86 spits black chit out just like that. And it runs just fine.
Again no cats, the old 86 is a smoke (steam) show when the weather is cool. Until the engine warms up.

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That's how my 81 is, too. It really gets people's attention that are driving or walking by.

 

[iflyfisher]

@Grit dog, Thanks! I love that color scheme too. It will look much nicer in a couple of years when it doesn't have the rust accents .
@DoubleDingo, The exhaust seems dirty, and makes a mess of my garage floor. I put up a cardboard box to protect the stucco wall. Sounds like some gunk is normal, maybe it will clean up more with some more time on the engine.

I did pick up a vacuum gauge this afternoon, but I didn't get much of a chance to play with it. I plugged it in to the port coming off the front that swings around the passenger side of the carb to the vacuum advance on the distributor. See the attached picture. I didn't get much vacuum until I blipped the throttle, so I figured that line is ported vacuum. The vacuum hose coming off the carb there was pretty loose fitting, so I cut a new section and replaced it. I did some searching on the net, and appears the port coming off the passenger side by the choke mechanicals is manifold vacuum. Is that correct, and I hook up the vacuum gauge at that port? This port is normally connected to a hose going up to the air cleaner canister. I took the truck for a drive, and the bit of vacuum hose I replaced seemed to have no impact as I still got backfires or misses under load or high RPMs.

I bought some more springs for the throttle return, but they ended up being too long. I cut off the ends and bent new hooks. I worked them to where they were more firmly closing the throttle, which did help bring down the idle. The idle was still a bit high, so I retarded the timing a bit. I had it set to 4 BTDC, and worked it lower while the engine was idling. The idle sounded best at 4 ATDC. That seems weird, so I split the difference and set it 0 BTDC. I don't have a tach, but the idle was much smoother and lower. When I turned off the ignition, the engine immediately stopped, where before it may have tic'd over a sec before shutting down. I took the truck for drive, and it ran much better. It didn't seem to lug as much going from 1st to 2nd up the incline in my neighborhood, and I couldn't get it to backfire unless I buried my foot in the throttle. So that was encouraging. I was tempted to retard the timing a touch more but didn't. Does having the timing near 0 BTDC make sense? I would have thought more advanced would give better results. But the lower idle and smoother operation seemed to make for a happier engine.

Sitting here typing this, I remembered that I had set the timing without unhooking the vacuum advance line and capping it. So the actual timing was probably a couple degrees off. I'll recheck it tomorrow when I get a vacuum reading. I also want to check the compression in each of the cylinders tomorrow.

 

[DoubleDingo]

A tight exhaust system will spit out condensate carbon droplets. Dirty, yes, concerning, no.

 

[squaredeal91]

I really love seeing that points distributor in their. I know they were changed recently last decade but have you tried carefully cleaning them? And how about the dwell set? Could make all the difference. I don't think it's been mentioned yet and I just thought of it.

 

[iflyfisher]

@squaredeal91, I had a few recommendations to swap the distributor for an HEI setup, but frankly I want to learn to tinker with the points one for now. I did floss the points a bit with some 400g paper when I had the distributor out. But you are correct, I haven’t checked the dwell setting. Something else I don’t know how to do :/. Seems like that list is endless. I’ll do some research on setting dwell and see if I can get to that after checking compression, vacuum, and reconfirming timing advance with the vacuum off the advance. Oh, and I also need to do do the wire pull at the distributor and salt water lightning test recommended by Ricko1966. May get to those tomorrow as well.

 

[squaredeal91]

You'll need a dwell meter to set dwell. Unless there's another way I don't know.
At least Delco made it easy with that fancy window.

 

[Wazzabie]

Yeah old engine, no cats to trap stuff. The 86 spits black chit out just like that. And it runs just fine.
Again no cats, the old 86 is a smoke (steam) show when the weather is cool. Until the engine warms up.

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This is what my 78 K5 looks like. How long does it take for the steam smoke to clear?

 

[DoubleDingo]

This is what my 78 K5 looks like. How long does it take for the steam smoke to clear?

Once the engine is up to operating temperature

 

[Ricko1966]

Get new points,points have a platinum coating,if you sand them you sand through the coating and they oxidize,fast,so then you have to sand them again. If one point has a t I T. on it you need a condenser. You can set dwell with a feeler gauge,it's not as convienent but you probably have a feeler gauge. I'll see if I can find you a point gap setting. New points, with the cap off loosen the distributor clamp rotate the distributor,until the points rubbing black is on the highest point of the distributor lobe. Open or close the point gap until a .019 feeler gauge just fits,if you are using old points use .016 . It's been a long time since I messed with points,done them by gap,done them with a dwell meter 50/50 split on those, but Trying to remember back to when I was 17. I think my GTO I use to run the screw in until the engine stumbled,back it out 1 turn then back in a 1/2 turn, that's before I had fancy things like dwell meters and was to lazy to pull the cap and check gap. I'd bet you @idahovette or @Turbo4whl or @keithseymor has done them by ear and can set you straight as to if I'm remembering that right.

 

[iflyfisher]

Thanks for all the quick feedback. Got a good list of things to tackle tomorrow.

@squaredeal91, I do have an old dwell meter of my dad’s. I did some reading on setting up a dwell meter and adjusting dwell. Think I can tackle it.

I downloaded the manual on the forum for the truck. When looking up the dwell numbers, I saw the shop manual had 0 BTDC for timing. That is a bit different than the book I have and is more consistent with what made there engine run better.

@Ricko1966, I have a fresh set of points and condenser that I purchased a week ago. I’ll drop them in before I do anything else tomorrow. Then set the dwell, then timing, and see how it runs. I’ll look up the point gap in the manual I downloaded. Thanks.

 

[idahovette]

Hallefukinluia he's got a Dwell meter....gets us off the hook @Turbo4whl !!!!......lol....I do think you are right on your instructions @Ricko1966

 

[Grit dog]

Once the engine is up to operating temperature

This

 

[iflyfisher]

Gents, we are getting very close.

Swapped out the points and condenser this morning. I tried doing this with the distributor in, but very difficult to get in there. The condenser screw was totally blind, so I decided to pull the distributor. I thought I had noted where the cap was, so putting it back in would be easy. I got in the points and condenser and reinstalled the distributor then started the truck. I got the dwell meter hooked up and set the dwell to 30, then grabbed my timing light. I was shocked when I pointed the light at the HB and saw nothing. Doh! Surprised it had been idling so well. I thought about taking the distributor back out, rotating 180 degrees and dropping it back in, but I decided to find TDC and make sure I got it in correctly. I set the advance to 0 BTDC then checked that the dwell was at 30.

I hooked up the vacuum gauge, and it held steady at 16" Hg. I'm not sure what normal is for this engine, but this seemed a touch low. I blipped the throttle and the needle dropped, but I didn't note whether it dropped to 0. In looking at the graphic, I can't say whether the vacuum is low enough to have a ring issue. I had added a bottle of Marvel Mystery Oil to the oil, which probably reduced the viscosity a touch. Also given how little the engine has been run since I got it, and how little over the previous 30 years, the valves and rings may still have some buildup or stickiness. I wanted to check the compression, but my wife reminded me we had a holiday party to go to, and I still needed to run a few errands. I decided to put on the air cleaner and canister and take the truck for my errands.

I drove three miles and pushed and held the RPMs fairly high once the engine was warmed up. I also shifted a bit early a few times to load up the engine a bit. No misses and no backfires. I made a few more stops then drove the three miles back home. The truck ran great until I made the final climb up to the house. On the steepest part of the climb, I got one small backfire from the engine when pushing it up the hill with high RPMs.

This was the best the truck has run. Previously, I would get a few misses even on level roads, and the truck did not like shifts at lower RPMs. I still haven't spritzed w/salt water however, given I have replaced almost all the ignition components but the coil, I am thinking the ignition is pretty good now.

Thinking about things, that seems to leave the carburetor. When I was a teen living at home my motorcycle and snowmobile were very sensitive to elevation changes. I don't know how sensitive these old Rochester carburetors are. My Dad was living at an elevation over 5000' and often drove the truck in the mountains at around 8 to 9K feet. I wonder if he would have jetted the carb for a high elevation. I am now driving the truck below 3K feet. If my Dad had leaned the mixture for the higher elevation, it could be a bit starved for fuel here. What do you think?

I'll check the compression next week and will check the vacuum again after the engine has a few more tanks of gas through it.

Guys, I admit I have been having fun tinkering with this ol' engine. Progress has been slow, but progress nonetheless. I do get frustrated that I seem to spend more time researching and watching YouTube than wrenching, but I am learning a ton. Thanks again for the patience and handholding!

Ken

 

[Ricko1966]

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