Timing and balancer help!

[kcstreetracer]

Ok fellas, I have a truck I've been building the past few years
And have it to the point I'm ready to get it running. But I am having some timing issues I believe.

I have it close enough on timing that it runs. But I can't get much run time because I'm worried it has some pre-ignition or detonation. Its not rod knock I'm sure of. Basically as the cam lopes as it fires it pops and it sounds like its coming out of the carb. Its not every cycle but almost. I've tried turning the distributor but no luck.

Motor is a 355 with 234/488 cam,sportsman 64cc heads,single plane,fts 750 mechanical secondary carb, hei with heavy and light springs.Have 93 octane in it. I believe compression is probably around 10 to 1

I'm not sure if my balancer is correct for my timing tabs. I can't seem to find anything solid on it. The # is 7704 which i believe is a pre 69 8" balancer? My timing tab is bolted on the cover and tdc is about 2 o'clock. The timing mark on the balancer is just a hair to the left of the keyway. I originally had dropped the dizzy in at tdc, but redid it to what I believe is 8° btdc which seemed to help a tad. Starts easier and idles a bit better. I have a piston stop coming to try and get it but this is all new to me, although I'm pretty decent with a wrench the old school stuff is new to me. Im just wondering if my issue is what I think it is or if I need to focus my attention elsewhere. Thanks

[truckster]

The only way to be sure of TDC is a piston stop. It replaces the #1 plug and lets you determine exactly where TDC is.

You can buy one:
https://www.summitracing.com/search/...e/piston-stops

or build one:
https://www.hotrod.com/articles/wren...y-piston-stop/

Once you know for sure where TDC is, you can set your timing with confidence.

[jocko]

Recall there are 2 TDCs, you want to set your distributor rotor up to just be starting to touch the #1 plug wire tower contact when your balancer is at approx 8-10 deg BTDC on the compression stroke. Thought I'd mention just in case.

[kcstreetracer]

Thanks for the replies. It is dropped in at 8° btdc on compression stroke.

Just curious, is that popping im hearing most likely pre ignition or detonation?

[geezer#99]

That popping might be a valve problem.
Was the motor broke in right?
Like 1500 to 2000 rpm on first start.

[kcstreetracer]

Originally Posted by geezer#99

That popping might be a valve problem.
Was the motor broke in right?
Like 1500 to 2000 rpm on first start.

Yes it was. First one got 10 minutes at 2-3k had a issue a d shut it down. Fixed problem and went another 15

[Willys_MB]

I was having this issue a year or so ago. It was all fixed once I spent the time and researched how to tune my carburetor (Holley 4150). I’d suggest you start there and work your way towards the more complex issues.

When checking timing are you plugging/pinching your vacuum advance line?

[RustyPile]

Originally Posted by kcstreetracer

Thanks for the replies. It is dropped in at 8° btdc on compression stroke.

Just curious, is that popping im hearing most likely pre ignition or detonation?

I don't remember the exact years, but some years the timing tab was located at 12 o'clock on the chain cover behind the water pump.. The balancer was marked accordingly.. If that balancer is used in conjunction with the tab located at approximately 2 o'clock, the engine can be made to run but the timing cannot be set properly.. Be sure you have "matching" tab/balancer..

If those two parts are correct, and the timing is set properly using a timing light, the popping sound is caused by something else.. Most likely causes are valves are set too tight or camshaft lobe is going away...

[kcstreetracer]

Yes vacuum is disconnected and plugged on carb and distributor

[truckster]

Originally Posted by kcstreetracer

I have a piston stop coming to try and get it but this is all new to me, although I'm pretty decent with a wrench the old school stuff is new to me. Im just wondering if my issue is what I think it is or if I need to focus my attention elsewhere. Thanks

OK, that's what happens when I'm reading posts and playing with my grandchildren at the same time. You're on the right track; I would start by verifying your TDC matches your timing tab. I read somewhere that 90% of carburetor problems are timing problems. I don't know how true that is, but I do know it's pretty much impossible to get anything else right until the timing is set.

[Ol Blue K20]

I had the symptoms that sounded like that once. I discovered 5 and 7 wires were crossed and that's why it had the pop out the carb. Check your wires, it's the little things we overlook sometimes...

[Grumpy old man]

Is this the same engine you were having problems with a few weeks ago ?

https://67-72chevytrucks.com/vboard/...d.php?t=820812


Post up a few pictures of the engine , Pictures always help .

[BigBird05]

You have a piston stop on order, thats good. But let me ask if you know how to use it to set TDC on the balancer? You rotate the engine either clock wise or counter clockwise till it stops. Put a mark on the balancer at 0 at the timing tab. Then rotate the engine the other direction till it stops. Put another mark on the balancer. Half way between those marks is TDC. It helps to mark TDC on the pulley also because faulty balancers do move over time changing the location of the timing mark.

[CC69Rat]

Originally Posted by Ol Blue K20

I had the symptoms that sounded like that once. I discovered 5 and 7 wires were crossed and that's why it had the pop out the carb. Check your wires, it's the little things we overlook sometimes...

My first thoughts too.. easy to miss it.

18436572. 5 and 7 are right beside each other in the firing order and on the block, so it's easy for those wires to get swapped.