Inliners International Forums General Discussion Engines Still Struggling with timing

I have most of the bugs worked out and major items like brakes ready to go on my 66 Chevy truck, but want to make sure I have all right with the engine before the maiden voyage.

The engine is a rebuilt 250 with a 1 barrel Rochester carb. I have tried setting the timing by the book with not much success. I'm assuming the marks on the tab are BTDC on the side farthest from the pavement and those closer to the ground are after.

There is no way I can get the timing to any less than 8 degrees before TDC without killing the motor. The truck seems to start best with the timing even more before TDc than that. When I get the thing where it starts really well, I get backfiring thru the carb when I hold the throttle open, but it runs ok when idling.

If I get the timing where I have the most vacuum...(around 18)the thing is really hard to start, but runs smoothe.

I have a HEI installed. Will that make some difference in the timing?

I have to wonder about the dist. being 180 out, but I didn't think it would run if that was the case.

are you setting the timing with the vacum line unhooked? after setting it hook up the line, watch the timing, it should advance even more with vacum. now rev it up without the vacum line. the timing should also advance with mechanical (centrifical) advance. tom

Didn't think the vacuum line would make that much difference, but tried that way. I can get the timing mark to be where it should be, starts good, seems to run ok. But, it just seems like the engine is working a little hard. I don't have much vacuum either (13).Difficult to describe..seems to have minor vibration and smells warm. I tried to keep the thing as close to original as possible, cause it was my grandpas, but I really need to put a set of gauges in this thing so I can see what is going on all the time.

Dear Curt;

Tom is correct; Set the timing with the vacuum line off & pluged. Then adjust the idle mixture & speed.

When the line is re-connected the idle speed will increase. Re set the speed control only and your "good to go".

After a few hundred miles re-torque the head and adjust the valves again (hot) running.

Good luck.

I set the idle, plugged the vacuum, adjusted the idle mixture to give best idle and then adjusted timing. Reconnected the vacuum line. It starts great, idles ok, but if I hold the throttle down it misses and backfires thru the carb.

Could there be another cause that I'm missing?

I went out to the garage and checked the plug wires to be sure....should be 153624 firing order, correct?

I also think this order is clockwise around the cap??

C;

Yes, both (wiring/direction) are correct. Did it speed up when the vacuum line was connected??

I couldn't really notice a speed up. There doesn't seem to be much vacuum on that line. The timing did advance when accelerated. I verified that with the light.

Do you think it could be a valve problem?

It's really hard to tell W/O seeing/hearing it. There sould be a major 'speed up', forcing you to reset the idle speed.

You may be 'a tooth off' (dist) somehow. Get #1 @ TDC & double check it & the position of the distributor.

Let it warm up @ idle & check/adjust the valves which will eliminate that too.

Do NOT try to drive with it this way.

Definitely not that kind of speed up when connecting.
I also hear a slight clicking noise (very brief) when it is cold and the throttle is pressed.It seems to go away after a couple minutes, but is definitely related to the idle speed. It is not a lifter sound...can't really describe it. It does sound like it is the passenger side though.

I've never adjusted valves.Is there a procedure for that that would be printed somewhere? I've done some searches, but didn't find anything very extensive, and some seemed to be done with the motor running. Not sure on this part.

Who adjusted the valves when the engine was assembled??

Double check the distributor first, which is the "most likely" cause as it does idle smooth.

It may be 'advanced' a tooth and you retarded it to make it run that way.

John,
Jasper engine rebuilt the motor, and test ran it at their facility. It does idle smoothe and is very quiet compared to the original motor.

Would it make sense to pull the valve cover to be certain of the compression stroke when rechecking the distributor? I just want to make sure I have it right, as this won't be a show truck, but could be driven as much as 50 miles round trip to my parents, and possibly a cruise in. Having power steering (added), good brakes and a reliable motor are really important right now. Sorry to be such a pain...obviously my first attempt at this kind of venture!

C;

DO NOT drive it and forget the valves for now.

Rotate the engine till the marks are at TDC & check the distributor!!

The advance can should point "8 O clock" and the rotor directly on #1 wire position (cap).

Your probably in wrong like I stated.

When it advances (running) It's so far ahead that It's firing before the intake valves are completly closed.

ok,

On my way out to try this.

the timing cannot be off a tooth if it runs and he can set the timing. you need to verify operation of both vacum and mechanical advance mechanisms. 13 inchs of vacum is alittle low but ok. the valves may need to be adjusted. but i would worry less about them and more about getting it up to 2000 rpm and hold it there for 20 minutes to break in the cam. engines can smell and sound funny when breaking in. they can run hotter than normal also. tom

T;

He can't set the timing** as it dies @ 8 degrees etc.


**The light's telling him It's near 8 degrees but It's really about 38 because It's one tooth advanced and he rotated the Dist back to make it start.

Found plugs to have alot of carbon, but suspect that was from the period where I was waiting for a choke cable, and was starting the truck and jumping out to manually take the choke off.

I reset all on timing. Starts good, runs good with no backfire. Still feel it misses a little at higher rpms, but might just need to get it out and drive it a little (somebody following of course).

Tom, I ran it at 2000 rpm for about 15 minutes. After the looks I got from a few of my neighbors I decided that was about as good as I could get!

I do get more vacuum when I advance the timing some. Up to about 17. It fluctuates a little at idle..only about 1" (16-17).

Dear Curt;

One word. OUTSTANDING!!

is 8 deg ok for your hei? i found this out the hard way when i switched over to it. the manual calls for 4 deg or something, mine ran awful at that. i have to advance mine off the timing tab for it to run great, like 15 or 17 deg. after it is broke in you might try setting it with the vacumm gage and trying some accel. runs up long hills and see if it pings back it off. then you can toss the light in the trash - just kidding. hey, i'm no expert though. but i scratched my head for a while trying to find out why it wouldn't run at original setting and finally gave up after all i wanted to drive it where it ran good. i tried the advancing it a tooth at the time it didn't help mine. once it did i would just have to rotate it more. good luck, those 66 chevies want to run and i bet yours will. hoggyrubber

Hoggy,
Thanks for the advice. I may end up trying that.

John and Tom, Thanks for all your help (and patience)!

again, i'm no expert. the 250 w/ hei i was talking about i rebuilt myself and put in a "stock" cam. i found out while doing research on the clifford performance cams for my 292 project that these other "stock" cams like the sealed power one i bought for my 250 don't even have the same duration and specs that the 66 manual says the true stock ones do. mabey that accounts for some of the difference in timing. clifford told me to set the timing 23 to 27 deg i think, it's written down at home. i know that is apples and oranges but my point is prob whatever cam jasper used it isn't exactly the same as true stock. when i do my startup in a couple of weeks i will start out on the low side of those #'s so i don't have a flamethrower for a carb. that is i hope. :rolleyes:

Here's a thought that may be worth looking into.
I had a used HEI distributor on my SBC in my 69 Pickup. The centrifugal advance had rusted enough that the weights would stick at full advance. When the engine stopped they would reset. So when I checked timing in the driveway it was fine. When I drove it, it would ping heavily and idle poorly. I finally discovered the problem by revving the engine with the timing light connected. I could see the timing advance "snap" to 20 degrees at about 2500 rpm, then stay there as the engine idled down. I replaced the distributor with a new one but I probably could have cleaned up the advance mechanism and greased it to make the old one work. Might be worth pulling the rotor to take a look, Curt.

regards,
Leon

It could be your damper has slipped & giving you an incorrect reading of your timing?

You can verify this by correctly finding your TDC #1 cylinder(with a piston stop),& then looking to see if your timing mark on your damper is in the correct spot.

MBHD

I had a Ford 302 V8 sometime ago and it had a similar problem at thigh rpms. In my case, I had to re-ground the distributor "shaft" and its gear. It solved the problem. Not sure if it would help, but you can see it just removing your distributor and moving its shaft. If it moves in an anormal way, it might have a problem. Another thing you can do is to check your carb base to intake gasket to be sure of its sealing to try to make more vacuum. Just trying to help... Tks & good luck!

Check your distributor cap for a small crack or moisture and make sure that your plug wires aren't cross firing due to improper routing. Either of these could cause a small miss. The vac ought to be stable at idle on a stock engine but I would drive it and see what happens if it doesn't go away then check valve adjustment. Always check the simple things first. Your small miss could be causing the unstable vac at idle.

what did you gap your plugs at???? using an HEI requires that you gap your plugs around 40-45..

Fire up the engine. rev it up to where it starts to skip and back off the timing.. My 250 did that also and on`ce I did that it ran good.
adjust the carb ans idle and run it..

Mike
I.L. # 3108

I gapped my plugs at 55. I'll have to double check that, but thought it was the setting suggested when I bought the distributor.

I'll double check those.

Thanks guys