355 Poor Performance

[78ScottsdaleK20]

I have a 350 bored .030 over. SpeedPro RV Torquer .448 lift 214 duration 112 LSA. Speed Pro Hypereuctectic flat top pistons, Edelbrock Performer EPS, Edelbrock 600 cfm #1406. HEI with 50,000 volt coil, and Heddmen Headers running through 2 1/2 inch dual exhaust. SM 465 trans.

Since new I have never been able to tune this carb in right. Changing rods, jets, springs, etc. Get tuning close, holds for a little bit, then starts to run erratic. I have replaced 3 Intake gaskets due to a suspected vacuum leak. I have checked with carb cleaner and propane to no avail. Last Intake gasket change, engine performed flawlessly, for 1 day, then erratic since. Spark plugs arent showing same type of A/F. #6 and #8 more rich fouled than the others. Timing has been set at 10 and 12 degrees BTDC. Found 12 is best. I get fine dirt particles in the float bowls, and have just put in new fuel filter (clear). All linkage especially throttle shaft, choke linkage, and air bleed screws gets pretty dirty. I clean them periodically.

I have a basic timing light, so I have not set total timing. I will be putting a timing tape on the balancer and making marks on it to check for total timing and do the valve lash adjustment. I should be able to check total timing with a basic timing light at the timing indicator if balancer is marked, correct?

I have put approximately 15k on the motor, and as of now, I am hearing some higher pitch chatter coming from the valve covers, sometimes it sounds as if the push rod has excessive play, only after a slight increase in RPM's. Is it common for a necessary valve lash adjustment neeeded at this mileage? Could my mysterious vacuum leak be coming form mal-adjusted valves, or even excessive worn valve guides?

This engine has been pretty good thus far...starting every time, and not acting too erratic, just needs some of that advanced tuning to be just right. So any other ideas, comments, or suggestions are welcomed.

Thanks,
Mike

[VileZambonie]

So what exactly is it doing? Does it idle poorly? Does it have poor acceleration? You should pull the fuel inlet off and take the air horn off of the carburetor. Remove the floats, the needle and seats and remove the factory sock filters. I never re-use them. Make sure the float level and float drop are set correctly. You may want to upgrade the needle and seat.

Explain more of your driveability symptoms.

[78ScottsdaleK20]

The idle and driveability for the most part is ok. The idle lopes a little (jumps around 200-350 RPMs) and shouldnt with this mild cam. Almost acts like it missing. But it also could be carb metering.

I had the carb jetted really lean, 2 1/2 stages lean and the A/F was spot on. Then a month to a month and a half the A/F got really thin (lean). So I bumped the jets and metering rods fat back to base calibration and seems to be the best there, but really fat at idle and cruise, and thin at part throttle.

Vacuum readings pulledat idle from the Intake are an average of 14" hg with a rapid floating needle between 13"-16". The throttle is opened and vacuum drops to 0"-2", raise back up to 20" with a rock steady needle with RPM's around 2,000-2,500.

Vile I will take your advice and tape a vacuum gauge to the windshield and take some readings as to what the engine is doing. This will give an accurate and real world scenario with engine load. I have have been eyballing an MSD ignition box for a while, but havent done enough homework to decide which one would be best for my application. Any suggestions...?

Thanks for the reply.
Mike

[VileZambonie]

An MSD 6A with a distributor and coil would be a great improvement. It also sounds like your timing is too retarded. TRy advancing it and then check your vacuum readings. If your needle is still boucing I would suggest a compression test.

[1976Scottsdale]

Definately set those floats man.  I just rebuilt an Edelbrock 1406 and is was WAY off on float settings.  I bought it from its original owner who let it sit and never cleaned it.  It had never been opened up or rebuilt before me.  It was seriously like bottomed out and then as soon as a touch of fuel came in, it would close the needle cause it was set too low.  Now it runs fine since I rebuilt it and reset the floats.  Also, go ahead and check your valves again, pull a valve cover and prepare to get messy.  Loosen each valve with a 5/8" socket until it taps, then tighten until it stops and go 1/8 to 1/4 turn more.(stop and back off if you hear it sucking through the intake.).  IT helps if ya cut out an old valve cover across the top, the you can just put a couple red rags(shop rags) over the valvetrain and move them over as you need them.  It's gonna be a lot of oil, min saoked the fender today when I ran mine.  My carb seemed like it had a dead spot in it until I adjusted the valves.  I had one a bit too tight and three that were just barely past ticking.  Now I am doing fine, no more erratic idle, no more seemingly missing engine, and a lot better takeoff.  Of course, that's just a suggestion.

[78ScottsdaleK20]

Floats were set correctly previously. Here are some Vaccum readings I have encountered.

During Idle, the needle on the gauge violently drifts between 13"-16".
When throttle gradually is opened, vacuum drops to around 10" then picks up vacuum usually around 20".

While driving, at idle vacuum is same as listed above.
When throttle opens gradually, vacuum drops to 10", cruises at 15-16", and wide open throttle is 0". When decelerating vacuum is just under or at 20". A/F ratio goes lean anythign under 12", unless you in the power mode, then the step up function kicks in and goes rich.

I expect the readings mentioned above with the exception of the idle, to be of the norm. Maybe a little less vacuum at idle, but even steady would be nice. I am definitely starting to hear the valvetrain cry out to me for an adjustment. More at higher RPM's than at idle. So I will set the valve lash today when I get off work and take some more readings.

The vacuum gauge I tested with was kind of a cheapo, and had some diagnosis marked on it. When at idle the needle fell to the area marked as late ignition timing. The timing is set at 12 degrees BTDC. If the timing was late wouldnt that be ATDC??? I should know this, but for some reason am now confused...If the timing is advanced wouldnt that be BTDC and retarded would be ATDC???

I may take some more readings with the Mity-Vac I have somewhere in the garage. If I get a little extra time I will do a comp test and get back here with some results...

Thanks for the replies and suggestions. I'll check out the MSD ignition boxes. I bet that is a sure fire way to know that you are using enough juice.

[zieg85]

Have you ruled out the power brake booster assuming you have one.  They will act up and then be fine for a while causing a vacuum leak.  Just a thought.

[78ScottsdaleK20]

That's a good idea ZIEG but I have checked that. At least I have checked for vacuum leaks before the check vlave and after.

Brake booster is connected to the back of the carb. There is an inline check valve and I tested for pressure between the carb and check valve and after the check valve at teh brake booster. There is no pressure loss at the Brake Booster, but there is a slight pressure drop (1-2 psi drop after 2 minutes) after the check valve, (between the carb and check valve) if that makes sense.

Its my understanding that this check valve is one way, and really is not required, its there in case brakes fail you get a couple of reserve pumps to the pedal. My brakes are extremely touchy, they work great almost too good to the point, where they lock up too easily. Especially when wet.

[VileZambonie]

I would re-adjust your valves -Personally I like to do it from zero lash -not while running. What is your timing at at 3,000 RPM's?

If you are still getting fluctuating readings do a compression test.

You should have a check valve on your booster. Some have a backfire valve too.

[78ScottsdaleK20]

I have not checked what the timing is at, at 3,000 RPM. When I install the timing tape on the balancer, to mark it when I do the valves, I will also mark it at the 28-38 degree marks so I can check the total timing. Ido not have an advanced timing gun just the basic.

I should be able to check total with these marks from the tape. Speaking of total timing, at what RPM should total timing be checked at? And should this be checked the same way base timing is set, with the vacuum advance plugged?

Thanks.

[VileZambonie]

Leave the vacuum advance hooked up and Set it at around 36° An advance timing light is a good idea but if you put a bright dot where you want your total advance that will work too.

[78ScottsdaleK20]

So I called the engine builder and asked him what the advanced timing should be set at. He recommended a guy he uses to set the distributor up. $30 later and he can dial it in depending on the cam, CR and what I am using it for. In a real world situation, this is my daily driver and that would mean having it down for however many days it takes him. Not gonna happen, when you work six days a week, and work at 2 am.

Sooo...I gave in and bought an advanced timing light, and checked timing. Base is set at 12 degrees BTDC, and programmed the light for 28 degrees (out of curiosity more than anything) and it came in on the 0 degree mark on the balancer at 2,400 RPM's.

The builder also said that some chatter (sounds like a typewriter) in the valvetrain with a little bit of a cam is normal, and unless its obvious or a knock is heard then it is probably fine. I also told him about the last Intake gasket change and how the A/F and performance of the engine was perfect then went bad, he mentioned that it could be a possibility that the center blocks of the gasket for the crossover could have blown out (meaning maybe not so much completely gone but torn), causing the erratic A/F and lack of performance.

Whatever it is I cant wait to tear into the Intake AGAIN! and check the gaskets. I may do this anyway to see just how exact the fitment of the head and Intake match up, and also ensuring the gaskets are trimmed to match the port. That might be a job for later.

For now I would imagine most of you following this thread are thinking why havent I tried a different known good carb to check and eliminate that possibility...me too. I took the carb off tonight and put an insulator on and cleaned up the carb and put it back on. Throttle shafts and linkage get pretty gunky on this motor.
Called it a night since it was 20 degrees outside and my hands were soaked with carb cleaner.

I'll do some more tinkering with it and just maybe I can get this thing nailed. How about changing up the weights and springs in the dist? If my base timing is set at 12 BTDC, and I advance the timing light for 34-36 degrees, shouldnt the mark fall where the base was at, which was at 12 BTDC? Doing this with the vacuum advance hooked up correct?

Thanks

[VileZambonie]

Where your zero marks line up on the balancer is where your timing is at based on the reading on your timing light. So if at 3,000 RPM you line up your mark with zero on your pointer whatever the light says is your timing. Try to get 36° total advance. It's always a good idea to tune your advance. Make sure the weights are moving freely. Make sure the vacuum advance is working correctly. Try running full vacuum advance at idle and adjust your base idle speed accordingly. Don't be too concerned about base timing.

As far as having a noisy valve train (sounding like a typewriter) is NOT normal. Re-adjust your valves from zero lash on the base circle of the cam. Example #1 TDCC adjust the rocker arm until you have no up and down movement of the pushrod. Twisting the pushrod can give you a false sense of lash. Make sure you take your socket off of the rocker arm when you are verifying lash because if you leave the socket on there it can seat the rocker also giving you a flase reading. Once you acheive zero lash tighten the rocker 1 full turn. Do this for both the intake and exhaust valve on #1. Then rotate the crankshaft clockwise 1/4 turn and do the same in the order of the firing order until you have adjusted them all. TDCC #1, rotate 90° adjust #8, rotate 90° adjust #4 etc (1-8-4-3-6-5-7-2). Also make sure none of your pushrods are bent.

[78ScottsdaleK20]

To eliminate as a factor, I checked the ignition circuits. Measure ohm resistance with the plug wires, and my readings were with the shortest wire 3.5 to the longest wire being 5.6. This was taken with the multimeter set at the 200k ohm setting. Chiltons calls for NMT 30k ohms of resistence. I think I am ok there if my readings are correct.

Took measurement of the primary coil resistance between the TACH and BAT terminals and got 0.9. Chiltons calls for "less than one ohm or nearly zero." Checked the secondary resistance between the rotor button and the BAT terminal and got infinite reading (no reading on the meter). Checked the resistance between the GROUND terminal and the button and got 12.9. Chiltons calls for both to be between 6k and 30k. With an infinite reading between the BAT terminal and ROTOR mean the coil is bad?

"Replace coil only if the readings in step one and two are infinite." So went to NAPA and put a known good coil in the distributor and checked the primary and secondary, and got the same exact readings. They checked the module and it checked out ok.

When I took the rotor off the distributor the screws were loose, and there was ALOT of carbon and fine metal shavings on the underside. Condition of weights and springs are slightly rusty but otherwise good-no bindage.

So in long, I imagine the ignition components are good, and that leads me to believe it must be fuel metering. Have not set the valves yet since it is snowing outside and freakin cold.

Feel like I am spinning my wheels here...so I will go out and have some more fun.

[VileZambonie]

General rule here -No more than 3K ohm per foot for ignition wires.

Set the timing and readjust your valves.