Timing & Tuning & Pressure, OH MY!!

[BrooklynCorvair]

Could really use some advice on this one. I just got my '66 Monza 110 Convertible about 5 months ago. I received it with points ignition and recently upgraded to an Ignitor II and Flamethrower II.

Timing was okay when I received it, but not perfect. I did have some minor backfiring. The twin carbs were definitely not synced or tuned properly. Right carb was sucking very little air compared to the left carb, based on suction when I placed my hand on top, so much so that if I'd completely seal only the right carb with my hand, nothing would happen, while if I'd seal only the left carb with my hand, the engine would begin to stall. Another issue I have is the fuel pump. It's most probably leaking into the crankcase as the oil smells of fuel, and I'm having acceleration issues and sometimes have to play with the gas pedal to accelerate smoothly or get a response.

So, after installing the Ignitor II and Flamethrower II, I tried adjusting the timing to no avail. I'm getting heavy backfiring! The timing position that rendered the least backfiring was around 10 degrees BTDC, but it didn't stop the backfiring completely. Also, at that timing position, my timing light was reading that the car was idling at 1050-1100 RPM. Waaay too high! So I figured the carbs should be balanced and tuned first, then I'd retry setting the timing. I figured this should be no problem, as I'd already purchased a UniSync to sync the twin carbs, and a Gunson ColorTune to tune the idle and mixture. It didn't work....

The method I first chose to sync the carbs was to turn all idle and mixture screws all the way out and then turn them equally until reaching the optimal settings. For some reason, equal turns did not render equal airflow between the carbs as indicated with the UniSync. So I then turned them individually until the airflow was equal. At that point, I plugged in the ColorTune spark plug on the right side and adjusted the mixture until the combustion color was the correct blue, then plugged it on the left side.. but I could not get the left carb adjusted to a blue combustion color; the best I could get was light purple (the point before blue) and this was with the fuel mixture screw turned as far as it would go out!! So I just accepted that that was the best color I could get and then worked on setting the idle to 600 RPM. Between turning the distributor and compensating with the idle speed screws, I got it set to 14 degrees BTDC and a 600 RPM idle. "Great!", I thought....
Well, not really. The car is running really rough, it's backfiring badly with huge detonations, and it's low on power at idle and therefore occasionally stalls while idling.

So, at this point, I'm thinking it's most probably the fuel issue, and my next steps are:

1. Install the Airtex electric fuel pump which I'd already purchased (which I've been holding back on out of intimidation and fear as a newbie)
2. Replace the fuel filters in the carbs
3. Re-attempt the carb tuning/syncing and ignition timing
4.

If I'm still unable to get it running smoothly after all that, I'll have to consider a carb rebuild (or perhaps replace the carbs completely with Grant Wolf's "Performance" carbs: http://www.ebay.com/itm/290706874682 )

AM I ON THE RIGHT TRACK???????????


Would really appreciate any input.

[USAF_vair]

hey. before you have to much spending on tryin to fix a possible fuel problem. i would check the basics.
have you checked the compression and make sure you check the oil and the valve adjustment if it is weak.

we had a corvair give us a problem of backfiring and we ran through fuel problems thinking it was getting to much gas as well as an spark problem. come to find out that the valves needed to be adjusted causing the weak power and excessive fuel in exhaust and intake runners.

now here is a far out story had this happen to my fuel injection corvair that has a lot of performance parts installed. drove great for months with no mechanical parts being changed out. then one day while driving 55 mph the engine just lost power. a small noise that sounded like a backfire and it completely killed the engine. so i just jumped the clutch and the engine fired right up. thought the computer messed up and car was fine for the rest of the day. the next day thought is was hotter out and the car started to backfire both out of exhaust and intake. the O2 sensors read a little on the rich side but nothing to badly. but stilol backfires every time i let off gass or tryed getting on it. got home thought it was a timing issue but found nothing. but while checking the timing i was hearing a rattle. i heard it coming from the valve cover. so i opened the driver side and found a very interesting thing inside my valve cover. on the middle cylinder both the intake and the exhaust push rods wear boken into three or four sections. also found that the rockers were both cracked. i just thought that maybe freak thing of bad adjustment of valves caused this or something. i installed new pushrods and the problem was fixed with backfiring.

hope this helps and gives some little fun to finding engine issues lol. and if you ever talk with a mechanic check the simples first before getting into something deep.

[BrooklynCorvair]

Thanks! Yes, I plan on checking compression. It's definitely one of the first things I need to do. I just wanted to address the faulty fuel pump first, but I guess I'm not prioritizing correctly. I think I'll pick up a compression gauge before I begin the elec. pump install.

Just to confirm (as I'm an inexperienced newb), to check compression, all I need to do is disconnect the coil plug from the distributor, plug in the compression gauge and crank the engine for a few seconds, right?

[USAF_vair]

Yes sir, one thing I like to do just as a little bit better test I think is remove all plugs. So you know the starter is only working on rotating one piston to compression point.

[BrooklynCorvair]

Yes sir, one thing I like to do just as a little bit better test I think is remove all plugs. So you know the starter is only working on rotating one piston to compression point.

Okay, so disconnect the coil wire from the distributor, remove all spark plugs, plug the compression gauge into the cylinder, crank the starter for several seconds and hope that the cylinder measures between 130 - 160 PSI. That pretty much it?

[cvair4life]

That's pretty much it - I always remove the trigger wire from the negative post on the coil - not sure if it's true or not but I've heard it's hard on the coil to fire it when not actually hooked up? Either way you don't want the car to start so whatever works.

[BrooklynCorvair]

That's pretty much it - I always remove the trigger wire from the negative post on the coil - not sure if it's true or not but I've heard it's hard on the coil to fire it when not actually hooked up? Either way you don't want the car to start so whatever works.

Cool, thanks! I picked up a compression gauge and will hopefully run the test later this afternoon.

[cvair4life]

I'm sure you're probably in good shape. 110's don't "usually" get as abused as 140's do. on another note... did you happen to make of video of setting your carbs with the Colortune?

[BrooklynCorvair]

I'm sure you're probably in good shape. 110's don't "usually" get as abused as 140's do.

I hope so. There are so many basics that I've neglected to inspect, in my naive newbness. I'm so focused on ignition and fuel and I just know something much worse will pop up out of nowhere, like a fried differential or something... I'm driving this classic around high and proud, and I'm not even carrying a spare belt and tools just in case. Heck.. I don't even know how to change the darn belt! I have a lot to learn!

on another note... did you happen to make of video of setting your carbs with the Colortune?

No, but that's a good idea! I'll be sure to shoot one on my next attempt.

[BrooklynCorvair]

So I got around 120 PSI on four of the cylinders and almost 130 PSI on the other two. I guess the difference is negligible and I'm in the clear compression-wise, right?

In other news, I bit the bullet and ordered the rebuilt "performance" carbs from Grant Wolf. They're due for delivery today.

[zappaz]

the colortune ? ive been wanting to pick one up or a pair more like it i rebuilt 6 carbs befor i found 2 that would tune right and this is gona sound way funky but the gauges i used wouldnt do right for me and i used 2 vac lines and placed both on my lower lip and tuned them that way not high tec by any means but after that last tune i rode my 63 over 1200 miles nonstop cross country given more time i mite have tryed sumthing differnt but lady luck was on my side

[cvair4life]

So I got around 120 PSI on four of the cylinders and almost 130 PSI on the other two. I guess the difference is negligible and I'm in the clear compression-wise, right?

In other news, I bit the bullet and ordered the rebuilt "performance" carbs from Grant Wolf. They're due for delivery today.

Pressures sound great. Hope the Wolf carbs work out for ya... haven't had a chance to tune mine yet but seams like people's opinions on em are 50/50.

[Luke Geis]

I would suspect a vacuum leak. This is a sure fire way to get backfiring. Using a uni-synch you should be at least able to get the two sides balanced. If that doesn't cure it and you know that the timing is good, it's one of two things. Either the vacuum advance is done ( which could mean vacuum leak ), or there is a leak between the carb and carb base. The right side carb is the one attached to the vacuum advance and is a likely culprit. It could either be the tube running to the vacuum advance or the diaphragm itself, or it could be the that the carb gasket is toast. One way to tell is to look at the vacuum advance while you give the car light amounts of gas. You should see the advance arm move in and out. If it doesn't then you have found a part of the problem.

[ensys]

Hopefully, a real mechanic will correct my errors, so I would venture these observations about this thread, if I may.

If you can't balance carbs, there is a problem and you must correct it before proceeding. A vacuum line not plugged, a carb jet that is, carbs subtly choked with deposits and crud left by evaporated gas, shrunken and/or broken and leaking base gaskets, etc. With old cars, it is often the case that the carbs need to be rebuilt and/or all vacuum lines checked (the plastic in use at this time does not age well in the presence of heat), and all intake gaskets replaced. First.

Isn't it funny how all cars, in the right hands, could be made to run quite well, thank you very much, on good old points before cheapo, failure-prone, add-on "electronics" were invented. Treat your analog spark components well and they will not fail you.

When doing a compression check, the intake to the cyl. (i.e. the carb butterflies, etc.) should be open.

Carbs are tough to tune if the valves are not right, and they are not right unless adjusted while the eng. is running. Messy? That's what spare valve covers are for.

Setting the advance must be done with the dist. vacuum lines plugged.

Trick tune plugs are cute, but short of a Sun machine, reading the plugs is still the way to get the mixtures right. (Though I will admit that it was useful in this case, if not necessary, to reiterate that you had a carb problem.)

Sure old cars are a lot of work (hence the number of working mechanics back in the day), but with them, as in life in general, the Right Way is most often the Hard Way.