1968 911L timing/running problem
 

I have a newly rebuilt 2 liter Weber carburetor motor that I am starting up for the time but am having problems with timing and running. The Webers and distributor have been rebuilt as well. I am using a Pertronix set up and did have to replace an initial bad pickup unit but all is fine on the Sun distributor tester now.

With the static timing at 5 degrees I can get the engine running with a reasonable idle with light coughing intermittently but cannot get the engine above the 3000 RPM range where there is backfiring, coughing and the intake sounding like it is starving for fuel. If I rotate the distributor to about 35 degrees BTDC the engine idles at a much higher RPM, has less backfire and coughing, and will rev to at least 5200 RPM (briefly) and possibly more, but I am reluctant to take it much higher until I am sure everything it correct. I have checked the timing light to make sure it is on #1 spark plug wire and checked the distributor rotor multiple times for static timing and location relative to the distributor cap and drive gear. I have checked the timing marks on the pulley and replaced the spark plug wires twice. I meticulously followed the carburetor set up with various literature and videos. I have triple checked the firing order and wires to the appropriate cylinder. I was thinking maybe I set up the cam timing wrong but discussing with the engine builder where I had the machine work done, he did not think this would be the issue as the problem would be different in not being able to get the engine to run well at any set up.

I am at quite a loss as where to go from here. Anyone else had this problem or any thoughts?

You need to verify the tdc mark by bring #1 piston to TDC and then if pulley TDC lines up with case mark.

I have verified TDC and rechecked valve timing which was 3.22 mm on the left and 3.04 on the right for valve opening at TDC. The manual says for this motor 3.0 to 3.3 mm with .1 mm valve lash. So from a mechanical viewpoint every thing looks ok. I am not sure what to try next. I suppose I could try another coil and maybe put the points back in instead of the Pertronix. Maybe I will try a leak down test as well and go through and check all the other valve lashes again.

helidoc,

Can you post a picture, with the #1 cyl at TDC on the compression stroke? Take a picture of the distributor with the cap off and the rotor installed, so we can see the position of the distributor relative to the engine. Also, take a picture of the timing marks on the crank pulley so we can see that Z1 lines up with the engine parting line.

When you rotate the distributor to 35 deg BTDC, are you turning the distributor clockwise or counterclockwise from the idle setting?

If your centrifugal advance is not working, you might see something like this. Does the timing change as you rev up the engine?

The fact that the engine starts and runs makes me think you have a very simple problem that will be easy to fix.

Thanks for your thoughts Walter. Attached are the pictures you requested. I am turning the distributor counter clockwise to advance towares 38 degrees. Centrifugal advance is working fine, both in the engine and on the Sun machine. I have on picture with a mirror so you can see the mark better as someone may have added some additional ones.

http://forums.pelicanparts.com/uploa...1699888597.jpg
http://forums.pelicanparts.com/uploa...1699888597.jpg
http://forums.pelicanparts.com/uploa...1699888597.jpg

Thanks Helidoc. I was just trying to eliminate problems I have seen before.

You are not using an RPM limiting rotor, and I have seen those timed incorrectly. Your rotor looks to be pointed in the correct location.

I have also seen the wrong crank pulley installed, or the locating key sheered off. Your pulley looks correct and is pointing at Z1. So this also looks good.

I would move on from timing. You mentioned the coil. It would be nice to try a known good one to see if there is an improvement.

It might be time to look at your freshly rebuilt Webers. Are they getting adequate fuel delivery and pressure? Are the floats set properly? I'm assuming jetting is at least in the range for a 2.0, even slightly off it wouldn't behave like this until you get it on the road, under load. It just sounds to me like you have exhausted everything ignition related, and like maybe it's "running out of fuel" when reved up a bit.

Another thought, being a '68: Does it have a CD box? If so, that might bear looking into.

Thanks for your thoughts Jeff. I have checked the fuel pressure and that is within spec. Floats are fine. Air flow is ok. I don't think fuel delivery is the problem because it only acts like it is starving with the l the static set timing but if you advance the timing it can get to the higher RPMs and not have that starving behavior. Not saying it couldn't be the carbs but there is nothing to rebuild or set on them at this point. I just checked the valve lashes again and all are at the .1mm mark. I think I will try another coil next after a leak down test, and if that does not work will take out the Pertronix and put the points back in. If that doesn't work I guess I will have to pull the motor and decide whether to re-time it again or send it off to an "expert" with maybe a dyno to play with it. What a bummer.

Try it with the vacuum hose removed and plugged.

Helidoc,

Is this the first time you've done cam timing on one of these?

How do the spark plugs look? Are #1, #2, and #3 OK and #4, #5, and #6 look different?

I am just wondering if you set the left bank correctly at TDC in overlap, and set the right side at TDC on the compression stroke. I've seen that one a few times too. Some repair shop manuals go into great detail on how to set the left side, then simply say to repeat that on the right without telling the reader they have to roll the engine over to get #4 on TDC in overlap.

Yes this is the first time I have done cam timing for this type of engine so anything is possible. The spark plugs all look the same, a little dark and moist when removed. At first I thought the car was running rich because of that. I closely followed the book by Wayne Dempsey but it has been several months ago. I did look at it again last night and did notice that you set up the timing differently in the later engines with the shorter duration cams. He discussed the shorter duration cams first so I may have used the wrong method (believe my vintage would be the longer duration cam). I did note last night that the onset of #4 valve opening seems to be earlier than I would expect using the dial method but did see elsewhere on this forum that the specs were based on 1 mm opening as the start point (as opposed to the first change on the dial indicator).

Thanks for your thoughts ed. I have tried it both ways, with and without the vacuum hookup but no difference except the vacuum affect with the retard seen on the timing light. Runs the same either way.

Just to be clear, when timing to the overlap method the valve clearance is .1 mm(.004") and you read the toral valve lift at the overlap point(TDC) of the exhaust stroke. When timing by opening and closing points using a degree wheel the valve clearance is set to 1.00mm. You are timing by overlap so you should read the total indicator movement. You may have set the cams way retarded which would cause your problem.

For the right side I set the valve clearance (lash) to .1mm in the non overlap TDC, then rotated 360 degrees to the overlap point TDC, placing the pin in the sprocket hole (best fit) with the dial gauge reading between the 3.0 and 3.3 mm range but as close as possible to the left side reading (spec for this motor). The tip of the gauge had been on the top of the valve spring retainer in the non overlap position where it was zeroed out. I hope that was the correct way giving total indicator movement.

Silly question, but did you read your dial indicator correctly? One full 360 sweep of the needle is 1mm, so your needle would have to make three full turns. The smaller "telltale" needle will tell you how many turns the large needle made.

To check timing on the 456 side ,since that is the right side that you started at,,,crank pulley at TDC,,,rotate cam to the both valves closed point, set valve clearance to .1mm. Now position dial indicator and zero both large and small dials, rotate crank one revolution you are now seeing lift at overlap.

I used a digital dial indicator so don't have to worry about how many times the needle goes around. ��

Originally I started on the left side, got that set then went to the right but I get your point. I did recheck it the same way in the car but not sure the chain is tight enough as I used the Stromski mechanical chain tensioners with the initial set up and relied on the existing tension from the hydraulic tensioners for in car testing. I have enough concerns that I might have to pull the motor an redo everything.

Using the tensioner against the chain will not be a problem. I realize it's easier to work on a removed engine, but you can do this in the car.

Ed - I was thinking the same thing. On my car (1975), I can check the cam timing in just a few minutes. Removing both upper valve covers is the hardest part, which is easy on these older models. I also use a "Z" block and metric dial indicator (reading in mm), which is a different setup than Helidoc is using - but should still be easy, and could save Helidoc from removing the engine if he doesn't have to. If the cams need adjustment, there should be room, just not as convenient with the engine installed.

Agreed, I've timed cams with the engine in the car several times. I've had occasion to repair oil leaks originating with the thrust plate gaskets, the triangle shaped ones, and have had no trouble accessing everything to re-time the cams in the car.

I think assuming there is something mechanically "wrong" internally with the engine itself is too big of a jump right now. You say it revs freely with the timing significantly advanced - it wouldn't do that if there were something mechanically amiss inside the motor.

So, keep looking. You never said if there is a CD box involved. If there is, it might bear looking into. Go through the ignition wiring again, fuel lines, all of it. I know it's frustrating.

Maybe a stupid question, but if there is no CDI box, and Helidoc is running Pertronix, is there a ballast resister that needs to be bypassed? So full +12V is supplied to the Pertronix?

The Pertronix system is the most unreliable system I have ever seen . I always throw them in the trash. I used to send them back so they could do some diagnostics for cause of death. Nope , they have no interest in the info. They expect the unit to last from 400 to 4000 miles and outlasting the 30 day warranty. It was part of the Biz plan to make MONEY.
Stick with points and CDI or go with 123 ignition

Just my thoughts and experience

Ian

I went through the timing process again after adjusting all the valves with the Stomski device. Everything is within spec on the low end for the valve overlap. One side was 3.07 and the the other 3.02 with the intake valve opening with 1 mm lift at 20 degrees BTDC. The specs are for 3.0 - 3.3 with desired 3.15 mm and the cam matches the duration for this engine. To get to the 3.15 mm figure would only amount to 1 degree on the crankshaft pulley which translates into around a 2 degree range. I pulled out the distributor and removed the Petronix and got another coil checking the ballast resistor as well. Would have tried to test this set up but they sent the wrong points and with the slight leak from the exhaust valve covers decided to order some Turbo ones. When I get the correct parts I will try again after setting up the distributor on the Sun tester. Probably will post something after Thanksgiving which I hope all following will enjoy as well.

When you are checking valve lift at over lap you do have the valve clearance set to .1mm,,,,correct.?

Yes, .1mm. Bought the Stomski tool to get it as exact as I could.

Since my last post I replaced the Flamethrower coil (3 ohm) with the stock (1.5 ohm) coil and took out the Pertronix system and put in stock points and condenser. I went back to stock spark plugs instead of the platinum ones I had previously used. I static timed at TDC. I set the Weber mixture screws to 2 turns out. On initial start up there was an erratic idle, light popping, and some light white puffs of smoke for a couple of minutes as the engine warmed up and fiddling with the idle screws. After several minutes things seemed to smooth out with the idle around 800 RPM and the timing light indicating a little after TDC so I turned the distributor counterclockwise to about 5 degrees BTDC which brought the RPM up to around 1200, still with some light popping in the exhaust but no backfires. I then decided it was time to see if the engine would rev, and to my delight it went happily to the 6000 mark. I played with the idle a little more slowing it down to 900 and then played with the timing by reving the motor until it would reach the 30 degree timing mark at 6000. Ironically when done the timing was at TDC at 900 RPM. After all this I tuned the carburetors and got a smooth idle with no popping. Hopefully it will translate to good driving characteristics but it will still be a few months before I will get it on the road.

So what do I think in retrospect was the problem? I think it was the coil. This car has a ballast resistor so I do not think the 3 ohm coil, which had been recommended by Pertronix, gave a hot enough spark. Spark plugs may have played some roll but I think very little. I don't think the Pertronic pick up unit had much to do with it as I mapped out the distributor curve with it and with points and they don't deviate much. I have attached a picture from a graph I made including the factory limits, with Pertronix and with points for interest sake. Hopefully if someone else has the same problem I did they will benefit if their internet search finds my journey here. Thanks for everyone's input. By the way this is for the Bosch 0 231 169 001 distributor. I also wanted to make a correction for the dwell in my graph. It is not 21 degrees but 38 degrees. http://forums.pelicanparts.com/uploa...1701187271.png
http://forums.pelicanparts.com/uploa...1701187271.png

I agree, you do not use the resistor with the 3 ohm coil, you now have too much resistance. The modern Bosch platinum spark plugs are not good with early rich running engines. Glad you figured ir out.

It's always nice to move past a problem, but never fun while dealing with it.

I've had a good Pertronix in my car for many years, but it took a while to find a good one. I still recommend them, but nothing wrong with the original points.

I'm not a fan of the Platinum spark plugs, but it sounds like you found a combination of points, plugs, and a coil that works for you.