engine stumbles/hesitates during onset of acceleration

frank Jacobs

frank Jacobs

Daily Driver
Hi guys, I am Frank from the Netherlands, and I am finally again a proud owner of a X1/9 1500 from 1981, my second X1/9, after I had to part from my previous X1/9 some years ago (1977 serie speciale)..

I have a question and I am sure you are the right people to ask:

After replacing the timing belt and setting ignition timing, I am experiencing some problems getting the car to drive smoothly. On the road, I have to be very careful with accelerating, to prevent the engine from stuttering. This is particularly the case accelerating after driving at ~2500 rpm. Once I press the accelerator pedal, the engine stutters, and then picks up speed. Once it picks up speed it eventually reaches 5000 rpm without apparent problems. With the car in place, Idling is fine, even revving above 3000 rpm when the car stands still shows no problems.

For diagnostics, here is what I tried:

- First, I set timing to 0 TDC when replacing the timing belt. I made sure the notch on the flywheel aligns with the 0 degree line on the little window on the left of the engine (bell house?), and at the same time the dimple on the camshaft wheel aligns with the metal finger on the metal belt cover backplate. So cam/crankshaft timing seems OK. I used a timing light to set ignition timing to 5 BTDC.

With this setting (recommended for carb version of the 1500), the engine idle speed was a bit low and I adjusted the idle speed with the idling screw to ~ 1000 rpm. Testdriving the car was pretty bad, almost impossible to accelerate, so I took it back.

Because the stuttering resembled what you get if some dirt is blocking the jets, I cleaned the bowl of the carb + jets thoroughly. I noticed the floatlevel was a bit off and I reset that to specs. The needle seemed fine to me. Confident that this would have solved the problem I took it for a drive but unfortunately I had the same problems.

I decided to change ignition timing a little bit to see if that made a difference, and it did. Putting it at 0 or 3 BTDC makes things worse. Putting it at 10 BTDC makes things better, but still if I press the accelerator a bit too fast it will stutter. (Strangely, I noticed that if I change ignition timing beyond 10 BTDC, the idle speed picks up a little and the engine runs smoother..)

Anyone any ideas what could be wrong? Why wont it run smoothly with the recommended ignition timing of 5 BTDC? Could it be that I messed up the carb settings?

I know you have the answers ;)

Best,

Frank
 
Have you checked the timing at engine speeds other than idle? It would be good to confirm that the advance is working.
 
Yes, with the timing light on the marks and the engine revving, I could see it going further advanced. (When I had it set at 5 BTDC it went beyond the 10 BTDC mark
 
Just double check the timing using the marks on the crankshaft pully end (cambelt end). Double check you have the cam timing correct. Was it running ok before you changed the belt
 
Sounds like your timing is out.
Its been a while, since I've done a timing job, on an X; but I seem to remember having the revs up around 2500/3k for some reason. The advannce on the timing marks at that speed would be like 30° or something, IIRCC.
I think static at idle was like 10° or a tad more.
Don't get too twisty turny on those carb adjustments.
If you lean it out too much, you'll be replacing a HG.
 
NEG said:
Just double check the timing using the marks on the crankshaft pully end (cambelt end). Double check you have the cam timing correct. Was it running ok before you changed the belt
Click to expand...

I checked and the marks seem to be lined up correctly, but of course this depends on the angle from which you look at it.. If it is off like you suspect, it would be by one tooth right, so by ~ 9 mm / fixed amount of degrees?
 
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Eastep said:
Sounds like your timing is out.
Its been a while, since I've done a timing job, on an X; but I seem to remember having the revs up around 2500/3k for some reason. The advannce on the timing marks at that speed would be like 30° or something, IIRCC.
I think static at idle was like 10° or a tad more.
Don't get too twisty turny on those carb adjustments.
If you lean it out too much, you'll be replacing a HG.
Click to expand...

Yes, I think you are right, but the marks seem be be spot on. My timing light doesnt have the advanced function so I'd have to estimate, but the dot moves wat out of the bell house window when revving, which could easily be 30 degrees.

About the carb adjustments: I think it wont hurt to get it back to original settings: I remember this could be done by twisting it in completely and then twist it out for a number of full twists, but I cant remember how many and where I got that info.
 
NEG said:
Just double check the timing using the marks on the crankshaft pully end (cambelt end). Double check you have the cam timing correct. Was it running ok before you changed the belt
Click to expand...

Remarkable thing is how I got if from the previous owner and before the belt replacement, the cam/crankshaft timing was advanced by 8 degrees. The car was running, but I noticed a clear difference in power (more power at high rpm) after the belt change and resetting the cam/crankshaft timing.
 
OK, hope this helps: I made photos of all three timing marks (notch in the cam-pulley, notch in the crankshaft pullyey and the flywheel dimple, shot from as straight angles as I could.

As you can see when the flywheel dimple is at 0 TDC, the notch on the Camshaft pulley is a little bit to the right of the metal pointer, but clearly not a full tooth. The notch on the crankshaft pulley is a little beyond the 0 TDC mark, but I have read that the metal three fingers can be off a little and the flywheel is more reliable for setting timing.

Please let me know if you feel I should refit the belt, or if you think the timing is set correctly. Thanks a lot for your help!

Cam pulley mark.jpg

flywheel mark.jpg

Crank pulley mark.jpg
 
frank Jacobs said:
..but the dot moves wat out of the bell house window when revving, which could easily be 30 degrees.

About the carb adjustments: I think it wont hurt to get it back to original settings: I remember this could be done by twisting it in completely and then twist it out for a number of full twists, but I cant remember how many and where I got that info.
Click to expand...
Yep. As it should. If your seeing the marks inside of the sight window, your car is not timed properly.

In your pictures. At idle the timing mark in the sight window should be in the middle, not aft, as depicted. There may also be some slight fluctuation in the marks position, while idling. The Italians have some pretty loose tolerances, and usually "ballpark" for things like this, are acceptable.

It might also be worthwhile to mention that these cars tachometers are ****, and should NOT be your base for getting your idle rpm in range.

For instance my cars tach reading at idle, is 0 rpm.

You could use a dwell/tach, or a digital timing light, but if you have an old craftsman timing light from the '70s, like I do; you learn to use your ears ;)
 
I think the timing marks look good for the cam being timed OK. (Not that they are GOOD, but good enough. It's kinda hard to make them line up exactly because a lot depends on the angle you're looking at it.) Does the decal on the timing belt cover indicate the date the belt was replaced?
As for ignition timing: I find that the X performs best when it's timed to 10' BTDC at idle - with the vacuum advance disabled (hose pulled off the canister and plugged to prevent a vacuum leak). Setting the initial advance to 10' BTDC will get you to roughly 36' BTDC at 3500 and above. 10' BTDC is the mark on the trans that's farthest right- toward the back of the car.
Inkedflywheel mark_LI.jpg
If you think you may have a problem with your ignition timing it might be a good idea to try and locate a dial back timing light to help you diagnose?
 
frank Jacobs said:
Remarkable thing is how I got if from the previous owner and before the belt replacement, the cam/crankshaft timing was advanced by 8 degrees. The car was running, but I noticed a clear difference in power (more power at high rpm) after the belt change and resetting the cam/crankshaft timing.
Click to expand...
Not sure what you mean about the cam/crankshaft timing was 8 degrees advanced. Do you have an adjustable cam gear. If so its possible that the previous owner installed a hotter cam. And now that you have put it to 0 degrees its running poorly. Just a thought.
 
nichol01 said:
Not sure what you mean about the cam/crankshaft timing was 8 degrees advanced. Do you have an adjustable cam gear. If so its possible that the previous owner installed a hotter cam. And now that you have put it to 0 degrees its running poorly. Just a thought.
Click to expand...

I mean that on the setup BEFORE the belt change, with the notch in the camshaft pulley aligned with the metal finger on the metal backplate of the beldguard cover, the notch on the crankshaft pulley was at the 10 BTDC finger (the left most finger towards the back of the car). But like I said, the car was not driving as well as after the belt change, apart fromt the misfiring... Is it possible the Cam pulley was improperly installed and the previous owner accounted for that by setting timing like this? Is there a way to check this?
 
MikeHynes said:
As for ignition timing: I find that the X performs best when it's timed to 10' BTDC at idle - with the vacuum advance disabled (hose pulled off the canister and plugged to prevent a vacuum leak). Setting the initial advance to 10' BTDC will get you to roughly 36' BTDC at 3500 and above. 10' BTDC is the mark on the trans that's farthest right- toward the back of the car.
Click to expand...

10' BTDC also for carb-fitted engines you mean? I noticed that if I advance timing even a bit more the problem of the engine hesitating when accelerating gets better. It also idles a bit better when I put it more advanced, as if the engine likes it that way: Is there any risk of having ignition timing advanced beyond 10'BTDC? Thanks for your input Mike
 
Instead of speculation, any further; it would probably be less time consuming (then updating this thread) to just pull the belt, set all of your static timing marks, and start over.
Also verify cam and ignition timing is correct.
Also check the number of teeth on the cam sprocket. 1300 and 1500 gears are different.
They are physically interchangeable, but not functionally so.
 
The cam timing/alignment looks good to me and if you can do 2 complete crank rotations and all comes good again then the belt's fine? This is a euro car car so no vacuum advance on the distributor. What's the dwell angle (contact set / points gap) set to? Given that the belt was wrong previously the chances are the dwell is out to. It should be 55 degree +-3. Anything in ignition timing range 5 to 10 btdc can be acceptable, 7 is good on my 82 with slightly bigger jets. The idle screw adjustment is unlikely to cause the problem on acceleration?. I'd rule out the dwell first as an easy constant.
 
I think the 1300 and 1500 cam pulleys have the same number of teeth but the timing marks are in a different spot.

If the car idles better with more than 10 degrees advance, it could be an indication that it has a high performance cam in it. Mine requires 20 degrees at idle.

Also worth checking that the pulley timing marks match the flywheel timing marks (unless the flywheel was put on backwards). The scale for the pulley marks is adjustable so it may or may not be calibrated correctly.
 
Haven’t read the thread carefully yet but.... stumble and hesitation on acceleration could be the accelerator pump in the carb?
 
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