OK here we go again....

The car went in for some work at the weekend, one job was the tune up.

When i bought the reconditioned QJET i had to upgrade the jets and rods and hanger as it was originally a 350 carb (1973 cutlass) and i've got a 425. I looked at some spec sheets and settled for .73 primary jet with K hanger and CK secondary rods. When I plopped it on top it gave me SUCH a noticeable performance improvement straight away, right through the range, however i always suspected the timing would need adjusting as it ran hot most of the time and started to ping at the very top end.

So... First problem was finding the timing marks. Nowhere to be seen???
In the end had to do it by ear. Not ideal, but it did confirm that the timing was way too advanced.
So then we adjusted the mixture on the carb using an emissions computer and the whole thing seemed to sit and run very nicely.
Took it for a drive... power was there as the tyres lit up nicely... but when it got through the range and up to high revs the carb coughed and spluttered slightly and let out a small pop.

it also seems to surge slightly on tickover??

My mechanic stopped me there and advised i see a QJET specialist.

So, since you have done such a great job of helping me in the past... first port of call is you guys...... :-)
Apologies in advance for our lack of knowledge on this matter

 

Before doing anything else I would find those timing marks and reset the timing. If your harmonic balancer is damaged then spend the money and get a replacement. Here is a bone stock replacement harmonic balancer:

http://www.summitracing.com/parts/RNB-594-117/

Once you set the timing with a timing light then you can trouble shoot any further driveability problems.

 

x2 on getting the timing straight. Seems to me you may be a bit advanced. However, without getting it properly checked there is no way of knowing. I'd turn the engine over by hand, find the timing mark on the balancer and use chalk or white paint to mark it. Then find TDC and determine if the balancer is spun. The pointer on my olds is on the driver's side just inside the power steering pump, mounted on a stud that holds on the timing cover. (That was a mouthful)

If you can find TDC and the mark lines up to the pointer all is well. No pointer? I have used metal coat hangers to make temporary pointers to get timing set. All this is predicated on finding TDC and making your mark on the balancer.

Good luck.

sb

 

I did the same thing on my 71 98. I marked the new harmonic balancer with white paint and the timing tab with white paint. It makes setting the timing STUPID easy.

 

Thanks guys.
OK, just relayed this back to the mechanic and he has a couple of questions.
His words not mine.....

Do these suffer from issues with the bobweights in the distributor?
There is a visible timing mark but it is way out advanced to a general "by ear" set up.
It also appears erratically and not in the same spot, varies by approx 20 degrees, but is way off and definitely not right.

 

OK. A couple of things.

1. Make sure the vacuum advance hose is not attached and the vacuum leak stopped. Generally I pull the hose from the distributor and stick a small bolt in the rubber line for a temporary plug.

2. Measure the idle with a tach. I don't know the exact specs for a 425, but it should be in the 650-725 range in gear.

Once those two parameters are met, check the timing with a light. IF you are still getting radical swings in the timing and your timing instrument has proven to be spot on, THEN I would start looking at the possibilty of broken or loose springs in the distributor.

By the way, which distributor do you have? Points or HEI? Either way, its really easy to pop the cap and rotor off and look at the weights and springs. So if you and your mechanic suspect that, take the five minutes and look under the cap and rotor.

sb

 

Thanks for the input.
it's the standard distributor with electronic lobe sensing points (Pertronix) and flame thrower coil

 

You can always find TDC on the #1 cylinder by removing the spark plug and then mark the harmonic balancer. If the #1 cylinder is at TDC of the compression stroke and the timing mark is no where to be found then you might have to replace the harmonic balancer.