Author Topic: 79 hesitation (Read 13898 times)

Lefty · « **on:** July 28, 2013, 07:47:36 PM »

Hi,

I recently bought a 79 corvette which was on Historic plates in the NSW club. Some of you most likely have sen it around. The car is fantastic and is too much fun.

I have noticed-the car hesitates, it's not obvious when at idle, but bulks under acceleration, sometimes.
It's a 350, rochester carburettor, and i assume a vertex magneto.

I read the carburettor can suck air through the pump plunger (?) and a bit of oil on this can seal this, albeit temporarily. On this basis I am thinking the carburettor is up for an overhaul. But looking at forums on magnetos there seems to be some opinions these loose their reliability over time and need overhaul.

Any definitive opinions?

Cheers,

Lefty

anychevy · « **Reply #1 on:** July 29, 2013, 03:32:22 PM »

Quote from: Lefty on July 28, 2013, 07:47:36 PM

Hi,
I have noticed-the car hesitates, it's not obvious when at idle, but bulks under acceleration, sometimes.
It's a 350, rochester carburettor, and i assume a vertex magneto.

Hi Lefty
Magneto's are pretty rare on street cars, it's probably an HEI (coil in the cap) but you're not sure, post a photo of it.

Q-jet carbs are excellent, but misunderstood and can suffer from "bog" if the air door opens too fast, the accelerator pump is not squirting enough fuel, or wrong secondary metering rods etc. etc.
It could also be retarded timing, a poor advance curve and many other issues.

Take the car to a knowledgeable mechanic and get it tuned.
This place is also good with Q-jets http://www.carburettorservice.com.au/ if that's the problem.
Don't "throw a Holley on it" it could be something simple and a "properly" functioning Q-jet, is music to the ears.

Lefty · « **Reply #2 on:** July 29, 2013, 07:13:24 PM »

Thanks Dave.

I did some investigations and its appears to be a vertex magneto, it does not have normal looking ht leads (silicone) coming out of it to the spark plugs. I went to Taylor's web site who have the magentos on it. http://www.taylorvertex.com/Vertex. I have a photo of the engine, but have difficulty uploading. I'll give this another go.

I did call the carburetor place a few weeks ago, they are close by. They have done work on previous cars and always were well priced and did great work. Good call.

I'll book it in to them in the first place and see if this resolves it, and advise back.

Cheers.

Lefty

sirfixalot · « **Reply #3 on:** July 29, 2013, 09:37:58 PM »

Contact Steve at SR Performance Arncliffe

Lefty · « **Reply #4 on:** July 30, 2013, 06:11:43 AM »

Sirfixalot,

Many thanks,

Lefty

StephenSLR · « **Reply #5 on:** July 30, 2013, 10:33:58 AM »

Quote from: anychevy on July 29, 2013, 03:32:22 PM

This place is also good with Q-jets http://www.carburettorservice.com.au/ if that's the problem.
Don't "throw a Holley on it" it could be something simple and a "properly" functioning Q-jet, is music to the ears.

I second that, I bought a reconditioned Q-Jet from CSC back in 2000 for my Torana and until last year I drove it twice weekly, it hasn't missed a beat and I've never had to adjust it.

Another time I had them recondition my electronic distributor when most told me to buy a new one, it's still going strong.

s

Lefty · « **Reply #6 on:** July 30, 2013, 01:42:09 PM »

Thanks steven.

picture of engine attached - see the blue cover, it has the magneto udner it, and the leads differ from HT elads,

Cheers,

Lefty

bfit · « **Reply #7 on:** July 30, 2013, 04:01:51 PM »

You would have to think that would through a biggggg spark
no fn about there! I would stay well clear of the leads when it s running
Bfit

72vet · « **Reply #8 on:** July 30, 2013, 04:32:21 PM »

Hi Lefty, congrats on the purchase of the Vette.

I had the same issue with the Rochester on my 72. Spent a small fortune on the darn thing.

We ran the car on the dyno, changed the primary & secondary metering rods, so many times, as soon as we drove the car on the road the hesitation was still there.
Adjusted the “secondary air door” on road but still had the bog down.

If you’re not a numbers matching man, I’d go and buy a new carb, it’ll be a few more $$$ than what you would spend on the rebuild but it won’t be 34 years old and who knows how many bubbers have had their mitts on it over the years.

I fitted a 650 Edelbrock to mine and after having it tuned I’m not complaining.

And yep, that’s a magneto and I’d take Bfit’s advice.

Nick

anychevy · « **Reply #9 on:** July 30, 2013, 05:53:43 PM »

Quote from: Lefty on July 30, 2013, 01:42:09 PM

I fitted a 650 Edelbrock to mine and after having it tuned I’m not complaining.

Q-jets can be intimidating and not a lot of guys want (or know how) to fix them.
Ross Burgess used to be the man for Rochester's, but he's retired (unfortunately)

Yep, it's a magneto, but why ????? And are you sure you have a Q-jet on there ?
If that intake is a "square bore", then maybe an Edelbrock or a Holley isn't such a bad idea.

And I would sell the MAG and stick an HEI back on it as well.
Just my 2c

Lefty · « **Reply #10 on:** July 30, 2013, 06:58:11 PM »

DVD,

Good call, I have assumed the carbie is a rochester and will investigate further.
RE the magneto, I'll need to think about what to do with it. I don't think I need a magneto,a dn from what I'm reading a hei would suit my driving. Having said that it spanks along and the car is a huge amount of fun.

Many thanks for your response, I'll move forward slowly, and consider the options.

Cheers

Lefty

Lefty · « **Reply #11 on:** August 08, 2013, 05:27:43 PM »

Gents,

Many thanks for all of the advice. I took the car to Tim and Allan at the carburetor place at BURWOOD. They were great,me dropped it off at 11. 11.02 Allan advised its the plugs. Too cold and well fouled. A simple fix and they called tonight to advise all well.

Again many thanks for the informationa nd advice. I would have never thought of this simple part providing such a problem.

Lefty

StephenSLR · « **Reply #12 on:** August 08, 2013, 05:39:06 PM »

So you have a Rochester and the magneto is all good for that set up?

s

Lefty · « **Reply #13 on:** August 08, 2013, 08:27:39 PM »

Yes, rochester is a Later model than came with the 79 and runs perfectly. The mag works well. Overall advice is if it isn't broken don't change it. New plugs might improve fuel consumption?

Lefty

StephenSLR · « **Reply #14 on:** August 09, 2013, 07:36:14 AM »

Quote from: Lefty on August 08, 2013, 08:27:39 PM

Yes, rochester is a Later model than came with the 79 and runs perfectly.

They're a very underrated carb, perfect for street use, never had any problems with mine.

s

Lefty · « **Reply #15 on:** November 11, 2013, 08:16:59 PM »

Quick update.
Problems persisted and got worse more recently, checked and found the leads were loose in a few spark plugs, crimped the ends for a tight fit. Took the cap of the magneto, it just looks like an old set of points in there. Cleaned it all up, worked well. Runs better, surges a bit on constant revs. Breaks down when pushed hard. Swapping out the mag and leads in the new year will remove some the unknown with the issues.

Also changed from 98 to 95 and think that helped some.

Many thanks for all the advice, getting there bit by bit.

Cheers,

Lefty

sirfixalot · « **Reply #16 on:** November 12, 2013, 08:22:20 AM »

Getting confused with this one so it is a 79 with what looks like a magneto with points. Get a HEI dissy keep it simple for every day driving put it in & forget about it

bfit · « **Reply #17 on:** November 12, 2013, 03:26:49 PM »

mate I have a few spare engines in the shed if you want a distributor to try in your to see if it fixes the problem let me know
I should have a points dissy and a HEI
Bfit

Lefty · « **Reply #18 on:** November 12, 2013, 04:21:51 PM »

Bfit many thanks I'm keen to try it out. Where are you located
Cheers
Lefty

bfit · « **Reply #19 on:** November 12, 2013, 04:27:34 PM »

Lefty I'm in Picton NSW
bfit