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OK, gentlemen. As some of you know, Bridget burbles a bit on decel and will crack like a rifle shot if you load up and then get off her–as I plan to do in the autoX (in fact, the problem came clear only during last year’s autoX when she was a crowd non-favorite and a figure of mirthful razzing because of this).
Ahem.
So, she was worse when I got her and last year’s carb adjust got her to the improved shape she’s in, but I just tried everything I know to improve her further and got zilch.
In order:
1. The valves were adjusted last year and should be good. I’ll do them again but am sure this isn’t the issue, as last year’s Carlisle popping happened just after they were set and continued, unchanged, through the summer.
2. Timing checks out at 7.5 BTDC at idle, 28-30 at 3000 rpm. Correct for a 1500 engine from 1966.
3. liberal sprays of starting fluid around all intake joints revealed no leaks. No sign of an exhaust leak either*
4. Just reset the carb again, twice, per the instructions found here (which are what i used last time as well). Strangely, getting the initial 850 RPM idle setting is very easy with the Bypass screw, but I have to turn it IN to do it (not out, as is the “most likely” way it should turn), and then turn the volume screw IN (not out, as expected) to get the idle any higher. She idles OK, runs strong (for an ancient SP 1500), no stumbles or hesitation after warm-up. Doesn’t backfire in the normal course of cruising here and there either.
But, you get on her and then off the gas, as for a red-turning light or an unexpected fellow driver in your lane, and POW!
So: Any ideas?
*I have not removed the lwer tins to inspect the rear Js yet; I have ordered a complete exhaust installation kit–all bolts, washers and gaskets, ’cause I love that kind of thing…. But it’s not here yet.
You may have already diagnosed your issue — a minor exhaust leak that sucks cold air into the exhaust under hard deceleration. Combine that with running a bit rich, and any unburned gas causes the backfire.
When was the last time you looked at the exhaust valves? A slightly burned exhaust valve can cause this symptom, also… Any indication that a valve may be stretching/burning when you’ve adjusted the valves? Have the exhaust valves (especially problematic #3) been tighter than the intake valves?
KentT2013-05-09 21:01:57Early FF TDr on 69 VW pan
Slowly coming back from the ashes...Number three was the “normal” amount of “too tight” when I first adjusted them two years ago. That is to say, the guage just barely fit at 004.
Last year she was still OK at 006.
As you know, these figures are not indicative of a big problem, as 004 was the correct spec when the engine was made.
All that said, I have never looked at this engine at all. Besides putting the muffler on, changing the disty to a Pertronix, and regular oil and screen changes, she’s as I found her.
Thanks though. I have not, in fact, ruled out an exhaust leak yet.
Ed, I have what I call a perfect condition 30PICT3 that I took off MiGi when I put the Bugspray on. I could bring it to Carlisle and you could do a quick swap. I don’t want to get rid of it, but truth is it would only take a moment to change carbs and rule that out. If you wanted to run my carb in the AutoX and you beat me, ……hmmm
Just let me know and I’ll pull it off the manifold.Thanks, Roy. I’ll consider.
Really thinking the carb is fine though–it was a year or two old when I bought the car.
Pretty sure the problem here is, as Click & Clack say, “the big nut behind the steering wheel.”
I’ll let you know by the end of the weekend.
Ed, Not sure I still have my left over 30 pict carb, but if I still have and can locate your welcome to it – I will get back to you.
Well, I took a look at a post on the Speedster Board and it gave me an idea: Later engines–the ones that came with the 34 PICT carb–were timed at 5 degrees After TDC, not straight up or 7.5 before, as I’ve had it. So I retarded my timing and reset the carb this morning. That did nothing, except, maybe, hurt acceleration just a little.
Tonight I climbed under to look at the front exhaust pipe connections. No sign of a leak there but–hey!–lookit these donut connections! The driver’s side was nicely blackened and the donut actually broke in half when i took the clamp off it.
Thinking it was maybe leaking there a bit.
I actually have a couple donuts, but not the rest of the many gaskets, nor the patience to reinstall the muffler tonight. I bought some RTV Copper gasket stuff and stuck the donut back together with that, then buried it in the stuff and put the clamp back on semi-tight. Coated the other one too, for good measure.
Tomorrow morning I’ll tighten both sides a little more and, weather permitting, take a ride. If the situation is changed at all I’ll know where the problem is, I think.
Maybe I’ll get lucky and all the little clamps and dohickies will come tomorrow FedEx, and I can enjoy the weekend completely reinstalling my muffler. This time, liberally coated with that high-temp RTV.
Wish me luck.
edsnova2013-05-10 21:30:24
As most of you know i am not a good mechanic but i am learning alot. My brother inlaw i a great mechanic. Talked to him about a small backfiring problem i had.He said turn up the idol which i did and it disapeared.
GOOD NEWS UPDATE: Well, the situation is changed. Almost no backfiring now. I can make it backfire only by revving way up and getting off. Even then, not every time and more of a “poot” than the old sound, which was like the report of a 9mm Glock on the firing range. The new sound is more like a misfiring spud gun.
BUT this (Bad news update): took her the long way around the block, driving a little spirited to try to make the backfire, and she dies on me again just before I make the turn to my street.
Same basic thing as the other day–power just fades, and then nothing. She’ll start but not run.
Then in a minute she’s all better.
Checked my wire to my idle cutuff solenoid again: it’s good. Could the solenoid itself be going bad?
OR… am I seeing/causing the dreaded carb icing maybe? This seems to only happen when I “test drive” around the block, running the rpms up, getting off, testing acceleration and backfire propensity. I felt the intake under the carb–very cool to the touch there, and some sweating condensation had formed.
What say youze?
The idle solenoid caused me more trouble than it was worth. I clipped off the end, so that it was non-functioning and reinstalled it so as not to have a vacuum leak. Never had any trouble again.
I was worried about carb icing when I went to my 2bbl Holley. All the old reports talked of it. But, I hooked up my intake manifold heat and have had no problems even when it was 40* outside. Go figger.Ed. Are you running a 34PICT3 with a 009 (mechanical only) distributor? They don’t work together well.
Allen Caron
VW based 53MGTD - "MoneyPenny"
"If one thing matters, everything matters" - from the book The ShackEd, I think you are right that the SVDA is better on a stock carburetor rig. When I got my MiGi it had a stock 30PICT3 on its single port manifold and a new Bosch 009 distributor. Didn’t run well.
I bought a SVDA from ebay and installed it. Instantly ran much better. Hesitation and stumble were all gone.I was quite happy. But, then one day I started wondering just how much better MiGi would run with more carburetion. I can’t fit dual carbs in my engine compartment so I went with the 2bbl Holley Bugspray which does not have a vacuum port and operates with lower vacuum. I had no choice but to change back to a 009. No flat spots nor hesitation now with the Bugspray. Maybe these 009’s were brought in at the same time that owners were “hopping up” to dual carbs and bigger singles like I now have??At Carlisle, you can take MiGi for a ride. I would be interested in your review.We can switch cars for a minute, Roy. Mine’s slow. BUT . . .
Fingers crossed, think I may have the backfire and the carb ice issues both licked. Took off the right hand top tin this a.m. and discovered that one of the nuts had fallen off the flange that bolts the right side carb heat tube to the number 2 cylinder exhaust pipe. The pipe and the top nut holding that on were nicely blackened.
I pulled it apart (a little–again, still waiting on a pack with all the necessary gaskets for a complete reinstallation of the exhaust system) and shot some copper RTV in between the flanges. Found a new nut and a lock washer for the bolt. Buttoned it back up.
Gonna let it cure all day. Hoping That will do it, at least for the next week or two.
While I was at it I also replaced my fan belt-as the old one was showing some cracks.
Now for the little bit of compound, polish and wax, vacuum, interior cleaning and stuff necessary for Carlisle.
UPDATE UPDATE: SUCCESS!
Well, boys, I drove a 15-mile round trip to pick up some Thai food and HOLY CRAP IS MY CAR QUIET!
I seriously had no idea these cars could sound this not-loud. The burbling on decel is all gone. Backfiring is gone and the car is now quiet enough that you could have a human conversation in her at 60 mph.
I never knew my tires made so much noise. I mean, this is amazing.
So what I did is a temporary fix at best. I’m hoping the ride to Carlisle doesn’t blow out all the Permatex but if it does I know just how to fix it AND what it will sound like when I’m done.
Also tightened down everything up front (including some loose lug bolts–never did that before!) and adjusted the sway bar brackets and the brakes. Semi-polished the paint with that “Speed Demon” stuff the Speedster guys rave about. It works good.
My car is ready to rumble. And it doesn’t even rumble!
See several of you in a few days.
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