Backfiring and Stalling?

[jonnyc]

Just got my SerIII back on the road in September (after 5 years in the garage) and so far it's been running pretty well. It is a 2.25 gas with a 1950s Rochester, K&N filter, and a Crane ignition. About 2 weeks ago I started getting a few backfires out the exhaust and an intermitent hesitation in the engine (I now think these might be little backfires), mainly when I let off on the gas. It has gotten a bit worse and a few times the truck has stalled while sitting at a light/sign. I had some new bits around so I replaced the in-line gas filter, cap, rotor, and wires...no change. I have been thinking I need to rebuild the carb or sort-out the fuel pump in some way.
Last night I had a thought...perhaps the intake manifold bolt and/or carb-fixing bolts could be loose? I will check that issue tomorrow.

Any thoughts on whether I'm on the right track or missed something important?
TIA

[jac04]

Yes, you are starting on the right track, but you need to go further. Check your timing and carb mixture.

[SafeAirOne]

My vote is for a leak in the exhaust manifold or manifold-to-downpipe joint. That's a common cause of backfiring on deceleration.

[jonnyc]

Thanks, gents. I'll tighten everything around the manifold tomorrow and post any changes. I'm pretty sure timing is where it should be, but the mixture and idle adjustments on the carb are a bit "iffy". It was rebuilt by Recarbco and I haven't been happy with their product. It is the best of the 3 or 4 Rochesters I currently have, however.

[o2batsea]

A rebuilt carb is never as good as a new one. If it were me I'd spring for a carb if I were in doubt.

[jonnyc]

I like the size and power of the Rochester in comparison to the other available carbs. Got a suggestion?

[o2batsea]

Well, actually my suggestion would be to put a TBI and a Megasquirt on it and be done, but I'm sure that's way too scary a proposition.

[Billy5]

I have a Weber 32/36. Zero issues thus far, easy to tune and adjust.

[4flattires]

5 years sitting, hopefully that fuel is not in the system. In Sept, did it run flawlessly, or had it some issues back then, and now it got progressively worse. How old is that fuel?

[jonnyc]

I had a bit of Staybil in the tank, and it ran fine from the get-go. It has been my every-day driver since the first week of September and the tank has been filled at least 10 times since. I haven't taken the pick-up tube out of the tank for a cleaning, perhaps I should look at that also.
Tightened everything in the intake/exhaust line today, nothing really loose. Had to take a family trip, so no testing done yet.
I'll investigate the Weber.

[jonnyc]

Situation is better after everything tightened, new plugs/cap/rotor/wires, fuel filter and pick-up tube replaced/cleaned. Still getting a bit of back-firing and hesitation, mainly when moving at idle (foot off gas). Serious carb rebuild on the school break schedule, everything else seems to be fine.
Always open for suggestions, but no plan at this time to switch to a Weber, one or two bbl.

[Alk-3]

my money is on a bad exhaust as well. I had one for ages, and it did just as you describe. I finally replaced it with the stainless one our host sells, which is louder than the old one, but doesn't backfire or sputter etc.

[jonnyc]

Things got worse after the carb rebuild (see my "Rochester Guru" thread).
Short of replacing the exhaust system at this time, I'm focusing my efforts on vacuum leak issues. After today's search I think I have lots of little ones adding up to a big one. Engine rev'd when sprayed at:
-head-manifold joints (mainly at the exhaust ports?)
-engine side of the int/exh manifold joint
-front of block betw manifold and carb
-front of carb base
-ends of throttle rod

Manifold gasket set is on the way, so I will take the manifolds off and do everything I can do to tighten up all the seam. I will also look for any problems in the int/exh manifold joint.

I hope all this solves my issues.:(

[Kiloengineer]

Any updates to this thread Jonny? I am having similar issues. I rebuilt my Zenith 36IV and have had a hard time getting it running correctly since. I had leakage from the top cover so I flattened all of the surfaces and cured the leak, some improvement in running. I also found that my PVC valve was not working so I replaced that temporarily with a simple check valve and that fixed the smoking issue I had. Now it idles great but when I accelerate I get backfires and has no power. I have cleaned the carb very thoroughly (4 times), all new jets with a genuine rebuild kit, checked the float level, new genuine Lucas 45D distributor, timing done dynamically, new aftermarket coil (suspect?). I am now leaning toward manifold leaks and/or cracks.

Hope you were successful in fixing yours.
Jason.

[Terrys]

Replace your condenser.

[73series88]

Replace your condenser.
second that\
exact same symptoms. took months to figure out it was a bad condenser. and it was in a brand new distributor
aaron

[jonnyc]

Glad to hear you guys are having success. I have a Crane ignition, so I don't have a condenser any more........right???

[NickDawson]

condenser would have been my guess too... think the crane rules that out.

[printjunky]

(EDIT: Yup, I missed it. I somehow missed the second page)

Nobody here's thinking vaccuum leak? Or did I miss it? That's what it sounds like to me. This is the behavior of my SIII (same exact setup, except Pertronix) when I lose one of the little (crappy) vinyl caps on one of the tiny tubes on the base of one of the connections (brake booster, I think) to the intake manifold. If you can't see an obvious leak, I'd try the starter fluid trick (spray some around the manifold see if you get a rev.)

[printjunky]

Kiloengineer (http://www.roversnorth.com/forums/member.php?u=32189), This may not be much help if you're determined to stick with the Zenith, but I struggled to get my Zenith to run right for about a year. It was rebuilt (not original kit), warp-fixed, checked and rechecked. It was just DUMPING fuel into the intake. So bad that I'd have to keep a second set of plugs, because about every 10 hours of running, they'd be so carbon-fouled the thing wouldn't run. I'd have to swap 'em and wire wheel the fouled ones. Eventually just to try something radical, I found a rebuilt Rochester on Ebay, and I couldn't be happier. All I did was jet it down (to a 51 I think). I think it's running a little rich, still, so I should get back in and check float level, and maybe jet down another step. But this is my third Rover - I don't remember the carb on the first, and my second had a Weber - and I had no idea these cars could run as well as my Rochester equipped one does.

The only other problem I've had is I had a tiny (TINY) piece of something get into my metering valve, and stop it from fully closing, so the bowl was overfilling, dumping gas all over the manifolds. Disconcerting, but now that I know what to look for, not as big a deal.

[Kiloengineer]

As an update, I am waiting for parts to fix up the manifolds - the exhaust manifold was cracked and the intake may have had a gasket leak. Then I will try a new condensor. I have also checked the fuel pick-up and adjusted the tappets. If none of that works I guess I start shopping for a new carb.

[Kiloengineer]

So this weekend I replaced the condensor (again), installed a good coil out of my Jaguar, replaced the exhaust manifold and the intake manifold gaskets, adjusted the tappets, checked the timing, checked the fuel pick up line, replaced the fuel line from the pump to the Zenith carb, replaced the wiring to the coil. It still idles great but has now power and spits and backfies under power. I am using plain clear hose for the vacuum line to the distributor, could that be an issue? I ordered a new line but it didn't arrive. Unless anybody has a good idea I will take printjunky's and terriann's advice and find a new carb. After spending so much time on the Zenith and using a Genuine rebuilt kit I thought I could save it....

[73series88]

get rid of te zenith and throwon a new weber.
had an old solex. rebuilt of but was still an issue
new weber fixed all that right up.
aaron

[bmohan55]

I vote Rochester....

TerriAnn has a great writeup on the various options

[Kiloengineer]

Here I am again, sorry if you are getting tired of hearing this. Today I bought a new weber, installed it and still have the same issue. Zero power up any kind of a uphill grade. Idles fine. So to summarize, I have a new Genuine Lucas 45D distributor (I found that the (new) points were not contacting so I thoroughly filed, cleaned and gapped them). I replaced the new condensor with another new one. New plugs and wires. New carb, replaced the vacuum advance hose twice. New exhaust manifold and intake gaskets. Checked the fuel pickup line for any clogs. Adjusted the valves. Ran a compression test - all ok. The only thing left is the fuel pump - there is always fuel in the filter but only about half full (this filter is new with the Weber). Or I worry about the gas hese days with 10% ethanol, but then I suspect I would hear about that issue elsewhere. Any other ideas beside a new fuel pump? My checkbook is running on empty. Thanks.

[jonnyc]

Tried everything, no change. My last resort was to try and fix the stripped air horn/top cover that I swapped out. A little JBWeld and 2 days later, it is now on and the idle has smoothed out. Weatherman says it will be over 60 tomorrow, so I'll spend the afternoon trying to get it all dialed-in and solve the old original problem I wanted to fix in the first place. First though, I'll have to fix the vac. gauge connection I broke today.
It's always something in Rover World!

[jonnyc]

Everything is sealed up tight, old airhorn is fixed and back on, mix and standing idle are good. Back to driving it, but the backfiring when decelerating is still there, and the idle sometimes drops right out and I stall when coming to a stop, or it stays high and won't drop down to driving idle. I have ordered new carb return springs (the straight one and the bell-crank), hoping that will steady the linkage and allow me to set the idle right.
What have I overlooked?
What should I revisit?

To add; vac. holds steady around 19-20.

[SafeAirOne]

Backfiring during deceleration suggests a leak at the exhaust manifold or downpipe that introduces fresh oxygen to the still-combustable, very hot exhaust gasses.

[jonnyc]

Actually went to order the exhaust system today, but was told to try adjusting the valves first. I'll try the valves and springs first. Hopefully those will seal the deal.

[SafeAirOne]

Actually went to order the exhaust system today.

Why? Is yours bad?

[jonnyc]

Nothing obvious, but it is pretty rusty and I was thinking there might be a problem along it that I'm missing. The vac gauge reads a pretty steady 20, so I think I got all/most of the vac leaks sorted out.
I guess I' grasping at straws here, trying to eliminate potential problems. Hopefully the return springs and valve setting will magically remove all the gremlins.

[SafeAirOne]

Don't forget that there are $5 gaskets between exhaust manifolds and heads and between exhaust manifolds and down pipes and that manifolds are held on to the head by studs, nuts and/or bolts that can loosen up. Same with downpipes to manifolds, yada, yada, yada...

Just a word of caution for you: Wholesale replacement of parts to solve problems can get expensive after a while. Troubleshooting to identify the specific cause of a problem is the method most often employed by us non-wealthy. ;)

[jonnyc]

Yes, I know, but I have been working with this problem (unfortunately it's probably more than one issue) since December. At some point you do have to begin to eliminate certain areas.
What gasket is there between the exh. manifold and down-pipe?

[SafeAirOne]

What gasket is there between the exh. manifold and down-pipe?


Actually, the 2.25 might not have one. I'm not sure, just going off my 2.5 setup. Either way, there's SOMETHING that performs sealing duties between the manifold and downpipe.

[bmohan55]

I hope not as I just replaced those parts w/o a gasket!

[jonnyc]

Relax, no gasket between the manifold and down-pipe.;)

[jonnyc]

Valves adjusted and backfire seems gone! The first 7 were spot-on, but #8 (an exhaust valve) was about .02-ish too big. Fingers are crossed tightly.
New carb return springs and a scrounged longer piece of linkage might have fixed my idle issues. Toes are crossed!