runs like crap

[andrew]

Hi folks,

I have a SIIA, 2.25 petrol that is a practically daily driver that has run beautifully for more than 15 years, with normal attention, maintenance, and problems of course. A few months back it started backfiring, according to wifey, on deceleration (didn't happen for me). It got progressively worse though -- rough and uneven running, difficult starting (but always did), sputtering acceleration, seemed to be low(er) power.

Time for some attention, obviously, so:
- new plugs (gapped at .030")
- new plug wires and coil wire
- new condensor, points (gapped at .015"; checked with dwell meter, approx 51-55 degrees), & rotor
- new dist cap
- new fuel filter
- new fuel lines near carb (literally saw a leak spring up when working on carb!)
- made a new LT lead line from distributor to coil
- checked to see it was pumping gas to the carb (though hard to say how much is enough)
- took (Rochester) carb apart (several times...) and found some buildup in screen (hoped that was the problem!), all else looked fine to me (minor adjustment to float level)
- new oil breather hose and some other worn out PCV lines
- dynamic engine timing (more on that below)

I haven't touched:
- coil
- fuel pump
- anything beyond top side of distributor
- other fuel lines

Setting the timing has been a painful trial and error (all error so far). My truck has a timing marker on the crankshaft pulley, but unlike the helpful pictures in the green bible and elsewhere it has only 2 prongs. I assume the leftmost one is 3 deg BTDC and the right one is TDC. I use 87 octane (always have) and have an 8:1 head. According to the gospel of others, my timing should be TDC or so.

After going on a scavenger hunt for the nearly invisible mark on the pulley, I used a timing light to adjust things. Set it up at TDC...no fun. 3 deg BTDC...no fun. About 3 deg ATDC (estimated)...no fun. By ear, ignoring the marks...no fun. In all cases it continues to run roughly -- more specifically, I can get it to run ok after very warm and on idle (at about 775 RPM), as well as when I drive about town AFTER it's fully warmed up. But if I try to start it cold it sputters, chugs, throws fits, and basically fights against me until fully warmed up. Then, it's basically ok (at TDC-ish setting). It never was so temperamental before, though. One thing I did notice is that with the timing light on it if I rev to about 2500 or so RPMs the timing mark wanders quite a lot (maybe 3 inches to the left as facing the engine; about 39 degrees according to the advance setting on the timing light, which I adjusted to get the mark back to the original one at idle speed -- I don't actually know if that makes sense, but it felt like an intuitively correct way to quantify the "wander"). I don't know if that is normal or if that indicates worn weights/springs? I'm out of my league on that one and am only throwing out a guess here...

So, if anyone has any ideas of what I try next, I'm all ears. I really appreciate any help or opinions anyone has to offer.

Thanks.

[ignotus]

Andrew,

You don't say how many miles on the motor but my guess is the timing chain/gears and tensioner need replacing. Heck, you've done everthing else! Like every thing else the timing chain and gears wear out. If your going in there do everything at once then you won't worry about it for another 15 years ;^)

gene

PS, great description!

[andrew]

The motor has about 15k miles on it since a rebuild (refurbished engine from our hosts). It has been leaking coolant from the front (one problem at a time!), which I suppose might be related -- my guess about that was water pump/gasket.

[artpeck]

Interesting problem. A few questions. Have you checked compression in each cylinder cold and hot? Might be a valve or head gasket issue and at least you could start localizing. What state are the plug tips in? Sooty, white, brown? Might also be worth pulling the pick up tube in the tank to see if there is weird blockage or the glass bowl...same thing. Also have you confirmed solid spark to each cylinder by pulling the plug wire and using as screw driver to arc it? I feel like you are at the stage of needing to eliminate stuff starting with fuel versus ignition versus mechanical per the post above.

[andrew]

I have not checked compression. When I replaced the plugs the tips looked perfect (light grey, no carbon or burning, not wet). Each cylinder is getting spark. My next instinct is to go to the fuel pump and/or the tank pickup to make sure it's getting sufficient fuel (seems like starvation at some level). Any thoughts on whether the wandering timing mark mentioned above is a concern or not?

[Les Parker]

Have you checked the vac advance on the distributor? Fit either a vac. pump to the line from the carb. or suck on the line to see if the base plate on the distributor moves. It could well be a vac. diaphragm that has perforated.

2p

[PavementEnds]

I second Les' suggestion. You should also check the retaining collar at the base of the distributor to make sure that both the retaining bolt and pinch bolt are tight. I once found that my pinch bolt had sheared in half -- still together enough to not show an obvious break, but broken enough to no longer do its job. In addition, I suggest that you use a vacuum gauge to set the timing -- it is slick! See http://sbftech.com/index.php/topic,3020.0.html I use the Mityvac.

[andrew]

Just checked it and, yes, sucking on the line from the carb does rotate the distributor base plate. And, the retaining/pinch bolt holding the distributor in place are solid (I've tightened them enough in the last few days!).

[mearstrae]

Maybe just try checking the vac. overall, for leaks or possibly a valve problem (may only need adjusted). The toughest problems often have the simplest solution.

'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[artpeck]

Maybe I missed it but does it idle rough? I would check fuel starvation. It's not rich or you would have fouled plugs. And since the plugs are all the same and you are getting a solid spark it isn't likely to be an ignition issue. As a side bar are you sure the ignition wires are properly connected to each cylinder in the right order? Otherwise it feels like a fuel flow or carb issue. Even as easy as a failed carb gasket or other air leak or something blocking fuel flow. Back firing which you mentioned is from running lean and or over advanced timing generally speaking. At least you seem to be narrowing it down.