Carb problems = spark plug wires

[grandfatherjim]

Last summer I spent lots of time fooling around trying to resolve intermittent poor performance. Main symptom was a bog in acceleration, sometimes, that seemed as though the timing might be off. So I first replaced and gapped the points, and then set the timing quite a few times. Still thinking it was ignition related, I swapped in a different rotor, and a different cap, which I have on a spare engine I acquired along the way. No change. Well, except once in a while, when it would run so much better - showing me how much power (I use the term loosely) it really could have.
OK, must be fuel delivery. Found the fuel filter inside the pump - and it was totally clean. Hmm.
As I had not touched the carbs since acquiring the bus three years ago, and since it hadn't run for many years prior, I tore them down for a good thorough cleaning and inspection. I did find a couple of issues and dealt with them, but they were pretty good overall and cleaner inside than I expected. Squatting over them for hours did in my knee...
A test drive yielded only the subtlest of improvement. I especially expected better idling, which I did not get.
The distributor on this ('72 1700 dual carb) engine is a one or two year only model. I have no spare, and this one has shaft wobble and a scored cam, so I decided to drop the bucks and get an optical pickup Crane system. Spent many hours trying to fit the pickup just exactly right (an interesting learning experience), and it fired right up. Down the road and it's running like a champ - for a while...then back to the same low power.
Fall came and I parked the bus for the winter. During that time it struck me that I had never replaced the spark plug wires, so I ordered a set and installed them last weekend. Yesterday, being a nice warm summery day, I installed the battery, put a tablespoon of gas into each carb, and it fired right up. After 30 seconds or so of teasing the gas pedal, it sat and idled at a nice low rpm, which it has hardly ever done until it was very well warmed up, and even then it was usually lumpy. Test drive and wow, smooth. haven't gone on anything resembling a trip but all is pointing to problem solved.
I don't mind that I cleaned the carbs, and the fuel pump. I can say that instinctively, deep down I felt they probably weren't the issue, but they needed the attention.
So this experience yet again proves the old adage: 90% of fuel problems are electrical in nature.

[Amskeptic]

replaced the spark plug wires, Test drive and wow, smooth.
all is pointing to problem solved.
So this experience yet again proves the old adage: 90% of fuel problems are electrical in nature.

Give us an update after a few weeks.
Colin

[grandfatherjim]

Good call - problems indeed persist.
More than a few weeks, but very little bus use, has gone by.

It seems like I have better power in 1st 2nd and 3rd, than 4th, where it bogs out. Feels it does when like timing is too retarded.
Before further timing tinkering I did a long overdue compression test, yielding 105-122 dry and 112-122 wet. Spark plug colours vary a little, but are generally quite good.

a) Thinking maybe I have a slow leak in the distributor vacuum can (allowing the gradual degradation of performance in 4th), I sourced another correct for the year and tried that - no change.

b) Tried swapping coils with another (not new) one - no change. Went back to first one as the second one's resistance is 3.6 ohms and the original is 4 ohms, which is what the Crane system wants.

c) My timing light was a garage-sale special that had a dial for canceling out advance. Thinking it was somehow throwing me off I bought a new one (without said dial), which proved that the old one worked. You can see I'm grasping at straws now.

d) As an experiment, I tried advancing timing from nominal 28 BTDC @ ~ 3200 rpm w/o advance hose by 6-8 degrees, and there was a very definite and measurable improvement in performance. The bogginess went away almost totally in 1st, 2nd, and 3rd, and quite a lot in 4th too. But after about a mile, I still just couldn't go above 55 mph, and it helped to gently use the accelerator pump to try and keep it at 55. (This is on the "drive west as fast as possible and check your speed when you go by the Baker's driveway" test.) When I stop and turn around and head east, I can generally get up to 60 or even 65 mph. I can't discern whether this is because I pulled over and the engine had a rest/cooled a bit, or because I am really going slightly downhill on the way home (really, it does look uphill).
(In both directions this is a 5-8 mph improvement over having timing set at nominal.)

I don't want to leave the timing there - too afraid of damage. And, as you would expect, it gets a lot hotter when set there. It's tempting though, since the vehicle is bordering on useable, and we have plans for a couple of trips pretty soon.

Questions:
1. Since adjusting timing seems to improve performance so much, could it be a fuel problem anyway, in disguise somehow?
2. Is it time to try a brand new coil, even though two give about the same results? I have certainly heard of a coil failure mechanism whereby they crap out as they get hotter. I'm thinking, if it (they) are borderline, maybe the spark can't quite burn the fuel when under load?
3. Is there something simple I'm overlooking? Sure seems like it.

I know this vehicle can perform much better. It feels like it has pneumonia - can't breathe, like it just wants to burst out and perform, but something is holding it back. I want to unleash its power!

Please help.
Desperate in Franktown.

[RSorak 71Westy]

Sounds to me like a lack of fuel problem....I read you been through the carbs and filter.....but this is just what it seems to me to be.

The increase in power with the increase in timing is completely normal. Until it starts pinging or running too hot.

[grandfatherjim]

I keep thinking it's fuel too but then can't explain why it seems to do fine on the speed run in 1st 2nd and 3rd, and then has trouble once up to speed, in 4th.

[RSorak 71Westy]

This is exactly what makes me think it fuel. The engines sustained fuel demands are the most in 4th under load. Short bursts of full thottle in the lower gears, while may demanding more fuel for a short time, give the fuel system time to refull the carb bowls, once you let off. sustained high speed gives no let up to the fuel demand.

[Amskeptic]

This is exactly what makes me think it fuel. The engines sustained fuel demands are the most in 4th under load. Short bursts of full thottle in the lower gears, while may demanding more fuel for a short time, give the fuel system time to refull the carb bowls, once you let off. sustained high speed gives no let up to the fuel demand.

I am guessing fuel too, a dangerous loss of *volume capability* due to restriction somewhere, not a dirt restriction that comes and goes, but a structural restriction like an eroded fuel pump pushrod or flat eccentric on the cam... if you have a mechanical pump. Lean-out loss of power is dangerous due to heat on the exhaust valves.
Colin

[grandfatherjim]

I do still have the original mechanical pump, and am prepared to switch to electric as I believe originals are unavailable.
Are there known models to avoid? Someone recently mentioned to go for rotary rather than pulse..
Are there some that conveniently output the right pressure, or am I looking at a separate regulator?
Thanks,
Jim
PS Are blanking plates out there for hole for the mechanical one?

[Amskeptic]

I do still have the original mechanical pump, and am prepared to switch to electric as I believe originals are unavailable.
Are there known models to avoid? Someone recently mentioned to go for rotary rather than pulse..
Are there some that conveniently output the right pressure, or am I looking at a separate regulator?
Thanks,
Jim
PS Are blanking plates out there for hole for the mechanical one?

Leave the original pump in place and just experiment for now. You want 5 psi.
Colin

[RSorak 71Westy]

Yes there are low pressure electric pumps out there. The SU's on many Brtitsh cars only will take 2-3 lbs. of fuel pressure and many of them have electric pumps.

[BellePlaine]

The distributor on this ('72 1700 dual carb) engine is a one or two year only model. I have no spare, and this one has shaft wobble and a scored cam, so I decided to drop the bucks and get an optical pickup Crane system. Spent many hours trying to fit the pickup just exactly right (an interesting learning experience), and it fired right up. Down the road and it's running like a champ - for a while...then back to the same low power.

How confident are you that everything is hunky-dory with your new Crane distributor? Have you thought about having your orginal distributor rebuilt?

[grandfatherjim]

Pretty confident. My timing mark is now rock steady - narrow instead of wide. The bus will idle down to very low rpms and stay smooth. I think it's good - but most significantly, the present problem was there before installing the electronic ignition.
The scored cam (which doesn't matter with the optical pickup) might not be something that can be rebuilt.
Best for me would be to find a decent one and travel with it on board as a spare. I recently did find one of the right model but it's pretty rough. I might have a go at disassembling it to see if (any part of) it is salvageable, now that I have got it unseized... if it goes really well I might send it off to one of the usual suspects for rebuilding.
Meanwhile though - I don't suspect anything's wrong with the Crane. The spark plugs look good and timing light is triggered, so I have high pot. happening.
High pot happening. Interesting how the words flow sometimes.

[grandfatherjim]

This is exactly what makes me think it fuel. The engines sustained fuel demands are the most in 4th under load. Short bursts of full thottle in the lower gears, while may demanding more fuel for a short time, give the fuel system time to refull the carb bowls, once you let off. sustained high speed gives no let up to the fuel demand.

I am guessing fuel too, a dangerous loss of *volume capability* due to restriction somewhere, not a dirt restriction that comes and goes, but a structural restriction like an eroded fuel pump pushrod or flat eccentric on the cam... if you have a mechanical pump. Lean-out loss of power is dangerous due to heat on the exhaust valves.
Colin

Or a restriction like a glob of some viscous goo in the main jet. Clean that out and watch Jerry go!
Not before I did replace the mechanical with an electric fuel pump - Carter P60504 is the model. Works like a charm and if it ever craps out I still have the mechanical one in place as a backup. (The pushrod for the pump wouldn't come out, so I guessed its end had mushroomed inside. I reduced the thickness of the phenolic spacer a bit to compensate which did bring the fuel pressure up by about half a pound.)

Well, now I have upgraded some things and we have been out camping twice so have put about 1800 miles on. I think I'm getting around 22 mpg (Canadian gallon) which is not as good as I've had in the past but at least now we can travel.

What a circuitous ordeal, er, I mean, learning experience....yeah, that's it.

Jim

[Amskeptic]

What a circuitous ordeal, er, I mean, learning experience....yeah, that's it.

Dang skippy.
It is what steadies your gaze and edits your spoken word, it is what makes you humble, it is what makes a man out of you.
Colin

[SlowLane]

One item I didn't see in the list of things you tried was reconditioning the mechanical advance. That is to say, disassembling, cleaning and lubing the centrifugal weights and springs. It's not a full rebuild, with re-bushing and all that, but it does restore the intended operation of the advance mechanism.

When I put my Westy back on the road six years ago I did just that, and it made an incredible difference in smoothness. When I took it apart, the 25-year-old grease had basically turned into wax, impeding the free motion of the weights, so the advance could either be too low when accelerating or too high when decelerating.

Good call on the Crane by the way. I've had mine for 12 years and never had a problem. And with the optical trigger, you don't need to worry about jitter in the timing due to the shaft wobble.

Good luck,
Lyle