Asking too much from my RB?

Hello all.

I've been trying to sort out my '78 since the day I got it. I fixed exhaust leaks and vacuum leaks and I've been trying to tune it ever since. I followed the Jack Austin method as best as I could. Checked valve clearances, replaced cap, rotor (has a CEI ignition so no points). I set the timing to 10 deg @ 1500 rpm vac disconnected as per specifications for a late model dizzy.

Trouble is that the car seems to really be a dog when it's set that way. Off the line it's slow and I can't even think about going up hill. I got on the freeway and I have to drive in the slow lane when I'm going up hill. If I start the hill at 65 mph I end up at 50 mph after about a 1/2 mile. I have to keep my foot to the floor get keep it from getting slower.

The carb is fresh and I've checked the throttle cable adjustment.

Am I expecting too much?

Thanks for you help.

I used to drive the B in low rpm. But she performs her best around 3000-4000rpm. Going up a hill on the freeway i dont let it drop below 3000, if that means shifting down to 3rd, so be it. and i really dont have a good tuned car. never checked the valves or the timing, i dont even know how.

i think some of us are used to driving big v8s with lots of torque at the bottom end.
my oldsmobile delta 88 used to spin the tires when i was merging to hwy at 50mph!

Eric,

Advance your timing until it starts pinging, and then back it off until it stops. You may have to do some testing, but there's a sweet spot you'll hit. Try around 13 degrees at 1500 rpms - it may be fine there. You can advance the timing further by running higher octane gas. My 76 is set at 13 degrees, and I run 93 octane. While its no power house, it will pull a hill. At 10 degrees I had no power at all.

You'll get some more responses - many people set the maximum advance at 3500 rpms, but you still need to find the sweet spot for your car - the distributor and the engine are old, so its really more a "figure out what works" process, IMHO.

What kind of carb do you have?

Eric, that does not sound normal at all. Of course, I have a 1974 MGB which is less "strangled" as they say with smog equipment than yours might be . . . . Mine accelerates just fine--not at all like a modern car, but it gets up to 65-70 pretty fast and goes up hills in good shape. I can cruise at 65-70 which it doesn't sound like you can very easily.

Something must be "restricted" or not operating correctly on your car. I think you just have to go through a checklist.

It might be worth running it by an experienced British car mechanic. I strongly recommend Frank Monise at Frank Monise Motors on Walnut St. in Pasadena He's pretty darn good. Tell him your symptoms. He might have some ideas and be able to sort it out for you. He's worked on Brit cars for years, and he keeps my car running smoothly. Why not give him a call? Heck, maybe someone stuck a potato up your exhaust pipe??? :)

I have the ZS since I live in California.

As far as highway driving I've started hills at around 3500 and it just gets slower and slower no matter how much I open the throttle. Just I'll try down shifting once I hit 3000 rpm. I've driven 4 cyl manuals for most of my time behind the wheel, never had one react this way, even an old BMW with a blown head gasket could maintain speed.

Not sure if this is a factor, but my '77 was the same way. I had replaced the stock aircleaner with an aftermarket one from Moss. I could never get the mixture rich enough. I put the original air cleaner assembly back on, richened up the carb, and set the timing as far advanced as I could, just off of pinging. MUCH better performance. You might try richening up the mixture and see if that helps.

Something isn't right. Advancing the timing should help.

I hope you have the factory carb, designed for the sole purpose of turning gasoline into noise without producing power. Tough living in California sometime.

But even factory set up can comfortablely cruise down an Interstate. Heck, for a while I drove my 80 with an effectively dead cylinder (burnt valves, no compression) with the stock carb and had more ump than you discribe.

Hey Drew.

I've been really trying to DIY since I don't have a lot of $$$ to spend. But I really am getting to the point of caving in.

You bringing up the potato in the tail pipe idea has me wondering...I replaced the manifold and I noticed that the stock cat is empty, but the PO had a replacement welded in just past the down pipe. It's a flat type, not the round stock one. Makes me wonder if that is causing trouble, too restrictive?

You're probably on to the thing Eric. I was about to say something about the exhaust being restricted when I read this last post.

You can do several things. One, you can pull the aftermarket cat and install a "test" pipe where it was. This will eliminate any restriction caused by a stopped up or collapsed cat matrix but it won't help in the exhaust velocity department as that big empty cat shell will still be there. Eventually, if you retain the single carb system you will want to replace the cat itself with a proper new one or install a straight pipe in its stead to keep the gas velocity up where it really needs to be.

This having been said there is always a possibility of a collapsed or otherwise obstructed center or rear silencer. It would be pretty obvious how to fix either one if it is discovered, just replace the unit. I don't encourage replacement of the silencer under the driver as it is pretty worthless and lowers the ground clearance. Having just the rear silencer is certainly within the realm of adult behavior as far a noise is concerned.

Another way to detect some of this is to use a vacuum gauge. They are cheap and can be bought at any parts house. The faces are graduated for several different engine conditions and all you have to do is Tee into a vacuum line near the intake manifold and read the gauge as you drive the car. You might have to buy a few more feet of hose to reach to the cockpit but that isn't expensive either.

Another cause for the power lose would be lack of fuel, but for some reason I get the impression that the exhaust is your problem. Check this stuff out before you start chasing other ghosts.

Jack

Eric, I second what Jack has suggested. Tuning with a vacuum guage is the oldest trick in the book. For under $20, I think you can get your motor close to optimum performance with your current setup. Google vacuum guage motor tuning and read, read, read...

My '78 runs like it's got an Expedition tied to it at low RPMs with the timing set to spec. With it advanced another 5 degrees or so, it's a different car altogether. That really only makes a big difference up to about 2000 RPM. though. Even with it set to spec, it has plenty of power (for an MG at least) above 2000. Mine has a DCOE and early exhaust though, so you can't directly compare my results to your car.

One thing you can check easily in about a minute is to see if your mechanical advance is operating properly. Hook up your timing light & unhook the vacuum advance just like you've done before, but rev the engine up and see if the timing mark moves. If it doesn't, you've found the problem - or at least one of 'em :D

Do it just exactly like John English suggested in the second response to your original post. That is what I did on my '77 and WOW! what a difference a couple of degrees makes!

I haven't put a light on it to see where I ended up, but let me tell you it is a different car!

Jeez, I love this place!

Since I live close and I'm compulsive, I advanced the timing on my lunch break to 13 deg @ 1500 vac diconnected. Response is much better but that top end at speed isn't...

I'm going to go with Mr. Austin's vacuum test suggestion. I've used one while checking for leaks, but never while driving. From Mr. Weimers article it appears that I should be looking for a drop towards 0 as the car slows or bogs down.

The more I think of it the more I like the idea of collapsed cat, especially since this one is right under the frame rail and qets quite a bit of hammering since there is not a lot clearance. One good speed bump and that's all she wrote, I'll bet. Its' purpose was obviously a cheap fix to pass a prior smog test....

You all are the best! I'll keep you posted....

You've got it Eric.

If the exhaust is stopped up there just can't be movement of the gases out of the combustion chambers in order to create a vacuum into which new fuel/aid mix is drawn. Like we said, just look at the little colored segments on the gage face. They are set up in a "one size fits all" configuration but you will get the idea of what is right and wrong very quickly.

Jack

BTW: Ain't that just great folks? A young man so into his B that he runs home to try a fix during his lunch break! Beats the living hell out of one who whines and moans about the quality of his drugs or the color of his tattoos! There is hope and I love it!

I hear ya Eric! My lunch break has often been spent syncing carbs and setting mixture. No rest for the wicked :)

Inspect that Cat and post some pics if you can.

fleshy1 Wrote:

fleshy1 Wrote:

My '77 with twin SUs is set to around 12 degrees; it runs like a scalded dog. :P

Eric, are you sure you are getting enough spark?

Often, when a car will run fine on the flat but won't pull under load (say, uphill) the problem is ignition, not fuel.

I agree with resetting the timing, but I would also see if someone wil loan you a high permormance ignition coil to try. How about the ignition wires, too.. if they are old, there are much better wires available now.
Mike

You're not expecting too much. My '79 set to spec zips around quite well.

Just a thought...if you're getting good accelleration up to a certain speed and then it sort of tops out...maybe it's your throttle cable. Maybe not moving freely enough?

OK. Here's the the scoop on the vacuum testing.

I picked up a T and 6 ft of vacuum line. I T-ed into the dizzy vacuum line since it is hooked on to the manifold vacuum. I did the test on my drive home from work which offers a lot of different driving conditions.

Results:
Idle - needle is buzzing around 16 Hg. +/- .5 Hg Indicating timing could be a little more advanced, but I'm getting a slight ping so I'm not going to mess with it.
Acceleration - needle drops to around 3 Hg and continues down toward 0 as I open the throttle. This action is more pronounced under load.
Decceleration - Needle pops up to 20 Hg and holds steady.

So if I read this right it is a plugged exhaust.

Mike J - I've replaced the stock coil with an MSD unit that put out 40,000 V so I think I'm good there. NGK Plugs are gapped at .035 as is indicated for the late model spec.

Jon - I checked the cable adjustment after finding your thread on the subject. Throttle opens full if I put the pedal on the floor, so I ruled that out. But it's good to know that I should be going a little better with a late model car.

Josh - Don't rub it in. I can only dream of the return of the 30 year window for us Californians....

Will post pics of the cat. tomorrow.

P-o-t-a-t-o, I say, up the old pipe . . . :)

pump your brake pedal. do the rpm's change? if so vacuum leaky brake booster. not a cheap fix

Yes! Victory!

I had my local muffler man take out the offending cat. and wow! The car actually drives now. My idle speed went up about 500 rpms from the way I had it set before. I could tell the difference in just the few blocks that I drove from the shop to work.

I'll give the car a freeway test at lunch, you know, my favorite wrenching time! :D

The guy said that the the interior of the cat was in good shape, but he did mention it possibly being carbon choked. How would a cat. get that way? Improper tuning? Putting too much oil in the crank case?

I only ask because I'm going to have to put a proper one in at some point and I don't want to have to replace it everytime I get it smogged.

Good to hear Eric! So you're saying that you had a piece of straight pipe welded in place of the cat?

Yeah, the guy put in a straight pipe where the aftermarket converter was. I still have the original cat in there (attached to the manifold) but its just a shell.

I'll replace it with the correct one from Moss or VB when I get the money. My main concern is that it will get fouled for some reason, just like the aftermarket one did.

You may want to query around for a high flow Cat. They meet smog standards and flow much better of course. I'm not sure if one would fit where the manifold cat is, but it is well worth the research.

Now that you have some of the obstruction out of the way, I think you can concentrate at tuning the motor as best as possible. It sounds like from previous post you have uprated most of your ignition components. Do you have a timing gun? It's a good investment and will yield some valuable information you'll need later. I have a feeling that your advance may be a little out of wack. Let's look at that next to start cleaning up your combustion burn. With a timing gun we'll be able to track your advance curve and compare it to more ideal curves.

BTW, has that cavin' in feelin' left yet? :)