new guy-74 B, HIF question

[artmck]

I just bought a 74 B roadster (had one 25 yrs ago) that has the HIF carbs. I have balanced them and gotten the engine to run well at all but full throttle above 3500-4000 RPM where it starts to lose all power and stumble. The mixture is at full rich just to get to this point. There are no obvious vacuum leaks. The pistons move well and have ATF in the dampers.

I have not taken anything apart, but wanted to get advice on where to look. It is better when choke is pulled, so I think there is sufficient fuel flow from the pump. It has all of its original emmision stuff in place. It seems to be worse when the car is fully warmed.

Thanks!

 

[lclark0624]

artmck,

welcome to the forum. good stuff here.

you might read the string "what's going on" that i started a week or so ago. there's some discussion of other than carborator problems.

 

[Dozuki]

Hard saying exactly whats going on... could be rich, could be lean... to check, run the car for a few minutes at full throttle (a street with 50 - 55 MPH speed limit) and then pull off on a side road and pull the plugs... Black powdery = rich, tan like hot coco = good mix, white = lean. You can do this at normal in town driving speeds too, and at idle. Could be that the carb needles are outta sync, it could even be ignition related as your advance won't go any farther at 3500 or so. But, I'd check the plugs to see what's going on, they will tell you alot.

BTW, Welcome to the forum /ubbthreads/images/graemlins/cheers.gif

 

[DrEntropy]

Doin' plug cuts in a car with an iggy column lock can be problematic /ubbthreads/images/graemlins/wink.gif

I'd say invest in a PAIR of ColourTune tools instead.

Points type dizzy? If so I'd check point gap and timing too.

 

[Dozuki]

Hard to read those color tune plugs at 3500 RPM under a load tho without a dyno ;P

Just don't turn the key ALL the way off and lock up the column. Works for me =)

 

[DrEntropy]

mehheh... granted. But ya aren't gonna get a good "read" from a plug if ya gotta decelerate and stop before you shut off the iggy either... and shutting off the engine with a column lock could, ummm... ruin yer day.

 

[Dozuki]

True it COULD ruin your day, I'll give ya that. Practice makes perfect =)

Guess this is just proof that 'There IS more than one way to skin a cat'

 

[artmck]

I assumed it was lean since I needed to richen up so much just to keep it running at lower load. It spits back through the carbs occasionally, and it runs better when choked.

As far as ignition, I have not checked timing, but it has one of the Mallory dual point distributors-not sure about its advance strategy.

I've been reading about the temp compensation on the HIF carbs, and it seems like something may be going on there. It will be messy to check, but I guess that is the next step.

 

[Dozuki]

It would be good to determine if it is in fact running lean. My car runs rich as all get out at idle, a bit rich at normal in town and lean at highway speeds. This I've determined is the needle for the most part and is the best compramise as I usually only putter around town. BUT ignition setting will make a BIG difference, especially between 3000 and 4000 RPM. I would make sure that your timing and dwell are spot on before doing too much to the carbs. '90 of carb problems turn out to be ignition related'

 

[Nunyas]

hmmmm... I second the ignition... when I got my car I thought i had carburetion problems, and racked my head about it for months... the engine even exhibited the back-firing through the carb... and sometimes through the exhaust. I even checked my ignition the timing always seemd fine... and then one day I replaced, the distributor cap, plug wires, and plugs... and that completely changed how the car behaved. I can get it to idle under 500RPMs now... rediculously low, but I keep it around 500 to 750. Since I've replaced my coil, the engine has enough torque to accelorate from 1000 RPMs in 3rd gear without any complaints.

I think I remember reading on these boards some time ago, someone mentioned the first things they change when they buy a used car, are the plugs, plug wires, distributor cap & points (if equpped), and coil. Those parts are relatively inexpensive, and if new you can reasonably rule them out as the problem. I wish I had done that on my car in the beginning, because that's what ended up making my car run better than I thought it ever would.

 

[Bob Claffie]

Nunyas: I did all the things you just mentioned and not long afterward was stranded on the side of the road with a bad condenser! (NOT the MG) Add that in for an extra couple of bucks. Bob

 

[PAUL161]

Check the ignition! Make sure it's on the money as per factory specs. A bad or weak coil, old ignition wires, etc. could cause this problem. PJ

 

[Bruce74B]

Artmck, welcome to the Forum!

First of all, I agree with what others have said about checking out the ignition completely...most carburation problems are ignition related. I would replace the double points with a stock set, just to see if that helps. Certainly, new wires, plugs and condenser will not hurt and may work miricles. Check the distributor hold down to make sure it is tight (simple things, I know) and free of gunk that might throw it out of wack at higher RPMs. Make sure the vacuum advance line is hooked to a good vacuum source and is clear of obstructions...blow the line out with air to be sure or replace it...30 years can suck a lot of gunk into a 1/4 inch hose!

On the fuel side, it does sound like it could be a supply problem...when you do the high speed shut down to check the plugs, take a look at your fuel filter to see how much gas is in it after a highter RPM run and shut down...AND ONLY SHUT THE ENGINE DOWN, DO NOT LOCK THE STEERING (your radio should stay on /ubbthreads/images/graemlins/grin.gif)

Finally, the mixture that I have found to work on my HIFs is rich...too rich at idle, but suitable for mid-to higher RPMs. I can redline mine in 3 gears (I haven't had the intestinal fortitude to try to wind 4th out the whole way yet...let alone in OD) on a closed track of course /ubbthreads/images/graemlins/devilgrin.gif

I tuned my car, ignition through carbs, 3 years ago and have not had to touch it since then. As I said, it is a little rich, but it works for me /ubbthreads/images/graemlins/driving.gif

good luck!

Bruce /ubbthreads/images/graemlins/cheers.gif

 

[artmck]

The Mallory does not have a vacuum advance. Is it suitable for a B engine with just whatever centrifugal advance it has? I plan to put a timing light on it and check the whole thing. I thought about looking for an original distributor just to be sure, but I'll check this thing out first.

Thanks for all the comments.

 

[JamesWilson]

Am I missing something here? A second or two to shut the engine off, shift to neutral and then turn the column lock off and ignition (but not the starter) on. Minimal risk, coast to a stop with a dead engine even if the ignition is on.

 

[artmck]

I am in the process of cooking crow; It looks like the ignition system may be the issue, not sure yet, but I advanced the static timing and turned down the idle and things are much better. I will put a timing light on it tonight to check the advance curve as it still loses steam at higher revs.

In looking at the Moss description of the mallory unit it states that various advance springs are available and that detailed instructions come with the unit on how to set it up. If other things on this car are any indication, the PO did not do this correctly and that may be the bulk of the problem.

Thanks to all.