Won't rev above 3K - running short of ideas

[xray]

Good work, Warren!

You and I are working in parallel it appears...I was having weak spark issues as well, fixed by new cap and rotor (new wires as well, but felt not to be the major issue.) I think my issue related to an inappropriate gap between the carbon tip of the cap's coil pole and the rotor. New plugs today, and cross the fingers for hope it runs!

Thanks for updating the progress,

Steve

[madkaw]

I have the same scenerio going on right now. I finally drove a clients car(240) after redoing the whole suspension. Before I tore it down i had done a quick tune-up on a engine that hadn't run in over 10 years. The engine ran strong after putting the rockers back on the valves(another story). I drove it around and it seemed to want to go over 3000rpm but the suspension was scary so I didn't push the issue. Now I have everything back together I want to drive it a little faster but it doesn't want to rev over 3000. I did take the tank out and cleaned it thoroughly when I first got the car. I did notice the SECOND time I took the tank out, when I was doing the suspension , I drained it I found some more crap in the fuel. I couldn't believe there was dirt in the tank because I really cleaned WELL the the first time. Where I'm going with this rambling is that I still might have a dirt issue that is causing a obstruction. I took apart the distributor to see if the mechanical advance was not working and it seems alright. This car still has points but i have convinced the owner to buy pertronix and i am awaiting the delivery of the goods. I want to eliminate the ign ition issues-if any- before looking elsewhere. I will also pull the sender to look at the pick-up to see if anything is clogged.

I had a similiar issue with a Kawasaki years ago where it didn't rev over 5k. I never figured it out until just beforte i sold it and it was the mechanical advance.

I also wonder about a fuel pump that has sat around dry for years. Is the diaphram cracked or worn that it will not supply ample pressure??

[7277]

madkaw: it sounds like you're very close to the problem... you state that you pulled the tank a second time and found more junk in there. good chance a few flakes of rust and whatever may be in the hard lines to the mech. fuel pump and filter. i'd start there first. take off rubber lines and blow through w/ air compressor to make sure eveything is out.

p.s. after redoing the suspension why was the ride 'scary'..it should be nice. ;o)

[beandip]

Warrenz,xray. I have been dealing with much the same issues. I even changed fuel pumps ,electric, and vacuum advance pot. Mine had a slow leak. Still could only get to 3K and she started shooting ducks! If I kept my foot in it at 4k she flat quit. I am running 3 screws now so I pulled them and re adjusted the floats. At .500'' as per Steve at ZTherapy . So far now she will rev past 4500 and seems fine in this respect , but I am experiencing a flat spot off Idle. By the way 20w oil is available at the Cycle shops. It is used for the front forks. It comes in various weights. I have only found it in qts. and this will last you a life time. I have been using it for years. I read a interesting article in today's paper about the gas we are getting , especially this time of year. This was for boat owners but applies to us all. Seems the additives and ethanol we are forced to use , especially in the winter , evaporates off rapidly and if you store your car or fuel for as short as 3 months . Residue forms that is difficult to remove. It clings to the screens and filters and plugs them. They were stating that it is best to have the tank full or completely empty . Preferbly full to avoid collecting moisture. Using stabilizer is recommended for even a 3 month storage. About the issue of turns of the mixture on the SUs , 2 1/2 has always been the starting point on everything I have read. This is just to get the engine started. Much depends on how tight the throttle shafts are, how much vacuum leaking is there. Do you have the needles mounted flush as recommended in the manuals. This can cause your richness on the rear cylinders if that needle is set too deep. Just a thought. Gary

[WarrenZ]

Beandip,

Do you have the needles mounted flush as recommended in the manuals. This can cause your richness on the rear cylinders if that needle is set too deep.

I have not checked that, thanks for the tip. Once I get my flowmeter back I will go over the carby's from start to finish.

Warren

[madkaw]

Gary,

In my case I did set up carbs according to the z therapy video and it ran great the first time. But now my car is acting like Warrens z and like it has a rev limiter. These fuel pumps spew gas when the diaphram goes bad don't they?

7727, I drove it the first time with the old suspension-which was scary.

Any how, I probably won't have time to mess with it until after the holidays so meanwhile i will watch your progress Warren.

[xray]

Warrenz,xray. I have been dealing with much the same issues. I even changed fuel pumps ,electric, and vacuum advance pot. Mine had a slow leak. Still could only get to 3K and she started shooting ducks! If I kept my foot in it at 4k she flat quit. I am running 3 screws now so I pulled them and re adjusted the floats. At .500'' as per Steve at ZTherapy . So far now she will rev past 4500 and seems fine in this respect , but I am experiencing a flat spot off Idle. By the way 20w oil is available at the Cycle shops. It is used for the front forks. It comes in various weights. I have only found it in qts. and this will last you a life time. I have been using it for years. I read a interesting article in today's paper about the gas we are getting , especially this time of year. This was for boat owners but applies to us all. Seems the additives and ethanol we are forced to use , especially in the winter , evaporates off rapidly and if you store your car or fuel for as short as 3 months . Residue forms that is difficult to remove. It clings to the screens and filters and plugs them. They were stating that it is best to have the tank full or completely empty . Preferbly full to avoid collecting moisture. Using stabilizer is recommended for even a 3 month storage. About the issue of turns of the mixture on the SUs , 2 1/2 has always been the starting point on everything I have read. This is just to get the engine started. Much depends on how tight the throttle shafts are, how much vacuum leaking is there. Do you have the needles mounted flush as recommended in the manuals. This can cause your richness on the rear cylinders if that needle is set too deep. Just a thought. Gary

Gary,

The ZTherapy video says the float level should be 0.55" or 9/16"--now they are saying 0.50"? Interesting. If it falls flat like you say, and is better with a higher float level, it sounds likely to be lean. I wonder if the presence of ethanol in the winter mix of gas has anything to do with it, since ethanol is not as potent on a per unit basis---wouldn't there need to be more in the combustion chamber to get the same combustion energy?

Warren, et al

My issues are mostly solved, as I mentioned above. New BP6ES plugs gapped at 0.036 and it runs well. Timing was a bit overadvanced, since then corrected--the car has a nice smooth idle at 900rpm (my mild cam likes a slightly higher idle apparently). Still fairly lean, though, so I need to Colortune it, readjust the float level as Beandip suggested, and continue mucking around as I have been...

Steve

[beandip]

Gary,

These fuel pumps spew gas when the diaphram goes bad don't they?

The mechanical pump has a flexible ''rubber'' diaphram that makes the thing pump when it is pushed up and down. Vary simple design that has been used for many years . Yes they have a habit of spewing gas when the diaphram fails. Unfortunately sometimes the gas isn't seen as it is shot into the engine near the cam chain thus diluting the oil in the engine. really a bad thing. There is a small weep hole on the bottom of the pump where the gas is supposed to spill/leak out. I had a pump like this on my first car '52 Chev. As I said they have been around a long time. Like Me. Gary

[Mat M]

WarrenZ and madkaw have it pinned, IMHO. IME,, after I cleaned the fuel tank, replaced the filter (5 times), AND installed an electric FP at the tank, the low revving/flat response while in gear (but free revving in neutral) persisted. It turned out to be the in-tank pick-up tube was rusted almost solid, only a trickle of fuel was getting through. Using a copper wire, I reamed out most of it, and VIOLA! I got power back! If only the pick-up assembly were accessible in the 71s...

[WarrenZ]

Good point you make Mat M and I will check that. I did notice once that the level in the fuel filter (the new one is clear) was lower than I expected but it did not happen again. I will take it for a run and stop immediately after pulling max revs and check the fuel filter level. Maybe after each run it filled up as I idled into the garage. Although I did monitor the fuel filter level when revving in neutral in the garage and it was OK.

It will all have to wait till after Xmas now as I am off to visit the family for Xmas and I get to drive my other Z (a 2004 red 350Z) 500 miles each way and get to stay at the beach. -eat your heart out in the northern hemisphere.

I will give you an update later, thanks everyone for all the tips and have a happy Xmas.

Cheers

Warren

[kenz240z]

Warren, leaving the ignition in the ON position for 24 hours will burn the points in the distributor. Sometimes filing the points will save them, sometimes they are toast and need to be replaced...

[JimmyZ]

Warren do you have regular SU's (early style) or the more complicated later style SU's which came on '73's??