at-jefft Posted May 31, 2011 Share Posted May 31, 2011 (edited) So, I have an early 260Z, its got an L26 with 72 dome top SU's. It sat over winter and when I started it up (early spring ~40F) it ran terribly. Barely moved under its own power as well as bucking terribly. Probably 10mph max. Fast forward to summer(now), I messed around with the carbs to find one of the carbs wasn't getting fuel. Fixed that. It runs a little better. It will accelerate (sluggishly) to ~25mph then hits a wall. Bucks once in a while. I thought it had a clogged fuel filter(s), so I relined the gas tank(lots of rust) and replaced the fuel filters. No change. So, Ideas on what it could be? I'm thinking it could be my ignition coil. I ohmed it out and got 17K for the secondary and .7 for the primary. Both of those measurements are slightly above the fsm specs of 12.7 and .55 respectively. Other Ideas? Thanks in advance, Jeff Edited May 31, 2011 by at-jefft Quote Link to comment Share on other sites More sharing options...
KillerBjt Posted May 31, 2011 Share Posted May 31, 2011 Clogged fuel line? Checked fuel pressure? Check the spark plugs? Quote Link to comment Share on other sites More sharing options...
rejracer Posted May 31, 2011 Share Posted May 31, 2011 Pull the spark coil wire from the coil and see how far it will arc to the plug wire. check the basics: 1. Check to see that the distributor mechanical and vacuum advance is working tip top. 2. Set your timing to factory spec, or advanced if you know what engine you have (open or closed chamber) and how much mechanical distributor advance you have. 3. Check to see if the carbs are getting heat from the cooling system. This in my experience it the biggest factor when it comes to hesitation on these cars. If the outlet on the rear carb is not warm, it's not getting enough heat. 4. Fix any vacuum leaks you may have. 5. Set your Fuel Mixtures if they need it. From your description, it sounds like the carbs are running out of fuel if that's the case, here is what I would do: 6. Check your fuel pressure at the carbs while the engine is under a load. If pressure is not good then: 7. It could be rusty fuel lines from the tank to the fuel filter, or between the fuel filter and the carbs. Corrosion can be removed with products like evapo rust. Once fuel pressure issue is fixed: 8. I cant remember if the SU's have the built in perforated brass filter on the carb inlet. Pull it and check to see if it does, and that the inlet is free of obstruction. 9. Pull the lower jet and give it and the line connecting it a good cleaning. 10. Pull the bowls and check the needle and seat. as well as the port going from the bowl to the jet. Quote Link to comment Share on other sites More sharing options...
at-jefft Posted May 31, 2011 Author Share Posted May 31, 2011 (edited) I'll definitely check out the fuel lines. The dizzy advance is working. The SU's have a brass filter at the fuel inlet. The SU's were rebuit using a ZTherapy kit last summer. So the fuel bowl to carb body lines are clear and I checked the needle valves, they are good. Edited May 31, 2011 by at-jefft Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 10, 2011 Author Share Posted June 10, 2011 (edited) Blew compressed air through the fuel lines. No change in fuel pressure. The coil will arc about an inch. Sprayed carb cleaner everywhere couldn't find any vacuum leaks though. Noticed one of the jets was sticking down when the choke was disengaged. Edited June 11, 2011 by at-jefft Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 11, 2011 Author Share Posted June 11, 2011 (edited) Update: Went for a drive with the fuel pressure gauge on. The gauge is for a FI car so its hard to tell how many psi I'm getting. But the Car accelerates nicely after its been idling and the fuel pressure gauge is showing around 3psi. When I hit about 4k rpm the car hits a wall; The fuel pressure gauge shows 0. I have to let the car idle before it will accelerate again. CLIF NOTES: Nearly positive, carbs are running out of fuel. I'm going to try and run some solid wire through the fuel lines tomorrow, and see if crap comes out. My electric fuel pump is not working and I have taken it out. I don't think it was working before though. Edited June 11, 2011 by at-jefft Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 12, 2011 Author Share Posted June 12, 2011 Can someone confirm that they are running Su carbs on just the mechanical pump? I've heard people running triples on just the mechanical pump and the electric was just for vapor lock. Today I put a bottle of fuel in the engine bay and ran the car off that from just the mechanical pump. No change in fuel pressure. I think I can eliminate clogged fuel lines. Really could use some other ideas here. The Mechanical pump was replaced by the PO and is pretty new. How can I test to see if it is bad? Quote Link to comment Share on other sites More sharing options...
morbias Posted June 12, 2011 Share Posted June 12, 2011 (edited) I have 2" SU carbs and only the stock mechanical fuel pump and it most definitely pushes enough fuel. In fact the first time I started it up there was fuel gushing absolutely everywhere as one of the fuel lines wasn't clamped properly to the float bowl. Do you get any backfiring out of the carbs? Edited June 12, 2011 by morbias Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 13, 2011 Author Share Posted June 13, 2011 (edited) I have 2" SU carbs and only the stock mechanical fuel pump and it most definitely pushes enough fuel. In fact the first time I started it up there was fuel gushing absolutely everywhere as one of the fuel lines wasn't clamped properly to the float bowl. Do you get any backfiring out of the carbs? Actually, they just started backfiring today. I'm pretty sure it is because I adjusted the mixture too lean though. Edited June 13, 2011 by at-jefft Quote Link to comment Share on other sites More sharing options...
XTCoX Posted June 13, 2011 Share Posted June 13, 2011 (edited) I would check the float levels in the carbs. recently I spoke with Bruce over at Z Therapy about a lean surge I was getting through the upper rpm range (A less severe version of this 'wall' maybe). Anyway, I adjusted the float level up, which pepped up the car and allows it to climb higher up without choking. You would probably want to consider replacing the Jets on the inside of the float bowls as well, and check the nozzles to make sure they aren't clogged. Let me guess, when you say it hits the power wall, it's like half the engine shuts off? Edited June 13, 2011 by XTCoX Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 14, 2011 Author Share Posted June 14, 2011 I would check the float levels in the carbs. recently I spoke with Bruce over at Z Therapy about a lean surge I was getting through the upper rpm range (A less severe version of this 'wall' maybe). Anyway, I adjusted the float level up, which pepped up the car and allows it to climb higher up without choking. You would probably want to consider replacing the Jets on the inside of the float bowls as well, and check the nozzles to make sure they aren't clogged. Let me guess, when you say it hits the power wall, it's like half the engine shuts off? I'll check the floats and nozzles. Hard to say on the wall. It just stops accelerating. It decelerates fast enough that the suspension settles back to level. Quote Link to comment Share on other sites More sharing options...
neotech84 Posted June 15, 2011 Share Posted June 15, 2011 I would clean out the pump. Also check to see if spraying starter fluid in the carbs will get you over the wall. This will eliminate the fuel system from your check list. Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 15, 2011 Author Share Posted June 15, 2011 I would clean out the pump. Also check to see if spraying starter fluid in the carbs will get you over the wall. This will eliminate the fuel system from your check list. Sorry for being unclear, but the wall is only under load when I'm drivng. in neutral the engine revs much past 4k rpm. What do you suggest to clean the fuel pump with? Carb Cleaner? Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 15, 2011 Author Share Posted June 15, 2011 I did lean out the fuel mixture too much, the plugs were ghost white. I richened the fuel mixture a bit, but didn't get to drive it since it is raining out. Played with the fuel pump, seems to be putting out plenty of fuel. Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 21, 2011 Author Share Posted June 21, 2011 (edited) I found an intake leak today. Source of the problem? Edited June 21, 2011 by at-jefft Quote Link to comment Share on other sites More sharing options...
rejracer Posted June 21, 2011 Share Posted June 21, 2011 Doubtful as vacuum leaks will be most noticeable at low rpm, much less so at high. Regardless it needs to be fixed. Problem you describe sounds like fuel starvation. Starvation can be in a couple of different things. 1. fuel level in bowl is getting low due to inadequate inlet flow. Check bowl, float, needle and seat, and brass filter at carb (if equipped). 2. fuel system is dirty / clogged not allowing enough flow from bowl to jet orifice. Check flex line from bowl to jet, cleanliness of jet. If you were checking fuel pressure after fuel pump then pre pump filter and pump are fine, problem lies between fuel pressure and jet orifice. Hitting a wall can also happen from jets being to far down like when the choke is on, but that would be noticeable in terms of running rich. Quote Link to comment Share on other sites More sharing options...
neotech84 Posted June 21, 2011 Share Posted June 21, 2011 If it slows that much I would think fixing the intake leak will help. There could be a problem with the advance on your dizzy. Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 24, 2011 Author Share Posted June 24, 2011 I Cleaned nozzles and adjusted the front carb float down 2mm and now everything is good! (did this after finding out that 72 carbs have different float levels for front/rear) Pulls way past 4k now. I still have some backfires through the intake here and there, so I'm gonna richen it up (plugs are very white) and hopefully those will go away. Thanks for your help everyone! Quote Link to comment Share on other sites More sharing options...
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