mx71 Posted October 30, 2017 Report Share Posted October 30, 2017 Ok, got the truck back, brand new (remanufactured) Hitachi carb. I've spent the better part of last week running vacuum lines to what I believe are the correct ports, based on many drawings from the manufacturer (federal HA Z24). The truck runs great and passed emissions with flying colors, but when starting cold, two issues arise (and a third when warm): 1. About half the time, it doesn't maintain idle when starting cold and shuts off (with me not touching the gas pedal whatsoever), so I have to give the gas pedal a few squirts after it dies and restart, then it stays running. Isn't the idle supposed to be high when cold due to the choke? Is my high idle circuit not working? 2. It's a real choppy idle until warm. Is this due to temperature and/or moisture in the carb? Is this normal? The only other time I've owned a carbureted vehicle is an 82 2wd 720 in Southern California, where cold is a foreign word. Here in Idaho, the average temperature in the morning the past week is around 35-40. Is there a vacuum line run wrong somewhere that would cause the choppiness? 3. Backfire. It has a deceleration backfire that almost seems worse than when it had the Motorcraft/Fake Holley/Fake Weber. Vacuum line or tuning issue? The truck does seem to have an exhaust leak either at the collector off the manifold or from an actual hole in the muffler, but the hole in the muffler looks to be by design. The exhaust system seems to have been replaced in the last few years from the manifold back, as there's very little rust on any of it. Quote Link to comment
racerx Posted October 30, 2017 Report Share Posted October 30, 2017 Is your base timing set at right degree? Spray some carb cleaner around carb base, intake and vacuum lines. You may have vacuum leak somewhere. Quote Link to comment
Crashtd420 Posted October 30, 2017 Report Share Posted October 30, 2017 I was also gonna say have you made any adjustments to the carb? Air/fuel Idle speed.... Definately check timing too.... Quote Link to comment
racerx Posted October 30, 2017 Report Share Posted October 30, 2017 Also check your spark plug colors. Quote Link to comment
racerx Posted October 30, 2017 Report Share Posted October 30, 2017 Forgot to mention, if you spray carb cleaner and your rpm goes up, then there's vacuum leak in that area where you sprayed. 1 Quote Link to comment
mx71 Posted October 30, 2017 Author Report Share Posted October 30, 2017 Not sure about the timing. The only thing I've done with the carb since it's been back from the shop is adjust the idle speed, as they had it too high (with my ear, tach doesn't work). I'll try with the carb cleaner this week and report back. Quote Link to comment
racerx Posted October 30, 2017 Report Share Posted October 30, 2017 They should have adjusted it to proper idle setting and drive it around the block to make it ran ok. Any shop should have a tachometer. I would take it back. Quote Link to comment
datzenmike Posted October 30, 2017 Report Share Posted October 30, 2017 Step on the gas two or three time before starting. This sets the choke and the fast idle. Check this next time the engine is cold. Take the top off the air filter and watch the choke close when the gas is stepped on. Engine should rev from 1,800 to 2,200 and will not rev down until warm and you step on the gas to release the fast idle. I'll check when I get home but the ported vacuum source closest the front of the engine on the carb base is the vacuum advance for the distributor. It will also have a tie in to the VVT on the intake and another down at the distributor to the charcoal canister. As long as the hoses are secure it should be ok. Quote Link to comment
DanielC Posted October 30, 2017 Report Share Posted October 30, 2017 You need to do a full tune up on the engine, including adjusting the valves. General tune up sequence, make sure the mechanical is right (compression check, valve adjustment) then do ignition, set timing, check spark plugs, their wires, other secondary ignition parts, cap and rotor, then work on the fuel system (carb). You need a low speed tachometer to set the carb. You also need a vacuum gauge. Do the tune up, and adjust the carb, with the engine warm. Make sure it runs good when warm. When you reach that point, then you can work on cold idle issues. It is normal for a cold carb engine to have a less than ideal idle. We are so used to smooth running cold engines now, because of all the improvements that modern multiport fuel injection engine gives us. Carb engines will not do that. Quote Link to comment
mx71 Posted October 30, 2017 Author Report Share Posted October 30, 2017 All helpful advice. I'll get on all that. Thank you! I also didn't know about having to hit the gas pedal. I thought the choke/high idle at startup was automatic. Quote Link to comment
mx71 Posted October 30, 2017 Author Report Share Posted October 30, 2017 Just tried 3 pumps and it didn't raise the idle, and it died after a few seconds. Did it again with two pumps and it continued running this time, but at normal idle, not high. Quote Link to comment
racerx Posted October 30, 2017 Report Share Posted October 30, 2017 You had a shop install the carb? They should fine tune it for you? The more u mess with it and the more you can fuck it up, the more reasons for them not to touch it. Quote Link to comment
mx71 Posted October 30, 2017 Author Report Share Posted October 30, 2017 They installed it and did the emissions retest, but they didn't run any vacuum lines. The only thing I messed with on the carb itself was the idle. Quote Link to comment
racerx Posted October 30, 2017 Report Share Posted October 30, 2017 That don't make sense. You paid them to install a carb and they don't hook up the vacuum lines. Or see where it idled at? Takes like 2 min. To hook up tachmeter and read rpm of said truck. Its like me taking my car to a mechanic to install a radiator and they put the thermostat or hoses back and test drive it to make there are no leaks or does not overheat. Quote Link to comment
datzenmike Posted October 30, 2017 Report Share Posted October 30, 2017 If you are under 30 you were born after carbs became obsolete. If 50 you probably were taught some carburetor theory in auto shop in school. You didn't pull the top off the air filter and look??? Should look like this COLD... By cold I mean overnight or after work. Step on gas, should look like this... Yes or no??? Quote Link to comment
mx71 Posted October 30, 2017 Author Report Share Posted October 30, 2017 I'll check in the morning. I haven't had the time today. I'm 33. Very familiar with motorcycle carbs, but they're much simpler and rarely electronic until lately. Quote Link to comment
datzenmike Posted October 31, 2017 Report Share Posted October 31, 2017 Does your air filter have two or one wing nut holding it on? Only carbs had the one wing nut. The two wingnut air filter is for the EFI on the Z24i after April '85. At the right rear there is an electrical plug. Do you have 6 wires or 2????? Six wire is an ECC (electronically controlled carb) and there will be an O2 sensor in the exhaust manifold. Two wire is a conventional carb Quote Link to comment
mx71 Posted October 31, 2017 Author Report Share Posted October 31, 2017 It's not the proper air filter housing being that I had to scrounge a housing on eBay. It's the one with the two emissions holes in the front, and my intake manifold has no inlets for them. It has one nut and four clips. It's a 6 pin plug with an O2 sensor. Quote Link to comment
mx71 Posted October 31, 2017 Author Report Share Posted October 31, 2017 Cold (not running) Full throttle (not running) Cold (running) Some throttle (running) The choke didn't open all the way, yet I have seen it open when it's either warmer outside or the truck is warm. Quote Link to comment
datzenmike Posted October 31, 2017 Report Share Posted October 31, 2017 Just to be clear the plug on the carb and the harness are 6 pin and it's connected? I'll get you the plug wiring. Looks ok, but the choke should have power to the choke heater that warms it up and opens it. Looks like the fast idle is not working also. ECC carbs have their own problems. Quote Link to comment
mx71 Posted October 31, 2017 Author Report Share Posted October 31, 2017 6 pin and connected, yes. I believe the fast idle is the problem, as the truck will start the second time after it shuts off and maintain normal idle. Quote Link to comment
mx71 Posted October 31, 2017 Author Report Share Posted October 31, 2017 In this thread here, mine is similar. The bent arm is not connected to anything on my new carb. http://720world.com/forum/topics/85-idle-problems Quote Link to comment
mx71 Posted October 31, 2017 Author Report Share Posted October 31, 2017 You know what, I think the shop didn't adjust the fast idle cam. I think they just slapped the carb on and set the idle then sent it out the door. The adjustment screw was a little loose, and after making contact it seems to be working now. Quote Link to comment
racerx Posted October 31, 2017 Report Share Posted October 31, 2017 /\...yep..read what I wrote. Quote Link to comment
mx71 Posted October 31, 2017 Author Report Share Posted October 31, 2017 /\...yep..read what I wrote. I did. You had mentioned that they should have set the idle, which they did, but they appear to not have set the fast idle. Quote Link to comment
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