Corradokid90 Posted August 30, 2015 Report Share Posted August 30, 2015 So I picked up a 1981 Datsun 720 with a z22 engine recently. It starts and idles perfectly fine but won't accelerate without bogging out. I pulled the carb and rebuilt it with the help of a few diy's (I've never worked on a carbureted vehicle). Got it all back together and replaced all the vacuum lines. I'm still having the same issue. I'm noticing if it's idling and I pull the throttle, the secondary isn't opening. If I do it manually with a screw driver or sonething to push it open, it revs perfectly. From what I gathered by pulling this thing apart, the secondary is operated by vacuum from the secondary diaphragm. I had also pulled that apart to check for tears or leaks but it looks fine. And pushing the rod in, it pumps air out the small hole. ANY ideas on what my next step is would be very helpful and appreciated. This is fairly new to me haha Quote Link to comment
banzai510(hainz) Posted August 30, 2015 Report Share Posted August 30, 2015 rev the motor up and then put your hand on the one the main side of the carb that is manually opertated . When you put your hand on the main side the 2nd side should open up cause of the vacuum. this is normal operation does the carb pump gas when you cycle the linkage? That's from the accel pump. Datzenmike will get this figure out time the motor. 2 Quote Link to comment
datzenmike Posted August 30, 2015 Report Share Posted August 30, 2015 The secondary you will never see open because you have to drive it under load. It's also go a linkage inter lock to prevent premature opening before about 2/3 throttle. Demand for more fuel and air is what pulls the secondary open. Bogging briefly after turning a corner in too high a gear is likely the accelerator pump, but you rebuilt this, so unlikely or was assembled incorrectly. As Hainz said look down the carb with engine off, and work the throttle. You should see a strong squirt of fuel into the primary side. Bogging under constant load is likely a plugged or partly plugged primary jet. These jets are interchangeable. Could you have the secondary in the primary side? Primary jets are around 100, secondary are around 160. Quote Link to comment
Corradokid90 Posted August 31, 2015 Author Report Share Posted August 31, 2015 Well it's not bogging when I go around corners, I can't even drive it ha. It's bogging when I hit the accelerator at idle. I'll give it another look after work. Any tips on cleaning the jets properly/effectively? Quote Link to comment
datzenmike Posted August 31, 2015 Report Share Posted August 31, 2015 Lets wait and see what you find after work. The blocked jet means the carb should come off to get at them. Much better to try easier things first. Is the valve lash set? Loose isn't a problem other than noise but tight can disrupt the intake vacuum. You want good strong intake vacuum at idle and low speed. Is the timing set? Around 5 degrees BTDC on the Z22. Retarded or too advanced will loose power. Inspect vacuum lines are correctly placed. There should be an emissions diagram on the under side of the hood. 1 Quote Link to comment
Corradokid90 Posted August 31, 2015 Author Report Share Posted August 31, 2015 Far as I know the lines were all put back in the right place. Labeled them and replaced them one at a time. Checked the manual I have to be sure, and everything looks good. Feels as tho the timing is set fine but I don't have a timing light. Idles fine, which is why I'm leaning away from a clogged jet. Does that sound out of the question? Ha. And I'm not sure what the valve lash is.. Btw thank you much for your replies! 1 Quote Link to comment
Corradokid90 Posted August 31, 2015 Author Report Share Posted August 31, 2015 Well it's got plenty of fuel shooting from the primary. Think maybe too much? Air/fuel mixture maybe off? Quote Link to comment
Corradokid90 Posted September 5, 2015 Author Report Share Posted September 5, 2015 Anybody? Quote Link to comment
datzenmike Posted September 5, 2015 Report Share Posted September 5, 2015 Far as I know the lines were all put back in the right place. Labeled them and replaced them one at a time. Checked the manual I have to be sure, and everything looks good. Feels as tho the timing is set fine but I don't have a timing light. Idles fine, which is why I'm leaning away from a clogged jet. Does that sound out of the question? Ha. And I'm not sure what the valve lash is.. Btw thank you much for your replies! The idle circuit is on it's own supply of gas. The primary jet can be completely plugged and it will idle just fine. Valve lash is a clearance measured between the rocker arm and the top of the valve. This clearance has to be large enough that the valve can close but not so large that they are noisy in operation. I think the Z series is 0.013". Too tight and the valve may not close tightly and intake vacuum is affected or compression lost. Valves are cooled during the time they are closed a tight valve lash can overheat a valve and burn it. 1 Quote Link to comment
Corradokid90 Posted September 7, 2015 Author Report Share Posted September 7, 2015 The idle circuit is on it's own supply of gas. The primary jet can be completely plugged and it will idle just fine. Valve lash is a clearance measured between the rocker arm and the top of the valve. This clearance has to be large enough that the valve can close but not so large that they are noisy in operation. I think the Z series is 0.013". Too tight and the valve may not close tightly and intake vacuum is affected or compression lost. Valves are cooled during the time they are closed a tight valve lash can overheat a valve and burn it. I'll get into it to check the valve lash. I'm gonna pull the carb back off too and I guess clean it again. It almost looks like it may be getting too much fuel. It's spraying pretty heavy out of the primary. Pulled two plugs, they were both pretty black. And they're new plugs Quote Link to comment
that-son Posted September 9, 2015 Report Share Posted September 9, 2015 have you checked the timing, idle speed and air fuel mixture? go ahead and spray some carb cleaner in there and lubricate all the linkages but check those three things first. also, my idle speed got wonky when my alternator was going bad. so check that too... Quote Link to comment
datzenmike Posted September 9, 2015 Report Share Posted September 9, 2015 I'll get into it to check the valve lash. I'm gonna pull the carb back off too and I guess clean it again. It almost looks like it may be getting too much fuel. It's spraying pretty heavy out of the primary. Pulled two plugs, they were both pretty black. And they're new plugs It shouldn't be spraying out of the primary. If you are looking into the carb with the engine off and pump the gas there will be a squirt of fuel into the primary from the accelerator pump... this is normal. At idle there shouldn't be any 'spray out of the primary'. 2 Quote Link to comment
that-son Posted September 10, 2015 Report Share Posted September 10, 2015 also, as mentioned double check vac lines. and... check all plug wires. make sure plugs are firing in the right order. Quote Link to comment
Corradokid90 Posted September 17, 2015 Author Report Share Posted September 17, 2015 It shouldn't be spraying out of the primary. If you are looking into the carb with the engine off and pump the gas there will be a squirt of fuel into the primary from the accelerator pump... this is normal. At idle there shouldn't be any 'spray out of the primary'. By spraying out of the primary I meant when I pull the throttle. It seems plenty healthy, almost like too much. Idles just about, if not perfect. Just acceleration is the issue. As soon as I get time to work on it again I'll be checking the timing etc. Quote Link to comment
banzai510(hainz) Posted September 17, 2015 Report Share Posted September 17, 2015 do the simple things first like time and adjust the carb Not pull of carb first 1 Quote Link to comment
DatzLOWsun Posted September 25, 2015 Report Share Posted September 25, 2015 This sounds a lot like the problems I'm having with my 1982 b310 a15 5spd it idles fine a little high but idles smooth but bogs down hard when accelerating and isn't drivable you have any luck with yours? I'm thinking of trying to check timing but I'm not sure about this stuff Does yours bogg worse under load? That's how mine is and now it dies anytime I stop when trying to drive it Quote Link to comment
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