Janksun Posted February 7, 2016 Report Share Posted February 7, 2016 I'm having trouble with the carb on a 79 620 with the stock carb. The secondary isn't opening when I give it throttle and as a result the engine bogs and doesn't want to rev up. I have been told it's vacuum activated but I can't seem to find the problem. I cannot convert to a Weber due to having to smog the truck so that option is out. Any help would be appreciated. Quote Link to comment
datzenmike Posted February 7, 2016 Report Share Posted February 7, 2016 The secondary can only open when two things happen. It certainly has to rev up and the throttle be1/2 or 3/4s open to release an interlock and there has to be sufficient vacuum produced to work the vacuum secondary. If the primary jet is part blocked or you have an ignition problem the engine would be weak and it might not open. Generally if the secondary does not open, not much happens it just lacks power but will rev up. slower if under load. What exactly does it do when it 'bogs'? and at what speed does it 'bog'? 1 Quote Link to comment
Janksun Posted February 7, 2016 Author Report Share Posted February 7, 2016 Haven't been able to drive it really 1 Quote Link to comment
datzenmike Posted February 7, 2016 Report Share Posted February 7, 2016 Don't think you are pulling the throttle far enough open or you aren't waiting long enough. It takes a few seconds to spin up the weight of the flywheel, tranny gears, crank and rods. You won't hurt it. Quote Link to comment
G-Duax Posted February 8, 2016 Report Share Posted February 8, 2016 And you almost must be under load, as holding the throttle wide open without a load, you can easily go beyond a safe rpm before they open. I had an old Toyota Corona that I would never see the secondary open just by free reving it. So I drilled out the jet size in the vacuum circuit going to the vacuum pod. They opened then ! First time I got on the throttle part way through a turn, like I used to do before the mod, I spun the car. Made a heck of a difference in mid range power. Quote Link to comment
Janksun Posted February 8, 2016 Author Report Share Posted February 8, 2016 Ok so if the secondary not opening isn't really doing anything until half or 3/4 throttle, why is the motor bogging when I just give it gas. It should rev up and not stumble on its face Quote Link to comment
datzenmike Posted February 8, 2016 Report Share Posted February 8, 2016 Engine off, look down the primary side and work the throttle. What you should see is a strong squirt of gas from the accelerator pump. The extra gas helps richen the otherwise lean spot when the throttle is suddenly opened. Oh, you're in California. Quote Link to comment
Janksun Posted February 8, 2016 Author Report Share Posted February 8, 2016 So if I don't see that then the accelerator pump is bad? Quote Link to comment
datzenmike Posted February 8, 2016 Report Share Posted February 8, 2016 Well not working at least. Idle has it's own gas supply, it's very small but adjustable. When idling and you suddenly open the throttle the engine isn't moving enough air in the primary barrel, it can't suck more gas it and it suddenly goes lean (too much air too little gas) and it will struggle. The idle circuit cannot supply this. The answer is a mechanical pump like a Windex sprayer to fill in the gap between idle and primary running. Quote Link to comment
datsunaholic Posted February 8, 2016 Report Share Posted February 8, 2016 As said above, it's almost impossible to get the secondary open unless it's on the road (under load). If it bogs at heavy throttle that's usually a plugged jet, not a secondary not opening. The secondary gets used so little that the secondary main jet is prone to collecting a lot of crud. Quote Link to comment
G-Duax Posted February 8, 2016 Report Share Posted February 8, 2016 Also look at how worn the accelerator pump linkage is. After a while the parts wear out, and you don't get full travel on the pump stem. It can be tweeked to gain some of it back. Just watch the pump rod to see how far you have to move the throttle before the linkage actually pushes the pump rod. And there are two holes in the rocker arm that pushes the pump rod, the one nearest the piviot point gives the most fuel. Quote Link to comment
banzai510(hainz) Posted February 8, 2016 Report Share Posted February 8, 2016 to me this has nothing to do with the 2ndarys. I think the accell pump is weak or not working. Should be more responsive. You can the 2nday to open rev the motor then put your hand on the main barrel of carb and then the 2ndary will open monentarily Quote Link to comment
Janksun Posted February 9, 2016 Author Report Share Posted February 9, 2016 Ok so the secondary opens. Cool. Can I get an accelerator pump somewhere or are they obsolete or what? Quote Link to comment
kelowg Posted February 9, 2016 Report Share Posted February 9, 2016 Rebuild kit,should come with new one Quote Link to comment
datzenmike Posted February 9, 2016 Report Share Posted February 9, 2016 Try Nissan... # 16151-N0919 it's for an L20B but they use the same 340 carb. Quote Link to comment
Janksun Posted February 10, 2016 Author Report Share Posted February 10, 2016 Had a hard time finding anything available with that part number. What about 16151-U6800? http://m.ebay.com/itm/New-Genuine-Nissan-16151-U6800-Piston-/181324169623 Or it looks like it's in the rebuild kit from rockauto like kelowg said http://www.rockauto.com/catalog/moreinfo.php?pk=987559&cc=1210150&jnid=426&jpid=0 Quote Link to comment
SPIDERSHACKOV Posted February 15, 2016 Report Share Posted February 15, 2016 Are you pushing on the accelerator pump to rev engine in the videos? Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.