high idle and no power up top

[]2eDeYe]

Have you done a compression test?

 

Also, from experience, I can tell you that without a tach, what you think the rpm's are and what they really are are 2 different things. After I installed my tach I was amazed at the difference ;)

[datzenmike]

That cam sprocket looks like it comes from a Z motor. All L series I've seen have 4 holes... all Z series have eight. If it's a Z the cam timing may be different????

 

L series Z series KA24E cam sprockets. (cam side)

 

http://i138.photobucket.com/albums/q251/datzenmike/IMG_0431.jpg[/img]"]

[yello620]

I recently had a problem very similar to this on my cousins truck with a stock hitachi. 1980 L20b. Ran smooth on the bottom end, but not a lot of power. Then about 3500rpm's it just ran out of steam. Found that the secondary vaccumn butterfly was rusted shut. Truck had sat for a little while. Stuck a slim screwdriver down the barrel to free it up and the truck ran great for a few weeks. now the problem is back-time to pull the carb and properly clean the rust and adjust the butterfly if it needs it.

 

Jason

[77Datsun620]

thanks all for the help, i know its hard to do over the internet, ok responses in order.

#1 Hainz, the "problem" is/was(i havent driven it for a few days now) i was in 4th gear(my trans is a 5 speed) it just seemed to me that it was having a hard time keeping 60 mph.

 

#2 ]2eDeYe, yeah i need to get a tach :D (im thinking im off on my RPM instinct)

 

#3 Datzenmike, well this motor was "rebuilt" in a good ole boi's garage from what i was told, so it wouldnt suprise me if it is off of a Z motor.

 

Ok, but from looking at all the great pics & advice you all have givin me in the last few days has been really helpful. a big thumb's up from me :thumbsup: every thing looks to be in the right spots, as far as cam lobes at 10 and 2, dizzy is free no sticking, full tuneup in the last few days. I'm beginning to think that im just really not use to having a NA 4 cyl, and this is the first vehicle that i have owned in a looooong time that hasnt had a tach. So i think i'll get it all buttoned up (i painted the vavle cover Red wrinkle) ;) and get a tach for it, so i know for sure what kinda RPM's im actually turning.

 

Thanks for putting up with me, if you all were closer i would buy beer for all.

[banzai510(hainz)]

I have seen cam sprockets with the multiple inspection holes so dont panic. Your propably fine.

I think its more carb related.

 

One more thing I thought of when driving home last night. If you have a eleltric choke make sure the butterfly is fully open when its warmed up It could be killing your top end. Maybe the plate is Half open?????

 

On the carb will be a round thing. It has a coil in there and when it heats up will open the choke plate up. Make sure the 12volt wire is hooked up to it.

also ck the seconadry butterfly as 2 of us have mentioned already/ maybe its stuck.

 

I seen 2 people at Rays BBQ bragging they gonna do this and that(KA/VG install) and I seen 2 Weber DGVs with electric choke and the 12v wire not hooked up and they saying I dont have top end. Well I just turned the coil so where they would just stay open(the choke plate) since it was a earlier car with no 12volt wire.

 

Both cars ran better!!!!!!!!!!

[77Datsun620]

yeah, im starting to think its the carb also, it has been rebuilt( i dont know when though) it has an electric choke, but the wire isnt hooked up, where should it hook too? i guess i could prop the butterfly open and see if that makes a difference.

[banzai510(hainz)]

I assume it has a electric choke carb on there!

where that round thing on the carb is the coil. the should be a little metal tab or a wire comming from the carb that goes to it.

 

more or less warm the truck up

 

look and see if the big choke plate is not opening up,thats it

 

let us know.

 

this will ytake about 15min to figure out.

 

I dont have a photo of a stock Hitachi carb but here is a weber DGV with electric choke

A) is the coil see how the plate is covering the ports as it warm it will open up all the way

[Guest DatsuNoob]

Let it run for a while and fully warm up, then loosen the 3 screws that clamp the choke, and turn the choke body until you see both the primary and secondary are open. That's where it should be after the truck's fully warmed up. Very important, make sure those screws are VERY secure. I went for a trip down the freeway and got a little under 20 miles from my house, then blew the entire choke mechanism out of the carb with a very loud bang. Nothing was damaged, but it costed me $150 to get home. I went to the hardware store the next day and bought some longer bolts for it and some lock washers for a little less than $2.00. Still dont like to think that may have saved me $150, but I dont like how short the stock ones are, and there's plenty of room for more threads. Always good to take things from other's misfortunes :D

[datsunaholic]

Almost all the aftermarket cam sprockets are 8-hole, so that isn't an issue. Stock ones were 4-hole. I have plenty of L20Bs with 8-hole cam sprockets.

[77Datsun620]

ok after further examination i think i have found the culprit, the second butterfly doesnt open. the choke plate and everything in the carb is free and working, the second barrel opens if I move by hand. I need a pic of the throttle cable side of the carb if anybody has one. from what i could see (im taking the carb off tomorrow) there is a "peg" that comes out of the backside, it is attached to the second butterfly, when i push it down it opens the butterfly. there is a lever right below it, and it moves down with the throttle cable, im thinking that the lever needs to be on top of the peg instead of below it or is there supposed to be some sort of connected piece between the 2? but a pic of a stock hitachi would be fine also. so i have a reference to go by.

and also the second barrel looks brand new, like it has never been working.

[Guest DatsuNoob]

Did you take the choke body off and see if the "snail spring" end is wound around the fork of the secondary's little spindle? What about adjusting it? Real easy to do just turn it until it's open after warm up.

[datzenmike]

The lever on the primary is in the proper position, and helps to close the secondary and keep closed at idle. The secondary is only able to open when the primary is 50% or more open and is opened by a vacuum diaphragm and lever. The secondary barrel will look cleaner because it has no choke butterfly and gets less use. It's possible that the secondary jet is dirty too.

 

BTW: I got both those cam sprockets out to-day and all the holes line up as well as the teeth. A 4 degree difference on a 4" circle is about 0.14" which would be noticeable. I believe the L and Z sprockets are virtually the same.

[77Datsun620]

ok, so the round piece is a vacuum diaphram, so why would it not open at all under throttle, but it opens and sounds 100 times better if i open the secondary by hand. would the diaphram have a rip in it? and the only vacuum line on the back of the carb goes right back to the carb, should it go else were?

[datzenmike]

The diaphragm may have a hole in it or the gasket between it and the main body of the carb might be leaking. Unlikely, but if you can get it apart you could check.

[77Datsun620]

so besides the diaphram,a gasket leak and a build up of junk in the carb, is there any other reason the second butterfly wont open? My carb is really clean and nothing sticks.

[Guest DatsuNoob]

pics?

[650savag]

I will try to post some pics here.

 

Top view;

 

 

diagnal view showing throttle and secondary linkage and anti-dieseling apparatus;

 

 

bottom view;

 

 

fender side view;

 

 

front;

 

engine side;

 

 

and the last one is the rear view.

 

 

This is several viewsof my stock Hitachi that I pulled off this afternoon to do a exhaust/intake gasket change. Hope these help. The wire with the blue, round connector attaches to the auto choke and the one with the flat, red connector goes to the anti-dieseling switch. These will connect to the blue and red wires that are in a group of 4 wires that come out of the wiring harness that runs near the radiator, above the drivers side headlights. Dan

[]2eDeYe]

Did you take the choke body off and see if the "snail spring" end is wound around the fork of the secondary's little spindle? What about adjusting it? Real easy to do just turn it until it's open after warm up.

 

You should never adjust a properly operating choke when the motor is warm. There should be about a 1/4" gap between the choke plate and the carb housing when the motor is cold.

 

If you adjust it when it is warm the 'spring' (it's more of a heat coil) is fully relaxed and the rate is much different than when it's cold.

Basically you want to set it for when it needs to choke the carb, which is when the engine is cold.

[77Datsun620]

not atm i can post some tomorrow, the carb seems alright (sans the second butterfly opening on its own), primary jet pumps good, inside the carb and both butterflys are really clean, it doesnt leak gas anywhere, and i have fixed all the vacuum lines on the motor, i can get a rebuild kit, a good family friend will rebuild it for me, just checking to see what else, if anything, would cause the second butterfly to not open. If i have the truck running and and give it gas, and manually move the vertical lever in the back for the SB, the motor comes alive like it should.

[650savag]

The seven pics of the Hitachi were labeled with titles but the title did not show so I will label them here from top to bottom: Top view; diagnal view showing throttle and secondary linkage and anti-dieseling apparatus; bottom view; fender side view; front; engine side; and the last one is the rear view. Hope this helps. Dan

[77Datsun620]

ok just to clarify, its not the choke it works fine, i was just wondering where the wire goes if i wanted to hook it up. my carb issue is the second butterfly not opening. thanks for the pics above, it matches my carb to a T, so i know mine is right.

[]2eDeYe]

 

Thanks for the pics savage...

 

Follow the speedo cable into the cam that turns the linkage. If you follow the linkage, you can see how the secondary is actuated.

 

Check your carb in this area. The tab might be bent or something or the pin missing.

[]2eDeYe]

620savage: Is the carb still off of the truck? If so, can you take a few pic's with the throttle wide open?

[77Datsun620]

Redeye my carb is the same as the pics that savage posted, if i move the lever coming outta the diaphram manually the butterfly opens with ease, and all the linkage looks good and all moves as it should, it just doesnt open on its own, I'm thinking its the diaphram, must have a pinhole, the truck was sitting for a while before i bought it.And we have had diaphrams go bad from non use before also, just never a datsun

[650savag]

I'll post some more pics tommorow with the throttle opened and try to show the linkage better. The blue wire with the round connector comes out the back side of the bi-metal auto choke mechanism and the red wire with the flat connector (see pics) comes out of the back of the anti-dieseling solenoid. Both of these wires run around to the front of the carb and should plug into two mating wires from a harness under your hood. On mine, the two mating wires (blue and red) come out of a harness just to the right of the top of the radiator and above the headlights on the driver's side. They come out of the harness with two other wires that aren't plugged up to anything. See if you can locate a group of four wires in this vicenity and see if one is blue with a round, female connector and another one should be red with a flat female connector. The connectors will be covered with insulation so it's hard to tell the shape of the female connectors but you should be able to plug the wires from your carb into them.