Fisch's '71 510 LZ22 - "Chapman" Fogs and Bre Spook+art

[fisch]

So after the car sat for a while, I went back out and fired it up. Once it warmed up it idled great at about 800-900. So I then revved the motor a bunch, and sure enough, when it dropped back into idle it just about died. I could only keep it alive by giving it gas. Remember I am like a noob under the hood.  The fuel filter doesn't look that bad, but I suspect it because it is almost like when I rev the motor under hi rpm it increases suction, maybe sediment collects at the filter, and when it drops to idle again, it is still there cause there is enough fuel pressure to hold it. But when I shut down the engine and it sits, the sediment falls down off the element so when I start it next time it is fine, until I increase the pressure by reving the engine. And the car sat for almost a year before getting it going a few weeks back. Or maybe I am just hoping it is the easiest solution!

 

As long as I've been around Datsuns, I feel like a babe under the hood. Especially with spooky SU carbs. I have the Z Therapy vid. Might be time to watch it again.

 

But in the meantime, I also checked my plugs, as I was worried it was running lean. Nope. More like carbon fowled. Not oily like it was rich. More like fine carbon dust. Could it be related to the idle conditions?

[datsunfreak]

Course the problem with Draglites is the wheels studs on the Datsun are way too short. So longer wheelstuds have to be put in.

 

Are you sure you have the right lug nuts? They should use a "mag style" lug nut so stock studs shouldn't be an issue?

 

 

[datsunfreak]

But in the meantime, I also checked my plugs, as I was worried it was running lean. Nope. More like carbon fowled. Not oily like it was rich. More like fine carbon dust. Could it be related to the idle conditions?

 

Black soot on the plugs is an indication it's too rich. That will cause it to idle like crap. 

[Jester]

 I have the Z Therapy vid. Might be time to watch it again.

 

 

Sounds like a good plan. Is there anyone around you that can take a look at it WITH you that understands SU's? 

[Charlie69]

Quit driving it like an old woman!

 

 

[fisch]

Sounds like a good plan. Is there anyone around you that can take a look at it WITH you that understands SU's?

 

Alas all of my local friends are artists, and they think I am the car expert. Scary. I have a import garage I take Chapman too here and there. I think they know SUs. But I'd love to figure it out.

 

Honestly I drive this car locally and for such short distances, I've really done little to it in all the time I've owned it. I've only checked the oil dampner level once in thee years. But I doubt I've put 500 miles on it in 3 years. It has been trouble free.

[fisch]

Quit driving it like an old woman!

 

 

LMAO you are right. I read that this was symptomatic of driving slow in town traffic. I got on it a bit today though. Bad ass car- When it is moving.

[datsunfreak]

I doubt I've put 500 miles on it in 3 years

 

This is the worst possible thing you can do to it. You will chase a lot of carb/ignition problems until you fix this problem first.  B)

[mklotz70]

Scott.....I know you know Dave(futofab) ....he has longer studs and spacers that should work on the 510.

 

I'm not an SU guy, but I had a friend that was into them, many, many years ago....like when I was 20....anyway......aside from the level of the oil, the viscosity of the oil matters too.  You may want to replace the oil in the SU's just to make sure that you've got the correct oil in there.  The oil determines how the pistons move up and down with the air flow.  The piston controls the needle that changes the fuel flow.  Do you have the smaller SUs or the bigger ones?  If it's the bigger ones, you made need to have the needles changed since it's too much carb for the engine and would be running rich.  It's been a long time since I've even thought about SU's, so I may be completely wrong, but this is what came to mind.

[fisch]

Thanks for the replies folks. Mike I have the bigger 46mm carbs, but Chris (the PO) spent a bunch of time custom profiling the needles so I don't think it is that.

 

I gave myself an education till about 2AM last night, LOL.

 

My lead suspect is a vacuum leak somewhere. I am hoping it isn't from the throttle shaft, but these are Z-Therapy ball bearing shafts. So at least that should be remedied. I read that I can spray carb cleaner on parts and if it boggs, I found my leak. I also read that you can use starter fluid and if it revs, I found the leak, but spraying starter fluid in a hot engine bay?

 

Next I suspect the dampner oil level. It has mobile 1 10w30 in the pot I believe. I've read a bunch of opinions about what to put in there. I have marvel mystery oil on hand so I may try that. Taking the dash pot off and wiping down the piston and dome might be a good idea too.

 

But mostly, I learned what I did wrong... which is I did not adjust the idle screws. I adjusted the throttle screws. Which I swear made it run a little better. (I am hoping I didn't mess them up but it was a slight turn.) I guess the real idle adjustment is a nut-like thing down underneath the carbs. Time to purchase a flow meter thingy. From what I've read this style is the one to get.

People also seem to like these Gunson colortune spark plugs. Which if nothing else, it would be cool to look inside the combustion chamber! I guess depending on the color of the explosion, you know if you are rich or lean.

 

And one more thing, Chapman has this cool Wastach dual EGT gauge installed. Ultralight pilots use it. But basically you attach one thermocoupler into each side of the exhaust and it measures the Exhaust Gas Temperature. So I suppose if one is hotter than the other, you know things aren't even and if one side is rich or lean? However the thermocouplers are fried... so right now it is just a cool looking piece of hardware.

[fisch]

Are you sure you have the right lug nuts? They should use a "mag style" lug nut so stock studs shouldn't be an issue?

 

 

I have two sets of these long nuts on the rear and they will attach the wheel. (Fronts are mag shanks and fit but barely reach the stud. But the studs, especially on the front, protrude so little into the shank hole on the wheel, I didn't know if it were enough. I read that in general the studs should come almost all the way out of the wheel. But they are really long nuts, so maybe it would be enough to compensate. I wonder if there is a general rule about ho many turns a lugnut should thread to be safe, lol. Regardless I need to order two sets for the front.

[Charlie69]

Fisch I ran SUs on my Harleys years ago and had thew same problem with in town riding.  I would get on the freeway and blow it out (run them real hard.  By changing my rpm shift points in town to a few hundred more rpm helped.

 

Not driving it is the worst thing you can do to a car.

[fisch]

Fisch I ran SUs on my Harleys years ago and had thew same problem with in town riding.  I would get on the freeway and blow it out (run them real hard.  By changing my rpm shift points in town to a few hundred more rpm helped.

 

Not driving it is the worst thing you can do to a car.

Thanks Charlie. Not driving it is the worst thing, i know. Trying to make up for it now. For a long time I had the little '89 suzuki GTi swift which was a killer little hot hatch, my daily, and easy with FI, so I would just hop into that and not drive the Datsuns. (But wish I were driving the Datsuns, but you know, they all needed something. Wouldn't pass MA inspection.) Path of least resistance. Best thing I did for my Datsuns is sell the Swift last year. Cause now I have no choice if I want to drive something cool.

 

Here though, it seems to be winter half the year, and I can't do new England salt to Chapman. Plus working from home, I basically never have to leave the house, and if I do it is often with my ladies in the Murano for a fam thing. It actually would do me good to get out more. I can be a bit of a hermit down in the studio making art. My record is not leaving the house for 22 days, lol. And I didn't even realize I'd done it.

 

Figures now that I am itching to drive Chapman more, he is running a bit rough, LOL.

 

But this is why I sold the Swift. So I would HAVE to deal with these things. Got tired of the guilt of them sitting and not being drivin. To me, Chris, the guy who put this together, was a wizard, cause it is all a mystery to me under the hood. But I need to learn it. Cause once I know the car inside and out, bumps in the night wont worry me and i will fix it and drive it. At least that is the plan till the snow flies.

[Charlie69]

So true Scott and I am impressed that you want to understand and get to know your Datsuns.

 

It saddens me that you know how many days you have not left your house.  You need to get out and see some of this great country we live in!  Take your ladies and go.  Schedule your self some time off and go!  GET OUT OF THE STUDIO!  LOL

[mklotz70]

I wouldn't use starting fluid.  Aside from the danger, if even the mist from it goes into the throttle bore.....it will raise the rpms so it's a bit harder to isolate problems close to the carb. 

 

This may help with your lugnut question.

http://community.ratsun.net/topic/6342-lug-nut-engagement/

[fisch]

I wouldn't use starting fluid.  Aside from the danger, if even the mist from it goes into the throttle bore.....it will raise the rpms so it's a bit harder to isolate problems close to the carb. 

 

This may help with your lugnut question.

http://community.ratsun.net/topic/6342-lug-nut-engagement/

Well ask and yee shall receive Mike, THanks! And I think I need longer studs based on this. But I will double check.

[fisch]

Well did some exploring while awaiting my Uni-sync. First thing I found that was interesting is that the idle nuts at the bottom of carbs were not adjusted evenly. the front one was almost all the way up when is should be somewhere around two turns down.

 

But worse than that, with the filter off, the front carb belched fuel out of the overflow tube when I accelerated. This shouldn't happen, and as I understand it, it means one of three things. Either my gas float has a crack and fuel is seeping into it, sinking it. Or the float needle valve (that shuts the gas off when the float rises) is malfunctioning. Or my fuelpump is sucking in air.

 

There was evidence of fuel being duped into the filter housing from the over flow hose.

 

So if the front carb is duping tons of fuel into the system on the front carb, might that explain my ilde woes? Like it is choking it out at idle, but with teh RPMs up it can handle all that fuel better, thus isn't as big a problem when flying down the road.

 

Also when I revved the engine, I noticed both pistons did not rise at the same time. The back one rose a split second before the front. I should think they would rise at the same time?

 

Anyway I fear engine fire, so I need to figure this out and it looks like taking apart the fuel bowl is in order. THough someone said if I lightly tap the top of the float chamber with a hammer or screwdriver, it may unstick the needle if that is the problem.

[Laecaon]

They do not pull the wheel in, or at least not as much. I helped install maxima struts on Rustina's wagon. But Im pretty sure the strut tube diameter is still 2" so anything that works on a 510 or ZX strut should work on the maxima strut as far as springs and strut inserts go.

 

 

Also the brake caliper is different than the ZX so who knows on the 13" wheel. Mike might know, he has maxima struts on the 710 wagon I believe.

[Sealik]

Well did some exploring while awaiting my Uni-sync. First thing I found that was interesting is that the idle nuts at the bottom of carbs were not adjusted evenly. the front one was almost all the way up when is should be somewhere around two turns down.

 

But worse than that, with the filter off, the front carb belched fuel out of the overflow tube when I accelerated. This shouldn't happen, and as I understand it, it means one of three things. Either my gas float has a crack and fuel is seeping into it, sinking it. Or the float needle valve (that shuts the gas off when the float rises) is malfunctioning. Or my fuelpump is sucking in air.

 

There was evidence of fuel being duped into the filter housing from the over flow hose.

 

So if the front carb is duping tons of fuel into the system on the front carb, might that explain my ilde woes? Like it is choking it out at idle, but with teh RPMs up it can handle all that fuel better, thus isn't as big a problem when flying down the road.

 

Also when I revved the engine, I noticed both pistons did not rise at the same time. The back one rose a split second before the front. I should think they would rise at the same time?

 

Anyway I fear engine fire, so I need to figure this out and it looks like taking apart the fuel bowl is in order. THough someone said if I lightly tap the top of the float chamber with a hammer or screwdriver, it may unstick the needle if that is the problem.

 

Those nuts on the bottom of the SUs are the mixture screws.....they raise (lean) or drop (richen) the jets.

Typically on a 'newer' SUs both screws will be turned out the same amount....but....over time the carb(s) can develop issues like worn throttle shaft bushings etc. which will introduce a vacuum leak. The one jet is then adjusted to compensate idle+.

But......since you have roller bushings from Z therapy.....disregard that little tidbit of info. :D

 

 

Sounds like there is some crud in the float bowl and or.....or the float is set at a incorrect height....or....

 

Should buy a wibeband...it will tell how rich or lean the engine is running at idle/cruise and WOT.

 

 

http://www.zcarz.us/TechnicalInformationPageCarburation.htm

[fisch]

Those nuts on the bottom of the SUs are the mixture screws.....they raise (lean) or drop (richen) the jets.

Typically on a 'newer' SUs both screws will be turned out the same amount....but....over time the carb(s) can develop issues like worn throttle shaft bushings etc. which will introduce a vacuum leak. The one jet is then adjusted to compensate idle+.

But......since you have roller bushings from Z therapy.....disregard that little tidbit of info. :D

 

 

Sounds like there is some crud in the float bowl and or.....or the float is set at a incorrect height....or....

 

Should buy a wibeband...it will tell how rich or lean the engine is running at idle/cruise and WOT.

 

 

http://www.zcarz.us/TechnicalInformationPageCarburation.htm

Thanks Sealik! Yup I felt a little grit on the pistons today. They need a wipe down. Watching the Z therapy vid now. I guess these carbs have a rubber float so no worries about them getting filled with gas like the 510's can. I am now thinking the overflow is due to a faulty valve. For some reason I can't remember the PO did not use the Z therapy grouse valves, but there was a reason. So these have the original valves, which were never great over the long haul I guess. Will take care of/ clean that little brass filter in there too.

[Sealik]

While you're at it...dump the oil out of the pistons, clean up and add 3cc of ATF

[fisch]

While you're at it...dump the oil out of the pistons, clean up and add 3cc of ATF

Have you tried Marvels? Curious what you thought if so.

[Jester]

ATF is roughly a 7 weight oil. Marvels is a little less. I wanna say 5. 

 

As for over flowing carb, I would lean more toward the needle being stuck. If this poor guy has sat that long it's probably just gummed up. 

[fisch]

ATF is roughly a 7 weight oil. Marvels is a little less. I wanna say 5. 

 

As for over flowing carb, I would lean more toward the needle being stuck. If this poor guy has sat that long it's probably just gummed up.

 

I'll try to get into it tomorrow. If it is just gummed up, hopefully a little carb cleaner will free it up. Though I see many rebuild kits come with a new one so it isn't hard to find at least. Appreciate your advise! I've gotten an education on these in the last 24 hrs. Not all that mysterious after all.

[fisch]

Well nothing new to report really, but I did change the fuel filter really quick. Safe to say it wasn't that, lol. Same problems.

 

It was interesting though, when I removed the hose from the top of the filter, the gas just kept coming out of the filter from the tank. Almost like the system was pressurized. I expected a little fuel, sure. It wasn't coming from the fuel pump line, that emptied and stopped. Just the line from the tank. That never happened on my 521 when I changed the filter. Maybe I should have removed the gas cap? Anyway I had to do some pretty quick filter swapping to beat the gas.

 

Edit: In thinking about the above, can it be that the gas tank sits higher that the fuel filter with Chapman's slight rake and gravity was just trying to equalize the fuel level? Thus dribbling fuel out.