lordy what a response!!
Fred Schroeder sez:
>I drove both a '69 and my present '70 all over the Arizona desert. I
>lived about half way between Phoenix and Tucson. Never had a vapor
>lock problem. Both were stock at the time.
Now THAT's what I'm talkin' about! Is this stop and go driving though?
Mine will run all day on the highway at 100+ (um, degree's. I haven't
tried ALL DAY at a 100+ mph ;) ). What kind of altitude is that?
Greg Burrows writes:
>... I assume that you do not have the glass fuel filter, right?
right.
>... Just as a thought, you might check your lines, connections etc
>and see if anything is amiss.
All hoses from pump forward are all less than 2 yrs old. But I'll
double check!
Paul OROC ponders:
> Almost sounds like you don't have a good fuel flow at low RPMs.
>Have you checked to see if the fuel return line is clogged?
not recently. I avoid that, as it's such a !@!!&$!@# stinker to
keep from leaking upon reassembly..
>Is the pump putting out enough volume?
It better, it's only a yr or 2 old!
>Could it be that the lever on the pump or the cam that activates it
>are worn so the pump is not making a full stroke? Or is the spacer
>between the pump and block too thick so the lever isn't ridding fully
>against the cam? I know these 'guesses' are out there, but it sounds
>like you've covered everything else.
I think Teddy answers those questions... :)
Teddy said:
>Paul is intent on having you check the fuel pump and return line, but
>that doesn't sound convincing to me since you report the problem only
>at warm/hot temperatures and not at, say, 60 degrees with the engine
>warmed up. What Paul suggests with the pump won't be temp sensitive.
righto.
>Let me try a different angle, as I am desperate to win some hot cakes
>from Paul. (He and I have a standing wager on these remote,
>sight-unseen diagnoses for Roadster problems.)
Wow, does the diagnosed owner get to partake too? :)
>I am thinking that your linkage at idle, where the cable comes in, is
>behaving strangely when it heats up. One possibility, which I've
>experienced from time to time on my 69 2000, has to do with the
>location of the main, idle set screw. ...
Well my main idle set screw is in a drawer. I only use the individual
carb set screws.
>The next time you have the problem, or if you can create it, check to
>see whether your carb linkage (where the cable connects) has shifted
>a bit moving the position of the set screw ... When the linkage
>cools down a bit, then all returns to normal, etc. If it is like my
>occasional problem, cleaning the linkage thoroughly helps to keep it
>in place, even at hight temps.
You may be on to something, as this winter I discovered Ztherapy
didn't put enough spacers in the front carb shaft, such that it IS
POSSIBLE for the shaft to misalign -- and not hit the little dimple
on the .. the.. ? front carb thingy :) . I've never observed it to
happen though.
Victor Laury poses:
>Dan, There something very wrong here. ...
>
>Never Had a Vapor Lock Ever!
Wow. It's never spluttered after sitting at an unbelievably butt
blistering long light? Wait, maybe you SoCalers don't HAVE
unbelievably butt blistering long lights?! (that's not the way _I_
remember SoCal!).
>I suspect your gas return valve is not operating and stuck
>closed. It's really a very effective system Nissan built to prevent
>vaporlocking. The gas keep circulating and the carbs take what they
>need.
Well, somewhere in the last year (Eric Frisbee, when did you give me
that return valve?), I replaced my valve because I couldn't stop it
from leaking. I tore my replacement apart and cleaned it up, so it's
fresh IMO. OTOH, I've also gotten cr*p gas since then -- bad enough to
stick a (stock) jet open (roadside repair: whacked it loose with a
screwdriver handle/end).
Laurie brags:
>I've driven my 70-1600 in stop-n-go traffic in the worst of the AZ
>heat and have *not* had the vapor lock problem.
Now THAT's what I'm talkin' about! But don't 1600's tend to run a
bit cooler?
>Stock f/p, but I did run hard line from the pump up to the carbs The
>extra insulation of the steel line may have helped, ane it does to
>bwteen the fan & the w/outlet. May be getting some extra cooling from
>the fan ?!?
Well, it seems that way to me -- that's why I didn't move it to the
front of the rad -- in stop'n go, at least the fan's pushing a little
air on that line!
>Or.... D'ya think some extra sheath of flexible whatitz from the
>hardware store might help ? Something that wouldn't melt if it leaned
>up against things of course !
Well, I've looked for some, and haven't felt comfortable about the
heat rating...
Keith Alan writes:
>Definitely check the vapor return valve on the carb inlet. ...
Ok, I'll clean that puppy out again.. now that I think of it, I wonder
if it would behoove me to blow the return line -- make sure it isn't
plugged up between the firewall and the tank? That would explain the
problem occuring all these years, without relating to the actual
performance of the engine...
Todd Osborn sez:
>Are you sure it's vapor lock?
Um, well.. no, I guess not.
>You may be fouling the plugs,
Part of my confidence in the tune is because a few months ago fellow
WyCROCer Tom Hoagland tuned my carbs for me with 2 colortunes and an
exhaust analyzer. I can't imagine fouling at this point..
>are you running N-17 needles in your SU,
yes.
>these run very rich at low rpm, worse at high altitude.
I have a .099 nozzle for that reason. Not that I'm convinced it FIXES
the problem, but Tom Hoagland and I are pretty happy with the tune/mix
we ended up with.
>... You might try some low speed runs to recreate the problem, then
>stop immediately and pull the plugs. ... if the plugs are gray or
>gray white, then it's too lean and it may be vapor lock.
Ok.
>If it's vapor lock I would check the return valve as already pointed
>out, I find this valve very funky and I think Tom Walter said you can
>replace it with a simple restrictor (~1/4" rod with small hole
>drilled through it).
I tried that. Made the problem worse as I recall, but I also had other
problems going on at that time too, so I might re-try it..
Well, thanks for all the pointers y'all!! I hope it's some minor
mechanical thing; will check return valve, return line, linkage, etc..
We're back in the 50's for a couple of days, so I can't test it right
away..
Have I heard from any high altitude drivers that have had NO vapor
lock problems (or better yet solved one)? Any petrochem wizards out
there that can tell me what the temp difference is for gas to boil at
7000' vs. 0'?
I'll keep y'all posted -- so Paul and Teddy knows who's buying
the hot cakes!
thanks,
dan neff '69 2000
colorado springs, co
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