A lttle Z help, please

[pballance]

:shrug:
I have a problem, At Nashville this past weekend after 3 laps in practice I entered Turn 2 and the motor went waaahhhhh and bogged down when I went to WOT. It would catch up a little but wouldn't pull above 4500 rpm. I chased the problem all weekend and even had GREAT help from David Plott.
Where should I start checking?
FWIW, I have had intermittent problems with a break up at 4500 rpm and then a loss of 5-750+ rpm on the straights when the problem appears. I found that hitting the rumble strips at CMP 8 would keep the car running fine for a couple of laps. I assumed it was fueling or a ignition problem.
So far I have rebuilt the fuel pump, replaced cell foam, filter, installed MSD box, new coil, cap, and wires. I put in new float valves, reset float levels, checked and re-checked timing. Adjusted and re-adjusted carbs. Changed pertronix, distributor with only minor results. CHecked alternator voltage, upped fuel pressure. Added fuel, etc.
This problem does not occur until the engine is under load. No break up in the garage and will rev to 7k.
I am at a loss. This problem seems heat related. I had a thought last night that I am wondering if I get a voltage loss through the master switch since the MSD box is connected there.
I chased this problem all weekend. The first three practice laps I saw 7k on the front straight and the car pulled great. then waaaaahhhh and problems the rest of the weekend.
Where do I look now?
BTW, I am on the road today so I may be a little slow in response
Paul

[JeffYoung]

Ron has been chasing this exact same problem for the past couple of weekends. You guys should converse.

[Ron Earp]

:shrug:
mble strips at CMP 8 would keep the car running fine for a couple of laps. I assumed it was fueling or a ignition problem.
So far I have rebuilt the fuel pump, replaced cell foam, filter, installed MSD box, new coil, cap, and wires. I put in new float valves, reset float levels, checked and re-checked timing. Adjusted and re-adjusted carbs. Changed pertronix, distributor with only minor results. CHecked alternator voltage, upped fuel pressure. Added fuel, etc.
This problem does not occur until the engine is under load. No break up in the garage and will rev to 7k.
I am at a loss. This problem seems heat related. I had a thought last night that I am wondering if I get a voltage loss through the master switch since the MSD box is connected there.

Paul,

This is the story of my last four race weekends - CMP, VIR, Roebling, and VIR again.

I first started with fuel issues, rebuilt the entire ignition system, and so on - basically doing what you have done.

I collected data and videos. I tried to find rhyme or reason to when it would happen. I thought I had it nailed down to high speed right hand sweepers, but then I'd get it in turn 3 at Roebling and turn 6 at VIR which sort of blew that theory.

On the dyno the car would pull to 7000 RPM with no trouble. No stumbles, no bogging over a period of 1.5 hours on the rollers and 8-10 pulls.

I did notice one thing though this past weekend while at VIR - when the problem occured the front EGT (plugged into cylinder #1) dropped out down to the 700 range or so, basically the front three cylinders were not firing at all. Sometimes it'd be really bad, like all three were out, sometimes all three would be intermittent, catching, coughing, and so on. Either way it'd be accompanied by some cool sounds and flame when they'd catch back up after dumping lots of unburned fuel. Spark plugs also told a tale of the front three being quite rich.

So, I narrowed mine down to a front carb problem, I think.

I have rebuilt the carbs numerous times and always set the float height as speced in the shop manual - 0.5-2mm from the power valve inlet, 12-13 mm from body of carb to tang that closes the float valve. However, I had never checked float level visually because it was just about impossible to do on my 260Z with the setup and old sight glasses in the carbs.

I finally fixed the carb surroundings to see the glasses and replaced them with clear ones and lo and behold - when the carbs were set up according to factory specs the fuel level went up, up, up, up, and gone past the top of the sight glass. Far too high and I think this could have been the cause of my flooding the front carb. When bumped, g loaded, etc. I figure the fuel level was so high that in certain orientations a whole lot of fuel would get sucked into the manifold and flood those cylinders.

So, I made some small adjustments in the way I set the floats up, basically bent the tang down a bit more than specs and the fuel level now sits in the middle or upper 1/3 of the glass. Probably where it should be.

I feel this should solve the problem but I won't know until on track. I will go back to the dyno this week and see if I can get some more power out of the motor. Last runs had EGTs down in the dumps and I imagine the float level had quite a bit to do with that.

R

[Parrish57]

I think Ron is on the right track. I had similar problems years ago. I fixed them with adjusting the float level, but more importantly, installing Grose Jets. The stock needle and seat sucks. The real problem is finding a set of grose jets.

I didn't know that the 260z flat tops had a sight glass. The 240 doesn't. Z Therapy sells a piece that screws into the float bowl plug hole. It's just a piece of clear plastic that turns up beside the float bowl for tuning. I think you could make one very easily. I just take the plunger/bell and the slide/needle off and look down the nozzle to check the float level with the fuel pump on. Works for me.....

[Ron Earp]

Hey Paul,

Here is a fairly decent view of what mine does:

http://www.youtube.com/watch?v=RVBG-are-rQ

Seem familiar? My foot was to the floor through there but no power.

I had to down shift to try and get it to maintain RPM/speed, it was dead below that. Then my little friends there, including Mr. Jeff, had to blow by and I couldn't keep up.

Ron

[Ron Earp]

I think Ron is on the right track. I had similar problems years ago. I fixed them with adjusting the float level, but more importantly, installing Grose Jets. The stock needle and seat sucks. The real problem is finding a set of grose jets.

I didn't know that the 260z flat tops had a sight glass. The 240 doesn't. Z Therapy sells a piece that screws into the float bowl plug hole. It's just a piece of clear plastic that turns up beside the float bowl for tuning. I think you could make one very easily. I just take the plunger/bell and the slide/needle off and look down the nozzle to check the float level with the fuel pump on. Works for me.....

I looked for Grose jets and called everyone I could think of, no dice. Do you have any leads? Maybe yours wouldn't fit but I could re-tap the hole.

I sort of knew the 260Z had sight glasses, but mine were old, scratched, and nearly useless. Some polishing and new gaskets which came with the rebuild kits and they are good to go.

Seriously, the flat tops are not bad carbs. While there isn't a body of knowledge out there about them, I'm getting there with collecting info and developing mine. The press in jet is crummy, but in race trim I think the carbs can work well. I don't know about street work but I don't care about that.

R

[Parrish57]

I looked for Grose jets and called everyone I could think of, no dice. Do you have any leads? Maybe yours wouldn't fit but I could re-tap the hole.
R

Z Therapy occasionally has them. I don't see anything on their current web site. The only lead I have at this time is out of Australia. The Aussies love their Zs as much as we do. Give this a try: http://www.sumidel.com/Products.htm

P.S. If you order some maybe we could do a batch and share the shipping costs....

[Ron Earp]

Hey Steve,

I have a bunch of buddies in Australia. I've emailed that company and will see about getting ten of those up here. I can get a local guy to get them and post them up.

Does that little short on in the picture fit your carbs? That would be what I'd need for the 260Z carb.


Ron

[pballance]

Ron, it is hard to hear as I am traveling down the interstate but that sounds like it. Dang ain't connectivity fun :)

Mine started with a stumble ~4500 and then loss of 700+ on the front straight at RR. It happened again at CMP and I have been chasing it for a year trying to find a reason. It is also not consistent, at least not since this past weekend.

I guess that old saying if you think it is ignition, it is fuel.

I have opend the plugs up and gone another heat range cooler (thanks David!) WHile it got better, it is still there. BTW, I checked the plugs during some of theis and noticed that #3 was WAAAY rich so It may in fact be all fuel issues.

Thanks for the pointers, it gives me another place to try again. BTW, even with a sick car I managed a 1:17. I think I could find 3-4 seconds if the car was right which would put me mid pack.

Count me in on the jets

[Ron Earp]

I have opend the plugs up and gone another heat range cooler (thanks David!)

With respect to the plugs, what do you guys run?

I think I remember some BP7Es or something like that as what I'm running. What plug is one range colder for the Z?

Ron

[Mike Mackaman]

Ron, I have grose jets in my carbs, I like them and if you can score some, I would love to buy a set as well. I have some carbs I have been working on that I need them for.

I tried the colder plugs and had lots of problems. I think they are 8's. I bought a set of NGK iridiums after detonating an engine at Lowes a few years ago. As cheap as I am, it killed me to take brand new plugs out because it wouldn't run with them. I'll make you a deal on 6 Iridiums one range colder, they are sooty black, but that was the problem.

Mike

[Parrish57]

Hey Steve,

I have a bunch of buddies in Australia. I've emailed that company and will see about getting ten of those up here. I can get a local guy to get them and post them up.

Does that little short on in the picture fit your carbs? That would be what I'd need for the 260Z carb.


Ron

I have no idea what the stubby thing goes on. The long one looks more correct for the 240........ There are several lengths depending on the year model.

[Ron Earp]

Mike,

What type of Grose jets do you have on yours? We should probably start calling them ball-type fuel valves, seems more correct. Who is Grose anyhow? The short one seems to mimic the little needle valve we have now.

Steve,

we can get either type. The guy emailed back and said he'd have a bunch of new ones in about 3 weeks.

Ron

[kthomas]

Okay, couple quick random thoughts. YMMV.

Never found a need to go to Grose jets. Factory new stock for me. Ran into too many people that had problems with them "back in the day" but I couldn't tell you what the problems were.

I've had similar symptoms with a closed "air box", open only at the front. Weird, but true. Just out of curiosity, what's your air cleaner setup again? You got an open Pipercross?

I never had problems with plain ole' NGK BPR7ES-11's. I think stock is "6" and one step colder is "7". Somebody check that, I been away for a long time. However, Sunbelt did use platinums near the end of their development program, but I was running a 4 prong NGK from a rotary. More prongs = more room taken up in the combustion chamber. How anal is that?

Two things happen under load that don't happen at 7000 rpm in the driveway. First the ignition is taxed more, and second the slide isn't in the same position at high vacuum as it is at no vacuum, although above 4500 rpm you should be making pretty good vacuum even under load at full throttle. If it's heat related that points to an ignition component, but everything else you describe points to carb.
What needles and how are you setting them relative to the slide? Damper oil and spring? How are you venting the float bowls? Ron is on to something wrt float level. Have you messed with the stock banjo fitting and filter where fuel enters the bowl? I've seen certain orientations of that fitting choke off the flow.

You gonna be at little talledega any time soon?

[pballance]

Okay, couple quick random thoughts. YMMV.

Never found a need to go to Grose jets. Factory new stock for me. Ran into too many people that had problems with them "back in the day" but I couldn't tell you what the problems were.

I've had similar symptoms with a closed "air box", open only at the front. Weird, but true. Just out of curiosity, what's your air cleaner setup again? You got an open Pipercross?

OEM backing plate and stacks, Pipercross filter the large oval style


I never had problems with plain ole' NGK BPR7ES-11's. I think stock is "6" and one step colder is "7". Somebody check that, I been away for a long time. However, Sunbelt did use platinums near the end of their development program, but I was running a 4 prong NGK from a rotary. More prongs = more room taken up in the combustion chamber. How anal is that?

I was running BP7ES, opened the gap up to .040 and then went to BP8ES and opened to .045


Two things happen under load that don't happen at 7000 rpm in the driveway. First the ignition is taxed more, and second the slide isn't in the same position at high vacuum as it is at no vacuum, although above 4500 rpm you should be making pretty good vacuum even under load at full throttle. If it's heat related that points to an ignition component, but everything else you describe points to carb.

I cannot say that it IS heat related. I tried to make it that way but it has occured at low engine tmep and high. If it was strictly heat related I would think it would have been worse at CMP where I kept it going for 13 laps (KVS got me 2 turns from his checker)


What needles and how are you setting them relative to the slide? Damper oil and spring? How are you venting the float bowls? Ron is on to something wrt float level. Have you messed with the stock banjo fitting and filter where fuel enters the bowl? I've seen certain orientations of that fitting choke off the flow.

Have not yet gone deep enough into the carbs to tell you exactly what needles so I have not verified needle position. Damper oil is 20wt redline. Bowls are vented from OEM location with a fuel line that is then inverted and poked into the opening between bowl and body. Float level is set per factory manual. (invert, measure, adjust) I raised the level from where it had been set after my first three laps. Banjo fittings are gone replaced with an fittings. Springs appear to be identical.


You gonna be at little talledega any time soon?

Don't have anything on the schedule right now, you got something set up?

FWIW, timing was set at 3000 rpm with a dial in style light at 31 degrees. At 5k we saw ~35 degrees advance so we retarded it down some. David was running the light and said my total advance was right at 34 when we stopped.

Fuel @ 4 psi and after the problem I ran it up to 5. Sounds like that may be contributing to my issues

FWIW, on my first trip to RR the carbs were flooding so bad that I thought I was going to get black flagged. Came in and reset floats, Don Ahrens helped balance and adjust the carbs. I have adjusted following written instructions and lots of internet reading. I have a synchrometer that I used but still not sure I got anything but the gross adjustment correct.

[JeffYoung]

We think the stock float settings are wrong on Ron's car (a 260z), he figured it out by watching the sight glass you don't have. Might want to try lower the float and getting an earlier fuel cutoff?

[pballance]

Forgot to add, during the changes I noticed an exhaust note change. Sounded like a tin can being hammered inside of the muffler. Never got a "spit" form the carbs during all of this except when we retarded the timing too far.

It went away at some point(I wish I could remeber what we did) and the car actually sounds pretty good right now, especially under no load. One other thing, David noticed a little "jump" in the timing occasionally and suspects the plates/weights/springs may be binding a little.

It was probably good I decided to load the car when I did. Had I gone out on schedule I would have entered the bus stop into an oil slick left by a '07 GTO that blew a motor. He was directly infront of me and only about 7-8 seconds ahead had I been on track. $$$$$ shift for him.

[kthomas]

"It was probably good I decided to load the car when I did. Had I gone out on schedule I would have entered the bus stop into an oil slick left by a '07 GTO that blew a motor. He was directly infront of me and only about 7-8 seconds ahead had I been on track."

Yeah, I try to stay off track when Detroit products are on- never know when they're gonna puke all over the place... (right Spillman?)

Dude, we gotta take a look at your carbs and distributor. Where you gonna be next?

[Ron Earp]

Hey Paul,

I think you need to focus on those carbs.

I’ve been very religious about keeping notes in my notebook on my car. Things like needle height, air temp, EGTs, impressions, and so on will find their way into my notebook after racing or testing.

With my recent carb rebuilds and setting the needle heights identically between two carbs I get EGT differences between the carbs with slightly different float levels. In this case the front carb has the fuel level in the middle of the glass while the rear is in the upper third. A slight difference in the float level leads to a significant difference in EGTs, enough to cost power for sure.

In my previous iterations the fuel level was above the glass (but I didn’t know it) and I’m sure it contributed to my problems.

You need to get your dizzy right too. Jeff and I and others we know have used:

http://www.advanceddistributors.com/

Email them and talk to Jeff S., he’s pretty good. Just tell him what you want and he’ll work it out for you and test the dizzy well. He’s not a racer, so he still gets hung up in street stuff, but if you just tell him “I want 34 degrees, all in at 2800 RPM” he’ll fix it up. I current have a few dizzys he’s rebuilt, the one I’m running now that has an advance and a locked spare.

Curiously enough, my car liked 32 degrees total advance on the dyno – 34-36 degrees cost 3-4 rear wheel hp, 28-31 cost hp as well as torque. You’ll have a sweet spot somewhere and you’ll need to find it on the dyno yourself. I know my 32 degrees probably isn’t 32 “real degrees” since I have some slop in assembly of my motor with degreeing everything – something else I need to fix.

Ron

[pballance]

I think you are right Ron. To make certain I am getting newly rebuilt/recurved dizzy and I may have to bite the bullet and talk to Ztherapy. I hope they are in need of cores as I have several I can send them to shave off some $$$$ for me.

[spawpoet]

As of 2 months ago ZTherapy was more than happy to take datsun cores, and I can vouch for their carbs as being well worth the money, esp after receiving your credit on the cores. We had some carb issues where we couldn't get our EGTs to balance before trading our used set in for a set ot their rebuilt units . It is significantly imrpoved with the new pieces.

chris

[Ron Earp]

Shoot, what you fellows need are what ZTherapy calls "boat anchors", my carbs!!!!