Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

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jrusso07
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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by jrusso07 » Sat Aug 17, 2019 7:19 am

To enrichen the carbs, turn the mixture nut/knob under the jet CCW. The jet should be low enough in the seat to be just below the fuel level in the fuel bowls at idle. To check, pull the carb domes off and remove piston. Look at the jet orifice- there should be a little puddle of gas on the jet.

And yes, pulling the choke knob will lower the jet and allow more fuel into the carb. So a test for leanness, pull the choke as you approach the 5.5K rpm and see if she runs better.
Joe

1969 SRL311 - Solex
1970 SPL311 - U20 mod
1970 SRL311

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 12:14 pm

Picking up another filter today, also going to order a wideband, any recommendations on brand, and gauge mount location? Cheers!

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 12:19 pm

Joe,

I am going to try the choke test, and will report back.

When I last synced the carbs they both were chugging along with the lift pin raised on each su, obviously not at the same time, under each carb, no initial increase in rpm and no sputtering like it's dying.


I am going to laugh if the new filter fixes the issue as this one is fairly new. Most of me hopes this is the fix, but at the same time I will feel pretty foolish, such are the perils of working on and old car and being cautious I suppose!


Cheers!

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by jrusso07 » Sat Aug 17, 2019 12:57 pm

Sounds like your carbs are properly set! Good luck with the new filter!
Joe

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1970 SPL311 - U20 mod
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Gregs672000
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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by Gregs672000 » Sat Aug 17, 2019 1:49 pm

I purchased a Glow Shift wideband several years ago and it's been without problem or issue. My O2 sensor is located just past where the four pipes collect in the collector on my aftermarket header. It sits at about 2 o'clock and will allow me to remove it with an O2 sensor socket for the required "free air" calibration process needed every once in a while. Access here probably requires that the triangle metal plate on the body that gets in the way of starter access be removed, as many are. You will have to go to a muffler shop to have a bung welded in. Finding a place to mount the gauge can be difficult. Mine is in the center radio console but the console is no longer stock, and I probably have a different interior than you. Now, I need to be able to monitor my motor regularly as its high compression and I never want detonation. However, unless you are regularly tuning then a temporary spot for the gauge may be more reasonable and easy. There was someone on this site that was offering a complete wideband to borrow for tuning. The biggest hassle will be the bung, especially if you don't have a header with a separate collector. I don't know if something could be hooked up to the end of the tailpipe that would allow you to use it for testing (including driving) instead of having a bung welded in, or if it will work correctly like that (ask the manufacturer?). I always consider the costs, so it may actually be more cost effective and less hassle if you can work out a deal with a repair shop if they have the right set up and knowledge. Here, there's a shop that offers "dyno tuning" for more "everyday" (i.e. non-race) cars. If I were in your shoes that would probably be what I would do if such a shop is available to you locally and they're upfront about their charges. However, first thing I would do though is learn everything you can about SU carbs (there are excellent resources on this site) so you will know exactly what you can do once you figure out what's happening. Then you can plan your dyno pull so you're potentially prepared to make adjustments while she's still on the rollers. One dyno here charges $70 for the first pull (plus another $50 for the wideband IF you have a bung welded in already), $10 each for the next 3, so the main cost is in getting the car ready for the pull. If you have changes you know you can make, you can check your work for $10 bucks. I do not know what the "dyno tuning" shop I mentioned charges for their "tuning."
Ain't old cars Fun?
All of this may be overkill... hopefully some easy solution will present itself. My car used to run out of power due to a leaking glass fuel filter set up allowing air in the lines. The problem wouldn't show up until I got on it hard for some time or had to climb a long hill.

Cam sound right
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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 2:17 pm

Ok, so I drove to Napa for a new fuel filter, along the way I tried the choke test, I ran up to 5500 in second, and when she lost power I pulled the choke, theoretically enriching the mixture, the noise immediately became louder and the power loss increased. So...

Replaced the filter and got more hose to route the filter to stock location. Tested again with no change in performance.

I did a bit of digging and it looks like my uncle did not replace the valve springs, at least I have yet to find the receipt, though he was meticulous about saving them all during his ownership. This would suggest they are pretty old, and on their third set of positions and rings. Additionally, David Witt from the sac Datsun club had said there was little adjustment left in the valves when he helped me with the initial low compression in cyl three diagnostics. So currently my hunch is leaning towards valve float.

I'm theorizing the increase in noise is caused by the valves not being able to close allowing combustion noise to escape through the exhaust, when I enriched the mixture, there's more gas so more bang(very technical analysis haha) thereby increasing the noise. Is there a way to test for valve float aside from removing springs and load testing them?

I will do some more research in to the wideband, even if it is not related to the issue at hand, I would really like to have a read out on my mixture. The car came with a header, and it collects four to one before the flex tube and exhaust system. I am not a master welder but have enough experience to confidently install the bung. Is there any good reason I should not install it on the bottom of the collector, so as to avoid removing the header and all that jazz?

I'm going to call a few local shops in town, try the analyzer test, otherwise a dyno pull somewhere in Sacramento.

If all else fails I will start throwing springs, valves and what not at her.....and once I'm done denting up the body, maby install them too!

Again thank you all!

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by Gregs672000 » Sat Aug 17, 2019 3:25 pm

Sorry she's still having issues. This kind of stuff can be very frustrating. If there is little space left to adjust the valves that means the seats are slowly being pounded into the head. As the valve stem literally moves upward you progressively lose adjustment on the other side. I'm afraid a head rebuild is not far off. Post a pic of the adjuster side if you can.

The O2 sensor must be installed somewhat upwards or moisture will cause problems with it if left in. The muffler shop had to cut off my collector, install the bung and then rotate it back into place. If just used for occasional testing it might not be a big deal.

The only way I know to check springs is off the head. Could be springs, but could be the way the cam is now actuating the valves due to the wear (geometry, beyond my knowledge base).

Sorry man...
Greg Burrows
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1969311
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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 6:53 pm

Greg,

Haha it's always a new journey and learning experience, I am grateful for the challenge, pretty soon here I will have laid my hands on almost every piece of this car, at least that's how it feels sometimes!

Not sure on posting pictures, I can most likely figure it out, I will take a few, good news is during the head rebuild I'll have the manifolds off and be able to properly install a bung for the wideband, always a silver lining.

So assuming this is what I'm dealing with, what components an I looking to replace; the springs, valves, lash pads? Valve guides? Any other, while you in there sort of components?


Thanks again, fuel filter would have been an epic fix, but I have more learning to do, and necessity is a wonderful teacher. Cheers!

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 7:18 pm

Ok hopefully this link will work, adjustment side of valves picture. If this works I have a few other pictures I will add!

Image

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by Gregs672000 » Sat Aug 17, 2019 7:36 pm

I like your attitude my man! Im sure a few locals can suggest a good shop, or maybe someone on the site will contact you. You want someone who is familiar with the engine. There can be any number of things that need replacement, or not. Have someone evaluate it, and we can help guide you to see if it makes sense if you're concerned.

As I'm sure you know, the pic didn't post. I'm not great at photos etc, but I take a pic with my phone, email it to me, save it in a reduced size to my computer, then upload it from there.
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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 7:48 pm

Thanks Greg, I appreciate it, my father always said a positive mental attitude makes life suck less:)

I will reach out to David with the sac datsuns, he is well reguarded, knowledgeable, and straight forward. I will try and have him take a look soon and post the recommendations, otherwise I'll limp, push, or trailer it to shasta

In regards to the picture, I am on a mobile but if I click and hold the image file it sends me to the Google site where the images are hosted, could you try a right click? Otherwise I will try your suggestion!:)

Thanks again,

Chris

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 7:49 pm


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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by nismou20 » Sat Aug 17, 2019 7:58 pm

I noticed one of your pics shows the timing chain and Cam. Was that pic denoting TDC? The Cam looks to be retarded. Or was that just a random pic of chain mounted? Reason I ask is if it’s TDC the dowel pin should be inline with arrow and the 2 Cam bolts should be parallel with head front edge.

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by 1969311 » Sat Aug 17, 2019 8:51 pm

It was a slightly arbitrary cam position, I was taking pictures while rotating to tdc this was slightly before. Thanks for the catch though!! Just uploading a few pics to test the album function. Glad you were able to view.

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Re: Abrupt power loss at 5.5k on flat and uphill. 1969 srl311

Post by Gregs672000 » Sun Aug 18, 2019 12:19 pm

I have just a quick chance to look at the photos right now. The plugs show its very lean. The insulator itself should be tanish, not white, so we know for sure at least some if not all of your issue is a lack of fuel. First glance of the valve adjusters doesn't overly concern me, will look closer. Head may not be that bad.
Greg Burrows
'67 2000 #588
Tacoma, WA