Mystery hesitation under load, worsens over time

[rundwark]

One piece throw away type with a non cleanable cartridge is all that matters. Nothing to come loose internally and block flow

 

Yup, both are one-piece throwaways.

 

Does your electric pump look similar to this one?? If so, 

There is a replaceable fuel filter built in.

 

 

It doesn't but I ordered another $20 generic pump with 5/16" outlets on Amazon that gets good reviews, so I can just swap that in to see if it makes a difference.

[Miles]

Just checking the floats for dirt etc, is not what the other poster meant by "did you check the floats".

 

Setting the height of the SU float level is critical to getting the correct amount of fuel to the nozzles. There is an adjustment on the float that has to be done correctly or you end up lean or rich.

 

 

Bowel Fuel Level:  See picture

 

 

The best answer to your question is:

 

You should buy the video "Just SUs" and watch it at least five times:  http://www.ztherapy.com/

Edited March 20, 2017 by Miles

[rundwark]

I hear you Miles. I didn't check with a clear tube, but when I opened up the float bowls just after running the engine they were both at a good and similar level.

 

Also, the car runs great when it first gets to operating temperature, the issue only happens after I run it under heavy load for a while, like a good 10 miles on the highway at high speed. So the symptoms don't seem to fit with maladjusted floats to me.

[rundwark]

Send us a few clear pictures of the engine compartment. Especially on the Carb side. We might be able to spot something.

Here's some pics, thx for taking a gander

 

 

 

 

 

[Miles]

http://forums.hybridz.org/topic/100400-hesitation-on-acceleration/?hl=hesitation

Edited March 21, 2017 by Miles

[rundwark]

Thanks Miles, I read that thread again (once before I started mine too and once again immediately after you posted it). I will look for some translucent hose that fits just to eliminate it but am convinced this is not my problem.

 

My car runs fine at operating temperature for a while, and then starts to bog. I don't see how a float level problem could be fine and then change with heat soak. I think I'm dealing with something else.

 

I did recently install a more efficient radiator, and my fans are electric and on a controller. This means they are pushing less air around the engine bay which means more heat soak. I'm going to drive the car until it happens again, pull over to wire the fans to run continuously and see if the problem disappears.

 

One issue that's become more prominent is very low idle (and sometimes stalling) after a highway drive at operating temp. Pulling the choke raises the idle. So it seems I'm running lean, possibly due to vapor lock. I'll also check that the restrictive hole in the fuel rail for the return line isn't plugged.

Edited March 23, 2017 by rundwark

[rundwark]

This seems relevant too and supports my heat soak idea somewhat: http://community.ratsun.net/topic/68156-rough-idle-rpm-drop-and-stalling-at-intersections/page-1

[rundwark]

This is the style of fuel rail I have in my Z, I wonder where the restriction for the return line (to maintain pressure at the carbs) would be.. anyone here know?

 

[rundwark]

Well, so much for that theory. Ran the car with the fan

controller on fail-safe mode (full on), problem was exactly the same.

[madkaw]

Another thing to check. I once had problems with the Float bowl to nozzle rubber lines collapsing under heat. They were collapsing at the bend . I could actually reach under there after the engine was warm and feel a flat spot in the hose. This cut off fuel flow to the carbs

[HuD 91gt]

This is the style of fuel rail I have in my Z, I wonder where the restriction for the return line (to maintain pressure at the carbs) would be.. anyone here know?

 

If you look at the return outlet, there is a small pin hole at the end.  That's it.

 

 

I developed a heat soak issues when I installed an aftermarket header with my SU carb's.   Car would run ok once moving, in idle is where it ran awful.  Once moving it went away.  Fuel rail would be very hot to the touch.

Edited March 25, 2017 by HuD 91gt

[rundwark]

So I think I figured out what's wrong, you're all gonna laugh. My front carb was way lean. Adjusted it to run richer, problem gone.

 

This doesn't explain why the issue occurred in the first place, before I took the carbs apart, but the car runs fine now. I found a few other minor issues along the way, I think the one that explains the rough idle was a mild vacuum leak in brake booster hose, but yeah the root cause for this was likely just user error.... smh.

[rundwark]

I did discover something interesting along the way, sharing here in case it's helpful to someone.

 

I've always had a really hard time telling whether my SU's were running lean, rich or just right using the damper piston lift method that's described everywhere. And just listening for differences in the quality of the idle and idle speed from adjusting jets doesn't really give clear results. So I've always struggled to tell whether I'm improving the mixture or making it worse.

 

At one point, while the engine was at operating temp and running poorly, I unplugged the vent tubes for each float bowl from my air cleaner to check if either was overflowing. I then blew into each vent tube, one at a time. Doing this on the rear carb slowed the idle down. But on the front carb, it immediately idled faster. This convinced me the front carb was running lean. This was a very quick test to do, and the results were very unambiguous. I've never read about anyone doing this, but it was a lot more clear to me than any of the usual methods.

 

I still haven't found transparent hose of the right size to measure float levels, but I'll try to still do that before I do my engine (and carburetor) swap and report back here.

[madkaw]

So why was it lean? Didn't you have the mixture wheels close to same adjustment ?

[jasper]

 

 

I still haven't found transparent hose of the right size to measure float levels, but I'll try to still do that before I do my engine (and carburetor) swap and report back here.

 Go to a lawn mower/professional lawn equipment sales/repair shop. They have various diameter clear fuel hose on spools for sale.

[Miles]

You are in the club now.

 

Interesting method for checking lean carbs. So, is it mixture or float adjustment causing the problem?

 

I usually read the plugs to check for lean/rich condition. Better  to go rich and ragged than too lean.

 

There is also a device called a "color tune". It is a spark plug with a window that allows watching the flame color inside the cylinder as you turn the mixture adjustment.

 

Recently, someone came up with a visual tool for setting float levels. Check the vendor forum or Google.

[rundwark]

So why was it lean? Didn't you have the mixture wheels close to same adjustment ?

I did have them close at about 2 turns down from where the jet sits flush, so best theory is that Miles' insistence for me to check float levels was spot on.

[rundwark]

Go to a lawn mower/professional lawn equipment sales/repair shop. They have various diameter clear fuel hose on spools for sale.

Thanks Jasper, will do!

[jasper]

Get one of these, you won't be sorry. 

 

https://www.amazon.com/AEM-30-4110-UEGO-Ratio-Gauge/dp/B00N3VGPYS/ref=sr_1_1?ie=UTF8&qid=1491339889&sr=8-1&keywords=aem+wideband

 

[rundwark]

You are in the club now.

Haha thanks! That was quite the rite of passage

 

Interesting method for checking lean carbs. So, is it mixture or float adjustment causing the problem?

Probably float, will report back when I know for sure. But yeah this method worked very well and results were completely unambiguous. I recommend trying it out sometime.

 

I usually read the plugs to check for lean/rich condition. Better to go rich and ragged than too lean.

 

There is also a device called a "color tune". It is a spark plug with a window that allows watching the flame color inside the cylinder as you turn the mixture adjustment.

Tried reading plugs without a lot of luck, should've grabbed my colortune from the drawer of forgotten tools. It's usually not been super helpful for me, but I bet it would've caught this issue since the carb was so far off.

Recently, someone came up with a visual tool for setting float levels. Check the vendor forum or Google.

Oh cool, I'll look that up! Thanks for all the advice so far